2019
Rebreather Diving Manual
CMAS scr & ccr diver
Collection: PTRD Diving Manuals
Contact: [email protected]
Edition 2019
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INDEX ...... 3 ...... 3 The SCR rebreather ...... 4 The CCR rebreather ...... 6 ...... 13 ...... 14 ...... 19 ...... 20 BEST MIX ...... 20 BAILOUT CYLINDERS...... 20 V-PLANNER ...... 21 ATTITUDE CONTROL ...... 26 ...... 26 1 PRE-DIVING CHECKS ...... 27 2-ADJUSTMENT OF THE VOLUME OF THE LUNGS ...... 27 3-WASH LOOP ...... 27 4-RESPIRATION WITHOUT MASK ...... 27 5-PpO2 CONTROL ...... 28 PpO2 control tests: ...... 28 6- REBREATHER COMPENSATION ...... 29 7-PASS FROM CLOSED TO OPEN CIRCUIT ...... 29 8-OPEN AND CLOSE TAPS ...... 30 9- BREATHING ...... 31 10-OVERPRESSURE VALVE ...... 31 11-BATTLES OF BAILOUT ...... 32 12-RESALTED FAST ...... 32 13-CONTROLLED DESCENT AND SURFACE RETURN ...... 33 14-SURFACE RETURN IN EMERGENCY ...... 33 15-SENSOR TEST UNDERWATER ...... 34 16-CONTROL OF BREATHLESSNESS ...... 34
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This manual does not replace the instructor's information, but will serve as a basis for being able to review some basic theoretical and practical concepts.
During training, you will need to follow a standardized program whose minimum requirements must be met for a student to learn how to use a closed loop rebreather ("CCR") for all course levels from using air thinner at 30 meters up to trimix for a maximum depth of up to 100 meters.
These programs meet the minimum requirements on all units regardless of the machine manufacturer. Each manufacturer adds their own requirements for CCR divers to learn how to use their rebreather safely, including unit specific procedures and additional classroom and water training.
The rebreather is nothing more than a recycle of breathing, an autonomous closed-circuit breathing system where the diver continues to breathe, exploiting the inert gas (diluent) in the air is nitrogen.
Our breath passing through a filter of soda lime is purified by CO2 and replenished by the oxygen used by our metabolism.
Who knows the first rebreather is the one designed by Hennry Albert Fleuss in 1876 who created an autonomous apparatus that recycled the gas breathed.
In 1904, Dräger, a leading German company in the field of gas pressure regulation, invented the first respirator that would be used to rescue people in mines. Then, in the 90's, he produced, for the recreational scuba diving, the "Atlantis", a Rebreather Semi-Closed (SCR) called then "Dolphin", limited to the depth of 40 metres.
Below, with the new "Ray" model, you could also use the EAN 50. This rebreather could be adapted to allow the use of EAN 40 and 22 blends thus allowing to reach slightly greater depths.
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At the same time, Italy is also moving. O.M.G. builds a new SCR system "l'Azimuth" and then the Azimuth AF (Alto Fondale). Built specifically for diving in Trimix is composed of two cylinders: one of Nitrox and one of Trimix.
John Kanwisher creates the first closed-circuit rebreather (CCR), a mixture self- contained breathing apparatus capable of controlling the partial pressure of oxygen through sensors and recycle the diluent gas and finally in 1968 the Electrolung is born and this could be considered the first operational CCR.
Basically the rebreather is composed of a breathing loop where the gas being breathed circulates in a one-way direction and soft bags or counter lungs that allow the diver to transfer the gas from our lungs to the machine. Usually they are two counter lungs: one for inhalation and one for exhalation, this also allows the diver to have, at a constant depth, an attitude that does not vary with breathing as happens in the open circuit where we have a variation in volume every time we exhale and inhale.
In the figure on the left we see the principle of operation of a rebreather and the cycle that the gas breathed performs to be purified of CO2.
THE SCR REBREATHER In the figure on the right we have the complete scheme of a rebreather SCR (semi closed), which uses a gas mixture enriched with O2, usually a Nitrox 32.
Rebreathers can mainly be divided into two categories: SCR Semiclosed Circuit Rebreather, CCR Closed Circuit Rebreather.
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Among the SRC there is the passive rebreather or PASCR, it is a machine with a very simple operation, does not need to be monitored and uses, as in all SCR rebreather, a default mixture. This machine discharges the ventilated gas outside and is then replaced by the mixture from the cylinder.
It consists of two bellows lung bags one inside the other. The mixture from the cylinder fills the two bellows. After exhalation, a part from the larger external lung passes through the soda lime filter before being breathed in again. The inner lung, which is smaller, is at some point crushed and opens a valve that discharges the gas outside emptying both lungs.
Breathing gas circuit diagram of a semi-closed circuit rebreather with passive addition.
1 immersion / surface valve with non-return ring valves
2 Exhalation tube
3 countercamps
4 Non-return valve for unloading the bellows
5 bellows of discharge
6 Overpressure valve
7 Main bellows
8 Additional valve
9 Scrubber (axial flow)
10 Inhalation tube
11 Breathing gas storage tank
12 Cylinder valve
13 First stage controller
14 submersible pressure gauge
15 Rescue request valve
Thanks to this system, after a certain number of ventilations we have a total change of the recycled gas, guaranteeing us a sufficient quantity of oxygen and a cleaning of the loop.
The depth limit is given by the mixture used.
Another SCR is the constant mass rebreather. It is the best known and most used of the SCRs, a rebreather of mechanical operation and easy construction. Also this SCR uses predefined mixtures, it is based on inserting in the loop on the side of the inhalation of the fresh gas enriching the mixture already breathed and filtered by the lime. Página71
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As you can see in the figure below, the functioning system is very simple, in the inhalation lung we have the injection of fresh gas through a flow regulator.
The loop in this case is composed of two lungs, one inhalation and one exhalation, we have an overpressure valve that serves to expel the excess gas and we find it on the side of exhalation, after being breathed passes through the filter is purified, put back into circulation and reenrichment.
