Limit values for noise
Limit values for noise
The law determines noise exposure levels that are considered dangerous in terms of the risk of hearing loss. The lower and upper exposure action values denote noise exposure levels that are likely to result in hearing loss. The law also sets a limit value for noise exposure, which is designed to ensure that noise levels inside a worker’s ear are never high enough to result in instant hearing loss (impulsive noise) or gradual deterioration over time. Any work that is found to expose workers to noise levels in excess of the limit value must be discontinued immediately, and steps must be taken to avoid any recurrence.
The action values and limit values relate to daily noise exposure and peak sound pressure/level. A worker’s measured or estimated daily noise exposure or peak sound pressure/level is always compared against the action values without factoring in the attenuation provided by hearing protectors, while comparisons against limit values take the effect of hearing protectors into account. Daily noise exposure cannot be evaluated solely on the basis of the noise levels measured during a working day, unless noise levels are constant throughout the day.
A worker’s noise exposure is deemed to equate to
- 80 decibels, if they are exposed to noise levels of 80 decibels for eight hours per day
- 85 decibels, if they are exposed to noise levels of 85 decibels for eight hours per day, and
- the limit value, if they are exposed to noise levels of 87 decibels for eight hours per day without hearing protectors.
Exposure action values and limit values
|Daily noise exposure||Peak sound pressure/level|
|Lower action value||80 dB||112 Pa / 135 dB|
|Upper action value||85 dB||140 Pa / 137 dB|
|Limit value (with the attenuation provided by hearing protectors taken into account)||87 dB||200 Pa / 140 dB|
Attenuation provided by hearing protectors
The attenuation provided by hearing protectors is indicated in the manufacturer’s instructions. However, the manufacturer’s values are measured in laboratory conditions and cannot be relied upon in comparisons between noise exposure levels and limit values. In practice, the attenuation provided by hearing protectors depends on the amount of time that the protectors are worn as well as their fit and snugness. A study conducted in Finland in the 1980s found that the attenuation provided by earmuff models during a working day was in fact no more than eight decibels among 10% of the surveyed workers. Ill-fitting hearing protectors have been found to attenuate noise by just four decibels.
Some idea of compliance with the limit value can be achieved by assuming that properly fitting hearing protectors that are worn appropriately attenuate noise by at least eight decibels. However, if a greater degree of attenuation is required, i.e. if a worker’s daily noise exposure exceeds 95 decibels or the peak sound pressure is more than 148 decibels, compliance with the limit value must be established by measuring the worker’s noise exposure or the peak sound level underneath the hearing protectors, inside the ear. If noise levels inside the ear cannot be measured while the worker is wearing ear plugs, compliance with the limit value can be based on an expert’s assessment.
Daily or weekly noise exposure
Noise exposure is always measured using what is known as the “A” frequency weighting, which assimilates the response of the human ear to different sound frequencies. The degree of exposure depends on the noise levels immediately next to a worker’s ear at different points of the day and the duration of the exposure. Daily noise exposure can be measured using a dosimeter or calculated as the average of the noise levels to which the worker is exposed during a typical working day. Both the noise levels during each period of exposure and the duration of the exposure are taken into account, and the average is adjusted to reflect an eight-hour period. If a worker’s noise exposure varies considerably from one day to the next, a five-day average is used.
Effect of the duration of noise exposure
The table below shows the impact of the duration of exposure and the noise levels experienced by a worker on their daily noise exposure. A three-decibel increase in noise levels causes an action value or a limit value to be exceeded in half the time. On the other hand, it takes twice as long for an action value or a limit value to be exceeded if noise levels drop by three decibels.
|Duration of exposure||Noise level equivalent to the lower action value||Noise level equivalent to the upper action value||Noise level equivalent to the limit value inside the ear|
Peak sound pressure or level
Peak sound pressure refers to the maximum value of momentary sound pressure or level. Peak sound pressure is always measured using “C” frequency weighting, which gives a roughly equal emphasis to all frequencies within the range of human hearing (20–20,000 Hz). The law gives the action values and limit values for peak sound pressure in pascals (Pa). In practice, however, peak sound pressure is usually measured in peak sound levels using a sound level meter.