I would like to add a mitigating factor hydrogen: Unlike propane, butane and more-concentrated vapors of flammable liquids, hydrogen is lighter than air. This aids dissipation of flammable gas presence.
Heavier-than-air flammable gases and vapors can pool and spread on the floor or ground, sometimes leading to spectacular flash fires. Some of these involve big eruption of flames from an area much larger than that which a spill of a flammable liquid covers, sometimes ignited by an ignition source such as a gas water heater pilot light. Gas-fueled water heaters even come with warning labels warning about this.