From Longman Dictionary of Contemporary Englishcrash helmetˈcrash ˌhelmet noun [countable] TTCa very strong hard hat that protects your head, and is worn by racing car drivers, people riding motorcycles etc
Examples from the Corpus
crash helmet• Never seen him without his crash helmet on; could be an albino or a Rastafarian for all he knew.• Tom had never before ridden pillion on a motorbike, but Andy the neighbour had a spare crash helmet. 