Gas has the disadvantage that in case of a collision its inflammability may assist ally fire that may be started.
Since the inception of the petroleum industry, most civilized countries have prescribed by law a test of flash-point or inflammability, designed in most cases primarily to afford a definition of oils for lighting purposes which may be safely stored without the adoption of special precautions.
The inflammability of coal dust varies with different coals, but none can be said to be entirely free from risk.