Diagram of a constant mass semi-closed circuit rebreather
1 immersion / surface valve with non-return ring valves
2 Exhaust pipe
3 Canister (axial flow)
4 False ceiling
5 Ring overpressure valve
6 Inhalation valve
7 Breathing gas supply cylinder
8 Cylinder valve
9 Absolute pressure regulator
10 submersible pressure gauge
11 Automatic thinner valve
12 Constant mass flow measurement orifice
13 Manual bypass valve
14 Rescue request valve
At the recreational level, it is an excellent device that is easy to use but not to be underestimated for this reason.
On the market we can find different models such as Azimuth, Dolphin, and others.
THE CCR REBREATHER Today, the most performing breathing apparatus on the market is undoubtedly the closed circuit
rebreather (CCR). The limit of the depth is given by the mixture of the thinner and has a range for the same gas, absolutely superior to any other rebreather. Página72
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There are mainly two types of CCRs, the mCCR (Manual Closed Circuit Rebreathers) manual or the eCCR (Electronic Closed Circuit Rebreathers) electronic.
In the JRC the functioning is based on the metabolic consumption of the user, i.e. the consumption of the oxygen actually used by our body.
In the CCR, unlike the SCR, where you have a fixed percentage of oxygen and varies depending on the depth of the PpO2, we have a constant PpO2 and a percentage of oxygen so variable that at any depth we have the best breathable mixture, the famous Best Mix.
The JRC consists of two cylinders, one of oxygen and one of thinner that could be very well even the air.
Inside the machine we have the usual soda lime filter that fixes the waste of our metabolism, then we have an injection of oxygen that is based on the actual consumption of our body and can vary from 0.5 lt/m to 0.9 lt/m under normal conditions.
The main difference between the electronics and the manual is the introduction of oxygen.
In the electronics, it is automatic, i.e. the electronics monitor the oxygen and keep it constant by means of electric valves (Solenoids) at the level set by the user.
In the manual we have displays called monitors where we read the oxygen value and the input to keep it constant we do it manually via a by-pass.
In addition, we have a mechanical flow regulator that continues to introduce into our circuit a constant amount of oxygen that must be about our metabolic consumption: this is regulated before the dive and if calibrated well at constant depth we have a correction almost nothing except that we do not change our physical effort.
In the drawing below we see the operation of the rebreather in closed circuit, as we can see we have a loop (circuit) of breathing formed by the corrugated, the mouthpiece that inside has check valves maintain
the cycle of breathing in a mandatory sense, the lungs and the canister, the container of the filter where is placed the soda lime that absorbs the carbon dioxide waste of breathing. Página71
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Diagram of the electronically controlled closed circuit mixed gas rebreather.
1 Check/surface valve and non-return ring valves
2 Exhaust pipe
3 Scrubber (axial flow)
4 False ceiling
5 Overpressure valve
6 Inhalation valve
7 Oxygen cylinder
8 Oxygen cylinder valve
9 Absolute pressure oxygen regulator
10 submersible oxygen pressure gauge
11 Manual oxygen bypass valve
12 Orifice for measuring the constant mass flow of oxygen
13 Electronically controlled solenoid-operated oxygen injection valve
14 Thinner Cylinder 19 Manual Thinner Bypass Valve
15 Thinner cylinder valve 20 Automatic Thinner Valve
16 Thinner adjuster 21 oxygen sensor cells
17 Submersible manometer thinner 22 Electronic control and monitoring circuits
18 Bailout demand valve 23 Main and secondary displays
We have two distinct cylinders one of oxygen and one of diluent, the diluent is composed of a mixture whose percentage of oxygen is depending on the depth we go to, and should have the PpO2 equal to 1 at the maximum depth planned.
It is highly not recommended to use as a thinner a mixture without oxygen (pure helium) because it is not breathable and in case of washing we have for some time inside our loop a mixture that if
breathed can cause a hypoxic syncope.
The thinner can also be air, or depending on the depth a trimix. Página72
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As we have already mentioned in the RACs we must have sensors that analyze the oxygen, the minimum are two the ideal is three because in the case that a sensor signals a different value for reasons of malfunction having two of equal value we can know for sure which does not work.
For the maintenance of ppO2 in the mechanic we have a flow regulator that introduces into the loop a continuous amount of oxygen equal to the consumption of our metabolism in a situation of rest or light work.
Usually it is set between 0.5 and 0.7 lt. /min. to find our ideal setting, we have to get to a constant depth by finning and if the PpO2 goes down it means that the setting is low if it continues to rise it means that it is high.
The flow regulator has a screw that allows us to adjust the amount of oxygen injected, using a tool the asameter, which is mounted at the outlet of the regulator.
The setting should be slightly less than the consumption otherwise we must continue to introduce thinner to lower the PpO2.
Surely after some dives you will find the right regulation for your consumption, in any case you will always have to continue to monitor the oxygen because even if you can have a perfect regulation just a change in altitude or a muscle effort to vary the Ppo2.
The Loop is the breathing loop and is composed of several parts. The main feature is that the gas being breathed moves in one direction only.
The main parts are the mouthpiece where the diver breathes, has very important characteristics, the first that contains the valves of no return, serve to maintain the obligatory sense of breathing, also must have a closing command to prevent the entry of water at the time that we must for any reason take it out of the mouth.
When we resume breathing, to allow us to empty it, must have a small opening in the bottom, blowing while we reopen the closing command empty the water contained in the space of the rubber mouthpiece, of course this maneuver we will learn during our training.
A mouthpiece that we recommend is the BOV, has incorporated the nozzle connected directly to the first stage of the diluent cylinder and in case of emergency allows us to switch very quickly to the open circuit, the cylinder even if small size allows us a few minutes of breathing, more than enough to switch to the bail-out cylinders in a quiet and controlled.
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Some nozzles have integrated the HUD: a lighting system that warns of certain problems.
Who has the classic mouthpiece is obliged to have connected to the cylinder of the thinner a second stage positioned in such a way as to be reached quickly with a quick tap type shutoff that can prevent the self- dispensing, the ideal is to have it hooked on the right shoulder strap where it does not bother but is
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As already mentioned above, the loop is the breathing circuit so everything where the breathing passes is part of the loop as the filter container and the lungs.
