Pyrotechnic Seatbelt Pre-Tensioning

Pyrotechnic Seatbelt Pre-tensioning:

A pyrotechnic front seat belt pre-tensioning device with independent electronic sensing and retractor unit is installed at the base of each 'B' post. In the event of severe frontal impact, this provides additional front occupant protection by removing any excess slack from the seat belt. Seat belt pre-tensioning activates when a frontal impact of sufficient force occurs within 30 degrees of vehicle center line. Under such an impact, electronic sensors in the retractor unit fire, igniting the pre-tensioner gas generator. The gas generator initiates a chemical reaction, producing gases under pressure. Gas pressure drives the piston/cable up a tube, rotating the retractor spindle and removing excess slack from the seat belt. When the pre-tensioner unit has been activated, the seat belt will lock and cannot be retracted or pulled from the reel. If a seat belt pre-tensioner activates, a small quantity (less than 1 liter) of gas is produced containing nitrogen, oxygen and water vapor.