View Full Version : Scenario
I aimed this same question at a batch of new master diver trainees, the answers were interesting.
so, open to question here.
You’re at 30 meters of seawater after 17 minutes of no stop diving;
decompression commitments will begin at 18 minutes.(average tables)
Your regulator starts free flowing full pelt at 10 bar (average interstage pressure).
The water inside the demand valve starts to freeze stopping the valve from closing
You don’t have an alternate air source & you can’t see your buddy due to the bubbles.
Your buddy is unaware of your problem.
You have less than 2 minutes to decide on your answer, as this is how long it will take a full cylinder to empty.
Time starts now.
This happened to me on the beagle at 32m and the cylinder was empty in 30sec. At the time I was a regional coach and teaching ascents quite often and a 32m ascent was no probs especially as my budy was a regional coach as well. So I fitted a flow stop to my demand valve and to the ADV on my rebreather. I was taught to bend the hose over and stop the freeflow, it doesn't work at 30m, fit a flowstop, £20 - £30 well spent
Gas Guzzler
04-12-06, 23:45
From 30 metres with no deco you need 4 minutes of air, (10 metres per minute plus a 1 minute stop at 3 metres).
Usual assumption of a 12 litre at 220bar, so 2640 litres of air at start. Assuming you went straight to 30 metres, you were breathing air at 4 bar for 17 minutes. so 17 x 20 x 4 = 1360 litres consumed when freeflow started. So 1280 litres left.
You need to control the loss to 320 litres per minute or you have to find your buddy. I've assumed you won't tell that you didn't have a 50 bar reserve
Fold hose to stop/slow free flow and buy yourself time. Octopus (if you have one) in. If not, deep breath, reg out and above your head. Wait for bubbles to clear and see if you can spot your buddy.
If you can't see them and you can control the flow by folding the hose then start your assent.
If not: Depending on how flexible you are, gag your main valve to slow the cylinder flow so you can have enough time to ascend. If your not that flexible kit off to get to the valve.
Why don't most regs come with secondary isolation valves so you can at least control a free flow?
Edit: I guess that's what Ding means by a flow stop. Come work in the chemical industry. Double isolation on every line is the minimum standard.
GG
I aimed this same question at a batch of new master diver trainees, the answers were interesting.
so, open to question here.
You’re at 30 meters of seawater after 17 minutes of no stop diving;
decompression commitments will begin at 18 minutes.(average tables)
Your regulator starts free flowing full pelt at 10 bar (average interstage pressure).
The water inside the demand valve starts to freeze stopping the valve from closing
You don’t have an alternate air source & you can’t see your buddy due to the bubbles.
Your buddy is unaware of your problem.
You have less than 2 minutes to decide on your answer, as this is how long it will take a full cylinder to empty.
Time starts now.
Your buddy should hear the freeflow, if not, make an immediate ascent at 15M per minute which will take 2 minutes:eek: However, a freeflowing reg will still provide air. I still tend to use Navy tables therefore 30M has 20min bottom time, so should not require a deco stop, anyway DCI can be treated, drowning can't. On the way up keep the tip of your tongue in the reg to stop ice/particles of water from hitting the back of your throat, sometimes the freeflow can reduce or stop when the ambient pressure reduces, though don't count on it. Another trick I've been told is to place your fingers over the exhaust port, reducing the exhaled air. The logic behind this is that the warmer exhaled air defrosts the second stage. Again don't count on it. Try and get to the pillar valve to reduce air flow or turn off altogether as this usually sorts things out. However, by this time your buddy should be looking for you and making an ascent. If they have not found you, you are likely to run out of air before breaking the surface. On my last drop of air I would free ascend the rest of the way which should only be a couple of metres.
Lizardland
05-12-06, 01:40
Bit of a rubbish answer but I wouldn't be diving at 30m without another air source to start with. People do, that's their choice but I wouldn't do it. Not in the UK anyway, in warm water not being able to see your buddy is a lot less likely.
Assuming that I was in the situation then I'd do the same as Bikerbill suggests. A freeflowing reg, while a pain in the arse, is still breathable and will get you close to the surface, if not all the way without having to do a massively fast ascent. Your within no deco limits, you can miss a fair old chunk of deco in an emergency if you're fit anyway, no skipper is going to begrudge you oxygen on the boat... at least your on the surface.
