2020 Extended Range Diver Manual

CMAS Ext. Range Diver, ISO 11207

Collection: PTRD Dive Manuals

Contact: [email protected]

Edition 2020

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CONTENT

CONTENT ...... 2 1. INTRODUCTION ...... 3 2. DIVING EQUIPMENT ...... 5

HOW ALL EQUIPMENT MUST BE WELL MAINTAINED AND FIT FOR USE ...... 5 HOW TO HANDLE OXYGEN EQUIPMENT SAFELY AND ITS SUITABILITY FOR DIVING EQUIPMENT ...... 5 HOW EANX USE IMPACTS DIVE EQUIPMENT (E.G. INCREASED OXIDATION AND WEAR), ...... 5 HOW TO USE STANDARD SCUBA EQUIPMENT WITH EANX, INCLUDING NATIONAL INSPECTION, LABELLING AND TEST ...... 5 2.1. STANDARDS FOR DIVE CYLINDERS AND OTHER EQUIPMENT ...... 5 2.2. THE MASK...... 6 2.3. THE FINS ...... 7 2.4. THE BOTTLE ...... 7 2.5. THE VALVE: ...... 10 2.6. THE REGULATOR ...... 11 2.7. THE REBREATHER SYSTEM ...... 18 2.8. BACK PLATE SYSTEM ...... 22 2.9. THE DRY SUIT ...... 27 2.10. LIGHTS FOR TECHNICAL DIVING ...... 30 2.11. CUTTING INSTRUMENTS ...... 30 2.12. ACCESSORIES ...... 30 3. EANX HAZARD ...... 31

3.1. OXIDATION AND COMBUSTION ...... 31 3.2. OXYGEN COMPATIBILITY ...... 32 3.3. OXYGEN CLEANING ...... 33 3.4. OXYGEN SERVICE ...... 33 3.5. THE WORKING ENVIRONMENT ...... 34 3.6. CONTAMINANTS ...... 35 3.7. IGNITION SOURCES ...... 36 3.8. HYPER-OXYGENATED MIXTURES ...... 37 4. MEDICAL ASPECTS ...... 38

4.1. SIGNS AND SYMPTOMS IN A HYPEROXIC CRISIS...... 38 4.2. SIGNS AND SYMPTOMS IN A HYPOXIC CRISIS ...... 39 4.3. MANAGING A DIVING ACCIDENT ...... 40 4.4. PHYSICAL PREPARATION...... 41 4.5. CONTROL AND TRAINING TEST ...... 42 5. NITROX DIVE PLANNING ...... 43

5.1. REMEMBERING THE BASIC NITROX CONSIDERATIONS ...... 43 5.2. OXYGEN TOLERANCE UNIT (OTU) ...... 45 5.3. COMBINED EFFECT OF HYPERXIA TOXICITY AND CUMULATIVE EFFECT ...... 47 5.4. INDICES OF OXYGEN TOXICITY ...... 47 5.5. DIVE PLANNING ...... 50 5.1. GAS MANAGEMENT ...... 55

6. CONTINUING EDUCATION AND PROFESSIONAL CAREER IN DIVING ...... 72 2

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1. INTRODUCTION This manual contains all the necessary contents required to obtain the title of PTRD Extended Diver, equivalent to CMAS Extended Range Diver and ISO 11207. It is the first step to be able to do the technical diving programs.. It has been drafted based on the guidelines of the EUF/ISO, CMAS. This training programme aims at widening the experience gained since becoming an Advanced Nitrox diver through theory and techniques. This course will include training in accelerated decompression techniques. It will make candidates aware of the additional risks involved while undertaking this type of Diving. Once you have completed the theory and practice at sea, and passed the evaluation, your instructor will certify you as a PTRD Extended Range Diver as you will be considered to have a professional level knowledge of dive theory, solid technical skills, dive management and supervision skills, exemplary diving skills and sufficient experience to plan, organize and perform open water diving activities and organized dives in a safe and competent manner. A PTRD Extended Range Diver has specialized training and appropriate experience.

A PTRD Extended Range Nitrox Diver shall be trained such that when assessed by a PTRD Instructor, he shall be deemed to have sufficient knowledge, skill and experience: • To plan, conduct, and log EANopen-water dives that can involve in-water, decompression stops using Nitrox mixes up to and including pure oxygen, when properly equipped with inservice oxygen clean Scuba and accompanied by a SCUBA diver of at lease equal training • To be aware of the additional risks attached to this type of diving and the use of pure oxygen • Able to undertake this type of diving at altitude depending on the National Federation rules • Be able to plan dives, select and use the correct mix and gas usage • Be able to demonstrate an understanding of depth discipline when using pure oxygen. The permitted depth is limited to a maximum of 56 meters (or to the maximum depth permitted by national standards) subject to a 1.4 pO2 for diving and 1.6 pO2 for stage stopsIf you are unable to successfully complete any of the sections, discuss with your instructor the options available, whether it is certification of a lower degree or the possibility of completing your course at another centre.

Keep in mind that you will need additional training if you are going to dive to places whose conditions are very different from those of your training. For example, if you have done your course in a quiet area of the Caribbean in short 1mm suits, and then you are going to dive in cold water with strong currents using 7mm or dry suits, you should train in this type of situation. REMEMBER: A PTRD Extended Range Diver must be prepared for dives of greater difficulty than a PTRD 3 Star Diver and with total autonomy: you must have the ability to plan, organize and control the dive with the greatest margin of safety. Record all the dives that you make in your logbook or log-book, it is also mandatory in various countries, such as Spain. In this way, you will be able to accredit your experience in different environments and diving situations and to be able to opt for higher courses. Keep in mind that, at the international level, each country may have its own diving regulations, and establish restrictions of any kind. Stay informed before diving. PTRD, in compliance with the most restrictive legislation, requires the participants of its courses the following requirements prior to its start: - Medical certificate indicating “suitable for diving”, which you will have to renew every 2 years.

- Have 3 Star Diver certification or equivalent - Have Technical Skills Diver certification or equivalent - Have Advanced Nitrox Diver certification or equivalent - Have a minimum of 50 Nitrox dives logged - Complete the medical history/statement form required prior to participating in any in-water activities; - Sign the appropriate form(s) acknowledging and assuming the risks of SCUBA diving prior to participating in any in-water activities.

- Minimum age 18 years old 3

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Your PTRD instructor must inform you beforehand of their school’s own requirements, the price of your course, the conditions of completion and completion of the course, as well as having at your disposal the documentation of your obligatory Civil Liability and Accident insurance. In addition to all the administrative documentation, you will need specific equipment for the activity and which is NOT normally provided by the school. Course Procedures: You may have already made a specialty dive or dive deeper than your certification allowed, but keep in mind that this does not normally exempt you from doing any of the parts, since, during the course in addition to diving, we perform control exercises, handling equipment, control instruments and accessories and the training is integrated, which means that each exercise relates to the rest as a whole, to make you go from not being a diver at all, to being one. The logical order of completion of the course includes studying the theory beforehand, then doing the practice. The instructor can make some changes in the programming, and repeat some practice, but always complying with the PTRD Standards.

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2. DIVING EQUIPMENT Your instructor will remember all you studies in your Technical Skills Diver course about the Diving equipment concerning the physical characteristics, operating principles, maintenance and use of EANx diving equipment. This will include the following:

• How all equipment must be well maintained and fit for use

• how to handle oxygen equipment safely and its suitability for diving equipment

• how eanx use impacts dive equipment (e.g. increased oxidation and wear),

• how to use standard scuba equipment with eanx, including national inspection, labelling and test

2.1. STANDARDS FOR DIVE CYLINDERS AND OTHER EQUIPMENT Like Technical Skill Diver you will only use equipment that you are familiar with.

Note: this is not a course for experimentation with new or unfamiliar equipment.

To participate in this course we recommended the following equipment:

• Dual tanks/cylinders with dual outlet isolator manifold valve for installing two DIN regulators; • Two sets of regulators, one of the second-stage regulators must be on a 1.5 -2.1 meter hose and the other must be fitted with a necklace. One of the first stages must supply a pressure gauge fitted with a bolt clip and provide inflation for a dry suit (where applicable). • A rigid back plate of metal construction with minimal padding, held to the diver with nylon webbing. This webbing must support five D-rings. • A twin bladder inflatable Buoyancy Control Device adaptable to the back plate (when diving in dry-suit single bladder BCD is • sufficient).Wing size and shape should be appropriate to tank/cylinder size. • two depth gauges or two suitable personal decompression computers (PDCs) or timing devices. • Two mask and fins: Mask should be low-volume; fins should be rigid, non-split. • Two cutting device. • One run-time underwater slate / Wet notes. • One reel and one spool each with 100 metres of line. • one Red Delay Surface Marker Buoy (DSMB) and one Yellow DSMB A compass. • dive-suit to accommodate the expected water temperature (dry-suit to have a separate suit inflation system • One primary light with Goodman handle. • Two reserve lights: reserve lights should have a minimum of protrusions and a single attachment at its rear. • One Jon-line

Note:

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2.2. THE MASK.

2.2.1. DESCRIPTION. The mask is one of the most important elements of the equipment and can make the difference between an excellent dive or a disaster from the discomfort that comes with a poorly fitted or defective mask. The mask for Technical Diving usually has a plastic frame, a tempered glass screen and a silicone. It is fastened on the head with a neopren strap. Choose the right mask: You must place it on your face without using the strap, then suck air through the nose, so that the mask stays stuck to your face without you noticing air inputs down the silicone skirt. If this works and you find it comfortable, then you can look at other aspects such as color, shape, size, etc... Visual defects: There is no problem if you want to dive with lenses, since between this and your eye there are no airspaces. But if you feel more comfortable, there is also the possibility of adapting your glasses, either by changing the glasses that come from the factory, or by going to your local shop with the mask to adapt it. Pull adjustment: To loosen the mask skirt, you should familiarize yourself with the mechanism you use, as they vary in each model. Remember that the mask should not go too tight to avoid breaking the fastening strap and leaving marks on your face.

2.2.1. RECOMMENDED MASK. Low volumen: • The faster the emptying will be. • Easier to store in suit pockets.

Black: • They create a tunnel effect that avoids light distractions and side reflections.

Single glass screen: • Provide greater field of vision • Lack of nose bridge to avoid pressure discomfort

Neopren strap: • Provides better fixation. • Prevents pressure discomfort by having little elasticity. • Longer duration.

2.2.2. MAINTENANCE AND REVIEW. Before the dive: check that there are no cracks in the silicone skirt, nor any other damage to the diving mask. Then check the water tightness. We recommend that you always dive with a spare mask. After immersion: Rinse with fresh water and protect it from bumps or crushes.

2.2.3. HOW IT’S USED. The mask is delicate, do not leave it anywhere. Place it into your fin to protect it, and whenever you enter or get out of the water, wear it on your neck, never on your forehead, as it’s the easiest way to lose it.

When new, they require treatment to remove the silicone layer from the inner face of the glass. To do this, you can burn the glass (beware of silicone) and wash it or use toothpaste or dishwasher soap to remove the layer. Regularly, before each dive, simply apply an anti-fog, either natural as saliva or commercial. From PTRD we recommend the

natural to avoid further consumption of plastics or chemicals, which in the long run could damage the environment.

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2.3. THE FINS Tech diving fins are a more rugged fin that work well with frog kicks and have minimal snag points. Tough rubber and monoprene materials with a short vented blade are preferred by many advanced divers for their efficiency and reliability.

Spring heel straps are quick and easy to don and doff even with thick gloves. Spring heels also self adjust to compressing suits so they stay on without having to be adjusted and can’t rip or tear like traditional rubber straps.

2.4. THE BOTTLE

2.4.1. DESCRIPTION The dive cylinder is a container containing air at high pressure. They are normally manufactured in steel or aluminium. The steel is heavier and the base is semicircular.

Normally we use them as back bottles. Aluminium is very light and does not have the problem of long-term corrosion, so it is often used in countries with high humidity and warm water (because you dive with thinner neoprene and less lead).

The base of the bottles is usually straight. Normally we use them as stage bottles.

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The pressure at which the bottle can be loaded is called “working pressure”, and is indicated on the bottle itself by a die, as well as other data such as year of manufacture and numbering. The working pressure is usually 200 bar, 232bar or 300bar, although the first two are the most normal values. In order to know the total amount of air in a bottle if we let it completely escape at 1 atmosphere or bar of pressure (i.e. on the surface), I will have to multiply the pressure at which it is charged by the volume in litres of the bottle (Vol.).

For example, in a 12L bottle loaded at 200 bar has: Cylinder volume x Working pressure = Total litres of air

12L x 200bar = 2400L of air (would occupy surface, at 1 bar ambient pressure)

I’m sure you’re also wondering how long this air lasts? Well, the answer is DIPEND.

The factors that determine how long a bottle lasts are: The ambient pressure in which you are breathing and the rate of breathing. The first factor implies that at higher ambient pressure the air is compressed and we must remove more from the bottle to maintain our lungs with the same volume as on the surface, because it must be borne in mind that our lungs are not compressed and do not become smaller. In short, the air will last us more at 10 meters than at 20mt, at the same breathing rhythm. The second factor is easy to understand, if I breathe faster, I will consume more air per minute. Therefore, you have to relax and breathe slowly. It is also true, however, that in the case of diving, for example, in currents, it is also often necessary to control the amount of air left in the bottle, because the situation will require more effort and more air consumption.

For example: if we take an average consumption of 20 L / min on the surface, a bottle of 12L loaded at 200bar will last us:

12L x 200bar = 2400L.

If we divide this by the consumption at 1 atm (on the surface):

2400 L L = 120 min (= 2 hours) 20 ⁄min

It would last us about two hours. But if you dive to 10 mt, so the consumption will be double:

At 2 atm: 20L/min x 2 = 40L/min. 2400 퐿 = 60 푚푖푛 퐿 40 ⁄푚푖푛

Therefore, at 10mt, 2 atm, the air from the same bottle would last us half as long.

Calculate the following (diving conditions are good and we take average consumption 20 L/min):

How long will the 12 L bottle charged to 200 atm last if we dive quietly to a depth of 15 meters (equivalent to 2.5atm).

What if we were to dive to 25 mt (3.5 atm)?

Keep in mind that, in real conditions, we have to leave reserve air, so we would take out the count 50 bar. We would therefore make the problem by taking 150bar instead of 200 bar.

At 15mt: 12L x 150 bar= 1800L / 20 L/min = 90 min / 2,5 atm= 36 min.

8 At 25mt: 12L x 150 bar= 1800L / 20 L/min = 90 min / 3,5 atm= 25,7 min.

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The following is a table of buoyancy of the most common bottles related to the environment where they are going to be used, the volume and material of the bottle and the air load they have.

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2.4.2. MAINTENANCE AND OVERHAUL. Although you will normally rent the bottle at the dive centre wherever you go, it is important that you know what its maintenance consists of: - Never let the bottle empty completely, not only because you must never finish a dive at 0 bar, but also because environmental humidity can enter the inside of the bottle and start a corrosion process. - Do not leave the bottle unattended in places where it may fall or hit. Obviously, the valve can get damaged and give you a good scare. If you’re not sure, leave her lying on the floor. - Check that the bottle does not have obvious corrosion or knocks that have left notches in the metal, this can weaken the packaging.

From time to time, the bottles are checked. In Spain every year they have to undergo a visual inspection, which consists of emptying it, opening it and seeing its external and internal state. And every 3 years they undergo a hydrostatic test, to check that the integrity of the package is adequate to support the load with the compressor. A bottle without these revisions cannot be loaded with pressurized air because the container might not withstand the process and burst.

Never try to recharge a bottle with a compressor that is not prepared for breathing air, because you would get a mixture of contaminated and toxic gases, and you could die diving because the pressure increases the toxicity.

2.4.3. HOW TO USE IT. The bottle must be attached to the hydrostatic vest by means of straps. Your PTRD instructor will teach you in practice to place these girths safely and properly.

Remember that care must be taken when transporting and handling the bottle in order to avoid knocks or falls to a different level. In addition to checking that the bottles have the appropriate revisions in force.

If when you breathe, the air tastes or smells, tell your instructor, because the filters that are loaded should make the air clean and dry.

2.5. THE VALVE:

2.5.1. DESCRIPTION The valve or valve of the bottle is the part that allows to open or to close the flow of air, and where we will connect our regulator, of which we will speak later. The material normally used is stainless steel, and when screwing it onto the neck of the bottle, we use O- rings so that the air does not escape through the joints.

There are several types: one or two outputs and modular.

Your PTRD instructor will explain you how the one you use during the course works, but just so you know them, we show you some images.

You can also see in the image on the left that there is a detachable piece inside the tap, and that we call DIN plug adaptor.

This piece is essential if you use first stage regulators such as stirrup or INT, but you will have to remove it if you use

the DIN system.

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They are also distinguished by their operation:

2.5.2. TYPE K VALVE:

A) High-pressure air enters through the junction-(1) B) Once the knob-(2) is opened, the air enters the chamber-(6), supplying the regulator through the outlet-(4). This output could be DIN or INT (with O-ring)

2.5.3. TYPE J VALVE WITH CONSTANT RESERVE A) High pressure air enters through the junction-(1). B) B) The air presses with more than 50 kg/cm2 on the spring of reserve- (5) that once opened the control (2) passes to the chamber-(6) supplying to the regulator by the exit-(4) C) The pressure inside the tank does not exceed 50 kg/cm2 and the reserve spring-(5), closes the air passage to the chamber-(5) D) The reserve is opened manually by means of the control-(3) E) The control-(3) releases the reserve spring-(5), which stops blocking the passage of air, allowing the passage of reserve air.

Function: Adjusts the air outlet of the cylinder.

They go screwed (by hand) to the previous tank o-ring (care with the saltpeter). There are 2 types (With or without reserve respectively).

