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First Responder Guide:
CNG and LNG Vehicle Fuel Systems

ENP-084 Rev. D
June 29, 2020

I. Proprietary Statement
The information provided within this manual is proprietary and confidential. All prior versions of
this manual, including updates and revisions forwarded separately, are proprietary. The
information provided by Agility Fuel Solutions LLC (Agility®) to its customers and clients is solely
for the use of those customers and clients. No portion of this manual may be reproduced or
distributed without express written consent from Agility®. Agility® reserves the right to utilize the
intellectual property contained within this publication as content for any other Agility publication.
Portions of this manual were drawn from information provided by suppliers of Agility® and used
with permission.
Agility® gives express consent to authorized dealers to utilize portions of this manual, or the
manual in its entirety for the purposes of providing customers and clients of Agility® with
information pertaining to the Agility® compressed natural gas (CNG) fuel storage system with
appropriate acknowledgement of copyright.

II. Preface
This manual is a supplemental guide for public safety first responders to compressed natural gas
(CNG) or liquefied natural gas (LNG) vehicle fuel system incidents.
It does not cover response tactics for liquefied petroleum gas (LPG or propane) or CNG vehicle
fuel systems using Type 1 or Type 2 CNG cylinders.
This manual is not intended to replace any formal training on the proper response techniques,
tactics, or procedures for responding to alternative fuel vehicle (AFV) accidents or incidents.

IMPORTANT:

Always consult the National Fire Protection Association (NFPA) and your own training programs
for the latest information and best practices for CNG and LNG emergency response.

III. Warning Statements Used in this Manual
Will cause death or severe injuries if procedures are not followed.

Could cause death or severe injuries if procedures are not followed.

Could cause minor or moderate injuries if procedures are not followed.

Practices not related to physical injury. Includes procedures to prevent vehicle damage as well
as hints to help an operation or procedure go smoothly.

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IV.

Obtaining Product Support, Service or Parts

Fuel system product support can be obtained by calling the Agility® Customer Care Hotline:
+1 949 267 7745
+1 855 500 2445 toll free
Customer Care: [email protected]
Parts: [email protected]
Visit the Agility® website for more information, including CNG and LNG fuel system videos:
www.agilityfuelsolutions.com
Agility Fuel Solutions LLC
3335 Susan Street, Suite 100
Costa Mesa, CA 92677
USA
Revision

Description

--

Initial Release

A

Changed format, no information changes

B

Complete re-write

C

D

Updated company address and logos, added
ANSI Z535 warning icons, updated NFPA
training URL, re-formatted manual
UPDATED: Section III Signal word definitions;
REVISED: Section 8 and Section 12. ADDED:
Metric values; AMENDED: Section 2 to
include LNG vehicle identification.
CORRECTED: LNG storage temperature

ENP-084 REV D June 29, 2020

Author

Approved By

Date

A. Durrant
W.
Yoshida
W.
Yoshida

Y. Coy

07/09/2013

C. Forsberg

08/24/2015

W.
Yoshida

M. Meyer

07/26/2017

C.Grasso

CCG and
Engineering
Team

06/29/2020

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1. Compressed Natural Gas and Liquefied Natural Gas Facts
Natural gas (methane) is flammable; however, it only burns within a narrow range when mixed
with air in a ratio of between 5 and 15 percent. Natural gas is odorless, colorless and tasteless.
Natural gas is lighter than air so it rises and diffuses into the atmosphere when released.
Natural gas has unique hazards not found in gasoline and diesel fuel: In order to be stored
efficiently, natural gas must be either 1) maintained under high pressure [3600 psi (25MPa)] in a
compressed natural gas (CNG) system, or 2) kept at an extremely low (cryogenic) temperature
of -259°F (-161°C) or cooler in liquid form as liquefied natural gas (LNG).

2. Identifying CNG and LNG Vehicles
The United States Department of Transportation (USDOT) requires vehicles equipped with
natural gas fuel systems to have a diamond shaped decal affixed the rear of the vehicle
identifying the vehicle as a powered by CNG or LNG. Additional CNG and LNG decals may be
affixed to the front and sides of the vehicle. Figures 1a and 1b

CNG

Figure 1a. Left: CNG fueled vehicles are identified by a blue and white decal on the right
rear of the vehicle. Right: A CNG decal may also be affixed to the left front of the vehicle.

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LNG

Figure 1b. Top: LNG fueled vehicles are identified by a blue and white diamond decal.
Left: LNG blue diamond decal location on lower right rear of cab on vehicles without
bodies such as roll-off refuse haulers. Right: LNG decal on the side mount fuel tank.
Bottom: LNG decal on the right rear of a transit bus.

