Compressed natural gas (CNG) unlike gasoline dissipates into the atmosphere in the event of an accident. In contrast, gasoline pools on the ground creating a fire hazard.
The fuel storage cylinders used in NGVs are much stronger than gasoline fuel tanks. The design of NGV cylinders are subjected to a number of federally required "severe abuse" tests, such as heat and pressure extremes, gunfire, collisions and fires.
NGV fuel systems are "sealed" which prevents spills or evaporative losses. Even if a leak were to occur in an NGV fuel system, the natural gas would dissipate up into the air because it is lighter than air.
Natural gas has a high ignition temperature of about 1,200 degrees Fahrenheit, compared with about 600 degrees Fahrenheit for gasoline. It also has a narrow range of flammability. In concentrations in air below about 5 percent and above 15 percent, natural gas will not burn. The high ignition temperature and limited flammability range make accidental ignition or combustion of natural gas unlikely.
Natural gas is not toxic or corrosive and will not contaminate ground water.