Acetylene leak, BOOM!

I have been told more than a certain volume of acetylene in "free air" can self detonate or detonate from turbulence. I had an accident here at the shop some years back where there was no apparent source of ignition. Just somebody in open air sticking their hand in front of the flow the flow from a cracked valve. There was no physical contact, and no obvious source for static. I mentioned it in this group not long after it happened. Gunner and a few others told me there had to be an ignition source, but I was standing right there. In fact I was reaching towards the valve to shut it off when it ignited. Then we had a blow torch pointed at the corner of my shop building. I went back in the shop to grab a welding glove so I could shut it off.

The person with their hand in front of the valve got burned, but not as badly as you might think. Their whole hand was red, and the outer layers of skin all sloughed off over the next few days. They got their hand out of the fire pretty quick. Worse than a regular first degree burn, but not the worst burn I've seen called a second degree burn. It was mostly bad because it was over their whole hand.

We could argue about whether it was an explosion or a conflagration. It had a pretty healthy pop for an uncontained event. Faster than a whoomp, but maybe not quite a crack.

I have been told more than a certain volume of acetylene in "free air" can self detonate or detonate from turbulence. I had an accident here at the shop some years back where there was no apparent source of ignition. Just somebody in open air sticking their hand in front of the flow the flow from a cracked valve. ...

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Acetylene's triply bonded carbon stores a lot of energy and it can explode without burning, by decomposing into carbon and hydrogen or polymerizing (combining with its neighboring molecules) into benzene or a metal-like film called polyacetylene.

In other words dirty hands may trigger it. In the cylinder it's dissolved in acetone to make it safer.

Free acetylene is unstable above about 14PSI and can detonate without external oxygen. If you are feeling particularly brave or stupid take a steel block and drill a hole in it then find a snug fitting steel plug/shaft to fit the hole. With the open end of the hole facing down (acetylene is lighter than air) fill the hole with pure acetylene fron a torch and insert the steel plug, turn it over on an anvil and hit the plug with a hammer. If you are even stupider or braver, use a copper "firing pin" as copper acts as a catalyst to promote the breakdown of acetylene.

Just make sure all your various insurances, including life insurance, are paid up!!!!

There's another, now obscure copper/acet connection. In the days of generating acetylene on the fly for torches, home lighting etc. the generator was sometimes made of copper. Over time, the acetylene reacted with the copper leaving copper acetylide deposits in the seams. A tinsmith, tasked with tightening up leaky seams on a generator could be greeted with a very loud suprise when striking a seam with a hammer.

Allegedly, you can make copper acetylide by bubbling the gas through a container of copper sulfate dissolved in water where tiny crystals of acetylide vivibly form and settle out. One of those substances, like nitrogen triiodide, that's cool but unwise to make.

In the 70s, I once visited a blacksmith shop that had an oxy tank on a dolly with an carbide/acet generator apparatus. I asked the smith if perhaps that was a bit dangerous. His reply, "She blows up sometimes" and pointed upward. The building had a plastered cathedral ceiling ca. 20' in the center and there was a big sooty starburst on the plaster over the generator. He was the only blacksmith I ever met who drank whiskey while working so maybe a few straws short of a broom.

What was the humidity then?

I'd bet on an unnoticed ESD (electro-static discharge), which can be caused by the air causing things to flutter against one another.

Just walking across a carpet can generate enough static electricity to make a sharp crack sound.

Joe Gwinn

Standing on concrete outside in one of the driest climates on earth. I wear rubber sole shoes pretty much all the time. Either sneakers or walking boots. The OP usually wears rubber sole shoes as well. I still have very good discrete hearing. (I still have my high frequency hearing as well.) The only sound I heard was the detonation. Its possible, but it sure didn't seem like it.

The ESD spark and the detonation would likely be too close in time to be told apart, and the boom is far louder.

Joe Gwinn

The ESD spark and the detonation would likely be too close in time to be told apart, and the boom is far louder.

Joe Gwinn

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High voltage electricity can discharge with little or no sound.

So how for does the invisible arc jump. His hand was 8-10 inches away. It wasn't me. My hand was maybe 6 inches away, and I felt no static pop. The only time I've seen a normal static arc jump much longer than an inch or so was in extreme circumstances. Arc gap generators, St Elmos fire discharging off an antenna cable in a fog on boat. That sort of thing. In those cases it was quite visible.

Maybe you are right, and I am full s*it, but the detonation happened at exactly the moment the OPs hand broke the flow from the valve. I was so surprised that I spent quite a bit of time researching it to see what could have caused it. There was no obvious arc source. Not even a nearby motor starting up. Closest motor was the AC heat pump condensing unit about 15 feet away and it was not running.

Is acetylene gas conductive? I guess if it is that could have provided the "invisible" arc path. I am aware that vulcanisates of acetylene black are conductive, but I can't find anything that specifically says acetylene gas is.

That acetylene "can" detonate from when certain conditions are met not necessarily requiring a spark is established. Whether or not that is what happened when a bottle turned into a blow torch outside my shop we will never know for sure. I have no desired to perform experiments to prove it one way or another. Okay maybe a little but I am not yet senile enough to let my curiosity over ride my common sense.

It's impossible to tell exactly what happened without high-def videos, and memory is famously unreliable about things not noticed.

No.

It's true that acetylene has all manner of ways to go boom, but most such methods are very unlikely in practice. But ESD is not rare.

Joe Gwinn

So how for does the invisible arc jump. His hand was 8-10 inches away. It wasn't me. My hand was maybe 6 inches away, and I felt no static pop. The only time I've seen a normal static arc jump much longer than an inch or so was in extreme circumstances. Arc gap generators, St Elmos fire discharging off an antenna cable in a fog on boat. That sort of thing. In those cases it was quite visible.

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I Googled to see if the flow of an insulating gas could transfer charge like the belt of a van de Graaff generator and what I found was that it has to contain particles, clean gas won't.

I thought I remembered a small shock from operating air tools.

So how for does the invisible arc jump. His hand was 8-10 inches away. It wasn't me. My hand was maybe 6 inches away, and I felt no static pop. The only time I've seen a normal static arc jump much longer than an inch or so was in extreme circumstances. Arc gap generators, St Elmos fire discharging off an antenna cable in a fog on boat. That sort of thing. In those cases it was quite visible.

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I Googled to see if the flow of an insulating gas could transfer charge like the belt of a van de Graaff generator and what I found was that it has to contain particles, clean gas won't.

I thought I remembered a small shock from operating air tools.

This says yes:

We are getting pretty far out in the weeds here. I don't recall ever getting zapped by air tools, but wood shop guys have to discharge static on dust collection systems. Lots of particles there though. I wonder if the minimal oil from the compressor and/or air tool oil counts as enough of a particle to create static build up. Maybe if using some types of plastic whip lines and an oiler at the wall instead of oil dispensed directly into the tool...

"I can imagine it spraying mice all over the place too but I'm not too sure how likely either is." HAHAHAHAHAHAHAHA

I've seen 1/2" or more sparks in my old sand blasting booth from the gun to the part before I added an earth to the gun.

I've seen 1/2" or more sparks in my old sand blasting booth from the gun to the part before I added an earth to the gun.

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That's likely what I remembered. However this material on spray can dusters does mention static buildup:

Bob - if the acetylene was exiting at significant speed it is very possible the "loca; pressure" where the gas hit the hand exceded

I was in Haiti in the 90's, and in Port-a-Prince there was a street called "Little Detroit" that was lined with all manner of mechanics working out in open air. This included body work, painting, and frame work. It all folded up every night, save for one thing: the large Carbide/Acetylene generators seeemingly standing guard...