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.

The criterion level, often abbreviated as Lc, is the steady noise level permitted for a full eight-hour work shift. This is 90 dB(A) in most jurisdictions, but in some jurisdictions it is 85 dB(A). The exception is in the Canadian federal noise regulations where the criterion level is 87 dB(A).

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 dB(A) exchange rate or the "3 dB rule," and 5 dB(A) exchange rate or the "5 dB rule." These two exchange rates, with criterion levels of 85 dB(A) and 90 dB(A), give two different sets of exposure guidelines, as Table 1A and 1B show.

The 3 dB(A) exchange rate is more stringent. For example, the maximum permitted duration for a 105 dB(A) noise exposure in the 3 dB(A) exchange rate is 15 minutes. With the 5 dB(A) 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 dB(A) increase in sound level. This is precisely the case if the 3 dB(A) 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		Impulse / Impact Noise
	Maximum Permitted Exposure Level for 8 Hours: dB(A)	Exchange Rate dB(A) +	Maximum Peak Pressure Level dB(peak)	Maximum Number of Impacts
Canada (Federal)	87	3	-	-
British Columbia	85	3	140	-
Alberta	85	3	-	-
Saskatchewan	85	3	-	-
Manitoba	85	3	-	-
Ontario (includes ceiling level of 140 dBC)	85	3	-	-
Quebec	90	5	140	100
New Brunswick	85	3	140	-
Nova Scotia	85	3	140	100
Prince Edward Island	85	3	-	-
Newfoundland (references ACGIH TLVs)	85	3	-	-
Northwest Territories	85	5	140	100
Nunavut	85	3 or 5*	140	-
Yukon Territories	85	3	140	90

+ When 3 dB exchange rate is used, generally there is no separate regulation for impulse/impact noise. The equivalent sound exposure level (L_ex) takes impulse noise into account in the same way as it does that for continuous or intermittent noise.

* In Nunavut, the General Safety Regulations reference a 5 dBA exchange rate. The Mining Health and Safety Regulations reference 3 dBA. Please contact Nunavut for further information. A contact list is available at:

http://www.ccohs.ca/oshanswers/information/govt.html

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.

Alternatively, using a 3 dB(A) exchange rate, impulse noise can be considered jointly with any continuous noise, in measuring the overall L_eq sound level.

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.

Canada

Canada Labour Code, Part II, (R.S.C. 1985, c. L-2)

Canada Occupational Safety and Health Regulations, (SOR/86-304)

Section 7.4(1)(b)

British Columbia

Worker's Compensation Act

Occupational Health and Safety Regulations (BC Reg 296/97 as amended)

Section 7.2 [B.C. Reg. 382/2004, s.1]

Alberta

Occupational Health and Safety Code

Section 218; Table 1 of Schedule 3

Also see Tables 16.1 and 16.2 (p.16-9) of OHS Code Explanation Guide

Table 1 and Table 2

Saskatchewan

Occupational Health and Safety Act, 1993 [R.R.S. c.0-1.1, r.1]

Occupational Health and Safety Regulations, 1996

Part VIII, Section 113 (1)

Manitoba

Workplace Safety and Health Act [R.S.M. 1987, c. W210]

Workplace Safety and Health Regulations (Man. Reg. 217/2006) Part 12

Ontario

Occupational Health and Safety Act [R.S.O. 1990, c.1]

Industrial Establishments (R.R.O. 1990, Reg 851)

Section 139

Quebec

Act Respecting Occupational Health and Safety [R.S.Q., c.2.1]

Regulation respecting Occupational Health and Safety (O.C.885-2001)

Division XV, Sections 130-141

New Brunswick

Occupational Health and Safety Act

General Regulation (N.B reg. 91-191 as amended)

Part V, Sections 29 to 33

Nova Scotia

Occupational Health Regulations

N.S. Reg. 112/76

Section 4

(references ACGIH TLVs, as updated annually)

Prince Edward Island

Occupational Health and Safety Act

Occupational Health and Safety Act General Regulations (E.C. 180/87)

Part 8, Section 8.1

(references ACGIH TLVs, as updated annually)

Newfoundland

Occupational Health and Safety Act

Occupational Health and Safety Regulations (C.N.L.R. 1165/96)

Section 50

(references ACGIH TLV, as updated annually)

Northwest Territories

Safety Act

General Safety Regulations (RRNWT 1990, c. S-1, R-028-93 as amended)

Section 30 and 31, Schedule A, Table 1

Nunavut

Safety Act

General Safety Regulations (RRNWT 1990, c. S-1)

Section 30 and 31, Schedule A

and

Mine Health and Safety Regulations, R-125-95

Section 9.19-9.26, Schedule 5

Yukon Territories

Occupational Health and Safety Act

Occupational Health Regulation (O.I.C. 1986/164)

Section 4