CONTROL OF EXPOSURE TO BIOLOGICAL OR CHEMICAL AGENTS

Occupational Health and Safety Act
Loi sur la santé et la sécurité au travail

R.R.O. 1990, REGULATION 833

CONTROL OF EXPOSURE TO BIOLOGICAL OR CHEMICAL AGENTS

Historical version for the period July 1, 2010 to November 4, 2010.

Last amendment: O. Reg. 491/09.

This Regulation is made in English only.

1. In this Regulation,

“ACGIH” means the American Conference of Governmental Industrial Hygienists;

“ACGIH Table” means the table entitled “Adopted Values” shown at pages 10 to 61 of the publication entitled 2009 Threshold Limit Values and Biological Exposure Indices published by ACGIH and identified by International Standard Book Number 978-1-882417-95-7;

“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;

“chemical agent” includes a chemical substance;

“exposure” means exposure by inhalation, ingestion, skin absorption or skin contact;

“Ontario Table” means Table 1 to this Regulation;

“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;

“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. O. Reg. 491/09, s. 1.

2. (1) This Regulation does not apply, at a project,

(a) to an employer who engages in construction; or

(b) to workers of an employer described in clause (a) who are engaged in construction. O. Reg. 491/09, s. 2.

(2) This Regulation does not apply,

(a) to a chemical agent listed in Table 1 of Ontario Regulation 490/09 (Designated Substances) made under the Act, in a workplace that is subject to that regulation with respect to that agent; or

(b) with respect to asbestos, in a workplace that is subject to Ontario Regulation 278/05 (Designated Substance — Asbestos on Construction Projects and in Buildings and Repair Operations) made under the Act. O. Reg. 491/09, s. 2.

3. (1) Every employer shall take all measures reasonably necessary in the circumstances to protect workers from exposure to a hazardous biological or chemical agent because of the storage, handling, processing or use of such agent in the workplace. R.R.O. 1990, Reg. 833, s. 3 (1).

(2) The measures to be taken shall include the provision and use of,

(a) engineering controls;

(b) work practices;

(c) hygiene facilities and practices; and

(d) if section 7.2 applies, personal protective equipment. O. Reg. 491/09, s. 3.

4. Without limiting the generality of section 3, every employer shall take the measures required by that section to limit the exposure of workers to a hazardous biological or chemical agent in accordance with the following rules:

1. If the agent is listed in the Ontario Table, exposure shall not exceed the TWA, STEL, or C set out in the Ontario Table.

2. If the agent is not listed in the Ontario Table but is listed in the ACGIH Table, exposure shall not exceed the TWA, STEL, or C set out in the ACGIH Table.

3. If the Table that applies under paragraph 1 or 2 sets out a TWA for an agent but sets out neither a STEL nor a C for that agent, exposure shall not exceed the following excursion limits:

i. Three times the TWA for any period of 30 minutes.

ii. Five times the TWA at any time.

4. Paragraph 3 does not apply with respect to an agent that is prescribed as a designated substance under Ontario Regulation 490/09 (Designated Substances) made under the Act. O. Reg. 491/09, s. 4.

5. In determining the exposure of workers to a hazardous biological or chemical agent under section 3 or 4, no regard shall be had to the wearing and use of personal protective equipment. R.R.O. 1990, Reg. 833, s. 5.

6. Airborne concentrations of hazardous biological or chemical agents and daily and weekly time-weighted average exposures shall be calculated in accordance with the rules set out in Schedule 1. O. Reg. 491/09, s. 5.

7. If the listing for an agent in the Ontario Table or in the ACGIH Table includes the notation “Skin” and the agent is present at the workplace, the employer shall take all measures reasonably necessary in the circumstances to protect workers from skin absorption of the agent. O. Reg. 491/09, s. 5.

