Regulators and Nitrox

[watergal]

Yup, If you have a plastic card from PADI it must be ok.

Oh, look! I have mail!

Dive within your training.

 

[roakey]

We had a similar discussion not too long ago where two studies were posted (http://www.scubaboard.com/showthread.php?s=&threadid=3271&perpage=15&pagenumber=1)

They both look quite official, are heavily footnoted and both are practically useless when it comes to SCUBA diving.

The more laughable one, titled (bear in mind I think the author was paid by the word) is “Evaluation of Contaminant-Promoted Ignition in Scuba Equipment and Breathing-Gas Delivery Systems” Note we’re able to get up to footnote 3 even BEFORE the title. These are by far the most professional taxpayer fleecers I’ve seen in awhile.

Readers digest version: This study “pneumatically impacted” small vials contaminated by a known flammable hydrocarbon (Mobile DTE 24 “which has been shown to ignite readily in oxygen systems”) in order to make sure they got positive results. “Pneumatically impacted” means they compressed the vial with 50% O2 at the rate of 100,000 -- 150,000 PSI per second. In other words they compressed the mix in a 19 cubic inch test vial to 3,000 PSI in 20 milliseconds.

Guess what? They got ignition!

I guess the fact that the real world does PP fills at 30-60 PSI per minute doesn’t matter to these folks.

Using the same lines of reasoning, if you soak your entire car with gasoline and drive it into a wall at 300 MPH, you’ll get one heck of a fiery crash. We can conclude from this that it’s dangerous to drive your car over 10 MPH even if it isn’t soaked in gasoline.

Not.

Finally the study moves on to something more useful, which was actually testing SCUBA regulators. The authors note: “When the scuba equipment was disassembled to the piece-part level, the contaminant level evaluation showed gross amounts of particulate and nonvolatiles in the oxygen-wetted portions of the assemblies, indicative of the ‘dirty’ environment that this equipment is exposed to daily.” But they conclude “The fact that the scuba assemblies tested showed no ignitions does not suggest that other components with slightly different configurations, even first-stage scuba regulators, will withstand ignition under the same conditions.”

So they found no evidence of ignition, but that doesn’t stop ‘em from issuing a dire warning. Of course they based the entire SCUBA “test” on three pieces of equipment, which a Statistics 101 student knows is completely bogus, so I’m not surprised they danced around the conclusion. Me, I would have simply stated “we didn’t have a large enough statistical sample to come to ANY conclusion” but that isn’t the kind of stuff that big government studies are supposed to say.

However, we can take solace in the fact that despite the statistically insignificant number of SCUBA regulators studied, that the final conclusion states:

Pneumatic impact ignition testing was conducted on three of the [SCUBA] assemblies, and contaminant levels were determined for all four assemblies. No ignitions occurred during any of the pneumatic impact tests on the component assemblies. The components were disassembled and shown to contain gross quantities of particulate and hydrocarbon.

So at least we have scientists basically saying 50% O2 is Ok despite “gross quantities of particulate and hydrocarbon.” Of course looking at the SCUBA industry as a whole, we already knew that.

Roak

 

[sharpenu]

Try this page:

http://www.nitroxdiver.com/Library/explode.html

 

[roakey]

Originally posted by sharpenu
Try this page:

http://www.nitroxdiver.com/Library/explode.html

This one case has come up before. This is the only case as far as anyone can tell that where there's been an SCUBA O2 fire/explosion.

As the article states (and as it appears in the pictures you pointed to), it was a pure oxygen cylinder (though over on the California board it was reported to be really 80/20).

One major factor seems to have contributed to the explosion. The diver reported that he possibly dragged the reg's mating surface through some oil in the back of his truck. This oil, combined with opening the valve quickly supplied the fuel and the heat required for the fire. The Atomic Ti regulator was throwing gas on the fire so to speak because Ti burns quite well in O2 (anyone remember the recent DAN recall of O2 regulators because they were aluminum?).

Note that the cylinder was filled without incident.

