Catalina U/W park dive report.

[drbill]

;-) is a wink-wink and a smile

VBG = Very Big Grin

The first I knew, it was the second I didn't. Thanks. Remember, my college classmate Al Gore hadn't even invented the Internet before we graduated!

Your suggestion re: Nitrox for my diving is a reasonable one, and I will be investigating it. However lately I've been diving too deep to do Nitrox without dying. For my diving in the Park it would make very good sense.

Perhaps the adoption of the most conservative "rule" by some shops is just to "ensure" that there is no grey area should a shop be claimed liable for a problem. Dealing with deceptive practices by tank owners, this might limit them to a higher degree (or might not).

Here on Catalina divers have the option of filling Nitrox at SCUBA Luv, or air at the Dive Park or Pier. It's not a big town and not hard to carry tanks from the Park to the appropriate shop if need be. I carry all my gear on a hand cart and I live up a steep hill. If a diver can't get what they want at the Park, it isn't difficult to bring the tank into town for the proper fill.

 

[scjoe]

I do not know how the standards were arrived at, but my guess is that they were either able to create a fire in a lab setting or by computer model simulation. I assume the fires were created at various settings (some more easily than others) and then judgments were made about what % of O2 was acceptable before a tank had to be O2 cleaned. I would guess that the tests were not done with a membrane system, but I don't know and many of the fills out in the real world are not done with membrane systems. Before I assume that the standards do not apply to membrane fills, I would want to hear something official from one of the gas associations.

With all due respect, long time blenders known to any one individual do not have the breadth of experience that exists with multiple trade groups and agencies in multiple countries that deal with pressurized gas issues beyond the very small world of diving. These blenders are assessing the risk based on what has not happened, not what could happen. They have no way of running the type of tests that the agencies or trade groups do. It is sort of like thinking the levy won't break because it hasn't before or that pouring the lighter fluid on the charcoal fire is not going to cause an explosion because you have been starting the fire that way your whole life.

Rember anything that can go wrong ultimately will go wrong.

 

[Frank O]

This in from DAN ....

http://diversalertnetwork.org/news/article.asp?newsid=75

DAN Workshop Presents Recommendations for Nitrox Diving

The DAN Nitrox Workshop, hosted by Divers Alert Network and chaired by DAN Board Member Michael Lang, was held Nov. 3-4, 2000, in Durham, NC. The purpose of the workshop sought to clarify nitrox diving in the year 2000 and to reach a consensus among dive industry professionals regarding the recreational use of Enriched Air Nitrox.

... no evidence was presented to show an unreasonable risk of fire or ignition when using up to 40% nitrox with standard scuba equipment.

 

[scjoe]

Obviously there is a disagreement between DAN and the dive industry on one hand and the compressed gas industry on the other as to what is a safe O2 % as far as fires go. Each has its own agenda. One wants to encourage the use of Nitrox, the other wants to reduce its risk of liability for accidents. I assume Luxfer believes it is more likely to get sued if one of its tanks catches fire than DAN or PADI, etc. Also, Luxfer and its industry group are looking at this issue from a perspective that is beyond that of just diving.

The problem is the consuming public does not have very much information on how either group arrived at its recommendations. The DAN conference report may be based purely on experience and the Compressed Gas Association may have created a fire at 23.6% under pressure way in excess of the norm. One problem I have with the report is the way it is worded. "No evidence was presented to show .." is not the same as saying they concluded that up to 40% does not present an unreasonable risk of fire.

At present, divers and dive shops are free to place their own intepretations on the 23.5% to 40% rules. It may stay that way for a long time. However, those that choose to follow the 40% rule are clearly assuming some greater risk (albeit perhaps very small) than the 23.5% group, unless you believe that positions cited by Luxfer are all irrational.

I don't have any problem with people coming to different conclusions based on the available information. I do have a problem with certain people claiming that those who choose to follow the 23.5% rule are doing so because they are "uneducated." The correct word is "conservative."

Luxfer has explained that the 40% rule comes from one OSHA reg that was applicable only to commercial diving, not recreational diving, and that no other trade group or governmental agency, including the US Navy subscribes to that rule. Commercial divers have a lot of safety systems (including fire suppression) and other surface support in place that rec and tech divers do not.