On the other hand if you have an alternate air source, it's a non-event. It happened to me a few months ago at 35m, switch off the freeflowing reg, switch to the other and after a minute or two turn the valve back on, chances are it won't freeflow when you do it. I once had a very entertaining 30min deco stop spent turning a cylinder valve on and off each time I took a breath as I'd knackered the 2nd stage.
The joys of a rebreather though... just switch the freeflowing diluent bottle off for a few minutes and continue the dive with whatever was in the loop and wonder what all the fuss was about :) I've done entire dives with the dil switched off for practice, it's just one of the many reasons I think rebreathers are safer in deep water.
Just a thought, but I know of at least one double fatality caused by a single cylinder diver's reg going into freeflow at 35m(ish). He started sharing with his buddy (also on a single), the extra load was enough for his reg to start freeflowing as well. Both divers died. If the conditions are cold enough to make your reg go then chances are your buddy's is close to doing it as well. Single cylinders, deep water and cold are not a good combo.
Cheers,
Stuart
Honest answer? In standard Scottish (low viz) conditions, if I couldn't see my buddy (or another diver) right away, I would assume a low likelihood of finding him/her in my increasing state of anxiety. I would ... STOP ... BREATH (sip air from the said unstoppable freeflow) ... THINK ... ACT ... and that action would be going for the surface as fast as poss without losing control and becoming positively buoyant ... something like Bill suggests: around 15+m per minute.
That's my honest answer without doing "the arithmetic".
alexmaclennan
05-12-06, 17:29
At 30m without a pony??
alex
for some reason i forgot my pony on a trip to anchor point last year. dived without it ... but kept a closer eye on my buddy than usual ...
novice divers often clock up a few ponyless dives ... or at least they used to ... i had been diving for nearly a year before I bought a pony ...
novice divers often clock up a few ponyless dives ... or at least they used to ... i had been diving for nearly a year before I bought a pony ...
I only got mine last Christmas - I had been qualified for 18 months by that time. There are so many other financial commitments in diving that ponies normally come down the line a bit. They probably shouldn't but I think generally they do.
On the other hand, gg got his pony a few months after qualifying as we were going to the Moray Fifth to do some deeper diving.
There's probably a good argument to say ponies should always be used, and we both do now in this country. It's pretty comforting to know that beyween the 2 of you, you have 6 second stages and 4 separate air supples.
When I was training, the club were not keen on trainees using ponies, presumably because it's another set of regs to get confused, and more equipment to contend with. Are Scotsac not thinking about recommending all divers carry separate air sources? Good plan I think.
as i said before, the question was aimed at a batch of master diver trainees.
the question was aimed at getting them thinking.
the real answer i was after was 'dive planning'.
the clues in the question were:-
You’re at 30 meters of seawater after 17 minutes of no stop diving;
why would you be here so close to deco if your not quallified to do deco?
You don’t have an alternate air source
pushing the limits too far on a single air source.
Your buddy is unaware of your problem.
why was he/she not close enough to know the situation?
if you had a dive plan & were contemplating being a master diver:-
you would have an alternate air source.
the mathimatical equations would have been done before hand.
you would have been diving alongside your buddy, not left behind.
most of you picked up on it in one way or another.
some provided good additional survival instincts.
well done.
Good scenario Stewart, I take it the MD trainees were not diving with a MD Instructor, anyway it got us thinking. As an aside, call me old school, but I / we who were qualified and experienced divers, dived 30M + with a single 10L or 12L with no problems whatsoever, no pony bottle either :D we did of course plan our diving and stuck to that plan regarding bottom time. In those day's we were taught the importance of the buddy system just in case of equipment failure. Maybe it is just me, but these day's I feel there is more of a reliance on equipment such as an alternate air source which, to me is taking second place to the buddy system.
Just remembered , we did have an alternative air source. On our Fenzy's and ABLJ's, in particular those fitted with a direct feed were the extra source and of course the Fenzy bottle which held a wopping 0.4L of air.
Just remembered , we did have an alternative air source. On our Fenzy's and ABLJ's, in particular those fitted with a direct feed were the extra source and of course the Fenzy bottle which held a wopping 0.4L of air.
Bill your showing your age here. You had beter explane what a Fenzy's and ABLJ is cause some of the readers here wont have seen one.
Easy......cry like a baby and hope youve made a will!!!!!!!!
