tech talk

Edited by Michael Menduno

Switching to after diving open circuit scuba But I want one... ed.— Instructor Mark Powell looks at switching A is simply a way to from traditional open circuit SCUBA to closed circuit rebreathers. reuse the gas breathed out by in conjunction with a method of Many of the pieces of equipment used by technical divers removing the produced look different to the equipment used by recreational divers. by the diver. The main advantage of a rebreather is that it is much more efficient However, for most of the time, the basic principles are the same. on gas usage. When normal air However, the use of rebreathers in technical diving completely at the surface we use up about 4% of the changes many of the basic principles that govern recreational in the air for our and diving. Some limits are removed almost completely but other breathe out the rest of the oxygen as wasting ten times as much gas with each of the gas. well as all the . This means that breath in order to obtain it. This is one of By reusing our gas this provides three complications are introduced. 96% of the gas we breathe escapes with the reasons why for open circuit divers key benefits to the technical diver. each breath. At depth this is made even gas planning and breathing rate is so Text by Mark Powell worse by the fact that we are breath- critical. The limiting factor for an open cir- 1 - Gas Duration ing gas under much higher and cuit dive to 90m is almost certainly going Firstly we don’t need to use anywhere so each breath contains a much higher to be the amount of gas that needs to near as much gas as an open circuit volume of air. At 40m we are breathing 5 be carried for the dive. A rebreather diver. The amount of times the volume of air with each breath avoids this problem by re-using the gas Oxygen required compared to the surface breathed out by the diver, as the major- by the body is and at 90m we are ity of the gas isn’t being wasted the diver roughly the breathing ten times the doesn’t need to carry as much gas in same at any volume that we would order to do the same dive. A rebreather depth and so be on the surface. works by catching this exhaled breath our Oxygen With every breath this and instead of allowing it to escape it will last the gas escapes from our reuses it in the next breath. The small same at second stage and bub- fraction of Oxygen that was used up by 100m as it will bles to the surface. This is inefficient as the body is replaced with more Oxygen. at 20m. The the body still only needs the same This means that rather than wasting the balance of the P eter S ymes amount of oxygen but we are vast majority of each breath we reuse all gas in the breath-

73 X-RAY MAG : 51 : 2012 EDITORIAL FEATURES TRAVEL NEWS WRECKS EQUIPMENT BOOKS SCIENCE & ECOLOGY TECH EDUCATION PROFILES PHOTO & VIDEO PORTFOLIO Despite taking these large cylinders they will still be used tech talk up very quickly and so the amount of available gas becomes the most critical part of our

