Natural Gas

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Natural Gas Vehicle and Fuel Station Safety

Any motor vehicle fuel can be dangerous if handled improperly. Fuels contain energy which must be released by burning. Gasoline is a potentially dangerous fuel, but, over time, we have learned to use it safely. The same is true of natural gas. Natural gas safely generates our electricity, heats our homes and cooks our meals. 

Natural gas has been used as a motor fuel for more than 60 years.  According to the U.S. Gas Research Institute, there have been no fatalities, burn accidents or serious injuries related to the use of natural gas in more than 430 million vehicle-miles of use.  Problems associated with natural gas fueling stations are extremely rare.

The excellent safety record of using natural gas in motor vehicles is due to three primary reasons: 

• the properties of the fuel itself;

• the integrity of the natural gas vehicle and its fuel components; and

• the redundant, fail-safe design of natural gas fuel stations.

Properties of Natural Gas

Natural gas has safety advantages compared to gasoline and diesel fuels.

Reduced spill hazard:  Natural gas is lighter than air, so it rises and dissipates rapidly in the unlikely event of a leak, as opposed to other fuels, both liquid and vapor, which tend to pool on the ground.   As a result, the potential for ignition is significantly reduced and natural gas cannot contaminate soil or water.

Reduced flammability:  Natural gas has a relatively high ignition temperature and has a narrow flammability range, posing a reduced risk of accidental ignition or combustion.   Gasoline and diesel fuels burn at much lower concentrations and ignite at lower temperatures.  Natural gas also burns at a lower temperature.

Readily detectable:  An odorant is added to provide a distinctive smell which is easy to recognize.  The odor is detectable at one-fifth of the gas’ lower flammability limit.  This equates to detection at 0.5% concentration in air, well below the weakest concentration which can support combustion and well below levels which can cause drowsiness due to inhalation.

Non-toxic:  Natural gas is neither corrosive nor toxic.

Natural Gas Vehicles

Natural gas powered vehicles are designed and built to be safe both in normal operation and in crashes.

Proven technology:  More than 85,000 natural gas vehicles in the United States and nearly 1 million worldwide.

Stringent safety standards for vehicles:  Vehicles must meet stringent industry and government safety standards, including the same crash tests as other vehicles.

Safety standards of natural gas fuel systems: Natural gas vehicle fuel systems must meet a number of federal and industry standards.  (For details, see below.)

Safety characteristics of fuel systems: Pressurized tanks have been designed to withstand severe impact, high external temperatures, and automotive environmental exposure, making them as safe as, if not safer than, gasoline tanks.  Natural gas cylinders are much thicker and stronger than gasoline or diesel tanks.  Industry standards require them to withstand 11,250 fill cycles and endure far beyond normal environmental and service damage risks.  Cylinders must even withstand a bonfire test and penetration by a 30 caliber bullet without rupture.  (See details below on strength of fuel tanks in vehicle accidents.)

Compressed Natural Gas Fuel Stations

Extensive Experience: More than 1,200 CNG fueling stations in the US. Accidents associated with natural gas fueling stations are extremely rare.  

Stringent Standards: Fuel station design, equipment and installation must comply with stringent federal, state and local government and industry safety standards, including standards developed by the American National Standards Institute, the National Fire Protection Association, and the American Society of Mechanical Engineers.  (For details, see below.)

Emergency shutoff:  Natural gas fueling stations provide automatic and manual shutoff valves at key points in the system.  These shutoff systems will cut electrical power as well as the flow of gas.

• Methane detection:  Stations and maintenance facilities are equipped with methane detection devices.  When the concentration of gas reaches 1% (which is 20% of the lower explosive limit), all compressors and dispensers are automatically shut-off.  In indoor facility, the detectors will activate increased ventilation into the building and the gas will be exhausted to the outdoors.

• Pressure release devices: Pressure release devices are installed at key points in the system, providing for venting in the event of excess pressure and for automatic shut down of the system should it be necessary.

Compressor Safeguards:  Compressor systems contain numerous redundant systems to ensure proper operation and provide for automatic and manual shutoff. This equipment includes:

• Inlet and outlet filters to trap particles and moisture.

• Pressure, temperature and vibration sensors coupled with automatic shutoff.

• Programmable Logic Controller (PLC) to monitor operating parameters.  PLC will automatically shut down compressor when parameters are out of design range.  PLC also allow for remote monitoring by station operators and will automatically dial out to station operator in the event of a problem.

• Storage cylinders must meet strict codes, including ASME rating, and are equipped with pressure
  release valves.

• Re-circulating tank to provide closed loop operation without venting of gas to the atmosphere.

Dispenser safeguards:  Natural gas fuel dispensers are designed to be easy to use and as similar to conventional fuel dispensers as possible.  Dispensers also provide substantial safety mechanisms.

