Range of flammability

Hydrogen is flammable over a very wide range of concentrations in air (4 - 75%) and it is explosive over a wide range of concentrations (15 - 59%) at standard atmospheric temperature, (4% of air are enough so that the combustion occurs), and the front of the flame is spread much more fast (approximately 265 cm/s in ideal conditions, in opposition to the 40 cm/s of the gasoline). However, the hydrogen presents little energy in a volume equivalent. It is a fuel that wide is used in rockets, including the Space Shuttle and can be used as combustible for an engine of internal combustion

Gasoline Range of flammability (1- 7.6%)

Diesel Range of flammability (0.6- 5.5%)

In contrast of fossils fuels, the hydrogen is part of a perfectly balanced cycle: after used hydrogen extracted from the water using electrolyse it is freed in the vapour form that returns then to the natural cycle of the water.