Which device is activated in conjunction with a seat belt pre-tension system during an impact?

The device activated in conjunction with a seat belt pre-tension system during an impact is an explosive charge. In the event of a collision, the seat belt pre-tensioner employs a small explosive charge to rapidly tighten the seat belt against the occupant's body. This mechanism serves to reduce the amount of forward movement that a passenger experiences during a crash, thereby enhancing safety.

The use of an explosive charge is designed to quickly retract the seat belt when sensors detect a significant deceleration, such as in a crash scenario. This immediate response helps to secure the passenger in place and minimize injury by ensuring that the occupant is as close to the seat back as possible at the moment of impact.

Other devices like pre-loaded springs or catapult mechanisms do not typically function in this way and are not standard components of most modern seat belt systems. While they might have a supportive role in some mechanical functions, they do not fulfill the primary role addressed here, which centers on crash response and occupant safety.