A Twinset of can cost anything from ing loop, known as the diluent, is reused 2 - Gas Costs compared to open circuit rather than wasted and so again we use One of the biggest factors £30 for a relatively diving. This can look very the same amount at 100m as at 20m. This that comes into the decision week mix for use in attractive when you are vastly decreases the amount of gas we to switch to a rebreather is spending considerable will need to complete the dive and rather costs. This has two aspects, 40m to over £100 amounts on each open than twin 20L cylinders we can use two 3L the costs of the rebreather, for a mix suitable for circuit fill. However this cylinders. including buying and main- must be set against the On open circuit we taining it, diving deeper than costs of the rebreather. breathe much more set against 100m. Depending on the model at depth due to the the cost a rebreather is likely to effect of pressure and of open circuit diving. cost between four and eight thousand so as we go deeper One of the biggest dis- pounds. If you go for an older second and deeper we advantages of open hand model then you might get one for have to take larger circuit trimix diving is less than this. In addition to the initial cost and larger cylinders. the cost of the gas. A of the rebreather you will need to factor Despite taking these Twinset of trimix can in training on the rebreather which is likely large cylinders they cost anything from £30 to add on another thousand pounds. In will still be used up very quickly and so the for a relatively week mix for use in 40m to addition there will undoubtedly be addi- amount of available gas becomes the over £100 for a mix suitable tional costs to add on most critical part of our dive planning. On for diving deeper than 100m. Depending on the extra equipment to the a rebreather our gas supply is used up at This makes each trimix dive model a rebreather is basic rebreather. As a the same rate irrespective of depth and an expensive proposition. On result it is not uncommon so the amount of gas we are carrying is the other hand a rebreather likely to cost between for the initial start up costs no longer the limiting factor. This means uses much smaller cylinders four and eight on a rebreather to be that running out of gas on a rebreather is because the gas is reused between 6 and 10 thou- much less of a concern than for an open rather than wasted, as a thousand pounds. sand pounds. Obviously circuit diver. Instead the critical factors result we use much less and you will need to do a lot become the amount of the gas costs are much lower. We might of trimix diving in order to save enough to we are incurring, the duration of our car- only be spending £5-£10 for the same justify this initial outlay. bon dioxide absorbent and our risk of mixtures discussed above. As a result The majority of divers do not do enough . there is a significant gas saving when diving to clearly justify buying a rebreath- er based on savings in gas costs. REBREATHER TERMS: Unless you are doing 20 or more trimix dives a year then it is not cost OC Open Circuit (traditional SCUBA) effective. If you also do a significant CCR Closed Circuit Rebreather amount of then SCR Semi-closed Circuit Rebreather each dive may actually cost you eCCR Electronically controlled Closed Circuit Rebreather more on a rebreather. mCCR Manually controlled Closed Circuit Rebreather On open circuit you may only HUD Heads Up Display (LED display of oxygen ) need to pay for an air fill but on BOV Bail Out Valve (Open Circuit bail out used in an emergency) even the shallowest dive you will still Diluent Gas used to make up the balance of the breathing loop, can be air or trimix need to use pure oxygen in one of Scrubber Module used to remove carbon dioxide from the breathing loop the cylinders and use carbon diox- ide absorbent in the rebreather. The P eter S ymes