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Additionally, CNG vehicles must display the appropriate diamond decal next to the USDOT
number on the left and right sides of the vehicle. Figure 2

Figure 2. CNG diamond decal affixed adjacent to vehicle USDOT number. NOTE: Driver
side shown; passenger side similar.
Agility® produces fuel systems for both CNG and LNG fuel vehicles for a variety of vocations
and in several configurations. Figures 3a, 3b, and 3c

ROOF MOUNT

FRONT OF BODY

BACK OF CAB WITH SIDE MOUNT

Figure 3a. Popular heavy duty Agility® CNG fuel system configurations.

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SIDE MOUNT

Figure 3b. Medium duty Agility® CNG side mount fuel system. NOTE: CNG fuel cylinders
(not visible) bolt to chassis frame rails and are protected by vehicle body and shields.

SIDE MOUNT

FRONT OF BODY

Figure 3c. Two LNG fuel system configurations offered by Agility®.

3. CNG Vehicle Cylinders and Fuel Systems
1. There are four types of CNG cylinders:


Type 1: All metal construction



Type 2: Metal liner with hoop-wrap around cylinder



Type 3: Thin metal liner with continuous carbon-fiber over-wrap



Type 4: Plastic liner with continuous carbon-fiber over-wrap

Of the four cylinder types, Type 3 and Type 4 cylinders are most prevalent in commercial
vehicles. Agility® uses Type 3 and Type 4 cylinders.
2. The CNG fuel cylinder or cylinders are housed in steel or aluminum structures secured to the
vehicle body and frame. These structures are engineered to protect the cylinders in a
collision.
3. The framework is covered with a composite or metal cover to protect the cylinders from UV
exposure and enhances vehicle appearance and aerodynamics.

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Figure 4. Typical refuse roof mount CNG storage system. Aluminum covers protect the
cylinders from overhead objects.

Figure 5. Type 4 CNG cylinders in a housing with the cover partially removed. PRDs are
located at each valve and at various locations along the length of the cylinder.
4. CNG cylinders may be mounted on the side rails of the vehicle, on the roof or behind the cab.
5. Fuel storage capacity can be increased by combining systems.
6. Each cylinder in a CNG system has a valve at one end to allow fuel to be isolated from the
rest of the system. During normal operation, all cylinder valves should be open.

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4. CNG Pressure Relief Devices (PRDs)
A. CNG PRDs vent system pressure. Systems are designed for a nominal working
pressure of 3600 psi (25MPa).
B. Vehicle damage and position may modify venting gas direction.
C. Venting gas may ignite, become a jet fire, extinguish itself and re-ignite several times.
1. CNG fuel cylinders are protected with one or more thermally-activated pressure relief
devices (PRDs).
2. CNG PRDs activate (vents gas) between 212°F to 220°F (100°C to 104°C).
3. Typical CNG PRD vent tube locations and venting directions are as follows:
a) For side mount and behind the cab systems, PRD venting is routed up to a vent tube
behind the cab or at the rear of the vehicle body. Figures 6a and 6b
b) Some older CNG PRD vent systems vent downward. Figure 6c
c) For roof mount refuse vehicle systems, a vent tube at the rear vents upward and to
the rear. Figure 7
d) On front of body refuse vehicle systems, a vent tube at the rear vents upward and
forward. Figure 8
e) On roof mount bus systems, a vent tube located at the rear of the roof vents to the
rear. Figure 9

Figure 6a. CNG PRD venting location and direction (arrows), side mount and behind the
cab systems.

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SIDE VIEW

REAR VIEW

Figure 6b. CNG PRD vent tube outlet location and vent directions (arrows),
medium duty side mount system.

Figure 6c. CNG PRD venting location and direction (arrow), older side mount systems.

Figure 7. CNG PRD venting location and direction (arrow), refuse roof mount systems.

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Figure 8. CNG PRD venting location and direction (arrow), front of body refuse system.

Figure 9. CNG PRD venting locations and directions (arrow), transit bus.

4. Remember, unlike a structure or utility fire, a natural gas vehicle has a limited amount of fuel
on board. Allow gas to vent and watch for secondary exposures and hazards.

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5. CNG Fuel Management Module (FMM)
The fuel management module (FMM) is equipped with a 1/4-turn manual shut off valve which
isolates the fuel storage system from the engine for maintenance or emergency situations. The
FMM may be separate from the cylinders or integrated into the cylinder housing. Although the