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Safety

CNG vs. Gas & Diesel


  Unlike other fuels such as diesel, petrol, or LPG, which are heavier than air and will pool on the ground, creating a fire hazard and potential pollution to waterways, CNG is lighter than air.

If a CNG leak were to occur, the gas would disperse rapidly upwards into the atmosphere

and dissipate.

 

  Reported incidents of CNG bus fires are related to engine failures, not the use of natural gas. Natural gas buses have onboard gas detectors and other safety devices such as tank safety valves that only allow fuel flow when the engine is on. Also, the tanks must be periodically inspected by the U.S. Department of Transportation.

 

 

  There are only some safety concerns that CNG buses have compared to diesel. For example, the extra weight of the CNG tank can cause the need for a greater braking distance and a slightly slower acceleration than a diesel bus. This is a relatively small concern, however, because the fuel system is a small fraction of a bus’ total weight.


CNG-bus clear

 CNG is very safe. The tanks go through many rigorous safety tests that ensure its sturdiness and safety. Take these factors into account:


Lighter than_Air2

 Natural gas is lighter than air. If a leak were

to develop, the gas would rise and disperse through the atmosphere, giving little chance

for ignition. Compare that to gasoline and diesel - both of which are dense liquids that tend to pool and easily ignite.



Odorless2

 Natural gas is odorless. A distinctive odorant that smells very much like strong sulfur is added prior to distribution. This strong odor makes the presence of a leak very easy to detect.

 Nontoxic2

 Natural gas is non-toxic. When it is inhaled, that are no poisonous ingredients that can be absorbed into the blood.

Leak Detection


 It comes as a surprise to many to hear that CNG is one of the safest transport fuels available, but CNG is actually safer than petrol. In its natural state, methane is odorless. As a safety measure, the gas

is odorized with mercaptan prior to distribution to provide a 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. 



Ignition


 

 CNG has a high ignition temperature -

about 1,200o Fahrenheit - compared with about 600oFahrenheit for gasoline. It also

has a narrow range of flammability, that is, 

in concentrations in air below 5% and

above 15%, natural gas will not burn.

 

 The high ignition temperature and limited flammability range make accidental

ignition or combustion of CNG unlikely. 

CNG is primarily methane, which is a greenhouse gas that could contribute to global climate change if leaked. Methane

is slightly soluble in water and under certain anaerobic conditions does not biodegrade.

If excess amounts accumulate, the gas can bubble in water creating a possible risk of fire or explosion.

 

BodyFact

CNG Fuel Systems

 

CNG Fuel Storage Cylinders

They are sealed, preventing 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. Natural gas is

non-toxic, non-corrosive, and will not contaminate ground water. CNG combustion produces no significant aldehydes or other air toxins,

which are a concern for gasoline and some

other alternative fuels.


 

They are much, much stronger than petrol tanks. The design of these cylinders is subject to a number of severe abuse tests such as heat/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, making them safer than 

the legal requirements stipulate.

 

CNG Cylinder Pressure

Safe Distribution of CNG

 CNG is stored at high pressure, and this is often perceived as the making it more hazardous than other fuels. This is not true. The resulting high concentration of gas and its tendency to dissipate upwards make it less likely for the gas to ignite.



CNGCylinder clear

 

 In most circumstances, CNG is delivered

via underground pipeline networks, the same networks that deliver natural gas to our homes and businesses. This method not only eliminates the need for road tankers to deliver fuel from a refinery, but also eliminates the need for ocean going oil tankers to deliver crude oil to the refinery.


  The CNG delivery system itself also has

an excellent and proven safety record. According to statistics from the U.S. Department of Transportation, the natural

gas transmission and distribution system is

the safest way to transport.


According to the Federal Transit Administration:

–Proof that CNG is better and safer.


  Data collected over time has demonstrated natural gas vehicles to be safe in actual operation. Based on a survey of 8,331 natural gas utility, school, municipal, and business fleet vehicles (NGVs) that traveled 178.3 million miles collectively on CNG:


The NGV fleet vehicle injury rate was 37% lower than the gasoline fleet vehicle rate.

 

• There were no fatalities compared with 1.28 deaths per 100 million miles for gasoline fleet vehicles.


• The collision rate for NGV fleet vehicles was 31% lower than the rate for gasoline fleet vehicles.


• The fleet of 8,331 NGVs was involved in only 7 fire incidents, only one of which was directly attributable to the failure of the natural gas fuel system. 

 

A Closer Look at Safety


 Because compressed natural gas (CNG) fuel systems operate at pressures in excess of 3,000 PSI,

the fuel tank and associated plumbing have to be incredibly rugged and strong enough to contain that pressure. On-board tanks are made of steel up to a half-inch thick and often wrapped in reinforced fiberglass sheathing. Newer tanks are constructed of aluminum, polymers, and composites that are stronger than steel.


 TankDiagram clear

A breakdown of one type of CNG leak.

  Contrast this with standard gasoline and diesel tanks in regular vehicles. These tanks are usually made from stamped steel shell halves, just a few sixteenths of an inch thick, that are welded or crimped together. In the event of a traffic accident, the ability of CNG tanks to withstand rupture

or puncture certainly exceeds that of simple stamped steel.


  But the safety of NGVs doesn’t just stop with the robust construction of the fuel tank. Most CNG systems have automatic release valves. In a situation of excessive heat or pressure build-up,

the valve will open and release the gas to the atmosphere—and since it is lighter than the surrounding air, it will rise and dissipate. The low threshold is set well above ambient temperatures and the high threshold is set well below the ignition temperature of the gas. In the event of a fire, 

the fuel is safely evacuated from the car before it ever has a chance to catch fire. Gasoline and diesel vehicles cannot prevent ignition by fire.


  A manual shut-off valve also exists just downstream from the CNG tank to allow user intervention

if the need arises. A side benefit of this valve might be the ability to use it as an anti-theft device.

Shut off the fuel supply and any would-be thief wouldn’t get much further than a mile down the road.


  The use of compressed natural gas as a motor fuel— from compression, storage, and fueling

to vehicle manufacturing—must meet stringent industry and government standards. 

 

 

 

 

 

 

 

 

 

YCNGA Public CNG Station 


975 W Main St, Rock Hill SC 29730

 

$1.80/GGE

 

Open 24/7

 

3,600 PSI

 

Accepted payment types: Visa, MasterCard, Discover, American Express, Voyager, WEX, and FuelMan 

 

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