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EXTRICATION "QUICK TIP" #51 (Compressed Natural Gas-CNG)

Compressed Natural Gas, with a name like that, it has to be bad. Right? I was recently asked to provide some information on Compressed Natural Gas (CNG) transport vehicles. Now remember, LNG differs from CNG in that it is super-cooled and compressed so that its storage is in a liquid form, which allows for a denser on-board energy storage, a key factor in long-range trucking. Being that we recently responded to a CNG (UPS) truck and multiple trailers that went off an embankment, I think it will make a good quick tip. In this situation, the CNG tank was damaged, although not leaking. With many large carries running CNG vehicles in their fleet (UPS) let’s look at some information that will help if you run into a situation with these vehicles.

LEAK DETECTION- Because CNG is mostly made of methane and methane is odourless CNG is odorized with Mercaptan to provide a ready means of leak detection. An average person can easily detect the smell of gas at a concentration as low as 0.3% by volume in air. That concentration is about 16 times lower than the level which will support combustion.

IGNITION TEMP- CNG has a high ignition temperature, about 1,200 degrees Fahrenheit, compared with about 495-536 degrees Fahrenheit for gasoline. It also has a narrow range of flammability, that is, in concentrations in air below about 5 percent and above about 15 percent, natural gas will not burn. The high ignition temperature and limited flammability range make accidental ignition or combustion of CNG unlikely.

TOXICITY- CNG has no known toxic or chronic physiological effects (it is not poisonous). Exposure to a moderate concentration may result in a headache or similar symptoms due to oxygen deprivation but it is likely that the smell would be detected well in advance of concentrations being high enough for this to occur.

DENSITY- The fact that CNG is lighter than air further enhances its safety. Unlike other fuels such as diesel, petrol or LPG, which are heavier than air, and pools on the ground creating a fire hazard and potential pollution to waterways. Should a CNG leak occur, the gas will disperse rapidly upwards into the atmosphere and dissipate.

SYSTEM- CNG fuel systems are "sealed," which prevents any spills or evaporative losses. Even if a leak were to occur in an NGV fuel system, the natural gas would dissipate into the atmosphere because it is lighter than air. CNG combustion produces no significant aldehydes or other air toxins, which are a concern in gasoline and some other alternative fuels.

STRENGTH- CNG fuel cylinders are much, much stronger than gasoline tanks. The design of the cylinders is subject to a number of "severe abuse" tests such as heat and pressure extremes, gunfire, collisions, and fire. The systems are also fitted with valves and other safety devices to prevent leakage and eliminate the risk of an explosion.

With CNG on the roadway, it’s a good idea to research and obtain information specific to your areas (IE. CNG fueling stations).

ISAAC FRAZIER is a Special Operations Lieutenant with St. Johns County Florida’s Heavy Rescue “Squad 4”. First due to the deadliest stretch of roadway in the nation, Frazier teaches from personal street experience providing tried and true tactics. Frazier is the owner of Tactical Advantage Training and creator of the course Tactical Extrication. Frazier travels nationally sharing his passion teaching fire and extrication courses. Frazier is a FDIC instructor, Fire Engineering Contributor, Fire Officer II, FL Paramedic, Special Operations Officer, Florida State Instructor, FLUSAR Tech, Diver, and FL Hazmat Tech.

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