• Fuel nozzle: The natural gas fuel nozzle consists of a compression coupling.  If not properly engaged, natural gas will not flow from the dispenser. The nozzle is designed to fit only vehicles rated for dispenser pressure.

• Breakaway hose device:  If the nozzle is torn away from the vehicle, such as when someone drives away while fueling, a breakaway device on the fuel nozzle dispenser ensures that the flow of natural gas will cease and that the hose will not rupture nor topple the dispenser.  The breakaway pressure for compressed natural gas dispensers is about 44 pounds, compared to 250 pounds for gasoline pumps.

• Safeguards against overfilling or uncontrolled fill:  Dispensers are designed to monitor, either mechanically or electronically, whether the vehicle is receiving the proper amount of fuel.  If the fill pressure or volume rises beyond a predetermined level, the dispenser shuts off automatically.  If there is no pressure or a sudden loss in pressure, as in the case of an aborted fill or a hose being cut, the dispenser will shut off automatically.

Limited Hazard:  In the event of a problem or leak, potential hazards are limited due to the properties of natural gas discussed above.

Natural Gas Vehicle and Fuel Station Safety Standards

Products manufactured for natural gas vehicles – from vehicle components to fuel-pump nozzles – are governed by a variety of standards to ensure safety. For example, vehicle components including pressure regulators, valves, fueling nozzles and fuel cylinders must be certified by International Approval Services, sponsored by the American Gas Association Labs. The National Fire Protection Association (NFPA) has developed safety standards, including NFPA, for equipment installation and fueling equipment.  The Uniform Fire Code also addresses safety issues relating to fueling stations. Strict voluntary standards have been developed by the natural gas vehicle industry.

The following is a sampling of the most relevant natural gas vehicle and fuel station standards:

Vehicle and Equipment Standards:

• National Fire Protection Association (NFPA) 52 – Standards for CNG Vehicular Fuel Systems  All specific equipment standards that are developed must be in compliance with NFPA 52 (developed with ANSI approval). 

• Federal Motor Vehicle Safety Standard (FMVSS) 304 – Compressed Natural Gas Fuel Container Integrity  Establishes durability, strength and pressure-relief characteristics for storage cylinders.

• ANSI/NGV2 – Basic Requirements for CNG Vehicle Fuel Containers  Specific Standard to certify NGV cylinders.

• ANSI/NGV1 – Compressed Natural Gas Fueling Connection Devices  Standard for fueling nozzles and receptacles.

• NGV 3.1/ A.G.A. 7-93 – Requirements for Fuel System Components for NGVs  Standard used to certify individual NGV onboard components.

• NGV 4.2/A.G.A. 1-93 – Requirements for Hoses for NGVs and Fuel Dispensers

 
Fuel Station Standards:

• A.G. A. 3-91 – Requirements for Natural Gas Compressors

• NGV 4.1/A.G.A. 2-92 – Requirements for CNG Dispensing Equipment for Vehicles

• NGV 4.2/A.G.A. 1-93 – Requirements for Hoses for NGVs and Fuel Dispensers

• ANSI/NGV1 – Compressed Natural Gas Fueling Connection Devices  Standard for fueling nozzles and receptacles.

• A.G.A. 3-93 – Requirements for Gas Operated Valves for High-Pressure Natural Gas

• NGV 4/A.G.A. – Requirements for Breakaway Devices for CNG Vehicle Fuel Dispensers and Fueling Hoses

• A.G.A. 2-90 – Compressed Natural Gas Fueling Appliances

• NGV 4.7/A.G.A. – Automatic, Pressure Operated Valves

How do natural gas vehicles behave in crashes? The strength of the natural gas cylinders and fuel system generally avoids any leakage or fire. For example:

• When a 1992 CNG pick-up was broadsided in Midland, Texas, the most vulnerable part of the fueling system bore the brunt of the hit. While the force drove an imprint of the tank safety valve into the side of the truck, the CNG tanks did not rupture, and the driver walked away.

• And in a tragic 1998 accident, a stopped bi-fueled Honda (a vehicle which could run on either natural gas or gasoline) was impacted by another vehicle moving at nearly 100 mph and a fire fed by gasoline broke out. The 50-liter natural gas fuel tank was intact and remained secured in its support brackets (4).

In summary: technical data, appropriate safety regulations and years of experience show natural gas vehicles to be as safe as, or safer than, conventionally fueled vehicles.

The safety of natural gas vehicles and fuel systems is demonstrated by the results of a rear-end collision involving a natural gas Honda Civic GX. Details.

The Puget Sound Clean Cities Coalition is grateful to the Natural Gas Vehicle Coalition for their assistance in developing this information.