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Back to basics

3K views 14 replies 9 participants last post by  divetheworld 
#1 ·
I read so much about how good and safe it is to have a BOV that I think sometimes its used as a crutch.

This is MY opinion and I know that opinions are like arse holes, everyone has one! However I think that more and more people are fitting these to their units and expecting to be so safe because of them.

What has prompted me to write this is this thread
http://www.yorkshire-divers.com/foru...ebreather.html
I have the utmost respect for Howard for posting that. Be honest with yourself if it had been you would you have posted?

Howard made an error and it's an error that I'm sure he will never make again. All education has an associated cost I've always found that it's better to learn from others mistakes and reading that post will ensure that I always double check the "O"ring, spacer and scrubber.

I have had a few units with BOVs fitted and although I think that a BOV is useful It's not the be all and end all that some would have you believe. I prefer to get off the loop. Now having a BOV gives me a couple of breaths while I get off the loop and on to my bail out but even on units without a BOV I've got a bungeed reg around my neck that I can get onto quite quick if I need to.

If you're using a BOV it's unlikely that you'll have enough gas to surface so if you plan to use off board then you need this plumbing in from the start or a quick connect system. This in itself can cause problems. If you've bailed out then you have to change and plug in off board pretty sharpish and you may not be in a state where this is possible. If you run off board from the start then you can say that you should have sufficient to at least get you to a state where you've got yourself comfortable enough to be back in full control.

Once the shit has hit the fan regaining full control isn't easy underwater and one thing that I learned from the HSE/Shy video is that whoever is leading the dive, if they have any problem then they are no longer leader as they will be to concerned with themselves so someone has to take over and get everyone out of the water. This is decided before the dive and everyone is aware in the briefing.

If I need to bail out then weather a BOV is fitted or not I'll get onto open circuit as soon as possible. If I'm on OC then I have much more control. I can swap stages with other divers if I need more gas. If I'm deep diving I can make effective gas switches and everyone knows what I'm breathing from the reg in my mouth. If I'm on a Hypoxic dil/bailout then faffing with a gas connect is the last thing I want to do to switch gas (this is quite easy on the Sentinel as it's designed for off board but this is the exception not the rule) but I still want to be fully open circuit on a reg and not a BOV.

Bailing out to me means get to the surface as soon as possible but stay in control. now some CCRs have a system that allows you to dump manually like the Meg and Inspiration where you can pull or push a dump on the lungs but if you're heading for the surface trying to maintain control on assent it will be a task. Have you turned off your O2? is it injecting/flowing as the PPO2` drops on assent? Can you dump the lungs quickly and keep control of buoyancy? If your diving a unit with back mounted counter lungs you are relying on auto dumps and their settings. I have a habit of exhausting through my mouth and nose and not letting the auto dump do it's stuff as I feel more in control but when i'm off the loop I can't dump through my noise and mouth. My training on units with back mounted lungs is to open the loop and let the gas expel as I ascend. This couldn't work if I was breathing off a BOV. It does work however if you just let the loop go it floats above your head, even the heavy loop of the Sentinel so holding it with the loop open will expel gas on ascent and keep you in control.

A BOV is a nice addition but it's something else, like an ADV was something else. CCRs are becoming more complex and doing much more for the diver. The diver will be reliant on the unit and it's tricks if they don't understand and practice the basic principles of CCR diving. The Apocalypse and the Poseidon are designed to simplify CCR and make it easier but I have real concerns that too much reliance is being placed on the unit and that's because we the divers are not to be trusted. If you dive a basic rebreather and understand the basics and the principles. Learn skills and practice them then I'm sure if you're disciplined and you set basic rules and stick to them then you will be safe and be able to get yourself out of the poo.

I have never had to bail out where my life would be in danger if I didn't bail out. I try never to push the life of the scrubber. I change batteries when they're a bit down and cells at the first sign of weakness. I like to have full cylinders and more than enough bailout. I never rush to get into the water and will can a dive if I have any doubts.

