RF3.0 - Anatomy of a CCR Dive

this is one of my favorite photos of me underwater us was taken by Kevin Dean Lee who's a seasoned technical diver you know I can't do this podium thing it feels like running for president of the United States right which would be a great honor to do but I'm not eligible so I'll come down here on can you you can hear me anyway can't you I just the podium thing doesn't really work and this is a little wreck called the Jennifer K off Brisbane in 80 metres of water there's a few people in this room who have dived it says me on a mark 15 five rebreather and it kind of exemplifies the kind of diving that rebreathers have opened up to us it you could do this dive on open circuit would it would be a lot more difficult so this kind of speaks to the slide speaks to the stuff that I've already said and what we were going to talk about and my final comments on safety challenges and how I really do not want to give the impression in talking about them that I think rebreathing is an appropriate thing to do it's just that we are a responsible community so we're going to address these things so the first question to ask is what is a rebreather and at the simplest level a rebreather is breathing in and out of a bag - the glue you would intend to use that you can do this if you're going to breathe in and out of a bag then two bad things are going to happen you're going to deplete the oxygen in the bag and carbon dioxide that you that you produce from metabolizing the oxygen will build up and the corollary to that is that if you're going to breathe in and out of a bag you have to do two things you have to remove the carbon dioxide and you have to replace the oxygen that you metabolize and it's interesting and I'm sure you all agree that there's not much room for error in performing those functions so that's what repeaters have to do and they have to do it accurately and well so I want to develop my model of breathing in and out of a bag a little bit further so here's the bag and a tube and and the arrows indicate breathing in and out of it now I struggled to find a picture of a model that looked sick enough to just be breathing in and out of a bag but I came up with this one I courtesy of dr. Pollock and when I use this photo not that long ago someone from the audience came up to me and said you know it's very disrespectful to use a photograph of somebody who's dead and as you'll find out later on in this this weekend this person isn't dead he's one of the presenters who's here and he'll be talking to you and your challenge is to identify that person who looks a little bit different in his normal daily life so you are breathing in and out of a bag but in fact you do it around a circle so rebreathers form a circle circuit and the thing that allows that happen is a mouthpiece with one-way valves that ensures that the flow through the circuit is unidirectional and make no mistake you're breathing in and out of a bag but you're doing it around a circle there's our model just to make sure you understand where the mouthpieces so you're breathing around a circle and these mouths this mouthpiece with one-way valves ensures that the flow is unidirectional and right there right there you have the first of the sort of unique things about a rebreather that can present a hazard or can fail these one-way valves are prone to failure and if that happens then the unilateral flow is lost and a number of problems can arise from that you will recall I said that if you're going to breathe in and out of a bag you have to remove the co2 and replace the oxygen now removing the co2 is the relatively simple part what we do for that is we place a co2 scrubbing canister with soda lime in it in the exhale limb of the loop soda lime is a compound mixture of calcium hydroxide sodium hydroxide and a few other things and essentially it makes it interacts with the carbon dioxide and removes it and there again is another unique feature of rebreathers that has the potential for causing problems carbon dioxide scrubber has a finite absorbing capacity it doesn't last forever so you have to replace it periodically and the right times these scrubbers depending on the designer potentially prone to packing errors so the way that you put the scrubber material into the scrubber and also to installation areas installing it in the rebreather sometimes that can be done incorrectly if you do that then the co2 may not be removed adequately and the second thing that the rebreather must do is replace the oxygen that you remove as you're breathing in and out of the bag this is a more complex process and in fact there are multiple ways in which can be done and is the oxygen replacement technique that is used to define rebreathers at the simplest level you can have what we would refer to as a pure oxygen rebreather so in this setting you have a cylinder of oxygen and for for simplicity I've left the oxygen regulators the pressure regulator off these oxygens are all the cylinders and my diagrams but these are pressure regulated cylinders and this is connected to a demand valve I also don't wish to represent all of these components as actually being inside the counterlung or the bag but just for the sake of clarity and my diagrams that's where I put them so what happens here is you've got pure oxygen in the rebreather as you consume the oxygen the volume Falls and it will activate this demand valve and bleed more oxygen in the same thing occurs as you descend and the pressure increases it compresses the bag and of