How do I calculate the exposure limit?Equal energy rule
Many regulatory agencies recommend a time-weighted average (TWA) sound level of 85 dB(A) to 90 dB(A) as a noise exposure limit for 8-hour work day.
The International Organization for Standardization standard ISO 1999:1990 -- Acoustics -- Determination of occupational noise exposure and estimation of noise-induced hearing impairment recommends the use of the equal energy principle (3 dB exchange rate) in calculating the TWA for a work shift:
Limit for a given shift = 85 - 10 log (T/8)
where T = duration of work shift in hours. Results of such calculation for various extended work shifts are listed in Table 1.
Table 1 also shows the noise exposure limit for extended shifts when the 5 dB exchange rate is used. The formula used for calculating these exposure limits for extended shifts is:
Limit for a given shift (5 dB rule) = 85 - 16.61 log (T/8)
Table 1 - TWA Method |
Work Shift Duration (Hours) | Noise Exposure Limit, dB(A)
[Assuming 8-hour exposure level = 90 dB(A)] |
Using 3dB
exchange rate | Using 5 dB
exchange rate |
| 8 | 90 | 90 |
| 9 | 89.5 | 89.2 |
| 10 | 89.0 | 88.4 |
| 11 | 88.6 | 87.7 |
| 12 | 88.2 | 87.1 |
| 13 | 87.9 | 86.5 |
| 14 | 87.6 | 86.0 |
| 15 | 87.3 | 85.5 |
| 16 | 87.0 | 85.0 |
The noise exposure limit for a 12-hour shift, based on the equal energy rule, is 88.2 dB(A). In other words, if the noise level is kept below 88 dB(A) then, according to equal energy concept, the maximum permissible limit is not exceeded.
Does CCOHS have other information on noise or noise regulations?If you came to this page directly from another site, you missed seeing a list of other topics about noise. You can see a list of these other topics by going to the Physical Agents topics page.
Information on hearing protectors is available in the "Personal Protective Equipment" section of OSH Answers.
If you want to find articles, research papers, government reports and other information that deal with the effects of noise exposure in certain situations, noise control, hearing protection, hearing conservation programs, etc., you can search our bibliographic databases like CISILO, NIOSHTIC, and HSELINE. Information on other CCOHS bibliographic databases and full-text products is accessible from the Health and Safety Studies, Research and Directories web page.
You can also link to descriptions of legislation-related information products by visiting the Legislative and Regulatory Information web page.
Free searches of Canadian enviroOSH Legislation are available at:
http://www.ccohs.ca/legislation
You can view the titles retrieved by your search but you must be a subscriber to display the full text of the legislation.
You can search for information related to noise that the Labour Canada Program at HRDC and several provincial and territorial OH&S agencies have put on their web sites by searching the CanOSH web site.
Document last updated on October 6, 2005
Copyright ©1997-2008 Canadian Centre for Occupational Health & Safety
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