Issued June 2020
Compressed Natural Gas (CNG) Option
Copyright 2020, Heil Environmental
Printed in U.S.A.
225
WELDING AND HOT WORK PROCEDURES
WARNING
Never weld on a compressed natural gas vehicle unless
the compressed natural gas fuel system has been purged
with inert gas.
DANGER
Never weld on any fuel system components. Welding can
ignite the fuel, resulting in an explosion or fire causing
serious personal injury or death.
If any welding or ‘hot work’ (i.e., any work that involves
burning or use of tools that produce a spark, flame, or
source of ignition) is required on a CNG fuel vehicle
excluding the CNG fuel system, you must perform the
following procedures:
1. Conduct work in a well-ventilated area.
2. Shut off every cylinder in the fuel system by turning
the valve clockwise to OFF.
3. Ensure the FMM Manual Shut-Off Valve is in the ON
position.
4. Start the vehicle and let it run until the engine stops.
5. Turn the ignition key OFF and remove the key.
6. Check the gauges on the FMM to ensure all pressure
is at ZERO.
WELDING AND HOT WORK PROCEDURES
(CONTINUED)
7. Slowly relieve excess pressure by turning the bleed
valve cap counter-clockwise until a hissing sound is
heard. Close the bleed valve when the hissing stops.
8. Purge the CNG fuel system with inert gas, including
the tanks. See Purging with an Inert Gas Prior to
Welding or Major Repairs.
9. Use a welding blanket to protect the fuel system from
slag and sparks produced from welding and hot work
operations.
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