74 X-RAY MAG : 51 : 2012 EDITORIAL FEATURES TRAVEL NEWS WRECKS EQUIPMENT BOOKS SCIENCE & ECOLOGY TECH EDUCATION PROFILES PHOTO & VIDEO PORTFOLIO Peter Symes tech talk The majority of Rebreathers The fact that divers do not do a rebreather enough diving to uses smaller cylinders makes clearly justify buying the logistics of a rebreather based on filling much easier savings in gas costs.

annual each dive. This the open circuit diver the The replace- requires lots of rebreather diver will not other ment of additional heli- use their stages unless there advan- the three um and oxy- is an emergency but will still tage of a oxygen gen each day need to carry them. However rebreather is that sen- and filling on open circuit the diver will it can reduce the sors and these large use the decompression stages decompression handset back gas on each dive and so they will obligation when compared batteries cylin- need to be filled each day. to the same dive on open also needs ders and circuit. For a diver using a twinset to be decompres- 4 - Decompression and a stage cylinder they may taken into sion cylinders Obligation plan their gas to have the account. each day is This means expensive, time that a shal- consuming low recrea- and labouri- tional dive may ous. only cost £5 for an The thing open circuit diver fact that a next day to but £10-£15 for a rebreather uses pick it up then the rebreather diver. smaller cylinders logistics of this can It is clear that makes the logistics of filling be significant. Similarly if you are unless you are much easier. The volumes diving somewhere without easy doing significant of gas needed are much access to a dive centre that can numbers of deep smaller when filling a 3L cylin- fill trimix the ability to take your trimix dives a year with little der rather than twins 12s and so it own gas simplifies the planning or no recreational diving then the becomes feasible to take enough and logistics. gas savings from using a rebreath- gas with you for even a weeks Of course this assumes that the er will not outweigh the initial start diving. This contrasts with the situ- rebreather will always work as up costs. However there are still ation when using open circuit intended. Just in case there are a number of other reasons why a where significant volumes of heli- any problems with the rebreather rebreather is an attractive option. um and oxygen will be required we also need to carry open cir- as the majority will be breathed cuit gas to get us safely to the sur- 3 - Gas Logistics out and wasted. This can make face. In this case we would need The third advantage that the a big difference if you don’t a bailout cylinder that we could improved gas usage provides have a local dive start using at the is in simplifying gas logistics dur- shop that can fill The fact that a maximum depth ing longer dive trips. Open cir- trimix. If you have and would then cuit divers may be using up twin to drive 50 miles rebreather uses smaller need sufficient bail- 12L, 15L or even 18L cylinders on there and back to cylinders makes the out to get to the each Trimix dive. In addition they drop off a twinset surface complet- may be using up to 4 stage cyl- for a trimix fill and logistics of filling much ing all our decom- inders for decompression gas for then do the same easier. pression. Unlike

