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.
Rollover System
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