Prevalence, causes, and prevention of oxygen fires

[2airishuman]

Anecdotal reports suggest that:

1. Fires, explosions, equipment incidents where combustion is believed to have occurred, burns, etc., are common in diving equipment using >40% oxygen. These take place despite widespread understanding of the risks, by people who believe they are using safe practices.
   
   
2. Most of these incidents do not appear in DAN reports because they do not occur during the dive itself. Those that occur during a dive are usually not fatal, and are not reported to DAN for that reason.
   
   
3. Oxygen is widely used for medical treatment, welding, and other industrial purposes. While fires etc. do occur with these uses, they are extremely rare on a per-cylinder-handled basis (with the exception of extremely common fires caused by individuals smoking cigarettes while using home oxygen)

I'd like to start a discussion on how we can improve the safety of this area of technical diving, and would welcome your thoughts.

 

[JackOfDiamonds]

Ive seen people smoke a cigarette while analyzing their tanks... i guess educating the people would be the best way to go about this.

I personally think it should be inserted in to OW & TECH courses, dive safety is not strictly beneath the waves, it starts on the surface.
The same way they teach you not to keep your tanks standing up or leave your weight belt on an elevated surface, stuff like this should also be included.

 

[2airishuman]

Having read through some anecdotal reports, I'd like to summarize the major risks as I understand them based on my reading knowledge:

1. Progressive accumulation of combustible contaminants on cylinders, valves, and regulators, in spite of reasonable efforts to keep them clean.
   
   
2. Serious mistakes made in servicing, such as the use of silicone grease.
   
   
3. Contamination of valves and cylinders from contaminated fill equipment or a contaminated source of gas.
   
   
4. Casual sharing of equipment between air/nitrox and oxygen cylinders, such as tank checkers, transfill whips, and adapters.
   
   
5. Ineffective attempts at cleaning equipment for oxygen service.
   
   
6. Contamination of equipment by skin contact, whether due to naturally present oils in the skin or the presence of cosmetics, lotions, etc.
   
   
7. Use of materials such as o-rings, hoses, and valve seats that are not suitable for oxygen service.

 

[electric_diver]

Anecdotal reports suggest that:

1. Fires, explosions, equipment incidents where combustion is believed to have occurred, burns, etc., are common in diving equipment using >40% oxygen.

What anecdotal reports? I would have said the number of Oxygen related incidents in the diving community is extremely low based on what I'm aware of. Do you have any data?

There have been explosions and fires in Florida. I read the fire report that was posted on line for one of them. Apart from those events, I don't know of any.

One point that I think is worthy of discussion and analysis is: are DIN valves appropriate for high concentrations of O2? The ridged nature of the DIN threading provides many times more potential combustion sites in the event of an accidental opening of the valve. Is it safer to always store O2 cylinders with DIN valves with a regulator attached?

 

[lowviz]

I am a huge fan of pure O2.

The one 'big deal' is to ALWAYS crack the valve open slowly.


"Compression Heating:

Compression heating occurs when gas is rapidly compressed
from low to high pressure. Compression heating is the most
efficient igniter of non-metals and contaminants.
• Pressure ratio
• Rapid pressurization
• Exposed non-metal or contaminant proximate to dead end

Example: A fast-opening valve can cause compression
heating ignition when it releases high-pressure oxygen into
a dead-end tube or pipe, which compresses the oxygen
initially in the tube and causes heat of compression at the
dead end.


https://www.flowserve.com/sites/default/files/2017-10/fsg-148-e.pdf"

 

[2airishuman]

What anecdotal reports? I would have said the number of Oxygen related incidents in the diving community is extremely low based on what I'm aware of. Do you have any data?

Well, a wise individual once said, "the plural of anecdote is not data." I don't have any data.

