There is absolutely no reason that firefighter helmets nor construction helmets resist firearms at all. They are plastic
Firefighter and construction helmets should require 2-4 swings from melee weapons to remove but bullets should just outright oneshot them.
Riot police helmets taking 4-6 mid sized rounds is ludicrous. Police riot gear is typically rated for .357 and under. any rifle rounds (especially .308) should just sail through riot gear helmets. anything .357 and under should maybe take 1-2 shots to knock off the helm of a riot cop.