Let me make sure I'm perfectly clear on one thing, I've never claimed you can't have an O2 explosion. My above post simply pointed out that the studies that rainreg (and as far as I can tell, blacknet) base their “danger factor” of O2 on are flawed. I'd love to see some applicable studies made so we really know what the risk factor is. Until then about all we have to go on is what's happening out there in the real world. And the real world says that many, many shops do PP mixing every day without incident, up to and including the WKPP that doesn't even believe in O2 cleaning. And the WKPP will PP mix literally hundreds of cylinders for a single weekend outing.

However, the base note question (and the question I’m specifically answering) was about using 40% and below. There’s no incidents that I know of where there has been any fire in a regulator exposed to O2 mixtures 40% and below.

My personal comfort level is I keep all my cylinders “ready for O2 service” and the regulator that I use for 100% (a Scubapro Mk20/G250 combo) has the nitrox conversion so it has the purdy green and yellow plastic parts. I use a standard Mk20/G250 on my 50% and below mixes (I use no mixes between 50% and 100%).

And I always open my valves very slowly with the purge button initially pressed.

Roak

 

[roakey]

Originally posted by blacknet
Just this past week I meet a cave diver who was not even open water certified. Said something about training was a waste of time and money and that 'real world experience' is the best teacher.

Really poor analogy blacknet. Anyone can point to a long string of deaths that prove that cave diving without training is a bad idea. If this analogy was applicable you could point to numerous SCUBA shops that had gone up in flames and cylinders that had caught fire.

But there’s not one regulator exposed to a 40% or below mix that has caught fire.

If you’re going to argue by analogy, pick ones that are applicable.

A ways back you asked our opinions if the SCUBA industry adopted the 23.5% limit for O2 cleaning. Given the fact that there’s zero data to suggest that 40% presents any kind of problem, my opinion would be:

“Logic, data and common sense has again kowtowed to the lawyers.”

Roak

 

[blacknet]

Roakey,

Ok here's one for you

But there’s not one regulator exposed to a 40% or below mix that has caught fire.

Guy in florida filled his nitrox O2 cleaned tank with compressed air and BOOM, fire happened. O2 level was 21%. True story.

Ed

 

[roakey]

Originally posted by blacknet
Guy in florida filled his nitrox O2 cleaned tank with compressed air and BOOM, fire happened. O2 level was 21%. True story.

So why are you a proponent of O2 cleaning only when you get to the obviously dangerous level of 23.5% O2? Sounds like you'd be a proponent for O2 cleaning for air, all dive shops should pump O2 compatible air, etc.

Can you give me a pointer to the incident? Any details? Any mitigating factors like their was oil slopping around in the bottom of the cylinder and he filled it in 15 seconds?

Point blacknet, but as a standalone datapoint it gives us no information.

Roak

 

[roakey]

Originally posted by roakey
Point blacknet, but as a standalone datapoint it gives us no information.

Perhaps I was a bit too hasty with that point. I have the PSI list of cylinder failures going back to 1960 and can find no failures due to an O2 fire. Perhaps the "BOOM" was merely hyperbole and it wasn't a true cylinder failure, only a fire.

In any case, if it's true as you say, please supply, at minimum, when and where.

Roak

Ps. Please don’t come back with something along the lines of “do your homework.” In such a case you’re asking me to prove a negative (that it didn’t happen) which a first year logic student knows is impossible. You can’t prove a negative, it’s up to the asserter to prove the positive.

 

[blacknet]

Hello,

Sure here's some info to chew on as i'm sure your side will discredit it for some stupid reason.

australia 1999, shop was filling a tank, 20 bars was the explosion pressure. 36% o2 and it was a membrane system. Cause of the accident? oil contamination.

One incident comes to mind (unverified) was a rb caught fire with in the breathing loop and the operator died. cause of the fire, oil contamination.

USN had a HUGE lab that was o2 clean to the highest level. Think they was doing hydrogen/oxygen work. Well the building is now destroyed by an o2 fire. Oh and btw the o2 levels was WAY under 40%

The incident in florida was recent, I don't have, yet, exact dates on that one.


