Natural gas: How safe is CNG?
David Pearl is Vice President of Infinity Resource Group, Inc., a professional mineral rights consulting firm, specializing in the leasing and sale of mineral rights in PA, WV and OH. He is also managing director of a natural gas fuel dispensing patent holding company and director of a natural gas fuel island development company. Your questions are welcomed by calling 412-535-9200 or by emailing IRGOilGas@gmail.com.
In my opinion, one of the neatest videos on the Internet is watching someone shoot a bullet into a compressed natural gas (CNG) fuel tank to see if it blows up! If you鈥檙e the sort of person who enjoys watching explosions, you will be disappointed.
Natural gas safely generates our electricity, heats our homes and cooks our meals. It powers our factories and boilers. And for the first time in history, in this last calendar quarter, natural gas exceeded coal as America蘑菇视频 primary domestic fuel. Natural gas is an environmentally clean, plentiful, low-cost, domestically produced fuel that is used in more than 70,000,000 homes and businesses throughout the U.S. and as a transportation fuel for motor vehicles. But how safe really is CNG as a transportation fuel?
CNG is one of the safest vehicle fuels available; CNG is safer than gasoline and diesel. The ignition point for CNG is about 1200 degrees Fahrenheit while the ignition point for gasoline is about 600 degrees and the ignition point for diesel is between 126 and 205 degrees Fahrenheit (depending on air mixture.) Because CNG is 90 percent methane, it is naturally odorless, so Mercaptan (the stuff that gives gas the familiar gas smell) is added so the average person can detect a leak. The pungent smell can first be detected at 16 times lower than the level that will support combustion. The flammability range of natural gas is very narrow, that is, natural gas will not burn in concentrations of air below about 5 percent and above about 15 percent. The high ignition temperature and limited flammability range make accidental ignition or combustion of CNG unlikely.
Gasoline, diesel and liquefied natural gas (LNG) are heavier than air, and will puddle if tanks rupture, which increases the possibility of a fire hazard or polluting the ground or waterways. CNG is lighter than air, so if a tank ruptures, the gas quickly dissipates into the atmosphere. And since methane is natural, CNG is not toxic. Exposure to a moderate concentration may cause headaches or similar symptoms, but that蘑菇视频 caused by oxygen deprivation and it蘑菇视频 likely the Mercaptan smell would be detected to avoid this. Mercaptan cannot be added to LNG due to LNG蘑菇视频 cryogenic properties; LNG has no odor.
According to the Federal Transit Administration, the natural gas fleet vehicle injury rate was 37 percent lower than the gasoline fleet vehicle rate and there were no fatalities compared with 1.28 deaths per 100 million miles for gasoline fleet vehicles.
CNG tanks are much safer than gasoline or diesel tanks. This is because CNG is compressed to pressures in excess of 3000 pounds per square inch (PSI), so the tanks have to be incredibly rugged and strong to contain that pressure. The on-board tanks are made of steel up to one half-inch thick and often wrapped in protective reinforced fiberglass sheathing. Plus, newer tanks are constructed of polymers and composites that are stronger than steel. Industry standards test them far beyond normal environmental and service damage risks. For example, cylinders must withstand a bonfire test and penetration by a 30-caliber bullet without rupture.
Contrast this with standard gasoline and diesel tanks in regular vehicles which are made from stamped steel shell halves, just a few thirty-seconds of an inch thick, that are welded or crimped together. In the event of an accident, the rugged, durable CNG tanks are far better able to withstand rupture or puncture over a simple stamped, thin walled steel tank.
In addition to superior tanks, CNG fuel systems are fitted with valves and other safety devices to prevent leakage and eliminate the risk of an explosion 鈥� making them safer than the legal requirements for tanks stipulate. These valves automatically release pressure, so if there is excessive heat or pressure build-up, the valve will open and release the gas to the atmosphere. And in the event of a fire, the CNG fuel is safely dissipated into the air, away from the car, before it ever has a chance to catch fire. Gasoline, LNG and diesel fuels will spill to the ground risking ignition.
The distribution of natural gas is primarily via safe, underground pipelines; however there is an emerging trend of transporting CNG by truck (referred to as the 鈥淰irtual Pipeline鈥�). All CNG tanks, whether they store CNG at a gas station or are on over-the-road vehicles, are subject to rigorous and stringent government regulations and standards. Tanks are subject to impact tests, bullet tests, fire tests and compression strength tests. The Department of Transportation (DOT) is the federal agency that regulates and enforces tank safety. DOT generally follows the standards recommended by the American Society of Mechanical Engineers (ASME) and the American Society for Testing and Materials (ASTM). And all CNG delivery systems are subject to the National Fire Protection Association (NFPA) regulations, enforced by the local fire marshal.
Natural gas vehicles have a stellar safety record, which makes sense considering the physical properties of natural gas make it safer than most other fuels and the fuel systems designed for natural gas vehicles are built to stringent standards. So it蘑菇视频 no wonder that CNG is emerging among fleet operators as the preferred fuel over diesel, gasoline and LNG.