location and arrangement of valves and gauges may vary, all FMMs are functionally the same.
Figures 10 and 11
HIGH PRESSURE
GAUGE

LOW PRESSURE
GAUGE

Indicates fuel storage
cylinder pressure,
nominal 3600 psi
(25MPA).

Indicates pressure
exiting the regulator,
nominal 125 psi (862
kPa).

1/4-TURN MAIN SHUT
OFF VALVE
Stops fuel flow to the
engine. Normally
OPEN. Turn OFF and
depressurize before
servicing.

DEFUEL RECEPTACLE
Used when removing
fuel from the cylinder.

FILL RECEPTACLE
Slow fill type shown.

INSTALL DATA LABEL
Water volume, liters,
install location and date,
cylinder expiration date.

Figure 10. CNG system fuel management module (FMM) gauges and controls.

Figure 11. Integrated FMM (left) mounted on a CNG side mount system (right).

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6. CNG Vehicle Emergency Response
CNG pressures are nominally 3600 psi (25MPa) or more when full. Do not cut fuel supply
tubing.

6.1. If a CNG Vehicle is Damaged or a Gas Leak Is
Discovered
1. Eliminate all sources of ignition such as fire, sparks, electronics, lights, or electrostatic
charges. Do not smoke near the vehicle and do not light road flares.
2. Turn the ignition switch off (this will close the solenoid valve), set parking brake and turn
off battery at main battery disconnect.
3. If it is safe to do so, close the 1/4-turn manual shutoff valve, close individual cylinder
valves, and check the fuel system near the damaged area for leaks using smell, sight,
and sound. CNG is odorized and can be detected by smell.
4. Use a combustible gas meter to monitor for potential fuel leaks.
5. Keep people and traffic away from the area.
6. Open vehicle doors to introduce fresh air to prevent natural gas accumulation.
7. If the vehicle is indoors, open building windows and doors to allow ventilation and avoid
turning on any lights or electronics which may create a spark. Pay attention to overhead
ignition sources because natural gas will rise to the ceiling.
8. Beware that residual gas may still leak from the storage system even after the ignition
switch is off and manual shut off valves are closed.
9. Advise towing and wreckage storage operators the vehicle is fueled with CNG.
10. Have a qualified natural gas vehicle service technician make necessary repairs or defuel
the vehicle.

6.2. In Case of a CNG Vehicle Fire
DO NOT apply water to CNG cylinders because this will prevent the PRDs from activating
and can result in a catastrophic cylinder failure (high pressure gas rupture).

1. Always assume a CNG cylinder is under pressure.
2. Establish a minimum safe perimeter of 80-ft to 100-ft (25m to 31m) around the vehicle
per NFPA recommendation.
3. If the CNG cylinders are not involved in the fire, the fire on the vehicle may be
extinguished with normal response tactics. For example, small blazes such as brake
fires and electrical fires.

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Fire exposure may not always be apparent.

When fighting a CNG fire, keep in mind CNG properties and storage methods.
Monitor the situation closely as changing conditions may require a change in
tactics.

4. If fire is impinging on the CNG cylinders, if cylinders are on fire, or if the fire is
fueled by an active leak, DO NOT APPROACH THE VEHICLE. Allow the fire to burn
while watching for secondary hazards, such as other vehicles or structures, and
protecting exposures.

5. If it is safe to approach the vehicle, always approach at a 45 degree angle.

6. If it is safe to do so, immediately chock vehicle wheels to prevent accidental movement.
7. When a PRD activates, the result is often a jet fire which may go out and re-ignite
several times.
8. Advise towing and wreckage storage operators the vehicle is fueled with CNG.

