View Full Version : Gas Explosion

06-01-2008, 01:53 PM
I'm writing a story at the moment which has an explosion in it.
The character has set two piles of gas cannisters on either side of a path and has spread some lighter fluid to be spread between the two piles and trailed back some so that they can light it and cause an explosion to kill some monsters that are chasing them.
I want the effect to be that a match is dropped into the fluid and it trails along the fluid and then blows the gas up.
Would the lighter fluid actually trail along as gun powder would or would it instantly light up? If it wouldn't work would anyone know of anything that would.
I would be grateful if anyone could let me know on the thread or by PM.
Thanks for your help.

06-01-2008, 03:40 PM
I can't help with most of this but I suggest you buy some lighter fluid, trail it along on a safe, inflamable surface then try lighting after one minute, repeat and wait five minutes and so on until you find the longest you can wait before the fluid evaporates and will not serve the purpose. That means you know, realistically, how long you have for action before you must light the fuse.

Have you thought of a slow fuse. You can find how to make it on the internet.

06-01-2008, 04:19 PM
Flammable fluids burn like gunpowder and you should be able to see it moving along the ground. I've never seen lighter fluid, but my guess is it would progress at a steady pace. As Mumut said, I'd put some down and play with it to get an idea of the speed.

The effect when it reaches the end might not be quite what you expect. Gas goes with a 'whoosh' rather than a 'boom.' Lighter fluid isn't going to produce a lot of heat, unless you have a lot of it. If the gas is in plastic containers, you'll have to produce enough heat for the containers to melt. With metal containers, you'll have to produce enough heat to cause the metal to burst from expansion. The bursting may or may not be powerful enough to produce shrapnel. And 55 gallon drums might not burst at all.

The heat would produce vapors, provided the containers are able to vent. This rising vapor would burn, sort of like a flame thrower.

The explosions you see of cars in movies don't happen normally. Cars have a lot of fire load, and burn very hot, but they don't go boom. The gas just tends to vent, producing a nice volume of flame but when the fire goes out, the metal of the car is still, in appearance, undamaged except for the loss of paint. Neither the gas tank or car body has been ripped apart by an explosion. Biggest danger in a car fire is not the gas tank exploding but the bumpers exploding off the car. Can break your leg very easily.

Your destructive force here is not high. Damage will be heat rather than explosive force.

On the other hand, people other than firefighters probably won't know this. And even though I know cars don't go boom, I like watching them on movies.

Best of luck,

Jim Clark-Dawe

Histry Nerd
06-01-2008, 05:26 PM
Hey, Nikki -

I'm not sure using gas canisters and lighter fluid is the best way to do what you're trying to do. I'll try to make some suggestions to make it more plausible.

First, the lighter fluid. I'm not an expert in the combusibility of lighter fluid, but I think its burn rate is somewhere between kerosene and gasoline--faster than the one, but slower than the other. It would go up much more quickly than you want it to--it may not flash, but it would burn too fast for your characters to get out of the way. Burn temperature is also a problem; lighter fluid won't get hot enough to ignite a closed gas canister. And it would probably evaporate within a minute or two of being poured on the ground. I'll talk some more on ignition options below.

The canisters themselves are also a problem. Gas canisters (I assume you're talking about propane or something similar) are much tougher than many people give them credit for. Unless a canister is defective, it takes a lot of force to breach it. You can cause it to burst by dropping it onto a hard surface from a height (higher than ten feet or so), but the effect will be like a big balloon popping; you'll get shrapnel but no flame. You can get the same effect by shooting one or hitting it with an axe, but of course you have to be pretty close to hit it with anything. Heating it up in a campfire will cause the gas to expand until it explodes, but the explosion is unpredictable: it may ignite at the nozzle and shoot off like a rocket, or it may burst along the side and spin rapidly as the propane burns off. It will probably not blow like a bomb, as you want it to do.

Your best bet for your trap is probably to knock the nozzles off, or open them somehow, and use the bottles as hasty flamethrowers; with the gas escaping already, it would only take a match to ignite them. You'll want to secure their bottoms to keep them from jetting off, but they'll produce a nice jet of flame once ignited, and your characters can eat the monsters after they're cooked. Of course, they'll need to open the nozzles at the last possible minute to avoid too much gas escaping. A molotov cocktail made with the lighter fluid and a glass bottle would be a good ignition source--but your character will have to duck after he throws it.

