DumpsterDiver emergency ascent from 180'

[tomfcrist]

Is there any difference between a Y and an H valve other than the shape? I mean, don't they work the same way?

I'm no expert, but it just seems to me that the value of a Y or H valve is really for people diving single tank in really cold water. In really cold water, you are more likely to get a 1st stage to freeze up and free flow. In that case, shutting down that side and breathing off the other side is a good capability to have.

H valves have additional failure points, and a common gas path. All the y valves I have ever had were separate gas paths(2 dip tubes).

The point of an h or y valve is indeed to combat the risk of first stage failure. To assume a freeze up is any different than an HP seat/diaphragm failure as it applies to risk management is silly. The fact is that first stages do fail...how is irrelevant.

 

[joe10540]

I need to repeat again that it is possible (and and shows good judgement) to make actual contingency plans for dives to this depth, or to any depth for that matter.

On the surface of it, saying, "any advantage is an advantage even if it's a small advantage" sounds axiomatic but there are better ways of going about this. Contingency planning does not need to be an intuitive process. What DD does isn't turning a small advantage into a win, as I mentioned before. His approach is "Jesus take the wheel" and he worms out of it using skills (which he does have) instead of judgement (which he does not).

Once again, I would like to point out to the less experienced people following this thread that the approach to safety of the diver in the video is haphazard, complacent and dangerous. If you want to learn more about contingency planning then ask the question in a new thread and we'll try to jump in.

R..

I won't disagree with you on the planning aspect of it. A baby pony bottle isn't redundancy and should have probably been a 40 if not manifolded doubles but there is something to be said about being able to isolate a blown first stage and still access the remaining gas in the tank.

 

[tbone1004]

If it even saved 700psi wouldn't that have been enough to get back to the surface or make that pony bottle last long enough for a proper safety stop? It might be pointless at the end of a dive that blows a seat but what if it just creeped up and started to freeflow? Any advantage is an advantage even if it's a small advantage.

if you are planning on a redundant air supply, you have to assume that there is 0 breathable gas and that you have to rely 100% on your contingency plan from maximum point of "penetration" which in OW is max depth, any situation resolution, and any stops until you get to the next bottle. Anything you get out of the remaining gas is great, but have to assume that something like the burst disc or neck o-ring failed and you have 0 breathable gas.

 

[CuzzA]

Or, possibly, inject some gas in his BCD, to get a little positive and start his ascent, and then shut it down.

That's what he did. He said he didn't want to kick up and use oxygen/retain co2. When he got to 70 ft. he arrested his ascent, switched to his pony, shut down the main, shot a bag and then noticed mono caught on the bag and aborted his safety stop.

 

[Diver0001]

Back to the actual discussion of DD's incident, my earlier post started me thinking.

Wouldn't it have been smarter for DD to shut down his tank valve immediately, rather than continuing to breathe it until it ran out? Or, possibly, inject some gas in his BCD, to get a little positive and start his ascent, and then shut it down. Either way (it's only maybe 2 seconds difference), the point being not to leave it open until it ran out.

You're talking about feathering the broken valve. If it were a stage bottle then you could get at it easily. In a singles configuration feathering the valve is very tiring and usually takes both hands. I don't know if you've ever tried it but I did during my technical training and my arm was seized up to the point of not having the strength to turn the handle before long. Don't forget that you can't just open the valve a little bit at that depth and expect to get enough air. At that depth feathering would require turning hard and fast on the valve in both directions for each breath in order to compensate for the effects of ambient pressure. You can't just crack it open and breathe like you would, for example, in a swimming pool. The pressure makes that impossible at those depths. If he were shallow it might have been an option.

In addition to that he had the complication of having his hands full with his anti-shark stick. He would have had to ditch some gear before even thinking feathering the valve and all that is going to take time. We don't know how the gear was attached to his arm but we do know that he was very deep. I don't know if you dive air much at those depths but I still occasionally do and believe me, even getting a lanyard off your wrist and ditching your shark stick while trying to formulate a plan for feathering while engulfed in a sea of bubbles isn't going to happen with much tempo or any kind of grace.

As for the BCD, he did add air to it. that's partly why the ascent was so fast in the first phase.

In that same situation (not that I would put myself in that situation because I usually dive at those depths with very different gear) I'm pretty sure I would have done exactly what he did. Breathe the back gas as long as it lasted and GTFO of dodge, which when you get right down to it, is the approach being shown here. Getting shallow quickly isn't only going to save gas, it's going to clear your head. Both things are important in a situation like this.

Those instincts to get shallow quickly and use whatever gas is still available before switching to the redundant back up are the right instincts, if you ask me. The fact that he should have been using proper gear and he wasn't doesn't take away from the fact that, given the situation, the actions taken were the right ones, in my opinion.

R..

 

[Diver0001]

I won't disagree with you on the planning aspect of it. A baby pony bottle isn't redundancy and should have probably been a 40 if not manifolded doubles but there is something to be said about being able to isolate a blown first stage and still access the remaining gas in the tank.