The canister is the filter container, it contains the filtering material such as Sofnolime 797 which has a grain size of 1-2.5 mm.
Sofnolime Data
Expiry date: see manufacturer's packaging.
Grade: 1 - 2.5 mm Sofnolime 797 - Degree of immersion
Storage: Sofnolime should be stored in a sealed container in a clean and dry environment and at a constant temperature (ideally between 0 and 35 ° C).
Storage at high temperatures can cause reductions in material efficiency and service life.
Storage at sub-zero temperatures should be avoided.
Properly stored Sofnolime should retain its absorption capacity for up to five years.
Sofnolime should not be stored where such circumstances may occur:
I) Strong sunlight.
II) Contact with other chemicals.
III) Contact with water.
IV) Atmospheric conditions with high concentration of acid gases.
Transport: Sofnolime contains less than 3.5% sodium hydroxide p / p and is therefore not classified as corrosive.
Sofnolime packaging must not be marked with any specific risk or hazard signs and can be transported by land, sea or air to the product without risk.
Personal protection: Sofnolime is slightly alkaline and care must be taken to prevent contact with skin and eyes and avoid inhalation of dust.
Pouring and disposal: if poured, the granules must be swept or sucked up and removed appropriately. Any residue must be cleaned with a good amount of water. Waste or Sofnolime used will contain some residual alkalinity, but can be deposited in any landfill.
In the various rebreather we can find various provisions of the filter but mainly the filters can be of two types, linear or radial and are distinguished mainly by their difference in surface area in contact with the gas breathed, the wider the surface area, the less the respiratory effort.
The lungs or counter lungs of the rebreather are like a collapsible bag and serve to transfer the gas we inhaled into a container with variable volume, it would be impossible to breathe in a rigid container. Página71
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They can be one or two depending on how the machine was designed, in some rebreather are in the front or placed in front of the lungs, in a horizontal position especially at shallow depth in inspiration is an ideal position because they are under the lungs while in exhalation the effort tends to increase.
In the figures we can see the arrangement in two types of rebreather of the counter lungs, as we can see in this way we have a footprint in the front that in tight environments could create problems.
Some manufacturers place their lungs inside a shell at the back as in the figure below.
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There are some physical laws that we must take into account: Pascal, Boile and Mariotte but above all Dalton. If you have any doubts, you should review them in the manuals of your previous courses
Pascal recalls: "The pressure exerted on the surface of a fluid is transmitted unaltered on all surfaces in contact with the fluid".
In our rebreather the same phenomenon occurs, that is, the gas or respiratory mixture is distributed in every part of the device: in the counter lungs, in the canister, in the corrugated mouthpiece and exerts the same pressure on their walls.
This also happens when we dive in fact we and our rebreather are wrapped in the pressure that is exerted equally on our whole body and our device, in fact, to be able to breathe and prevent it from imploding we must make sure that the pressure inside our rebreather is always like the external one.
We remember Boyle and Mariotte: "At a constant temperature, the volume of a gas varies inversely proportional to the pressure to which it is subjected.
One very interesting thing about these devices is that they work at ambient pressure, in fact since they do not have to be subjected to high pressures, the rebreather can go to any depth without any leakage problem.
Let's remember Dalton: "The total pressure exerted by a gas mixture is equal to the sum of the pressures that each single gas component of the mixture would have if it occupied the entire volume".
We know that air is
composed of 21% oxygen (20.9) and 79% nitrogen, at sea level we have an atmospheric pressure of 1 atm, hence:
PpO2 = (1*21) /100=0.21
Oxygen exerts a partial pressure of 0.21 atm
As we already know, these calculations allow us to derive the partial pressure of oxygen in our mixture.
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We already know what happens to us and what could happen to us when we go underwater, that is, we have already studied what is tympanum rupture, hypoxia, hyperoxia and hypercapnia, decompression disease, nitrogen narcosis, over pulmonary distension.
If there are doubts we can go over all this in the manuals of the previous courses, while we will mention the advantages especially in the decompression due to the use of rebreather, the danger of hypercapnia, hypoxia and hyperoxia and.
An important part of the physiology we are going to treat concerns the metabolic consumption of oxygen.
This is one of the great advantages of our JRC, since our body takes only the necessary oxygen from the inhaled gas, returning the metabolic carbon dioxide (CO2) that will be absorbed by the JRC filter, while the machine will return the same amount of burned oxygen and the recycled diluent gas to the circuit.
In the table below, we can see some theoretical metabolic consumptions, the interesting thing is that these consumptions do not vary with the increase in depth, but may change according to effort or temperature.
At rest 0 .5/0.7 l/min.
For light activities 0,8/1 lt/min.
Medium effort 1,2 lt/min.
High effort 1,4/2 lt/min.
If we do not consider the waste of oxygen due to various washes and changes in altitude and if our rebreather has a cylinder of 2 lt of oxygen loaded at 150 bar, we have 300 lt available, if ours is a consumption of 1 lt / min. we have a theoretical autonomy of 300 minutes.
Your instructor will teach you how to calculate and adjust your rebreather based on your consumption and other factors that we do not list at this time.
Remember: decompression is due to the absorption of inert gas into the tissues, with the increase in depth, we vary its amount. With a CCR we can increase the percentage of oxygen to have a decrease in decompression times: with a constant partial pressure of oxygen we always have our BEST MIX. This advantage will be noticed with the CCR on the rise: having a constant PpO2 is as if while we go up again we continue to change mixture and it is in fact what happens but automatically inside the device. With the open circuit, to obtain this, the mixture was changed trying to use hyperoxygenated gases.
With the JRC if we use air as a thinner we can use tables for open circuit air, the important thing is that while we go deep the calculated pO2 is always lower than the one we breathe, using this system we will do safer dives.
Remember: with less inert gas, less decompression. Página72
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With a modern CCR we can fully exploit its capabilities and decrease decompression by using a computer that, connected to the oxygen probes, makes calculations based on the actual ppO2 inside the machine.
We must bear in mind that at high pressures oxygen becomes toxic.
