To best accomplish your hearing loss prevention goals, most companies follow these general rules of thumb for fit testing/retesting:

• new employees and those new to the hearing conservation program
• when a worker changes to a new type of hearing protector
• when an employee has shown Standard Threshold Shift (STS) or other significant shift in hearing
• in cases of physical changes to the ear such as injury, surgery, etc. that affect the fit of the hearing protector
• when a worker expresses concerns or complaints about hearing protector fit/attenuation
• some employers conduct routine retesting (every few years for example) for all employees, while others choose to target routine retests only for individuals with very high noise exposures (using dual hearing protection), for those working hearing-critical jobs, or those who have experienced past shifts in hearing or other concerns

For more information:

Individual Fit Testing for Hearing Protectors

How Individual Fit Testing Can Complement Your Hearing Conservation Program