course if that happens you won't be able to breathe and so the demand valve will open and introduce more oxygen into the unit and most of them also have a manual addition system so you can push a button and add oxygen if you want to that is the simplest rebreather but of course there's an obvious problem with that and all of you will know that that when you're breathing pure oxygen you're very depth limited so there's the you can't take these devices very deep they are use they're used mainly by the military for shallow attack swimming but not very often in the recreational community the second style of rebreather based on its oxygen addition system is what we call a semi-closed rebreathers in that setting we have a single cylinder of and I should preface this by saying that there are multiple types of semi-closed rebreathers I'm trying to be generic here if I don't include a design that exactly corresponds to the rebreather you use please don't be offended I'm not I'm not trying to pick one out here I'm just trying to be simple and generic so you have a single cylinder that contains an oxygen enriched mixture such as night rocks in the usual circumstance and the idea is that the oxygen is bled into the rebreather circle at a constant rate at all depths regulated by what we call a constant mass flow regulator and that's designed to introduce that gas with its oxygen content at a rate that maintains a predictable and appropriate level of oxygen in the loop at all times now of course that of itself is not going to preserve the loop volume as you descend and the counterlung or the bag gets compressed so you also and these devices have a demand valve which can respond to the bag being compressed or emptied for any reason and these also have a manual bypass which I have omitted for simplicity they're often referred to as semi closed because the amount of gas you've got to have flowing in there as such that it usually produces an over filling of the of the loop and it needs to bleed off periodically so these units produce bubbles and and they're not completely closed circuit so they're often caused called semi closed the problem with these is that although the flow of gas into the unit is designed to produce a predictable level of oxygen the reality is that you're not absolutely certain what it is unless you add an oxygen monitoring system it can be variable it varies with your workload for example and it is prone to changing with depth particularly during ascent so you have to be very careful ascending with the pressure decreasing and the po2 decreasing when you're using these units the next kind of ox replacement system is what we refer to as a manual closed-circuit rebreather and you can see that as we go from it from system to system we're increasing levels of complexity so in this setting what we've done is we've separated out the oxygen supply from the gas that dilutes the oxygen so we have a cylinder of pure oxygen and again you have a constant mass flow regulator or something akin to it which trickles a small amount of oxygen into the unit into the loop constantly and that's designed to be sufficient to keep you alive even if you didn't do anything else but it's probably not sufficient to keep the loop oxygen level at optimum levels for decompression for example you have to do that yourself so you have a manual addition system you can top the oxygen up as as appropriate of course if you're going to do that you need an oxygen monitoring system so these units have oxygen fuel cells in them of galvanic fuel cells which are connected to a po2 display these cells are like oxygen powered batteries they produce a current that's directly proportional to the oxygen to the po2 that they're exposed to and that can be read out on this display allowing the user to top up the oxygen using a manual addition button then of course you have to remember that we're not using pure oxygen here we're diluting the oxygen with a diluent gasps now the diluent gas can be different for different situations but for a relatively shallow nitrox dive you might use a diluent of you might use air as your diluent so that you're going to be mixing oxygen with air to bring the po2 up or the fraction of oxygen up so your breathing nitrox if you're diving deeper you would probably choose a diluent that contains a helium mix probably a tri mix with an amount of oxygen that's appropriate to the depth of your dive and I'm going to talk about the selection of diluent a little bit later in this presentation so we'll leave it there and the diluent is added by a demand valve so that as you send the bag gets compressed the diluent gets added and there will also be a manual bypass with these units as well the interesting thing about this type the style of rebreather is that the normal operation and when I say normal operation I mean the maintenance of a of the ideal po2 does rely on the diligence of the diver so you've got to be watching what your po2 is and you've got to be adjusting it yourself whereas the life-support function is relatively simple this unit is going to trickle oxygen into the unit at a rate that should keep you alive no matter what without you having to think about it one of the points I want to make here and this applies to the next kind of rebreather I'm going to talk about too is that the weakest link in all of these units that measure oxygen levels are these cells it's an imperfect technology for our purposes and they are prone to failure and clearly if there's failure in the oxygen levels that