The reserve is regulated at 50 kg/cm2

2.5.4. MAINTENANCE AND OVERHAUL. Just like the bottle, and as part of it, beware of falls that can break the pieces. Also, try not to over-tighten the tap when you close the bottle, you could break it. If it offers a lot of resistance, it will need maintenance, tell your instructor.

If your regulator system is INT, the core is the one that has the O-rings for the correct functioning of the block, check its state regularly and change it if it is damaged.

2.5.5. HOW TO USE IT. Once you have your equipment ready and your regulator mounted, you will need to slowly open the bottle, counterclockwise. When you reach the top, your instructor will tell you to close the water half turn so that the tap is not blocked after the dive.

2.6. THE REGULATOR

2.6.1. DESCRIPTION

The regulator is the piece of equipment used to reduce the pressure inside the bottle to a breathable pressure.

This is done thanks to a system of pistons and/or membranes, and in two steps, one of them is done in what we call the first stage and is connected to the bottle, and the second step in the second stage, which contains the nozzle to 11

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jacket or hydrostatic vest and a manometer that allows us to know how much air we have in the bottle at any given time and we will talk about later.

RECREATIONAL INTRO TEC TECHNICAL

The first stage of the controller can be of two types: DIN or INT. And this will determine whether or not the bottle needs a core. The INT, international or Yoke or stirrup system requires the fitting to have a core with an O-ring. However, the DIN system does not need a core and the O-ring is in the same regulator.

First Stage INT: A) High pressure air intake-(1), through hollow piston-(2), loads chamber-(4) and all hose-(6) B) The air expands until it reaches the chamber-(4): approx. 8kg/cm2, overcoming the resistance of the spring-(3) plus the pressure of the water that enters by (5). C) The hollow piston-(2) seals the air inlet at high pressure-(1). D) The Second Stage demands air through the hose-(6). E) Lower the pressure in the chamber-(6), the spring-(3) plus the pressure of the water entering through (5), move the hollow piston-(2). The cycle is restarted.

The second stage can be of different shapes, but it always consists of a rounded piece with a nozzle and a purge button on the front, which when pressed activates a continuous flow of air through the nozzle. Once you release the

12 purge button, the airflow should stop, otherwise close the bottle and notify your PTRD instructor, the regulator may need to be replaced.

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Inspiration: A) There is a pressure drop in the chamber-(2) when inhaling through the nozzle-(1) B) The water pressure through the inlets-(5), presses on the diaphragm-(7). C) The diaphragm-(7) when deformed, pushes the cam-(3) allowing the entry of air at low pressure- (8), coming from the 1st stage. D) The air expands in the chamber-(2), and provides inspiration for the nozzle-(1). E) The remaining air, expanded in the chamber-(2), compensates for the water pressure, pushing the diaphragm-(7) to its equilibrium position. F) The diaphragm-(7) drags the cam-(3) and closes the low pressure-(8) air inlet.

Expiration normal: A) The expelled air enters the chamber-(2), through the nozzle-(1). B) The overpressure in the chamber-(2) overcomes the water pressure by opening the exhaust valve-(9). C) The expelled air comes out through (4), in the form of bubbles.

Expiration for emptying A) When the camera is full of water-(2) B) The air exhaled in the form of a blow through the nozzle-(1) evacuates the water through the exhaust valve-(9). C) This process can be aided by pressing the manual demand button-(6) allowing air to enter at low pressure-(8). D) Normal breathing cycle begins.

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Cutted of a type assembly with the second stage with flow regulator and the first stage with balanced piston.

2.6.1. RECOMMENDED REGULATOR IN TECHNICAL DIVING. As an open-circuit technical diver, you will be carrying more than one tank, and consequently, you will be using more than one set of regulators. Each set has slightly different components depending on its purpose, but all will consist of a first stage, a second stage and a high-pressure hose with SPG — with one exception we’ll get to later in this post.

Which components are part of your individual regulators depends on when you are planning to use them on the dive. Roughly speaking, you can divide tech dives into three phases: the bottom part, travel to and from the bottom part, and the decompression phase. However, all technical diving regulators must:

• To be solid and quality construction. • To be designed for cold and deep water. • To have DIN type connection: reduces the risk of leakage. • To facilitate the correct routing of the hoses: they reduce possible friction. • To be assembled with appropriately sized hoses: avoids potential tangles.

2.6.2. BACK-GAS REGULATORS Bottom, or ‘back-gas,’ regulators attach to your twinset or your main sidemount tanks. While the term bottom gas is pretty self-explanatory, ‘back-gas’ refers to the fact that the twinset containing this gas is usually on your back. Whether you are diving air, nitrox or trimix, these are the regulators that you will be using during the deepest phase of your dive, when your breathing gas is most dense and therefore hardest to breathe. That means you are looking

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2.6.3. REGULATOR CONFIGURATION If you are diving twinsets, you need a first stage each for your left and right tank, also called left and right post.

While there are some variations, most tech divers will have a second stage with a 1,5-2,1 mt hose on the right as well as their inflator hose leading to their wing. The long hose connects to the second stage that tech divers generally breathe from. The hose is longer to allow divers to share gas and exit a restriction while swimming behind each other. The left tank typically holds a second stage on a short regulator hose with a ‘necklace’ made from bungee cord or surgical tubing, as well as a high-pressure hose and an SPG. There may also be another inflator hose here for a drysuit or the second bladder of the BCD if it has one. The necklace allows the diver to easily reach their second stage in case they need to donate their long hose. Did you notice there is no SPG on the right post? When diving manifolded (connected) twinset tanks, the diver accesses gas from both tanks through one regulator as long as the manifold isolator valve is open. This means that as long as there is no equipment failure, one SPG is enough.

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2.6.4. SIDEMOUNT SETUPS

Sidemount setups can vary more as the configuration in general is more individual.

One common option, however, is to rig the right tank with a first stage, a second stage on a long hose, and an SPG on a short high-pressure hose, usually about 6 inches (15 cm) long.

There may also be an inflator hose for a drysuit or a second BCD bladder here.

On the left tank is a first stage with a second stage attached to a short hose and again equipped with a necklace.

Often, there is an angled ‘elbow’ piece between the second stage and the hose, allowing divers to easily identify which tank they are breathing from.

Additionally, there is a short high-pressure hose with an SPG and an inflator hose connecting to the sidemount harness and wing.

Many sidemount divers run their inflator across their body rather than over their shoulder.

This means that suitable regulators often have a fifth low-pressure port at a right angle to the other ports.

It’s also easier to streamline a sidemount setup by using first stages that have the capacity to swivel and therefore allow cleaner hose routing.

Some manufacturers have started offering dedicated twinset and sidemount regulator sets.

This is a good way to purchase all the bits and pieces in one go. In the case of twinset regulators for example, they might have low-pressure ports pointing downward at an angle for better hose routing.

Sidemount sets will have swiveling first stages with five low-pressure ports, one of which is at a right angle.

2.6.5. DECO REGULATORS

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Tech divers use these regulators with oxygen-rich nitrox mixes to help accelerate decompression and, therefore, the units must be suitable for use with oxygen.

In practice, this means choosing a regulator that is made of a material with a high flash-point: titanium, for example.

The regulator must also be cleaned for oxygen use, and any O-rings and greases used in the process must be oxygen- compatible.

Not every regulator will be suitable fresh out of the factory, so it’s important to check on this when you are buying your deco regs.

As we generally use these regulators on shallower parts of the dive, we can use unbalanced first stages. However, this is still life-saving equipment, so the general recommendation to buy the highest quality possible while remaining practical.

2.6.6. TRAVEL GAS REGULATORS Trimix divers usually use ‘travel gas,’ a breathing gas that does not contain enough oxygen to sustain life on land.

Their components will often resemble deco regulators, although they may not need to be oxygen-clean depending on the gases the diver uses.

If all that sounds daunting, consider this: you can usually rent equipment for your tech courses from the instructor or shop that is conducting the course.

Most budding tech divers qualify initially to dive a twinset or sidemount tanks for the bottom part of the dive and one deco gas, so that’s ‘only’ three regulators.

Additionally, you may be able to reconfigure some of the components you already own.

Last, but not least, consider where you will be diving. If you’re going to be in cold water, make sure your regs are suitable for that.

If you will be spending a lot of time in remote areas, some brands will be easier to maintain than others due to the availability of spare parts and service technicians.

The first step when it comes to choosing regulators for technical diving is to speak to your instructor and other tech divers about what they use. Spend some time researching before going on that shopping spree.

2.6.7. MAINTENANCE AND OVERHAUL. Rinse your regulator with fresh water, but be careful not to allow water to enter the first stage or into the inside of the pipes because they may deteriorate.

To do this, never press the purge button with the second stage in the water, nor submerge the first stage without the cap that covers the part that connects to the bottle, or cover it with your finger while rinsing it.

2.6.8. HOW TO USE IT. In the first equipment assembly class your PTRD instructor will explain in detail the use of the regulator. Still, here are some recommendations:

Breathe deeply and slowly, emptying your lungs before the next breath.

Treat your regulator well, keep in mind that it is the piece that will give you the air, if you hit it can be damaged.

Do not drag it into the sand or stones, they can get inside the mechanism and damage it.

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Check your regulator and all your equipment before leaving the dive center, where you can replace what doesn’t work. Not only that air comes out, but that the mouthpiece is in good condition and that when you breathe, you can do it easily and do not notice resistance.

Close the bottle to transport your equipment from the dive centre to the dive site. And it protects the second stages and the pressure gauge from dragging on the ground.

REMEMBER:

the regulators are “fail-safe”, i.e. if there is a fault the regulator goes into continuous flow, leaving air continuously. This will allow you to finish the dive with enough time to make a correct ascent, while breathing.

2.7. THE REBREATHER SYSTEM The aim of this section is to let you know the basic information about rebreather like back gas.

To use this apparatus you must to do the specific course.

The rebreather is nothing more than a respiration recycler, an autonomous closed-circuit breathing system where the diver continues to breathe, using inert gas (diluent) which in the air is nitrogen.

Our breathing, passing through a soda lime filter, is purified of CO2 and the oxygen used by our metabolism is restored.

Basically, the recycler consists of a breathing circuit (Loop) in which the breathing gas circulates in a single direction and by soft bags or against the lungs that allow the diver to transfer the gas from the lungs to the machine.

This also allows the diver to have, at a constant depth, a buoyancy that does not vary with breathing as, on the contrary, occurs in the open circuit where we have a change in volume each time we exhale and breathe.

In the figure on the left we see the principle of the functioning of a rebreather and the cycle that the breathed gas has to make to be purified of CO2.

2.7.1. THE SCR RECYCLER In the figure on the right we have the complete diagram of an SCR rebreather, which uses a mixture of gases enriched with O2, usually a nitrox 32. The recycler can be divided into two main categories: Semiclosed Circuit Rebrather (SCR), Closed Circuit Rebreather (CCR). Among the SRCs is the passive recycler or PASCR, is a machine with a very simple operation, does not need to be monitored and is used, as in all SCR rebreather, a predefined mixture. This machine expels the ventilated gas to be replaced by the mixture from the bottle. It consists of two bellows-lungs-bags inside each other.

The mixture from the tank fills both bellows.

As a result of exhalation, a part, coming from the larger external lung and before being breathed in again, passes 18 through the soda lime filter.

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Diagram of the breathing gas circuit of a semi-closed passive-addition rebreather circuit.

1 immersion / surface valve with non-return ring valves

2 exhalation tube

3 contra lung antechambers

4 bellows non-return valve for discharge

5 discharge bellows

6 pressure relief valve

7 main bellows

8 addiction valve

9 Scrubber (axial flow)

10 inhalation tube

11 bottle of breathable gas

12 bottle valve

13 first stage regulator

14 submersible manometer

15 bailout valve

Thanks to this system after a certain number of breaths we have a total change of recycled gas, ensuring a sufficient amount of oxygen and cleanliness of the loop.

The depth limit is set by the mix used.

Another SCR is the constant mass recycler. It is the most known and used.

It’s an easy-to-build mechanical rebreather. Also this SCR uses predefined mixtures, it is based on injecting fresh gas into the inspiratory part of the Loop to enrich the mixture already breathed and filtered.

As you can see in the following figure the system is very simple: fresh gas enters the inspiratory lung through a flow regulator.

The Loop in this case consists of two lungs, one inhalation and one exhalation, we have a pressure relief valve that serves to expel excess gas and is located on the side of the exhalation.

After being breathed, the gas passes through the filter to be purified and re-established in oxygen.

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Diagram of a constant mass SCR:

1 immersion / surface valve with ring check valves 2 exhalation tube 3 Scrubber (axial flow) 4 against lung 5 Loop overpressure valve 6 inhalation tube 7 breathing gas bottle 8 bottle valve 9 first stage of the regulator 10 submersible manometer 11 automatic diluent valve 12 orifice for constant mass flow measurement 13 manual bypass valve 14 bailout valve At the recreational level is an optimal device, easy to use, but not to be underestimated. In the market we can find different models like the Azimut, the Dolphin, and others.

2.7.2. THE CCR REBREATHER Today, the Rebreather with the best performance on the market, is undoubtedly the closed circuit (CCR). The depth limit is given by the diluent mixture and has an autonomy absolutely superior to any other Rebreather. There are mainly two types of RCC: manuals (mCCR) and electronic (eCCR). In RCC, functioning is based on the metabolic consumption of the user, i.e. the consumption of oxygen actually used by our body. In the CCR, unlike the SCR, where there is a fixed percentage of oxygen and varies according to the depth PpO2, we have a constant PpO2 and a percentage of the oxygen variable so that at any depth we have the best breathable mixture, the famous optimal mixture. The CCR consists of two cylinders, one of oxygen and one of diluent which could also be air.

Inside the machine we have the soda lime filter that fixes the discarded CO2 during our metabolism, then there is an

20 oxygen injection based on the actual consumption of our body and can vary from 0.5 lt/m to 0.9 lt/m under normal conditions.

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In the electronics it happens automatically, that is, the electronics monitors the oxygen and keeps it constant by means of electric valves (solenoids) at the level preset by the user.

In the manual we have screens called monitors where we read the oxygen value and the injection is done manually through a bypass. In addition, we have a mechanical flow regulator that continues to inject into our circuit a constant amount of oxygen that must be adjusted to our metabolic consumption: this is regulated before the dive and if it is calibrated well, at constant depth we have almost no correction, except that we change our physical effort.

In the drawing below we see how a CCR works, as we can see we have a breathing loop formed by corrugated tubes, the nozzle that inside has non- return valves to maintain the breathing cycle in a forced sense, the counter lungs, the bottle and the filter container where the soda lime is placed that absorbs the residual carbon dioxide from breathing.

Diagram of an electronically controlled eCCR. 1 immersion / surface valve with ring check valves 2 exhalation tube 3 Scrubber (axial flow) 4 Against lung 5 overpressure valve 6 inhalation valve 7 oxygen tank 8 oxygen tank valve 9 Oxygen Absolute Pressure Regulator 10 submersible oxygen manometer 11 manual oxygen bypass valve 12 orifice of constant mass flow of oxygen 13 Electronically controlled electromagnet-operated oxygen injection valve 14 bottle of diluent 15 Thinner bottle valve 16 diluent regulator 17 submersible diluent manometer 18 bailout valve 19 manual diluent valve 20 automatic diluent valve 21 oxygen sensor cells 22 electronic control and monitoring circuits 23 main and secondary screens

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2.8. BACK PLATE SYSTEM Backplate systems consist of three basic components: a rigid (usually metal) plate, a harness system and a back- inflation air cell. These components can be mixed and matched to fit a diver’s unique body shape or customized to the needs of the dive. Florida cave diver Greg Flanagan has been credited with inventing the first backplate design in 1979. It was intended to prevent heavy twin cylinders from shifting during the dive, but the technical divers who adopted backplates found other advantages. In addition to rock-solid stability, simple harness systems left the diver’s chest unencumbered and, when incorporated with a back-inflating air cell, they provided a more horizontal swimming position while also providing ample lift without squeezing the diver. Of course, these are all benefits for recreational divers, too. The important thing to consider when evaluating backplate systems is that they are endlessly customizable. No one size fits all divers, and no one configuration fits all dives. Here are the basics to consider.

2.8.1. THE BACK PLATE Typically made of stainless steel (although hard plastic and aluminum are options, too), the plate is designed to hold cylinders securely to the diver’s back. Holes and slots cut into the plate allow for a variety of tank bands, harnesses and attachment points for accessories. Stainless-steel plates, which provide about 6 pounds of negative buoyancy, are preferred by coldwater divers to help offset the positive buoyancy of drysuits and undergarments. Plastic and aluminum are often the preferred choice for traveling divers facing airline weight restrictions. For divers considering a backplate system, it’s important to try on the plate for size. The base of the plate should be even with the diver’s waist and the top of the plate parallel with the top of the shoulder blades. This is a basic suggestion as various body shapes can alter the sizing. The most important thing is the diver’s comfort. The length of a standard plate works well for most men; however, a woman’s torso length is shorter compared with a man of equal height. A standard plate can be too long and press on the top of the buttocks, which is uncomfortable and interferes with the diver’s fin kick. Smaller-length plates, which are now on the market, address this issue. Typically, they are made of aluminum since a diver needing this size generally does not need added ballast.

2.8.2. THE HARNESS The original backplate systems featured a harness made from a single piece of 2-inch webbing routed through the notches of the plate to form shoulder straps and ending in a belt cinched at the diver’s waist. Most divers also add a crotch strap to keep heavy tanks from shifting forward when swimming in a head-down position.

HORGARTHIAN HARNESS ASSEMBLY Here is the recommended procedure to assemble and adjust our hogarthian harness on to a backplate. Tools that will make assembly easier are a measuring tape and a pair of needle nose pliers. All mention of left, right, front, and rear are interpreted from the perspective of the diver when wearing the harness.