It is necessary to keep very clear about the time ratio of PpO2 linked to the central and pulmonary nervous system, cellular exchanges and what happens if the hemoglobin is saturated with oxygen. If you are in any doubt, you should review these concepts in the previous course manuals.
Below is a table with times that are the limits of exposure to oxygen related to the various partial pressures:
O2 partial pressure Time Max. Exposure Time Max. Daily Exposition 0,6 720 720 0,7 570 570 0,8 450 450 0,9 360 360 1,0 300 300 1,1 240 270 1,2 210 240 1,3 180 210 1,4 150 180 1,5 120 180 1,6 45 150
Let's remember the Paul Bert effect: the toxicity for exposure to oxygen is calculated as a percentage of the maximum exposure time based on the oxygen pressure. We do not have to pass 100% of the CNS (central nervous system) and for greater safety it is better to stay under 80%.
With the CCR, it is very important to take this into account because if you use a constant PpO2 in demanding dives during the dive, you may tend to exceed this limit.
During the course you will have certainly added to this manual another specific machine that you will use, but you will also have to keep by hand your previous manuals where they are more detailed on the physiology and various decompression methods. Your instructor will introduce you to various computer programs such as Vplanner or others that will help you make any decompression tables and how to use dive computers such as VR3 or others.
These dive computers can be connected to the JRC's oxygen probes, so that they can apply their decompression algorithms to the partial pressure of the oxygen we actually breathe.
We have just mentioned how to calculate the CNS therefore the concept of hyperoxy or excess oxygen. Values greater than 0.50 bar partial pressure can cause toxicity phenomena:
- Paul Bert effect toxicity of oxygen at the level of the central nervous system
- Lorraine Smith effect Pulmonary oxygen toxicity Página71
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What interests us most is the Paul Bert effect.
The degree of effects of oxygen toxicity depends on it:
- by the partial pressure of oxygen (PpO2);
- the duration of the exposure;
- from individual susceptibility.
Nervous tissue is susceptible to the effects of O2 pressure, which manifests itself in changes in brain and nerve function.
If excess oxygen can lead to death, even lack or too low a PpO2 is lethal.
Our body needs oxygen and if we breathe it below the pressure of 0.20 bar it becomes a hypoxic mixture or with a quantity of oxygen not sufficient for normal metabolic functioning:
-at 0.16 bar we can have the first symptoms of hypoxia
-at 0.12 bar we can have serious symptoms of hypoxia
-at 0.10 bar we can have loss of consciousness
< 0.10 bar could be lethal
Remember: the danger of hypoxia, in rebreather, is a constant danger. In the manual ascending CCR we have a drop of PpO2 and we have to compensate it manually through a bay-pass. This also happens when the regulated oxygen flow on our rebreather is lower than our metabolic consumption.
Hypoxia, like sometimes hyperoxia, does not give us warning symptoms and if it occurs we will have a loss of consciousness and then death. It is very important to make sure that the O2 level in the loop is well above the hypoxic level.
If the oxygen deficiency or excess can be lethal, so is the waste of our metabolic process: carbon dioxide or CO2. For each respiratory act a part of the assimilated oxygen is transformed into CO2 (about 5%). Breathing with a normal open circuit we eliminate it completely while with a rebreather is put back into Página72
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circulation and could become toxic if not eliminated by the breathing gas. This situation is Hypercapnia, initially we could have a syncope until we get to a cardiac arrest.
Inside our Rebreather we have a soda lime filter that, if it works correctly, eliminates the CO2 produced by our breathing.
This filter must be replaced after a maximum of three hours of use later we will explain how to do this.
One of the dangers of the Rebreather is precisely the increase of CO2 that if it reaches toxic values without prior warning: it is an odourless gas and that gives virtually no symptoms.
To avoid this problem we have to:
- always have lime working
-make washes in such a way that, if inside the machine we have an accumulation of CO2 for an exceptional situation, this is expelled.
One of these situations could be an effort that makes us produce a greater amount of carbon dioxide, not allowing soda lime to eliminate it completely.
"Breathing must maintain normal levels of oxygen and carbon dioxide in tissues and blood; those who breathe air at sea level unconsciously adapt breathing to metabolic and exercise Página71
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needs, but this is not always the case in immersion, where non-physiological concentrations of oxygen, nitrogen and carbon dioxide can have independent, cumulative or interactive effects that are exacerbated by the depth, effort, ventilation resistance and density of the gas being breathed. You have to "think" about your breathing when you're underwater."
"The primary stimulus for breathing during the dive is the concentration of carbon dioxide. Respiratory gases have a higher partial oxygen pressure than in air and the blood is not "designed" to carry oxygen and carbon dioxide in hyperoxic situations. At sea level, at low concentrations of oxygen in venous blood, carbon dioxide is linked to hemoglobin, but at higher oxygen pressures the bond is not stable; this causes the partial pressure of carbon dioxide in blood and tissues to increase. Under normal conditions, raising the CO2 level stimulates more lively breathing and more vigorous ventilation eliminates excess CO2. If this does not happen, the result is dyspnea (breathlessness). CO2 can be retained for several reasons; during diving, the limiting factor is generally the respiratory system itself. Immersion in water causes blood to be transferred from the limbs to the lungs, which reduces both lung volume and maximum ventilation capacity. The latter is further reduced by the greater "work" by the need to move a denser gas through the airways and the dispenser. Resistance increases with depth and exercise level. CO2 can also be retained as a result of external stimuli, fear, inhibition of ventilation caused by narcosis. “
Article published by DAN in Alert Diver 4/2000
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The maintenance of our equipment is very important, because it allows us to have the machine always in order and working but above all safe. It is advisable to consult the manual of the machine, but we will make some suggestions later.
We have two types of maintenance, the ordinary one and the annual one that is done by the house or by an authorized center, where in addition to the replacement of some gaskets are made the checks and any adjustments as well as leak tests and operation.
The ordinary one you have to do every time you use the machine, and is based mainly on cleaning and disinfection of those parts that involve breathing. We have to extract the lungs that have to be washed and disinfected each time, the mouthpiece with the corrugations, the canister, the head and the parts of the filter.
We must always grease the o-rings with oxygen-compatible grease, check them and replace them if necessary, see the low and high pressure whips and also carry out leak tests on the system and replace them if we see a bad condition.
