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SCCA Magazine |
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SCCA Magazine May-June 2010 |
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Sure-fire rules
Truck fires have
taken on a greater significance as they become
more comprehensive and catastrophic.
Truck fires have been with us since trucks began
to carry freight. But more recently, it seems
like there has been a proliferation, and where
once a few wires would burn up and the handheld
fire extinguisher would deal with the problem,
now the truck burns to the frame rails.
“I don’t know if there are more truck fires
today or if now they are catastrophic when they
happen,” says Bruce Purkey of Purkey’s Fleet
Electric. “When it melts the tires, you know
it’s a pretty hot fire.” Purkey is a major
contributor to the efforts of the Technology and
Maintenance Council (TMC) of the American
Trucking Associations when it comes to things
electrical. He and industry electrical veteran
Charlie Groeller are part of the TMC’s vehicle
fires task force, investigating the causes of
truck fires to develop some recommended
practices. When fleets were asked to bring
examples of trucks damaged in “thermal events,”
as they were called, the pictures showed burned
equipment barely recognizable as trucks.
The electrical problem
As you would expect,
electrical issues are the main cause of truck
fires. For the most part, truck manufacturers do
an excellent job with wiring, but over time,
things can change.
One factor
contributing to fires is changing out one
component for another, especially a starter
motor or alternator. The issue here is that a
fleet might use a different component in service
than those fitted by the manufacturer. In those
cases, often the terminals are located in
different positions on the component. This can
lead to wiring being stretched beyond its
designed length and position. Putting additional
stress on the cables can lead to chafing or
terminal breakaway, either of which can lead to
exposed wiring contacting grounded metal and
subsequent arcing.
Starter motors have
been identified as a potential cause of fires
even when the terminals are not compromised.
According to Groeller, there are conditions when
the starter pre-engages before the pinion
engages and a high current is drawn over a long
enough period that the unfused starter cables
start a fire.
Another condition
reported by Ron Szapacs, maintenance specialist
at Air Products, was a starter that remained
engaged after the engine had started. Because of
the noise from the engine, the driver was
unaware of it and the cables started a fire.
Technicians can play an important role in
the prevention of fires, not just through the
change-out of different components. The task
force is recommending techs take a proactive
role during preventive maintenance (PM)
inspections in looking for potential electrical
hazards by inspecting the routing and clipping
of harnesses and wires to ensure that cannot
chafe. Technicians are encouraged to be
especially vigilant in checking around the
starter and alternator, and Groeller says PM
instructions should be modified to stress the
importance of correctly attached wiring.
Trucks are also burning to the ground after an
accident. If the engine and transmission are
displaced, starter terminals or cables can tear,
contact the frame and ignite. There is little
chance of avoiding this except to specify an
inertia switch in the high-current circuit or a
battery isolator switch within the driver’s
reach. However, expecting the driver to have the
presence of mind to shut off the electricals
after an accident may be a lot to expect.
Add-on electricals
A recurring theme is the
driver’s role in vehicle fires. Fires have
occurred when a vehicle is sitting parked on a
weekend with no apparent cause. Purkey says
inverters are the issue, especially if a driver
is less than conscientious about keeping the cab
tidy. A blanket or a jacket covering an inverter
in a sleeper, especially under load, can result
in overheating and fire.
One of the
problems with inverters is installation by a
less than qualified technician –maybe the driver
himself – can be a fire risk. If the inverter is
connected directly to the battery with wiring
run through a hole drilled in the sleeper floor,
it’s a fire just waiting to happen. It will not
take long for the wiring to chafe through on the
exposed metal edge. Even when a rubber grommet
is used, the rubber will eventually become aged
and crack or fall out.
Purkey builds
inverter kits that use a Fuse Cube that attaches
to the terminal of a Group 31 battery with fuses
sized to the power of the inverter. The wiring
is also matched to the inverter’s power
requirements and made the correct length so it
can be correctly routed and clipped.
There’s also an issue with 12-volt demand from
lighters and power sockets. If a lighter is
over-used, the pop-out function of the lighter
can be compromised. Then a lighter pushed into
the socket may not pop out and can trigger a
fire.
With auxiliary wiring, the problem
is two-fold: Wire size may not be adequate for
the application and the wire insulation may not
be suitable either from a chafing standpoint or
from a temperature stability perspective. Wire
selection is critical when technicians install
equipment on a vehicle.
Wheel-end fires
Wheel-end fires are commonly caused by a
dragging brake or defective wheel bearing.
Either is difficult to spot, especially as they
are usually on the trailer, which gets far less
maintenance than the tractor. Drivers should be
encouraged to walk around the vehicle looking
for hot spots whenever the truck is parked on a
break.
Oil or grease radiating out on a
wheel is an indication that something is amiss
in the bearing. A dragging brake will heat up
the wheel, but don’t be tempted to discover this
by putting your hand on it. The heat can be
extreme.
A wonderful product for wheel-end
issues is the ThermAlert, which can be used with
Pressure Systems International’s tire inflation
system. A plug in the system’s air supply is
designed to melt when the temperature at the
trailer wheel-end becomes excessive. The loss of
air and - replenishment by the system is
immediately apparent to the driver who can bring
the truck to a halt and find out very quickly
from the noise of the escaping air which
wheel-end has overheated. James Burg, president
of James Burg Trucking says “This system should
be a recognized by the Commercial Vehicle Safety
Alliance (CVSA) as an accepted accident reducing
technology. We’ve included it on our vehicles.” | |
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