Airbag Supplemental Restraint Systems

SUBJECT: Airbag Supplemental Restraint Systems

TOPIC: Understanding airbag deployment criteria

OBJECTIVE: The responder will list and explain the conditions that must be met to deploy airbags in vehicle collisions

TASK: Given a scenario of a vehicle frontal collision where airbags did not deploy, the responder will be able to list and explain possible reasons why the airbags might not have deployed and safety precautions to assure responder safety around these units.

In this day and age, responders expect that when they arrive at a crash scene, each of the vehicles involved will have at least two frontal airbags and probably side-impact seat and roof airbags as well. A new vehicle today can have just two airbags or may have up to 12 different airbags to protect the occupants.

As the number of airbags in vehicles increases, so does the possibility that responders will encounter "live" bags: undeployed airbags. A frontal crash won't deploy the roof, door, or seat airbags for example; just the front airbags and knee bags if present. A T-bone collision will leave the frontal airbags and the side-impact airbags opposite the collision side "live." As rescuers, we need to anticipate the presence of undeployed airbags and have operating guidelines for working near to these "live" bags. Staying clear of the inflation zones is the cardinal rule for our safety. Taking away vehicle electrical power early in our on-scene actions is another progressive action for crews to accomplish.

"10, 20 & 5" Guideline

Remaining outside of the 10-inch inflation zone for the driver's frontal bag and maintaining 20 inches of clearance from the passenger's frontal airbag will keep inside personnel out of danger. Side-impact door, seat, and roof airbags are typically five inches thick at the moment they fully inflate so we say five inches is their inflation zone. Remember, although roof curtain airbags cover the side window glass area, they can be as long as from A-pillar to rear pillar; nine feet long for a Ford Expedition with third-row seating, for example. Knee bags generally inflate toward the front-seat area a distance of five inches as well. So the "10, 20, & 5" inflation zone guideline is a good one to keep in mind when working an incident.

Airbag Non-Deployment

Another airbag deployment reality for responders that is becoming increasingly common is to encounter a seemingly severely crashed vehicle only to find that no airbags deployed. The front end is mangled; fluids are leaking all over the place. Glass lies all over the road and the front of the car looks mutilated. The surprise is that inside, all airbags are completely intact. What went wrong? Is this a manufacturing defect or what?

Our case study this month looks at a two-vehicle collision where a Honda sedan ran into the rear of a stopped Ford Explorer SUV. Both vehicles were in the same lane of traffic. The SUV slowed and came to a stop, waiting to make a turn when the Honda rear-ended it. The unbelted driver of the Honda struck the windshield above the steering column. The front of the Honda crumpled significantly as it rammed the rear of the Explorer and went underneath its rear bumper.

Incidents like this are occurring all across the country and responders are surprised to find the frontal bags intact. It seems that we get caught up in "judging a book by its cover." We tend to look at crash damage and mentally assess the severity of the collision based upon what we see. This is an acceptable size-up procedure as far as gathering information about potential mechanisms of injury where the patient is concerned or when considering potential extrication challenges but it isn't the whole story when it comes to airbag deployment.

Airbags deploy when they experience what engineers refer to as a "delta V" — the instantaneous change in movement or direction that the vehicle experiences as a result of an impact over a specific period of time("delta T"). Most car companies say a vehicle has to experience an impact that generates at least seven Gs of force before it will trigger the frontal airbags. For most vehicles, this would be the equivalent of hitting a solid barrier at 12 to 15 mph, or hitting another vehicle at a speed of about 25 mph. In reality, the airbag may deploy at higher or lower speeds. When we arrive at a collision, all we initially see is the end result of the collision; the debris scattered across the road and the crumpled vehicle. It usually isn't until after the patients are cared for and we catch our breath that we have time to really stop and look at what happened.

So for a non-scientific answer to an event that is very closely engineered by the automakers, there are several reasons why airbags may not deploy in a collision. First, the airbag system could be defective and really should have deployed. Over 15 million cars are built each year, each with at least two airbags, so a defective airbag inflator, crash sensor, airbag brain, or wire connection is a possibility.

