DumpsterDiver emergency ascent from 180'

[beaverdivers]

I knew there were reasons that I always dive with a pony.

Thanks, for the post.

 

[tbone1004]

@elbig yes this is a unique concern to diaphragms however pistons have their own issues and isn't something that concerns me enough to switch to pistons

@2airishuman how can you say that carrying 2x the amount of reserve gas is of marginal safety benefit?

 

[CuzzA]

No, he just frequently posts about his extremely aggressive dive practices, he's been doing it for years. If that's not 'advocating' I don't know what is.

If an unknown diver posted half the crap that he has, he would get skewered on this board. It's not much different than a kid posting a video of his speedometer at 120 on facebook.

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.

Which I assume is why very early in this thread many pointed out DD's experience. I imagine that with 10 average divers and that incident occurring, even within recreational depths of 130 ft., at least half would not survive.

As far as his threads... well, he's not here and able to defend himself so it's not something I want to engage in.

 

[Basking Ridge Diver]

Physical limitations.

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

 

[2airishuman]

@2airishuman how can you say that carrying 2x the amount of reserve gas is of marginal safety benefit?

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.

 

[wheeledgoat]

Also, consider why your 4 wheeled vehicle typically only has 1 spare tire.

 

[victorzamora]

Also, consider why your 4 wheeled vehicle typically only has 1 spare tire.

Mfgs are cheap???

....but a blanket recommendation of an AL40 is just plain old tech bleedover and excessive conservatism.

I would tend to agree, but the ease of slinging an AL40, its buoyancy characteristics, and the amount of gas....I think an AL40 makes tons of sense. Having seen people struggle to cleanly mount and carry everything from an AL9 to an AL19 makes me want to stay away from those. I've tried them and I can't get a good clean mounting method for them. AL30s float like crap.

Taking into consideration more than just gas volume, my de-facto tank is an AL40.

 

[CuzzA]

I would tend to agree, but the ease of slinging an AL40, its buoyancy characteristics, and the amount of gas....I think an AL40 makes tons of sense. Having seen people struggle to cleanly mount and carry everything from an AL9 to an AL19 makes me want to stay away from those. I've tried them and I can't get a good clean mounting method for them. AL30s float like crap.

Taking into consideration more than just gas volume, my de-facto tank is an AL40.

It's definitely personal preference and dive plan dependent, though I think one should also consider if it's too big, a pain in the ass, etc., then those items tend to stay home or are left on the boat.

 

[wheeledgoat]

Mfgs are cheap???

Actually, I was thinking "practicality" (I mean, where you gonna put 4 wheels in a sedan?)

But you might be closer to the truth than you realize! When we were car shopping earlier this year, Jeep dealer told us some models didn't come with a spare !?!?! BECAUSE: of the MPG savings!

(manufacturer model year fleets have to hit a certain MPG average, across all cars, else pay a penalty)

anyway, back to the regularly scheduled programming...

 

[uncfnp]

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

I can honestly say that I have not.