One of the primary hazards rescuers will encounter will be the electrical systems that power the vehicles. The most common system will be the 12-volt system, but it will look much different than the automobile 12-volt system. Commercial vehicles will utilize multiple batteries to provide enough power to turn the engine over and provide voltage for the rest of the vehicle. Batteries will be wired either in Series or Parallel. Series wiring involves sending a path of current through each battery in a single direction. In this case, disconnecting the negative post closest to the frame will break the loop and shut down the electrical system. Parallel wiring involves sending paths of current through each battery concurrently (photo 5). In this case, the rescuer must disconnect all of the negative connections to power down the system. There are also Hybrid Powered Trucks that are on the roads today. Many of these utilize a 60-volt hybrid drive unit in conjunction with the vehicles transmission to drive the vehicle. The unit is powered by a hybrid converter system and can involve well more than 300 volts of electricity. The improvement in vehicle performance shows increases is fuel economy, improved power and performance, and less brake wear as the hybrid unit slows the hydraulic drive of the vehicle’s transmission to assist the braking system. However, be wary of secondary equipment that is installed on the vehicle; there may be a secondary voltage system that powers this unit (photo 6). This power source needs to be secured as well as the main electrical system on the vehicle.
The primary fuel source for these types of vehicles will be diesel fuel, but many other types are still in service. Diesel fuel has four properties that make it popular for use: it is combustible, and provides a more efficient “burn” in the cylinder when it is atomized; it removes heat from the fuel system components; it acts as lubrication for fuel injection parts; and the viscosity of the fuel limits gelling, aiding in flow in colder weather, as long as water can be kept from contaminating the fuel system. Fuel loads for these vehicles do not only sit in saddle tanks on the sides of the vehicle; based upon application, there may be other powered components on the vehicle. For example, tractor trailers that haul perishable goods carry them in refrigerated trailers, or “Reefer Units,” so to speak. These units have a refrigerant system powered by a second engine, and the fuel tank will be found underneath the trailer for this engine (photo 7). Other fuel systems for powered units include road sanders, dolly trailers, and Sani-Vac equipment. No matter the system, the concerns are similar; controlling the flow of fuel is vital. Be sure to shut down the vehicle, keep the fuel shut-off set in the “no-fuel” position, and close all shut off valves on all fuel tanks on the vehicle.
Commercial vehicles utilize pneumatic controls for various devices on the truck. It can be used for climate control settings, wipers, split-shift transmissions, starting systems and suspension/cab ride systems. However, the primary function is the vehicle braking system. Air will be necessary to both release and apply the brakes for the vehicle. There will be a dual air system in these vehicles; the Primary Air System is used for braking, and the Secondary Air System will run other functions on the truck. Keep in mind that if the primary system was to suffer a catastrophic failure (leak), the secondary system will provide enough air to control the braking system for about a minute. After about a minute, as the air exits the vehicle, the brakes will begin to apply by themselves. On the accident scene, it will be necessary to control the pneumatic system. Be sure the parking brake for both the tractor and trailer are applied, chock all wheels where applicable and bleed off all air tanks in both the tractor and the trailer. It is also advisable to disconnect the “glad hands” that provide air delivery to the trailer, and lock them out in a plug bucket type lockout/tagout device (photo 8).
One of the most serious hazards associated with these vehicles are the hydraulic drive systems that operate the truck’s equipment. Hydraulics can be found operating components on trash collection vehicles, cement delivery vehicles, drop deck trailers, lift gates and more. Pressure in these systems can range from 25 psi at idle to upwards of 2,200 psi, based upon the needs of the component. It is critical that these systems are secured and stabilized prior to any extrication operations. Be sure that the vehicle power is shut down, as some of the power for these systems can come from the tractor. Next, block and stabilize the components in place. Do not jog the system or attempt to move the component. Many rescuers will not be familiar with a specific hydraulic component’s controls, and trying to figure it out on-scene has resulted in further injury to the patient, and additional injury to the rescuers.
Next, shut down the hydraulic feed to the system. There will normally be a main shut-off valve somewhere within close proximity of the oil tank. Next, identify any hydraulic components and piping in relation to the extrication. It is very important that rescuers do not cut through any piping during the extrication. Failure of the system may occur, resulting in catastrophic movement of a component, injury from high-pressure atomized oil exposure, and crush injury by being struck with overhead supported loads (photo 9).