you're measuring or an inaccuracy in the oxygen levels then that is potentially a serious problem the final type of rebreather is what we refer to as an electronic closed-circuit rebreather now this is another step up in complexity so what happens here is we don't have a constant trickle of oxygen into the loop what we do is we rely on these oxygen fuel cells to measure the oxygen accurately they pass their information to a microprocessor and you have told that microprocessor what pressure of oxygen you want to breathe throughout the dive and when the po2 in the loop falls below that level then it opens an electronic solenoid valve which bleeds oxygen into the loop and restores the loop po2 and when that happens the solenoid valve closes of course there is a po2 display so that you can watch what's happening and some units have one that's linked to the microprocessor and others have an additional po2 display that is independent of the microprocessor and of course just like the manual closed-circuit rebreather you have a cylinder diluent which is chosen on the same basis i've the manual edition feeds from this diagram just for the sake of simplicity but all of these devices allow you to add oxygen manually and add diluent manually if the situation arises when you need to the normal operation of these units requires little divert input now and what I mean by that is I'm not saying you shouldn't have input but you could get away with not having input if it's working properly the amazing thing about these units is you can put them on your back and you can swim underwater and you could forget about it and if nothing goes wrong with the rebreather the likelihood is you'll be just fine but the life-support function is complex and the difficulty with these devices is that they work so well that they foster complacency it's easy to swim around get preoccupied with another task like taking a photograph and forget entirely that you've got a very complex life-support system on your back that needs to be watched carefully it's not a criticism it's just an observation these are the devices I use and there are many failure points so we'll come back a little bit to the safety issues around these rebreathers later but they are complex devices and you have to be very cautious in using them this is an example of a closed-circuit Rianne electronic closed-circuit rebreather this is a military device US Navy mark 16 the identifier you probably can't see this pointer but the counterlung the bag that you breathe in and out of and the co2 scrubber are contained in this center section here there's the diluent cylinder there's the oxygen cylinder there's a pod there that contains the microprocessor and the battery the solenoid valve is buried down in the plumbing and there somewhere the hoses are up here this is just to show you some of the components that I've been speaking about diagrammatically and this photo shows a few other features that I also mentioned but didn't have photos of so there's a po2 display there which is connected to the microprocessor there's another po2 display independent of the microprocessor most of these units these days also have a head-up display which is an LED based display that essentially gives you a in-your-face indication of what's going on in your loop at all time so the idea is that it makes you diligent by having it there you can't ignore it so green is good flashing is is something you need to sort something out readers bad get off the loop they all have a different slightly different algorithm but that's what they're there for and another safety feature that many of these units have these days is what we call a bailout valve where the mouthpiece is connected into an open circuit gas supply so that you can switch on to open circuit with just the flick of a switch without having to remove the mouthpiece from your mouth to change breathing sources okay so so why bother with all of this what you know it's complex technology what's the big deal why do we bother well by way of example this is a few years ago well actually this is going back a we way 2002 scientific organization in Australia was doing side scan sonar surveys off the New South Wales coast and they found this that looked like a shipwreck and they thought it might be a historic shipwreck called the Cumberland but the depth was 300 feet 90 meters too deep for them too deep for the for the police and military and it would have presented a number of occupational safety and health issues to dive it professionally at that time I was diving with a group of wreck divers called the Sydney project and we were known for diving between depths of sort of 80 to 140 metres we were doing quite a lot of deep stuff at that time and these scientific guys brought this thing to us they said look at this we've found this trace on it you know it looks like a shipwreck and you know what you can actually see the exact position here the GPS coordinates here and they lift and set and they said their parting shot was well what you do with that information is entirely up to you now knowing that within five picoseconds we would be heading off down there to dive it so here we go we've got a challenge a 90 meter 300-foot dive we want to speak 20 minutes on this wreck to have a look around it and see if we can find anything that identifies it is it the Cumberland so let's look at how you might approach that if you're an open-circuit diver first of all I want to convince you if you aren't already convinced that strapping a holida ear on