Let me refer you to the previous thread on this topic:
Helmets in offshore ops?
They should never be made compulsory in North Sea ops in my opinion, for safety reasons stated in the thread and because no civilian accident in the UK North Sea sectors has ever resulted in deaths due to the non-wearing of helmets.
The statistical risks relating to non-wearing of helmets in this theatre come nowhere near the increased risks due to discomfort and fatigue which would be caused by being obliged to wear them.
I speak from much experience in military, agricultural, forestry, underslung and offshore operations as a pilot over 4 decades.