75 X-RAY MAG : 51 : 2012 EDITORIAL FEATURES TRAVEL NEWS WRECKS EQUIPMENT BOOKS SCIENCE & ECOLOGY TECH EDUCATION PROFILES PHOTO & VIDEO PORTFOLIO tech talk Rebreathers go quietly, amid the noise and haste...

[ 3 hours @ 20m - no deco ]

At depth the diver can ensure that the optimum mix on the bottom, i.e. breathing loop of breathing loop of the buying a rebreather the highest oxygen percentage in the rebreather rebreather contains the is an expensive order to reduce the amount of contains the proposition. Prices inert gas absorbed by the body. maximum amount maximum amount of vary from £3500 to They will also make a choice of of oxygen and oxygen and hence the over £8,000 for the the decompression gas carried in hence the unit alone. When the stage cylinder with a view to minimum amount minimum amount of combined with ensuring that they get rid of the of inert gas. This will inert gas. training and the inert gas as fast as possible during reduce the rate of inevitable extra bits the rebreathers of choice from 6m to 160m the decompression. However, the ongassing. As the diver ascends of kit it is a false economy to buy choice of each of these gasses and completes his decompression a rebreather in order to save will always be a compromise. The stop the diver can ensure that the money on gas fills. In addition to bottom gas will be chosen to be mixture again contains the the cost there are a number of as rich as possible but with some maximum amount of Oxygen other risks introduced by using a margin for error in case the dive is which will accelerate the rebreather. a little deeper than expected. If offgassing and reduce the Whenever we breathe out as the diver ascends up from the required decompression. In this well as exhaling the remaining planned maximum depth then the way the rebreather is constantly oxygen and inert gas the body

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a m have provided faster these problems by rebreather is must be removed by a chemical I offgassing. A sometimes unofficially process. This takes place when the rebreather avoids constantly adjusting called a best mix exhaled gas passes through a these problems by the gas being generator. scrubber which is packed with a third party test-house approved patented dual oxygen controllers with independent displays and power sources constantly adjusting We can see that suitable chemical designed to optional open circuit bailout mouthpiece high performance scrubber proven to 160m trimix or decompression with the gas being breathed to ensure rebreathers offer a remove the carbon dioxide. user variable gradient factors and multiple gasses polyethylene fibre-optic dual head up displays future proofed software breathed to ensure the minimum number of significant Correctly packing the scrubber is upgradeable by user uploads & hardware upgradeable with plug and play versatility pc log download 9 language options the minimum amount advantages over one of the most important steps in crystal clear primary display hard memory storage - gas, options and history retained even when the batteries are removed of inert gas is being amount of inert gas open circuit diving. preparing a rebreather as patented scrubber monitor with effective warnings full customer support and aftersales - spares & service the equipment of breathed. The However a rebreather incorrect packing can allow choice for underwater photographers, film-makers, marine biologists, cavers, under-ice explorers, deep dive specialists, deep support is being breathed. teams, expedition divers and sport & technical diving enthusiasts worldwide - all achieving time and depth profiles previously unthinkable rebreather (or the introduces a number carbon dioxide to be ‘channelled’ diver in the case of a manually of significant additional costs, risks through the scrubber and cause a operated rebreather) adds and complications to any dive build up in the breathing loop and A M B I E N T P R E S S U R E D I V I N G oxygen to ensure that the and should not be seen as a lead to carbon dioxide poisoning. t e l : 0 0 4 4 1 3 2 6 5 6 3 8 3 4 e m a i l : i n f o @ a p d i v i n g . c o m w e b : w w w . a p d i v i n g . c o m minimum amount of inert gas is magic wand to solve all of the This can cause headaches, lack being breathed. At depth the potential problems of deep of , unconsciousness s p a r e s & a c c e s s o r i e s o n l i n e a t w w w . a p d i v i n g d i r e c t . c o m s e e a p d i v i n g . c o m f o r y o u r n e a r e s t i n s t r u c t o r diver can ensure that the technical diving. In the first place and death. Unfortunately the

