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Occupational exposure limits (OELs) for noise are typically given as the maximum duration of exposure permitted for various noise levels. They are often displayed in exposure-duration tables like Table 1A and Table 1B. The OELs depend on two key factors that are used to prepare exposure-duration tables: the criterion level and the exchange rate.
| Table 1A Noise Exposure Limits when Criterion Level = 85 dBA | ||
|---|---|---|
| 3 dBA Exchange Rate | Maximum Permitted Daily Duration (hours) | 5 dBA Exchange Rate |
| Allowable Level dBA | Allowable Level dBA | |
| 85 | 8 | 85 |
| 88 | 4 | 90 |
| 91 | 2 | 95 |
| 94 | 1 | 100 |
| 97 | 0.5 | 105 |
| 100 | 0.25 | 110 |
| Table 1B Noise Exposure Limits when Criterion Level = 90 dBA | ||
|---|---|---|
| 3 dBA Exchange Rate | Maximum Permitted Daily Duration (hours) | 5 dBA Exchange Rate |
| Allowable Level dBA | Allowable Level dBA | |
| 90 | 8 | 90 |
| 93 | 4 | 95 |
| 96 | 2 | 100 |
| 99 | 1 | 105 |
| 102 | 0.5 | 110 |
| 105 | 0.25 | 115 |
The criterion level, often abbreviated as Lc, is the steady noise level permitted for a full eight-hour work shift. This is 85 dBA in most jurisdictions, but it is 90 dBA in Quebec and 87 dBA for organizations that follow the Canadian federal noise regulations.
As the sound level increases above the criterion level, Lc, the allowed exposure time must be decreased. The allowed maximum exposure time is calculated by using an exchange rate, also called a "dose-trading relation" or "trading ratio." The exchange rate is the amount by which the permitted sound level may increase if the exposure time is halved.
There are two types of exchange rates currently in use: 3 dBA exchange rate or the "3 dB rule," and 5 dBA exchange rate or the "5 dB rule." These two exchange rates, with criterion levels of 85 dBA and 90 dBA, give two different sets of exposure guidelines, as Table 1A and 1B show.
The 3 dBA exchange rate is more stringent. For example, the maximum permitted duration for a 100 dBA noise exposure in the 3 dBA exchange rate is 15 minutes. With the 5 dBA exchange rate, it is one hour.
Most experts recognize the 3 dB rule as more logical. They argue that it is logical that if the sound level is doubled, then the allowable exposure time should be cut in half. It follows, then, that the allowable time should be halved for every 3 dBA increase in sound level. This is precisely the case if the 3 dBA exchange rate is used.
The table below shows the criterion levels (i.e., maximum permitted exposure levels for 8 hours) and the exchange rates used in different Canadian jurisdictions.
| Jurisdiction (federal, provincial, territorial) | Continuous Noise*1 | Impulse / Impact Noise1* | ||
|---|---|---|---|---|
| Maximum Permitted Exposure Level for 8 Hours: dB(A) | Exchange Rate dB(A)2 + | Maximum Peak Pressure Level dB(peak) | Maximum Number of Impacts | |
| Canada (Federal) | 87 | 3 | - | - |
| British Columbia | 85 | 3 | 140 | - |
| Alberta | 85 | 3 | - | - |
| Saskatchewan4 | 85 | 3 | - | - |
| Manitoba | 85 | 3 | - | - |
| Ontario | 85 | 34 | - | - |
| Quebec | 90 | 5 | 140 | 100 |
| New Brunswick | 85 | 3 | 140 | - |
| Nova Scotia3 | 85 | 3 | 140 | - |
| Prince Edward Island | 85 | 3 | - | - |
| Newfoundland and Labrador3 | 85 | 3 | 140 | - |
| Northwest Territories4 | 85** | *** | 140 | 100 |
| Nunavut4 | 85** | *** | 140 | - |
| Yukon Territories | 85 | 3 | 140 | 90 |
1* For more information about continuous, impulse and impact noise, please see Noise - Basic Information.
**2 When 3 dB exchange rate is used, generally there is no separate regulation for impulse/impact noise. The equivalent sound exposure level (Lex) takes impulse noise into account in the same way as it does that for continuous or intermittent noise. Noise regulations in several jurisdictions treat impulse noise separately from continuous noise. A common approach is to limit the number of impulses at a given peak pressure over a workday. The exact figures vary slightly, but generally the regulations in which the exchange rate is 5 dB permit 10,000 impulses at a peak pressure level of 120 dB; 1,000 impulses at 130 dB; 100 impulses at 140 dB, and none above 140 dB.
3. The regulations in these jurisdictions do not specify a value but reference the ACGIH TLVs.
**4 The regulations in these jurisdictions indicate that over an exposure limit of 85 dBA Lex or an “at any time” sound level limit of 90 dBA, the employer is required to provide hearing protection, train workers and implement audiometric testing. dBA Lex means the level of a worker’s total exposure to noise in dBA is averaged over an entire workday and adjusted to an equivalent eight-hour exposure. These jurisdictions also do not allow unprotected exposures for sound levels that exceed 90 dBA. Even when the equivalent exposure is less than 85 dBA, if a worker is exposed at any time at sound levels equal or above 90 dBA the employer is required to take the protective measures.
**** In both territories, the Mine Health and Safety Regulations reference the 3 dBA exchange rate and the maximum impulse level of 140 dB. Please contact Northwest Territories and/or Nunavut for further information.
The following are references to the federal, provincial, and territorial legislation where you will find the occupational noise exposure limits from the different jurisdictions in Canada. Since legislation is amended from time to time, the jurisdiction should be contacted for the most current information about the noise exposure limits and how they are enforced. This information is intended as a guide only and may not apply to specific occupational sectors (for example, mining). The regulations should also be consulted for information on requirements for hearing protective equipment and other control measures that may be prescribed for protecting the hearing of workers. Please contact your local office of the occupational health and safety agency for your jurisdiction if you have specific questions that apply to your workplace.