Alternativly,if you can slow down the free flow,the it shoulld stop the freezing process and allow you to take some form of breath from the faulty reg.allowing you to make for the surface or attract your buddys attention.poor diving practice if your buddy doesnt see you,low viz means stick closer. My other suggestion was,depending on how calm you were,is to attempt to breath through your bcd,kink the reg hose and alternate between pumping a bit of air in and then suck it back out (tried it once when bored on a safety stop,kinda works)!!!!!
And if i was really smart,id thank god for my pony and start using it!!!!!!
We should all have some form of alternate air source, and i would be hesitant to dive with someone who doesnt have a pony or an octopus.
and hope youve made a will!!!!!!!!
I can assist in that regard - contact me on..............
Good scenario Stewart, I take it the MD trainees were not diving with a MD Instructor,
bill,
the question was thrown at them on a forum, much like this.
all our trainees doing master diver training are accompanied by master diver instructors.
perhaps people are more dependant on equipment these days, we have came a long way from ABLJ's in a short time.
who knows what diving will be like in years to come.
the rapid introduction of computers & electronics, will no doubt take control one day.
look at rebreathers & how they are advancing.
i personally try to be totally independant & self supportive, but i do dive in a buddy pair (well...perhaps 99% of the time;) ).
i try to put the least amount of reliance on my buddy i can, just knowing he/she is there is comforting enough.
should all else fail, i now know where to get a will :)
should all else fail, i now know where to get a will :)
If all else fails, it will be too late to get one.....!
Hi Stewart
I have been talking with Ding regarding rebreathers and I am getting tempted. What is putting me off is the price :eek: I could not justify that cost and after 30 odd years diving, should I be thinking about hanging up my fins :D
not sure if your asking me or lizardland this question?
i know Lizardland has an RB. i sadly dont http://cusac.org/phpbb2/images/smiles/cusac-cry.gif
thinking about it myself, the cost is an issue if you couple it with the course price & holiday to go with it.
my intentions are to do adv. trimix early next year, get some practice in the deep n scary on OC first.
then...who knows.
after 30 years of diving...your just starting :)
if your in any doubt, you might want to speak to Claire first
since bussiness is bad she has taking to touting on CA. http://cusac.org/phpbb2/images/smiles/cusac-tongue.gif
Lizardland
07-12-06, 21:33
Hi Stewart
I have been talking with Ding regarding rebreathers and I am getting tempted. What is putting me off is the price :eek: I could not justify that cost and after 30 odd years diving, should I be thinking about hanging up my fins :D
Depends on what diving you are doing. For normal 40m or less, air/nitrox diving then I wouldn't bother. It'll take a very long time to see any saving, for a lot of diving it'll actually work out more expensive. You can do everything a rebreather can do with a pair of 12's filled with nitrox that you can on a rebreather for a hell of a lot less. Weight isn't a saving either, twin 12's are about 26kg, my RB is about the same and you need to carry a bailout bottle as well.
They are definitely more dangerous than OC in <40m range too. It also adds pressure onto a buddy that isn't on a RB, air sharing is different, rescue is different, more things for him to watch you for.
For anyone considering trimix then I wouldn't bother doing OC mix. I think on deep dives rebreathers are far better than OC, the risks are more than outweighed by the advantages. As for cost then you'll make back your money on a rebreather after about 40 trimix dives.
For anyone whose normal diving is easily done on a twinset then a rebreather is a waste of money. For a diver who does most on a single set then a rebreather is a massive waste of money.
Cheers,
Stuart
alexmaclennan
08-12-06, 11:30
Stuart,
Sounds like a good summary of pros and cons of RBs.
Definitely a twinset for me
I guess that you could also say RB is good if getting air is a pain eg spending a week in the wilds of west coast scotland or for UW photography
alex
Lizardland
08-12-06, 11:52
I guess that you could also say RB is good if getting air is a pain
That's one of the main reasons I got one. I go diving in France a few times each year and really struggle for air, forget nitrox or trimix. In the past it has meant either taking enough cylinders for a week (which for two people is a lot) or taking a compressor (not ideal as I usually camp and most campsites aren't overly happy at a compressor running for a couple of hours a day). For a week's diving I can take the RB, a couple of 12's of air and another of oxygen to fill the rebreather tanks from and never need to visit a compressor.
Gas cost is the other big reason. I went on a trip last year, other divers spent £300 each in the week for gas, I spent £30.