7.1 If the listing for an agent in the ACGIH Table includes the reference “Simple asphyxiant” and the agent is present in the air at the workplace, the employer shall take all measures reasonably necessary in the circumstances to protect workers from,

(a) exposure to an atmospheric oxygen level that is less than 19.5 per cent by volume; and

(b) related hazards such as fire and explosion. O. Reg. 491/09, s. 5.

7.2 (1) An employer shall protect workers from exposure to a hazardous biological or chemical agent without requiring them to wear and use personal protective equipment, unless subsection (2) applies. O. Reg. 491/09, s. 5.

(2) The employer shall provide, and workers shall wear and use, personal protective equipment appropriate in the circumstances to protect the workers from exposure to the agent, if engineering controls required by this Regulation,

(a) are not in existence or are not obtainable;

(b) are not reasonable or not practical to adopt, install or provide because of the duration or frequency of the exposures or because of the nature of the process, operation or work;

(c) are rendered ineffective because of a temporary breakdown of the controls; or

(d) are ineffective to prevent, control or limit exposure because of an emergency. O. Reg. 491/09, s. 5.

8. (1) If a worker has been exposed to a hazardous biological or chemical agent and,

(a) the worker or the worker’s physician has reason to believe that the worker’s health has been affected by exposure to the agent and the worker or the worker’s physician has so notified the employer in writing; or

(b) the employer has reason to believe that the worker’s health is likely to be affected by the exposure and the employer has so notified the worker in writing,

the worker, if he or she agrees, shall undergo medical examinations and clinical tests, at the employer’s expense, to determine whether the worker has an occupational illness because of exposure to the agent and whether the worker is fit, fit with limitations or unfit to continue working in exposure to the agent. O. Reg. 491/09, s. 6.

(2), (3) Revoked: O. Reg. 491/09, s. 6.

(4) The employer shall provide the physician who examines the worker or under whose supervision clinical tests are performed with a copy of the records, if any, of the exposure of the worker to the hazardous biological or chemical agent. R.R.O. 1990, Reg. 833, s. 8 (4).

