Perhaps the issue of most concern to people regarding natural gas powered vehicles is safety. Many people believe natural gas to be far too volatile a fuel to be used in vehicles. However, a review of some of the properties of CNG reveals that this view of volatility and danger is ill-founded.

Flammability and Ignition Temperature

Natural gas has a limited range of flammability, i.e. the correct mixture of air and fuel to burn. This range for natural gas is approximately 5-15% and the ignition temperature of natural gas is approximately 1100 degrees F.

Both gasoline and diesel have lower flammability mixture ratios as well as ignition temperatures than natural gas; thus making natural gas a safer choice.

Fuel Density

Natural gas is lighter than air, thus generally rises and dissipates into the air if a leak occurs. Contrast this to gasoline which pools upon the ground presenting a clear danger in case of a leak or accident.

Vehicle Safety

The fuel tank and associated tubing on a NGV (natural gas vehicles) are designed to work with and contain the operational pressure of the system, which usually exceeds 3000 psi. Moreover, the fuel tanks are comprised of tough polymers that are extremely strong.

Compare this to the typical fuel tank in a standard, gasoline powered vehicle. These are made of stamped steel halves that are usually only a few sixteenths of an inch thick.

Sources:

About.com: Scott & Christine Gable-The Lowdown on CNG Safety
Scribd.com: Randy Lieber-Fuel Tank to Think Tank