Posted by Adam Quinan on November 28, 2008 at 22:06:33 user Adam.
In Reply to: Re: Starting a fire posted by John Lambert on November 28, 2008 at 19:43:39:
The chances of a cigar butt starting a fire in a tank is a question of mixing fuel vapours and oxygen in an explosive mixture. Liquid fuel will put out most ignition sources like matches or cigar(ette) butts.
There is an upper and a lower explosive limit of fuel vapours to air ratio that means no explosion if the ratio is outside that range. In an open tank, the vapours may blow away so that the ratio is less than the lower explosive limit. For gasoline (petrol) the range is from 1.7% to 7.6%.
If an enclosed tank was full or nearly full, the cigar would probably just be extinguished when it hit the liquid surface. If it was empty there would be a possibility that it might ignite the vapour before hitting the liquid and being put out if the vapour to air ratio was in the explosive range.
A hot climate would increase the vapourisation but that might just displace the oxygen as fuel vapour is more dense than air and so the concentration might be above the upper explosive limit and again no explosion.