Why do seat belts lock up after a crash?

Last week when I was coming home from work, a car ran a red light and nearly T-boned me. I slammed on my brakes, and thankfully, nothing happened—but I did notice my seat belts locked. Why does this happen, especially after a crash?

Andrea Barrett · Updated on
Reviewed by Shannon Martin, Licensed Insurance Agent.
Seat belts lock up after a crash because a gas charge ignites, locking the seat belt in its place. The igniter triggers a small explosive device known as an inflator, a component of the seat belt retractor mechanism. The igniter must deploy quickly for the seat belt to work correctly.
Whether it’s the seat belt retractor or the buckle pretensioner, once either one is activated, it cannot be used again and will need to be replaced.
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