Noise is measured in decibels, abbreviated by dB. Noise exceeding 85 dB requires protection. A rule-of-thumb is that if you have to adapt the sound level when talking to a person at one metre's distance, then you are exposed to noise exceeding 85 dB. We can be exposed to a noise level of 85 decibels for 8 hours during one day, but a noise level higher than that causes a risk of hearing damage. The maximum permitted exposure time is halved for each 3 dB rise in the noise level. For example, if the noise level measured is 91dB, the exposure time must not exceed 2 hours. Hearing damage, in effect, is not only due to high noise levels.