That’s an actual fire hazard.
Um–if you pierce a pressure vessel (scuba, welding gas, etc) that is at 3000+ pounds of pressure it sure as shit turns into a missile. Scuba tank valves are more robust than welding tank valves, but it’s illegal to transport a welding tank without a valve cover for this reason.
Yeah, that’s when I start wondering what the LEL is and wondering if it could get up to 4% in the car.
Yeah, your risk here is getting wet. Not hurt. Altho putting it up to your face is contraindicated.
I think a trash can would be better.
Mostly true. If you somehow broke the valve out of the neck of the tank at 3,000 psi (for a standard aluminum tank), it could certainly propel itself many tens of feet; probably not a lethal hazard but it could knock some teeth out. Fortunately, the valve on a scuba tank has a burst disk that should prevent tank rupture by relieving before the tank hits proof pressure. I have seen exactly one scuba tank rupture, which was actual older 2,200 psi w.p. steel tank; as it was strapped into a BCD that itself was strapped onto a bench, it didn’t go anywhere but it did create a big spiral fracture nearly the length of the tank. I never saw a definitive answer of the root cause but it was almost certainly due to a combination of drop damage and solar heating.
Oxyacetylene welding tanks and other volatile gas tanks have a tank cover during transport to assure that nobody leaves a regulator or hose hooked up to them. The cover won’t actually prevent leakage but does assure that they are configured for safe transportation and that nobody can just come along and casually open the valve. A 125 cu ft tank can for sure launch itself across a field or flying through the air, at least according to the chem lab safety briefer who ironically told a story about how he and a buddy took a bunch of unlabeled tanks into an open field and shot at them with a rifle with predictable results, i.e. one of the tanks backflipped and landed about 20 feet away, and another speed off laterally and across a road, narrowly missing a car.
I’ve never futzed around with pressure tanks to try to intentionally break them because “fuck around and find out” is rarely a good policy when it comes to pressurized systems, but I was once in a lab where 9000 psi ullage tanks were filled with helium. Somehow, a tank the size of a basketball fell off its stand and bounced with almost perfect resilience across the lab and back a couple of times, fortunately not rupturing. I later went and calculated the mechanical energy that would have been released by a rupture and the result made me slightly ill.
Stranger
Nuke it from orbit.
Space lasers! 
Ages ago I worked at a scuba shop. Someone was filling a rack of six tanks (you could wheel the rack around, all tanks were upright). All the aluminum tanks in the shop were painted blue and all the steel ones were painted yellow…except for one. You can see where this is going.
The person did not check the stamp and assumed they were all aluminum which could take a higher pressure than steel. The burst disk on the steel tank ruptured and made an almighty whistling noise. Nothing could be heard over that. It knocked the rack of six tanks over on their side but that was it. After a minute (or whatever) it ended. Of course, we all came to look. There was a big chunk of ice on the top of the failed steel tank from the air cooling so much when released.
No one was injured. I do not want to think of what would have happened if the burst disk didn’t do its job correctly.
1960s style ray gun?
I drove to event A & event B started the next evening further north of there; it’d didn’t pay to go home in the interim so I went to the Event B hotel a night early, check in, get my stuff out of the car & lock it up for the night. I worked in the hotel room most of the day & then went out. The car was brutally hot when I got into to it as it had been closed up on a summer day. I put the windows down & drove off. About two miles down the road I come upon a light as it changes so I stopped for the red. I was the only car sitting there for most of the light (IOW, I didn’t cut anyone off, I wasn’t going too slow in the fast lane, etc.; nada, no one could be road raging on me.)
Just as the light turned green I heard a gunshot & immediately felt the wetness on the back of my neck. M-Fer, I’ve just been shot…& I have no idea where it came from!. I press one hand there to put pressure on the bleeding & mash the pedal to the floor & drive a couple of blocks so that I’m out of any line of fire & screech into a parking lot to see how badly I’ve been shot. Imagine my confusion when I pull my hand from the back of my neck & look at it & it’s not bright red & rear seat window is still intact. Whiskey, Tango, & Foxtrot???
Liquid doesn’t heat or cool as quickly as air does. There had been a can of soda on the rear floor. Despite the air in the car now being comfortable I guess the can didn’t cool off enough & when the top explosively popped it sounded like a gunshot & the immediate wetness on the back of my neck was soda & not blood. If I was driving & not at a light when it happened, or had the can been in the front it may very well have ended up differently.
Here are some people who did. First, the Mythbusters, who took sensible precautions.
Then these rocket scientists who managed not to kill themselves, but who knows what happened at the other end of this cylinder’s flight?
The A-Team did that in an episode many, many years ago - lined the cylinders up on a rack, and knocked the necks off with a sledgehammer to make missiles/projectiles out of them.
ETA: The guy in that second video was an absolute dumbass - I wouldn’t have gotten anywhere near the business end of that thing after whacking it the first time.
Color me somewhat unimpressed with the “sensible precautions”; did they not think build up a sandbag berm against the back wall of the building to catch the tank and distribute the impulse? What if the tank had punched through that wall as well?
Stranger
Reminds me of Punkin’ Chunkin’; if you ever get the opportunity to see one…go! They can launch over 3/4 of a mile
I was chased by an errant cylinder one time. Two of us were in a tool/stock crib that had several rows of cabinets and a workbench with a massive vise mounted in the middle. The tool crib was made of heavy metal chain-link fence material. The other guy had a small CO2 fire extinguisher cylinder he wanted to check to see if it had pressure. CO2 extinguishers eject solid carbon dioxide when you use them and thus they can develop tremendous thrust. But the extinguisher handle has a small orifice to limit the amount that can come out. The bare cylinder however, does not have this device. Ahem.
Other guy barely cracks the valve and the damn cylinder tears out of his hand and goes all I’m-a-rocket on him.But the valve is pointing sideways, not inline like when you break one off. So the cylinder proceeds to corkscrew all over hell’s half acre and chases us around the tool crib which by now is completely obscured by CO vapor. Every now and then the cylinder would rise above the vapor cloud and make a pass at my head.
Amidst all this the other guy lets out a blood curdling scream. He has just run into the vise with his privates! I seemed like it lasted forever but was probably about 10 seconds. When the vapor cleared a bunch of people were staring into the crib. Small parts were scattered everywhere. everything was covered in dust. And other guy was doubled over holding his crotch.
Then of course there is the tale of the woman sitting in her car in the hot sun and a can of biscuit dough explodes. A hot, wet biscuit hits the back of her head. When she touches it she thinks she has been shot and her brains are exposed. I forget what Snopes had to say about this one.
Now if this happened to Becky she would fall back on her country gal/pioneer ethic and plop the remaining dough on the engine and have fresh biscuits when she got home.
“I wonder if this grenade has a live fuse installed…”
Stranger
Hell, yeah. Who gonna do the gravy?
Home canned food. In glass jars, can be death traps.
I saw destruction caused by a quart jar of chow-chow that exploded. The flying shards broke several jars of canned tomatoes. Looked like a murder scene.
I have heard of chow-chow but have no idea what it is. A quick Google shows there are countless varieties. How do you make yours? Or should this go to Cafe Society in a new thread?