Precautions while using CNG
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.