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Supplemental Restraint System Airbags: How Does It Work?

Supplemental Restraint System Airbags: How Does It Work?
26 November, 2021

The acronym SRS stands for Supplemental Restraint System which is the proper name for the Airbag System in your vehicle. This is the dash warning light that was not mentioned in the prior articles on warning lights. This system is considered a passive safety device, meaning that it takes no action from the vehicle occupants to activate the device, like a seat belt that takes action from the occupant to activate the device.


When the SRS light is illuminated on the dash, this means that the Airbag Control Unit sees an issue in the system and has disabled the system. This means that the airbags will not deploy in the event of an accident.


The original design of an airbag was developed in 1952. Vehicle airbag systems went into use in the early 1970’s and have gone through a series of developmental changes throughout the years. They were designed to be used as a safety supplement to seat belts, most injuries that are caused by airbags, are due to the fact that seat belts were not being worn when the airbag was deployed.


The main design concept is quite simple. There is a central Airbag Control Unit that monitors a number of related sensors within the vehicle. These sensors include accelerometers, impact sensors, side door pressure sensors, and seat occupancy sensors. When the requisite “threshold” has been reached or exceeded, the airbag control unit will trigger the ignition of a gas generator propellant to rapidly inflate a nylon fabric bag. As the vehicle occupant collides with and squeezes the bag, the gas escapes in a controlled manner through small vent holes. The airbag’s volume and the size of the vents in the air bag are tailored to each vehicle type, to spread out the deceleration of (and thus force experienced by) the occupant over time and over the occupant’s body, compared to a seat belt alone.


Over the years this basic system has become more complex. Triggering algorithms are used to reduce deployments when they are unnecessary. The signals from the various sensors are fed into the Airbag Control Unit, which determine the speed of the vehicle, the angle and severity of the impact, and the force of the crash along with other variables. Depending on the results of these calculations, the Airbag Control Unit may also deploy additional restraint devices, such as seatbelt pre-tensioners and pertinent airbags. These seatbelt pre-tensioners can actually tighten the seatbelt, driving all slack out of the seatbelt in a crash situation to tighten the harness of the occupant holding them into the seat. Today’s vehicles can also come equipped with a lot of different airbags. There are frontal airbags for both the driver and passenger, along with seat mounted side bags, and “curtain” airbags which cover the side glass.


If your SRS light is illuminated on your dash, this safety feature in your vehicle has been disabled. We would recommend having your trusted repair facility diagnose the issue and have it repaired. Statistics shows airbags save lives when the occupant is in the proper seat and using the seat belt properly.


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