Big Truck Extrication - Part 1: Anatamy 101
David Pease, Carolina Fire/Rescue/EMS Journal
Basic Styles and Construction
We will now look at some basic truck construction and configuration. The conventional style construction is the trucks that have the engine in front of the passenger compartment and are longer. The engine compartment is either hinged down the center or may pull towards the front. These cabs are usually made of a combination of steel, aluminum and fiberglass. The other style of truck is the cab over with the engine being located under the midline of the driver and passenger compartment. These units tilt forward to access the engine.
These are also constructed of a combination of steel, aluminum, and fiberglass. Many tractor trailers have sleepers. These allow for the drivers to stop and sleep or a pair of drivers to rotate off driving so they do not exceed their federal driving limit. Sleepers are an extension of the cab and not a separate unit. There is access through the cab and usually through a side door. Rescuers should always consider there may be a driver trapped or pinned in the sleeper compartment when assessing the wreck scene.
Doors on tractor trailers are usually heavy and have one of two types of hinges. They will either have a conventional style hinge like that found on a standard automobile or a piano style hinge. Both are heavy and well attached. The door latches are found at the lower rear corner of the door due to their height above the ground. They usually have a single latch with a two step locking mechanism.
The windshield and rear window are the standard laminated safety glass as found in automobiles. However, the glass will be set in a rubber gasket that will make it easier to remove and normally it will not need to be cut out. The side windows are tempered safety glass that is heavier than those in autos.
The roofs are made of steel ribs that usually run from front to back and are covered with either aluminum or fiberglass. Some trucks have a fiberglass wind faring or deflector on the roof as well. Behind this you may also find the air conditioner unit or air horns. Most trucks have multiple batteries that are wired in series.
Most large trucks utilize diesel fuel to reduce the possibility of a flashover. The fuel tanks are usually saddle tanks that are attached to one or both sides of the truck. The size of the tanks can vary from fifty gallons to three hundred gallons. If the truck has duel tanks, most are interconnected by a fuel line that equalizes both tanks. There is a cut off at one or both ends of this tube, so fuel can be shutoff should a leak occur.
Most large trucks are equipped with air braking systems. In 1995 NHTSA (National Highway Traffic Safety Administration) made it mandatory that anti-lock brakes be on all heavy and medium duty trucks. In 1997 they required that all new tractors manufactured have anti-lock brakes and in 1998 all trailers, single unit trucks, and buses were required to have them as well.
Some slightly smaller trucks may have hydraulic brakes or a combination of hydraulic and air. With air brakes the system uses compressed air to apply the brakes under normal operations. The air tanks for this system can be located at different locations around the truck depending on the manufacturer. If there is a problem with the air system that engages the brakes and air pressure is lost, heavy springs will activate the braking system. The trailers being pulled also have an air brake system that connects into the tractors air system and work in conjunction with the tractor.