At what percentage of nitrox does combustion really become a concern?

[thedragon]

I would be interested to hear if there were any reported incidents of exploding cylinders with 50% O2. I remember hearing about 40% being the general limit for non-O2 cleaned cylinders and regulators but I guess my question was more related to the hazard of a cylinder igniting if dropped or say if I had cylinders in the trunk of a car and I'm rear-ended. I heard some stories of a man who worked at a fill shop and would smoke a cigarette and wave around the O2 hose just to make everybody go berserk! Of course, as NorCalDM said, Oxygen is not flammable itself, it is only an oxidizer. But then of course there was the incident over at Renakers shop, cave excursions in florida, where the lady dropped the pure O2 cylinder on its valve and it went off like a grenade. For these reasons I usually keep any mixes with higher than 40% O2 in the back seat, not the trunk just as a precaution. If anyone knows of incidents with explosion of cylinders containing less than pure oxygen, I would be interested to hear them.

Thanks for the replies!

 

[tridacna]

Note that unless your local dive shop has banked Nitrox, they will do partial pressure blending. This means that your tank and it's valve will be exposed to 100% oxygen during the fill.

100% O2 is always worth thinking about as a combustion hazard

We don't bank Nitrox - we use a Nitrox stick. I avoid partial pressure blending whenever possible.

 

[Basking Ridge Diver]

I do not dive Nitrox - but I treat every full cylinder like a loaded weapon. Because it is. Does it matter if it explodes due to oxygen content or just that every cylinder is under pressure and needs to be handled appropriately?

Carry on.

 

[NorCalDM]

For a fire you have to have three things: fuel an oxidizer and an ignition source the ingnition source could be a spark, flame, heat etc. The cylinder that thedragon states went off like a grenade was that rapid decompression from the valve being broke off or was there a fire along with it? If the cylinder was steel you could have a spark when it hit the ground and there is your ignition or by releasing pure oxygen you created an oxygen rich enviroment were items that are not typically flammable become flammable like fabrics and another source set off the reaction. I have never heard of a cylinder blowing up because is was set off like a bomb "ignited" but I have heard of cylinders exploding due to some type of failure like a crack or the valve is broke off and you have a rapid decompression which is just as deadly.

 

[rjack321]

If anyone knows of incidents with explosion of cylinders containing less than pure oxygen, I would be interested to hear them.

There's generally at least 1 to 6 cylinder explosions per year worldwide. Some more publicized than others. Most are not combustion events but they frequently kill or maim people despite being "just" an explosion of an air cylinder.

 

[Basking Ridge Diver]

For a fire you have to have three things: fuel an oxidizer and an ignition source the ingnition source could be a spark, flame, heat etc.

They now teach the Fire Tetrahedron - Fourth is Chemical / Chain Reaction..

 

[DogDiver]

Cylinder in Florida was AL 30 with 2200 psi. 100% oxygen. Was dropped from just off the floor. A fireball ensued sending part of the cylinder into the employee. The valve was found a few hundred yards away. Fire half way up the fill whip heading for the liquid oxygen tank.
One fatality, three injured with burns and shrapnel.
Yes this was my cylinder she was filling. In short, just a very tragic accident.
Oh it was a Luxfer cylinder made in 1988.


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[thedragon]

Cylinder in Florida was AL 30 with 2200 psi. 100% oxygen. Was dropped from just off the floor. A fireball ensued sending part of the cylinder into the employee. The valve was found a few hundred yards away. Fire half way up the fill whip heading for the liquid oxygen tank.
One fatality, three injured with burns and shrapnel.
Yes this was my cylinder she was filling. In short, just a very tragic accident.
Oh it was a Luxfer cylinder made in 1988.


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Here's the thread about it. There was definitely a combustion and fire involved. Very sad. It's a fantastic dive shop. Was just there last week.

http://www.scubaboard.com/forums/accidents-incidents/65766-accident-cave-excursions.html

 

[SillyQuestions]

For a fire you have to have three things: fuel an oxidizer and an ignition source the ingnition source could be a spark, flame, heat etc.

Ever seen a lump of coal being thrown into liquid oxygen? That concentration of O2 makes coal go up like a firework just from the impact of the coal landing on it!

Since you can't get a higher percentage than 100, I tend to treat all cylinders as lightly as possible.


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[Windmutt]

Here's the thread about it. There was definitely a combustion and fire involved. Very sad. It's a fantastic dive shop. Was just there last week.

http://www.scubaboard.com/forums/accidents-incidents/65766-accident-cave-excursions.html