I practice often and I never rely on my unit, I always have a bailout plan. I think that CCR divers should be able to dive without ADV, BOV, HUD and computer. You should always know your PPo2 and you should understand it.

I buy and sell quite a few rebreathers and it saddens me when someone is selling because they aren't that sure of the unit, some people take longer to get to grips with it than others but good skills and understanding will never be replaced with anything that can be manufactured. You can have the most tricked out CCR in the world but if you can't hold it together when the going gets tough then it's never going to be a happy ending.

I hate reading about the loss of a diver. I don't like reading about any indecent but if that makes diving that bit safer for me and if I can learn from it then I will and I'll try and pass it on.

Nobody wants to have these incidents and we all have an opinion, this is my opinion nothing more.

Dive safe.
 
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#2 ·
The first time I needed a BOV it was my fault for packing the scrubber badly I didn't have one. That's when I discovered that "Just come off the loop" is easier said than done. It certainly gave new meaning to the phrase "Sanity breath". This was 2002.

The second time a wire broke in the Vision head and the displays froze.
I had a BOV so coming off the loop when I realised I hadn't a clue what I was breathing was one twist.

If that's a crutch in your eyes so be it.

I don't like the attitude that divers are big tough guys who ought to look after themselves better. Most CCR problems are insidious and by the time you realise you have one you can be well down the incident pit chemically. We need simple solutions and getting off the loop isn't simple without a BOV. To my mind it is an obvious 'must have' and I certainly would not have bought the Sentinel without it.
 
#3 ·
Obviously l think they are a good for the user l also think that if you were unconcious still breathing off the loop your buddy could just switch the BOV and you would be on oc. They would have very little chance of getting an oc reg in your gob.
 
#4 · (Edited)
A couple of years ago I bought myself a FFM for this very reason. It was the Drager Panorama Nova R. "R" standing for rebreather. This has a expendable bite piece and not a nasal cup. The idea is that you have an open circuit reg that you could breathe through your nose so even of you fell unconscious you would theoretically breathe an open circuit gas through your nose. It took a bit of setting up but when it was set it did work.

I tend not to use it now though as deeper diving means gas switching and it's never going to be easy. You really need to come off the loop and the mask at the same time which adds more complexities in itself.
 
#5 ·
CO2 & BOV's

Simon

From the moment I did the MOD 1, the most worrying issue, in my mind, with Rebreathers is the consequence of CO2 breakthrough.

From everything I have read, & been told by those that have either intentionally or accidentally experienced a CO2 problem, is that getting off the loop is almost impossible. The ability of the individual to mentally overcome the primeval urge to breath is limited in the extreme.

Whilst I understand your concern over people using equipment solutions to make up for their poor discipline or practice when preparing rebreathers. You must accept that, with the best will in the world, the best of us make mistakes, in addition, equipment failure, or even sofnolime failure all present a real risk of a potential CO2 breakthrough. My limited understanding is that high PO2's also mask a lot of the initial physiological warnings of CO2 poisoning, when the symptoms become apparent you are already descending rapidly into the incident pit.

A BOV allows the diver to switch to OC without having to attempt to hold his breath (an impossibility once CO2 poisoning is apparent), in fact with minimal interruption in his breathing rhythm. The status of the BOV can be visually checked by a buddy or others in the dive team. In the event that the diver has blacked out or is unable to help himself (herself), then a BOV has the very real advantage of being easy for the buddy or dive team to operate.
You are quite right that if piped into an inboard DIL cylinder there is a very limited amount of gas. But I would expect those using a BOV would carry a stage (or multiple stages), ensuring sufficient OC gas, or at least a reasonable volume to stabilise the situation, prior to making use of team bailout. Deeper dives do present additional problems, multiple bailout gases, but the issue is about the diver regaining control, once fresh gas is in use the breathing rate will drop allowing gas switches to be made. At worst, a temporary switch back onto the unit whilst the gas switch is being made would be viable.

I am very aware that I currently don't have a BOV, it is however on my list of goodies to purchase.

My (personal) view is that BOV's are like an octopus, pony or twinset. You may never need it but when shit happens you will be very pleased its there!

