Comment by kens
7 years ago
One of the dangerous things about hydrogen is its wide flammability range: from 4% to 75% concentration of hydrogen in air. Hydrogen will detonate in concentrations between 18% and 59%. In comparison, gasoline has a surprisingly small flammability range of 1.4% to 7.6%.
What drives this wide range of flammable concentrations? Is it just an issue of low activation energy?
Also the upper end is impacted by the low number of oxygen atoms each hydrogen molecule can react with, in this case it's just one, compared to gasoline with say 8 carbon and 18 hydrogen atoms which bounds to 25 oxygen atoms. Mind you, the size of a gas molecule doesn't affect how many you get per volume at a certain pressure and temperature. So 50% gasoline vapors and 50% hydrogen are both molecule counts, with the former requiring 25 times as much oxygen for full combustion, compared to the latter.