Table 2: Comparison of fuel safety properties in air [18, 24, 25, 27].

Fuel Autoignition temperature Flammable limits Explosive limits Buoyant velocity Ignition energya
K Vol.% Vol.% m s−1mJ

Hydrogen 673–858 4.1−74.2 18.3−59.0 1.2–9.0 10
Methane 923 5.3−15.0 6.3−13.5 0.8–6.0 20
Ethane 788 3.0−12.5 b
Propane 723 2.3−9.5 3.1−7.0 b
Butane 678 1.9−8.5 b
Gasoline 553–729 1.4−7.6 1.1−3.3 b
Ethanol 696 3.3−19.0 b
Methanol 743 6.0−36.5 b

Ignition energy at the lower flammability limit. For stoichiometric mixtures, the value is significantly lower (e.g., 0.02 mJ for hydrogen) [18].
Nonbuoyant, due to higher density than air (1.2 kg m−3) under standard conditions.