Frontal Airbag Deployment Failures Expert Article

In this article, automotive engineer Chase Nalls examines frontal airbag deployment failures. He offers lawyers a simplified anatomy of airbag systems, highlighting some of the key components relevant to airbag deployment investigations.

Airbag Non-Deployment Forensic Investigations

Frontal airbags are one of the most critical safety components in modern vehicles. They offer vehicle occupants involved in forward collisions a level of protection that cannot be achieved with seatbelts alone.

According to the National Highway Traffic Safety Administration (NHTSA) frontal airbags alone have saved over 50,000 lives in the United States since their introduction.

Depending on the severity, frontal airbags begin to inflate within milliseconds of a frontal crash occurring and are fully deployed in 30-40 milliseconds. These airbags create a large surface to spread out the impact forces on an occupant, allowing the occupants to slow down over a greater period of time, and reduce how far forward the occupant moves.

Typical Anatomy of Frontal Airbag & Restraint System

A vehicle’s frontal airbag and restraint system have multiple components located throughout the vehicle.

During a significant frontal collision, the frontal impact sensors will detect a local high jerk measurement or rate of change of acceleration over time and will send a signal to the Airbag Control Module (ACM).

For context:

• velocity = ∆distance/∆time
• acceleration = ∆velocity/∆time
• jerk = ∆acceleration/∆time

When the ACM determines the jerk is high and the vehicle is involved in a frontal collision, it will calculate the expected crash severity. At the same time, the ACM measures the accelerations experienced by the vehicle in multiple directions.

Based on the jerk measured by the frontal impact sensors and the acceleration measured by the ACM, the ACM will determine what restraint or airbag components need to be deployed, and at what level, to properly protect the front seat occupants. The ACM will then send signals to those components, and the airbags will deploy.

What Happens When These Systems Do Not Perform as They Should?

One of the most common failures of an airbag system is non-deployment incidents. An airbag non-deployment can leave belted occupants partially unprotected or unbelted occupants completely unprotected.

Frontal airbag non-deployments can have several causes:

• Defects in the:
  • Frontal collision sensor
  • ACM sensor
  • ACM algorithm
  • Airbag’s inflator
  • Electrical system
• Fuse issues
• Loose connectors
• Low voltage issues
• Service issues

Case Study

The incident vehicle was involved in a frontal collision with a telephone pole, offset to the right (passenger) side of the vehicle. The driver was not belted at the time of the crash and the frontal airbag did not deploy. As a result of the crash, the driver was ejected through the windshield, sustaining severe injuries.

The first step in the investigation was to examine the vehicle, download the Event Data Recorder (EDR) data, determine the crash severity, and compare the crash severity to known frontal airbag deployment thresholds. This information provides insight into whether a properly functioning system should have deployed the airbag in the collision.

During the inspection, the EDR information was downloaded, vehicle damage was measured and documented, and the lack of airbag deployment was confirmed. Data from the crash revealed that the vehicle experienced a change of velocity exceeding known deployment thresholds. A properly functioning system should have deployed the airbag in the collision.

The process of determining why the airbag did not deploy can involve teardown and examination of the airbag and restraint system components, reviewing the vehicle’s service history, reviewing the relevant recalls and technical service bulletins, and reviewing documents collected from the manufacturer during discovery, including algorithm development.

The teardown of the airbag did not reveal any clear defects. The vehicle’s restraint system had not previously been serviced. There were no open recalls or technical service bulletins that affected this vehicle’s airbags. There was a significant amount of documentation on the design of the driver airbag, ACM, and restraint system that was uncovered during discovery from the manufacturer of the vehicle.

After reviewing and analyzing the documents, it was discovered that the ACM module logic deploys the frontal airbags based only on the inputs from the frontal crash sensors. Unlike other systems available at the time, the acceleration measured in the ACM was not being utilized in the deployment determination.

Based on the offset nature of the crash, the frontal impact sensor did not detect the impact.

Expert Findings

Because this vehicle did not utilize the acceleration measured in the ACM to determine deployment, the frontal airbag system was defective and exposed the driver to an unreasonably dangerous condition.

Had the acceleration data from the ACM also been utilized to determine airbag deployment, it’s more likely than not that the driver would have been retained within the vehicle and his forward motion would have been slowed, preventing or mitigating his injuries.

Vehicle Crashworthiness Expert Investigations

From complex crash reconstruction to developing demonstrative evidence for court testimony, the transportation experts at Robson Forensic are well equipped to assist in your investigation. The vehicle experts at Robson Forensic are more than just mechanical engineers and reconstructionists, they are automotive engineers with industry experience in the design, development, and manufacturing of gasoline and electric vehicles.

For more information, submit an inquiry or call us at 800.813.6736.

Featured Expert

Chase Nalls

Automotive Engineer & Crash Expert

Chase Nalls is an automotive engineer specializing in the design and performance of airbag and restraint systems. He applies his expertise to forensic casework involving crash reconstruction and… read more.