The noise level is dangerously high when you have to raise your voice to talk with someone a few feet away. It's also dangerously high when you can't understand someone speaking to you from less than 2 feet away. Another sign is ringing in the ears or slight deafness for several hours after exposure.
Under rules from the U.S. Occupational Safety and Health Administration (OSHA), employers must offer hearing protection when sound levels average more than 85 decibels in an 8-hour day. OSHA says employers must make sure workers use that protection when sound levels average more than 85 decibels in a day. You'll hear about this much noise from a lawnmower, bulldozer, forklift, shop tools, or truck traffic.
The two main hearing-protection choices, earplugs and earmuffs, can cut noise by 15 to 30 decibels when correctly fitted. Earplugs protect better against low-frequency noise, such as a loud tractor. Earmuffs do well with high-frequency noise, such as pneumatic tools.