7. LNG General Information
A. LNG is stored at cryogenic temperatures [-259°F (-161°C) or cooler] and is odorless.
PPE should include gloves and face shields to prevent frostbite, a methane/flammable
gas detector and self-contained breathing apparatus (SCBA).
B. LNG fuel is a multi-phase mixture of liquid and gas at cryogenic temperatures: The
fuel pressure inside the LNG tank is not indicative of fuel level. A full tank could read
zero pressure, and an empty tank could read 230 psi (1.6MPa).
LNG cannot be odorized because of its very cold temperature; therefore, methane detection
systems are mandatory. One sensor is located in the engine compartment and one is located
inside the cab.
1. LNG is extremely cold, and if spilled, will vaporize and dissipate into the air.
2. LNG fuel storage containers are highly insulated stainless steel tanks to keep the
cryogenic fuel cold. Figure 12

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Figure 12. Stainless steel LNG fuel tank with LNG blue diamond decal.
NOTE: Passenger side shown; driver side similar.
3. Systems are usually mounted on the vehicle sides, but can be located in similar locations
as CNG systems, such as the vehicle roof.
4. Pressure relief devices for LNG are not thermally activated, so there is no danger of
defeating or damaging the relief valves with water.
5. Manual valves are located on one end of each fuel tank. Figures 13 and 14

Figure 13: LNG fuel tank valve end with protective shield installed.
NOTE: Driver side shown; passenger side similar.

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PRIMARY
PRESSURE
RELIEF VALVE

RED LIQUID VALVE

Vents excess
pressure at 230 psi
from the tank due
to normal
operation.

Normally open to
allow fuel to flow to
the engine.

SECONDARY
PRESSURE
RELIEF VALVE
(RED CAP)
Vents at 350 psi.

GRAY VENT VALVE
Normally closed, opened when
fueling to relieve pressure.

Figure 14. LNG system valve locations and functions.
6. Pressure gauges are mounted on or near each LNG tank. Figure 15

a

Figure 15 Pressure gauge (a) is typically located on each LNG tank for easy viewing.
7. An LNG fuel system may normally vent (via the primary relief valve) when the pressure
inside the tank rises above 230 psi (1.6MPa) due to normal reaction (expansion) to
ambient temperatures. Figure 14
a. The relief valve will automatically reset when the pressure decreases to 230 psi
(1.6MPa). Figure 14

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b. LNG venting is considered normal, but excessive venting may indicate a problem.
Figure 16
1

2

Figure 16. LNG vent line (1) runs from LNG fuel tank (2) along the rear of the cab to
above the vehicle roof to vent gaseous fuel (arrow). LNG vent tubes resemble CNG PRD
vent tubes, but LNG vent tubes are not capped. Also, be aware that LNG vehicles may
vent in normal operation. Refer to text for more details.
8. Remember, unlike a structure or utility fire, an LNG vehicle has a limited amount of fuel
on board. Allow gas to vent and watch for secondary hazards, such as other vehicles or
structures. Figure 16

8. LNG Vehicle Emergency Response
A. LNG is stored at cryogenic temperatures [-259°F (-161°C) or cooler] and is odorless.
PPE should include gloves and face shields to prevent frostbite, a methane/flammable
gas detector and self-contained breathing apparatus (SCBA).
B. LNG fuel is a multi-phase mixture of liquid and gas at cryogenic temperatures: Fuel
pressure inside the LNG tank is not indicative of fuel level. A full tank could read zero
pressure, and an empty tank could read 230 psi (1.6MPa).

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8.1. If an LNG Vehicle is Damaged or a Gas Leak is Found
Use caution when handling an LNG leak. LNG is stored at temperatures below -260°F (-162°C)
and can cause first degree burns and frostbite if it contacts skin. It is best to remove sources of
ignition and allow leaking LNG fuel to vaporize and disperse into the atmosphere.

