The Apparatus Architect: Part 25 - Designing Rescue Squad Apparatus

Tom Shand and Michael Wilbur discusses the line voltage generator system as one of the most important fixed components on any rescue vehicle.


One of the most important fixed components on any rescue vehicle is the line voltage generator system. The generator and 120-volt lighting system that is designed into the rescue truck will provide much-needed scene support on the fireground and other emergency incidents. The type of generator and...


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The power take-off generators are located between the chassis frame rails and occasionally may protrude above the frame level into a compartment. Adequate protection needs to be afforded around the generator frame from road hazards and care must taken to avoid running these units through high water during periods of flooding. These types of generators require the vehicle engine to be running and cannot produce power while the vehicle is in motion. Care must be taken when powering motor-driven equipment, that these units be protected by a time-delay circuit or power switch to prevent the generator from starting under load.

Hydraulic generators, while generally more expensive than their diesel or power take-off counterparts, are becoming more common on all types of apparatus. Smaller six- to 15-kilowatt units work well on pumpers and aerial ladders with larger 20- to 30-kilowatt generators being used on rescue vehicles. Hydraulic generators offer the advantage of being able to produce their rated output within the full range of engine rpm as well as producing power while the apparatus is in motion. This enables units equipped with hydraulic generators to check street addresses or provide scene illumination while the apparatus is moving. The hydraulic generator has no engine, fuel supply or exhaust system and can operate over a wide range of engine speed, where the power take-off generator must run at a constant speed. For this reason, apparatus configured with both a fire pump and generator system lend themselves to using hydraulic generator equipment.

The use of both 120-volt fixed-body lighting and telescopic light towers can produce a vast amount of illumination at the scene of an incident. Consideration should be given to the total demand of vehicle lighting together with the demand for other motor-driven components that will be carried on the unit before choosing the appropriate size of generator. You should consider the startup loads for equipment, such as hydraulic rescue tool motors, large exhaust fans and other electrical equipment to make sure that you are not choosing too small a generator package. Some larger rescue apparatus are equipped with dual generators combining both a power take-off unit and a hydraulic unit, which offers the best of both worlds with respect to using valuable compartment space as well as providing power when the vehicle is in motion.

(On a personal note, while one of the authors was on a truck committee in the early 1990s working on the specifications on a rescue pumper, the size of the diesel generator was discussed. Unfortunately, we went too small with the generator and did not have enough power to run everything on the apparatus. However, with that said, it is unwise to specify the largest generator without the need, as it could substantially increase the cost of the apparatus.)

Apparatus manufacturers can be helpful in suggesting mounting locations and providing guidance in the proper sizing of generator components for special applications. If your vehicle is going to be equipped with computers or other sensitive electronic equipment, you need to ensure that a continuous source of clean power will be available for these components at all times. No matter what type and size of generator is chosen, make sure when designing the apparatus body that there is sufficient room to maintain and work on the unit when necessary. Many fire departments have made the mistake of "burying" the generator inside of the body, only to find out then when the unit needs attention that the mechanic cannot get into the area to work on the unit without cutting something apart.

The generator system on the rescue apparatus is the backbone of the entire rig. Spending an appropriate amount of time in selecting the right generator for your needs will pay off in the long run over the life cycle of the apparatus. In the next installment of The Apparatus Architect, we will discuss some of the other major body components that your department should consider when developing the specifications.


Tom Shand, a Firehouse= contributing editor, is a 33-year veteran of the fire service and works with Michael Wilbur at Emergency Vehicle Response, consulting on a variety of fire apparatus and fire department master-planning issues. He is employed by American LaFrance and is assigned to the Hamburg, NY, facility. Michael Wilbur, a Firehouse contributing editor, is a lieutenant in the New York City Fire Department, assigned to Ladder Company 27 in the Bronx, and has served on the FDNY Apparatus Purchasing Committee. He consults on a variety of apparatus-related issues around the country. For further information access his website at www.emergencyvehicleresponse.com.