When a fire truck is involved in a motor vehicle accident, there are often many questions to follow.

Firefighters may be injured, the fire truck may be damaged beyond repair, and emotionally, the toll an accident has on the entire fire department can be significant.

Understanding the safety features of a fire truck and the sequence in which they deploy to protect firefighters during a collision may help answer some of these questions.

This blog will walk through some basic principles associated with safety systems and explain exactly what a fire truck does to help protect firefighters during a motor vehicle accident or collision.  

Passive Versus Active Safety Systems

A passive safety system is always present and reacts to a collision in an effort to keep the occupants of a vehicle safe. Active safety systems are designed to be active pre-collision and minimize injury based on real-time data collected by the vehicle.

Fire trucks are equipped with both passive and active safety systems.

Passive Safety Systems

Occupant-sensing seatbelts

All fire trucks today come standard with occupant-sensing seats. A chime in the cab will operate continuously if weight is sensed in a seat without the seatbelt clicked on to protect the occupant.

Seat belts
Seatbelts are designed to keep occupants in a vehicle in a safe position during a collision. Pre-tensioning of seat belts secures seat occupants and ensures they are in the proper location if airbags are deployed.

Airbags

Airbags are designed to protect vehicle occupants in a collision. Pierce Manufacturing offers two different types of airbag systems.  

• Frontal airbags are airbags designed to protect the driver and officer during a collision. These airbags deploy from the steering wheel and the dash located in front of the driver and officer positions.
  
  
• Side-Roll airbags are designed to protect vehicle occupants in a side-roll event to prevent them from hitting the side structure of the fire truck cab. Side-roll airbags are available in the front and rear seats in the outboard positions.

A Hierarchy of Passive Safety Systems

When you think of passive safety systems, it's important to recognize that they are built in a hierarchy.  

Appropriate seat belt use is the foundation of the passive safety system hierarchy. A seatbelt must always be worn and in the appropriate manner. When this is accomplished, it will provide the necessary primary protection to occupants.

Active safety systems

• Tire air pressure monitoring helps to ensure the tires are at the proper inflation pressure. A tire pressure monitoring system alerts the operator if the tire pressure is low and air must be added. A truck with one or more partially deflated tires could present a hazard.

• Anti-lock braking systems are required by law and prevent the tires from locking up when attempting to stop the vehicle. When applying the breaks, if the wheels begin to skid as a result of too little friction between the road and tires, the system "pulses" the breaks to maintain control.

• Automatic traction control is designed to prevent the tires from slipping if there is insufficient friction between it and the road surface. While this is currently optional on fire trucks, it is likely to be adopted as an NFPA standard along with anti-lock braking systems as early as next year.

• Electronic stability control (ESC)  At speed and in a turning motion, the system will monitor if the fire truck has surpassed the vehicle’s capabilities and will reduce the throttle, slowing the vehicle down. Electronic stability control systems also kick into action in low-friction events, like sliding on ice. If an operator loses directional stability or countersteers and the vehicle begins to rotate in the opposite direction, the ESC system will strategically apply individual brakes to regain stability.

With a general understanding of passive and active safety systems, let’s move on to discuss when each of these systems is activated.

Which Safety Systems Are Activated In A Collision?

In the aftermath of a fire truck collision or motor vehicle accident, it can be difficult to survey the damage and not question whether everything possible was done to protect the occupants and the vehicle itself.

Understanding how active safety systems work is straightforward. Active safety systems kick into action based on real-time data. Alerts notify fire truck operators when systems are in use to help maintain vehicle stability and prevent a collision from occurring.

But for passive safety systems, it can be a little more challenging to understand when they are activated. There are a few key considerations that can help, and really, it all comes down to physics.

The Breakdown of a Collision 

First, it is critical to remember that all vehicles, fire trucks included, have components that are designed to crumple and break in a strategic manner to protect the vehicle occupants. 

Fire truck bumpers, frame extensions and cabs are designed to crumple when they are hit to absorb some of the energy from a collision. Absorbing energy in this fashion helps to preserve the protective space within the cab itself. As a result, is why occupants of a fire truck collision can sometimes walk away with only minor injuries while the vehicle itself sustains significant damage.

It’s also important to remember the sheer size of a fire truck as this plays a significant role in how much damage occurs. Rapid deceleration can cause injury, but it is all dependent on the mass of the vehicle.

There are two basic concepts that need to be understood. First, the deceleration of a vehicle is the rate at which the speed or velocity decreases with respect to time; the more quickly it stops, the greater the deceleration. The second is the change in speed as influenced by momentum; the heavier something is, the harder it is to change its speed.  

The momentum of a large fire truck can be 10 to 12 times that of a car, so when a truck and car collide, the deceleration of the car is significantly higher than the deceleration of the fire truck. Even though both vehicles are involved in the same accident, the different decelerations may result in a car with airbags that fire, and a fire truck with airbags that do not.

Because vehicle safety systems rely on real-time data to react in collisions—the change of velocity and angle of stability with respect to time determine which safety systems react.

A Reaction to Changes In Velocity, Deceleration and Angle of Stability

Airbags are a passive safety system that reacts only if the probability of injury reaches a specified threshold.

An onboard computer is continually monitoring vehicle velocity and deceleration. If a collision occurs, a split-second calculation determines whether the airbags deploy.

• For a head-on collision, airbag deployment is based on deceleration and how much time it takes to decelerate.
  
• For a rollover event, airbag deployment is based on the change of angle, essentially measuring if the truck is tipping over sideways.

There is a reason why not all fire truck collisions result in the deployment of airbags. If the probability of injury is low—if the physics of the incident shows that the vehicle velocity, deceleration and angle of stability are within safe limits, the airbags are deemed unnecessary and remain stowed.

It’s very difficult to change the momentum of a large vehicle like a fire truck. Safety systems are designed to protect vehicle occupants based on pre-engineered parameters and the probability of injury. A seatbelt, worn correctly, is the primary safety restraint in a fire truck; all other safety systems depend on the seatbelt to work appropriately and are there to protect you when the seatbelt safety threshold is met.

Do you have more questions about fire truck safety systems? Your local Pierce dealer is always available to help.

Interested in learning more about Pierce’s commitment to firefighter safety systems? Here are some additional resources:

• Fire Truck Cab Safety: Maintaining Cab Mounts In A Collision Test
• Fire Truck Collisions: Increase Public Safety with HAAS Alert
• What Is Fire Truck Crash Testing and Crashworthiness?
• UL Testing: Minimum Requirements and Pierce’s Vehicle Inspection Program
• Trends in Fire Apparatus Emergency Warning Lights
• Product Support Offerings to Consider Before Buying a Fire Truck