9. Revoked: O. Reg. 607/05, s. 3 (2).

TABLE 1
ONTARIO TABLE OF OCCUPATIONAL EXPOSURE LIMITS

Agent [CAS No.]	Time-Weighted Average Limit (TWA), Short-Term Exposure Limit (STEL), Ceiling Limit (C) and Notations
	TWA	STEL/C	Notations
Acetic anhydride [108-24-7]		C 5 ppm
		C 21 mg/m3
*Acrylonitrile [107-13-1]	2 ppm	C 10 ppm	Skin
Aliphatic hydrocarbon gases
Alkane [C1-C4], except Butane, All isomers	1,000 ppm
Butane, All isomers [106-97-8]; [75-28-5]	800 ppm
*Arsenic, elemental arsenic and inorganic compounds [7440-38-2], and organic compounds (only where both inorganic and organic compounds are present), as As.	0.01 mg/m3	0.05 mg/m3
*Asbestos – All forms [1332-21-4]	0.1 f/cc (a)
Actinolite [77536-66-4]	0.1 f/cc (a)
Amosite [12172-73-5]	0.1 f/cc (a)
Anthophyllite [77536-67-5]	0.1 f/cc (a)
Chrysotile [132207-32-0]	0.1 f/cc (a)
Crocidolite [12001-28-4]	0.1 f/cc (a)
Tremolite [77536-68-6]	0.1 f/cc (a)
Benzaldehyde [100-52-7]		4 ppm
		17 mg/m3
*Benzene [71-43-2]	0.5 ppm	2.5 ppm	Skin
Beryllium and its compounds, as Be [7440-41-7]	0.002 mg/m3	0.01 mg/m3
sec-Butanol [78-92-2]	100 ppm	150 ppm
tert-Butanol [75-65-0]	100 ppm	150 ppm
Calcium chloride [10043-52-4]	5 mg/m3
Carbon monoxide [630-08-0]	25 ppm	100 ppm
Carbon tetrachloride [56-23-5]	2 ppm	3 ppm	Skin
Charcoal, except activated [16291-96-6]	10 mg/m3
Chlordane [57-74-9]	0.5 mg/m3	2 mg/m3	Skin
Chlorinated diphenyl oxides [55720-99-5]	0.5 mg/m3	2 mg/m3
o-Chlorobenzaldehyde [89-98-5]		4 ppm
		23 mg/m3
Chlorobromomethane [74-97-5]	200 ppm	250 ppm
Chlorodifluoromethane [75-45-6]	1,000 ppm	1,250 ppm
Chlorodiphenyl (42% chlorine) [53469-21-9]	See listing for Polychlorinated Biphenyls (PCBs)
Chlorodiphenyl (54% chlorine) [11097-69-1]
Chloropicrin [76-06-2]	0.1 ppm	0.3 ppm
o-Chlorotoluene [95-49-8]	50 ppm	75 ppm
Clopidol [2971-90-6]	10 mg/m3	20 mg/m3
N-Coco morpholine [1541-81-7]	5 ppm		Skin
	52 mg/m3
*Coke Oven Emissions1	0.15 mg/m3
Cotton dust, fabric knitting	0.5 mg/m3
Cotton dust, raw	0.2 mg/m3 (G)
Cotton dust, slashing and weaving	0.75 mg/m3(G)
Cotton dust, waste	0.5 mg/m3(G)
‘Coumin 100’ Polymer Flakes (total dust) [63393-89-5]	5 mg/m3
Crufomate [299-86-5]	5 mg/m3	20 mg/m3
Cymene (sum of o-,m-and p-isomers) [25155-15-1]	50 ppm		Skin
	274 mg/m3
Diacetone alcohol [123-42-2]	50 ppm	75 ppm
	240 mg/m3	360 mg/m3
Diatomaceous earth (uncalcined) [61790-53-2]	10 mg/m3 (I)(E)
	3 mg/m3 (R)(E)
1, 3-Dichloro-2-Propanol [96-23-1]		1 ppm	Skin
		5 mg/m3
1,2-Dichloroethylene, All isomers	200 ppm	250 ppm
[540-59-0; 156-59-2; 156-60-5]	790 mg/m3	990 mg/m3
Diethylene glycol monoethyl ether [111- 90-0]	30 ppm
	165 mg/m3
Di(2-ethylhexyl)phthalate (DEHP) [117-81-7]	3 mg/m3	5 mg/m3
Diisodecyl phthalate [26761-40-0]	5 mg/m3
3-(Dimethylamino) propylamine [109-55-7]	0.5 ppm		Skin
