Originally Posted by
AmuDarya
I know Jet-A has a relatively high flashpoint, but still, if that low-altitude dumping had resulted in relatively concentrated spray landing on some backyard barbecues, the results would have probably been lively. Good thing it didn't happen on the Fourth of July.
Flashpoint is about the volatility of the fuel; the temperature above which sufficient vapor will evaporate off the surface to form a flammable mix with the surrounding air. In the case of kerosene, that temperature is about 36degC.
Upper and lower flammable limits are the proportion of fuel to air which will ignite. If you adjust a petrol carby particularly too rich, for example, then the resulting mix simply won't ignite. The range for kerosene is roughly 0.6% to 5% kerosene in air.
So if you can achieve a cloud of a bit over 0.6% kerosene in air, you have the potential for a fireball.
Air has a density of about 1.2kg/m^3 at STP, liquid kerosene is about 0.8kg/litre. One litre of fuel dispersed into one hundred cubic metres of fresh air would do nicely.
I have no idea what discharge rates in either litres or kg per second are achieved, so I'll leave space on the back of my envelope for someone else to continue... Given an airspeed and a discharge rate, you can get the cross sectional area of a path through space left filled with a flammable mix.