An air bag puncture device extends from the torso of a vehicle occupant and has a pointed outer end. Upon inflation of an air bag against the torso of the occupant, the device punctures the air bag to soften the outer surface of the air bag and thereby prevent injury to the occupant. The puncture device is mounted on a resilient clip for removable mounting to the shoulder harness of a vehicle seat belt system and comprises a cylindrical cutting device having a serrated outer end opposite the resilient clip for puncturing the inflating air bag. A spring-loaded hollow cylindrical collar which normally shields the serrated outer end of the cutting device is pushed out of the way by the inflating air bag, allowing the serrated outer end of the cutting device to puncture the bag in controlled fashion.