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2011 Review of Occupational Exposure Limits in Ontario:
Current and Proposed Exposure Limits


Changes to Occupational Exposure Limits (OELs) For Substances Regulated Under Regulation 833, Control of Exposure to Biological or Chemical Agents
Current Substance Current
TWA		 Current
STEL/C		 Proposed Substance Proposed
TWA		 Proposed
STEL/C		 Change
Acetic anhydride
[108-24-7]		   C 5 ppm
C 21 mg/m3		 Acetic anhydride
[108-24-7]		 1 ppm 3 ppm TWA and STEL added. Ceiling withdrawn.
Allyl chloride
[107-05-1]		 1 ppm 2 ppm Allyl chloride
[107-05-1] - Skin		 1 ppm 2 ppm Skin notation added.
Carbon black
[1333-86-4]		 3.5 mg/m3   Carbon black
[1333-86-4]		 3 mg/m3 (I)   OEL developed for inhalable fraction.
Ethyl benzene
[100-41-4]		 100 ppm 125 ppm Ethyl benzene
[100-41-4]		 20 ppm   TWA reduced. STEL withdrawn.
Maleic anhydride
[108-31-6]		 0.1 ppm   Maleic anhydride
[108-31-6]		 0.01 mg/m3 (IFV)   OEL developed for inhalable fraction and vapour.
Methyl isopropyl ketone
[563-80-4]		 200 ppm   Methyl isopropyl ketone
[563-80-4]		 20 ppm   TWA reduced.
2,4-Pentanedione
[123-54-6]		 Not listed   2,4-Pentanedione
[123-54-6] - Skin		 25 ppm   Addition of substance to regulation.
Soapstone 6 mg/m3 (E)
3 mg/m3 (E,R)		   Remove listing     Separate listing withdrawn. Substance to be regulated under listing for Talc [14807-96-6]
4,4’-Thiobis(6-tert-butyl-m-cresol)
[96-69-5]		 10 mg/m3   4,4’-Thiobis(6-tert-butyl-m-cresol)
[96-69-5]		 1 mg/m3 (I)   OEL developed for inhalable fraction.

Endnotes and Abbreviations

TWA or time-weighted average limit means the time-weighted average airborne concentration of a biological or chemical agent to which a worker may be exposed in a work day or work week.

STEL or short-term exposure limit means the maximum airborne concentration of a biological or chemical agent to which a worker may be exposed in any 15-minute period;

C or ceiling limit means the maximum airborne concentration of a biological or chemical agent to which a worker may be exposed at any time;

(E) The value is for particulate matter containing no asbestos and < 1% crystalline silica.

(I) Inhalable fraction

(IFV) Inhalable fraction and vapour

(R) Respirable fraction