Level and time together
A single instantaneous reading is not exposure. The shift is split into periods spent at different levels; each period carries a level and a duration, and they are summed as energy and normalised to eight hours. This is why fifteen minutes at 100 dB and eight hours at 85 dB can come out close together — short bursts of high noise must not be dismissed.
Protection comes from the right protector, not any protector
The attenuation printed on a protector comes from laboratory conditions; what is achieved in the field is lower and depends on how consistently it is worn. Over-protection is also a problem: a protector that hides warning sounds and speech gets taken off. The aim is to bring the level under the ear into the safe range, not to zero.
Exposure thresholds and the actions they trigger vary by country; Optifora evaluates the measurement record against the thresholds of the country the organisation operates in.