The tipping point for the HANS seemed to be the death of Dale Earnhardt Sr. in a NASCAR race. Cause of death was a basilar skull fracture, often a fatal injury. In F1 Roland Ratzenberger's death was due to this injury but it was several years before Earnhardt's death focused attention on HANS devices and their adoption by many racing organizations.
In 2001 the FIA mandated use of HANS in all F1 races.
More on HANS here:
http://en.wikipedia.org/wiki/HANS_device