An even better option might be to set your trap in an enclosed space (a room, a cave, etc) and lure the monsters into it. The space will trap the escaping gas, and when you toss your molotov cocktail, you'll shortly be serving up Kentucky fried monster.

Just a couple of suggestions. I can give you more detail (a little) if you want it.

Hope this helps.

06-01-2008, 08:32 PM
If you're talking propane (I assumed gasoline) you can see videos on the net. For example http://www.metacafe.com/watch/438988/exploding_propane_tank_extreme/ and http://video.aol.com/video-detail/shooting-small-propane-tank/3935952178

You'll notice that until you get into the big tanks you really don't get much bang for the buck. Probably unless your monster is sitting on the tank when it goes boom it's not going to be hurt. Explosions require a concentration of force to do damage. Without knowing what you're doing, it's hard to get good booms.

Best of luck,

Jim Clark-Dawe

06-02-2008, 10:05 AM
Why not check DVD's of the Mythbusters. They've blown about everything up you could think of, except themselves. They might have a crazy idea to get the effect you want.

06-02-2008, 10:35 AM
For some strange reason I feel it is the fumes that explode, not the liquid. Am I right? Crazy? Don't know. Mythbusters is a cool place to look.

06-02-2008, 12:10 PM
Was just going to come on here and suggest Mythbusters, but I see I've been beaten to it. :D

06-02-2008, 01:04 PM
For some strange reason I feel it is the fumes that explode, not the liquid. Am I right? Crazy? Don't know. Mythbusters is a cool place to look.

that is correct. You need the vapour/air mixture to have an explosion otherwise the liquid burns only on the surface

Sandi LeFaucheur
06-02-2008, 01:34 PM
Just last week, Mythbusters were trying to get disposable lighters to blow up, an had a good deal of difficulty doing it. If it's that hard with a $1 lighter, imagine how hard it would be with a proper propane tank.

06-02-2008, 04:33 PM
To continue the question about stuff burning, with gasoline what burns is the vapor, not the fluid. But it can turn into vapor very quickly. Propane is normally a gas, although at extremely low temperatures it becomes a liquid.

For either gasoline or propane to burn requires oxygen.

In the case of either, what would happen here is actually a two step process, which if high speed film is used, you can see. The first is that the stuff in the container heats up, causing it to expand. If not allowed to vent, or if the venting is inadequate, it will eventually expand to the point where the container ruptures. You can do the same thing with a can of soda.

Once the container ruptures, the gasoline or propane will ignite, if there is an ignition source available. But this occurs a split second after the rupture of the container.

If the container is allowed to vent and there is an ignition source, then you will probably have a flame thrower effect (depending upon the pressure). However, as long as the container can vent faster than the contents expand, you'll never have an explosive type event. It will just cook off.

Containers are rather robust things, and with propane containers, are designed to rupture in certain ways to minimize destruction.

Best of luck,

Jim Clark-Dawe

Kathie Freeman
06-03-2008, 08:19 PM
I dn't know about lighter fluid, but gasoline does not "trail along". It flashes instantaneously. I know this because I was standing about 10 feet away when my husband very nearly set himself on fire this way. We were trying to set fire to a big pile of alder saplings that we had cleared from our property, and he poured a quart of gasoline on the pile and then a "trail" about 10 feet long. He droped a lighted match on the end of the "trail", and there was a flash and an explosion you could have heard half a mile away. The flames came within inches of my husband, the dog yelped, disappeared, and didn't come back for nearly an hour. Whatever you've seen in the movies or on tv, forget it.

06-08-2008, 06:25 PM
I know in Iraq it's common for US troops to destroy buildings using propane tanks, and igniting the gas through an ignition source. Basically it's a fuel air explosion.

However the big thing is that for something like propane to combust, it needs to have the right amount of air, and the effect of the explosion is EXTREMELY dependent on topography. In an enclosed space like a house, it'll be devastating, but in the open, it's most likely just going to flare up as a big flame, as opposed to explode.

Tsu Dho Nimh
06-09-2008, 01:46 AM
To get the earth-shatering kaboomn, uyou need to open the tank inside a confined space, then set off the ignition source.

Outside, it's just a big fireball.