Gareth
 
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#11 ·
The ability of the individual to mentally overcome the primeval urge to breath is limited in the extreme.
Just a small comment Gareth.
The urge to breathe is not a primeval one but a chemical one in the case of hypercapnia. The carbonic acid build up in the blood due to the high PCO2 causes the body to react with hyperventilation. I believe they call it metabolic acidosis.
It is as hard to overcome as trying to breathe normally when out of breath after excessive work effort, that is the same as an individual who has just done a run and is out of breath.
You have to imagine the mental effort you will require to remove the DSV from your mouth under these conditions whilst underwater.

Brent
 
#6 ·
There are a lot of valid points in your OP Simon.
My personal view based on very limited experience is simply practice your skills untill they become second nature.
I have fitted a BOV because I can see that if ever the time comes where I need to get onto gas that is external of the loop I would much rather:
flick the switch on my BOV, breathe.
than:
close the loop, take it from my mouth and flick it behind me, grab the reg from my bailout tin, stuff that into my mouth, purge it, breathe.
I know I can do both of these and I also know which one I would rather do.
Part of my 6m bubble check is now to check the BOV is working in the water (I also check on land when putting my unit togeter) thanks to Andy Hayhurst & Simon Lawrence for taking away the complacency of not doing that.
There is an extra failure point in the offboard plumbing but if I am deeper than 50m I do not want to bail onto a 3l tin. I am willing to take on the extra maintenance of the APD offboard kit for the added security that bailing onto an ali 80 will bring.
Bottom line for me is I will always have a BOV on whatever unit I dive. I do not see it as a crutch but I do see it as improving my confidence that when the unit does what we all expect it to do eventually (fail at depth) I will have enough gas immediately available to be able to deal with it.
 
#7 ·
I'm a big fan of BOV's but equally it shouldn't encourage complacency. Both the CO2 hits I've had were human error (not getting a good seal on the mouthpiece so water was leaking past, blowing a big gob of water into the loop on the second).

If I could be 100% confident that a properly set up rebreather isn't going to have any CO2 problems then I'd dive alpinist without a second thought. Having swapped units I'm a lot more confident in the resilience of the scrubber so time will tell. After four years on a KISS I have just done my first year on the my new unit so I'm really only now getting a feel for it.

I still wouldn't be without a BOV, I do think they are a vital piece of kit. Especially on backmount lung rebreathers which don't have particularly convenient ways of getting offboard gas into the loop. If it came to a choice then I'd choose a BOV over a HUD any day.

Cheers,

Stuart
 
#9 ·
From an OC buddies point of view, the ease of switching a BOV and the re-assurance of knowing from the switch position that your buddy is on OC gas is really nice in a sticky situation.

Also, I imagine it is way easier than trying to stuff an OC reg into someones mouth when they are potentially 'breathing like a train'.

I'd certainly think hard about buddying a non-BOV equipped rebreather diver now, but I guess my recent experience colours that a bit. YMMV.
 
#10 ·
From an OC buddies point of view, the ease of switching a BOV and the re-assurance of knowing from the switch position that your buddy is on OC gas is really nice in a sticky situation.
Not all BOVs are the same and have an easy to see position like Howards. You can tell if the person is breathing off the BOV as the reg exhausts bubbles rather than the mouth if they're exhausting from the loop.

Let me make this quite clear I don't think that BOVs are bad. It's better to have one than not to have one but I don't think that any diver who bails out should stay on a BOV. I believe that they should get on an OC reg asap.

I don't think that HUDs are bad either but they shouldn't be used as a substitute for monitoring the handsets.

The basic skills of CCR diving are still the basic skills. Units are on the market and coming to the market that enable someone without basic skills to dive CCR but what when they go wrong? the skills are needed and should be maintained.

If anyone really believes that their unit (no matter what is fitted to it) will do everything for them and get them out of the water when it goes wrong then there's a bad day awaiting them.

When you did your MOD 1 you flew manually and descended with no ADV etc. These are basic skills of the CCR diver. How many people practice this?

The title of the thread is "back to basics" retain those skills.
 
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