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?
I don’t exactly know whether this strat is redundant or not but I wear noise cancelling earbuds with full earmuffs overtop and it seems to do a good job. Plus i get the added benefit of being able to listen to music and hear phonecalls while on a machine.