Weave Shoulder Straps: Two removable long webbing sleeves are shipped already threaded onto the harness webbing. Check the position of the webbing sleeves to verify the ends are centered approximately one inch on each side of the grommet. Position the grommet of the webbing over the upper bolt hole on the tank side of the plate. Thread the webbing through the angled slots to the diver’s side of the plate, and back through the upper slots. With the grommet aligned over the bolt hole, only the webbing sleeves should be in contact with the plate slots.

Add Shoulder D-Rings: Install one bent D-ring and slide on the divers right shoulder strap, positioned approximately 12-inches of webbing length from the top of the plate. The bent D-ring is turned up to extend slightly from the strap.

Thread the webbing up through one side of the slide, over the base of the D-ring

and back down through the slide. Weave the left shoulder D-ring in a similar

22 manner to the right. Along with the D-ring also include the bungee loop, so that both the D-ring and bungee loop are captured and held together in place by the

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Add Elastic Bands and Webbing Sleeves: T hread one or two of the elastic bands onto each shoulder strap. Then thread a short webbing sleeve onto each shoulder strap. Position the sleeve so that the center of the sleeve is approximately 18-inches from the base of the shoulder D-rings.

Weave Waist Straps: Thread the webbing thro ugh the inside slots at the bottom of the plate, then through the slots closest to the edges of the plate to form the waist straps. Each of the webbing sleeves should be centered between the slots and only the sleeves should be in contact with the plate. The outside edges of the webbing should be at the top of the inner slots so that the outer faces of the shoulder straps become the inner faces of the waist straps. Properly threaded, the shoulder straps should lay flat against your sides without twisting.

Add Waist D-Ring: Install one straight D-ring and slide on the left waist s trap, positioned approximately one hand width of webbing length from the plate.

Add Waist Strap Accessories: A loose black plastic buckle is provided for securing removable right side accessories, such as a light canister or pocket. For now, thread the right waist strap webbing through the plastic buckle gate and position the buckle close to the plate. Thread the strap through the end slot of the plastic buckle and close the tongue. Lace any non-removable left side accessories that will be permanently retained by the S/S buckle, such as a waist belt sheath for a line cutter, on to the left waist strap.

Weave S/S Belt Buckle: Starting from the front of the metal buckl e, thread the left waist strap through the larger end slot of the buckle. Position the buckle approximately 18-inches of webbing length from the plate left waist slot. Then thread the webbing from the back through the center slot and through the front of the inner most slot. Then thread the webbing through the back of the larger end slot so there are two thicknesses of webbing through one slot and pull the weave tight. The excess webbing will now be doubled back and lay flat along the inside of the left waist strap.

Weave Crotch Strap: A bent D-ring with a non-serrated slide, along with an abrasion sleeve, is shipped already laced onto the crotch strap, position the D- ring approximately 12-inches from the un-sewn end. With the bent D-ring pointing away from the diver, lace the tail of the crotch strap through the front of horizontal slot at the bottom of the plate and back through both slots of the non-serrated slide a second time, forming a loop about 4-inches in length. Pull the abrasion sleeve near the rear D-ring and tuck the excess of the tail end of the webbing into the sleeve.

Variations: The webbing sleeves can be omitted and serrated slides woven behind the plate waist slots. The abrasion sleeve can be removed from the crotch strap.

Particularly if scootering, the rear loop used to attach the crotch strap to the plate can be formed using a serrated belt slide separate from the one used to hold the rear D-ring. Use only two elastic straps on the harness and thread

one on the inflator assembly near the elbow. 23 Omit the bungee loop and thread one of the elastic straps on the left shoulder webbing above the D-ring for use in

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Omit the plastic buckle and weave a long left waist strap so the metal buckle will reach far enough to the right to retain the canister.

ADJUSTING A HOGARTHIAN HARNESS There are some initial dry adjustments of the harness that should be made to achieve a proper fit. Be patient; some adjustments may require partially disassembling and rethreading components of the harness. Avoid the temptation to trim any excess webbing from the straps until after final in-water adjustments are made and you are certain you are satisfied with the configuration. If the webbing is trimmed, seal the ends of the webbing with a flame or hot knife to prevent unraveling.

• A common error is making the shoulder straps much too tight. Having the straps too tight will cause the plate to ride too high on your back and can also impede your respiration. Shoulder straps should be left loose enough that with your wrist resting on the top of your shoulder, you can reach down your back with your hand and touch the top of the plate. The top of the waist belt should fall at or slightly below your navel.

• The shoulder straps should also be loose enough that you are able to e asily slip your fist under the shoulder straps. Keep in mind that later you must be able to don your harness while wearing your exposure protection. The BC inflation hose assembly is threaded through, and retained by, the left shoulder bungee loop.

• The waist D-ring is positioned along the mid-line of the diver’s left side, about in line with where a tailored shirt side seam would lay.

For most divers this will be about a hand width of webbing in front of the plate.

• Adjust the position of the S/S buckle on the left waist strap so that the buckle is to the diver’s right of center, allowing the crotch strap to be at the diver’s center. If the right waist strap is excessively long, instead of trimming, you can weave it through the loop of waist belt sheath and even double back through the loops again if necessary.

• After adjusting the harness, adjust the length of the crotch strap to be snug. It should not be so tight as to pull the waist straps down. While adjusting the length of the strap, the rear D-ring should be positioned as high as possible where the D-ring can still be reached with your right hand and yet not be blocked by the cylinder(s).

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• The primary light canister is pushed all the way back to the plate on the right waist belt and secured with the plastic buckle. If the light on/off switch is on the canister lid, some divers prefer to mount the light canister with the on/off switch pointed toward the divers feet in order to make the switch easier to reach. Using a separate plastic buckle to retain the canister instead of the metal buckle avoids scoring the canister, and allows harness doff and don without accessories sliding off the strap. The backup lights are clipped to the shoulder D-rings and secured with an elastic band.

Once you are satisfied with initial dry adjustments, you are ready to make final minor adjustments. The most efficient and safest method is with assistance of your buddy or instructor in a swimming pool or other body of confined water. In shallow confined water you can work together and can make easy entry/exit to evaluate adjustments. While everything is soaking wet, repeatedly don and doff the harness with your entire diving configuration of cylinders, regulators, accessories and exposure suit. Tweak the length of the shoulder and waist straps along with the crotch strap until you can gear up easily and remove the harness quickly. Check the in-water trim. Many divers have said that when everything is correct, the configuration just ‘feels right’ and seems to automatically achieve proper trim. Next practice repeatedly clipping the SPG, primary regulator, stage/deco bottles, lights and reel. Tweak the D-ring positions until everything can be performed smoothly underwater and you can easily clip to the D-rings with every attempt. By https://www.divegearexpress.com/

2.8.3. THE WING OR BACK-INFLATION AIR CELL The ability to swap air cells to fit the diver and meet the demands of a specific dive is one of the most useful features of backplate buoyancy systems. Often called wings, back-inflation air cells are available in a variety of sizes, with lift capacity ranging from less than 30 pounds to more than 100 pounds. They come in two different styles. The original and still-popular horseshoe style extends from the top of the tank down along the sides, while newer “donut” styles wrap completely around the tank (or tanks). The advantage of the “donut” is the easy transfer of air from one side of the wing to the other in any swimming position. A diver using a horseshoe wing may find air shifting to only one side of the wing if he is descending and leaning to one side when adding air to offset negative buoyancy. The additional air will move only to the highest point of the wing. Restoring balance requires moving to a slightly upright position. Some horseshoe wings use bungee cords to help control air movement. Divers new to the concept of backplates are often surprised to learn that the amount of lift is not the main feature to consider when selecting a wing. More important is the size of the wing. Single-tank divers generally need a wing with approximately 30 pounds of lift. A diver wearing a set of double 100-cubic-foot tanks will require a wing with approximately 60 pounds of lift. Even though the double tanks are not so negatively buoyant as to need this amount of lift, the width of these wings will position nicely along the edge of the tanks, enabling easier buoyancy control at depth and on the surface. Individual body shape is the second feature to consider. A large, 6-foot-tall diver wearing double 80-cubic-foot tanks could use a wing with 60 pounds of lift and be very comfortable; however, an individual who stands 5 feet 2 inches wearing the same configuration may feel the gear is diving him! The shorter diver will be dealing with two problems. The wing will extend too low (over the buttocks) and will shift the diver to a head-down position. The extra material will also create drag, leading to unnecessary work. If the wing is too short (above the kidneys), the diver will be in a head-up or standing position, causing him to drag his feet. A properly sized wing should extend no further than the end of an individual diver’s torso. An overly large wing used on a single tank will wrap around the single tank when the diver is in the horizontal position. This “taco” effect will create a space for air that will not vent easily. Surface use of an oversized wing will force the diver into a face-down position if the wing is fully inflated. An undersized wing, on the other hand, may mean the diver is unable to ascend easily from depth or float comfortably on the surface.

2.8.4. SUGGESTIONS FOR SELECTING A WING

In the technical market, this is commonly referred to as a “Hogarthian Rig,” a reference to Bill Hogarth Main, the technical diver who popularized this simple and efficient configuration. Manufacturers also offer prebuilt harnesses 25

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Imagine if someone said to a diver, “Carry this sea anchor on every dive. You don’t need it now, but there is a possibility you will need it on a dive some time a few years from now.” Silly, yet this is what happens when a recreational single tank diver purchases an oversized wing primarily intended for use with doubles because they have a vision of someday becoming a technical diver. Selecting a wing oversized for their needs creates a lot of unneeded drag for which they will pay the price in extra effort and higher gas consumption on every dive, for years!

In our opinion, too much emphasis is placed on lift capacity when choosing a wing. If the diver is overweighted, they need the extra capacity to counter the excess weight, but “getting the lead out” is a separate discussion. In most diving, assuming the diver is properly weighted, the wing only needs enough lift capacity to counter the negative buoyancy of the complete cylinder configuration carried by the diver as they enter the water.

One often hears justification for needing excess lift is because the diver carries a very large amount of lead weight to counter the buoyancy of their thick wetsuit or drysuit and needs the excess lift capacity “just in case.” The solution is not to have an oversized wing to counter the weight, but rather, to configure the lead so it can be incrementally dropped in an emergency. Yes, we acknowledge there are special circumstances in extreme technical diving that require enormous excess lift capacity, but these are pretty rare. In general, lift capacity when choosing a wing is a minor consideration.

Beyond the issue of drag, there is a special buoyancy control concern when using an oversized back-inflation style BC wing inappropriate for the size of the tank or tanks. The figure below illustrates an oversized aircell. Air inside the cell causes the wing to wrap around the tank in a manner similar to a taco. This ‘taco’ effect traps air above the level of the BC hose elbow when the diver is in a normal swimming position, which may interfere with venting (deflating) the BC.

The figure below shows the benefit of eliminating tank wrap by correctly sizing the aircell with the tank or tanks. The entire wing is now below the level of the BC hose elbow, allowing the diver to vent (deflate) the aircell either by using the remote exhaust valve in the hose elbow or by holding the end of the hose up and depressing the oral inflation/manual deflation button.

Some circumstances create a need for “backup” lift capacity (“backup” does not mean “more”). When diving larger

26 steel doubles configurations, the typical diver has such negative buoyancy when entering the water that it would be

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will serve for backup buoyancy control, especially if the diver is able to remain horizontal at all times. Many disagree and the diver should perform a controlled trial to prove they may rely upon their drysuit as a backup BC. When diving with very negative configurations and a wetsuit or unproven drysuit, the need for a backup buoyancy becomes critical and this is the justification for redundant bladder wings.

Our Recommendation: The cylinder size, type and configuration is the best guide to selecting the correct wing. While many doubles wing designs can be compressed to a more compact size for occasional use with singles, keep in mind they are not designed to be used primarily as singles wings and when compressed they are not optimal. Realistically, there is no wing perfect for both singles and doubles, or even a wing perfect for all doubles. That’s why there is a range of wing sizes, each one best suited to a specific range of cylinder configurations. Wing selection is not difficult if you first determine which cylinder configuration you will most likely be diving and only then choose the wing best suited to that configuration. For obvious budget reasons a diver would like to own only one wing, suitable for “all occasions.” But if the range of cylinder configurations you dive is broad, then the best choice for efficient, safe and comfortable diving may be to own more than one wing.

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2.8.5. PROS AND CONS OF BACKPLATE SYSTEMS So why use a backplate system? Maintaining trim and a horizontal swimming position is easier with back inflation and is the primary reason for selecting this style of dive gear. In a horizontal position, the diver’s fins are off the bottom, which reduces silting that can damage coral or other sessile marine organisms. The simple harness of a backplate system leaves the chest area unencumbered, and inflating the wing doesn’t create a feeling of squeeze. Women, in particular, have discovered that the versatility in plate sizes and the ability to rearrange straps to their torso shape allows for a better, custom fit.

The drawback in backplate systems is the tendency of back-inflation air cells to float the diver in the face-down position at the surface. This tendency is exaggerated if the diver is using a wing that is too long and/or is overinflated. Weights that are positioned in the front will also create this effect. Backplate divers will find swimming on their back is the most comfortable position at the surface.

2.9. THE DRY SUIT Usually a technical diver plans his dives in adverse weather conditions due to the dive site or the chosen depth that generally exceeds 30 mt. Generally a technical diver has to prevent low water temperatures.

A dry suit or drysuit provides the wearer with environmental protection by way of thermal insulation and exclusion of water,and is worn by divers, boaters, water sports enthusiasts, and others who work or play in or near cold or contaminated water. A dry suit normally protects the whole body except the head, hands, and possibly the feet. In hazmat configurations, however, all of these are covered as well.

The main difference between dry suits and wetsuits is that dry suits are designed to prevent water entering. This generally allows better insulation making them more suitable for use in cold water. Dry suits can be uncomfortably hot in warm or hot air, and are typically more expensive and more complex to don. For divers, they add some degree of operational complexity as the suit must be inflated and deflated with changes in depth in order to minimize “squeeze” on descent or uncontrolled rapid ascent due to excessive buoyancy.

A great advantage to keep in mind is that a drysuit can be considered as a secondary element of buoyancy: backup in case of wing failure.

Dry suits provide passive thermal protection: They insulate against heat transfer to the environment. When this is insufficient, active warming or cooling may be provided, usually by a hot-water suit, which is a wetsuit with a supply of heated or chilled water from the surface, but it is also possible to provide chemical or electrically powered heating 27

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There are two types of dry suits:

constant volume: membrane dry suit

variable volume: neoprene dry suit

2.9.1. MEMBRANE Membrane dry suits are made from thin materials which have little thermal insulation. They are commonly made of stockinette fabric coated with vulcanized rubber, laminated layers of nylon and butyl rubber known as Trilaminate or Cordura proofed with an inner layer of polyurethane. With the exception of the rubber-coated stockinette, membrane dry suits typically do not stretch, so they need to be made slightly oversized and baggy to allow flexibility at the joints through the wearer’s range of motion and to allow the hands and feet to pass through without difficulty. This makes membrane dry suits easy to put on and take off, provides a good range of motion for the wearer when correctly sized and sufficiently inflated, and makes them relatively comfortable to wear for long periods out of the water compared to a wetsuit or close-fitting neoprene dry suit, as the wearer does not have to pull against rubber elasticity to move or keep joints flexed.

To stay warm in a membrane suit, the wearer must wear an insulating undersuit, today typically made with polyester or other synthetic fiber batting. Polyester and other synthetics are preferred over natural materials, since synthetic materials have better insulating properties when damp or wet from sweat, seepage, or a leak.

Reasonable care must be taken not to puncture or tear membrane dry suits, because buoyancy and insulation depend entirely on the air space in the undersuit, (whereas a wetsuit normally allows water to enter, and retains its insulation despite it). The dry suit material offers essentially no buoyancy or insulation itself, so if the dry suit leaks or is torn, water can soak the undersuit, with a corresponding loss of buoyancy and insulation.

Membrane dry suits may also be made of a waterproof but breathable material like Gore-Tex to enable comfortable wear without excessive humidity and buildup of condensation. This function does not work underwater. Sailors and boaters who intend to stay out of the water may prefer this type of suit.

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2.9.2. NEOPRENE The neck seal, the zip, the inflator, a wrist seal, and the manual cuff vent of a neoprene dry suit.

Neoprene is a type of synthetic rubber which can be foamed during manufacture to a high proportion of tiny enclosed gas bubbles, forming a buoyant and thermally-insulating material, called “foamed neoprene”, “foam-neoprene” or “expanded neoprene”. Wetsuits are made from this material as it is a good insulator, waterproof, and is flexible enough for comfortable wear. The neoprene alone is very flexible, but not very resistant to tearing, so it is skinned with a layer of knit fabric bonded to each side for strength and abrasion resistance. Foamed neoprene may be used for the shell of a drysuit, providing some insulation due to the gas within the material, as in a standard wetsuit. If torn or punctured, leading to flooding, a foam-neoprene suit retains the insulation and buoyancy of the gas bubbles, like a wet suit, which is proportional to the thickness of the foam, Although foamed-neoprene dry suits provide some insulation, thermal under-suits are usually worn in cold water.

Neoprene dry suits are generally not as easy to put on and remove as are membrane dry suits, largely due to a closer fit which is possible due to the inherent elasticity of the material, and partly due to greater weight. As with wet suits, their buoyancy and thermal protection decreases with depth as the air bubbles in the neoprene are compressed. The air or other gas in the dry fabric undergarments providing insulation under a dry suit is also compressed, but can be restored to an effective volume by inflating the drysuit at depth through an inflator valve, thus preventing “suit squeeze” and compacting of the air-filled undersuit. Foam-neoprene tends to shrink over the years as it loses gas from the foam and slowly becomes less flexible as it ages. An alternative is crushed or compressed foam neoprene, which is less susceptible to volume changes when under pressure. Crushed neoprene is foam neoprene which has been hydrostatically compressed so much that the gas bubbles have been mostly eliminated, this retains the elasticity of foamed neoprene which allows freedom of movement, but does not provide much insulation, and is functionally more like a membrane suit.