One could even have some design flaws, using the wrong/improper parts or what not. Check this passage for more info

Oxygen fires can be caused by any of the following: (A) system design errors, (B) use of the wrong metals or plastics within the gas pathway, (C) dirty/contaminated systems, (D) errant operating procedures due to mistakes by careless or untrained personnel. As already pointed out, increased oxygen concentration and / or pressure changes the ignition temperature at which a material will burn. Thus many substances that would not burn in air at atmospheric pressure may readily ignite in oxygen environments, especially if the temperature or pressure, or both, is raised. To design 02 systems correctly, one must select the best oxygen-compatible components available, i.e. those which will resist ignition under the prevailing conditions. Nonetheless, be aware that no system can be infallible in this regard!

Another source of unexpected ignition is PARTICLE IMPINGEMENT. This happens when a small metal particle, teflon fragment, or plastic seal shaving gets accelerated within a high velocity gas stream. If such speeding material strikes another component or hits an obstruction in the gas passageway, it may ignite much like a meteor hitting the Earth's atmosphere. In pure oxygen, this could be disastrous since the reaction is usually self-sustaining once it's been initiated. Impingements are prevented by selecting and assembling components carefully and by using particle filters at the gas source, since large commercial gas cylinders are notorious sources of rust particles.

Steel components which can rust and release debris into the gas stream are a common source of particulate matter. Never use plain steel fittings in oxygen systems; brass or stainless must be employed, depending on the pressure. Brass is suitable to about 3,000 p.s.i.; stainless should be used for higher pressures. Exotic materials like Monel and lnconel are also excellent alloys, but are usually too expensive for dive facility use. In general, brass/bronze is the preferred metal for use with pure 02.

Thermoplastic air hoses with steel end fittings should NEVER be used in oxygen systems. Most dive store air systems employ synthetic hoses which have plated steel end fittings, since brass or stainless models are rather uncommon. While the core of such hoses may be oxy-compatible, the fittings are NOT and will corrode internally with age. Hose fires instigated by rusty end fittings have already occurred during gas mixing operations. A common mistake is to use an air filling whip (having steel hose fittings) to add OCA to an oxygenated scuba tank. If a rust particle is released from the air hose, it may impinge and detonate the 02 at the tank valve! ALL hoses used in mixing systems should be Teflon-core types with stainless steel sheathing and brass or stainless end fittings.

The danger of particle impacts can be lessened by proper design. For example, eliminate sharp angles such a 90o elbows and minimize long, narrow, or blind passages when plumbing your system. Right angle bends create flat surfaces where particles can impact or ricochet. In addition, blind passageways or large cavities can be collecting points for minute debris, thereby promoting contaminant buildup. Also, examine all fittings for sharp edges, protruding metal burrs, or loose threads. Design/inspect your system to eliminate or minimize such unwanted hazards.

Aluminun and low allowy sttel can ignite easily and burn rapidly in high pressure oxygen, producing tremendous heat and generating explosive molten debris. In oxy-environments, aluminum can be set afire by frictional heating or adiabatic compression. Therefore, aluminum or low-alloy steel components SHOULD NOT be used in high pressure O2 systems. Also, the medical gas industry has recently issued a national recall on all aluminum-bodied oxygen regulators because of a rash of fires in such devices! Titanium is also TOTALLY UNSUITABLE for use with pure oxygen. Other metals which are undesirable for 02 service include cadmium, beryllium, magnesium, and mercury.

February 21, 1996, japan, a hyperbaric chamber exploded due to one of those pocket warmers. It was operating at 2.7 ata on compressed air.


Ed

 

[roakey]

Originally posted by blacknet
Sure here's some info to chew on as i'm sure your side will discredit it for some stupid reason.

Blacknet, I fill. I don’t discredit stuff for stupid reasons because I don’t want to die in a cylinder explosion. I discredit stuff for good reasons only.

What I think you fail to understand is that I, and I *think* I can speak for Lost Yooper both realize that O2 is not something to be trifled with. What we stress, however, is control over the filling process to avoid problems. I look at contamination control as a secondary consideration (but still important). As far as I can tell, since neither you nor rainreg have ever really come out with a position except to post pointers to studies, FUD and “do your homework” statements, is that you consider contamination the paramount consideration.

I think that’s a very dangerous position to take.

