Thanks Bobbsy. EU-Law requires the employer to supply noise protection equipment to the employee when the average SPL is >80 dB (A) over 8 hours. Over >85 dB (A) the use of such equipment is mandatory. Now for a 12 hour intercontinental flight, that levels would be even lower. Just imagine all the flight crews wearing those big noise protection headsets.
Interesting to know, that noise levels present in today's long range airplanes are considered to cause at least temporary hearing impairments.