I found this account which is at odds with some other reports.

"In 1970 he competed in the Isle of Man TT Lightweight 250cc race. He crashed at Bradden Bridge but remounted and caught and passed Stan Woods. As they approached the fast left hander at the 13th Milestone, Herrero's Ossa wobbled on the melting tar and he crashed into an earth bank at 160kph. Woods also crashed avoiding the bike and rider. Herrero sustained such severe injuries he died two days later at Nobles Hospital, Douglas."
Extract from http://www.findagrave.com/index.html

Another report has Stan with two broken collar bones and a broken ankle.