Here are Scubaboard members who have personally experienced some sort of combustion event involving oxygen:
* @The Chairman who, iirc, once became ill after diving a cylinder that had been partial-pressure blended and where spontaneous combustion of prior contamination was found to have taken place
* @northernone, who reported having "scorched" an o-ring in his 1st stage
* @Texas Torpedo, who was badly injured after an aluminum oxygen cylinder spontaneously ignited
* @Chris Richardson, who (if memory serves) had a regulator burn up while at a deco stop
* @DogDiver who says he has survived not one but two deco bottle explosions

There are more than twice that many secondhand reports.

One point that I think is worthy of discussion and analysis is: are DIN valves appropriate for high concentrations of O2? The ridged nature of the DIN threading provides many times more potential combustion sites in the event of an accidental opening of the valve. Is it safer to always store O2 cylinders with DIN valves with a regulator attached?

I've never really understood why removable 1st stages are used for deco bottles (other than tradition). The integrated valve and 1st stage setups seem like a natural fit, and eliminates a bunch of the problems.

This is what I mean by an integrated valve and first stage:

 

[nadwidny]

Anecdotal reports suggest that:

1. Fires, explosions, equipment incidents where combustion is believed to have occurred, burns, etc., are common in diving equipment using >40% oxygen. These take place despite widespread understanding of the risks, by people who believe they are using safe practices.
   
   
2. Most of these incidents do not appear in DAN reports because they do not occur during the dive itself. Those that occur during a dive are usually not fatal, and are not reported to DAN for that reason.
   
   
3. Oxygen is widely used for medical treatment, welding, and other industrial purposes. While fires etc. do occur with these uses, they are extremely rare on a per-cylinder-handled basis (with the exception of extremely common fires caused by individuals smoking cigarettes while using home oxygen)

I'd like to start a discussion on how we can improve the safety of this area of technical diving, and would welcome your thoughts.

How about we start by discussing how seriously flawed your conclusion is that >40% O2 fires are a common occurrence?

 

[2airishuman]

The one 'big deal' is to ALWAYS crack the valve open slowly.

I agree that is a best practice that should always be followed by any prudent diver.

But it shouldn't be necessary. If the equipment is clean and properly designed, opening the valve quickly should have no effect.

 

[2airishuman]

How about we start by discussing how seriously flawed your conclusion is that >40% O2 fires are a common occurrence?

Sure, help me out here. What are the facts?

 

[TrimixToo]

Having read through some anecdotal reports, I'd like to summarize the major risks as I understand them based on my reading knowledge:

1. Progressive accumulation of combustible contaminants on cylinders, valves, and regulators, in spite of reasonable efforts to keep them clean.
   
   
2. Serious mistakes made in servicing, such as the use of silicone grease.
   
   
3. Contamination of valves and cylinders from contaminated fill equipment or a contaminated source of gas.
   
   
4. Casual sharing of equipment between air/nitrox and oxygen cylinders, such as tank checkers, transfill whips, and adapters.
   
   
5. Ineffective attempts at cleaning equipment for oxygen service.
   
   
6. Contamination of equipment by skin contact, whether due to naturally present oils in the skin or the presence of cosmetics, lotions, etc.
   
   
7. Use of materials such as o-rings, hoses, and valve seats that are not suitable for oxygen service.

#7 is interesting. Medical O2 uses BUNA-N O-rings according to The OxyHacker book. We use Viton. So it's not clear what O-rings are worse for O2 service until you get into less common compounds. Our valve seats are almost uniformly nylon or nylon compounds that are not used elsewhere for O2 service as far as I know, and not truly best for it, either. Moreover, the gas path through most valves used in diving could be, um, better for O2 service. The HP hoses have very little flow unless a spool O-ring blows (and even then it's restricted by the regulator design in most cases), and the LP hoses are, well, LP and don't impose that much risk as far as I can recall. (If anyone knows better please chime in.)

With all that in mind, that we have so few accidents with O2 is slightly astonishing. Not just O2 fires but gas contamination.