[header] How to select hearing protection [title] Familiarize yourself with noise reduction ratings (nrr). [step] Nrr is the standard rating system across all hearing protection devices. Under nrr, hearing devices are classified by their potential to limit decibels (db) in professional and occupational environments. 
Nrrs are determined by both the american national standards (ansi) and the occupational safety and health administration (osha). Understanding this rating system will allow you better understand the noise you are exposed to as well as the type of protection you will need.