Why do vapours of flammable substances pose such a serious hazard?
The vapors of flammable substances are often heavier than air and can “flow” a considerable distance to an ignition source, then ignite and flash back to the source and ignite the whole thing possibly even causing an explosion. For example, somebody using gasoline to clean parts in a basement, the vapors may flow along the floor and reach the pilot light of a gas water heater and ignite. Numerous fires and accidents have happened this way and by similar scenerios.