The DAN conference report was in 2000 before Luxfer put forth its position and, I believe, before the Navy changed its position. I do not know when the other agencies or countries cited by Luxfer chose their positions. Since most divers look to DAN or their certifying agency for guidance in this area and are unlikely to seek out the position of manufacturers, trade groups or government agencies. I think it is incumbent upon DAN and the various certification agencies to address head on the different standards and explain how they arrived at the 40% standard and why they believe the Luxfer 23.5% standard is overly conservative. It would be extremely useful to know what tests were conducted by each group before it decided on its standard.

Perhaps those members of the board that are affiliated with DAN or the training agencies could raise this issue directly with them. Does anyone know what prompted the Navy to change its position?

 

[Frank O]

It would be extremely useful to know what tests were conducted by each group before it decided on its standard.

Yes, I think until we have some new hard data here, we're just sort of treading water with this discussion. Although my own experience is that nitrox under 40% is perfectly safe when used with non-O2-clean tanks and regs, I'm very open to revising my thinking if anyone can point to any incidents that have occurred in that scenario. All of the accidents I've heard of involved the handling of high-O2-content (> 40%) mixes.

So -- over and out for me until some crunchy facts come along ...

 

[LAJim]

I'll put on my chemist hat for a minute (actually its been on all day). When my 3442 HP steel tank is full of 21% O2 it has a pO2 of 49 atm. If one of my students wanted to fill an oily metal cylinder in the lab to 49 atm of pure oxygen I would tell them to stop and clean out all of the organic matter first. If they wanted to fill it to 94 atm. pure oxygen I would say that was only slightly more crazy. Of course 94 atm. is the pO2 of 40% Nitrox at 3442. To my mind these are both dangerous - almost equally so.

I can't find ANY standard on what pressure of oxygen is safe with oily deposits. Organic matter with high pressure oxygen is dangerous. Its certainly true that 40% O2 at 3442 is a little bit more dangerous than 21% O2 at the same pressure, but to my thinking (about 200 research papers in chemistry journals including a lot of cover articles, etc.) both are far more dangerous than I would tolerate in my lab.

As has been pointed out it takes fuel, oxidant and a spark to start a fire. If a scuba tank has a bunch of oil in it, it is full of HP air or nitrox, and a spark is somehow struck, the organic matter will immediately and fully combust to CO2 and water with a predictable heat release leading to an equally predictable pressure pulse. We call this an oxygen bomb calorimeter - a useful device to measure heats of combustion of a gram or two of some organic matter. Its about the size of a small pony bottle and its pressurized to 30 atm pure oxygen. Probably not a good idea to try it with ten or twenty grams of organic matter.

So oil in your tank is dangerous - period. Why do people focus on nitrox? I found a lot of non-specific warnings about oil or lubricant on the HP side of oxygen regulators and a lot of things about lubrication in breathing O2 supplies. Sensible advice, but a pure oxygen tank 21% full is the same as an air tank 100% full. The nitrogen does nothing.

So, I'm going to conclude that the real problem is oil in the tank - and its about equally unsafe for any O2 concentration of 21% or higher at high pressure. Keep oil out of your tank. As in a handful of oil. That would be very dangerous and could explode. Probably would hurt your lungs too.

Jim

 

[cool_hardware52]

Thanks Jim.

It makes sense. It seems odd and abitrary to me that 20.9% O2 is deemed safe, and 23.5% is deemed as dangerous as 100% O2. That's only about 12% greater concentration.

My guess is the 23.5% number is based more on measurement resolution. In other words the rule makers probably would prefer to make anything greater than 21% subject to greater regulation, but recognize that in practice it's difficult to reliably and repeatably measure O2 concentrations between 21 and 23.5%

This much like speeding tickets, very few are written for less than 10% over the posted speed.

I doubt there is any data to support any increased risk from 23.5% vs 40%


Tobin

 

[scjoe]

I don't think the gas industry is stating that 23.5% is as dangerous as 100%, they are saying it is signficantly more dangerous than 20.9%. My guess is that these positions evolved out of experience in oxygen enriched environments unrelated to scuba. The following are a couple of exerpts from the BOC Industrial safety page
http://www.bocindustrial.com/safety/gases_risks/risks_of_oxygen.asp

"Oxygen enrichment of the atmosphere, even by a few percent, considerably increases the risk of fire."

"Many so-called non-flammable textiles will burn fiercely in air containing as little as 30% oxygen, and no material should be considered safe unless it is known to have been subjected to a proper test."


"The accuracy of the measuring method should be such that, when indicated 21%, the real value is between 19.5% and 22.5%."