2.9.3. RECOMMENDED DRY SUIT FOR TECHNICAL DIVING It is recommended to use a constant volume suit: The buoyancy of the suit does not vary because its density does not vary with the increase in pressure. It is very important that is very flexible, with telescopic body and

always equipped with two pockets and positioned on both thighs.

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2.10. LIGHTS FOR TECHNICAL DIVING We distinguish 2 types:

2.10.1. MAIN TORCH, WITH OR WITHOUT UMBILICAL CORD. • Battery mounted on the right hip, if it is separated from the head. • Light carried on the left hand with a Goodman handle. • Rechargeable battery preferably lithium ion: less maintenance and care than lead batteries.

2.10.2. -LIGHT RESERVE. • A mandatory light mounted under the armpits chest harness. (certain types of diving will require 2 lights). • Of non-rechargeable batteries.

2.11. CUTTING INSTRUMENTS

2.11.1. MAIN INSTRUMENT. • Knife (required by law), small dimensions: with two cutting systems. • Placed on the waist of the harness in an accessible position with both hands.

2.11.2. SECONDARY INSTRUMENT. • Several options: scissors, trilobites, ... • Stowed in suit pocket.

2.12. ACCESSORIES

2.12.1. MAIN INSTRUMENTS • Clock • Located on the right wrist. • Depth gauge: located on the right wrist, with medium depth information. • Compass: located on the left wrist.

2.12.2. -SECONDARY INSTRUMENT. (BACKUP) • Computer.

2.12.3. BOUYS AND REELS • SMB: is a buoy swollen on the surface, mark the position of the diver. • DSMB (it is suitable for this type of diving): is a decompression buoy, it swells underwater, mark the position of the diver. It must to be in two colours: RED to indicate normal situation normal and YELLOW to indicate emergency, that help is required. • Reel: with at least 100 meters of line • Spool: with at least 30 meters of line, with retractable carabiner, it can be mounted with the buoy or unassembled, we will place it in the left pocket of our suit .

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3. EANX HAZARD Your instructor will remember all you studies in your Advanced Nitrox Diver course. concerning hazards related to the handling of EANx mixtures with elevated oxygen levels. This shall include at least the following: • Risk of fire or explosion when using pure oxygen • Factors likely to increase the risk of fire or explosion, including location and ventilation

Any combustion phenomenon, both slow and explosive, requires three elements simultaneously present and distinct: a fuel, a comburent, and a source of ignition. If only one of these elements is missing, a burning phenomenon cannot happen. This condition is defined as a “triangle of fire”, a name whose significance is unequivocal 2Oxygen is a burning phenomenon and this means that in order to avoid incendiary events, systems operating in the presence of high-pressure oxygen or high concentrations should not act as fuel (a simple o-ring in rubber) or offer themselves as a source of triggering (a small static electricity discharge). Any equipment and any machinery that comes into contact with or operates with oxygen must comply with specified parameters as a degree of “oxygen / oxygen compatibility”. Given that high oxygen pressures and gas mixtures with high oxygen percentages are omnipresent in technical immersion, non-compliance with these procedures means serious and predictable risks of explosion and / or fire resulting from serious consequences for operators and users of mixtures.

3.1. OXIDATION AND COMBUSTION Another property of oxygen is his remarkable ability to react with numerous other substances by starting a chemical process call Another obvious property of oxygen is its remarkable ability to react with many other substances by initiating a definitive chemical process “oxidation”. This phenomenon is responsible for rust formation, hardening of rubber gaskets, and many other phenomena. Human cells are also subject to oxidation and in particular those that are responsible for the wonderful and complex breathing phenomenon. Rapid oxidation is even able to generate a certain amount of heat that, beyond a certain level, could trigger so-called autocombulating phenomena. Combustion is a process of chemical transformation in which a fuel and a comburent, reacting to each other due to a source of triggering, produce energy. Although oxidation is not a per se dangerous phenomenon, oxidized materials can act both as a source of ignition or as a fuel. Combustion in the presence of high-pressure oxygen and / or concentrations is always a violent and incendiary phenomenon.ed oxidation “. This phenomenon is responsible for the formation of rust, the hardening of the rubber seals and many other phenomena. Even human cells are subject to oxidation and particularly those devoted to the wonderful and complex phenomenon of breathing. A rapid oxidation can even generate a certain amount of heat that in addition some level could trigger so-called phenomena of spontaneous combustion. Combustion is a process of chemical change in which a fuel and a for combustion, reacting together thanks to a source of ignition, producing energy. Although the oxidation is not a phenomenon in itself dangerous, oxidized materials can acting both as a source of ignition is as combustible substance. Combustion in the presence of oxygen at high pressures and/or concentrations is always a phenomenon of violent

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3.2. OXYGEN COMPATIBILITY Any material is said to be “compatible oxygen” if it is able to stay in touch and operate with both pure oxygen and high-concentration oxygen blends without making it combustible. Though there are no fully compatible materials (even reinforced concrete and metals burn in the presence of high oxygen concentrations), the degree of compatibility of a material with oxygen primarily depends on two properties of the material: from its temperature of oxygen ignition, otherwise defective self-ignition, which is the temperature beyond which a material will ignite even in the absence of a source of ignition and its ability to disperse heat. As long as a material can be defunct compatible oxygen, its ignition temperature must be greater than the temperature reached by a system during its operation. The following graph illustrates the ignition temperatures of certain metals depending on the oxygen pressure in which they are immersed. The data in the tables are obtained through laboratory tests whose implementation is not free from risk. It is also important to understand that some of the mitigating factors (dangers to contain the hazard during the tests), the same modalities as the test material (physical form), and many other factors affect the data itself. Graphs therefore only have an indicative value.

The most important consideration emerging from graph is that the self-priming temperature of the metals listed, with the exception of zinc, decreases as the oxygen pressure increases. In a more detailed analysis it will be found that some of the temperatures highlighted are well above the melting temperature of the metals themselves. This should not be surprising because the differences that lie behind scientific mergers and combustion are not to be confused. This phenomenon also occurs for non-metallic materials with the only difference that the value of the auto-ignition (self-priming) temperature decrease is within a range of a few hundred degrees as evidenced in the next graph. Deciding which material is the most suitable for a system that works in the presence of oxygen is a fairly complex issue and can not be solved simply by giving the data of the two graphs. Other factors affect the degree of suitability among which it is important to cite: the degree of resistance of the material to the oxidizing agents, the behavior as a result of oxidation, the degree of burrs attitude, workability and more. The decision on the choice of materials to be used in a system, whatever it is that operates in the presence of oxygen, must therefore be entrusted to personnel specializing in the management of such systems.

Although the in viton o-rings are widely used, nitrile o-rings would be preferable despite having a lower ignition 32 temperature than that of viton. Viton when burning produces toxic fumes.

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material, but is used for in-water cylinders containing mixtures with high oxygen percentages. The table below shows some definible materials such as “compatible oxygen” that can be used with reasonable safety, provided that they are not contaminated by the presence of other materials. Metals: • Stainless steel 316L • Monel alloy (nickel-copper) 400 • Inconel alloy (Nickel-Chromium) 600 • Copper and copper alloys (brass)

Not Metals: • Nylon 11 • Viton • Nitrile • Teflon (TFE and PTFE)

It is good to remember that although the metals and alloys listed in the table have a good corrosion resistance, they may be affected by some acids or undergo an oxidation process. Acids are sometimes used to clean some of the components of the dispensers, taps or other equipment, while oxidation is an inevitable phenomenon that must be counteracted by proper maintenance. Stainless steel, unlike the name that distinguishes it, easily oxidizes into superfine, covering a layer of invisible oxides. However, these oxides have the property of protecting the underlying metal from corrosion. In addition, stainless steel has the ability to be easily cleaned and therefore has a good hygienic coefficient. Copper is another not overly expensive metal often used for the construction of oxygen systems (connection pipes), however it shows a certain tendency to oxidize, sometimes suddenly, so its use must never be given it takes for granted and demands, as well as for stainless steel, caution and maintenance practices determined by the architecture and the typology of the system to which it belongs. Even the place where a system is set up, which can be a charging station, has many parameters. The proximity of the sea makes the atmosphere particularly aggressive to metals, so the maintenance and inspection program of systems operating in “aggressive” environments will have to be particularly severe and frequent. 2

3.3. OXYGEN CLEANING “Oxygen cleaning” refers to the degree of cleansing of the system or component, or more specifically due to the absence of contaminants and / or particles that may act both as a fuel and as a source of initiation. The condition that the degree of cleansing may be “certainly adequate and sufficient” can be achieved through a genuine cleaning work. A system or component once it has been cleaned up with oxygen must remain so until the next oxygen-cleaning operation or at least for a given period. Attention should be paid to the valves, the connection elements, the inlets of tubes and whips and to all those parts which can act as traps for contaminants. During this period of operation, we must avoid accumulation of contaminants in localized areas of our system or component. Therefore, the use of such systems or components requires greater attention and commitment than the systems for which oxygen cleaning is not required. Do not leave them exposed to dust and dirt in general. Nylon clean envelopes can be a valuable container to keep a clean oxygen component during unused use. or to keep it clean while awaiting re-assembly. It is also advisable not to allow these components to be handled by individuals without them being adequately prepared.

3.4. OXYGEN SERVICE Oxygen service means a system or component that is both oxygen-compatible and oxygen-clean, and therefore suitable for use in the presence of oxygen. One of the two conditions is not sufficient. The oxygen service is the condition for the combustion and triggering elements to be removed from the fire triangle.

Once a system or component has been brought to oxygen service, these must be labeled in such a way as to be immediately recognizable. It is a good rule, where possible, to place the date of certification by the maintainer of the successful commissioning of oxygen. 33 if a dispenser, cylinder or any oxygen - servicing equipment is also used only once with compressed air or any other

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suitable for the use of oxygen, oxygen use. Oxygen delivery of a system or component involves performing the following general address actions: 1. Disassemble the system or component. 2. Remove non-oxygen-compatible components from the system and replace them with components built with compatible oxygen materials that can perform the same functions at the same efficiency level and which have been approved by the manufacturer of the system. 3. Perform cleaning operations to remove the contaminants present on any oxygen-sensitive or hyper-oxygenated system components. It is also good to clean those components that are believed to be able to accidentally contact oxygen due to operator error or system failure. 4. Assemble the system or component again 5. Ensure the oxygen service of the system as long as necessary

3.5. THE WORKING ENVIRONMENT The working environment and the tools with which it operates must always be kept reasonably clean. This good rule should, however, be adopted, as far as possible, for systems that do not work in direct contact with oxygen to the benefit of mixing quality and therefore diving safety. Cleaning is always a good thing, “but you do not have to be hysterical.” In any case, even the absence of odors from hydrocarbons in general, oils and dust is already a good indicator of how a charging station is held. Proper ventilation with clean fresh air must always be guaranteed and, if necessary, interrupted (even by simply closing the filter) whenever it is suspected that contaminants may enter the outside, especially during cleaning operations. The operator should wear protective goggles and a white coat (better than those used in laboratories that do not release volatile fibers and offer some protection) to reveal excessive dirt that may be dangerous. The use of surgical gloves is recommended during the cleaning procedure without talc or any other dust. The basic equipment to be supplied is: • Protective clothing • Ultrasonic cleaner for baths in water, acid or detergents (possibly with heater to accelerate cleaning processes) • Various stainless steel containers and glass or plastic for rinsing • Ultraviolet light source, possibly directional for post-cleaning inspections • A little torch • Set of Pliers (some stainless steel) • Various hardware tools • Brushes of various sizes, including at least one in nylon • Containers for the containment of objects and liquids, of which at least one graduated (in steel, glass and / or transparent plastic) • Venetian maps • Non-hair absorbing paper and lab paper • Oily lubrication oils compatible with oxygen • Demineralized and pure water • Appropriate light source (better equipped with magnifying glass for inspections) • Envelopes and nylon bags • A source of clean air or nitrogen free of pollutants under pressure • A working plan possibly of light color • First aid kit including systems for the treatment of burns and burns

This list does not contain all the tools useful for a global maintenance service. It is appropriate to refer to the set of tools provided in the maintenance manuals of any equipment, which should be

kept separate from the rest of the equipment and kept clean. Complex systems and equipment in general such as cylinders, taps, regulators should be adequately protected from 34 dust and moisture when not in use: this is a good rule to use for equipment that does not work with pure oxygen. Particular care must be taken in the gas inlet and outlet routes: these must be kept protected by means of special

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3.6. CONTAMINANTS The most common contaminants that can act as fuel and trigger source are: • Silicone grease • Oils engine, compressor oils and lubrication songs • Gaseous or condensed hydrocarbons • Many solvents and detergents • Paints and some types of ink • Chromates subject to exfoliation • Rust and rust powders • Carbon dust and ashes • Powder and dust deposits in suspension • Oils for the skin • Some piping sealants • Soaps and detergents • Metal particles (filing powders and metal chips) • Derivative products from hydrocarbons (tires, plastics, etc.)

Contaminant agent means not only a foreign body or substance but also any non-oxygen compatible material. It is to be considered as a contamination of the system and therefore it must be removed or it must be put in a condition not to harm it. Among the most dangerous contaminants there are all those materials derived from hydrocarbons: these are often small in size, in some unexpected aspects, such as a simple rubber o-rings, and therefore must be infallibly identified and suitably substituted. Some contaminants may also be involuntarily introduced into the non-operational phases or the preparation of a charging station where the need to treat oxygen is not contemplated. If the need arises to begin to treat oxygen in an already functioning but not dedicated working environment, it is necessary to first clean both the environment and the systems (including cylinders) that in it and with it will continue to operate (the cleaning of the systems and the equipment is discussed in the following paragraphs). The design of a mixing station generally does not provide for the creation of two really separate rooms for compressed air and one for blends (a solution that does not always bring advantages). It follows that the various operations are all in the same environment, so that the entire charging station must take all the necessary attitudes.

3.6.1. BURRS Metal and non-metallic shavings and burrs (English burrs) are an extremely risky presence. These are mainly caused by bad use of cutting tools, or during operations involving metal clutches. Even the use of dentist specimens for the removal of o-rings may cause chipping of the chips from the seats to damage the fixtures. Operations such as the cutting of gas pipes, the tightening of the fixture connections, only to mention two examples, must be carried out with all the precautions of the case. If such particles are present, a system can not be considered as oxygen service despite being composed of oxygen- compatible and clean materials. These chips can be extremely dangerous for the following reasons: • Block black orifices, and this could create shocks with temperature rise above system tolerance limits • They can prevent proper closing of the valves • Their impact with the inner surfaces of pipes, intersections, valves, whips, etc. could locally dissipate enough energy to generate combustion both on the particles themselves and on the affected area.

A normal cleaning with brushes or dedicated cloths may not be sufficient and the stewardship could generate enough static electricity to adhere the shavings to the cleaning object. Therefore, further cleaning practices are required to remove such particles such as compressed air or nitrogen (not contaminated by hydrocarbons), pressurized steam purge operations or high-pressure pump cleaning liquids along

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3.7. IGNITION SOURCES The consequences of a trigger in a plant that works in the presence of oxygen are always disastrous. Understanding how a trigger can occur and predicting a potential risk for the operating life of a charging station are among the core tasks of the OSM. The most common sources of triggering at a charging station are due to the following phenomena: • Mechanical Impact: When an object impacts against another, the absorbed energy becomes heat, sometimes sufficient to trigger the combustion of the material in the impact zone. • Burrs Impact: See previous paragraph. • Friction: rubbing between two solid materials, such as that generated by blocked valves, violent manipulation of a component, excessive friction between elements of a system, could generate enough heat to ignite the combustion. • Sonic flow (adiabatic compression heating): When oxygen (or any other gas) passes abruptly from a high pressure condition to a low pressure condition, with a pressure ratio greater than 2, that is, the higher pressure is at least double the smaller one, passing through an orifice (such as when a valve suddenly opens), downstream of the orifice, oxygen reaches sonic speeds, ie about 1,200 km / h (this is a phenomenon widely described in physics books).

The high velocity generated can compress the gas particles against any obstruction (such as a closed valve or flow regulator), generating sufficient heat to reach the autosensor point of the contaminants that may be present ( burrs and foreign bodies in general) and the materials with which the system is made.

Adiabatic is said to be an event in which the gas does not exchange heat with the medium environment in which it is contained, that is, thermal energy is not sold due to a transformation so rapid that it does not leave time to heat to dissolve. The oxygen is therefore able to reach the ignition temperature of the containment material following, for example, the operation of a ball valve which opens completely with only ¼ of a turn, or acting as a opening that opens and it closes in a very sudden way. In any case, even by opening any type of valve quickly into an oxygen system whose downstream end is closed, the same effects can be produced. The combination of high temperature and pressure can cause an explosion. Adiabatic compression is the main cause of the energy dissipation to the loss of an oxygen reducer (or any other obstruction), where initiation occurs first at a molecular level, so that the resulting combustion then expands rapidly (less of 0.5 seconds) does not consume any available fuel.

Conductive studies conducted by entities such as NASA and EIGA (European Industrial Gases Association) describe how these events are what differentiates a fuel powered / generated from oxygen by one powered by air. The same

36 entities in their operating manuals describe the methods and approaches that can reduce the likelihood of adiabatic compression. Generally speaking, a pipeline is narrow and long, the greater the chance that adiabatic compression

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(generally brass) or alternatively, install one of these upstream of the gearbox. • Single or repeated pressure shocks: heat generated by adiabatic compression. • Excess gas velocity in the pipes or components of a system. • Contamination with materials that are offered as a source of ignition or fuel. • Exposure to open fixtures, cigarettes, combustion engines, heat sources in gender. • Electric sparks or static electricity.