1. Always assume an LNG tank is under pressure.
2. Establish a minimum safe perimeter of 80-ft to 100-ft (25m to 31m) around the vehicle
per NFPA recommendation.
3. Use a combustible gas meter to monitor for potential fuel leaks.
4. Small LNG leaks may be observed as vapor escaping from the leak, usually at fittings.
5. Large liquid leaks may spill, but will vaporize and rise almost immediately. Be aware of
the extreme cold and make sure PPE is in place for any exposed skin.
6. Turn the ignition switch off (this closes the solenoid valve).
a. Set parking brake.
b. If it is safe to do so, turn off the main battery switch.
7. If it is safe to do so, close the red liquid valve (Figure 13) and check the fuel system near
the damaged area for frost, ice, or condensation which is an indicator of an LNG leak.
8. If the tank is damaged or there is frost on the tank, and the sound of fuel escaping can
be heard, the gas will vaporize and rise into the air.

9. Be aware the pressure gauges may indicate zero, but some residual liquid may remain
in the tank.
10. Keep people and traffic away from the area.
11. Open vehicle doors to introduce fresh air and prevent gas accumulation.
12. If the vehicle is indoors, open building windows and doors to allow ventilation and avoid
turning on any lights or electronics which may create a spark. Pay particular attention to
any sources of ignition overhead because natural gas will rise to the ceiling.

13. Beware that residual gas may still leak from the storage system even after the ignition
switch is off and all manual valves are closed.
14. Advise towing and wreckage storage operators the vehicle is fueled with LNG.
15. Have a qualified natural gas vehicle service technician make necessary repairs.

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8.2. In Case of an LNG Vehicle Fire
1. Establish a minimum safe perimeter of 80-ft to 100-ft (25m to 31m) around the vehicle.
2. If the LNG tanks are not involved in the fire, the fire on the vehicle can be
extinguished with normal response tactics.

Fire exposure may not always be apparent.

a. Apply copious amounts of water to the LNG tanks.
b. If LNG tanks are not kept cool with water, there is potential for a boiling
liquid expansion vapor explosion (BLEVE). Therefore, if a sufficient water
supply is not available, suspend water application and evacuate to a safe
distance.
3. If fire is impinging on the LNG tanks, or if the fire is fueled by an active leak, allow
the fire to burn while watching for secondary hazards, such as other vehicles or
structures, and protecting exposures.

4. If it is safe to approach the vehicle, always approach at a 45 degree angle.

5. If it is safe to do so, immediately chock vehicle wheels to prevent accidental movement.
6. Water can be used to extinguish the fire because LNG tanks are well insulated.
a. LNG tanks are well insulated so temperature and pressure rise should be small.
b. The LNG pressure relief valve will open causing CNG to vent.
c. LNG pressure relief valves are self-resetting (resets when pressure is below about
230 psi (1.6MPa).
7. If it is safe to do so, turn off the main battery switch.
8. Advise towing and wreckage storage operators the vehicle is fueled with LNG.

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9. References and Additional Information
The following resources and publications will help increase understanding of CNG and LNG fuel
systems:
National Fire Protection Association. Emergency Field Guide: Hybrid, Electric, Fuel Cell, and
Gaseous Fuel Vehicles, 2018. (Free PDF download).
NFPA also offers a free Alternative Fuel Vehicles Safety Training Program to U.S. emergency
responders:
http://www.nfpa.org/training-and-events/by-topic/alternative-fuel-vehicle-safety-training
LNG training video:
Pipeline and Hazardous Materials Safety Administration. “Liquified Natural Gas Safety
and Emergency Response.”

Accessed June, 23, 2020.
Go to the Agility Fuel Solutions website – Product Support Group page to download or view these
publications:
https://agilityfuelsolutions.com/support-documents/
 Agility Fuel Solutions, “Truck and Tractor CNG Fuel System Operation, Maintenance &
Inspection Manual,” ENP-516
 Agility Fuel Solutions, “CNG System Users’ Manual,” ENP-314
 Agility Fuel Solutions, “Safely Working on CNG Fuel Systems,” ENP-391
 Agility Fuel Solutions, “Dual Tank LNG System Operation Manual,” ENP-064
 Agility Fuel Solutions, “LNG System Users’ Manual,” ENP-334
 CNG and LNG fuel system videos

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