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U.S. Department of Energy Energy Efficiency and Renewable Energy

Natural Gas Safety after a Traffic Accident

As with conventional vehicles, a collision or physical impact may compromise the fuel system of a natural gas vehicle (NGV). What is different with NGVs following an accident is the potential for drivers, bystanders, and first responders to be unfamiliar with NGVs and therefore less able to recognize and respond to a compromised fuel system. Below are some tips for drivers of NGVs in the event of an accident.

  • LNG: Liquified natural gas (LNG) is heavier than air when it initially leaks and is stored at extremely cold temperatures, so people should clear the area of any significant LNG leak. The fuel may create a fog-like appearance near the ground. Do not walk through this fog and keep people and ignition sources away from it. In time, the vaporized natural gas will warm, become lighter than air, and eventually disperse. Close the manual shut-off valve for the LNG tank in the event of a leak, if it is so equipped. However, do not expose yourself to hazardous conditions to do so. Call the local fire department and let them address any fire hazards or other safety issues.

  • CNG: Compressed natural gas (CNG) is lighter than air, and leaking CNG will safely disperse in an open area. However, there is a risk of CNG accumulating in enclosed spaces, which could pose a high risk for ignition. Drivers who notice a "rotten egg" odor in the vicinity of their vehicle after an accident, or hear a hissing noise indicative of leaking natural gas, should close the vehicle's manual shut-off valve if possible. If the vehicle is in an enclosed space, avoid using that space and warn others not to enter. Owners should contact the local fire department to ensure that any fire hazards are properly addressed.

  • Inform First Responders: Regardless of whether there is an indication of a leak, if the vehicle is in an accident, the driver should tell the first responders that the vehicle is an NGV. NGVs must also be equipped with a label identifying the vehicle as LNG or CNG in the form of a diamond on the lower right-hand side of the rear of the vehicle. First responders are trained and equipped to handle such hazards.

  • Stay Clear of Leaks: It is best to avoid coming anywhere near leaking LNG and CNG.

  • Get a Tow: If an NGV is involved in an accident that may have damaged the integrity of the fuel storage or delivery system, close the manual shut-off valve for the storage tank, if it has one, and have the vehicle towed to the nearest qualified service facility for inspection. Do not drive the vehicle if there is a danger of a leak.

  • Inspect the Tank: Following an accident or any significant impact, the vehicle should always be evaluated by a Natural Gas Vehicle Institute- or CSA Group-certified inspector to look for any damage to the tank, the engine, or the fueling system. Natural gas fuel systems are pressurized, making proper connections critical to performance and safety. For CNG vehicles, if there are chemicals involved in the accident that may have contacted the CNG tank, the CNG tank should be inspected because certain chemicals can weaken the integrity of tanks.