My wife has worked for ear surgeons for over 20 years and here is what I have picked up from them:
1. If you have to yell to be heard you need to be wearing protection.
2. Hearing loss occurs several ways: a. Traumatic injury. A shotgun blast or explosion too close. b. Gradual. Constant source of loud noise over time. A jet engine, chain saw, lawn mower, rock music, machine tools etc. c. Disease. A tumor on the nerve or other process inside the ear. d. Drug abuse. Some drugs are ototoxic (just ask Rush Limbaugh). e. Old age. Not true for everyone but normal for others.
Of these the most common is B, a gradual damage to the ear that may go unnoticed for a very long time. The damage is cumulative so each time you are exposed you don't notice any difference and figure it is OK. But over many exposures the damage occurs and cannot be reversed. Good news is that this one can be prevented.
Even rock and roll musicians have figured this out. For years they have been wearing in-ear monitors that are fitted like hearing aids. They can hear the music and other vocals at a comfortable level while exposing fans to a near painful level of sound. It is a practical matter for them. If you can't hear you can't play anymore!
Keep some soft disposable ear plugs in your shop for visitors. They are available at most shooting sport stores. Get some good ear muffs, they work much better than plugs. For extreme noise like a jackhammer, use both.
Good topic Thm: Thanks for the reminder and the tip on the sound meter!