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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 Firehouse.com "MembersZone" and serves as the Forum Moderator for the extrication section of the Firehouse.com website. Moore can be contacted directly at Rmoore@firehouse.com.
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.