your back and going down to 90 meters ain't a good idea I think you all know this I think the narcotic effect would incapacitate you the knife cutting effect of nitrogen decompression on air is inefficient air only contains 20% oxygen will take you a long time to decompress from a very deep dive breathing 20% oxygen if you breathe air at 90 meters or 10 atmospheres 300 feet 10 atmospheres the pressure of inspired oxygen would be two point one atmospheres that's toxic level of oxygen when you're diving so that's no good one point three atmospheres of oxygen is often considered an advisable maximum to be breathing underwater and the gas density would be about 13 grams per liter so your work of breathing would be very high all talk a lot about gas density when I do give my physiology lecture this afternoon but eight grams per liter is often considered an advisable maximum so to do this dive you need a helium base mix for the deep phase of the dive to mitigate some of these risk helium's non-narcotic it's light it's not dense so it's a much better gas for these sorts of dives now all of you trained divers you've seen this kind of diagram before and the point I want to make is that when you're down at 90 meters and you exhale one liter of gas by the time we get to the surface it's 10 liters of gas so if you're going to do this on open circuit you're going to use a lot of that very expensive helium now I know in the United States you're very privileged you can buy these big cylinders of helium for a few hundred bucks so let me tell you that in Australia or New Zealand a G cylinder of helium costs about $1,000 it's a lot of money to be doing open circuit helium diving so let's listen let's put that to one side don't say okay we're going to go and do this dive on open circuit the first thing you need to do is choose what guesses you're going to use so what guess are we going to choose to breathe at the bottom well you ask yourself how much oxygen can I breathe you to breathe as much as you can because the more oxygen you're breathing the lessen it guess you're absorbing so that's a good thing so we say we're going to breathe 1.3 atmospheres of oxygen and a 10 atmospheres total pressure that gives us an oxygen percentage of 13% so we're going to use 13% oxygen and the next question you ask is how much nitrogen are we going to have in this mix and people often figure that out by saying well how much nitrogen and how much narcosis and I'm I prepared to tolerate on an air dive and many people might say well I'd dive to Iran 40 metres and I feel pretty good that's about as far as I'd like to go so you can do the maths and 40 percent nitrogen gives you the same level of narcosis at 10 atmospheres as an air dive to 40 meters so we have 40 percent nitrogen and the rest will be helium and that's designated trimix 10 sorry try max 1347 so 13 percent oxygen forty-seven percent helium balanced nitrogen and then you would say well what are we going to decompress on because you can't breathe that all the way to the surface it's a hypoxic gas and you wouldn't decompress very efficiently so on the way to the surface will change to save now look I know there's lots of ways of doing this and some of you would have different approaches to this but we'll change tonight rocks 36 that's 36 36 percent oxygen balanced nitrogen and we can start breathing that at 27 meters because that's where the po2 will be 1.3 atmospheres and we'll use oxygen from 6 meters for our final decompression so those are our gases the next thing you do is plug those gases into some form of decompression algorithm this is Kevin goose vgm platform and it will spit out a decompression algorithm for you and here it is here just so you can read it a bit more easily so these are your depths down here 19 minute sorry about the meters I I forget that I'm in a country that still works and furlongs and qubits and stuff like that but that's huh not 90 meters 300 feet and these are your your dips and you stop times and the white is your bottom guests of the 1347 we change at 27 meters to drop 36 and then oxygen at 6 meters and the total run time is just over 2 and a quarter hours that's our decompression plan you take that decompression plan and you start figuring out what guess you're going to need this is a process that many of you will have been through I know that but there's some of you in here who probably haven't so you generate tables like this where you list out your depths and the ambient pressure and the times you're going to spend at those depths and your surface air consumption rate that's something that people who train as technical divers figure out for themselves very early in their careers they figure out how much gas they use swimming at the surface when they're swimming gently like a typical dive and also when they're at rest so on decompression and then you can use those numbers and extrapolate them to different depths using this kind of table and then you multiply the ambient pressure by the time by the surface air consumption rate you get a total volume of gas and liters you add all that up and then you multiply it by a safety factor say 1.3 and you get a final number 7800 liters of bottom mix is what we're going to need okay it's quite a lot of gas and then you do the same for your nitrox 36 and your oxygen you don't need so much of those same math same process and then you sort of figure out how you're going to put all that together so you need to carry a lot of gas and and that's one of the big problems with open