Commercial truck fires present a serious fire risk, right? The American Trucking Association’s Technology and Maintenance Council (TMC) thought so when it established a task force to investigate the causes of commercial truck fires and prescribe possible solutions.
TMC members felt a sense of urgency for the issue because truck fires today tend to be much more intense. Like homes, the modern commercial truck cab contains composites and flammable glues that are a recipe for turning a small spark from an electrical short into a fire that engulfs all parts of the truck in minutes.
So what does this have to do with fire apparatus? Isn’t the heart and soul of any piece of fire apparatus a commercial truck? From its motor to its transmission to its electrical system, every piece of fire apparatus has commercial truck DNA.
And because of that, fire and emergency apparatus are not immune to fires. Here’s a look at a few recent ones.
- Baltimore: Mechanical issues caused a Baltimore fire engine to catch fire in its quarters. Engine 50 had just returned from a call when the fire started.
- Auburn, Maine: A group of firefighters found themselves engulfed by smoke as they rode south on Washington Street aboard one of their pieces of apparatus.
- Philadelphia: Ambulance catches fire and torches a Philly fire station
- Mahanoy City, Pa: Flames destroyed the aerial truck of the Washington Hook and Ladder Co. and caused heavy damage to the station.
Here are some of TMC’s recommended actions that vehicle operators, fire departments, and emergency vehicle technicians should be on the lookout for to mitigate the chances of a fire breaking out.
Electrical wiring
TMC’s initial findings were that the majority of commercial truck fires result from the routing, clipping or chafing of the vehicle’s electrical wiring. Even though most truck manufacturers wire their vehicles cleanly and safely, over time the wires grow old or wear out, especially in certain configurations.
Technicians should look for thinning, cracked or otherwise compromised wiring that poses a fire risk.
This potential hazard is a red flag for any fire department and its maintenance technicians given the amount of aftermarket electrical equipment like radios, computers and portable equipment chargers, which most fire apparatus undergoes following delivery.
Ensure that such work is always done by knowledgeable and skilled technicians who are licensed to do those types of installations.
Replacement components
The wiring configurations may be different on aftermarket engine parts. Replacing a starter or alternator may require the wiring to be stretched beyond its original configuration.
This new configuration can cause additional stress on the wires and produce a greater risk of damage to the wire’s insulation. When this happens, the exposed wiring can come in contact with grounded metal causing arcing and creating a flame.
Add-on electrical components
Additional electrical equipment such as inverters, hazard warning signs and charging stations for biomedical equipment and hand lights, are another cause of truck fires.
Aftermarket installation of such equipment requires drilling holes for the passage of wires, and it doesn’t take long for the wiring to chafe against the edges of the hole. Even when rubber grommets are used, the rubber can become old and cracked, causing wire casings to erode and make contact with the metal edge.
The use of 12-volt outlets, “cigarette lighter sockets,” as power outlet can be another potential cause of fire. When these sockets are used for powering portable devices the pop-out function may diminish, causing the electrical coils to become stuck and overheat.
When I was a company officer, my crew and I awoke one night in our second-floor bunkroom to the sound of the station’s smoke detectors alarming. When we went to investigate, we encountered a light haze of smoke filling the apparatus bays.
The source? Upon returning to the station following a call earlier in the evening, the volunteer driver of our station’s utility vehicle had failed to turn off the master electrical switch. A handheld spotlight had been left on the bench seat in the cab, lens down, and in the on position; the heat from the light had ignited a smoldering fire in the seat upholstery.
Improper wire
When the wire size is inadequate for the application used, it can overheat and present a serious fire hazard. Volunteer departments should be especially aware of this potential fire hazard since often times aftermarket electrical installations or repairs are done by their members or mechanics who are not familiar with the electrical requirements of fire apparatus.
If a wire is improperly insulated, it may likely be too unstable to resist chafing or high temperatures, which greatly increases the chances of a fire. Before any such work takes place, determine what types of wire are appropriate for various applications and do not allow installers not to use improper wire just to save money — the risks far outweigh the perceived benefits.
Monitoring performance
The electrical system of your apparatus revolves around its source of power: the batteries to get things started and the alternator to keep things going and recharge the batteries for the next start. To do this, the system must handle all electrical loads that may be placed into use simultaneously in an emergency situation.
Total connected load (TCL) is basically the sum of all the current consumed by all the electrical loads when they are operating. As a rule of thumb, a vehicle’s alternator should be able to provide for the TCL and still have a 20 percent reserve.
When the TCL for a particular piece of apparatus exceeds alternator output, the alternator is being unduly stressed and its life-cycle is being dramatically reduced. It also means that batteries on your apparatus are not charging properly.
The cumulative affect can be shortened battery and alternator life and undue fluctuations in the electrical current throughout the vehicle’s electrical system. Fluctuations in the electrical current can lead to unwanted heating and cooling of the wiring, which will cause the wires to elongate or contract.
This elongation and contraction can led to the dreaded wire insulation chafing and cracking and lead to an electrical arc or overheating that can precipitate a fire.
Dashboard gauges
Train your apparatus drivers to use the information from their instrument panel’s voltmeter to assess the performance of the vehicle’s electrical system. The voltmeter directly measures the result of charging-system performance — the alternator’s ability to meet the TLC.
When the voltmeter reading is between 14 and 14.5 volts, the alternator is meeting the apparatus’s TCL. In the event of a failing alternator system, the voltmeter reading will fall below 14 and continue to drop as the battery discharges.
This indicates that the alternator is not able to power all electrical devices and maintain the batteries at full charge. Apparatus operators should know that a 12-volt battery is fully charged at 12.66 volts — six cells at 2.1 volts per cell.
If the voltage output from the alternator dips below 13 volts, the batteries are discharging, and that is not a good thing. In the event of an overcharge condition, the voltmeter will climb above its normal zone, an equally undesirable sign.
In-station charging
Many department use in-station charging systems, or a shoreline, to maintain fully charged apparatus batteries and to provide power to on-board charging stations to maintain a trickle charge to devices such as computers, biomedical equipment and portable lighting equipment.
A common problem encountered with such systems is the failure of the driver to disconnect the power cord prior to moving the apparatus. This can cause damage to both the cord and the connecting port; damage to the latter can lead to arcing or overheating of wiring inside the apparatus.
Newer models include an auto-eject feature that ejects the external power cord from the apparatus upon apparatus startup. Therefore, a critical driver behavior must be to ensure that the external shoreline is properly disconnected prior to moving the apparatus forward.