Sensors are the most delicate part to test them you have to use gases with different percentages and subject them to pressure. This is not always possible, but if they go below a certain voltage value declared by the manufacturer, they must be replaced. In any case, after one year of use, replacement is recommended.
The ideal is to make calibrations in pure oxygen and check the calibration with air which is a gas of which we are sure of the composition.
Check that there is no dirt, sand or gravel inside the lid of the ADV that can create a self-dispensing.
After the dive, especially at sea, wash as soon as possible with fresh water our rebreather.
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Our rebreather as we have seen previously has two cylinders: one of oxygen and one that is called diluent. In addition to these we must always have with us one or more safety cylinders called Bail-out cylinders.
BEST MIX In the diluent cylinder there must be a mixture of gases with characteristics that vary according to the planned depth, in any case the diluent at maximum depth must be breathable and have the PO2 equal to 1.
For dives over 40 meters you must have the authorization to use ternary mixtures, END recommended 30 meters. For those using hypoxic mixtures the danger is that at a shallow depth it is not breathable. In the case of switching to the emergency dispenser connected to the diluent bottle, the minimum breathing depth must be taken into account. In addition, the PpO2 must also be monitored at all times during washing.
To know the maximum working depth (PMO) for a 20/80 thinner (20% oxygen and 80% helium) and considering the PO2 equal to 1:
PO2 / FO2 = 1 / 0,20 = 5 atm = PMO 40 mt
To know which is the best operational thinner (Best Mix) at a PMO 100 mt with End 30 mt and PpO2 = 1:
PMO 100 mt = Pressure 11 Bar
FO2= 1 / 11 = 0,091 = 9% O2
End 30 mt = 4 Bars
PpN2 = 4 * 0,79 = 3,16 Bar
Given the partial pressure of nitrogen at 30 meters we find the fraction at the planned depth of 100 meters and unlike that of helium so we get our best-mix.
FN = 3.16 / 11 = 0.287 = 28%.
He % = 100% - O2 % - N2 % = 100 - 9 - 28 = 63 %
Our Best-Mix is a trimix mixture 9/63
BAILOUT CYLINDERS
In diving we must always have with us emergency cylinders complete with dispensers and pressure gauge, ready to be used at the time of failure or flooding of our rebreather. Even if a fault or a flooding such as to Página72
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have to abandon breathing with our car is always possible far enough away, for this reason we must prepare ourselves and plan the possible passage to the open circuit.
During our training we will try exercises and simulate emergencies so that we are always ready during our dives. In addition to flooding due to a failure of some gasket, the rupture of a lung or a corrugated, we must abandon the dive even when we can not control the Po2 or we do not know what we are breathing, this happens when our reading on the monitors no longer reliable and we have the readings of the three sensors different from each other or a failure in the monitors. Another reason may be the poor functioning of the filter that increases the percentage of carbon dioxide (CO2) and that causes us to breathlessness and symptoms difficult to identify. Whatever the reason why we believe that we must abandon the rebreather, the only thing we can do is pass to the open circuit using our Bailout tanks that we will always have with us. To do this we must have planned our dive before, prepared the gases in the quantity necessary to finish the dive taking into account the time and the maximum depth planned as well as having prepared our tables for open circuit.
The preparation of these is done with the same criterion of open circuit dives taking into account the worst case, maximum depth and maximum bottom time, remember the minimum safety margins, have at least a third more than the gas you really need.
V-PLANNER To make our plans we can use decompression software such as V-Planner or others, the important thing is that they are known and above all reliable.
Below the main screen where the CCR is selected, below we have two columns one for the diluent and one for the deco cylinders in OC (open circuit), we also have another value that is the initial Setpoint.
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Planner allows us to plan in both CO (open circuit) and CCR. We must first enter the configuration menu and set the various settings, in this window V-Planner asks us to enter or change some parameters:
In addition to the main parameters you can also choose the decompression model, from the original VPM to the VPM-B and other parameters that if you do not know the operation well should leave those by default.
To insert the data in the left column we can click on the button at the bottom "Add layer" or go to the column with the cursor and right click and select new layer as in the figure below.
A new window will appear where we will set the data for our dive, the composition of the diluent and the setpoint.
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After setting the thinner you must tick the part where the surface interval is indicated, if you have not been diving for several days click on 5 days or enter exactly how many days have passed since the last dive, bear in mind that after 48 hours you are already desaturated.
When you select the icon is available on the menu bar "Calculate", clicking on it V-Planner will perform the calculations showing you on the right side of the decompression table with a set of useful data.
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In the right part of the screen shown above, you can read the table with the depth of the various stages, the time spent at the various depths and the sum of the time from the surface start with the detachment from each stage. In the table above the total time of surface arrival is 85 minutes.
Other interesting data in addition to those configured are, the CNS, OTU and especially when the gas release begins to rise.
V-Planner below the table gives you the consumption in litres of the various gases according to the consumption you initially set in the parameter configuration.
Always with the same data set you can make the table with the bailout gases by clicking on the icon at the top. In the settings window you will find the various gases previously set in the right column (deco OC) in addition to the diluent that serves as the background gas.
You can create tables from the main one even with the time or the depth increased in case you outdated the estimated one: click on the icon "- or +".
In the window that will appear you can add time and depth as you like, giving OK the program creates additional tables in addition to the base one.
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With V-Planner you can also view the graph of the profile of your dive.
Another very interesting graph is that of the behaviour of the partial pressures of the gases in the rebreather, as you can see the PpO2 is constant (green line).
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Together with your instructor you will try to plan the dives with the various gases you need for the emergency. Always remember, in addition to any computer, to have with you tables for both CCR and OC.
Under water the first impression will be the breathing that compared to OC is more natural, but it may seem harder at first. The difference is that the dispenser, as soon as we start the flow, this is sent in a forced way avoiding any inspiratory effort.
ATTITUDE CONTROL It is very important to find the right ballast. At the start of the loop there must be the minimum quantity for our breathing, with the watertight and the jacket deflated we must be slightly negative. In immersion we must not be positive when we detach the bailout cylinders, these must not be too negative eventually become neutral by connecting laterally to the floats in high-density foam material, perfect that used to make the floats of fishing nets that has a variation almost nothing increasing the depth.
