Propane Explosions

I am currently reading a book about the Columbine massacre. The two killers had made makeshift propane bombs from BBQ propane containers. Experts say that had the bomb worked (thankfully it did not) it would have destroyed an entire wing of the school.

I have a propane tank on my deck.

Should I be worried? Can they explode that easily?

The phenomenon is called a BLEVE. Flammable BLEVEs are very dangerous but without something to compromise the canister or a sufficent heat source I’d say your bigger concern would be the fire that sets it off.

the tanks have pressure relief valves to release pressure before it gets hot enough to explode the tank. the vented gas will burn but not explode. so sitting in the sun on a hot summer day will not cause it to explode.

if your house were on fire and the tank heated slowly it would vent the gas and it burn off. if your house were on fire and the tank heated quickly then it might explode but being outdoors it probably wouldn’t hurt your house more than the fire already had.

Even in the sun, in the desert southwest United States, in the heat of summer, the tank is not likely to get much over 150 degrees, at which temperature the vapor pressure is only 330 psi. The tank will happily hold this kind of pressure; the standard calls for a design burst pressure of 960 psi, which is a safety factor of about 3. You’d have to throw the tank in a fire to get it hot enough for the internal pressure to activate the relief valve.

If the tank is stored in an enclosed area (basement or garage), and it vents or leaks for some reason (e.g. relief valve or main valve malfunction) without a nearby ignition source, the gas will accumulate. An ignition event AFTER a massive cloud of flammable gas has accumulated is likely to remove your house from its foundation.

If the tank is stored outdoors, you’ve got little to worry about, as ambient winds will likely carry away any vented gas before you develop a large cloud. Check the side of the propane tank: mine warns against storing indoors.

Given the general level of smarts that we as a species demonstrate, especially around our BBQs, I think that if those little 1lb and 20lb propane tanks were all that dangerous the average American neighborhood would sound like a bombing range.

As noted, they have blowout safety valves and the tanks themselves are pretty rugged. If you follow the safety label and use some common sense (keep tanks out of direct sunlight and away from flames, don’t try to modify them, don’t expose them to drop/puncture hazards) you should be good.

You almost never have to worry about propane tanks ‘exploding’.

Bad LP tank or LP line leaking into a space that contains it? YES… A BBQ tank’s worth would take out a small home:

Just watched some show like Destroyed in Seconds the other day and they showed a house in Brazil (?maybe) that had a bunch of propane canisters in the garage and was on fire. The explosions were pretty big, house was destroyed.

You have three basic types of explosions; chemical, mechanical, and nuclear. You can get two of the types with the propane tanks. The chemical comes when the gas (propane) escapes, combines with enough air (oxygen) to form an ignitable mixture, and then gets ignited. You can look up fuel-air effect bombs for a deeper explanation. No the gas won’t explode just coming out of the container; it will just burn. You may get an exciting demonstration of a rocket motor. If the pressure relief valve fails to open or is obstructed, a mechanical explosion will result. The metal tank will fail with lots of overpressure, metal shrapnel, and later chemical explosion of the contents. Nuclear - fission or fusion - won’t pay a role here.

Just for the record, reports that I read indicated that there were multiple propane bombs. A single tank wouldn’t have caused the devastation they were after (i.e., a whole wing of the school).

How would you even build a propane bomb? For a propane explosion, you need to have a bunch of propane already mixed with a bunch of oxygen (and then something to light it). A leaking tank/hose inside an underventilated room will build up enough propane, mixed with the air in the room, to go boom nicely if you come along at the right time and throw in a match/spark, but that’s hard to translate to a bomb.

The only way I could think of is a propane tank with some kind of timer-spark mechanism that will start making sparks in, say, 2 hours. Put the tank in a closet, start the timer, open the tank valve, close the closet door, and in a couple hours you might get a boom. But if someone opens the door in the meantime or the closet is too big or well ventilated, the gas is going to dissapate and you end up with no or small boom. If the spark goes off too early, you get only a small boom plus maybe a burning jet of gas. If the spark goes off too late, or you’ve got too small a closet, you don’t get a boom because there’s no oxygen left and propane can’t burn or explode by itself. So, I guess possible, but it’s not surprising they couldn’t pull it off.

I live in a house where a propane fireplace is being installed, and Im worried about it. (I also think a propane fireplace is kind of silly.) The tank is outside, but of course there is a gas line that goes inside to the fireplace. Does anyone know anything about the safety of these things?

If I recall correctly, the Columbine kids left their “bomb” in the kitchen. The kitchen will likely have a pilot light going.

properly installed it should be no more dangerous than a gas kitchen range.

OK, but that relies on a bit of luck, where an explosive amount of gas/air drifts over to the pilot light at the same time as a large amount of explosive gas/air is also present in the room. Plus school kitchens are probably fairly large and well ventilated.

Years ago, as a young lad, I witnessed a house fire, behind the house were two propane tanks, the relief valve of either tank would open every now and then releasing gas that ignited right away causing a WOMP type of sound. I do not know if the gas was hot enough to ignite on its own or if there was open flame close enough to ignite it.

Understandably, I was quite some distance away but there were others fighting the blaze and emptying the house of whatever they could get a hold of, my father was among them and he did say afterward that hearing those tanks go made him uncomfortable.

As an aside, the fire was caused by someone refuelling a tractor in the attached garage and spilling fuel on the hot exhaust manifold.

This summer, my parents house burned to the ground. The fire was hot enough to bend the steel I beam that was supporting the second floor, but the 20# propane tanks did not explode. They did vent. I bet they made some pretty blow torches for a while.

It will probably be as safe as a propane gas kitchen range.

Natural gas is much safer.

Experts suggest that the safety record of propane is less than exemplary.

“Accidents with [propane] gas are dramatically out of proportion” for the number of people who use the fuel, said chemical engineer Alan Bullerdiek of Buffalo, NY. “They represent ten times the number of accidents as natural gas.”

Propane also has 20 times the energy of natural gas.

Wanna feel safer? Get a propane fume detector, because the chems they add to stink up propane often fade too fast or are absorbed by things like… MASONRY. :eek:

(all from my earlier link)

Gee, and listening to the 911 “truthers” would lead one to believe that steel doesn’t soften in a fire.

I have had them in my campers. The dogs regularly prove that they detect methane as well as propane…even somewhat better than the human nose it would seem.

Propane is more hazardous because it is heavier than air, and so tends to pool and get ignited by pilot flames like gasoline fumes.

If I were disposed to create a destructive device from a propane bottle, I would use appropriate explosives to rupture the bottle and disperse the liquid, and a second charge to set off the fuel air mixture. But I’d use a 5 gallon bucket of gasoline instead of the propane…easier to disperse than the cryogenic (once you split the bottle) propane.

And if you do it right, it looks like this.