RAH wrote:
Peter, I'm not going to get into a fisking match with you, but I didn't just make this stuff up, and I resent you saying I did.
OK, I agree I was a bit snarky. Mea culpas below.
At 10:26 AM -0500 3/31/04, Trei, Peter wrote:
* Evaporating LPG (liquids do not 'sublimate') will burn at the interface where the proper mixture is obtains - and the heat from that will speed the evaporization of the rest.
Right.
And, uncontained, it doesn't explode, either, which was my main point. It'll burn like hell, but that wasn't what the sanctified idiots at the Bulletin of the Atomic "Scientists" were FUDding on about.
Not only that, but it doesn't burn that fast: http://northstarind.com/lngfaqs.html "Natural gas is only combustible at a concentration of 5 to 15 percent when mixed with air. And, its flame speed is very slow. These facts may best be experienced by a simple demonstration often done at LNG fire schools. A large pit, i.e., 20' x 20', is filled with LNG, allowing the vapor cloud to drift with the wind. The cloud is ignited with a torch from a downwind side. Ignition typically occurs near the visible fringes of the cloud. The resulting flame front moves back toward the pit at a speed only slightly faster than a walk."
As for "sublimate", when you toss a cup of boiling water into the air at extremely cold temperatures it converts straight into a gas, all at once. That's what I was talking about. A chemist I bumped into with that story called it sublimation, and when I said I thought "sublimate" was meant for solids only, he said no, that instantaneous conversion to a gas is sublimation whether origin state is a solid or liquid.
Go figure.
Well, I tried. Every dictionary I checked refers only to direct solid->gas transition. I'm aware of the effect you describe, but its not sublimation. See: http://www.coolantarctica.com/Antarctica%20fact%20file/antarctica%20environm ent/weather.htm If you throw boiling water into the air at -32C, much of it evaporates instantly (the humidity is near zero), and some of the larger droplets freeze, falling to the ground as ice. No liquid will hit the ground. Volcabulary flames are about as pointless as they get, so I apologize for starting this one.
As for
* LPGs (both butane and propane) are denser than air. Propane has about the same density as CO2. Butane is even denser. They will both travel downhill and pool in low spots.
I did actually look this up when I wrote my rant. LNG floats on water, and, as a gas, it's lighter than air by about half the weight of same.
Mea culpa. I was confusing LPG and LNG. (Some of the sources I looked at refered to liquid propane and butane is LNGs.) Those gases are denser than air. Correctly speaking, they are referred to as Liquified Petroleum Gases (LPG), not Liquified Natural Gas (LNG). LNG is primarily methane, which, as you say, is lighter than air. Peter