Hi Joe. I don't want to be hard on you but you're still looking at this intuitively. I want to help you understand the thinking involved here....

How do you know he needed a 40 as bailout? How do you know that manifolded doubles are the right gear solution? How big are those doubles? You can twin up 35cf tanks... Is a manifolded twin set of 35's good enough for this dive? Is a manifolded twin set of 35's with a bailout of a single 40 enough?

... or maybe he needs a twinset of 100cf tanks and a bailout of 80? .... who knows, right?

What I want to get you to understand here is that reaching for a solution before you have certain facts isn't the right order of thinking. You are absolutely right to be thinking in terms of solutions and alternatives but you need more information.

- What is the diver's air consumption? In my case with a full tech set on and swimming (no scooter) I use about 12l/m (I think that's a SAC of 0.4 or something in your measurements). If your SAC is higher or lower than that maybe you could use bigger or smaller tanks.

- How long are you planning on staying? If the run-time of dive, including deco is an hour than it's going to need different gear than if the dive takes 90 minutes.

(fast forwarding)
- Which gasses are you using?
- Do you have a buddy? Maybe you have 2 buddies?
- What kind of reserve does your buddy (or buddies) have?
- What gasses does your buddy have available?
- Do we want to calculate that into the contingency plan?

(and then)
- what risks are we running? Could we get lost or delayed, perhaps significantly?
- what happens if we lose our back gas and we have a buddy? or if we are alone?
- what is the chance of losing our buddy and having to finish the dive solo?
- what happens if we lose our deco gas? Do we finish using back gas or do we air-share with a buddy?
- do we do that in parallel or do we do it one after the other?

etc. etc. etc. I'm not giving you a check list here, just lifting the skirt on how to think about creating the parameters for a contingency plan.

The actual contingency plan then consists of

1) which scenarios (failures) are we planning for?
2) what is the effect of those scenarios?
3) what gear solution (size and number of tanks, gasses, procedures etc) would allow us to account for the failures we are planning for?

See what I did there? I made it into a process that involves logic and facts. I'm not trying to cover everything about this in one post, however, so don't trip over details. The point I'm trying to make is that there are ways to think about this that will allow you to make fact based decisions about risk mitigation.

You will see things like this in your technical training but depending on the type of work you do for a living you may have seen similar things at your work. The ideas are not specific to diving. Risk mitigation is common to many vocations, from fire-fighter to project manager to contractor building and airplane runway. One thing that all of it has in common is that there is (a) a process of structured thinking involved and (b) as much as possible facts are used to support the logic.

So let's make it concrete.

Suppose that the parameters of the dive are this:

- I am solo
- my SAC is 12l/m
- I intend to stay within the NDL's
- I intend to visit 55m and ascend/descend with 10m/min
- I can manage a single catastrophic failure without my SAC being significantly affected
- I intend to use the rule of 3rds because of being solo.
- Reserve for my bailout is 25%
- I intend to ascend and descend at 10m/min

So... Let's do some calculations:

- I think (without looking it up) that the NDL at 55m is 5 minutes. In any case I would be willing to stay 5 min because any deco obligation I incur will clear on the ascent. At this depth (6.5ATA) I use 78 (let's call it 80) liters per min of gas. In 5 min that's 400 liters. Let's remember that number.

- descent and ascent will take 15 min (6 down, 9 up). To keep things conservative, let's work with 6.5ata for that as well and we get 1170 liters for travel.

- we want a 1/3 reserve, so (400+1170) (the gas we used) divided by 0.66 (the 1/3 reserve) and we need 2355 (let's call that 2400 to be conservative) liters of gas for the main part of the dive assuming EVERYTHING goes according to clock work. Safety stop etc. should fit in the slack because we're working with conservative numbers.

What's 2400 liters? that's a 12l tank. So an AL80 (10 liter) is too small but a 12l would be enough to make this dive *IF* everything goes according to clockwork.

Ok, so let's decide to do the dive using a 12 liter tank. This is a single tank, which means it has one major malfunction. This is that there is a single point of failure, namely the 1st stage of the regulator. We need to account for the risk of a first stage failure.

Let's assume that the failure happens at the worst possible moment. ie.... we are at 55m and we need to make a 9 minute ascent. To make things easy let's assume we need to switch to bail-out at 55m and do the entire ascent on bail out.

We said taht we want a 25% reserve on bail out but if something bad happens at 55m I'm going to assume a couple of things:
a) that my SAC goes up from 12l/m to 18l/m (not unrealistic)
b) that it takes 1 min to swtich to the backup, making the ascent 10 min instead of 9
c) that nothing else goes wrong
d) that all of my back gas is unavailable from the moment that the failure occurs.

To make it easy, let's assume that the average depth of the ascent is 1/2 of the maximum depth, or 27.5 meters. let's call it 28. The ascent takes 10 min and our sac is now 18l/m. That means <clicking> that we need 855 liters of air to bail out, including the reserve of 25%. Let's call that 900 liters. The smallest bail out tank we could use (if full is 200 bar) is, therefore 4 liters. 5 litre tanks are common, so let's use that as a bailout.

