Are Natural Gas Vehicles Safe?

Natural gas is an environmentally clean, plentiful, low-cost, domestically-produced fuel for motor vehicles. But is it a safe fuel? Any automobile fuel can be dangerous if handled improperly. Fuels contain energy which must be released by burning. Gasoline is a potentially dangerous fuel, but, over time, we have learned to use it safely. The same is true of natural gas. Natural gas safely generates our electricity, heats our homes and cooks our meals. But, like gasoline, natural gas must be understood and respected to be used safely.

Natural gas is a naturally occurring fuel which requires very little processing before use. Chemically it normally consists of over 90% methane with smaller amounts of ethane, propane, butane, carbon dioxide and other trace gases. The high methane content gives natural gas its high octane rating (120-130) and clean-burning characteristics, allowing high engine efficiency and low emissions. As with all vehicle fuels, natural gas can be used safely if simple, common sense procedures are followed. In fact, natural gas has safety advantages compared to gasoline and diesel: it is non-toxic, and has no potential for ground or water contamination in the event of a fuel release. An odorant is added to provide a distinctive and intentionally disagreeable smell which is easy to recognize.

The odor is detectable at one-fifth of the gas’ lower flammability limit. Natural gas vehicles have an excellent safety record for two primary reasons: the properties of the fuel itself and the integrity of the natural gas vehicle and its fuel delivery system. Natural gas has a very limited range of flammability – it will not burn in concentrations below about five percent or above about 15% when mixed with air. Gasoline and diesel burn at much lower concentrations and ignite at lower temperatures. Although it takes very little energy to ignite a flammable mixture of air and natural gas, gasoline, or diesel, natural gas burns at a somewhat lower temperature.

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From the gas field to the vehicle’s engine, natural gas requires very little processing to make it suitable for use as a fuel. Gasoline and diesel must be processed from crude oil in large and complex oil refineries. After water vapor, sulfur and heavy hydrocarbons are removed, natural gas flows by pipeline (the safest way to transport energy) directly to the fueling station where it is compressed for use. Alternatively it may be liquefied at cryogenic temperatures on site or at a central facility and delivered by truck. Gasoline and diesel are delivered to fueling stations by tank trucks over the highway. At a compressed natural gas fueling station the gas is compressed before being provided to vehicles at 3000 to 3600 pounds per square inch (psi). Stations can deliver a “fast fill” to vehicles in minutes or, using a “slow fill” strategy, in a few hours to overnight.

Although the use of high storage pressures might appear dangerous, compression, storage and fueling of natural gas vehicles meet stringent industry and government safety standards. Natural gas powered vehicles are designed and built to be safe both in normal operation and in crashes. New natural gas vehicles are subjected to the same crash tests as other vehicles. Natural gas vehicle fuel systems must meet Federal Motor Vehicle Safety Standards 303 and 304. Natural gas cylinders are much thicker and stronger than gasoline or diesel tanks. Industry standards require them to withstand 11,250 fill cycles, and endure far beyond normal environmental and service damage risks.

Although there are approximately 85,000 natural gas vehicles now operating in the United States, there has not been a fuel tank rupture in over two years. In Italy, with over 300,000 NGVs in operation, there was only one fuel tank rupture during the last three years.

In conclusion, technical data, appropriate safety regulations and years of experience show natural gas vehicles to be as safe as, or safer than, conventionally fueled vehicles.