sets as you're going to hear me say when you dive on a rebreather you have to carry almost similar amounts of gas for the decompression in case you would be the fails but the lot the likelihood is you're not going to use it so you save a lot of money you necessarily cut down on having to carry the cylinders not quite as many as you see here of course another problem with open circuit scuba and this is an important one as a rebreather diver who doesn't like to spend lots of time being jerked around on an anchor line out in mid-water being shark bait is that it takes longer to decompress and the reason for that is that you're not breathing the optimal po2 at each depth you're decompressing at so what I've shown here on the y-axis is the pressure of inspired oxygen and remember I've said the optimal po2 for our dive is 1.3 atmospheres and what I've shown on the x-axis is your depth as you decompress so there's 90 meters or 300 feet right at the bottom and these are we doing prison stops and look we've optimized our bottom mix so that you're breathing 1.3 atmospheres at the bottom right here that's great that's what we want but the minute we start ascending the po2 starts falling until we change to our nitrox 36 it goes back up to 1.3 but then we start ascending again and it starts falling again and it doesn't become optimal again until we get on to our oxygen at 6 meters it goes above 1.3 briefly at 6 meters but when you're at rest on decompression we accept that that's probably fine so you're not breathing the optimal po2 at each stage during the decompression when you're on open circuit now look I agree you could carry more cylinders of different gas and fill this gap in here a little bit but every time you do that you're adding another cylinder to what you're carrying so how does it rebreather help with all of this well rebreathers have a couple of advantages I haven't kind of alluded to yet they don't produce bubbles or not many in most cases but gas your breathing is warm and humidified but the point that the key point is that they minimize gas consumption and that's important for deep dives when you're using this expensive helium I said seven seven thousand eight hundred liters didn't I look in theory all you need for a rebreather dive to that depth is the loop volume I know 10 liters times the pressure that you're going to ten atmosphere is a hundred liters of helium you could almost get away with that now in reality you use a lot more dealer than that because you go up and down a bit and and that consumes diluent and many people use diluent in their wings or they do not not often not their dry suits depending on what the duty one is but you use more than that but in theory you use tiny amounts of dillamond so the rebreather is a big advantage in this regard and look here's another photo from that Rick I showed you before and this is me on my mark 15 five and he seen no bubbles and here's an open-circuit diver there's about five bucks worth of helium on its way to the surface there I might use five bucks with it that's a bit of an exaggeration but I might use five bucks with the helium for the whole dive so that you know there's no question that they are conservative of gas the other advantage that I've added at the bottom here is that with a rebreather you are breathing the optimal mix for decompression at all stages during the Essene I showed you this diagram before this is the situation for open circuit scuba but look with a rebreather you tell the rebreather a clothes an electronic closed-circuit rebreather you tell it I want to breathe 1.3 atmospheres of oxygen so this is what you breathe the entire period of the dive 1.3 atmospheres of oxygen and that's because the rebreather keeps adding oxygen to get the po2 up to the preordained setpoint so in fact I should point out that breathing one point three episodes of oxygen constantly like that does marginally increase the risk of oxygen toxicity but I mean that's something that we take into account in cope with the way the rebreather does it and this is just to illustrate this concept of constant po2 diving what's changing is the fraction of oxygen in your mix so at 300 feet or the bottom we're breathing 13% oxygen and as we come back towards the surface the po2 stays the same but the fraction of oxygen in the mix increases and the rebreather is doing that for you or you're doing it manually if you're on an MC CR you can optimize your po2 at every point during your decompression and this is a good example of that this is a recording of one of my dives in a cold water lake in New Zealand there's an 80 meter dive and this is the depth here the depth profile of the dive and this trace here is the po2 and I have I've put in you can't read the scale but that's the po2 set point was 1.3 and you can see the rebreather has a pretty good job of maintaining my po2 at one point three atmospheres during the dive the interesting thing is there's a little bit of waviness around this line the reason for that is that the solenoid puffs oxygen in and that sort of reaches the cells and a slightly unmixed form so it causes these little spikes around the mean of 1.3 you can see that those spikes are maximal while I'm working on the bottom and during ascent because during ascent the po2 and the loop is falling so the rebreather is working to bring the po2 up so there's a little bit more spike activity but as you level out on the decompression and stop working becomes a bit more of a smooth line these two dips here correspond to these little