Initially we will find difficulties in adjusting the trim, the small variations must be corrected with the gas of the car, expelling from the circuit through the nose in case of positive trim and introducing diluent or any oxygen if we are negative, remember that entering the diluent PpO2 drops and to bring it back to the correct value we must add oxygen by changing our trim and becoming positive.
During the various dives of the course we will learn to find the right trim by keeping our PpO2 under control.
Although it is so much that we go underwater and the use of the machine may seem simple we must train ourselves to solve any problems that may occur to us, for this we must do a series of exercises and make automatic certain maneuvers in addition to reviewing our trim that is completely different from that of the open circuit.
Speaking of the trim we must remember that at constant depth the specific weight does not change with breathing as we are used to with our OC this because the air we have in our lungs we do not disperse it in the water but we send it in the bags of the lungs of the machine, in fact if our trim is negative even holding our breath the trim will remain the same.
If we are positive and have the watertight we must empty the gav, the watertight and the lungs exhaling from the nose or intervene on the overpressure valve placed on the right lung bag. To facilitate this we try not to use the gav but the counter lungs, the ideal is to try to keep within it half of their capacity, so that if we have to do a deep inhalation we have enough air without having to intervene the ADV or enter manually the thinner, and in the case of maximum exhalation we have some space.
Even if we do not use the gav this is mandatory because in case of flooding of the machine we become very negative and even if we have the watertight this will not be enough to make us neutral or almost.
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1 PRE-DIVING CHECKS After the various checks before entering the water, do some loop washing and start breathing to make the lime of the filter go to temperature, set the PpO2 to a planned value (0.4/0.5) and check and correct any leaks.
Even when we are in the water we have to do the checks of any leaks, together with the companion we check when the machine is completely immersed that it does not have leaks that would affect its operation. Check that the PpO2 remains constant, the pressure gauges for both diluent and oxygen, test the by-pass, open and close the bailout tanks, various instruments, etc..
2-ADJUSTMENT OF THE VOLUME OF THE LUNGS If the amount of air inside the lungs is correct with our rebreather the breathing is very natural as if we breathe on the surface. We will have two abnormal conditions, when there is little air will be hard in inhalation at that point if the ADV struggles to compensate manually by-pass the diluent, this happens when we begin to fall and is due to the increase in ambient pressure that decreases the volume of gas inside the rebreather, the other condition is when inside the machine there is too much gas, usually rising when the decrease in ambient pressure increases the volume of the lungs of the rebreather, in this condition we will have difficulty to exhale and we will have to empty the excess gas expelling it from the nose or acting on the overpressure valve.
3-WASH LOOP A maneuver that we will have to learn and that we will also try dry are the washings of the loop that in immersion must be performed every 15 minutes or so, to make them we will have to empty our rebreather inspiring and exhaling with the nose in such a way as to expel all the gas and introduce into the fresh gas, this serves to eliminate any accumulation of CO2.
When we do this maneuver we have to keep under control the PpO2 that will certainly tend to go down, we do the washing even when for any reason the PpO2 tends to go up or when we are at a shallow depth and we struggle to keep high the PpO2, in this case while emptying the machine we must intervene with the introduction of oxygen before the ADV intervenes.
If you need to do a quick purge just continue to inject thinner, the old gas will come out of the overpressure valve.
4-RESPIRATION WITHOUT MASK A maneuver that we should not underestimate and that we will certainly know how to do is the mask change of course while maintaining the trim. There are no major differences, eventually it may happen that to empty the mask we waste a lot of gas even emptying the machine, if the ADV fatigue, initially breathing will become difficult. Página71
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We will also do routes without a mask to get used to, the main problem is that not being able to read our monitors, going up we will have a drop in PpO2 and going down an increase creating a situation that could become dangerous, this is one of the reasons for not underestimating the change mask and must be performed while maintaining a constant altitude.
5-PPO2 CONTROL Once we have learned to keep our PpO2 under control in all those situations that change it, we can make safe dives. At first it may seem difficult, also because you do not know yet the amount of oxygen that you enter when you press the bay-pass. Surely the first few times you will be afraid to put too much oxygen but you do not have to worry because the first dive must be made within six meters so that in any case the maximum PpO2 that you can reach is 1.6.
PPO2 CONTROL TESTS :
1. We enter the water after adjusting the PpO2 to 0.5 and arrived at an altitude of 4/5 meters bring it to 1, and follow a short path keeping our PpO2 under control. When adjusting the oxygen pressure you need to maintain a regular breath, remember that when you press the bay-pass the oxygen value will initially tend to rise and then fall and stabilize after some breathing act. This is because the oxygen injection takes place in front of the exhalation lung and must have time to circulate and mix well, this only happens if you continue to maintain a constant breath.
2. After the path we try to lower our PpO2 to 0.5 to do this we have to put some thinner: we do some short washes by manually putting some thinner so as not to lose the trim. We can have the diluent injection in an automatic way, sending the rebreather in depression and making the ADV intervene, this manoeuvre, however, will make us lose the attitude because we will empty the machine completely.
3. Bring back to 1 our oxygen value, and simulate a quick wash, without breathing squash the bay-pass of the diluent until we feel the overpressure valve intervene, while you feel the outflow of the gas resume breathing so as to obtain a complete wash, remember that with this maneuver is easy to lose the trim and become positive.
After repeating these maneuvers several times and learning to control the trim while we do we can try to control the oxygen on the way up, taking us to a depth of 10 meters where we adjust our PpO2 to a value of 1.2 we go up to a height of 3 meters while keeping an eye on the value of oxygen.
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6- REBREATHER COMPENSATION
As we have explained before, our rebreather must be constantly compensated. The ADV is activated when the lungs of the machine are empty, we have this condition while we go deep or when we make deep inhalations and the amount of gas is not enough.
The ADV also starts working when the machine is not empty but also when we have a fast increase in ambient pressure, this happens in case of rapid descent, the membrane of the ADV moves together with the counter lungs introducing the gas.