Instructions for proper oxygen-management systems management and related risk mitigation / elimination procedures are not obvious or easy to find and are often contained in English-language manuals. This specific information can sometimes be found at companies that design and build oxygen-working systems or are provided by the same systems or component systems dealers. The complexity of the subject and the variety of systems require specific knowledge and cautions that can not be exhausted in this manual, so it is advisable for the operator to investigate the relative safety and management procedures on a case-by-case basis. EIGA, as well as other industry organizations or associations, makes available useful English documents on its website, among which we recommend reading and understanding the document titled “Oxygen Piping Systems”. This document can be consulted at the Internet address: http://www.eiga.org/fileadmin/docs_pubs/Doc%2013%2002%20E.pdf

3.8. HYPER-OXYGENATED MIXTURES In addition to systems that work with pure oxygen, equipment that operates with hyper-oxygenated mixtures requires the same precautions and preparations as previously stated. The various training agencies sometimes do not agree on what the oxygen percentage limit beyond which the gas mixture must be managed as pure oxygen.

The US Oceanic and Atmospheric Administration (NOAA) has estimated that systems that operate with gas mixtures containing up to 40% oxygen do not require special cleaning or reclamation treatments.

Nonetheless, if the preparation of a mixture containing oxygen, whatever its percentage, involves maneuvering the individual gas separately, the entire system must be oxygenated. That is, if to load a binary mix into the cylinder separately pure oxygen, air and / or helium (regardless of the order in which they are introduced), both the oxygen input system and the air intake system (compressor) or helium (ramp), they must be in oxygen service. This safety rule must also be applied to any ternary mixture.

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4. MEDICAL ASPECTS The usefulness of these mixtures is that with them the decompression time is reduced, which means for the diver greater safety, greater comfort and less amount of gas required.

As the blood pressure of the inert gas, nitrogen, rises, it becomes much lower than the tension of that gas in the rest of the diver’s tissues and a very rapid passage of nitrogen into the bloodstream and lungs.

Nitrogen always passes from the place of highest to lowest tension and with a speed that is proportional to that difference in tension. The lower the tension of nitrogen in the blood, the more nitrogen per unit of time the tissues will yield to the bloodstream, an amount that will be transported to the lungs, the nitrogen being eliminated by breathing much earlier.

In order to reduce the tension of nitrogen in the blood during the ascent, we have to replace the bottom mixture with a mixture enriched with oxygen, that is, with less nitrogen. Then, the reduction of the partial pressure of nitrogen in the lungs causes its passage from the blood into the air of the lungs and as a consequence of which the tension of nitrogen in the blood drops.

Breathing air on the way up there is a difference between the nitrogen stresses in the tissues (supersaturated) and the blood, which causes nitrogen to pass from the tissues into the blood.

Changing to EAN50 the differences are greater and increases the amount of nitrogen that passes into the blood.

Your instructor will remember all you studies in your Advanced Nitrox Diver Course about the causes, symptoms, prevention, first-aid and treatment of enriched EANx diving medical problems.

We know that oxygen becomes toxic from a certain value of the partial pressure, this toxicity not only depends on the partial pressure but also influences the amount that has been introduced into the body. The situation, although not completely analogous, is somewhat reminiscent of what happens with nitrogen, that although it is inert, the longer we are breathing at a certain pressure and the higher the pressure of the air we breathe, the more it accumulates in the organism and can cause a decompression sickness.

In reality with oxygen the situation is different since the body tends to consume the oxygen that we introduce through the respiratory tract. However, when the partial pressure at which we breathe said oxygen, as is the case with Nitrox, is high, the organism is subjected to continuous “oxygen overpressure”, which causes the cells to be affected.

This excess pressure has two effects on the body, one of Neurotoxic nature, above a partial pressure of oxygen of 1.6 ATA, the aforementioned Paul Bert effect, and another of a cumulative nature above 0.5 ATA of partial pressure of oxygen, the so-called Lorrain Smith effect.

As a result of the aforementioned, the organism has a tolerance to oxygen not only due to excess partial pressure, but also due to “cumulative effect” when it is exposed for a certain time to a certain partial pressure of oxygen.

4.1. SIGNS AND SYMPTOMS IN A HYPEROXIC CRISIS. When the body breathes oxygen, either pure or as part of a mixture, at partial pressure above 1.6 ATA, what is known as a hyperoxic crisis occurs, which usually has very serious consequences.

The hyperoxic crisis manifests and evolves in the same way that an epileptic crisis does, which once started continues its normal course until it ends, with no way to stop or interrupt it. This means that the hyperoxic crisis, once started,

will continue even if the injured person is given to breathe air with partial pressure of oxygen below 1.6 ATA.

This process takes place in three clearly differentiated phases, the tonic phase, the clonic phase and the post- 38 convulsive phase. The following diagram shows the symptoms that a victim of a hyperoxic crisis shows in each of the

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Tonic pase Clone pase Post-convulsive phase (approx. Half minute) (approx. One minute) (undetermined) •Rigidity • Seizures begin •Muscle relaxation • Stop breathing • The respiratory block continues •Fast breathing • Loss of consciousness • Glottis block • Risk of syncope and death • Fasciculation of the larynx • Glottis block

The hyperoxic crisis is easily detectable through its symptoms, which are cited in the following table:

Paul Bert PO2 effect> 1.6 ATA

Anxiety Nervous tics and muscle spasms Euphoria Nausea Seizures and unconsciousness Fainting and vertigo Irritability Tunnel vision Echoes and ringing in the ears

If we notice in us or in a partner any of these symptoms, it is convenient that we ascend quickly unless the diver has seizures, in which case we will wait for them to pass before beginning the ascent.

It is important that during the ascent it is verified that the injured diver breathes normally through the regulator and expels it as it rises. If not, we will try to force the expulsion of the air by pressing on your stomach.

4.2. SIGNS AND SYMPTOMS IN A HYPOXIC CRISIS The use of Nitrox mixtures with oxygen percentages above 21% corresponding to atmospheric air can not present hypoxia risks in any case since the partial pressure will always be above 0.17 ATA. However, when respiratory mixtures with oxygen percentages below 21% are used, the risk of hypoxia is present, even in immersion.

The use of low oxygen mixtures is useful on dives below 40 meters, where the partial pressure of oxygen begins to be dangerously high. It is enough to make a simple calculation to verify that with atmospheric air, a partial pressure of oxygen of 1.4 ATA is reached, which is the recommended limit in international standards and allowed in some countries (such as Spain), only 56 meters deep, and that in those dives carried out in adverse conditions where the limit is established at 1.3 ATA, the depth is limited to 51 meters.

It is true that sports and recreational diving limits the depth of the dives to 40 meters, but if we want to enter the world of technical diving in the future, and descend below 40 meters deep, compressed air is only “useful ”Up to approximately 57 meters, and conventional Nitrox, which uses mixtures with oxygen percentages from 32% to 40%, limits the depth to just over 30 meters.

The need to use mixtures with lower percentages of oxygen than atmospheric for deep dives, also recommended in the case of diving below 40 meters depth, can cause a hypoxia picture when we return to the surface.

Another frequent cause of hypoxia is an inadequate respiratory rhythm. When the brain detects that the partial pressure of oxygen is below 0.16 ATA, it begins to show symptoms of malfunction, with concentration problems, loss

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Signs and symptoms of hypoxia

• Loss of concentration ability • Inability to think clearly • Loss of fine control of muscles • Inability to perform delicate tasks • confusion • Mental instability • Loss of the ability to make or make judgments • Weakness and dizziness • euphoria • Loss of consciousness

Unfortunately, these symptoms and signs do not serve as a warning to prevent the consequences of hypoxia since the diver who suffers from this effect is not able to realize that he is in trouble. When the euphoria picture is reached, one is unable to react properly and prevent hypoxia from causing serious damage to the body. In this situation, the diver continues to fall into a severe hypoxia situation, which when reaching the partial pressure of oxygen of 0.12 ATA, completely disables him to react or make decisions, degenerating into a critical hypoxia picture from partial oxygen pressures below 0.10. ATA, which cause irreversible brain damage and can end up causing death.

For this reason, when a person suffers from hypoxia, the injured person must be brought to the surface immediately and supplied with oxygen or air with a sufficient percentage of oxygen. In the event of cardiorespiratory arrest, a CPR would be performed (Cardio Pulmonary Resuscitation)

4.3. MANAGING A DIVING ACCIDENT Diving incidents are something that no one wants to deal with but, just like anything else, the more you do it the more likely you are to be involved in an incident. When incidents happen, there is a lot to think of and to deal with when it comes to divers using nitrox. There is an added piece of information that is needed: their PO2 exposure. For the sake of ease we will break this down into two types of diving:

• Multiple days of single tank nitrox diving • Technical diving involving decompression

Before we get into that, a reminder of the two types of oxygen toxicity is important. The type that affects recreational and technical divers the most is Central Nervous System (CNS) Oxygen Toxicity. This is generally caused by a high dose (high PO2) with short term exposure. The second type, which is general only seen in commercial diving or medical treatment, is Pulmonary Oxygen Toxicity; this is low dose (low PO2), long term exposure.

For divers doing multiple days of single tank nitrox diving, they generally do not come close to the single exposure limits, mostly because of air consumption rates, but they can be right on the edge of the 24 hour limits. It can be very difficult to ascertain exactly what their long term exposure has been unless they have programmed all mixes into their dive computer, or have logged all their dives, including the mixes they used, in their log books.

For divers conducting decompression, the tracking of dives becomes a little easier because it is either one or two dives per day or they operate on a fixed PO2. In both situations, the information is usually right at hand, as either the cylinders are labeled, th decompression schedule has been written down as a back-up, a multi gas computer has been used or the CCR’s built in dive computer has stored all the information.

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most diving incidents do. Medical treatments generally start with a PO2 of 2.8 and go up from there, so it is easy to see why hyperbaric doctors would want to know the oxygen levels in a diver prior to starting a treatment. Prior oxygen exposures aside, chamber operators will run whatever the appropriate schedule is, it is just best to provide as much information as possible to them.

The best way to handle this is: send the diver’s computer along with them, send their logbook or send their decompression schedules, but, if time permits, get copies of all of this information. When items start changing hands, they have a tendency to get lost and as any diver knows, you need a backup plan.

At minimum, the diver’s dive computer should be downloaded and their dive profiles can be quickly hand written or scanned.

The best time management technique to accomplish all necessary tasks is to assign a person for each task and collect all the information as soon as time permits. Fingers crossed you will never have to deal with a diving incident, but if you do find yourself in such a situation, be prepared and everything will go as smooth as possible.

4.4. PHYSICAL PREPARATION. Physical training is one of the most important aspects of Nitrox diving, since the body’s oxygen tolerance is directly related to the state of physical fitness. A bad state can limit tolerance to values of 1.3 ATA or even 1.2 ATA of partial pressure of oxygen in adverse conditions.

To avoid this problem, it is advisable to maintain an adequate state of physical and diving preparation. It is not enough to be in good physical shape, you have to practice diving with Nitrox, or simply diving with a certain frequency. It is recommended several times a month, but at least one monthly immersion is recommended.

As for the physical training program to maintain an adequate state of preparation and training, swimming is usually one of the most advisable methods. Swimming has undeniable advantages for diving in general, and for diving with Nitrox in particular, among others:

• Increase self confidence and feeling of comfort

• Reduces fatigue

• It reduces stress

• Improves ability to tackle problems

• Reduces mix consumption

• Increase energy level

• Increase self-esteem

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4.5. CONTROL AND TRAINING TEST Next, we show the Hanauer table to establish our own control system to achieve the desirable state of physical fitness: Task Beginner Intermediate Advanced Experienced Warming up before 5 minutes gentle 200-400 meters of 400 meters of free 500 meters of free training contact with wáter free swimming swimming swimming. Last 100m sprint

Training 200-800 meters of 1200 meters of free 1800 meters of free 3100 meters of free free swimming in 20- swimming in 35-45 swimming in 45-60 swimming in 60 30 minutes minutes minutes minutes 4 series of 100 6 series of 100 3 series of 200 100-400 meters meters in 2 ’each meters in 2 ’each meters in free Free swimming freestyle with 40” stop with 30” stop swimming using only between series of between series of arms. free swimming free swimming 400 meters in negative sprint Swimming with fins 200 meters 300 meters 300 meters Free swimming 6 series of 100 meters in 2 ’each with 30” stop between series of free swimming Swimming with fins 300 meters of free swimming. Last 100m sprint Sprints 6 series of 50 meters 10 series of 50 in 1 ’each with 30” meters in 1 ’each stop between series with 20” stop of free swimming between series of free swimming Last task 100-200 meters 200 meters freestyle 300 meters freestyle using only legs Finished tasks Relaxation Relaxation Relaxation Relaxation

The correct way to know if we are doing the training properly is to control our heart rate. A limit is established that is given by the following relationship: Heart rate = 0.8 x (220 - age) NOTE: If you are over 35 years of age, it is advisable to carry out a medical examination prior to the indicated personal control program to ensure that we are in a position to carry it out without risks to our health.

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5. NITROX DIVE PLANNING Your instructor will remember all you studies in your Technical Skills Diver and Advanced Nitrox Diver courses about using dive tables, dive computers and/or dive planning software.

5.1. REMEMBERING THE BASIC NITROX CONSIDERATIONS By increasing the percentage of oxygen in the air, we are increasing the chances of oxygen poisoning. It is taken to work with any mixture, lower limits and upper limits of partial pressure of O2 (ppO2). This prevents the diver from suffering from hypoxia problems (low ppO2) or hyperoxia problems (high ppO2). The lower limit of O2 is 0.16 atm and the upper limit is 1.4 atm (1.6 for professional diving). This means that each mixture has a roof and a floor where the diver can move around without any risk. Because it is air enriched with O2, there is a risk of hyperoxia. For this reason, the maximum depths of each of the N1 and N2 mixtures were limited. Applying Dalton’s law and using the maximum Pp of O2 we can obtain the limit depths of each of the mixtures N1 and N2.

Maximum Pp of O2 for a professional diver =1,6 atm

%O2 100 PpO2 = PT ∗ >>>>>>> PT = PpO2 ∗ 100 %O2

ퟏퟎퟎ ퟏퟎퟎ 푃푇 푁푖푡푟표푥 1 = 푃푝푂2 ∗ = 1,6 ∗ = 5,0 푎푡푚 %퐎ퟐ ퟑퟐ

ퟏퟎퟎ ퟏퟎퟎ 푃푇 푁푖푡푟표푥 2 = 푃푝푂2 ∗ = 1,6 ∗ = 4,4 푎푡푚 %퐎ퟐ ퟑퟔ

By applying the maximum Pp of O2 to each of the mixtures we can obtain the maximum depth. For N1 it gives us a Ptotal=absolute pressure of 5 atm and for N2 a Ptotal=absolute pressure of 4,4 atm. For N1 means 40 meters the immediate lower depth of the board is 39 meters and for N2 means 34.4 meters, the immediate lower depth of the board is 33 meters.

Not only the high ppO2 can limit the dives, also the permanence to the same partial pressure can be harmful, for this reason a table of maximum permanence time according to the partial pressure was made:

pp O2 (ATA) Maximum pp O2 (ATM) Maximum duration (min) duration (min)

1,6 45 1,0 300

1,5 120 0,9 360

1,4 150 0,8 450

1,3 180 0,7 570

1,2 210 0,6 720

Based on Dalton’s formula and U.S. Navy tables, NITROX tables were developed for each of the mixtures used.

In the table we see the comparison between the no-decompression limits of the U.S. Navy and those of N1 and N2.

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Prof. (mts) U.S.Navy (min) N1 (min) N2 (min)

15 100 200 200

18 60 100 100

21 50 60 60

24 40 50 60

27 30 40 50

30 25 30 40

33 20 25 30

36 19 25 #

39 10 20 #

What you can do is dive with Nitrox using the air tables, decreasing considerably the concentration of N2 in the tissues, giving greater security in relation to decompression and less fatigue after diving. Diving with NITROX does not oblige us to use special equipment, we can use the same as for air dives. But before using this equipment, we must wash it to remove any type of contaminant particles. The high partial pressure of oxygen in the presence of hydrocarbons can produce a reaction generating an explosion. For this reason, all the equipment used in NITROX must be clean of this type of elements. The cleaning levels of the equipment depend on the different concentrations of oxygen in the mixture to be breathed. Cleaning is done with solvent or detergent, when cleaning with solvent we must be very careful to do it in open places to avoid toxic vapors, in addition to making sure to remove all traces of this substance before starting to use the equipment. To wash the valves (regulator and faucet), the first step is to disassemble them and immerse them in the cleaning substance. Then with ultrasound equipment.

After the two stages of cleaning the parts are dried very well and an inspection is made to determine the effectiveness of the cleaning. For complete inspection a UV or black light lamp can be used where any particle of grease or oil will fluoresce in the presence of UV light.

Tanks should also be cleaned, first they are visually inspected to evaluate the rust particles in them. The rust is removed and then filled with the cleaning substance, left to act for about 20 minutes and rinsed until we are sure that there are no deposits of the cleaning substance.

In the cleaning we must not forget the rubber parts: o-ring, hoses, diaphragm, etc..

Before the equipment is assembled, it is lubricated with an oxygen compatible grease and clearly marked as NITROX ready equipment.

It is very important to prevent contamination of already washed parts. Those elements that are not installed immediately can be stored in polyethylene bags. The same caution must be taken with tanks. Once washed, do not load them with compressors that can dirty them again. They are fitted with a stiker that says NITROX in yellow and green. Also they can be painted of yellow with a green band, the important thing is that it is clear that this tank is destined to NITROX and it cannot be loaded with a compressor that does not have the necessary filters that assure the purity of the air. There are companies that brought out exclusive equipment for nitrox, these models can be distinguished by their green and yellow color. Mechanically they are the same, the only change made is the material of the o-ring and diaphragm.