ascents but you can see the rebreather corrects that pretty fast just here I went on to open circuit oxygen for various reasons I won't describe that but it wasn't a problem with the rebreather it was something that I did intentionally went on to open circuit oxygen here so the rebreather fell down to its surface setpoint which I switched it to so there you go it's that's how they maintain these po2 s interestingly that dive was done in in a search for this this is a engine off a helicopter that crashed into Lake Wanaka in the South Island of New Zealand a few years ago the engine became separated from the mainframe of the helicopter they managed to retrieve their the mainframe with the pilot in it using a remote operated vehicle but they couldn't get a line on the engine they wanted it back so they asked him is Lee and I to go down and try and find this engine you can see that the depth here on the ROV image was 74 meters when they asked me when they asked me if we would go down and do this they say well we know what do you need what do we need to provide and I said well we we're going to need a boat where it needs to be big enough for two rebreather divers and cylinders and a few extra people to help us out and you know shot lines and boys they said like a big runabout would you know it would do the job so we tuned up on the day and this is what they bought for surface support and I was not expecting an aircraft carrier and I and I took I took a look at this thing and because the helicopter is actually out here some you know so we're going to be offshore and I looked at the singing I thought I could have visited myself jumping off it but getting back on board would be a bit of a problem and I pointed this out to the guy who'd bought this thing along and he said I'll we see that front-end loader on the back and I said yes and it will next thing you know I'm sitting in the front of the singing yeah I can tell you I've gotten out of the water and some unique ways in my time but this really was the most incredible of them a very unusual event so look to finish off and what I'm going to do now is walk you through the Aneta what I call the anatomy of a rebreather dive so just a brief look at some of the things about running the logistics of running a rebreather diving it a little bit different to open circuit and we're going to keep going without with the with the theme that I've had so far that it's a a closed circuit rebreather dive to 90 meters or 300 feet for for 20 minutes now I'm not going to go through all the details of planning and executing a dive like this that we could talk about that all day but I'm just going to focus on some of those interesting things from a CCR point of view obviously there's logistics and and you know the boat you choose the people you have the support that you have this is Pete and I on a on on a similar dive in another location but look let's go through some of the key decisions you've got to make the first thing you're going to do is decide what set point you're going to use for your dive so what you're going to tell the rebreather that you want to breathe in terms of the pressure of oxygen or if you're using an MCC are what pressure of oxygen you're going to maintain and there's a few things that go into that decision so the first thing you would do is consult a decompression algorithm and the oxygen exposure tables and marry those two up how long's their dive going to be and is this a safe oxygen exposure it's always a trade-off between decompression efficiency and the risk of oxygen toxicity but the the resolution I come to for a 90 meter dive for 20 minutes would be that our po2 of 1.3 atmospheres is fine because our dive is going to be about 2 - recorder hours long and the exposure limit for oxygen is about 180 minutes at one point three atmospheres so that will use a po2 of 1.3 then you need to choose a diluent gas that's a it's actually quite a complex process when you break it down it actually turns out that the diluent you choose can be quite similar to the bottom gas that you would choose for an open-circuit dial the first thing the key thing is we always have oxygen in our delivery yes so in case you have to breathe it at any point but the oxygen content think about this the oxygen content mustn't be such that at the bottom it would exceed the po2 set point of your rebreather because otherwise you won't be able to get your po2 down to the level you want for example if you had 20% oxygen in your Diliman gas for a 90 meter dive to 10 atmospheres you got down to the bottom the po2 just from your dillamond which is supposed to dilute the oxygen would be 2 atmospheres 10 times 0.2 10 times 20% so that would be no good that's why you have a hypoxic diluent so that's why we're going to use our 13% that we would have used for open circuit and and similar to the choice of an open circuit bottom gas the nitrogen content mustn't produce more narcosis then you're prepared to tolerate at that depth so we could use our nitrox 13 trimix 1347 that we decided to use for an open circuit dive many rebreather divers would choose edeliant known as trimix 10 50 or more correctly Healy air 10:50 it's one of the great conveniences of technical diving that if you add equal parts air and helium you get a mixture of 10 50 10 % oxygen 50 percent helium and 40 percent nitrogen so that's 10 50 many people would do that just for the convenience that ease of the blending but something along those lines for our Dylan you would plan bail out gas requirements I