A second consideration for collision situations such as the Salisbury, NY, incident and most likely the reason the frontal airbags never went off may be because the Honda never really decelerated suddenly enough to trigger the bags. When it hit the Explorer stopped in front of it, the collision wasn't like running into a non-moveable object such as a tree or bridge pillar. Crash scene evidence shows that in fact, the SUV moved forward several feet on impact as evidenced by both vehicles coming to a stop several car lengths ahead of where they first contacted each other. Thus, the Honda "slowed" more gradually as it pushed the SUV ahead of it, although it could have come to a stop in maybe two seconds worth of time or less. That seems insignificant but it might have been gradual enough to not "trip the trigger" on the airbags.

Another consideration in the airbag deployment scenario is the importance of the mass ratios or relative weights of the objects colliding into each other. For example, if the Honda Accord ran into an 18-wheeler or a large tree, the smaller and lighter car will experience a more sudden delta V and the airbags will most likely deploy. When a heavier vehicle runs a red light and collides with a smaller and lighter vehicle at an intersection, chances are that the frontal airbags on the larger striking vehicle may not deploy. The mass of that vehicle may push the smaller vehicle sideways upon impact, allowing it to slide and even spin on the street. Therefore, the striking vehicle never instantly stopped; it slowed gradually and may never meet its airbag's deployment threshold. The delta V wasn't sudden enough over too long of a delta T timeframe. The front may be mangled but the bags may be intact.

Responders must be alert to the fact that the appearance of a crumpled crumple zone is not the only determinant of impact severity or airbag deployment. Our New York State case study today proves this. Lesson learned: crumple zone crumple does not necessarily mean airbag deployment. Be heads up! Respect "live" airbag inflation zones. Take away electrical power during your initial rescue operations on-scene. Scan the vehicle to determine where your hazards are. Don't judge a book by its cover. You may be wrong.

TASK: Given a scenario of a vehicle frontal collision where airbags did not deploy, the responder will be able to list and explain possible reasons why the airbags might not have deployed and safety precautions to assure responder safety around these units.

RON MOORE, a Firehouse® contributing editor, is a battalion chief and the training officer for the McKinney, TX, Fire Department. He also authors a monthly online article in the "MembersZone" and serves as the Forum Moderator for the extrication section of the website. Moore can be contacted directly at

Emergency Responders Back Traffic-Incident Management Project

In a show of unity among highway agencies, emergency medical professionals, firefighters, tow truck operators and 911 call centers, 19 national organizations have launched the National Unified Goal for Traffic Incident Management, pledging to work together to improve communications and coordination at crash scenes to minimize factors that can delay road clearance. In turn, the responders ask motorists to slow down and move over when they approach traffic incident scenes to reduce the number of responders injured and killed from being struck by passing vehicles while working at crash scenes and to let the responders reopen travel lanes quicker.

"The International Association of Fire Chiefs (IAFC) endorses the National Unified Goal, and is strongly committed to its implementation," IAFC Executive Director Mark Light said. "Firefighters recognize the need to work with other disciplines to make crash scenes safer and to get the roads open as quickly as possible. We join with our NTIMC partners in calling on motorists to use extra care as they approach and pass roadway emergency scenes. Vehicle-related incidents account for roughly 20 percent of firefighter deaths. A growing number of those are firefighters who are struck at the scene while helping others. Hundreds more are injured. It is a problem we share with all roadside responders, and together we need to work toward a solution."

Kevin McGinnis, program advisor to the National Association of State EMS Officials (NASEMSO), said, "NASEMSO endorses the National Unified Goal and is working through NTIMC to improve overall coordination and communication among all responders at traffic incident scenes, so we can maximize the chances that our patients will survive crashes with minimal injuries. We also share concern about keeping roadways open, so our ambulances can respond swiftly to all types of medical emergencies."

Federal Highway (FHWA) Administrator J. Richard Capka underscored the importance of safe, quick crash clearance. "Traffic incidents account for about one-quarter of all congestion on U.S. roadways," he said. "For every minute that a freeway travel lane is blocked during a peak travel period, four minutes of travel delay results after the incident is cleared. More efficient traffic incident management will reduce congestion and protect travelers and responders."

The National Unified Goal was launched in November 2007 at the Montgomery County Public Safety Communications Center in Gaithersburg, MD.

"The National Unified Goal is responder safety; safe, quick clearance; and prompt, reliable incident communications," said NTIMC Chair John Corbin. "NTIMC developed the 'NUG,' as we call it, through a consensus-generation process that has taken about 18 months. The coalition is proud to have pulled together such a broad spectrum of national organizations representing the traffic incident responders."