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5.1.1. THE MANUFACTURE OF THE MIXTURE There are different methods to build a mixture, the simplest and most economical is through a cascade or partial pressures. This method was already featured in the U.S.Navy Diving Gas Manual in 1971. By cascading you can achieve the required 02 percentages simply by applying the partial pressures law or Dalton’s law. The first step is to incorporate the oxygen pressure necessary for the mixture we want to build. Once the tank has that oxygen pressure we’re looking for, it finishes filling with air. Introducing oxygen first allows us to work with lower pressures of this gas minimizing losses and away from the dangers of an explosion.

An example of loading a tank can be seen below:

If we want to load with N2 (36% oxygen) a tank of 200 bar, to obtain the oxygen pressure that we must incorporate, we carry out the following step:

0.36 - 0.21 ______x 200 = 38 bar

0.79

We need to get 38 bar of oxygen into the tank. NITROX mixtures require a shorter homogenization time than any other type of mixtures. Once the mixture is homogenized the gas is not stratified, (areas of higher oxygen concentration and areas of lower oxygen concentration).

Once the construction of the mixture is finished, the final percentages of oxygen should be checked. In order for the mixture to be correct, its final value cannot vary by + or - 1% of the desired value. After checking the percentages of oxygen in the tank, a card is placed in the neck, this card contains the percentages of the mixture, the maximum depth allowed, the date of measurement and the signature of the person responsible for the measurement.

To control the oxygen percentages of the mixture, equipment called oximeters are used. These equipments measure the oxygen concentration with a sensor through which the mixture is passed. They are calibrated with pure oxygen, it is important to calibrate the equipment before starting to use it.

After calibration, the mixture is passed through for a few seconds until the meter stabilizes and we verify the percentages of oxygen it has. The diver may require the person responsible for the load to measure the percentages of oxygen in front of him before taking away the tank. We must not forget that a mistake in these values can lead to an oxygen intoxication accident or a decompression accident.

5.2. OXYGEN TOLERANCE UNIT (OTU) When we do more than one dive daily, or within 24 hours, even on consecutive days, we must take into account the “cumulative effect” of oxygen from successive exposures. Since the method explained in the previous section only allows the determination of the level of exposure to oxygen for simple dives, we will use an alternative system based on the Oxygen Tolerance Unit.

The Oxygen Tolerance Unit is an index that measures the body’s level of exposure to oxygen, referred to a base value.

OTU is defined as the dose of oxygen received by the body when breathing oxygen at partial pressure of 1 ATA for 1 minute.

However, and since the organism is capable of withstanding partial oxygen pressures of 0.5 ATA for a practically

unlimited time, we will establish as index 0 the partial pressure of 0.5 ATA, so it is accepted that the OTU for said

partial pressure is 0 always.

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The OTU (Oxygen Tolerance Units) are based on empirical data from which the following best-fit formula has been derived:

OTU = t [ [ (PO2 - 0.5) / 0.5 ] 0.83 ]

Being:

t = the exposure time in minutes. PO2 = the partial pressure of O2 in ATA 0.5 = the threshold below which no significant pulmonary oxygen toxicity has been observed. 0.83 = the exponent that offers the best fit with the experimental observations.

Grossly, 1 OTU is equivalent to 1 exposure ATA per minute. The maximum exposure in one day is 850 OTU. On successive days it drops to 300 OTU per day for missions of 11 to 30 days.

These limits are not normally reached on raid dives. From here we will establish the values corresponding to the different partial pressures. This set of values is expressed in the table shown below: O2 Partial Pressure OTU / min 0.5 0 0.6 0.263 0.7 0.490 0.8 0.656 0.9 0.831 1.0 1,000 1.1 1,160 1.2 1,320 1.3 1,470 1.4 1,620 1.5 1,770 1.6 1,920 1.7 2010 1.8 2,200 1.9 2,340 2.0 2,480 2.1 2,610 2.2 2,740 2.3 2,880 2.4 3,000 2.5 3,140 To determine if the accumulated quantity is dangerous or not, it is necessary to know the limit values that the organism can support. These values are given by the OTUs Table of maximum dose shown below. Exposure time Maximum dose (OTUs / day) Accumulated amount 1 day 850 850 2 days 700 1400 3 days 620 1860 4 days 525 2100 5 days 460 2300 6 days 420 2520

7 days 380 2660

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prolonged exposure periods on consecutive days. As can be seen, the greater the number of days in a row during which oxygen exposure is being received, the lower the daily dose that can be received. In the case of our example, since it is a single day, the amount received, 152,325 OTU is well below the maximum allowed (850 OTU), representing 17.9% of said maximum. If the dives that were carried out in the proposed example were repeated for three consecutive days, the total amount accumulated after those three days would be: Total dose = 152,325 x 3 = 456,975 OTU which is below the maximum daily allowable (620 OTU per day) and of the maximum accumulable in the period of 3 days (1860 OTUs). In this case, the accumulated daily amount would represent 24.6% of the daily total (152,325 / 620).

5.3. COMBINED EFFECT OF HYPERXIA TOXICITY AND CUMULATIVE EFFECT If we now consider both effects, hyperoxia and the cumulative effect of oxygen, together we can see that “cumulative effect” poisoning is very difficult, at least in sport and recreational diving. In effect, establishing the table for maximum accumulated dose for oxygen and comparing it with the maximum values that would be reached for the limit of hyperoxia crisis we would have: Oxygen partial pressure (1)Maximum single Daily cumulative OTUs Maximum OTUs (ATA) exposure time (min) allowed daily 1.6 45 86.4 850 1.5 120 212.4 850 1.4 150 243.0 850 1.3 180 264.4 850 1.2 210 277.2 850 1.1 240 278.4 850 1.0 300 300.0 850 0.9 360 299.1 850 0.8 450 295.2 850 0.7 570 279.3 850 0.6 720 190.8 850 (1) HYPEROXIC CRISIS LIMIT FOR SINGLE EXPOSURE

Oxygen partial pressure (2)Maximum 24H Daily cumulative OTUs Maximum OTUs (ATA) exposure time (min) allowed daily 1.6 150 288.0 850 1.5 180 318.6 850 1.4 180 291.6 850 1.3 210 308.7 850 1.2 240 316.8 850 1.1 270 313.2 850 1.0 300 300.0 850 0.9 360 299.1 850 0.8 450 295.2 850 0.7 570 279.3 850 0.6 720 190.8 850 (2) HYPEROXIC CRISIS LIMIT FOR 24-HOUR EXPOSURES.

5.4. INDICES OF OXYGEN TOXICITY When we want to make a more precise calculation for a multilevel dive, or when we want to determine the oxygen dose for dives with stops, or for successive dives, we must use the CNS method. This method is based on the determination of an index, called CNS, which must not exceed an established limit.Another method is the determination of the HPHT index (High Pressure Hyperoxia Toxicity index), which measures the level of oxygen received by the body in relation to the maximum allowed before suffering neurological damage from hyperoxia (Paul 47 Bert effect).

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the body and compares it with the maximum value allowed before beginning to suffer pneumological damage due to excessive accumulation of oxygen at intermediate pressures (Lorrain effect -Smith).

5.4.1. CNS INDEX The CNS index is a method that allows the determination of the dose of oxygen received by the body in successive stages, such as a multilevel or successive dive. The following table is used to determine the oxygen dose in successive stages, known as the Table of maximum exposure to O2 and monitoring of the% CNS. The% CNS index indicates the percentage of oxygen received over the maximum allowed by the body before damage to the CNS begins. PpO2 %CNS Max. Expos. 0.60 0.14 714 0.64 0.15 667 0.66 0.16 625 0.68 0.17 588 0.70 0.18 556 0.72 0.18 556 0.74 0.19 526 0.76 0.20 500 0.78 0.21 476 0.80 0.22 455 0.82 0.23 435 0.84 0.24 417 0.86 0.25 400 0.88 0.26 385 0.90 0.28 357 0.92 0.29 345 0.94 0.30 333 0.96 0.31 323 0.98 0.32 313 1.00 0.33 303 1.02 0.35 286 1.04 0.36 278 1.06 0.38 263 1.08 0.40 250 1.10 0.42 238 1.12 0.43 233 1.14 0.43 233 1.16 0.44 227 1.18 0.46 217 1.20 0.47 213 1.22 0.48 208 1.24 0.51 196 1.26 0.52 192 1.28 0.54 185 1.30 0.56 179 1.32 0.57 175 1.34 0.60 167 1.36 0.62 161 1.38 0.63 159 1.40 0.65 154 1.42 0.68 147 1.44 0.71 141 1.46 0.74 135 1.48 0.78 128 1.50 0.83 120 1.52 0.93 108 1.54 1.04 96 1.56 1.19 84 48 1.58 1.47 68

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To find out the % that the received oxygen measures, it is enough to enter the table with the value of the partial pressure of oxygen corresponding to the depth reached and multiply the value of the CNS index (% CNS per minute) by the time of exposure to said depth.

Repeating the process for different depths and times, and adding the percentages of each of the stages, we obtain the total percentage.

5.4.2. HPHT INDEX The HPHT index determines, like the other indexes in this chapter, the amount of oxygen accumulated in a multilevel dive, and takes into account the fact that, even when the allowed limit has not been exceeded while remaining in the bottom. This can be reached or exceeded on the ascent if we have to make decompression stops.

In addition, the HPHT index, in accordance with NOAA recommendations, establishes as an additional safety margin that, if the index reaches 50% at the end of the dive, you must allow at least 2 hours on the surface before dive again.

The following table is used to determine the HPHT index:

Depth AIR (EAN 21) % HPHT (m) 10 20 30 40 50 60 70 80 90 100

4.6 72 144 216 288 360 432 504 576 648 720 6.1 72 144 216 288 360 432 504 576 648 720 7.6 72 144 216 288 360 432 504 576 648 720 9.1 72 144 216 288 360 432 504 576 648 720 10.7 72 144 216 288 360 432 504 576 648 720 12.2 72 144 216 288 360 432 504 576 648 720 13.7 72 144 216 288 360 432 504 576 648 720 15.2 72 144 216 288 360 432 504 576 648 720 18.3 72 144 216 288 360 432 504 576 648 720 21.3 57 114 171 228 285 342 399 456 513 570 24.4 45 90 135 180 225 270 315 360 405 450 27.4 45 90 135 180 225 270 315 360 405 450 30.5 36 72 108 144 180 216 252 288 324 360 33.5 30 60 90 120 150 180 210 240 270 300 36.6 30 60 90 120 150 180 210 240 270 300 39.6 24 48 72 96 120 144 168 192 216 240 42.7 21 42 63 84 105 126 147 168 189 210 45.7 21 42 63 84 105 126 147 168 189 210 48.8 18 36 54 72 90 108 126 144 162 180 51.8 18 36 54 72 90 108 126 144 162 180 54.9 15 30 45 60 75 90 105 120 135 150 57.9 12 24 36 48 60 72 84 96 108 120

The values indicated in the table indicate the time necessary to reach a certain percentage of the maximum oxygen rate when we breathe compressed air. Thus, if we are diving at a depth of 30 meters for 35 minutes, we will enter the depth column (first on the left) and we will take the value of our depth or the immediate superior if it did not appear, 30.5 meters in our case , and we will look for the immersion time or its immediate superior, in our case 36 minutes. Ascending through that column we find a value of 10%, which will be the percentage index of accumulated oxygen.

In the case of using Nitrox mixture, we must resort to the HTHP tables for EAN 32 or EAN 36 shown below. The same immersion for EAN32 shows us that the HPHT index is 20%, double that if we used compressed air, while if we breathe

EAN36 the percentage rises to 30%. 49

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Depth NITROX (EAN 32) % HPHT (m) 10 20 30 40 50 60 70 80 90 100

4.6 72 144 216 288 360 432 504 576 648 720 6.1 72 144 216 288 360 432 504 576 648 720 7.6 72 144 216 288 360 432 504 576 648 720 9.1 57 114 171 228 285 342 399 456 513 570 10.7 57 114 171 228 285 342 399 456 513 570 12.2 45 90 135 180 225 270 315 360 405 450 13.7 45 90 135 180 225 270 315 360 405 450 15.2 36 72 108 144 180 216 252 288 324 360 18.3 30 60 90 120 150 180 210 240 270 300 21.3 30 60 90 120 150 180 210 240 270 300 24.4 24 48 72 96 120 144 168 192 216 240 27.4 21 42 63 84 105 126 147 168 189 210 30.5 18 36 54 72 90 108 126 144 162 180 33.5 15 30 45 60 75 90 105 120 135 150 36.6 12 24 36 48 60 72 84 96 108 120 39.6 5 9 14 18 23 27 32 36 41 45

Depth NITROX (EAN 36) % HPHT (m) 10 20 30 40 50 60 70 80 90 100

4.6 72 144 216 288 360 432 504 576 648 720 6.1 72 144 216 288 360 432 504 576 648 720 7.6 57 114 171 228 285 342 399 456 513 570 9.1 57 114 171 228 285 342 399 456 513 570 10.7 45 90 135 180 225 270 315 360 405 450 12.2 45 90 135 180 225 270 315 360 405 450 13.7 36 72 108 144 180 216 252 288 324 360 15.2 30 60 90 120 150 180 210 240 270 300 18.3 24 48 72 96 120 144 168 192 216 240 21.3 21 42 63 84 105 126 147 168 189 210 24.4 18 36 54 72 90 108 126 144 162 180 27.4 15 30 45 60 75 90 105 120 135 150 30.5 12 24 36 48 60 72 84 96 108 120 33.5 5 9 14 18 23 27 32 36 41 45 This shows us that both methods, CNS index and HPHT index, are equally precise, although the use of the THAP index without interpolation gives us a very large margin of safety.

5.5. DIVE PLANNING In the procedures for preparing ascent plans using oxygen-enriched mixtures, the following are considered: • The development of the ascent plan using tables designed for specific oxygen-enriched mixtures to be used in the decompression, such as the MT92, which are designed for the use of oxygen in the last decompression stop. • The development of the promotion plan with computer software. These programs are based on decompression models based on Haldane’s compartment theory (specifically on the Bühlmann model ZH-L16) or on new models that take into account the role of microbubbles. The advantage that these programs offer us is that with them we can plan the dives with the specific data of the dive and calculate the decompression (DECO) according to the gas mixtures we have.

50 • The use of computers that allow, when we change the respiratory mixture in the dive, to enter this data to

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5.5.1. THE BEST MIX It is the mixture that has the lowest Pp (N2) and causes the lowest nitrogen tension in arterial blood. That is, the one with the highest Pp (O2), remember that the sum of the two partial pressures is the absolute pressure. And to achieve a higher Pp (O2) we can increase the external pressure and / or the oxygen concentration.

Increasing the external pressure will lead us to use the mixture as deeply as possible with the limitation of the POM but increasing the oxygen% reduces the POM, therefore, there will not be a single ideal mixture but one for each DECO stop.

Pure oxygen is the most effective mixture because in it the inert gas has a partial pressure equal to zero atmospheres regardless of depth. The difference between using pure oxygen and EAN 90 at the 3m stop is that with the EAN90 the Pp (N2) = 0.1x1.3 = 0.13 atm and with oxygen it is zero as we have said.

It has been proven that breathing 100% oxygen also reduces the supersaturation of venous blood in addition to producing other physiological benefits that have made this gas the essential therapeutic measure for the treatment of decompression sickness.

We must bear in mind that according to some National legislation, pure oxygen can only be breathed at 1.3 atm pressure, that is, at 3 m depth at the last stop. And that we must breathe it with a regulator nozzle fixing system so that in the event of a seizure, it does not fall out of our mouths.

As we cannot have all the ideal mixes for each DECO stop, two mixes are usually chosen, in addition to the background mix that can also be used in the first stops, one such as the EAN50 that can be used in almost all stops and oxygen for the last one. The EAN40 is also widely used because, although it is less effective than the EAN50, the cylinder and regulator do not need to be in oxygen service and can be used in more depth.

5.5.2. 100% OXYGEN IN DECO STOPS We know that oxygen is toxic in certain circumstances and using more oxygenated mixtures in DECO will significantly increase the risks of acute or chronic oxygen poisoning.

In principle, the fact of breathing mixtures with a higher Pp (O2) assumes that in each dive the% of the time of maximum exposure will be greater and the number of units of oxygen tolerance (OTU) as well.

But let’s see with an example how they continue to have insignificant values.

Using V-Planner software and VPM-B (varying permeability model), we show in the following Table the results of the calculations of the% of maximum exposure time (Total CNS) and the OTUs (*) for two different ascents of the same dive, maximum depth 45 m and time at the bottom of 20 min. The first ascent is carried out with air and the second with EAN50 and O2, the decompressions being calculated based on the gases used.

DECO with AIR DECO with EAN50 and Oxygen Bottom Time Gas PpO2 CNS OTUs Time Gas PpO2 CNS OTUs Depth 45m 20 Air 1.15 20 Air 1.15 DECO Depth 21 1 Air 0.65 Air 0.65 18 2 Air 0.59 1 EAN50 0.59 15 2 Air 0.52 1 EAN50 0.52

12 3 Air 0.46 2 EAN50 0.46 9 6 Air 0.40 3 EAN50 0.40 6 26 Air 0.34 7 Oxygen 0.34 51

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In the first ascent the total DECO time would be 40 min. The amounts of % CNS and OTU are 9.8 and 27 respectively.

In the second ascent the DECO time would be 14 min.

Ten minutes less than the air ascent, this is the “acceleration” of decompression caused by the EAN50 and O2 mixes.

The amounts of % CNS and OTU have risen to values of 24.6 and 48 respectively, but they are still a long way from 80% of CNS and 850 OTU daily.