don't think there are many rebreather divers who you use rebreathers without bailout yes in other words a guess that you can go onto open-circuit guess if you rebreather fails and you would use a similar process to those tables that were used for planning our open circuit guest requirements for that purpose one of the caveats on that is that I talked about the surface air consumption rates that you use for planning an open circuit dive if you bail out from a rebreather it's usually because you've got some problem with the rebreather and if you have a problem it's likely that you're breathing heavily particularly if it's a carbon dioxide problem so when you're planning bail out you need to bear in mind that the surface air consumption rates might be much higher than you think then you need to mix and analyze and label your gases and reanalyze them and be totally and utterly anal retentive about this process because the related errors in this area are a major cause of accidental deaths in rebreather divers and an open circuit divers also then you assemble your rebreather and look I just can't emphasize this enough this is where you need to be like if we will all Swiss or all German we would be good at this right because they are the most culturally the most focused anal-retentive people in the world I mean Dame if there's any Swiss or Germans and they actually mean it as a compliment I you know I'm in a profession where I have to be anal retentive all the time I wish I had the same characteristics as the average swiss or german for attention to detail you need meticulous attention to detail no shortcuts never rush a methodical standardized approach that you don't change from time to time and use checklists use checklists I want to point this study out to you and look if any one of us today Nick if you've got appendicitis you'd go to hospital right you're heaven operation grant if you if you if your heart valve in your and your heart started leaking you needed a valve replace you go to a hospital you'd have surgery you would go to a 21st century operating theatre and expect that they would do a job on you with no mistakes because this is first world country and it's the 21st century and things mistakes they get made in operating theaters right this is a study I was involved in this is 2009 published in the New England Journal of Medicine where we introduced a surgical safety checklist to operating theater practice we monitored outcomes for 4,000 patients before and after the introduction of the checklist the introduction of a checklist a basic safety checklist in 21st operating theatres 21st century operating theatres halved mortality and half to the rate of complications check that out these this is in an environment where you would expect mistakes don't get made well they do get made and they get made in assembling rebreathers a similarly complex technical activity so you need to use checklists they can take many forms they can be written they can be electronic and I'm not going to go any further with us I wanted to get that message across but Ritchie Cole is going to talk more about checklist so the next couple of days so then you assemble your rebreather and that typically involves packing and installing the scrubber checking the one-way valves making sure they're working putting the thing together doing a positive and negative pressure check that's a way of checking the integrity of the loop to make sure that it's not leaking check your diluent pressures your oxygen pressures switch the rebreather on calibrate the sensors pre-breathe the scrubber if you breathe on the unit for five minutes and you don't get short of breath and you feel fine and everything seems to be working and the oxygen oxygen addition system seems to be working that's a great thing why wouldn't you do that before you jump in the water and trust that it's all happening before descending straight down pre-breathe the unit and if you're not going to use it straight away shut it down and isolate it so at the start of a dive a final kick make sure your cylinders are on and they're open believe it or not rebreather having a breather switched off or one or both of your cylinders switched off or not even full has been a factor in many accidents you usually start with a po2 set point of naught point seven or something around that because if you had your po2 set at one point three atmospheres at the surface and you switch you rebreather on it would start going at oxygen at oxygen at oxygen in a futile attempt to bring the po2 up to one point three but at the surface one atmosphere can't do that so you start with a lower po2 set point make sure your mouthpiece is closed when it's out of your mouth if you're in the water and your mouthpiece is open and not in your mouth all the guests floods out of the loop it loses buoyancy and in fact if the mouthpiece goes in the water it can flood that you don't have to think about that on open circuit you can take them off yourself put it back in okay I've put it in blow earrings put it back in well rebreather you can't do that much more complex the surface is a dangerous place with rebreathers this is a place where problems first become apparent if there are some and there are lots of distractions people jumping in people needing help there's exertion there might be some current at the back of the boat it's a dangerous place one of the things we often do during the first part of the descent check each other for leaks and on a rebreather you have to think about things that