Nitrox BCD Question

[redacted]

But the crotch strap is flammable nylon. You should fill your spare air with CO2.

 

[Scared Silly]

If only that were true. Agencies and shops seem to be fairly confused regarding equipment protocols for recreational nitrox, with lots of mention of 'nitrox clean' and 'nitrox regulators' and the various scenarios in which O2 clean is necessary for gear. You see statements floating around about the CGA (or some gas authority) recommending O2 protocols for anything over 23% O2, I have no idea if that's true, half-true, or outright fabrication, and each shop seems to their own ideas about what's 'correct.' Don't forget, the nitrox courses are typically taught by the very same people that are making up these rules at the shops.

Add that to the fact that at least two of the regulator manufacturers, atomic and scubapro, have released somewhat complicated legalese-esque policies about nitrox with titanium regulators. It's very easy to get confused.

Now, if in fact, as some polices imply, regulators 'should' be O2 cleaned for nitrox use, then in fact it would be appropriate to require the same of BC inflator valves hoses, and bladders. It's the same gas, and there's WAY more combustible material. How about drysuits? It's a slippery slope when you start talking about nitrox as being handled like pure O2.

The oddball thing is that exactly what constitutes "O2 clean" and how to maintain it is likewise not clear. Hence the reference to not being able to use 'regular' scuba air in a tank that's O2 clean. That's only true if the air is not modified grade E, i.e not filtered to the same standard as air used in partial pressure blending. And of course there's a great deal of trust involved; trust that every single fill on a given tank is truly up to clean standards, for example.

And yet, somehow thousands of nitrox dives take place world-wide every day and you don't hear about tanks exploding or BCs bursting into flames.

The reason I believe that the recreational dive industry is confused is because they are simply that recreational. Most of the standards in place were done for commercial diving. For instance, I recently did some research to find out where the 40% rule came from. From what I can find it has to with caisson workers and that the maximum O2 percent they used was 40%. But that those rules applied to the gas delivery systems not the cylinders which held the gas that are used.

Now if ones looks at the gas cylinders DOT CFRs which reference some but not all of CGA rules said that because the gas is under high pressure that above 23.5% that the cylinders needed to be specially cleaned.

So now there is the conflict the regulators which handle the high pressure are okay to 40% but not the cylinders? For the commercial dive industry the conflict is not a big deal as they are fewer in numbers and have bigger fish to fry. I am also willing to bet that the commercial dive industry creates the vast majority of their gas mixes via partial pressure blending so conforming to the rules is easier.

But for the recreational diving industry which has lots of dive shacks it is a problem. Right next to maintaining a swimming pool, compressors are probably the biggest loss leaders for a dive shop. But they have to have them. Shops want to offer NITROX to attract customers so they bank NITROX like they bank air using the same compressor. Some will maintain a mod grade E filter stack on their compressor while others will not. There lies the problem. When non Mod Grade E gas is introduced into a cylinder/regulator it is now contaminated. By how much is the issue. But the gas was under 40% O2 so no worries. Sort of until a PP fill is done.

Maintaining O2 clean equipment is easy - do not put any gas through it that is not at least Mod Grade E gas.

As to the OP's original question, the issue high O2 percentages and combustion is more relevant at high pressures. The pressure of the gas coming out of a first stage is typically under 150 psi. As such, it is not of concern.

 

[halocline]

But the crotch strap is flammable nylon. You should fill your spare air with CO2.

I prefer viton crotch straps. Fire resistant and sexy.

 

[ams511]

I prefer viton crotch straps. Fire resistant and sexy.

Just go commando!

 

[KD8NPB]

There is one special consideration : When using Nitrox with a drysuit, DO NOT USE HANDWARMERS. They are activated by oxygen. Additional O2 content will make them burn SCORCHING hot.

 

[Zung]

I guess you need nitrox-certified underwear as well.

 

[NAM001]

use the same reg for air and nitrox. the air, however, should be hyperfiltered so you have no problem in contamination from less than grade e air contamination. grade c and d can be soem bad stuff. the hyperfiltered air is what is used when mixing nitrox. The sticker on the tank should tell the monkeys that no less than hyperfiltered air is to be used whether it is in nitrox blending of not. In reality non hyperfiltered certified systems are ok but there is less room for compressor and filter degradation in air quality. That increased margin of degradation is is provided by the the hyperfilter standard. This issue has always been a hot item of discussion between those who understand the process and those raised on the hype to the point of (and there are those that are out there) say the tank should be o2 cleaned prior to each gas fill.

---------- Post added March 5th, 2013 at 02:51 PM ----------

o2 and methane, cool
let me gat my cam

I guess you need nitrox-certified underwear as well.