76 X-RAY MAG : 51 : 2012 EDITORIAL FEATURES TRAVEL NEWS WRECKS EQUIPMENT BOOKS SCIENCE & ECOLOGY TECH EDUCATION PROFILES PHOTO & VIDEO PORTFOLIO Peter Symes

... rebreathers offer Many rebreathers tech talk are supplied with a a number of significant Bail Out Valve (BOV) Rebreathers advantages over open circuit which allows the diver to switch from diving. However a rebreather the rebreather loop introduces a number of to an open circuit regulator at the flick significant additional costs, of a switch. risks and complications to diver suffering from this condition they are any dive and should not be preparation of added cuts or start to neglect basic may be unaware of the condition taught to seen as a magic wand... the unit or by complication of checks. It is typically divers who or may be so incapacitated as to bailout to a managing the the kit also have around 50 hours of be unable to respond to the known source of gas. For this problem on the unit rather increases the experience who tend to fall into problem. Overusing the scrubber reason rebreather divers carry than by bailing out to open problems whilst allowing it to fall chances of a problem occurring, this complacency trap. material is another potential open circuit bailout gas. In circuit. too low can lead to and either before the dive causing it cause of carbon dioxide addition many rebreathers are In addition to excess carbon a blackout. to be aborted, or during the dive But I want one poisoning and for this reason it is supplied with a Bail Out Valve dioxide the other big danger that The equipment used in a causing potentially more serious Even if you wont save money and vital to monitor the amount of (BOV) which allows the diver to faces rebreather divers is an rebreather is more complicated problems. These considerations don’t need a rebreather for time that the material has been switch from the rebreather loop to incorrect partial pressure of than open circuit and the are covered in extensive detail logistic reasons there are still other used and to replace it at the an open circuit regulator at the oxygen. In an eCCR the procedures required are more during any rebreather training reasons to switch. Diving is a appropriate time. If there is any flick of a switch. Of course once rebreather itself maintains the detailed and intensive. Preparing course but one of the biggest hobby and so doesn’t always doubt in the diver’s mind that the diver has bailed out to open partial pressure of oxygen within a rebreather to dive will inevitably dangers for rebreather divers is have to be justifies on cost they may be suffering from circuit they are limited by all the the breathing look whilst on an take more time than preparing complacency. As they build their reasons. The cheapest option is carbon dioxide poisoning then same gas consumption issues that mCCR it is the divers responsibility open circuit equipment. The experience they start to take short not to dive but most of us don’t the open circuit to maintain the partial pressure. REBREATHER CLOSED CIRCUIT DIVING (CCR) diver has to face. Either way it is always the diver’s This is one of the responsibility to know their partial reasons why a pressure at all times and this is E ABOARD EXP Organised by uw3some.com/ADEX CCR ADVANTAGES EXPO LIV O rebreather is not one of the golden rules of DIVE ● Reduced gas requirements ASIA ● Reduced decompression obligation necessarily the full rebreather diving. All rebreathers ● Warm air for deep will have a display which shows LIMITED EDITION ● Simplified gas logistics technical diving. the partial pressure of oxygen. This EX BIG BLUE The diver will can be an electronic gauge AD KID’S CCR DISADVANTAGES need to carry which is often wrist or console BOOK ● Risk of CO2 poisoning enough gas in mounted or can be a visual ZONE WHALE SHARKS ● Risk of CNS toxicity order to be able display using coloured LEDs. These 13 to safely ascend Head Up Displays (HUDs) can 0 ● High initial costs 2 since 1995 ● Additional complication in the case of a provide instant warnings of OF problem with their incorrect partial pressure levels. O VOIC THE ● Non-standard equipment procedures ED T S E rebreather and so During the dive a diver will usually E DEDICAT RK ● Need to relearn diving skills EKDIV W SHA will have to carry aim to maintain a partial pressure T & Greet HALE OCEA the same amount of between 1.0 and 1.4 bar of eet CO N OPEN CIRCUIT (OC) M MPETIT DEADLINE ATER ION JANUARY 15, 2013 of decompression oxygen. This NDERW MISS ADEX AMB gas as an open is known as U O ASSA OC ADVANTAGES Correctly OTO+VIDE DOR 2013-14 ● Simple equipment configuration circuit diver. The packing the a ‘set PH ● Simple to set up alternative point’. s approach, known Allowing ar FEAR NO ART ● Standard equipment allows for easier repairs scrubber is one n SA TRE i N EN D m S EX ION C as the alpinist the partial e MARIN PO & CONVENT RE -21 A PO ● Standardised procedures S 19 BA SINGA l approach, is of the most pressure to apri Y SANDS assume that any important steps rise to high OC DISADVANTAGES Of cial publication Held in Endorsed by In association with ● High gas costs problem can be in preparing a can lead to ● Gas consumption limits deeper dives avoided by oxygen Network ● Complicated gas logistics careful rebreather toxicity

