No selection without measurement
Selecting hearing protection starts from measured noise. Without knowing the daily exposure level and the peak sound pressure, nobody can say what attenuation is needed. “It is a noisy place, give them ear defenders” produces under-protection and over-protection at the same time.
How attenuation enters the calculation
The manufacturer publishes the attenuation values. Two approaches are common: a single-number value for a rough calculation, and high–medium–low frequency values for a closer one. Where the frequency content of the noise is known, the second is preferred; for impulsive and low-frequency noise a single number misleads.
Over-protection is a defect
A protector that drops the level at the ear further than necessary also removes speech, machine sounds and warning signals. What follows is predictable: the worker lifts it for a moment, that moment coincides with the loudest part of the day, and the protection calculation collapses. The aim is to bring the level at the ear just below the limit, not to zero.
Wearing time breaks the arithmetic
The benefit is proportional to the time the protector is worn. One taken off for half an hour of an eight-hour shift does not deliver its catalogue attenuation in the field. Comfort, weight and compatibility with a helmet are therefore not details that come after the technical criteria — they decide the protection.
The link with health surveillance
Above a given exposure, hearing tests are carried out. A threshold shift in those results is the earliest sign that the selection or the wearing is not sufficient, and that finding reopens the selection.