I don’t think it’s accurate. I use ear plugs every day. I’d be stone deaf if your equation were true. Shooting, however, is a tough case because of the huge (how ever transient) pressure levels. I’d wear plugs and muffs.
That high pressure wave would tickle my insides while firing. Was long ago and I don’t recall using ear plugs at the time. All we did was open our mouths and cover our ears with our hands. That M29 made about 180 dB.