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Belt Tensioners

The seat belt must restrain the occupants as quickly as possible in the event of an accident, and so must be worn tightly. Because of the occupants’ clothing in particular, this is not always the case. This effect is known as belt slack.

Modern-day belt tensioners incorporate a small pyrotechnic device that tensions the belt when triggered. This then eliminates belt slack.

Belt tensioners are triggered electrically by the airbag control unit and tighten the belt within a fraction of a second. As the belt is then tighter to the body, the occupants decelerate along with the vehicle at an earlier stage, and the loading on the body is distributed evenly across the full restraint process, thereby reducing the risk of injury.