Definition - What does Flammable Gas mean?
A flammable gas is a gas that burns in the presence of an oxidant when provided with a source of ignition. Flammable gasses can include methane, acetylene, ammonia, hydrogen, propane, and propylene. The risk of a fire starting increases in relation to the amount of gas present. If the concentration exceeds the higher value (UEL), the air will become too rich to burn, which will actually reduce the chance of ignition. OSHA does not categorize aerosols as flammable gasses.
Safeopedia explains Flammable Gas
Regardless of how secure a gas containing container is, there is always the possibility that a small amount of gas may escape. Under the right conditions, this can form an ignitable mixture. Escaped gas can mix with the surrounding atmosphere, which may result in a fire or an explosion. There is also a negligible risk of fuel gasses reaching their lower threshold limit in open air spaces.
By odorizing gasses, escaped gas can be more readily identified.