Safety stop on Oxygen or Nitrox

[BlackDog8]

In light of the recent Rick Allen case (exploding Tank), I am wondering if anybody has compared the benefits of doing a safety stop (5 min at 15-20 ft) on 100% Oxygen or a 50% Nitrox mixture? If there isn't much of a difference, handling/filling a Nitrox tank would be preferable. I am looking at a 100-120ft dive on 30-32% Nitrox with a deep safety stop. Usually I go 2-3 minutes under my max bottom time.

Thanks in advance for any responses.

 

[Blackwood]

I doubt there is any data whatsoever about doing unnecessary (per the algorithm) stops on accelerated deco gas versus backgas.

 

[robertarak]

I doubt there is any data whatsoever about doing unnecessary (per the algorithm) stops on accelerated deco gas versus backgas.

What he said.

 

[kanonfodr]

One time a guy I was diving with finished his recreational-limits dive with 50% because he had to fly the next morning, then did the second, shallow dive on that gas as well.

Peace,
Greg

 

[rjack321]

I doubt there is any data whatsoever about doing unnecessary (per the algorithm) stops on accelerated deco gas versus backgas.

Not only that but 50% is actually more dangerous to deal with than just transfilling 100% O2 (because you have to top it off with gas that is even more likely to carry contaminants).

Just do 6+mins instead of 3min on a different gas. Maybe even spread that time across of few stops something like:
40-1
30-2
20-2
10-3

Would be as good or better than a short 3min stop on 100% where you blood as barely made one trip around your tissues before you're ascending. Also reduces the risk of inadvertently breathing a deco gas at the wrong depth and toxing to zero (since you never brought it).

 

[DevonDiver]

Stock answers:

If you want to accelerate decompression, do the appropriate technical diving course.

If you haven't done any technical training, then you shouldn't be doing mixed/multi-gas diving or using O2 >40%.

IMHO:

Using a nitox pony for ascent/safety stop is going to increase your nitrogen off-gassing. This could be done on a 2-gas computer or software dive planner/custom tables. The 'con' is that you'd still need the appropriate training to ensure the gas switch, MOD etc were done properly, or else it would be an unsafe proposition.

If it were for a safety stop, then you are below your NDL anyway, so the level of risk/benefit offered by (untrained) gas switching is not justified.

 

[String]

The chances of recreational DCS are so slim already there's unlikely to be any statistically measurable benefit to using a rich mix for 3 minutes.

And with 100% O2 id say the risk of someone screwing up their buoyancy and getting hurt (or switching at depth) is great than any potential benefit.

Risk/Benefit analysis for me comes out as "don't do it."

 

[fdog]

The way this is phrased

doing a safety stop (5 min at 15-20 ft) on 100% Oxygen

tells me you don't have the skills yet.

Not that using 100% after a recreational dive is a bad thing - we clean up with O2 routinely after recreational NDL dives, before driving from sea level over a 7000' mountain pass - but that's divers that understand the procedures and risks of what they are doing.

So, like everyone else said:

• Please don't do it
• Please take the appropriate classes

All the best, James

 

[Crowley]

In the context of recreational diving, the whole concept is meaningless. The safety stop allows for a reduced pressure gradient between gas in solution and the ambient pressure and therefore makes the "ascent" less risky in terms of susceptibility to decompression sickness.

There are clear benefits to decompressing on oxygen rich gas mixtures, and therefore there is a theoretical benefit to making a safety stop on a rich gas, but the benefit is a few minutes here and there on a surface interval. If somebody is pushing the limits of recreational diving so close to the bone that they require an O2 rich safety stop, they are no longer diving recreationally and should invest in tec courses.

Cheers

C.

 

[h90]

My guess would be:
If would like to have more safety in the safety stop: do it a couple minutes longer or add 2 min at 3 meter.
If want to reduce N2 in the body: Take an O2 emergency mask and sleep with it half an hour.
(there are some dive operators in Thailand which staff (non diver) is doing that if they have a terrible hangover.) (I always ask myself if someone needs the O2 is there real any left??)