NGVs (natural gas vehicles) have a stellar safety record which is based upon two facts:
- The physical properties of natural gas make it safer than most other fuels.
- The fuel systems designed for NGVs are built to stringent standards.
A Closer Look at Natural Gas
- Physical Properties: Yes, natural gas itself is a safer fuel than either gasoline or diesel fuel. It has a limited range of flammability, meaning it requires the correct mixture of air and fuel to burn—somewhere in the 5 to 15 percent range, and an ignition temperature of approximately 1100 degrees F. Compare that to gasoline and diesel fuel which both have lower concentrations of flammability and lower temperatures of ignition.
- Fuel Density: Natural gas is lighter than air. If a leak were to develop, the gas would rise and disperse through the atmosphere giving little chance for ignition. Compare that to gasoline and diesel fuel, both of which are dense liquids that tend to pool and are easily ignitable.
- Odor: Raw natural gas is odorless, so a distinctive odorant that smells very much like strong sulfur is added prior to distribution. This strong odor makes the presence of a leak very easy to detect.
- Toxicity: Natural gas is non-toxic.
A Closer Look at NGVs & Safety
Natural gas vehicles are very safe, for not only do they have all the same standard safety equipment as conventional cars (passive restraints, air bags, head restraints and anti-lock brakes), but they are subjected to the same crash safety tests as well.
Because compressed natural gas (CNG) fuel systems operate at pressures in excess of 3000 PSI, the fuel tank and associated plumbing have to be incredibly rugged and strong enough to contain that pressure. The on-board tanks are made of steel up to one half-inch thick and often wrapped in protective reinforced fiberglass sheathing. Plus, newer tanks are constructed of polymers and composites that are stronger than steel.
Contrast this with standard gasoline and diesel tanks in regular vehicles. These tanks are usually made from stamped steel shell halves, just a few thirty-seconds of an inch thick, that are welded or crimped together. In the event of a traffic accident, the ability of rugged, durable CNG tanks to withstand rupture or puncture certainly exceeds that of simple stamped steel.
But the safety of NGVs doesn’t just stop with the robust construction of the fuel tank. To take it a step further, most CNG systems have automatic release valves. In a situation of excessive heat or pressure build-up, the valve will open and release the gas to the atmosphere—and since it is lighter than the surrounding air, it will rise and dissipate. The low threshold is set well above ambient temperatures and the high threshold is set well below the ignition temperature of the gas. In the event of a fire, the fuel is safely evacuated from the car before it ever has a chance to catch fire. Gasoline and diesel vehicles simply can’t do that.
A manual shut-off valve also exists just downstream from the CNG tank to allow user intervention if the need arises. A neat side benefit of this valve might be the ability to use it as an anti-theft device. Shut off the fuel supply and any would-be thief wouldn’t get much further than a mile down the road and off shuts the engine. That is the epitome of clever thinking.
So fear not, the use of compressed natural gas as a motor fuel— from compression, storage and fueling to vehicle manufacturing—must meet stringent industry and government standards. And it’s all in the name of clean, efficient and utterly safe motoring.