One of the most common phone calls we receive is from consumers wondering why their air bag did not deploy during a crash. This article describes how air bag deployment thresholds are established, the kinds of crashes during which air bags should deploy, and crashes where they may not deploy. It also provides information on several different defects that may be responsible for the air bag failing to deploy when it should deploy.

Air Bag Deployment Thresholds

Conventional air bags are generally designed to deploy in certain frontal crashes above the thresholds selected by the manufacturer. Unfortunately, the consumer often cannot determine the thresholds for their car, as they vary widely between manufacturers, and even vary among different models from the same manufacturer. However, there are some general guidelines that are helpful for consumers.

Although there were some variations, most frontal air bags from the 1990s were designed to deploy in crashes above a threshold level of 14 mph into a solid concrete barrier. At the same time, most air bag systems were also designed to never deploy in crashes below 8 mph into a solid concrete barrier. Between these two speeds, the air bags may or may not deploy, depending on the specifics of the accident and vehicle.

However, please note that these speeds are based on crash tests into a solid concrete barrier. Therefore, if your car has struck something that moved or deformed (like another car, utility pole or guardrail), these thresholds could be considerably higher. For example, a 14 mph barrier test may be equivalent to a frontal crash at 28 mph into a parked car. Also, these thresholds for air bag deployment have generally increased since the 1990s, with some now reaching 18 miles per hour, recognizing that air bags can cause more injuries than they prevent in minor accidents.

If your crash severity exceeds the car company’s thresholds, and yet your air bags did not deploy, you may well have a defect in your vehicle’s air bag system.

Crashes Where the Air Bag Should Deploy

Your air bags should deploy in every crash where they will help prevent your injuries. This means that your air bag should deploy in those crashes where you would otherwise suffer injuries of the type that the air bag is designed to prevent: head, neck, and chest injuries. For example, your frontal air bag should deploy in an accident where your head would otherwise be injured from hitting your steering wheel.

Although frontal air bags are generally not designed to deploy in side impacts or rollovers, in some cases they should deploy in those kinds of crashes. That is because some side impacts or rollovers also cause front-to-back deceleration that causes you to move forward inside your vehicle. One example would be if you were driving at highway speed and were hit on the side of your car: in addition to crushing in the side of the car, your car would also slow down its forward motion rapidly, which could be enough to deploy your frontal air bags. Similarly, frontal air bags should generally not deploy in rear impacts; however, if you are hit from behind and pushed into a car in front of you, that second impact to your car’s front end may justify deployment of your air bags.

For side impact air bags, they should generally deploy on the side of the car experiencing the side impact. Similarly, rollover “curtain” air bags should deploy when the vehicle experiences a rollover, to help prevent head and neck injuries and to reduce the risk of being ejected through an open or shattered window.

Examples of crashes where air bag deployment would be expected include moderate to severe crashes involving your front bumper or the front corners of your vehicle, frontal impacts to a utility or telephone pole, and under-ride impacts where the front of your car goes under the side or back of a truck.

Crashes Where the Air Bag Should Not Deploy

Your air bags should not deploy in those accidents where they will not prevent your injuries. After all, air bags can deploy at speeds of more than 200 mph, and you should not be exposed to those kinds of forces if it won’t help you. Thus, your frontal air bags should not deploy in side impacts, rear impacts and rollovers where there is no significant deceleration from front to back.

Other examples of crashes where your air bags should not generally deploy include:

o Minor frontal crashes
o Most impacts to the undercarriage of the vehicle, such as when crossing a railroad
o Impacts with animals such as deer or dogs
o Impacts with street curbs or parking blocks
o Driving on rough roads, including those with large potholes, gravel or bumps

Of course, your air bags should never deploy when your vehicle is not in an accident. Although this seems obvious, there are actually many cases where this has occurred, often due to poor design of the air bag system software, or due to electrical issues with the air bag system.

Why Your Air Bag Did Not Deploy

There are several reasons why your air bag may not have deployed during a crash. The first reason is that perhaps your crash is not the type of accident where air bag deployment would be helpful. For frontal air bags, this includes many, but not all, side impacts, rear impacts and rollovers. This category also includes minor accidents in which the driver and front passenger (if there was one) did not suffer any significant injuries requiring medical treatment.

The second reason is that there could be a defect that prevented the crash sensors from detecting the crash properly. Our investigation and analysis of air bag systems in hundreds and hundreds of crashes has revealed numerous causes that fall within this category. In some cases, the air bag deployment threshold is simply not set appropriately, often due to inadequate testing. In other cases, a flaw in the software of the air bag control module has caused it to ignore the data from one of the crash sensors. In still other cases, there are simply too few sensors to properly detect real-world crashes; this often results from overly zealous cost-reduction efforts by car companies that are trying to improve their finances. In a few cases, quality control efforts have failed to prevent defective sensors or air bag control modules from reaching the public.

The third reason is that there could be a defect that prevented the deployment signal from reaching the air bag modules and deploying them. Here, the problem usually lies with the electrical components and wiring between the crash sensors, control module and the air bag modules. The most frequent defect in this category that we see is when the driver air bag fails to deploy, but the passenger air bag does deploy. In many cases, this is due to a defective clockspring located in the steering column. Millions of defective clocksprings have been recalled, generally due to poor quality control at either the supplier’s production plant or the car company’s assembly plant.

Another defect in this category is when the wiring is routed through vulnerable areas, resulting in wires that get cut early during a crash sequence. Although the sensor then detects the crash, the cut wires prevent the signal from reaching the air bag modules.

The fourth reason is that there could be a defect that prevented the actual air bag modules from deploying correctly. In a few cases, the crash sensors and air bag control modules have commanded deployment of the air bags, but the air bags failed to respond. This is almost always due to defects within the air bag modules themselves, usually due to poor quality control.

By: Taras Rudnitsky

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