Consider a shop for a moment. Once a Nitrox cylinder leaves the store, the store has NO control over its exposure to contamination. Heck, the cylinder might have been innocently left next to the exhaust of an idling car and the valve’s ambient pressure surfaces might be thick with hydrocarbons by the time the shop gets the cylinder back. Or maybe the diver brought the cylinder to a disreputable shop and had it filled with “dirty” air. As the shop owner you have no idea what happened to the cylinder from the time it went out the door until the time it came back in.

The ONLY way you’re going to control contamination is to demand that each and every cylinder and valve get a complete cleaning each and every time it’s returned. At $50-$100 a fill to pay for a cleaning, no one will sell Nitrox for long.

The only control a shop has over a Nitrox cylinder is the rate of fill, or more correctly, the heat that’s generated during a fill. This is why LY and I keep poo-pooing your contamination hand-wringing -- such control can only be maintained in a lab, not on the deck of some diesel burning boat. So we focus on a different leg of the equation, the heat side. Let me stress that we don’t think that O2 compatible components and cleaning are a waste of time (the fuel side of the triangle), but it isn’t as important as the heat side of the triangle. After all, the heat side is the only leg that can be controlled with a level of precision that approaches a laboratory environment.

My personal comfort level is that I transfill air from a bank that’s sat for 12-24 hours to allow any suspended hydrocarbons to settle out. I never fill directly from a compressor. scubatrurek boosts from partially filled Nitrox cylinders into other Nitrox cylinders all the time without incident. I also happen to know that his shop maintains their compressor well above the required maintenance level.

So in conclusion, I want to make it perfectly clear that LY and I don’t dismiss the dangers of O2, we simply disagree with your level of paranoia on the topic.

Now onto your events…

australia 1999, shop was filling a tank, 20 bars was the explosion pressure. 36% o2 and it was a membrane system. Cause of the accident? oil contamination.

According to the Australian safety online page oil contamination is what they suspect, but it’s not definitive. Nevertheless, compressors generate huge amounts of heat both from adiabatic heating as well as friction. I agree, if you’re going to run anything but air through your compressor, being anal about O2 cleaning is quite justified. Also it’s nice that in this case the cleanliness of the system IS under your control, unlike SCUBA cylinders. Again, when I talk about my paranoia level of O2 cleaning, I’m talking about going from a bulk O2 cylinder to the SCUBA cylinder and a bulk air cylinder to the SCUBA cylinder. At this point in time I don’t deal with compressors and compressor issues don’t figure into my replies.

One incident comes to mind (unverified) was a rb caught fire with in the breathing loop and the operator died. cause of the fire, oil contamination.

Unverified but you’re quite sure of the cause. We’ll ignore this for the time being until you can supply more definitive information.

USN had a HUGE lab that was o2 clean to the highest level. Think they was doing hydrogen/oxygen work. Well the building is now destroyed by an o2 fire. Oh and btw the o2 levels was WAY under 40%

Seems to me the only conclusion that you, as a shining star of O2 safety, can draw from this is “If the Navy can’t keep an explosion from happening in a lab environment, we have no hope in the SCUBA industry, so we better stop dealing with Nitrox right now.”

Is that your conclusion, and if not, what are you doing out in the field (ocean?) that makes your protocol better than a Navy lab? Because if you’re not doing anything better, you have no leg to stand on to support the use of Nitrox, period. It’s best to offer examples that support, rather than undermine your position.

However, I will keep this example in mind when I’m doing hydrogen-oxygen mixtures. Which will be never. So this is similar to the fancy studies that KN/rainreg posted that had little information that was applicable to the SCUBA industry.

The incident in florida was recent, I don't have, yet, exact dates on that one.

I’ll wait.

One could even have some design flaws, using the wrong/improper parts or what not. Check this passage for more info

No need to discuss this one, we’re in complete agreement. Again, make no mistake, I feel that O2 compatibility and cleanliness is important. It’s just that the heat side is the MOST important in my eyes.

February 21, 1996, japan, a hyperbaric chamber exploded due to one of those pocket warmers. It was operating at 2.7 ata on compressed air.

ATTENTION EVERYONE! IMPORTANT SAFETY TIP! DO NOT UNSCREW THE VALVE AND JAM A HANDWARMER INTO YOUR CYLINDER BEFORE SPIKING IT WITH O2!

Whew! Glad we caught that problem before it reached epidemic proportions!

Roak