DIN Plugs in O2 Cylinders. Good Idea? Bad Idea?

[ianr33]

After hearing of David Frisks recent horrible accident my initial response was to always ensure I have a Stainless DIN plug in my O2 tanks.

Benefits:
1)If the valve is accidentally rolled on, O2 will not leak out.This would prevent the possibility of the O2% in a truck or building increasing to a level that could be explosive.
2)If a tank is knocked over or dropped there is less chance of high pressure oxygen hitting a dusty floor and causing a major fire.

Either of these can have catastrophic consequences.

Con:
Once a valve is pressurized with a DIN plug in place a wrench is needed to remove it.Frictional heating during removal,brass shavings, and the high pressure O2 trapped between valve and DIN plug could lead to ignition. My opinion is the amount of O2 involved is small so would not be a significant problem.

So which is safer? DIN plug In or Out ?

 

[syntaxerrorsix]

Don't store your O2 where it could accidentally roll on and don't knock your tank over.

It works for me.

 

[w ripley]

I put plugs in everything, but not to keep the contents from spilling out, but to protect the fitting from being deformed if the cylinder is dropped on the valve fitting (had this happen) + to keep the fitting clean. I'd rather lose the contents of the tank than to replace another valve. I do have holes drilled in all of the plugs so that they can be released under pressure, although I've never heard of anyone not being about to unscrew a solid plug.

O2 is handled everyday under pressure, in the industrial world as well as the scuba world. It's just that anything you do, like loosening a solid plug under pressure, just has to be done slowly. Your Din fitting should be clean anyway + any "O" rings non-combustive. Follow normal O2 safety rules and don't worry about it.

I Haskel my O2 to 3,400 psi and Rennaker, in cave country, banks his at 3,600 psi. Just take the time to understand what makes this stuff catch on fire and avoid it. Respect it but don't be afraid of it, IMO.

 

[PfcAJ]

I think determining one to be 'safer' than the other is tough. O2 explosions are somewhat rare when compared to the number of cylinders in use, so coming up with a meaningful recommendation for a procedure (either way) is hard to do.

DIN plugs with a bleed screw are probably a better choice than plugs without them for the reason you mentioned. A regulator is probably a reasonable choice, as well.

 

[cavemn]

I put plugs in everything, but not to keep the contents from spilling out, but to protect the fitting from being deformed if the cylinder is dropped on the valve fitting (had this happen) + to keep the fitting clean. I'd rather lose the contents of the tank than to replace another valve. I do have holes drilled in all of the plugs so that they can be released under pressure, although I've never heard of anyone not being about to unscrew a solid plug.

I am keeping DIN plugs in everything for the same reasons. I don't see the amount of O2 trapped in a pressurized plug to be an issue. I always make sure the valve is firmly off before removing the DIN plug.

The change I plan to make. I will be moving to steel LP 45s for my O2 or maybe even one LP45 and one LP 19 with vendable plugs. 100% in a 40 cuft HP aluminum cylinder has always bothered me a bit. Especially when I stupidly leave them upright.

 

[azchipka]

I keep DIN plugs in everything as well, but I use the DIN plugs that have pressure release pins, that way if the valve does get turned on its no big deal the Pressure release pin just blows out.

 

[James R]

I am not sure that the heat from slowly using a wrench to remove a plug would be enough to flash, but I am not any sort of expert and I didn't stay at Holiday Inn Express last night.

I usually keep a DIN plug in mine at home just enough to save the valve if it falls over, so not too tight, and a reg on it (not charged, valve off) when I am on the way to go dive. I rarely transport with a din plug, but I have before. I usually transport in the cab of my truck too. I think I will start transporting my o2 cylinder in the bed of the truck going forward. Also I will switch to my delrin din plugs for 02 bottles b/c they don't trap air.

Sucks this had to come up the way it did.

 

[Wookie]

It's not the amount of O2 that is the issue. it is the concentration. Which is 100%. Under high pressure (whatever is in the tank). Then, remove the plug under pressure and heat that 100% O2. Shave off a little brass during the removal of the plug and give the O2 something to light on fire, bad things happen. I think it's a bad idea.

With that said, The recent case in Austin is a one in a billion case (Have there been a billion al-40's filled with pure O2?) Maybe the odds of the DIN plug scenario I spelled out above are 10% more, or a 1 in 100,000,000 chance? Long odds if you ask me.

Sometimes in life we have to ask ourselves if the risks we take are worth the chances we have of dying/getting seriously injured. Obviously, those of us that choose to dive, or choose to deco dive or choose to cave dive (all varying degrees more difficult, risky, and rewarding) are taking chances and playing the odds with our lives. I don't think that worrying about a leaky O2 bottle counts for crap in the scheme of diving Jacobs Well or Lake Amistad.

 

[ianr33]

I keep DIN plugs in everything as well, but I use the DIN plugs that have pressure release pins, that way if the valve does get turned on its no big deal the Pressure release pin just blows out.

Doesn't that rather defeat the point though?

 

[fdog]

I use DIN plugs in everything, except 100% O2.

What pushed me over the edge was this YouTube video, because the mechanism that caused the problem strongly resembles unscrewing a DIN plug:






You can certainly make the argument that as the DIN plug is unscrewed, the o-ring will deform and "follow" the plug up the threads, separating the oxygen from the thread-on-thread contact. You can tell that this happens by the way you have to wrench a DIN plug out for a long ways, all the while being under pressure, until the o-ring reaches the vent hole. As the preventative mechanism to separate O2 from friction, however, that's a little to much for me to take on faith.


I am uneasy about relying on the reservoir of available oxygen (in the void at the bottom of the DIN plug) being too small to cause a problem. All a flash fire has to do then is burn past the nylon seat, and it has access to a huge volume of oxygen at pressure.


So, for bottles of 100%, I'll continue to use regulators (or) "donut inserts" to help keep the valve body from being turned into an oval by impact.




All the best, James