you don't have to think about on open circuit like keeping the rebreather bag at a relatively empty level so that when you breathe in you just bottom it out we call that minimum loop volume and the reason for that is if your loop is full of gas it's you're very buoyant your buoyancy changes with with the volume of the counter line so minimum loop volume your buoyancy is very poor voiding controls poor if you don't do that and then there are recurrent task loads during descent and I'm contrasting open circuit and rebreather divers here with open circuit think about it we've all done open circuit descents what do you do you're going down you're just your buoyancy you add a little bit of gas to your dry suit you check it at you're clear is buoyancy dry so is buoyancy here's what you did maybe beer but situationally aware where's my buddy what's going on with a rebreather it's more complex you've got to kick your just your buoyancy put a bit of gas in your dry suit do you is check your po2 maybe add a little bit of diluent to the counterlung if it's bottoming out as you descend in quickly you need to be situationally aware in ways that go beyond that for open circuit scuba not only where is my buddy but is my solenoid firing right is there some funny noises coming from my Roo breather can I hear this little bit of gurgling there's a whole lot of little nuances about rebreather diving that you have to be so much more aware of in comparison to open circuit scuba during the typical descent on open circuit for a technical dive you probably need to make a guess which at some point and that is that is sort of equated to the need to change your set remember I said we start with a set point of naught point seven atmospheres of oxygen at the start of the dive some point you need to change that to one point three we usually do that when we first get to the bottom so when you when you arrive at the bottom it's a good idea to just sit there for a minute not sort of suddenly take your camera and start taking photos but just sit there and make sure everything's fine change your set point Oh most of us will open our bailout valve and just take one or two breaths from it to make sure it's working and then change your set point if you don't do this and your decompression computer is not plugged into the actual po2 of your circuit so your computer thinks you're breathing one point three atmospheres of oxygen but you're actually breathing naught point seven atmospheres of oxygen during your dive that can result in a bad decompression calculation as you can imagine you need to check your po2 frequently because your life depends on it and it's a but that mantra is a bit like the old you know breathe normally never hold your breath on open-circuit scuba it's it's equivalent to that it is the one thing that rebreather divers have hammered to them all the time check your po2 because your life depends on it there are many potential causes of hypoxia hypoxia and hyperoxia and both of those problems can sneak up on you and cause you to go unconscious with no warning you need to be situationally aware rebreathers send you messages that are subtle they're nuanced it's not like open circuit scuba so you need to be situationally aware and you need to minimize exertion because existin on a rebreather where all the effort of moving gas around the circuit comes from your lungs promotes come dioxide retention and I'll talk about that in my physiology lecture with the ascent cents on rebreathers are a potentially dangerous time because as you ascend the pressure around you drops of pressure in the loop drops so the po2 Falls electronic closed circuit rebreathers will cope with that other forms of rebreathers you normally have to add gas in some form or another to cope with the drop in po2 but check the po2 because your life depends on it you need to be very conscious of maintaining minimal loop volume because otherwise the gas and the bag is going to expand and expand and expand and you'll become very buoyant you need to be situationally aware as I've already hopped on about many of us will manually add oxygen to help the rebreather along even if it's an electronic rebreather and it's doing it automatically you can add a little bit of oxygen especially on the shallow stops to help the rebreather maintain po2 and of course on arriving at the surface you need to shut your mouth piece off and remove it but shut it off before you remove it otherwise you lose all the gas and you become negatively buoyant so here's a walk through a typical rebreather dive and some of the things that make it different to an open-circuit dive I want to make this point again and I want to make it very clearly rebreathers have facilitated many fabulous examples of exploration and discovery they are in short a fabulous tool however they're complex devices they're used by us fallible humans in a hostile non respirable environment and so that is a heady mix for problems and what we're about this weekend is critically looking at the way we use these devices what the problems are and trying to mitigate them and once again I'd like to congratulate the organizers on bringing together such a successful event thank you very much

Channel: DAN TV

Views: 59,748

Rating: 4.8674464 out of 5

Keywords: Diving, Scuba, Scuba Diving, Underwater, Rebreathers, RF3, Rebreather Forum 3.0, Research, Physiology, Simon Mitchell, Divers Alert Network, DAN, AAUS, PADI, Technical Diving

Id: EKQLc7UtUzM

Length: 47min 2sec (2822 seconds)

Published: Fri Feb 08 2013