We have to try to keep in the counter lungs a quantity of gas almost equal to a maximum inhalation (about 2/3 lt) from our normal breathing condition, in this way we can use our rebreather to help us find the trim by entering or eventually discharging.
7-PASS FROM CLOSED TO OPEN CIRCUIT
One maneuver that we absolutely must know how to do is to remove and put the mouthpiece without flooding the machine. There may be several reasons for this, such as trying the bailout cylinder dispensers or trying the emergency dispenser, but whatever the reason, the important thing is that during this manoeuvre the water does not enter so as not to compromise the operation of the machine.
Exercises:
Close the mouthpiece by lowering the lever placed in front, at this point take it out of the mouth, without ever letting it go back into the mouth and while we open it again by raising the lever blow into the mouthpiece, the water inside it will come out of the hole located in the lower part. Let's try this maneuver two or three times or until we're confident.
2. After having closed the mouthpiece, let it go completely, being very light it will be positioned over our head at the same time we close the tap connected to the whip of the flow regulator to prevent that when we resume breathing the partial pressure of the oxygen is too high, we open our bailout tank and at the same time we take the dispenser starting the breathing.
After a few breaths we resume contact with our rebreather, first we must recover the mouthpiece, we bring our right or left hand on the head where the wrinkles are connected and we recover our mouthpiece.
After having recovered the mouthpiece, remove the dispenser and resume contact with the machine, remember to blow during opening and to reopen the tap of the flow regulator.
During the manoeuvre you must always hold the dispenser in your hand, put it back in its place on the side of the cylinder, of course all these exercises must be done keeping the trim in a horizontal position and always keeping our PpO2 under control.
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push forward the flow-stop that must be placed between the second stage and the whip, help yourself with two hands. Very important this accessory because it prevents that the dispenser during the dive loses air or goes into the car dispensing emptying in a short time the bottle of thinner.
Remember the tap on the regulator, repeat the reverse operation as in the previous year. This exercise must be repeated several times until it becomes an automatic manoeuvre that we must do without thinking about it.
4. After having become familiar with the previous exercises, while we are finning we will take off the mouthpiece and we will travel in apnea about ten meters (remember to close the tap) and we will resume contact always in motion, in case you fail, use your emergency dispenser, in any case you will have your instructor ready to intervene with the dispenser.
8-OPEN AND CLOSE TAPS A maneuver that we must know how to do is to open and close the taps of our rebreather, both of the diluent and of the oxygen, this can serve us in the case we have problems in the first stages or inadvertently ... making some particular passage our taps tend to close and also in the case ... absurd that we enter the water without opening them.
If a first stage will be or will be ruined knowing how to do this maneuver we can return to the surface without abandoning the machine, of course the dive is over.
Exercises:
1. Maintaining always a horizontal position without making to vary our trim, we will begin with closing the thinner, remember that the closing of the thinner to constant depth does not affect the operation of the machine and we can go up again without problems, of course if the gav is connected to the cylinder of the thinner we can not use it unless we connect a whip of the bailout cylinders (a whip for the gav or watertight we will always have to have connected on the first stage of the bailout).
The thinner cylinder is positioned on our left, with our left hand we will try to intercept the tap and close it, if we do not have leaks in the machine and do not drain, the breathing will not be affected.
With the same manoeuvre as before, we reach the tap and reopen it, check your pressure gauge and pressing the bay-pass make sure it does not drop in pressure.
This maneuver can be useful if the ADV should go into continuous delivery, we can use the tap to inject the thinner when we need it, also when the tap is closed we can connect a whip of the bailout bottles to the bay-pass of the thinner in this way the ADV is excluded.
2. Bring our PpO2 to a value of 1 and repeat the same exercise with the oxygen bottle on the right, with the right hand close the tap.
Again, we do not have an immediate emergency, we must keep our PpO2 under control, which will tend to drop, and when it has dropped to 0.5 we will reopen our tap, you will have noticed that to reach this value you have taken several breaths. Página72
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The danger is on the rise where we will have a further drop in PpO2 due to the decrease in external pressure.
Also in this case if we have a problem at the first stage that makes us increase the flow in an excessive way we can use the tap to inject oxygen when needed or if you have with you a cylinder of pure oxygen with a whip, you can connect it to the bay-pass excluding the supply system of the rebreather, in this case our flow regulator would work equally, the important thing is that the first stage is calibrated as that of the machine.
If you ascend under these conditions and the control of PpO2 becomes critical, switch immediately to the open circuit and change your decompression plan as well.
9- BREATHING
Very important is to know our rebreather, try breathing in various positions allows us to understand if the operation is correct when the respiratory effort changes.
When we position ourselves in various positions we will have differences in breathing due to the situation of the counter lungs, in any case this does not affect the operation of the machine during immersion.
Exercises:
1. From our usual horizontal position we will move to a vertical position with our head downwards, resting our hands on the bottom and pivoting we will verticalize.
After a few breaths and felt any difference that will be minimal we will move to the supine position.
2. Letting us fall backwards we will find ourselves leaning with the back in this case the difference in position of the lungs will be noticed, the only problem that we may encounter is the facilitated trigger of the ADV being positioned in the rear of the machine.
In this position we try to close the thinner tap, we press the bay-pass to empty the system and we notice the difference without the possible operation of the ADV.
After reopening the thinner tap we will take ourselves to a lateral position first right and then left, when we are in the various positions we stay for at least 6/7 respiratory acts and we always try to feel even if minimum the difference.
Listen to your rebreather that with any noise will try to provide you with information, try to hear when the ADV goes into operation even if minimal the introduction of the diluent in the silence is heard.
10-OVERPRESSURE VALVE
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On our right lung of the rebreather, the inhalation lung, is placed the overpressure valve, this as well as automatically discharge when the machine exceeds a certain pressure inside, you can have it discharged manually. This allows us in case of fast ascent to quickly empty the rebreather.
Exercises:
We try in both horizontal and vertical position to reach and crush the valve, using the left arm we try to reach it helping us to push the elbow with the right hand, making a slight pressure over the valve the air escapes.