	2 mg/m3
N, N-Dimethyl-cyclohexylamine [98-94-2]		5 ppm
		26 mg/m3
N, N-Dimethyl-ethanolamine [108-01-0]	3 ppm	6 ppm
	11 mg/m3	22 mg/m3
Dimethyl terephthalate [120-61-6]	5 mg/m3
Dimethyl 2,3,5,6-tetracholoroterephthalate [1861-32-1]	5 mg/m3
Dipropylene glycol monomethyl ether acetate	100 ppm	150 ppm
[88917-22-0]	776 mg/m3	1,164 mg/m3
Diquat [2764-72-9; 85-00-7; 6385-62-2]	0.5 mg/m3		Skin
	0.1 mg/m3 (R)
Enflurane [13838-16-9]	2 ppm
	16 mg/m3
Ethyl-3-ethoxy propionate [763-69-9]	50 ppm
	300 mg/m3
Ethylene dibromide [106-93-4]	(L)		Skin
Ethylene glycol dimethyl ether [110-71-4]	5 ppm		Skin
	18 mg/m3
Ethylene glycol mono-n-propyl ether [2807-30-9]	25 ppm		Skin
	110 mg/m3
Ethylene glycol mononitrate [16051-48-2]	0.05 ppm		Skin
	0.22 mg/m3
*Ethylene oxide [75-21-8]	1 ppm	10 ppm
	1.8 mg/m3	18 mg/m3
Ethyl methacrylate [97-63-2]	100 ppm
	470 mg/m3
Flour dust	See listing for Wheat Flour Dust (total dust)
Forane [26675-46-7]	2 ppm
	15 mg/m3
Formaldehyde [50-00-0]		STEL 1 ppm
		C 1.5 ppm
Halothane [151-67-7]	2 ppm
	16 mg/m3
Heptyl acetate [112-06-1]	50 ppm
	320 mg/m3
Hexamethylenetetramine (HMT) [100-97-0]		0.35 ppm
		2 mg/m3
Hexamethyl phosphoramide [680-31-9]	(L)		Skin
Hexyl acetate (isomeric mixture)[88230-35-7]	50 ppm
	294 mg/m3
Hydrogenated terphenyls2 [61788-32-7]	0.5 ppm
Isobutyl acetate [110-19-0]	150 ppm	187 ppm
*Isocyanates, organic compounds
Toluene diisocyanate (TDI) [584-84-9] [91-08-7]	0.005 ppm	C 0.02 ppm
Methylene bisphenyl isocyanate (MDI) [101-68-8]	0.005 ppm	C 0.02 ppm
Hexamethylene diisocyanate (HDI) [822-06-0]	0.005 ppm	C 0.02 ppm
Isophorone diisocyanate (IPDI) [4098-71-9]	0.005 ppm	C 0.02 ppm
Methylene bis (4-cyclohexylisocyanate) [5124-30-1]	0.005 ppm	C 0.02 ppm
Isopropylaminoethanols [109-56-8] [121-93-7]		400 ppm
		1,900 mg/m3
Isosorbide dinitrate [87-33-2]	0.2 mg/m3		Skin
* Lead [7439-92-1] elemental lead, inorganic and organic compounds of lead, as Pb
Elemental lead, inorganic and organic compounds of lead, as Pb except tetraethyl lead [78-00-2]	0.05 mg/m3		Skin (organic compounds)
Tetraethyl lead, as Pb [78-00-2]	0.10 mg/m3	0.30 mg/m3
* Lead chromate [7758-97-6]
as Pb (see listing for lead [7439-92-1])	0.05 mg/m3
as Cr	0.012 mg/m3
Lincomycin [154-21-2]	0.1 mg/m3
Lithium hydroxide
Anhydrous [1310-65-2]		1 mg/m3
Monohydrate [1310-66-3]		1 mg/m3
Magnesite (total dust) [546-93-0]	10 mg/m3 (E)
*Mercury [7439-97-6], elemental mercury, inorganic and organic compounds of mercury, as Hg
All forms of except alkyl, as Hg	0.025 mg/m3		Skin
Alkyl compounds of, as Hg	0.01 mg/m3	0.03 mg/m3	Skin
Methoxyflurane [76-38-0]	2 ppm
	13 mg/m3
Methyl acetylene [74-99-7]	1,000 ppm	1,250 ppm
Methyl n-amyl ketone [110-43-0]	25 ppm
	115 mg/m3
Methyl tert-butyl ether (MTBE) [1634-04-4]	40 ppm
