Thoughts on safety

In Technical by Glyn DemmerLeave a Comment

Vehicles today are incredibly safe and include a variety of safety features. These are known as active and passive safety features. They are designed to keep occupants safe in the event of an accident. Active features prevent accidents whilst passive reduce injury in an accident.

On a trip to the Northern Cape, I noticed some scary behaviour. It indicated that people do not understand how safety features work and how dangerous they could be.  Let’s discuss the operation of an airbag. Most vehicles come standard with at least two forward airbags, many also have curtain and thorax airbags. Airbags are known as “Supplemental Restraint Systems”.You will see SRS embossed into the site of an airbag and as a label on upholstered areas.

The airbag is designed to slow the driver and passengers forward movement in a split second. It stops them from hitting the steering wheel or dashboard. It consists of three main components;

  • The bag is made of thin nylon material folded into the steering wheel centre boss and the dashboard ( passenger). Lately, they fitted into the side at head height and the head restraint.
  • The sensor is known as an accelerometer, an integrated circuit built into a microchip. It responds to rapid deceleration and sends a signal to deploy the airbag by activating the inflation system. 
  • Deployment is thus a function of the rate at which speed changes and not the speed itself. The system will disregard collisions below a minimum speed. This is around 25 kmh, dependant on the manufacturer. This means the airbags will not deploy in the event of a minor low-speed accident.
  • The inflation system is not unlike rocket ignition. A solid propellant is ignited to produce a gas that forces the bag from its resting position. It does this at a speed of around 300 kph which is incredibly quick. Once inflated it softens through tiny holes in the rear. This gives a soft cushioning effect for either the driver or passenger. A powder is also released which is used to keep the airbag pliable.

The system is engaged via the seat belt when the latch plate is inserted into the buckle. And now we touch on one of the most important components in your vehicle. The seat belt pre-tensioner. Designed to hold you back in a collision and then release you into the softened airbag. It firmly positions you in the seat allowing you to receive maximum benefit from the airbag. Once the sensor detects that an accident has occurred the pre-tensioner acts to remove slack from the belt.

Considering the speed involved in deployment, understand that an airbag can injure a person who sits too close to it. So what can we do?

  • We were taught to hold the steering wheel in a 10 – 2 position. Lately, a 1/4 – 3 position is advocated as it takes your arms out of the radius of the airbag should it deploy.
  • To get a safe distance from the airbag sit comfortably and drape your hands over the steering wheel so that your wrist touches the top of the wheel. That should determine the seating distance. You will still be able to reach the pedals comfortably.
  • You may also adjust the tilt of your steering wheel at the same time. The airbag will be directed to your chest rather than your head.

So now that we understand the operation and the inherent dangers what were the mistakes that I saw and what impact could they have?

The first one was fairly common, a vehicle passed me and I noticed that the passenger was sitting with their feet on the dashboard. In the event of an accident, the airbag would deploy. This could result in the legs being pushed back which could more than likely crush the pelvis.

The next error I saw while at a service station buying diesel. A couple drove in, I noticed that they were not wearing seat belts.  Seat belt latches in both cases were clipped into the buckles, obviously to stop the warning tone. In the event of an accident, they would be thrown forward into a hard airbag with possibly fatal consequences.

Your other passive safety features would be items such as the crumple zones built into a chassis as well as automatic braking ( which could fit into both categories ).

Active safety features include traction control, lane alert radar, blind-spot monitoring, driver alert alarms and anything else that may warn you of a potential problem.

We urge you to practise safe driving at all times and if travelling over the festive season be careful and have a safe, happy holiday.

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