developing a relationship with the AHJ at the beginning
of a modifi cation project is such an important step.
“Th e AHJ is typically the local fi re marshal,”
Th omason says. “In some instances, they are not familiar
with the code for natural gas in a building. When
this is the case, the fl eet’s natural gas consultant or
building engineer can become an educator. I was once
involved in a modifi cation project at a large dealership
in New Jersey. We gave a 30-minute presentation
on codes and standards.
Th ey really appreciated
it. Th at’s much diff erent
than just putting a bunch
of drawings and permits
in front of them.”
Th e U.S. Department of
Energy’s Offi ce of Energy
Effi ciency & Renewable
Energy has released a
handbook outlining fi ve
elements that must be
considered when developing
36 Fleet Maintenance | November/December 2018
a NGV maintenance
facility design:
Ventilation
Containment (paths
of migration)
Space heaters
Electrical wiring
Methane detection
systems
While all fi ve areas
need to be addressed,
there are options to help
fl eets ensure safety and
compliance while also
containing costs. For
example, it might be
possible to section off
part of the facility for major vehicle repairs; only that
section would be subject to any required modifi cations.
Another approach could be to establish a certain
number of bays as NGV bays, and then modify only
the part of the facility where those bays are located.
Regardless of which approach the fl eet adopts, the
principle engineer for GTI, Tyler Manley, has a few
words of advice.
“We like to say there are three main areas of focus
when modifying a maintenance facility: detection,
dilution and extraction,” Manley says.
Let’s look at how each component works to help
ensure a safe environment for servicing NGVs.
Ventilation, dilution
and containment
Ventilation must provide suffi cient airfl ow to properly
dilute and evacuate any escaped natural gas.
Operators of traditional fl eet facilities may need to
reverse their thinking.
“In most cases with gas and diesel, fl eets introduce
air in the ceiling cavity and exit it out the doors,”
NGVi’s Th omason says. “So the fl ow of air is from the
top of the facility to the bottom. But since natural
gas is lighter than air, that doesn’t work. We have to
bring air from the bottom of the facility and exhaust
it out the top.”
GTI’s Manley says fl eets can install fans either near
the fl oor or near the ceiling, or in both locations if the
extra cost isn’t a deterrent.
“Most of the time we’ll simply see fans up high,”
Manley says. “Th is is likely because they were located
on the roof prior to the facility modifi cations, so there
is no need to relocate them.”
Keep in mind that anything within 18” from the
ceiling may be rated as a Class 1, Division 2 electrical
hazard zone. Th us, any electrical wiring and
CNG and LNG:
diff erent, but
the same
Gas weight, odor
and density set
the two apart.
Today’s natural gas vehicles are
being powered by both compressed
natural gas (CNG) and liquid natural
gas (LNG). Leo Thomason of the
Natural Gas Vehicle Institute (NGVi)
says the important thing to understand
is that CNG is lighter than air,
and LNG is both lighter and heavier.
Here’s why: At roughly minus 160
degrees F, LNG transitions from liquid
to gas. Once in a gaseous state,
the vapors are initially heavier than
air. As it warms up, the gas becomes
lighter than air.
“This is why fleets have to do all
the same facility modifications for
LNG that need to be done for CNG,”
Thomason says. “You also need all of
the same modifications necessary
for liquid fuels such as gas and diesel.
But a fleet maintenance facility
is typically set up for that so it’s not
an issue.”
A big difference between CNG and
LNG is that LNG is not odorized.
Thus, with LNG, fleets are required
to have a methane detection system
installed in both the facility and on
the vehicle. With CNG, a detection
system is optional.
Why would a fleet opt for an LNG
vehicle? Thomason says it’s a storage
strategy.
“A cubic foot of natural gas at
atmospheric pressure is 14.7 psi,”
Thomason says. “If you compress
that to 3,600 psi, you increase energy
density 300 percent. If you take
that same amount and liquify it, you
increase energy density by 600 percent.
So you can put twice as much
natural gas on a vehicle when it’s in a
liquid state. When the fuel ultimately
gets to an engine, though, it’s all the
same: natural gas at roughly 125 psi.”
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