3. What are current sound protection limits?
Limits have been set to protect workers from excessive noise.
So far, limits have only been set to protect workers from excessive noise exposure and not for other situations such as the use of personal music players with headphones. The limits are nonetheless relevant to other situations where sound can have harmful effects.
The risk of hearing damage depends on sound level and on exposure time. For long-term exposure of workers, time periods of 8 hours per day are typically considered in order to set protections standards. In cases where exposures vary markedly from day to day, weekly sound exposure levels (8 hours per day for 5 days per week) can also be useful.
Because sound levels vary in time and from worker to worker, protection standards are expressed as an equivalent continuous sound level (Lequ) that would contain the same amount of energy as the sound heard.
In the late 1990s, international standards established limit values for long-term exposure of workers to noise. According to these standards, action should be taken to protect workers who are exposed to an equivalent continuous sound level of 85 dB(A) or more for 8 hours per day, 5 days per week. This limit was set by the International Organization for Standardization (ISO) and the US National Institute for Occupational Safety and Health (NIOSH). However, this limit did not guarantee the safety for the auditory system of workers.
More stringent action levels were introduced in the EU since 2003 with the EU Noise at Work Regulations (Directive 2003/10/EC) which came into force in 2006. It recommends three protection levels at the workplace depending on equivalent noise level for an 8-hour working day.
- At 80 dB(A) employers shall make hearing protectors (e.g ear plugs or muffs) available to workers. Below this limit, the risk to hearing is assumed to be negligible.
- At 85 dB(A) protection of workers is mandatory.
- 87 dB(A) is the maximum exposure limit value.
Because the risk of hearing damage from long-term sound exposure depends both on the level of the sound and on the exposure time, there is a trade-off between the two factors.
As a result, listening to loud sounds over many hours per day entails a similar risk as listening to an even louder sound for a shorter period per day. In order not to increase overall exposure, each 3 dB increase in sound levels must thus be compensated by halving the listening time.
For instance, listening to a personal music player at 95 dB(A) during 15 minutes per day is equivalent to being exposed at work to 80 dB(A) during 8 hours per day, under the assumption that these exposures are repeated over a long period of time.
Further equivalents are presented in the following table. Increasing either exposure time or sound levels beyond the above limits could lead to hearing damage. More...