Supplemental Restraint System

Seatbelts, SRS indicator, airbags and impact sensors


Supplemental Restraint System

The airbags are a critical component for passenger safety, Let me explain how they work.

The components of the supplemental restraint system consist of:

  • Seatbelts
  • SRS Indicator light
  • Airbags
  • Impact sensors

Cars are dangerous! Hazards abound! Accidents happen! People make driving errors! Supplemental restraint systems DO save lives . . . if they are used and used properly!!

Imagine This….

You are driving on the freeway, keeping up with traffic . . . around 65, maybe 70. Traffic is pretty light. Out of the corner of your eye, you see something moving erratically up ahead. You quickly glance up in time to see a black Volvo station wagon with a blowout sliding sideways toward the center divider. It comes to a stop, barely missing several other cars, directly ahead of you. You slam on the brakes, hard. Surprised….you feel the brake pedal kick back on the bottom of your foot. The anti lock brakes are working! You feel the seatbelt lock up, pressing hard into your chest. You quickly look to your right to see if you can possibly go right and miss him, but the guy in the car next to you is sliding out of control. You brace yourself for the impact while slamming right into his left door with a tremendous crunch. Your front bumper is the first part of your car to touch his. The impact sensors under both front fenders are instantly crushed. The sensors have already sent a message to the supplemental restraint system computer telling it that something has happened. In a millisecond, the computer instructs the airbags to deploy. The vehicle has not even come to a stop, yet, the seatbelts and airbags have already done their job.

Exercising restraint!

Exercising restraint!

You open your eyes and all is quiet. The first thing you notice is a big gray bag in your lap and the strong smell of sulphur. You move the bag over the steering wheel, unbuckle your seatbelt and open the door. At first the door seems hard to open, but it opens. You get out and lean on the center divider on very shaky legs. When you look toward the front of the car you are surprised to see that the whole front of the car is crushed. The driver of the Volvo is just starting to move around. You ask her if she is all right, and are relieved to find out that her car was equipped with side airbags and is not injured.

Cars can be repaired . . . people are a little more difficult!!

The SUPPLEMENTAL RESTRAINT SYSTEM is designed to restrain a body in the event of a sudden deceleration. The supplemental restraint system is designed to work without any actions from the driver or passengers except putting on the seatbelt. The reason why the AIRBAGS are called “supplemental” restraints, is because the SEATBELTS are the first line of defense in a collision. For the airbags to work effectively, seatbelts should be worn at all times. The seatbelts keep the body restrained in the seat, so that the only body movement is bending from the hips. However, seatbelts do stretch. Sometimes they stretch to a point where the driver’s head could strike the steering wheel. The hands holding the steering wheel should be in the “10 & 2 o’clock” position, instead of the “11 & 1 o’clock position. The reason being that when the airbag deploys and your hands are in front of the bag, you could be injured when your hands are forced into your face. Any rings or watches you may be wearing would do considerable damage.

Airbags are located in the hub of the steering wheel and sometimes on the dash on the passenger side. Some vehicles now have airbags on the side of the front seats in case of a side impact. The airbag is constructed of a cloth bag folded in a particular way, propelled by a chemical explosion of the mixture of sodium azide and potassium nitrate, triggered by sensors built into the body of the vehicle. When the airbag has been deployed, it is of no further use. It is a one time only device. The airbag takes advantage of the forward motion of a body in a collision and cushions the upper body from the force of the impact. The airbag deploys to full size within three milliseconds. By comparison, the blink of an eye is about 300 milliseconds. When an airbag deploys it stays inflated for about 2 seconds. By the time the airbag inflates and deflates, only about two and a half seconds has elapsed. Contrary to popular belief, the airbag does not stay inflated after deployment.

The SRS INDICATOR LIGHT on the dash illuminates for about two seconds when the vehicle is started to check the supplemental restraint systems circuits. If a problem is found, the indicator light stays on. The system should be checked out immediately.

The IMPACT SENSORS are located on both sides of the front area of the vehicle. On newer cars, the impact sensor is located centrally, under the dashboard. The sensors are very sensitive to impacts, and are designed to transmit the information of their activation to the airbag instantly. All the electrical contacts of the airbag system are gold plated to eliminate the possibility of corrosion forming.

The seatbelt is adjustable to accommodate just about every size of person comfortably. The latches of the seatbelts are designed to be released easily from any position. In the event of a collision, the seatbelt locks in position by an inertial reel latching mechanism. Some vehicles have what is called “passive restraint systems”. In these systems, the shoulder harness seatbelt is brought into place automatically. The lap belt must still be applied to provide adequate protection in a collision. Without the lap belt, the body tends to slide under the shoulder harness. With airbags, the body “submarines” or slides under the airbag inflicting severe injury of the legs as they strike the dash.

All seatbelt problems are covered by the manufacturer’s warranty for the useful life of the vehicle. It doesn’t matter who owns the car, or for how long, the seatbelts are still covered.

  • Be safe…
  • Buckle your seat belt before starting the car.
  • Drive defensively…
  • Don’t follow too closely… Remember, one car length for every 10 miles per hour is the safe rule.
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