By James Chinni, Marius Magdun, and Marissa Cotten
Saving the lives of others can be a very dangerous business, especially for firefighters whose job it is to protect our communities.
In 2012, 81 firefighters died while on duty-18, or one fifth, died while responding to or returning from the scene.1 To address and reduce deaths in vehicular accidents, many fire chiefs across the nation stress the importance of buckling up. However, many take their firefighters’ safety a step further by specifying supplemental restraint systems (air bags) on their apparatus.
History of Air Bags in Passenger Vehicles
The first commercial air bag systems were offered on some GM cars in the early and mid 1970s. These systems were much larger, heavier, and slower than today’s air bag systems. They were strictly a supplement to seat belts and were marketed by GM as the Air Cushion Restraint System.
In the late 1980s and early 1990s, frontal air bags were reintroduced and federally legislated in passenger vehicles as supplemental restraint systems (SRS). Mercedes-Benz and Chrysler were among the first manufacturers to introduce a driver-side, steering-wheel air bag as standard equipment. Within a few years, driver- and passenger-side frontal air bags were standard in most vehicles sold in North America and Europe. By the mid 1990s, side-impact air bags started showing up, either integrated in a door panel or within the side bolster of the front seats. The 1995 Volvo 850 was the first vehicle to offer side air bags. The pyrotechnic air bag inflator was mechanically triggered by intrusion of the front door into a pyrotechnic primer charge. Today, all air bag systems are monitored and triggered by electronic sensors. It was the same company, Volvo, that introduced the first rollover air bag in 2003.
Rollover Air Bags
Although most people are familiar with air bags in their personal vehicles, their application in fire apparatus is specially designed for the unique seating environment, duty cycles, and crash characteristics of their installation. Air bags in fire apparatus originated with the discovery that rollover crashes accounted for roughly five percent of all heavy truck crashes, but were the cause of more than 60 percent of fatalities and 45 percent of incapacitating injuries to heavy truck occupants involved in a crash.2 To improve the outcome for firefighters and truck drivers in crashes, the industry researched rollovers to develop effective countermeasures. The first step in addressing this issue was to understand what happened to people inside a vehicle cabin during a rollover. That need drove the construction of a one-of-a-kind 90-degree dynamic rollover impact machine.
Engineers discovered that rollovers in heavy trucks are dramatically different than those in a passenger car or SUV. The air bag systems needed to protect the occupants would have to be different as well. After years of extensive testing and validation, including the rollover test of an entire vehicle, the first roll-protection-equipped fire apparatus was introduced in the spring of 2003. About the same time, Volvo introduced the XC90 SUV with roll stability control (RSC). The RSC contained an algorithm that deployed rollover curtain air bags and was touted as the first of its kind in the world. Today all makes of custom fire apparatus offer roll-protection systems as an option to better protect firefighters in a rollover. In addition to fire trucks, rollover air bags can also be found on commercial trucks and ambulances.
The brain of the system in a fire apparatus is a roll sensor that is mounted centrally within the cab. As soon as the driver turns the vehicle ignition on, the sensor goes through a self-diagnosis that typically lasts five to 10 seconds, then begins to sample vehicle status and conditions every 12 milliseconds, or about 80 times per second. In addition to the roll sensor and the outboard air bags, most rollover protection systems also include pyrotechnic pretensioners that tighten the seat belts. If the fire apparatus is equipped with air ride seats, a seat-pull-down device will significantly reduce injuries to the occupant, especially to the head and neck areas.
This is how rollover protection works:
- A roll sensor monitors the truck’s position, and when an irrecoverable rollover is detected, up to three components are deployed per seating position.
- Seat belt pretensioners first tighten the seat belt at each seating position.
- Seat pretensioners rapidly lower the front seats to their lowest positions, holding the driver and officer securely and increasing survival space in the cab.
- Side air bags then deploy to cushion the head and neck.
Since introduction on fire apparatus, rollover-protection systems repeatedly have proven effective in the field. In February 2010, one notable crash involved three California-based firefighters who found themselves in an apparatus rolling 360 degrees down a steep embankment. They traveled 40 feet before hitting a large tree where the vehicle abruptly came to rest. All three were able to extricate themselves from the apparatus. One was treated for a minor shoulder injury. The other two had no injuries at all.
Frontal Air Bags
Although rollovers present the highest injury risk to firefighters in apparatus, frontal crashes with other large vehicles or objects may involve tremendous amounts of energy. Lap shoulder belts still provide the primary protection in these scenarios. But again, air bags are used as supplemental restraints, very much the same way as in roll events. The biggest difference is timing of the deployment-the bags have to be in position much faster than in a roll scenario. Where a roll event can take several seconds, a frontal crash is all but over in 100 milliseconds (1⁄10 of a second), or about the time it takes an average person to blink.
Extensive testing to understand different types of fire apparatus crashes and varying build configurations led to developing sensors that properly discriminate between severe frontal crashes and minor “no fire” events. A typical system consists of a sensor, a steering wheel air bag, knee bolster air bags, and seat belt pretensioners. These devices further reduce injuries to belted occupants. In 2007, the first frontal impact protection system was unveiled in fire apparatus. Today five apparatus manufacturers now offer frontal crash protection systems.
Here is how frontal protection works:
- An electronic sensor monitors the truck’s accelerations. When a crash event occurs and its characteristics fit within a predetermined algorithm, the sensor initiates up to three components per seating position.
- The system tightens seat belts at all seating positions to hold firefighters securely in their seats.
- The system inflates a steering wheel air bag to protect the head and neck of the driver while inflating knee bolster air bags to protect the driver’s and officer’s legs.
Today’s air bags are a result of decades of development and testing to provide the reliable systems available in fire apparatus today. These supplemental restraint systems offer additional protection to firefighters who are wearing their seat belts. An accident can happen anywhere, anytime. For the best possible outcome in a crash, always wear your seat belt when a vehicle is in motion.
The Fire Apparatus Manufacturers’ Association (FAMA) is commited to the manufacture and sale of safe, efficient emergency response vehicles and equipment. FAMA urges fire departments to evaluate the full range of safety features offered by its member companies.
1. FEMA, US Fire Administration, Firefighter Fatalities in the United States in 2012, p.17, August 2013.
2. Winkler, Blower, Ervin and Chalasani, Rollover of Heavy Commercial Vehicles, SAE Research Report 00-104395, 2000.
JAMES CHINNI is the director of engineering for IMMI, where he has worked extensively on the design, development, and testing of occupant safety systems for fire apparatus and emergency vehicles over the past 22 years.
MARIUS MAGDUN is the senior technical engineer for inflatable restraints at IMMI, where he has worked on the design, development, and testing of occupant safety systems for fire apparatus and emergency vehicles over the past 11 years.
MARISSA COTTEN brings more than 16 years of promotion, marketing, broadcast, and strategic branding experience to her position as marketing communications manager at IMMI. She has been with IMMI since 2012.