Liquid Natural Flatulence

[Trei, Peter]

R. A. Hettinga wrote:

> A *cryogenic* liquid, mind you, meaning that you'd have to heat the
> stuff up a lot, and very quickly, in order to set it ablaze, much
> less blow it up. A liquid which is busily sublimating directly into
> the gas that it is at room temperature, and diluting, accordingly,
> with the vast amount of normal air around it in the process. More to
> the point, as a gas, it's about half the weight of air itself, so it
> *rises*, as it dissipates, straight up, again, very quickly. It
> doesn't hang around, flowing down hill, and pooling like, say, C02
> might, with the potential to asphyxiate people in the process.

Bob: Get your facts straight:

* 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.

* 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. 

* LPGs can most definitely asphyxiate you.

Check:
http://www.lpga.co.uk/safe_handling.htm

"LPG can form a flammable mixture when mixed with air. The flammable 
range at ambient temperature and pressure extends between approximately 
2 % of the vapour in air at its lower limit and approximately 10 % 
of the vapour in air at its upper limit. Within this range there is 
a risk of ignition. Outside this range any mixture is either too 
weak or too rich to propagate flame. However, over-rich mixtures 
can become hazardous when diluted with air and will also burn at 
the interface with air."

"LPG vapour is denser than air: butane is about twice as heavy as air 
and propane about one and a half times as heavy as air. Consequently, 
the vapour may flow along the ground and into drains, sinking to the 
lowest level of the surroundings and be ignited at a considerable 
distance from the source of leakage. In still air vapour will disperse 
slowly."

"At very high concentrations in air, LPG vapour is anaesthetic and 
subsequently an asphyxiant by diluting or decreasing the available 
oxygen.."

The 'rise to the sky and disperse' stuff you're talking about applies
to hydrogen, not LPG. A massive LPG spill will spread out over the 
surface of the ground and water, and when a source of ignition is found,
the whole mass will burn at the interface where it mixes with air.

You might also want to take a look at
www.respondersafety.com/downloads/standoff.doc 
"Improvised Explosive Device (IED) Safe Standoff Distance Cheat Sheet"
which reccomends in the case of an 18 wheeler LPG truck to keep
people at least 1996 feet away.

I would not want to be nearby when a tanker - or a massive storage
tank - gets hit.

Peter Trei