Accidents and Fires: Practice Questions & Explanations

Water should not be used on fuel, oil, grease, or electrical fires. Water on burning fuel or oil floats the burning liquid across a wider area and can splash flaming material onto the firefighter. Water on an energized electrical fire conducts current and creates a serious shock hazard. Class B fires (flammable liquids) require a foam, dry chemical, or CO2 extinguisher. Class C fires (electrical) require a non-conductive agent like CO2 or dry chemical. Most commercial vehicles carry a B:C-rated dry chemical extinguisher. Water is acceptable on Class A fires: wood, paper, fabric, and rubber. For a tire fire, water can help if you can get enough flow on it, but for a small contained fire on a paper or cloth load, water is the right call.

The first priority at an accident scene is to prevent another collision. Stop your vehicle in a safe location, activate your four-way flashers, and set out the required warning devices: three reflective triangles or three flares for the standard daytime configuration. Triangles go on the traffic side: one within 10 feet of the rear, one about 100 feet behind, and one about 200 feet behind. On divided or one-way highways, all three go behind the vehicle. Moving wrecked vehicles before assessing injuries can worsen injuries and disturb the scene before police arrive. Photos and insurance details matter, but only after the scene is safe. Calling 911 is essential, but you do that from a position of safety after warning devices are out, not by walking off into traffic.

On a two-way or undivided road, the three warning triangles are placed as follows: one within 10 feet of the rear corner of the vehicle on the traffic side, one about 100 feet behind the vehicle on the shoulder or in the lane traffic uses to approach, and one about 100 feet in front of the vehicle in the direction of oncoming traffic. The forward triangle is what most drivers forget — it warns oncoming traffic on a two-way road that there is an obstruction. On divided highways, all three triangles go behind the vehicle: one at 10 feet, one at 100 feet, and one at 200 feet. At night or in low visibility, you may use flares instead, but be cautious of flammable cargo. Activate four-way flashers as soon as you stop, before getting out to set triangles.

Under-inflated tires and loose fuel system connections are among the most common preventable causes of commercial vehicle fires. Under-inflated tires generate excess heat from flexing as they roll, and the heat can ignite the tire's rubber or nearby flammable surfaces. Loose fuel connections leak diesel or gasoline that can be ignited by hot exhaust components or a spark. Other risk factors include short circuits caused by frayed wiring, leaking hydraulic lines near hot surfaces, and accumulated grease and dirt around the engine. Pre-trip inspections should check tires for proper inflation and damage, verify all fuel and hydraulic connections are tight and free of leaks, and confirm that wiring is intact. Most commercial vehicles carry a B:C-rated fire extinguisher and reflective triangles by regulation.

ENGINE COMPARTMENT FIRE requires immediate, controlled action. STEP-BY-STEP RESPONSE: (1) PULL OFF: Get off the road immediately — don't continue driving except to reach an immediate safe pull-off; (2) SHUT ENGINE OFF: Cut fuel supply by killing the ignition; (3) CALL 911 if the fire is beyond a small extinguisher-manageable size; (4) GET OCCUPANTS AWAY from the vehicle — a burning CMV can explode if the fuel tank is involved; keep passengers and yourself upwind and at least 300 feet away; (5) ATTEMPT EXTINGUISHING only if: you have the right extinguisher (dry chemical Class B:C for engine fires), the fire is small, and you have a clear escape path; (6) DO NOT OPEN THE HOOD FULLY — lifting the hood suddenly introduces oxygen and can cause the fire to flare dramatically; instead, crack the hood slightly (enough to aim the extinguisher nozzle underneath) or discharge through the front grill opening; (7) AIM AT THE BASE of the fire, not the flames; (8) BACK OFF if the fire doesn't respond to the extinguisher — do not stay near a vehicle that may explode. WHAT YOU CARRY: CMVs should carry an ABC or B:C extinguisher rated for vehicle fires; inspect it during pre-trip; know its location; know how to use PASS (Pull-Aim-Squeeze-Sweep). NEVER: use water on an electrical or fuel fire; re-enter a burning vehicle for cargo; allow bystanders near a burning CMV with a fuel tank.