77 X-RAY MAG : 51 : 2012 EDITORIAL FEATURES TRAVEL NEWS WRECKS EQUIPMENT BOOKS SCIENCE & ECOLOGY TECH EDUCATION PROFILES PHOTO & VIDEO PORTFOLIO Peter Symes

Rebreathers are significantly more complicated pieces of equipment than an open circuit .

Whilst rebreathers do not require a huge amount of effort they do nonetheless require more care and maintenance than open circuit.

For divers that throw their kit into the back of the car or into the garage and then don’t look at it until the next dive this can cause a problem.

includes not diving the unit if a 10m dive must be approached there is any problem with it. Many with the same mindset as a 100m divers become complacent and dive. As such there is no such will dive with known problems with thing as a casual rebreather dive. their rebreather. They are Not all divers have the mindset to confident that they can adjust to rebreather diving but overcome the problem and in the without this mindset they should majority of cases they manage to not consider rebreather diving. deal with the known problem. In order to be a safe rebreather However if there is any problem diver there are a number of skills during the dive the impact of the that need to be mastered over initial problem can be significantly and above the basic open circuit increased by subsequent skills. Some of these are related to problems. It requires a significant the normal operation of the level of discipline to call a dive for rebreather and some are related what might appear to be a minor to emergency situations. Like any problem but becoming skill it takes practice to mater complacent about these failures these skills and practice to is one of the most common maintain them. When moving causes of rebreather accidents. from open circuit to a rebreather consider this a possibility. In the number of reasons why many throw their kit into the back of the hobby rather than an added During the dive the diver must there are skills, like same way that some people divers want to switch to a car or into the garage and then chore they must do. This type of constantly control which spend their money on motorbikes, rebreather. However the risks of don’t look at it until the next dive person is ideally suited to monitor the unit must be re-learnt. horses, home cinemas, model rebreather diving mean that there this can cause a problem. This rebreather diving. to ensure it is Most rebreather accidents This takes time helicopters or any other hobby are some people who are better type of person is not really suited In addition to cleaning and operating are caused by the divers and effort. For an there is no reason why someone suited to rebreather diving than to rebreather diving unless they maintenance rebreathers require correctly. This is not following the correct experienced diver shouldn’t spend their money on a others. can discipline themselves to discipline whilst diving them. There summed up by this means the rebreather just because they Rebreathers are significantly ensure they maintain the is a certain mindset that is the golden rule procedure. This includes not frustrating process want one. Other people may more complicated pieces of rebreather. On the other hand required to ensure that the unit is of rebreather diving the unit if there is of going back to switch to a rebreather to equipment than an open circuit there are many divers who enjoy assembled correctly each time diving “Always basics and challenge themselves to learn scuba set. Whilst rebreathers do cleaning and maintaining their and that all of the pre-dive know your any problem with it. building up their something new. not require a huge amount of equipment almost as much as the checks are rigorously followed. partial experience. effort they do nonetheless require dive itself. They get pleasure from Most rebreather accidents are pressure”. It doesn’t matter if the Unless you are prepared to put in Should you switch? more care and maintenance adjusting the kit until it is just right caused by the divers not following diver is at 10m or 100m the level the time to master the basic skills As we have seen there are a than open circuit. For divers that and it is viewed as part of the the correct procedure. This of monitoring is the same and so you will always be diving on a

78 X-RAY MAG : 51 : 2012 EDITORIAL FEATURES TRAVEL NEWS WRECKS EQUIPMENT BOOKS SCIENCE & ECOLOGY TECH EDUCATION PROFILES PHOTO & VIDEO PORTFOLIO tech talk e v i d . w w w

base of weak rebreather skills, essential way to progress their this reason it is a very personal even if you were previously a very technical diving. For others the decision and not one to be taken BREATH-TAKING ADVENTURE experienced open circuit diver. advantages do not necessarily lightly. First you must decide For everyone who dives. These skills also need to be outweigh the disadvantages. For whether there is a good reason to An action-packed event featuring: practiced regularly in order to depths between 30m and 80m dive a rebreather and then ensure that they are maintained. open circuit technical diving is still whether you have the right This means that it is essential to a very feasible option and there mindset to be able to dive it • the world’s foremost diving authorities dive a rebreather regularly in will always be open circuit safely. Like many things the • a full-scale dive exhibition

order to maintain the appropriate technical divers in this range. correct decision will vary from k e t z o • talks, seminars and workshops skill levels. Beyond 80m then rebreather one person to another. ■ • live-aboards, resorts and For these reason’s not all becomes the more dive travel destinations technical divers have adopted common tool and it is likely that For more information on any • equipment updates rebreathers. It is clear that for for dives in excess of 80m aspect of technical diving visit: • rebreather and some people a rebreather is a rebreathers will continue to be www.dive-tech.co.uk u a . m o c . desirable and in some cases an viewed as the tool of choice. For side-mount workshops, • underwater film and video presentations, • ‘An Evening With Diving’s Explorers’, • Underwater Photographic Competition, • Gala Dinner, OZTeK Awards presentations and more ...

Dive Exhibition & Conference Image courtesy of 16 – 17 March 2013 Australian Technology Park Locomotive Street (off Garden St.) Eveleigh, Sydney, Australia E-mail: [email protected] OZTeK - Tek Diving Conference

Supporting organisations include: R ichard L undgren It is likely that for dives in excess of 80m, rebreathers will continue to be viewed as the tool of choice OZ_Ad_v2.indd 2 18/07/12 10:30 PM 79 X-RAY MAG : 51 : 2012 EDITORIAL FEATURES TRAVEL NEWS WRECKS EQUIPMENT BOOKS SCIENCE & ECOLOGY TECH EDUCATION PROFILES PHOTO & VIDEO PORTFOLIO