Propane gas is nontoxic and insoluble in water, so it poses no threat to aquifers or the groundwater supply. It is also not harmful to soil.
It is one of the lightest hydrocarbons in existence, and one of the cleanest burning of all alternative fuels; new propane-fueled vehicles can meet the very tough Ultra-Low Emission Vehicle (ULEV) standards, and one model even meets the Super Ultra-Low Emission Vehicle (SULEV) standards.
Propane is non-poisonous and is a ‘simple asphyxiant’ (i.e. asphyxiants which have no other health effects) where vapor replaces oxygen available for breathing and may cause suffocation in confined spaces. However, it does have slight anesthetic properties and higher concentrations may cause dizziness. The sulphur odor is added for leak detection.