DumpsterDiver emergency ascent from 180'

[tbone1004]

@2airishuman
on some of the arguments for redundancy and how much is practical to carry you are correct. That is why we don't dive to quarters in most caves and don't reserve stupid amounts of backgas when diving in open water.

The difference of slinging an al13 vs an al40 is pretty simple. no matter how you spin it, an al40 is actually easier to carry. It's less negative when full, only an inch larger in diameter which means reg and valve clearance is usually less of an issue, and because of the extra length, it's easier to sling and handle in the water.

When you do safe and sound math using rock bottom which allows 1 minute at depth, and no safety stop, but very slow ascent. You need an AL40 to make a safe ascent from 130ft factoring a 1.0cfm SAC rate which is safe average considering it may well be higher during the minute allotted to situation resolution but lower during the shallower portion of the ascent

Now, to use your comparison of a good thought out reasoning.
I have no reason to use smaller cylinders because the AL40 handles better in the water from a buoyancy standpoint and the smaller cylinders are not small enough to be able to justify carrying.
An al80 however provides twice the amount of gas, but is significantly more cumbersome to carry due to the size, but it is also more negative when full. These two factors go against the added safety and practicality of carrying such a large cylinder.
We agree there. Where we disagree is that in recreational diving where a dive plan that only calls for say a LP95 wouldn't be safer if conducted with a LP108 to get the extra gas for no reduction in safety.

If you believe that you can dive with a smaller cylinder than an al40 when diving to 130ft you are accounting for one of two things.
Lower SAC rate. If you KNOW for a fact, without a doubt, that you will be able to maintain a SAC rate below 1.0cfm regardless of whatever situation could ever cause you to have to utilize that bottle
Faster ascent rate. If you believe that you don't need any time at the bottom, if you believe that an ascent rate faster than 30fpm is prudent to half depth and faster than 10fpm to surface is prudent, if you believe that no safety stop is required, then calculate that way. It's your math, your safety buffer, not mine.

I think 10fpm is too slow and I don't like not having a safety stop. When I do my personal ascent gas requirements I do 3 minutes at bottom, 30fpm ascent to surface, and 3 minute safety stop. For me that gives basically the same amount of gas that the DiveNerd calculator spits out and theirs is usually more conservative. For this example they say 34, I get 32.3, close enough so I just use their numbers.

What math do they use that you don't agree with that says that a smaller tank is better/safer to take than an al40?

 

[stuartv]

Well, I think there's a little bit of difference between a kid posting a video of his speedometer at 120, than say an experienced race car driver posting a video of his speedometer at 120.

I agree. But, I would say that an experienced race car driver posting a video of his speedometer at 120 on public roads is actually worse.

Who is more likely to engender others to mimic them? Someone who is seen as "experienced and knows what he is doing"? Or someone who is seen as "a young idiot"?

People get hurt trying to do what they see their "betters" doing. I've seen it a hundred times among motorcycle riders. "He got his knee down going around that corner. I have the same bike and tires. Therefore, I know the bike can do it. So, I can do it too."

"He knows what he's doing. He's been to 180' on a single tank many times and he's fine. Therefore, I know it's totally doable. So, I can do that, too."

 

[KevinNM]

But I was not aware any agency required it as part of recreational training, except maybe GUE.

It's required for a Rec fundamentals pass that you can reach it and rotate it on. No single tank shutdowns are required, taught or suggested.

 

[Russoft]

IP creep due to HP seat failure caused the diaphragm to unseat which resulted in pressurized air entering the ambient chamber. Once pressurized, the silicone environmental seal extruded *he'll have a donut inside the cap and somewhere in the ocean is the plug that extruded out* which resulted in HP air going directly through the first stage.
Not something caused by a 1+yr old o-ring, bad HP seat and likely had IP creep prior to the dive which proper pre-dive checks would have identified *use your IP gauge folks!*

Note, this is the exact situation that happened on my HOG D1's during my first ever cave dive in training. You will be able to use the LP side of the regulator because the whole thing is pressurized, but not for long as you have lots of air going straight out the end of the regulator

This explanation was why I came here. Thanks!
(I bought myself an IP gauge ages ago but subsequently forgot how to use it to diagnose regulator problems.)

 

[tbone1004]

 

[lermontov]

Well, let's do a thought experiment for an open circuit, open water dive, within recreational limits.

If you had, say, an HP120 of reserve gas, you would have enough gas to deal with any emergency where having more gas would help. There would be no additional benefit of instead having, say, two HP120s of reserve gas, because there aren't any plausible accident scenarios that are survivable on two HP120s but not survivable on just one.

This would also be true comparing one HP100 of reserve gas to two HP100s of reserve gas, again, there aren't any plausible accident scenarios where the second HP100 will help.

As we work our way to smaller cylinders, we can come up with some plausible but extremely low probability scenarios, like being silted out and inadvertently ending up lost in a cave that adjoins an open water area, where having a good deal more air really does help. These situations are rare. Basic OOA emergencies caused by equipment failure are not rare, but can be resolved by making an immediate ascent. If the reserve gas supply is sufficient to allow an emergency ascent, most of the safety benefit of having a reserve is obtained. The rare situations that might benefit from an oversize reserve gas supply lead to only a marginal improvement in safety when an oversize supply is used.

The balance point is when the reserve gas supply system becomes large enough to pose additional practical difficulties of one kind or another that lead to decisions being made to dive without it. I believe that the best practice is to encourage the use of reasonably sized pony cylinders that allow a safe, immediate ascent to the surface based on actual gas planning using the intended depth and SAC rate (and a reasonable multiplier for stress). For most recreational divers this will be an AL13 or AL19. Some divers may need something larger on some dives, but a blanket recommendation of an AL40 is just plain old tech bleedover and excessive conservatism.

so what happens if the gas loss had happened at 10 or 12 minute mark when he had clocked 8 or more minutes of deco

 

[Akimbo]

Consider inverted tank(s)? Much easier on the joints and muscles...

I can honestly say that I have not.

It works for me.

I have become fond of those double Faber 45s/50s.

 

[DIY]

Anyone know which wreck he was at?

 

[CuzzA]

I agree. But, I would say that an experienced race car driver posting a video of his speedometer at 120 on public roads is actually worse.

Who is more likely to engender others to mimic them? Someone who is seen as "experienced and knows what he is doing"? Or someone who is seen as "a young idiot"?

People get hurt trying to do what they see their "betters" doing. I've seen it a hundred times among motorcycle riders. "He got his knee down going around that corner. I have the same bike and tires. Therefore, I know the bike can do it. So, I can do it too."

"He knows what he's doing. He's been to 180' on a single tank many times and he's fine. Therefore, I know it's totally doable. So, I can do that, too."

Fair argument... though if you consider just about every diver has been taught to not exceed their training and so if you've been doing 60 ft reef dives for the past year and wake up one day and say. "Today I'm going to dive a wreck in 180 ft." Well, Darwin finds a way, right?

Your example could be said about every extreme sport video on YouTube where the experts make it look so easy. And maybe that's true... Those videos lead to more deaths and injuries by people trying to duplicate those actions... and maybe people should exercise some common sense.

I know I sound like I'm defending him, but in reality, he didn't post the thread here and can't defend himself so I'm playing a little devil's advocate.

 

[StefinSB]

@uncfnp
Why are you unable to do a valve shutdown? We require all of our students to perform this in the pool and use their ability to reach the tank valve as the height requirement for their rig. No exceptions. It is easier than reaching the isolator in doubles

No it isn't. I have no problem whatsoever reaching both valves and isolator wearing my doubles but can't easily get to the valve using a single cylinder ......