Inflatable vehicle occupant protection device

Apparatus (10) for helping to protect an occupant of a vehicle (12), said apparatus comprising: an inflatable vehicle occupant protection device that is inflatable into a position between a vehicle part (16) and a vehicle occupant; and an inflation fluid source (24) that provides inflation fluid for inflating said inflatable vehicle occupant protection device, said inflation fluid source containing a stored inflation fluid consisting essentially of 65-95% helium gas and 5-35% nitrogen gas stored under pressure.