Ritesh,
We would normally give a Level 2 – Meets with restrictions.
My understanding is that the threshold is set to an average of 90dB over 0.5, 1 and 2 KHz so that hearing is good enough that when ear defenders are worn, the individual can still hear warning signals, train horns etc.
The restriction I would put on Sentinel is that the individual cannot be the lookout, when ear defenders are worn they must be in arms reach of a colleague to protect their safety, and if the threshold is 40, 40, 45dB (as per rail standards, and if wearing hearing aids) they can move about independently when not wearing ear defenders.
Regards,
Mark