Seat Belt Buckle Release Force: Cause for Entrapment?

This study was concerned with buckle release resistance under full load. Although the incidence of entrpament among restrained occupants in rollover accidents is extremely low, there is concern that inability to release the buckle contributes to entrapment in the vehicle. The purpose of the present study was to assess the adequacy of current safety regulations in this regard. Human strength measurements were obtained from male and female driver volunteers using top-release and side-release buckles. The strength data obtained in this study indicate that about 80% of drivers are not capable of exerting a force on the buckle equivalent to the mandated limit of 133N (30 lb). Taking into account the influence of loop load on buckle resistance, over 90% of drivers would be expected not to be able to release a buckle which marginally meets current regulations. While it would appear that existing buckles release at lower forces than specified in the standard, still about 40% of drivers would not be able to release their own belts. Strength was influenced primarily by gender - driver age and weight had negligible effects. Contrary to a priori expectations, no significant differences were observed between side-release and top-release type buckles.