All joking aside, a flame test will not always find a propane leak. The range of flashpoint for propane is between 2% and 10% density in air (all numbers are approximate; if anyone wants the percentages to the last decimal point I can look them up /forums/images/graemlins/smile.gif ). In other words, if there is less than 2% propane in the air it won't light, and if there is more than 10% propane in the air it won't light. Propane dissipates very quickly. In the open, there will be a very narrow band of distance where the mixture is high enough to light - beyond that, it falls off quickly to less than 2%. In a closed area, the mixture can build up quickly beyond 10%. The real danger is in a closed area that is opened. As the air is freshened, the mixture will fall off until it his the 10% point, and then, if there is a source of ignition, you have a Floomph.
Also, even though I use the term myself, propane does not "explode" in the sense that something like dynamite does. What it does is flash burn very, very quickly, which creates so much pressure that things around it tend to get knocked over - like walls and ceilings, for example. In the open, what you get is a big flash of fire which goes out once the fuel is consumed. The pressure can knock you over but you aren't going to disintegrate... /forums/images/graemlins/crazy.gif
One of the more interesting things about the Columbine tragedy a few years ago was that the kids had constructed "bombs" consisting of propane cylinders with nails taped to the outside. I'm not sure how they intended to set them off, because what is inside the tank is pure propane which won't light, and once you let some out, it might knock over the cylinders but it isn't going to disturb the nails.
When a propane storage tank develops a leak (usually a valve failure of some kind), they don't want the propane spewing around where it might reach flash point near a source of ignition. So, what they do in some cases is light the leak and let it burn until the tank is empty. Makes a pretty neat tower of flame but doesn't bother the tank...
Propane boils at -44 degrees F to produce the gas we burn. Normally, room temperature is plenty to make it boil (it won't boil as long as it is at stable pressure, but as soon as you use some vapor, it boils to produce more and stabilize the pressure again). But if it's pretty cold, it will draw all of the heat it can from the surrounding air, then stop boiling (this is what causes the rime of ice around the outside of a cylinder). If it's cold enough, below -44 F, you can carry liquid propane around in an open bucket. In cold climates, and in situations where the vapor is being used rapidly (like for a boiler), they have to wrap the tank with heated blankets to vaporize the liquid. One trick of the "old timers" (before our society got so litigious, back when people accepted responsibility for their own actions) was to build a wood fire under a tank to help vaporize the liquid.
Sorry to get a little off topic, but I always found some of these facts interesting. Please, no Hank Hill jokes... /forums/images/graemlins/wink.gif