As the most significant increase, in terms of its limits, is the% of CNS that is related to acute oxygen poisoning, let's review some concepts about this effect, also called Paul Bert.

5.5.3. DEEP DECO The experience gathered in technical diving dives has shown that ascent plans that respond to classic decompression models do not prevent "unjustified" decompression accidents, that is, they occur without any step in the plan being omitted. of planned ascent. It soon began to be suspected that those responsible for these accidents could be the microbubbles that were visible in the blood of the divers with the "Doppler meter".

Today we know that the profile of the dive, the speed of descent and ascent determine the number of microbubbles that appear in the diver's tissues and that when there are a high number of them, they can fuse and produce the macrobubbles that triggered decompression sickness, regardless of the state of tissue supersaturation.

The presence of these microbubbles has been the reason that the ascent speed has been reduced, both in tables and in computers, to favor their elimination with breathing during the ascent.

Also, it has been proven that making stops during the ascent, at depths greater than the standard decompression stops, drastically reduce the presence of microbubbles, so it has become common practice to do so in technical diving. The only drawback is that this stopping time must be considered as the bottom time for DECO calculations since we would not go up to the constant speed of 9 m / min and this would force us to recalculate decompression (the tissues more slow can continue to load with delay in ascent).

The classic models used for the decompression calculations make a series of approximations to reality to establish the ascent plans and do not take into account for these calculations the existence of the microbubbles, their number and size. What's more, they can't even explain their presence.

Initially, solutions were proposed as a result of observation and experimentation. Thus arose the method of promotion proposed by Richard L. Pyle that we will explain below.

Then the classical decompression models were modified, such as the Bühlmann model to start making deeper stops while maintaining the classic algorithm, which has been called the gradient procedure. This procedure tries to apply the usual calculations but to an immersion profile that includes deep stops in the bottom time, which according to these models were not necessary.

However, nowadays new theoretical models have appeared, such as RGBM (Reduced Gradient Bubbles Model), which explain the behavior of microbubbles and which allow calculations of ascent plans to be carried out taking it into account. In Appendix 2 you can find the explanation of how microbubbles are formed, which is the key to be able to evaluate, knowing the profile of the dive, its number and size.

In any case, we still do not have a 100% reliable decompression model, they are all approximations to a situation that is difficult to know due to the complexity of the physical, biochemical and physiological phenomena that occur, the

physiological variability of each diver and the countless environmental situations that can arise.

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In the computer programs that are used to calculate the ascent plans, we can test and choose the decompression model that we believe is most convenient for introducing deep stops: new or classic ones with the corresponding modifications.

5.5.4. THE PYLE METHOD The American biologist Richard L. Pyle discovered experimentally that when he ascended stopping at depths less than those established by the tables, because he carried a fish specimen that forced him to stop to extract the air from his swim bladder, the light ones did not appear. symptoms of decompressive illness that he noticed when he did not make those stops.

To systematize a slower ascent, he established a method that consists of ascending in stages, making stops of one minute (or two at the last stop) at depths greater than those marked during decompression. The depths are obtained by making at each stage the average between the depth we are at and that of the first mandatory decompression stop.

Richard Pyle's method for incorporating deep safety stops is:

A decompression profile is calculated for the planned dive, using conventional decompression software (without deep stops).

The first stop is midway between the depth at the start of ascent and the depth of the first decompression stop required by the program. The stop would be about 2–3 minutes long.

The decompression profile is re-calculated including the deep safety stop in the profile (most software will allow for multi-level profile calculations).

If the distance between the first deep safety stop and the first "required" stop is greater than 30 feet (9 m), then a second deep safety stop is added halfway between the first deep safety stop and the first required stop.

This procedure is repeated until there is less than 30 feet between the last deep safety stop and the first required decompression stop.

The depth midway between the depth at start of ascent and first decompression stop depth (the average of the two depths) is half the sum of the two depths.

For example:

Bottom depth is 60 m and the first required decompression stop depth is 15 m,

Average of these depths is (60 m + 15 m) ÷ 2 = 37.5 m, which may be rounded to 38 m. This would be the depth for the first Pyle Stop.

The difference between first Pyle stop and first required stop is 38 m - 15 m = 23 m

This is more than 9 m, so another Pyle stop is indicated.

Average of 38 m and 15 m is (38 m + 15 m) ÷ 2 = 26.5 m, which may be rounded to 27 m. This would be the depth of the second Pyle stop.

The difference between second Pyle stop and first required stop is 27 m - 15 m = 12 m

This is more than 9 m, so a third Pyle stop is indicated.

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This is less than 9 m, so no more Pyle stops are indicated.

Image y wikipedia.org

Opinions on the efficacy and safety of Pyle stops is varied, as are opinions on whether they should be practiced by recreational divers, technical divers and professional divers. Some of these opinions are based on theoretical considerations, and others are supported by some systematic experimental evidence.

A theoretical disadvantage of Pyle stops and some other deep stops is that they are done at a depth where some tissues are still in-gassing, and this will increase the gas concentration in those tissue compartments, requiring additional decompression time for the same decompression risk, and hence they should be used only by professional divers. No-decompression dive profiles are not shown to be safer when a deep stop is added, and in particular a deep stop should not be added at the expense of reducing the shallower stop times on a decompression dive.

On the other hand, adding a deep stop while following the computer mandated shallower stops has not been shown to be harmful. Deep Stops are performed for 2–3 minutes, at depths where any extra nitrogen loading is likely to be small compared to the total gas load. During short deep dives it is the fast tissues that load up and may saturate with inert gas. The deep stop could reduce the saturation of those fast tissues, while the slower tissues are still in-gassing by a small amount. Some experimental work has shown reduced venous bubble counts after deep stops combined with the computed shallow stops in comparison with the shallow stops alone.

US Navy experimental research at NEDU indicated that lengthy deep stops as calculated by RGBM created more supersaturation and would result in more incidence of DCS than a Haldanean schedule of the same duration. This result did not relate to Pyle stops of just a couple of minutes at each stop, which were considered only as better control of the ascent rate.

In the UK, the Sub-Aqua Association has adopted a system of deep stops as an integral part of its training program.

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5.5.5. FINISHING THE DECO STOPS It is a very widespread practice among technical divers to make the last DECO stop at 6 m instead of 3 m since, when breathing oxygen, the elimination of nitrogen is done at the same speed but increases safety by being at a higher ambient pressure .

When ascending from the last stop to the surface, in addition to the rapid change in ambient pressure from 1.3 to 1 atm, three other changes occur:

- First: Abruptly we stop breathing oxygen at 3 m, with a partial pressure of oxygen of 1.3 atm, to breathe air from the surface, with a partial pressure of oxygen of 0.21 atm. Inspired oxygen at elevated partial pressure produces a vasoconstrictive effect that does not disappear instantly when the partial pressure changes. Then, at that time, less oxygen will reach the tissues, producing hypoxia in the tissues that would have previously reduced their irrigation.

- Second: The step from a muscular relaxation situation that we have maintained during decompression to a notable activity to swim on the surface, get out of the water with the equipment, move around equipped by the boat, etc.

- Third: The severity that can affect the distribution of blood.

After periods of time of weightlessness when we join the blood moves from the central part of the body to the lower extremities.

Therefore, although there are no data to establish a direct relationship between these factors and the appearance of symptoms of decompression sickness, experience indicates that with all these measures we will reduce the impact that leaving our water after a decompression supposes for our organism.

5.1. GAS MANAGEMENT

5.1.1. FACTORS INFLUENCING THE DURATION OF A DIVER'S AIR SUPPLY Breathing with the scuba the air consumption depends on the amount of air that is inhaled, the breathing rhythm and the depth at which we dive.

Breathing out of the water without the regulator, and at rest, we only use one-tenth of our lung capacity.

Pulmonary capacity is all the air that fits into the respiratory system, i.e., the mouth, nostrils, larynx, trachea, bronchi, bronchioles and alveoli and will therefore be different depending on the complexion of each diver.

This would explain why women's consumption is usually lower than men's: they have lower lung capacity.

However, breathing with a regulator we use a greater amount of air so that the lungs remain ventilated and do not accumulate in them the CO2 produced in the muscle work involved in breathing with the regulator. Both inspiration and exhalation work, even if they are not very intense, are carried out in a constant way which causes the accumulation of CO2 if the lungs are not ventilated.

It is convenient to use a regulator of great flow so that this work of inspiration and expiration are reduced, otherwise we will have an increase of the respiratory rhythm and consequently the consumption will be increased.

Keep in mind that we do not have the same needs floating at rest or in a decompression stop as flapping against a strong current. If we dive deep the air is denser and if we are also under stress the flow of a low quality regulator could be insufficient and could be the cause of an accident.

The number of respiratory acts we perform in one minute is caused by the nervous system that acts on the musculature of the heart to establish a certain heart rhythm. There is, therefore, a synchronization between the heart rate and the respiratory rate. The respiratory rhythm is maintained by the impulses emitted by a nerve centre located in the spinal 55

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then the blood becomes more acidic and the nerve centre, which regulates breathing, induces an increase in the frequency and depth of respiratory acts.

If we lose the respiratory rhythm and take shallow and frequent breaths, the CO2, not being expelled, accumulates in the lungs and arterial blood, and as a consequence the nervous system will increase the respiratory rhythm. If we do not regain the proper rhythm we will have a respiratory crisis with gasping and a feeling of shortness of breath.

We have already said that not all divers will consume in the same way and each one of us will have to carry a bottle with the adequate capacity.

Inexperienced divers tend to have a faster breathing rate and consume more.

Another reason you might increase your breathing rate is cold. Adequate thermal protection provided by the suit, booties and hood should reduce this effect.

As depth increases, pressure increases, air density increases, and we will use more air in each breath as we descend.

5.1.2. BASIC PRINCIPLES OF GAS MANAGEMENT If we plan a dive but can't carry enough gas to do it, it won't do much good to plan. The first step will be to determine our Surface Consumption (CS), i.e. the litres we consume in one minute on the surface at 1 bar pressure.

A good method is to descend to about 10 m (Prof) or any other depth, note the initial pressure of our manometer (Pi), swim about 5 min (t) trying to maintain the depth and a reasonable speed and finished the journey, note the final pressure of the manometer (P2) and elapsed time.

It is convenient that when doing this exercise we breathe from a bottle of reduced size because being smaller there will be a greater change of pressure and the calculation will be more accurate than if we do it with a bottle of 18 liters, as soon as the needle descends.

With this data we will be able to calculate the CS in the following way:

Consumption C is related to CS and to the Total or Absolute Pressure of the form:

C = CS x PT x t

On the other hand, we can deduce it from what has lowered the pressure of the bottle:

C = (P1 - P2) x L

where L is the capacity of the bottle in liters, equaling

PT x CS x t = (P1 - P2) x L

and clearing

(P1 – P2) x L CS = PT x t

If, for example, we begin to breathe from a 6-litre bottle that makes 200 bar and after 5 min we have 180 bar at 10 m depth, we will calculate our CS applying the above expression:

(P1 − P2) x L (200 – 180) bar x 10 litres CS = = = 12 liters/minute PT x t 2 bar x 5 min.

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- Normal activity (descent, bottom diving and ascent to the first deco stop) 20 litres/min at 1 bar pressure

- High activity (moderate stress) 30 litres/min at 1 bar pressure

- No activity (at rest or deco stop) 15 litres/min at 1 bar pressure

Obviously these data are indicative and will depend a lot on the constitution, sex or state of the diver, his level of experience and the conditions of the dive.

5.1.3. GAS MANAGEMENT TECHNIQUES Some expert divers boast very low gas consumption as an expression of their diving experience and skill. This must be considered with caution.

In general, when the consumption of the average is too low, it can produce a CO2 retention by not ventilating enough. With depth this situation is aggravated due to the greater density of the gas.

The retention of CO2 is one of the main factors that contribute to narcosis, oxygen toxicity and hinder the exchange of gases in decompression.

Therefore, an excessively low consumption is not necessarily better in deep diving.

To stay within the average of divers of similar physical constitution is the best thing, and of course we will not try any respiratory technique to diminish that consumption beyond the relaxation and the slow and calm breathing, but without excesses.

When planning a dive with a buddy we should try to bring the same dive plan and equipment and of course, the same amount of air adjusting it to the needs of the diver who consumes more.

Another consideration to bear in mind is that the bottles must never reach empty surfaces. Always leave approximately 10% (or 20 bars) of the initial gas.

This will guarantee the integrity of the cylinder and an extra gas that may be useful in an emergency.

No less important is the profile of the dive. One of the profiles that most require reserve gas is forced return diving: cave diving or wreck diving.

A simplified method would be to use the rule of thirds: Gas for the diver's outward journey, gas for the diver's return and emergency gas for the partner's return if he runs out of air.

5.1.4. GAS MANAGEMENT CALCULATIONS As an example we will consider a forced return dive using the data detailed below:

Maximum depth = 52m

Bottom time = 16' = actual bottom time + descent time

Lowering speed = 15 m/m'

Speed ascent to first stop = 9 m/m'

Climbing speed between stops = 3 m/m'

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To the right the Run Time (chronological forecast of the dive I'm 0 meters away with a 0' stopwatch.

starting with zero stopwatch) considering the data of the US I reach 52m at 4'. Table. Navy : 54m / 20'

We obtain the following data: I leave the 52m when my chronometer marks 16'.

Downhill time = 4'. I get to the 9m past 21'.

Bottom real time = Bottom time - Descent time = 12'. I leave the last 9m 22'.

Total ascent time = 31'. I get to the last 6m 23'.

Total dive time = 47'. I leave the last 6m 28'.

I get to the last 3m 29'.

Let's consider standard consumptions: I leave the last 3m 46'.

I get to the last 0m 47'. Decompression Consumption: 15 l/m'.

Normal consumption: 20 l/m'.

Consumption Stress: 30 l/m'

And with all this data we are going to calculate consumption:

To the time of the deco stops, we have added 1' corresponding to the time of ascent until the next stop, in this way we round to obtain a very little appreciable extra gas.

Otherwise we should calculate the consumption of that small rise separately and it would result in a little less gas in total.

Total gas required 2733 liters, considering a standard consumption and making the dive in optimal conditions but leaving the bottle at zero. Let's round it up to: 2800 litres

CS Pressure Pressure Time Litres Activity l/m' initial bar final bar in min. consumed

downturn 20 1 6,2 4 288 backdrop 20 6,2 6,2 12 1488

ascent 20 6,2 1,9 5 405 stop 9m 15 1,9 1,9 1+1 57

stop 6m 15 1,6 1,6 5+1 144 stop 3m 15 1,3 1,3 17+1 351

total 2733

We now make a rough estimate for consumption management, taking into account:

-the gas that the diver needs to make the outward journey with an average consumption of 20 L/m',

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-the gas necessary for the return considering that you could have a stress which would lead you to consume 30 L/m' instead of 20 L/m',

-the gas you'd need on the way back to rescue a stressful partner from running out of air.

From the estimated consumption calculated above (2800 liters) we will say that half will be used for the outward journey, the other half that was calculated based on the CS of 20 L/m' we recalculated it for a CS of 30 L/m' and of course the same amount would need to assist a companion who ran out of air right at the time of return: outgoing 2800/2 = 1400 litres turn 1400/20*30 = 2100 litres partner 1400/20*30 = 2100 litres total 5600litres of gas required total

At the end of the dive, the bottle should be left with approximately 20 bar or 10% of the initial charge: we add a 10℅ to the 5600 liters = 600 liters approx.

We add the 600 liters found to the 5600 liters of total gas needed to know how much gas I have to fill the bottles: 6200 liters.

The following is to calculate the necessary equipment to make the immersion, we refer to that or how many bottles we need to make the immersion.

Recreational scuba tanks are usually loaded at over 200 bar, and this load can be increased if the tanks allow it.

Initially we make a first attempt to find a bottle loaded at 200 bar in which the necessary total gas could enter.

6200 liters / 200 bar = 31 liters, this is the volume of the bottle we theoretically need.

There are usually no bottles of this size so we will need 2 bottles and if possible symmetrical for example 2 bottles of 15.5 liters.

If we have 18 litre bottles then the problem will be solved. If we have 15 litre bottles we should make a small adjustment.

We are going to put in a 2x15 litre bibottle the 6200 litres of gas necessary.

Logically, in order to achieve this, we will have to increase the loading pressure that we had initially foreseen to 200 bar.

In order to know what the new charging pressure will be, we take the 6200 litres and divide them by the volume of the two bottles:

6200/30=207bar, rounded to 210bar

For this dive we need a 2x15 litre equipment charged at 210 bar.

A very important fact is to know at what moment I have to abandon the immersion:

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-before a forecast of lack of gas due to having used it in unplanned activities and which could compromise decompression

I mean, we need to know how much gas we need for the return. We can calculate it in detail, but we could also approximate it with the rule of thirds: approx. 1/3 for the outward and 2/3 for the return rescuing a companion.

Of the 210 bar of gas that we have we can not use everything for immersion, 10% or 20 bar we have to keep it so that the bottle does not reach empty surface.

usable gas = 210 bar -20 bar =190bar usable gas

Calculation of the gas for the flow to estimate the forced return gas:

190 bar /3=63bar, set to 60bar to give more gas for the return.

Gas required for forced return: 210 bar - 60 bar =150bar

Conclusion:

for a 52m dive with a 16' bottom time, the 54m table will be used with a 20' time and the return is expected to start before reaching 150 bar. pressure gauge.

Two other run-time will also be calculated for security:

54m/25' considering that we might need more time to fix an incident.

57m/20' more considering we might need more depth to solve an incident.

5.1.5. DECO PLANNER SOFTWARES PTRD like V-planner software but other could be good. Here a V-Planner tutorial by Erik Brown.

