Lethal mechanisms in cases of inverted suspension from the lap component of seat belts

A retrospective review of autopsy files at Forensic Science South Australia in Adelaide, Australia, was undertaken over a five-year period from January 2014 to December 2018 for all motor vehicle crashes with rollovers ending with the vehicle inverted and the occupants suspended by the lap component of their seat belts. There were five cases, all male drivers (aged 18-67 years; M_age = 32 years). Acute neck flexion or head wedging was noted in four cases, with facial petechiae in four and facial congestion in one. Deaths were due to positional asphyxia in four cases, with the combined effects of positional asphyxia and head trauma accounting for the remaining case. Although all drivers had evidence of head impact which may have caused incapacitation, in only one case was this considered severe enough to have contributed to death. A blood alcohol level above the legal limit for driving was detected in two cases, but no other drugs were detected. This series demonstrates another subset of cases of seat belt-associated deaths where suspension upside down by the lap component of a seat belt had occurred after vehicle rollovers. Predisposing factors include incapacitation of the victim and delay in rescue. The postulated lethal mechanism involved respiratory compromise from the weight of abdominal viscera on the diaphragm, as well as upper airway compromise due to kinking of the neck and wedging of the head.