Cheers,
Stuart
Yes Alex is a twin set just another rung in the ladder an expensive rung, why not miss a step and get a RB and save lots of cash. :D Tell she who must be obeyed buying the twin set, regs, wing etc will cost about £1500 and a RB is £5000 but you save so much on gas that it will pay for itself in a couple of years then you save money and can take her out more...
Lizardland
08-12-06, 13:09
buying the twin set, regs, wing etc will cost about £1500
Bloody hell... where do you shop? :D
I aimed this same question at a batch of new master diver trainees, the answers were interesting.
so, open to question here.
You’re at 30 meters of seawater after 17 minutes of no stop diving;
decompression commitments will begin at 18 minutes.(average tables)
Your regulator starts free flowing full pelt at 10 bar (average interstage pressure).
The water inside the demand valve starts to freeze stopping the valve from closing
You don’t have an alternate air source & you can’t see your buddy due to the bubbles.
Your buddy is unaware of your problem.
You have less than 2 minutes to decide on your answer, as this is how long it will take a full cylinder to empty.
Time starts now.
Brilliant scenario, I posted this on another forum to see what the reaction was, (I hope you dont mind). I'm still waiting for two same answers...
So, I guess I need a pony then..
Bloody hell... where do you shop? :D
The £1 shop, yes I know its cheap but Alex will price it and he will see a RB is not so expensive ;)
Brilliant scenario, I posted this on another forum to see what the reaction was, (I hope you dont mind). I'm still waiting for two same answers...
So, I guess I need a pony then..
i dont mind at all, where did you post it?
post the link so we can all take a peek at the answers.
if i knew you didnt have a pony i could have sold you one.
im in the process of selling one just now, but its not sold yet.
visual, august 2006 & o2 clean.
it's been lying around unused for a while as i have a 7 litre sidemount now.
as you live not 2 miles from me, i would be happier not posting it.
make me an offer by pm if your interested.
here's the link, watch out for flying handbags.......
http://www.divernet.com/forumvb/showthread.php?t=578
here's the link, watch out for flying handbags.......
http://www.divernet.com/forumvb/showthread.php?t=578
flying handbags indeed!
i could count on one hand how many of them i would consider to be a buddy.
most missed the obvious point & assumed they had 2 minutes of air to calculate their answer.
in actual fact, the scenario suggested they were already 17 minutes into the air usage.
most probably had less than a minute of air left giving the freeflow rate.
even less if they used a high performance regulator.
always think outside the box.
cheers for the pm.
stewart
here's the link, watch out for flying handbags.......
http://www.divernet.com/forumvb/showthread.php?t=578
Flying handbags, rattles thrown out the pram, you caused an international incident there
Keep up the good work....
Lizardland
10-12-06, 23:34
The £1 shop, yes I know its cheap but Alex will price it and he will see a RB is not so expensive ;)
£340 for complete 12's including bands and manifold, about £80 for a backplate and harness, £150 for a DiveRite Classic wing and you can pick up a pair of Apeks TX40's for £300. All that and enough left over for a curry and a couple of pints from £900 :)
Then the backplate and wing can be used for attaching a KISS to next year:D
"You’re at 30 meters of seawater"
"You don’t have an alternate air source", :eek:
I don't know what grade a "Master Diver" is but if you are diving in the UK and the above is true, then you are a fool and don't deserve to live imho!
My original tutor taught me well, redundancy is next to godliness(!) If your buddy is there to help you then that's nice but don't bet your life on it!! ;)
If you are in 30m of uk seawater then imho the *least* you should have is a 3l pony as redundant supply.
When people say "but it's expensive" I ask them to imagine being at 35m in the dark near the end of a dive when their set gets snagged on something behind them and their contents gauge is showing about 70bar, (far from impossible if you dive near wrecks in the uk I'd say!) they struggle to get untangled but it's not working and they can't see their buddy (viz is probably ruined by them struggling anyway), their gauge is now dropping below 50bar and they know they are breathing too hard. They know in a couple of minutes they will drown.
Now if I could magically appear there and offer to sell them a full pony/stage or whatever... how much would they be willing to give for it at that point? ;) £100 or die? £200? £1000? Your house and your car? What would *you* trade for an extra five or six minutes to get yourself free?
Suddenly a pony starts to look like a real bargain......! :p