Big Truck Extrication - Part 1: Anatamy 101
David Pease, Carolina Fire/Rescue/EMS Journal
These airlines run behind the cab and connect into the front of the trailer. These lines are equipped with a breakaway valve or a glad-hand connector. These airlines are colored coded for easy recognition. The blue line is for normal operations. The red line is the emergency airline that serves to lock the brakes on the trailer, should an emergency arise.
Should the air to the trailer be interrupted, there are air chambers located under each axle that will activate a large spring that is used to mechanically apply the brakes. These are sometimes called piggyback chambers. Most large trucks also have air ride suspension. These are large air bellows that are fixed under each axle. These can hold up to 120psi of air and should this pressure be suddenly lost, the truck could settle several inches or more.
Mounted on the back of the tractors is a flat piece of steel called the fifth wheel. This plate has a wedge shaped slot cut into it that allows for the “king pin” on the trailer to slide into it. This pin is locked into place by two spring loaded jaws. These locks can be released by using the pull handles located on the drivers side. This system allows for the trailer to rotate up to 90 degrees.
By understanding some of the trailers being pulled, a rescuer may have a better idea of what they may be up against. This could range from a tanker full of fuel to a livestock trailer full of angry and confused cattle.* Trailers that are pulled behind tractors come in a variety of sizes and shapes. These are as unique as the cargo they carry.
Trailers are freestanding units with wheels in the front and back. Semi-trailers have only wheels in the rear and are supported in the front by the tractor. Several of the more common types of trailers you might see are; flatbeds for hauling supplies and equipment, tankers for hauling grain, fuel, chemicals and other liquid and gaseous substances, box trailers for hauling a wide assortment of materials and cargo, and livestock trailers for moving animals. When semi-trailers are not attached to the tractors, they are supported in the front by a set of landing gear.
This device has a handle for lowering and raising the front of the trailer. The rear of the trailers will have a bumper for collision control. The older trailers had bumpers that offered little protection on rear end collisions. In 1998 all trailers had to be equipped with a much stronger bumper that would help prevent vehicles from running under the trailer and resulting in serious injury or death.
In this first article we have looked at some real basic large truck construction and design. We have given you a basic knowledge of truck construction that will aid you in deciding how you should approach, stabilize and extricate your victim. In our next article, we will look at scene assessment and approach, as well as vehicle stabilization. Until next time, stay safe, train to your best, and remember that to have not achieved, is to not have tried.