"Before people enter a space which may be subject to oxygen enrichment, the atmosphere should be analysed for oxygen. Free entrance is permissible only if the oxygen concentration is between 20 and 22%."

Most scuba diveres accept 40% simply because that is what they learned in their nitrox class and the anecdotal evidence that the few scuba accidents that have occurred were above 40%. However, I doubt there is any discussion in the average nitrox class about the lower standards of agencies and groups outside of diving or how the diving industry arrived at 40%. Also, there is no discussion about the number of industrial accidents that may have occurred outside of scuba in lower concentrations than 40%. Remember the vast number of oxygen enriched environments that are created are created outside of the realm of scuba diving.

Since for the time being no one seems to have any real information on how these numbers were chosen, whether you accept 23.5% or 40%, you are doing it to a large degree on your faith in the group that selected the number.

 

[cool_hardware52]

I don't think the gas industry is stating that 23.5% is as dangerous as 100%, they are saying it is signficantly more dangerous than 20.9%.

Asking that 23.5% and up be treated the same as 100% draws an equivalency between the two, I am not aware of a seperate set of regulations for greater than 21% and less than 40%.

"Many so-called non-flammable textiles will burn fiercely in air containing as little as 30% oxygen, and no material should be considered safe unless it is known to have been subjected to a proper test."

A 30 mix has a 44% greater concentration of O2 than air, not the ~12% that a 23.5 mix would have....

"The accuracy of the measuring method should be such that, when indicated 21%, the real value is between 19.5% and 22.5%."

My Point exactly, 23.5 was likely choosen based on ability to measure the O2 fraction.

Most scuba diveres accept 40% simply because that is what they learned in their nitrox class and the anecdotal evidence that the few scuba accidents that have occurred were above 40%.

I agree here, the accidents cited all involved deco mixes or Rebreather O2 Tanks. Do you know of others?

However, I doubt there is any discussion in the average nitrox class about the lower standards of agencies and groups outside of diving or how the diving industry arrived at 40%. Also, there is no discussion about the number of industrial accidents that may have occurred outside of scuba in lower concentrations than 40%.

I guess I had a better than average class, the existance of various standards was specifically discussed.

Since for the time being no one seems to have any real information on how these numbers were chosen, whether you accept 23.5% or 40%, you are doing it to a large degree on your faith in the group that selected the number.

Show me the data that concentrations as low as 23.5% merit O2 service, and perhaps my current opinion will change. Alternatively show me the incident reports from scuba applications that indicate that 40% and lower poses an unacceptable risk.


Tobin

 

[LAJim]

I'll state my conclusion a little more strongly. But let me qualify that I'm speaking from a reality-based point of view and not a regulatory or faith-based perspective. Also I am not telling anyone to go against practice that is mandated by law, regulating or certifying agencies, or their employers. Here it is: 3000 psi 21% air is far more likely to cause ignition of organic matter in tanks than 1 atm. of 100% O2. There is no practical difference in safety between 21% at 3000 psi and 40% at 3000 psi. The difference is analogous to having a big piano dropped on your head and a really big piano dropped on your head. If anything goes wrong the pO2 in the tank is far greater than necessary to ensure instantaneous detonation of all of the organic matter in the tank. Doubling it will make no difference. The amount of organic matter in a tank with the faintest coating of oil is trivial, as is the energy release from burning it. From a reality-based perspective the nitrox issue is either fictitious or the same rules should apply to fills with 21%.

As far as outside the tank goes - there is a difference. A class A/B/C fire next to the fill station will get far more intense if 40% O2 at 1 atm. is passing over the fuel. But if we lived on a planet with 200 atm of pressure and 21% O2 every fire would result in the immediate detonation of all combustible material and any increase in the % O2 would be some minor overkill.

I hope no one is offended. But I've detonated organic matter in 30 atm. of oxygen in a pressure vessel, and beyond 10 atm or so it doesn't matter if the O2 concentration is greater. The one exception I'm aware of is liquid O2, where the effective concentration is vast and the detonation mechnaism is probably different.

Supposedly the last act in the crushing of a submarine hull (ca. 2000 ft. or 900 psi 21% O2) is the detonation of the organic matter (people) trapped in the air pocket. 3000 psi air and organic matter is dangerous. Scuba tanks are safe because the organic matter in them is trivial. Nitrox in the tank is, in my opinion, no more dangerous, or the increase in danger is trivial.

Jim