On a slick road, the tires on the fire apparatus may break traction and start to slide before enough lateral g-force is created to cause the vehicle to roll over.
As long as the combined g-force does not exceed the available grip of the road, the vehicle will hold its grip on the road.
While the friction circle is an important aspect of safe driving, it is an often-overlooked aspect of fire apparatus driver training programs.
When the amount of lateral g-force exceeds the rollover threshold of the vehicle, the g-force will “push” the vehicle over. Most fire apparatus have a high center of gravity, and it does not take much lateral g-force to push them over.
Many fire apparatus crashes are the result of the driver drifting off the road and then overcorrecting to regain control of the vehicle. When the driver overcorrects, he turns the wheel and creates an artificial curve in an otherwise straight road.
One of the many ways that lateral g-force can contribute to a rollover crash is by inducing a “weight shift.” It is common to hear driver trainers and crash investigators refer to “weight shift.” But what is “weight shift,” and why is it bad?
Under no circumstances should a fire apparatus operator drive so close to the upper limits of the apparatus’s capabilities! Driving in this manner leaves no room for error. Therefore, it is important for the fire apparatus operator to understand how to judge the amount of lateral g-force acting on a vehicle based on the sensation of g-force the driver experiences on his body.
The moral of the story is this: as speed increases, or a curve gets sharper, the amount of lateral g-force acting on the vehicle will increase substantially.
In this series of articles, we will examine some of the more serious safety issues faced by the fire apparatus operator. By reviewing recent case studies, it is apparent that our first topic should be that of fire apparatus rollovers. Rollovers are a common cause of fire apparatus crashes.
It is hard enough to bring a fire apparatus to a safe stop. Adding improperly adjusted brakes to the equation significantly compounds the problem. CHRIS DALY