The V Planner is an essential tool for any technical diver. The available options of settings and configuration make it the primary choice for any serious diver. As with any dive planner, the output of information will only be as reliable as the information inputted. The planning of each dive must be taken seriously, as it’s this outputted dive profile that will be followed precisely on every dive. Mistakes in the primary planning of dives can have serious consequences in each dives outcome.

Every dive is different. Personal preferences of conservatism, environmental factors of fresh vs. salt water, and dive profiles of depth and bottom times must almost certainly change from dive to dive. For each dive, it is important to make sure that these small discrepancies are known.

Initial steps in dive planning always start in 'config' - 4th icon from the left on the top. Inside 'config' there is a list of options and information that is imperative to make sure is correct pertaining to each dive. Most will remain static, but must be double checked each time to ensure that no settings or parameters have been changed or altered. Most mistakes will be easily noticed in the outputted information, but simple inaccuracies such as salt vs. fresh water might be overlooked.

These discrepancies can change a dive profile enough that serious consequences may occur.

The following is meant as a tutorial for new users and a refresher for divers with substantial time out of the water

ONLY.

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It is NOT an instructional guide. Dive planning must be taught in depth by a technical diving professional.

1.

This column deals primarily in basic parameters; mostly in the units (imperial vs. metric) desired in the dive plan. Double check each is correct.

2.

'conditions' will remain relatively static unless changes are needed as result of environmental conditions.

-'Stop Size' represents the interval (in meters) that is desired for your profile. This is set to 3m. There are options available for CCR dives if necessary.

-'Max Depth for 100 O2' is typically set to 6m - the deepest depth to safely breath pure oxygen based on 1.6pp02. This may change if surface swell is a factor. A 1m swell can drastically change the PO2 levels, so decreasing the max O2 levels to a more conservative depth might be appropriate.

-'Max ppO2 for deco mix...%O2' enables you to set the desired partial pressure (pp02) for each range of oxygen percentages. The standard and default setting are as follows:

Up to 28% 1.4 pp02 28-45% 1.5 pp02

45-99% 1.6 pp02 61

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This coincides with the industry standards of 1.4ppO2 in your back gas or working part of the dive. Gases with high oxygen content (50% and 100%) are most often used, falling into the range and industry standard of 1.6 ppO2 for deco gases.

-The ‘RMV’ (aka SAC rate) must be altered based on each individual’s gas consumption.

This information will be used to calculate the gas consumption for each dive. This accuracy of this information is essential (correlated with depth/time) for the overall gas consumption of each dive. This is crucial as dives are planned/carried out down to the meter and minute.

Its imperative that your SAC rates are known before planning any decompression dive, always conducted in initial training dives or after long periods out of the water. Everyone dives the same plan, ensuring the highest sac rate of the group to be used as the parameters. Most SAC rates seem to be around 16 or so. Increasing this to 20 increases a level of conservatism. Your training will provide you with the ability to fix any problem with enough time. This time is a byproduct of safe and conservative dive planning.

-SCR is...fiO2 adjustments. This setting (for SCR) adjusts the inspired mix by the values supplied.

3.

‘Extended Stops’ can be enabled for training level dives where NOTOXs (gas switches) might take longer then ideal. Debates behind extending stop where gas switches occur in dealing with your oxygen window are also viable.

4.

‘Conservatism’ Nominal is for navy divers and the super fit. Plus 2 or 3 is the normal setting for most divers. Set a plus 3 or 4 with strenuous, cold, a series of multi day dives, extra safety, or a prior history of DCS or symptoms.

5.

‘Elevation Data’ is simply used by inputting the appropriate information when diving in elevated situations.

6.

‘VPM Model’ The VPM-B is the current model in wide spread use today. VPM-B/E is an extention made for divers undertaking very deep and long dives. For most divers, the B and B/E plans are the same, because B/E only begins to deviate after large gas loads (90-100 mins deco required).

7.

-The ‘Decent Rate’ might vary depending on your dive profile. 15 is standard. Increases to 25 might be desired on deeper dives

-The ‘Ascent Rate’ will definitely vary each and every dive. Changes in ascent rates are based on the ‘off-gassing point’. Our recommendation is 9m/min from the bottom depth to the off-gassing point providing a safe ascent without affectting the on-gassing portion of the dive. Once the 'off-gassing' point is reached, the ascent rate is slowed further to 6m/min in the off-gassing and important decompression part of the dive. Decent rates from 3m to surface are further slowed for added conservatism and safety. Treat the surface as another decompression stop; leave mask and

regulator in place for an extended period of time.

Double check all information and click ‘OK’ 62 Now that the appropriate information is provided to formulate a dive plan, the parameters of the dive itself must be

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‘Bottom mix & travel’ lets you input the depth, time and gas contents. Double click on an existing dive to edit or 'add a level or mix' at the bottom to input new information. Keep in mind that the decent time is included in the inputted time.

This could be substantial on deeper trimix dives.

Times of 'zero' indicate the use of a travel gas. Input the oxygen contents of your back gas and helium content (if any) and click OK.

Make sure the box in front of the ‘Bottom mix & travel’ is the only icon enabled, unless planning a multilevel dive or use of a travel gas.

‘Deco gas’ permits you to input required decompression gases. Any number of gases can be added/enabled depending on the dive profile. It does not matter what order they are arranged.

Input helium level is required to avoid IDC or left vacant if not.

Before you’re allowed to ‘calc’ your plan, a surface interval must be chosen. Choices of 5 days, 48hr, 24hr, or precise hours/minutes are options. Once the surface interval is entered the 'calc' bottom above lights up and becomes active.

Once you ‘calc’, the dive plan information is displayed over 6 columns.

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1.

Designates the particular ‘actions’ of the dive. Whether the information is a decent, ascent, level (bottom time), or stop at (deco) time are the available outputted options.

2.

Delegates the depth that the subsequent information conforms too.

3.

Depicts stop time. This is very important and the most vital information that informs us our ‘bottom time’ and subsequent ‘deco time’.

4.

The ‘run time’ is only really important in the planning part of a dive. It’s very important that we never chase our run time and use this information only as a guide of our whereabouts within the dive.

5.

This is simply the chosen/inputted gas mix. It will inform the diver of the type of gas, the O2 and helium contents, and required depths of gas changes (NOTOX)

6.

Vital information regarding the particular gas properties at that depth are shown. If it is a ‘decent’ or ‘ascent’ rate it

will inform the diver of the rates entered in the ‘config’. If it is a ‘level’ (bottom time) or ‘stop at’ (deco level) then information about its PP02, EAD, and END are shown. This data is important and might cause changes in the dive

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1.

The ‘off gassing’ point is presented directly under the dive profile. This information will be used to control our ascent rates back in the config. Remember the desired ascent rate from the bottom level to the ‘off gassing’ point is 9m/min, 6m/min from the ‘off gassing’ point to 3m, and then 1m/min from 3m to the surface. This can be left to the end of dive planning because changes in depth and time will alter the ‘off gassing’ point.

2.

The OUT’s and CNS Total deal with oxygen exposure. Deep trimix dives with long periods of breathing 100% 02 can cause complications. OTU's must remain under ‘300’ and the CNS Clock is simply a percentage, so anything under 100% is acceptable. It is rare to see these close to their limits unless you are doing multiple deep dives over consecutive days or extremely deep/long trimix dives.

3.

Gas consumption is vital to safe dive planning. With a virtual ceiling existing in every decompression dive, making sure you have the required gas allowance is critical. With the SAC rate entered in the initial ‘config’, total amount for each gas are calculated using depth and time.

This is the minimum required gas needed and does not include any concept of reserve gases.

That must be done manually depending on your philosophy. Standard is the ‘rule of thirds’ requiring 33% more gas then needed.

The presented information must be appropriate for the dive mission. Bottoms times, PP02s, END's, OTUS, gas consumption, and decompression obligation must be checked. Return and altering the depth, time, or gas contents if appropriate.

Red or Yellow warnings will appear if problems occur with hypoxic gases, ICD, or oxygen exposure. The absence of these warnings does not mean that the profile is perfectly safe and should always be doubled checked with a dive buddy to ensure trivial mistake are not overlooked.

Additional information about the dive can be found in the tool bar on the top

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‘Lost Gas’ will automatically recalculate your gas consumption and decompression obligations if you were too lose a deco tank.

Keep in mind, any malfunction with the tank that makes it unbreathable at depth should be considered a lost gas. Broad calculation (next highest gas X 2) are nice concept to know, but the presented information is precise and important for most deeper dives with multiple gases. This information is often kept in the wet notes for emergency purposed.

The rule of thirds is not applied to lost gas situation as this is the logic for implementing such rules in the first place.

The '+ or -' is another function that automatically recalculates your gas consumption and deco obligation in the event you break your desired profile in regards to time and depth.

You may choose from a few standard depth and times or input your own.

This is important to know in emergency events if you drop passed your desired depth or for any reason stay longer.

This info is also important to have in your wet notes.

Multiple dives can be calculated by clicking on 'Dive 2' in the top middle. A surface interval will be needed along with the dive profile of the second dive. Make sure to pay attention to the OTU's and CNS clock as spikes may often occur during consecutive or multiple deep dives.

The 4 icons at the top right corner allow information for the dive to be presented in specific methods depending on its purpose.

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is the standard text version of the dive that has the vital information needed to plan a dive. It is also the best option fortransfering the profile to your arm slates and wet notes.

is a graph showing the partial pressure levels for each gas.

A visual representation helps to ensure you have no large spike in any of the gases and are kept under manageable and reguired safety limits

shows the dive profile again with increased info on the CNS, OTUS, and gas consumption at each level without including relavent decent or ascent data

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Is a graph of the dive profile represented by depth vs. time. This helps visualize the dive and how the profile should look if followed perfectly. Please note that 'stop' depths' of 1 min are not decompression stop, but steady slow accents over minimal distances. It isn’t until you have 2mins or more then actually decompression stops occur.

Transferring this information to your slate can be done a number or ways. It’s most important that the profile makes sense to the user and it is easy understood. Be sure to fully look through the plan and think it through before starting, as minor changes may be necessary to achieve a safe and easily understood dive profile. Ascent times that cover a large depth range may be confusing. 30m over 3min is a long distance over quite a long time to keep track of your where abouts within a dive. Breaking these gaps into 10m increments may help in making sure you don’t loose your place. Don’t get too complicated with abstract depth and time. Keep it to 10m increments until deep stops or deco occurs. Round times to the appropriate minute, always being conservative. Most bottom timers’ only show minutes. Seconds will only confuse the process further. If there are extra min left over when breaking down long gaps, be sure to add them to the lowest possible level (denoted in a 1+1 rather then a 2 so not to confuse it with a decompression stop). Never deviate to far from the original plan and only make minor changes if necessary to avoid confusing or increase safety.

The dive profile used through this tutorial should look similar to the below profile:

Action Depth Stop Run Gas Dec 50 3 3 Level 50 16 19 50 16 19 Asc to 40 1 20 40 1 20 Air Asc to 35 1 21 35 1 21 Asc to 30 1 22 30 1 22 Asc to 24 1+1 24 24 1+1 24 Asc to 21 1 25 21 1 25 Stop at 18 2 27 18 2 27 Stop at 15 2 29 15 2 29 EAN 50 Stop at 12 2 31 12 2 31 Stop at 9 4 35 9 4 35 Stop at 6 4 39 6 4 39 Stop at 3 6 45 3 6 45 Oxygen

Stop at 0 3 48 0 3 48

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5.1.6. DOING DECO STOPS Decompression stops are made in such a way as to remove the nitrogen that supersaturates the tissues. So we have to follow the following guidelines:

1. The exact depth to which it is programmed must coincide with our chest and would be more effective if we were in a horizontal position, thus, the pressure on our body is uniform.

2. We have to avoid the cold so, in addition to bundling up, we must move a little to get it.

3. We must avoid efforts that accelerate our respiratory rate and produce carbon dioxide, so movements should not be abrupt.

4. The scheduled times to go from one stop to another must be strictly followed. In this sense, the use of the run time that marks the minute in which it is necessary to leave each depth guarantees, if we comply with it, that the correct speed is reached or that it is corrected if it is exceeded.

The anchor line of the boat is usually the most common place where decompressions are performed. It has the advantage that it is in the same place as the boat from which we jumped into the water and to which we have to return, avoiding trips to the surface.

However, performing DECOMPRESSION while holding the anchor can have its drawbacks:

- Due to the effect of the current, it may not be perpendicular to the bottom and be curved, having to exert a great effort to remain subject to it.

- If the waves are intense, it causes the boat to buck and pull from the anchor line. Which makes it uncomfortable to be there.

- As it is the place where most divers descend and ascend, it is uncomfortable that movement surrounded by hundreds of bubbles.

An element that can assure us some comfort is a Jon Line, which we can manufacture with a 1.5 meter rope with two carabiners. With it we hold on to the ascent and thus avoid jerks and receive all the bubbles.

Another very common place to decompress on oblique bottom dives is on the stones of a slope or bass. We can make smooth movements and be distracted during stops. The downside is when there is surf, staying on the stones can make it uncomfortable and even dangerous. We must not forget, if we practice this type of stops, respect for the flora and fauna in the background because, inadvertently, we can harm their development.

A drop rope with buoy and ballast is a good procedure because the effect of the waves (the pulls) is reduced and its location on the bottom to which we want to descend is usually more precise than the anchored boat. But it can still be uncomfortable if there is current or if there are many divers, so the ideal complement is the trapeze.

The trapezoid is made up of bars separated by chains forming several floors (6, 9 and 12 m) that will hang from two buoys.

The hanging bars, once the ballast line has been anchored with its buoy, are attached to this line with a carabiner or shackle so that divers who climb the descent line can be placed next to the bars to make decompression stops.

We gain in comfort and precision at the stop.

In the event that there is a strong current, the trapezium with all divers can detach from the descent line and drift.

Divers adapt to the sea and their situation is as comfortable as possible. Logically, the support boat will follow the 69

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The only drawback of this procedure, and it is not for divers who are in the water, is that the trapezium must be transported and the maneuver must be carried out to carefully launch it into the water so that nothing gets entangled or dragged with him.

The alternative method to all that we must always have in mind is to use the decompression buoy or a lift balloon. We can fix it at the bottom and in that case we will lose the line and the reel since we cannot go back down to them, or not fix it and go up picking up the reel and drift. In case of current and waves it is comfortable to drift if we know that they are following us from the boat or they are going to look for us. The buoys must be at least 25 l and have an anti- tip valve.

It is convenient that we practice the buoy launching regularly because it is not easy and the hooks can give a good scare.

Surface assistance

The role of the skipper of the boat is very important not only for the location of the dive site but also for the precise choice of the descent point (either by the anchor line or by a weighted line). 80% of the success of the intervention depends on finding the desired place in the fund and reaching it as soon as possible.

The maneuvers when going down the ballast line to drop off and pick up the divers have to be done with great care and if the sea conditions are not good they require some skill.

In addition, the presence of a support diver is required. This diver must be fully equipped and willing. When it is calculated that the divers at the bottom begin to ascend, you must submerge to wait for them at the first decompression stop. He checks that everything is fine and assists them in whatever is necessary (bringing unused bottles to the surface, lowering more gases, etc.). If no incident occurs, they must remain with the divers while they finish the decompression.

If an incident occurs and you have to accompany a diver to the surface, their function will be to assist you until you are picked up by the main boat and then you must return with information or instructions to the water. If, due to the condition of the diver who has been taken out of the water, the evacuation plan would have to be implemented with the main boat, the backup diver should stay in the other boat that will be next to the buoys of the divers who decompress with a radio station.

DECO stop failed

If a diver skips a decompression stop and appears on the surface, we should act as follows:

1. If you have skipped a small decompression and do not show any signs or symptoms of a decompression accident, it is best that once you get out of the water, you are given normobaric oxygen for one hour, hydrated and kept under observation 24 hours.

2. If the diver has skipped a stop and shows any signs or symptoms of a decompression accident, it is best to administer normobaric oxygen, hydrate him and transfer him to a hyperbaric assistance center.

3. If the diver has skipped the 6 or 3 m stop, he is well and can return to the stop in 1 min, he will descend to the stop and remain there for the expected time (surface time can be counted as stop).

4. If the diver has skipped the 6 or 3 m stop, he is fine but cannot return to the stop in 1 min, he will descend to the

skipped stop and will stay there for a time equal to the expected time multiplied by factor 1, 5.

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b. There is a back-up diver who can descend with him. c. There is enough gas and the sea conditions allow it.

So:

I. Descend to the depth where you should have made the first stop.

II. Stops with depths equal to or greater than 12 m are repeated.

III. A minute of time is spent ascending between stops.

IV. The duration of the planned stops is multiplied by 1.5 at 9, 6 and 3 m.

The new ascent plan should be written on a table and the safety diver must descend and show it to all divers waiting for confirmation that they have understood it.

In all cases, even if decompression is repeated, normobaric oxygen should be continued at the surface for at least half an hour.

These emergency procedures may be appropriate in some circumstances, but the risks involved must also be considered.

Weather conditions, the appearance of signs and symptoms underwater, hypothermia and dehydration are factors that make this type of action very risky.

Putting all the means to avoid situations like the ones described here is the best way to solve them and that is what is largely the objective of this course.

If you comply with the safety regulations that we have set out and follow the procedures for planning the dives with the rigor that we have described, you will be in a position to enjoy this type of diving and make it a safe dive.

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6. CONTINUING EDUCATION AND PROFESSIONAL CAREER IN DIVING Once you have completed the PTRD Extended Range training program and obtained the corresponding certification you will be opened the possibility to achieve a unlimited Deep Diving qualification as Trimix Diving. The different PTRD diver training programs you can attend once you have completed the PTRD Extended Range Training Program are: • PTRD Normoxic Trimix Diver • PTRD Trimix Diver • Dry suit, necessary if your diving area is characterized by cold water.

Below is a summary of some of the courses you can find at PTRD:

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