2. Repeat the same exercise using the right arm.
11-BATTLES OF BAILOUT
Another exercise that is very important is the management of bailout tanks, we must learn to release and attach them without losing the trim Going forward with the dives and making them more challenging we will certainly have to bring more tanks, know how to manage them while maintaining the altitude is essential.
Exercises.
1. Maintain our horizontal position by first unhooking the rear carabiner and then the one placed on the shoulder strap and placing the cylinder in front of us horizontally.
Let's relocate the tank to our left.
2. Repeat the exercise by placing the cylinder on the right.
12-RESALTED FAST
Surely a maneuver that we have to do is regain control from a fast ascent, remembering that in ascent we have to check in addition to the gav the lungs of the rebreather and any watertight.
Exercises:
1. Bring us to a maximum depth of 10 meters, partially inflate the gav and start to introduce the thinner keeping under control the PpO2, when we are starting to rise we must resume control of the speed and attitude within 6 meters, raise the left arm allowing any watertight to discharge and with the hand keep up the command of the gav unloading it, looking slightly upward we can release the excess pressure
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In this case, the vertical position can help us to regain control of the speed more easily, by releasing the gas more quickly.
13-CONTROLLED DESCENT AND SURFACE RETURN
In the various exercises we have seen and understood how to control our trim, the PpO2, how to go up again being careful not to take speed and how to manage the various emergency situations.
Now we will try to go down and up while maintaining the correct speed and keeping the trim and PpO2 under control. I remember that the descent at a controlled speed and not excessive with the rebreather is important, while we go down the PpO2 tends to rise and the reading of the sensors may not give a real situation of what we breathe.
Exercises:
1. We reach a depth of 10 meters maintaining a constant speed, once we reach the altitude we set our PpO2 to 1.3, we climb up to 6 meters at a speed of 9 meters per minute (one meter every 7 seconds), of course keeping controlled the trim and the PpO2 where we stop for 3 minutes and set the oxygen pressure to 1.5.
2. Diving at a depth of 20 meters for a time decided with the instructor, we set our PpO2 to 1.3 and after our tour we will make a climb from the maximum depth by controlling speed, trim and partial pressure oxygen up to an altitude of 10 meters where we will stay for 1 minute, climb up to 6 meters with a stop of 5 minutes bringing the PpO2 to 1.5.
14-SURFACE RETURN IN EMERGENCY
All the exercises we have done so far have allowed us to understand and control our rebreather, to intervene and solve any problems trying not to abandon the breathing of the machine. The exercise we are going to perform now is in case the problems that arise to the rebreather are not solvable in water, flooding, unreliable reading of partial oxygen pressure or feeling that the filter is not working properly.
Whatever the reason that leads us to the abandonment of breathing we must move to the open circuit using cylinders and tables planned for the emergency, computers we must absolutely remember to pass them from CC to AC. Página71
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Exercises:
1. After having made the dive to a depth of 15 mt, at the start of the instructor we leave without closing the mouthpiece making sure that it is positioned above us, we immediately make contact with our emergency dispenser then we move on to our bailout.
If we have the computer we absolutely have to pass it from CC to AC and we take the tables planned for the emergency.
The ascent must be controlled, even if we have an emergency is not serious if it has been planned correctly and we have sufficient gas supply to exit. We will do the various stages that have been programmed before without ever resume breathing with the rebreather. On the way up, the mouthpiece at the top will remove the excess gas and let in a minimum of water, most likely depending on the water that enters the machine we will have an increase in weight that we will have to compensate. If the GAV is connected to the thinner we must be careful that if the cylinder is discharged we will be obliged to use the watertight and connect the whip of the bailout cylinder.
15-SENSOR TEST UNDERWATER
During the course we understood why we have to have three sensors and consequently three monitors that read us the value of PpO2, in case one reading is different from the other two we have a high probability that the sensor with different value is wrong ....
But if we have any doubts, we can perform an underwater test to see if the two identical readings are really reliable.
Exercise:
At a depth of 10 meters we wash with thinner and check our PpO2, if in the thinner we have the air that has 21% oxygen and we are at an ambient pressure of 2 atm our monitors must mark 0.42 (0.21 x 2).
Thanks to this test we can know if the reading is reliable
16-CONTROL OF BREATHLESSNESS
One of the most dangerous things in diving is the breathlessness because it can lead us to a panic situation, with the rebreather the control is more problematic because when we strive and we begin to increase our respiratory rate not always the machine manages to give us the amount necessary for our ventilation, of course with the depth and the increase in the density of the gas breathed the danger of breathlessness is
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With a deep inhalation if in the loop we have a minimum volume of gas even if enters the ADV the effort of breathing is greater, we must manually inject gas through the bay-pass of the diluent, in case of breathlessness the best breathing we have it in a vertical position. In case we struggle to recover we pass in open circuit until the normalization of breathing.
Exercises:
1. With a minimum volume of gas in the loop at a maximum depth of two meters we walk 10 meters at a fast pace, as the breathing increases we stop and in an almost vertical position we start manually through the bay-pass to inject the diluent keeping under control the PpO2 that does not fall below values that can be dangerous (0.21). As we stabilize our respiratory rhythm, we restore the partial pressure of oxygen.
2. With a minimum volume of gas in the loop at a maximum depth of two meters we travel 10 meters at a fast pace, at the increase of breathing we stop and in an almost vertical position we go into the open circuit using the bailout cylinder closing the mouthpiece before leaving it and the tap of the oxygen flow regulator. After stabilizing our respiratory rhythm we return to CC.
This exercise should be repeated if necessary by increasing the distance, it is recommended to create the path with a line.
These exercises, like the whole course, are performed under the supervision of the instructor, the evaluation and repetition of the various exercises are at his discretion.
For the use of the rebreather in dives out of curve and with ternary mixtures we must make courses that enable us to use the trimix in open circuit and know what are the problems, before using this device in a demanding way we must make several dives (at least 60 hours) making certain maneuvers automatic.
Remember that the emergency is not always plannable and at that point only our experience can save us.
Even at the end of the course continue to keep you trained especially with the various emergency simulations, keep informed about the development of the techniques of use and training, do not underestimate and never leave anything to chance we go underwater to have fun and to explore.
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