A Safe Place to Vent

To vent the fuel that remains after the engine stalls or if the engine cannot be run to consume the fuel, the CNG can be vented safely into the atmosphere. Special precautions are necessary to safely vent the CNG without causing a fire. NFPA 52 Vehicular Gaseous Fuel Systems Code, the International Fire Code and some state and local regulations require that any venting system be approved by the Authority Having Jurisdiction AHJ, generally the fire marshal. Always use a vent system approved by the AHJ. If the vehicle is equipped with a special connection to transfer fuel out, it can be connected to the approved vent system and emptied as in the direct defueling example, making sure that the solenoid valves open.