00:00then what really explodes the vapors the oil evaporates especially its lighter
00:06components even in an apparently full tank above the liquid there's a space
00:10with hydrocarbon vapors these vapors mixed with air can become much more
00:16dangerous than the liquid itself in fact this is the principle we use every day
00:21in a car engine it's not the liquid gasoline that burns like a puddle of
00:25fuel a mixture of air and gasoline vapor enters the combustion chamber the
00:31piston compresses this mixture the spark plug ignites it and the hot gases
00:35expand and push the piston down that's how we get mechanical work in a
00:40gasoline engine this process is controlled in the auto cycle we have
00:44intake compression combustion and exhaust everything happens in a small volume at
00:49the right moment with a mixture of air and fuel vapor as precisely measured as
00:53possible here a fundamental concept in combustion appears the flammability
00:58range fuel vapors can only burn within a certain concentration range if you have
01:04too little fuel combustion won't propagate if you have too much fuel and too little
01:08oxygen the reaction gets choked if the ratio is right the mixture ignites
01:14violently in the car engine this ratio is controlled but what happens if a rocket
01:19hits an oil tank and suddenly creates a cloud of vapor and fine droplets mixed with
01:24air then we're no longer talking about an engine we're talking about a dangerous
01:29explosion
