If I recall correctly the maximum Noise Reduction Rating (NRR) for earplugs and earmuffs is around 30db. You can combine the two for a slight increase in hearing protection but you still hit a limit because of bone vibration.
Is there PPE out there to go even further beyond this? Where would it be commonly used?
When I was in the Army they put us in a room with a jet engine bolted to a concrete block, and the exhaust routed outside of the building. They fired that thing up and it was overwhelming. My hearing is fucked up today, and I sometimes wonder how much of the damage was due to that demonstration. Standing near a fucking Howitzer without ear plugs when it was fired off probably didn’t help much either.