So the MINIMUM gear we would need to safely make a bounce to 55m within the NDL is a 12 litre with a 5 litre bailout. This gives us very little margin for error and ZERO margin for error in the case we go over the NDL, even by a little bit.

So to add an additional safety buffer to that, you might want to go with a 15 litre main tank and a 7 litre bailout. The gear isn't that much more bulky than what we calculated but it would make everything nice and comfortable even if something unexpected happens that you didn't plan for.

A 15l tank is a 104cf and a 7 litre bailout is a 50cf tank.... so in your measurements I'm saying that you probably would be comfortable on this dive with a 104cf main tank and 50cf bailout. As an absolute minimum you should be looking at a 100cf main tank and a 35cf bailout. Those are the parameters you can use with confidence.

Looking at the video, the diver is presumably using an AL80 (too small) and a 20cf bailout (too small). We now have calculations to back up that opinion and we have calculations to back up our choice of a 104/50 configuration assuming we stay within the NDL's

Does any of this make sense? Do you see how I'm thinking about this?

R..

 

[HantsDiver]

Looking at the video, the diver is presumably using an AL80 (too small) and a 20cf bailout (too small). We now have calculations to back up that opinion and we have calculations to back up our choice of a 104/50 configuration assuming we stay within the NDL's

If he was diving with a buddy would it be acceptable for him to share the reserve with another diver? So in that case if both he and his buddy had 20cf ponies would that be enough as the total would be then 40cf?

 

[2airishuman]

Is there any difference between a Y and an H valve other than the shape? I mean, don't they work the same way?

I was once, briefly, a true believer in H valves, and thought it would be wise to set up my singles with H valves, so I could use the same regulator configuration on singles and doubles.

It was, well, a disaster, and so I sold my H adapters and now have a singles reg and a doubles reg set.

I think that a Y valve would have worked out much better. A good deal of the problem is that an H valve extends beyond the diameter of the cylinders I have (7.25") making it susceptible to damage during ordinary handling topside. Part of the problem also is that the H adapter outlet is low on the cylinder, and for my preferred placement of the cylinder in the cambands, places the reg in the H adapter in an awkward spot. It interferes with the wing and leads to poor hose routing. In my situation I was trying to use left and right modular valves so some of the H adapters were mirror images of others, which made matters worse, because there was no one hose length that would be ideal for all of them.

I've never dived a Y valve but I believe that they do not have these drawbacks. There do exist Y valves with two separate air paths to the cylinder, including two separate dip tubes, but they are no longer in production and very difficult to find used.

I'm no expert, but it just seems to me that the value of a Y or H valve is really for people diving single tank in really cold water. In really cold water, you are more likely to get a 1st stage to freeze up and free flow. In that case, shutting down that side and breathing off the other side is a good capability to have.

Despite having made a number of cold water dives, I have never experienced a freeflow due to 1st stage freezeup. Nonetheless, my preferred configuration in cold water is a twinset of suitable size, and I have twin 72s and twin 100s which I tend to use on dives of this nature.

But, in warmer water, the 1st stage isn't going to freeze. So, the Y/H is just insurance against the exact kind of problem that DD had - i.e. blowing a HP seat. In that case, a Y/H valve just seems like a bit of gear to instill false confidence. If you blow a HP seat and you're diving a single tank, by the time you get the valve shut down, depending on where you are in your dive, you could easily have lost enough gas to be below your appropriate minimum reserve. So, it just seems like if you're doing a dive in warm water and you think you might need the redundancy afforded by a Y/H valve, it probably really means that you need the full-on redundancy of double tanks.

The only benefit of doubles in this situation is, possibly, greater total gas capacity. Either way you have to be prepared to shut down a freeflowing post quickly. The only real redundancy benefit of doubles is that you have a degree of protection against failure of the burst disc or neck o-ring.

That is somewhat based on THINKING that a blown HP seat will dump gas faster than a frozen/freeflowing 1st stage would. I could be totally wrong on that, though.

Either way, you're flowing gas as fast as the HP orifice in the 1st stage will permit. I doubt if there is a difference. That said, you'll lose all your gas in a matter of minutes. If you respond in a matter of seconds, you'll end up ok.

 

[tomfcrist]

The only benefit of doubles in this situation is, possibly, greater total gas capacity. Either way you have to be prepared to shut down a freeflowing post quickly. The only real redundancy benefit of doubles is that you have a degree of protection against failure of the burst disc or neck o-ring.

Really? How about shutting down the free flowing post and still having access to all of the gas not lost in a free flow?

In this situation, manifolded isolatable doubles would have been a much better option than losing ALL of his backgas. Even with tiny doubles(45's) he would have had a huge redundancy advantage.

 

[2airishuman]

Looking at the video, the diver is presumably using an AL80 (too small) and a 20cf bailout (too small).

I doubt very much if that is an AL80. DD in the past had held forth on the value, from both a safety and practicality standpoint, of larger cylinders. I am uncertain what he now dives routinely but would imagine it is a larger steel, perhaps an HP100 or HP120 or LP105.