Liquefied natural gas, or LNG, has been cooled to negative 260 degrees Fahrenheit for conversion to a liquid.The typical storage pressure in the vehicle LNG tank is 120 psi, far less that of CNG.Due to its cryogenic properties, LNG cannot be odorized.PROPANE PROPERTIESPropane is liquefied by pressurization at 200 psi and is stored at approximately 240 psi.Propane vapors are approximately 1½ times heavier than air and will settle into low lying areas when released.