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Threshold braking is accomplished when the operator depresses the brake pedal until just prior to wheel lockup. Then, the operator is supposed to ease up on the brake pedal, keeping the tires rotating, which causes friction. When the operator is assured the wheels are moving, he again depresses the brake and keeps repeating the procedure until the vehicle comes to a complete stop.
This is a great procedure in theory; the reality is that the driver will probably panic, lock the wheels and lose control of the apparatus. The threshold braking procedure is the manual equivalent of anti-lock brakes. Although anti-lock brakes will be covered in a future column, there are several things you need to know about anti-lock brakes.
Anti-lock brakes are now required on most fire apparatus as per National Fire Protection Association (NFPA) 1901, the motorized fire apparatus standard (August 1996). Anti-lock brakes must be applied with steady, even pressure on the brake pedal and not the threshold braking procedure. It is imperative that the operator identify anti-lock brake equipped apparatus, prior to the movement of the apparatus.
I recently taught an emergency vehicle operators' course for a department that had a rescue truck that was 6 months old. Very few drivers knew that the rescue truck was equipped with anti-lock brakes and nobody understood how anti-lock brakes work. This was an accident waiting to happen.
Unfortunately, this situation is not unique to that fire department. I have said it before and I will say it again: in many cases we simply just do not know enough about what we are trying to do. With the introduction of electronics, technology and special systems, fire apparatus have become more complex and the fire service has fallen behind in understanding these complexities. What are the answers? Emergency braking training sessions and a driver's manual.
What preparation is necessary for emergency braking exercises? First and foremost, all apparatus must have successfully completed a DOT heavy-duty truck inspection and must be in top mechanical shape.
Next, find an appropriate location in which to conduct the test. We found a school with long, flat entrance and exit roads. We received permission to use the school facilities on a Sunday. We also arranged to have the emergency braking drill videotaped from two different angles.
We assigned a driver and one firefighter to be seated and belted in the cab. The first apparatus was sent down the entrance road attaining a speed of 50 mph. Upon passing the first set of traffic cones, the driver began to threshold brake. Drivers were given prior instruction that locking the brakes up was unacceptable and an unsafe act. Prior to the test, information had been compiled on the apparatus, including engine size, horsepower, transmission type, pump size, booster tank size and any auxiliary braking devices, if the apparatus was so equipped. Other information included vehicle height, overall length, width, weight and the wheelbase.
All the information and the distances needed to stop each of the apparatus were recorded. These measurements represent the total stopping distance for each of the apparatus included in the testing. Two emergency braking tests were completed on each of the seven apparatus that took part in these exercises. The average stopping distance was 154.83 feet, at an average speed of 48.91 mph, during the 14 emergency braking tests that were done.
The drivers who took part in this exercise now realize the limitations put on them by apparatus, their environment and even themselves. These limitations include, but are not limited to, the size of the vehicle, vehicle weight, speed, water surge, condition of the brakes and tires, road conditions, and the driver's ability and experience. Drivers also learned that these limitations are all interconnected and that they drastically affect the driver's ability to stop in an emergency.
What about the videotape of the emergency braking test? The tapes can be used for indoor driver training. Also, the tape could be invaluable in any future litigation. Although the test results are valid only for that date and time, they will prove to an outside third party that the department has some degree of competence and knowledge in the operation of its emergency vehicles.