Natural gas in compressed form (CNG) has been used for more than three decades as a vehicle fuel in Canada. CNG vehicles can be recognized by their CNG blue diamond decals on the rear of the vehicle or back of truck cab. CNG vehicles have fuel cylinders that store the natural gas at high pressure. By compressing natural gas to 3,000 to 3,600 pounds per square inch, this increases the amount of energy that can be stored on the vehicle and allows for adequate driving range.
Natural gas fuel cylinders have pressure relief devices that are designed to safely vent the natural gas in the event of extreme heat or accidental overpressuring. When released, CNG will always rise to atmosphere as it is a gas that is lighter than air.
What is new in Canada in the last two years is the use of liquefied natural gas (LNG) as a vehicle fuel. LNG vehicles can be recognized by their LNG blue diamond decal on the rear of the vehicle or back of cab. LNG is natural gas that has been cooled to its liquid state at –162 degrees Celsius. LNG is a cryogenic liquid which must be stored in insulated, thermos-like containers on vehicles and at stations in order to keep the fuel at its cold temperature.
If released, a small amount of LNG will rise to atmosphere. In the event of a larger spill, LNG may run to ground or pool in low spots. Unlike CNG, LNG does not have odourant added as it interferes with liquefying the gas. This means that in an accident situation involving a LNG vehicle or station, there may be natural gas present even though you do not smell the distinctive rotten egg smell associated with natural gas.
An Emergency First Responder Guide is available that details the properties of natural gas compared to other gases, descriptions of CNG and LNG and their hazards, and what to do in the event of an accident involving a natural gas vehicle or refueling station.