Bigtop
"Additionally the provision of helmets etc insinuate a compliance with duty of care"
Not so. The MoD were advised that the passive attenuation offered by the various aircrew helmets was insufficient. They accepted this, evidenced by the various endorsed requirements to reduce the noise dose of helmet wearers to 85dB(A). The important point is that, when helmets were the ONLY available protection, they were seen to be meeting Duty of Care. Since the advent of a viable system (i.e. one that can actually be engineered into a helmet) then the Duty of Care has not been met. See my previous post about notification, plus reasonable time to implement. To avoid getting bogged down in decibel notation, the concept of "allowable flying hours" was raised. That it was accepted is again evidenced by it being the justification for endorsed requirements.
Googe "anr + Farnborough" and you'll find people who know far more about it than me and will provide the necessary evidence to support you.