Methyl n-butyl ketone [591-78-6]	1 ppm		Skin
	4 mg/m3
4,4'-Methylene bis(2-chloroaniline) (MBOCA; MOCA®)	0.0005 ppm		Skin
[101-14-4]	0.005 mg/m3
4,4'-Methylene dianiline [101-77-9]	0.04 mg/m3		Skin
N-Methyl-2-pyrrolidone [872-50-4]	400 mg/m3
Mineral Spirits	525 mg/m3
Morpholine [110-91-8]	20 ppm	30 ppm	Skin
	70 mg/m3	105 mg/m3
Nepheline syenite (total dust) [37244-96-5]	10 mg/m3
Nickel
Elemental/metal [7440-02-0]	1 mg/m3 (I)
Insoluble compounds, as Ni [7440-02-0]	0.2 mg/m3 (I)
Soluble compounds, as Ni [7440-02-0]	0.1 mg/m3 (I)
Nickel subsulfide, as Ni [12035-72-2]	0.1 mg/m3 (I)
2-Nitropropane [79-46-9]	10 ppm	20 ppm
	35 mg/m3	70 mg/m3
N-Nitrosamines, including	(L)		Skin
n-Nitrosodimethylamine [62-75-9]
Nitrous oxide [10024-97-2]	25 ppm
	45 mg/m3
Ozone [10028-15-6]	0.1 ppm	0.3 ppm
	0.2 mg/m3	0.6 mg/m3
Paraquat [4685-14-7]	0.1 mg/m3
Particles (Insoluble or Poorly Soluble) Not Otherwise	10 mg/m3 (I)
Specified (PNOS)	3 mg/m3(R)
Penicillin (total dust) [1406-05-9]	0.1 mg/m3
Pentaerythritol tetrabenzoate [4196-86-5]		2 mg/m3
Pentane, All isomers	600 ppm	750 ppm
[78-78-4; 109-66-0; 463-82-1]	1,770 mg/m3	2,210 mg/m3
Perlite	10 mg/m3(E)
Petroleum coke (total dust) [64741-79-3]	3.5 mg/m3 (b)
2-Phenoxyethanol [122-99-6]	25 ppm		Skin
	141 mg/m3
Phosphorus oxychloride [10025-87-3]	0.1 ppm	0.5 ppm
	0.6 mg/m3	3 mg/m3
Picloram [1918-02-1]	10 mg/m3	20 mg/m3
Picric acid [88-89-1]	0.1 mg/m3	0.3 mg/m3	Skin
Platinum [7440-06-4]
Metal	1 mg/m3
Water-soluble compounds of, including chloroplatinates (as Pt)	0.002 mg/m3
Polychlorinated biphenyls (PCBs)2	0.05 mg/m3
Poultry dust (total dust)	5 mg/m3
Precipitated silica (total dust) [1343-98-2]	10 mg/m3
1,2-Propylene glycol [57-55-6]	50 ppm (V)
	155 mg/m3 (V)
	10 mg/m3(H)(c)
Propylene glycol monomethyl ether acetate [108-65-6]	50 ppm
	270 mg/m3
Selenium hexafluoride [7783-79-1], as Se	0.025 ppm
	0.1 mg/m3
Shellac dust (total dust) [9000-59-3]	10 mg/m3
* Silica, Crystalline
Quartz/Tripoli [14808-60-7; 1317-95-9]	0.10 mg/m3 (R)
Cristobalite [14464-46-1]	0.05 mg/m3 (R)
Silica fume [69012-64-2]	2 mg/m3 (R)
Silica fused [60676-86-0]	0.1 mg/m3 (R)
Silica gel [112926-00-8]	10 mg/m3
Silicon (total dust) [7440-21-3]	10 mg/m3
Silicon carbide [409-21-2]
Non-fibrous	10 mg/m3 (I) (E)
	3 mg/m3 (R)(E)
Fibrous (including whiskers)	0.1 f/cc (R)(F)
Sisal dust (total dust)	2 mg/m3
Soap dust [68918-36-5]	5 mg/m3
Sodium fluoroacetate [62-74-8]	0.05 mg/m3	0.15 mg/m3	Skin
Spectinomycin [1695-77-8]	2 mg/m3
140 Degree C Flash Aliphatic Solvent, Type of Stoddard	525 mg/m3
Solvent
Styrene - monomer [100-42-5]	35 ppm	100 ppm
Sulfur dioxide [7446-09-5]	2 ppm	5 ppm
	5.2 mg/m3	10.4 mg/m3
Synthetic Vitreous Fibres (Man Made Mineral Fibres)
Continuous filament glass fibres	5 mg/m3 (I)
Continuous filament glass fibres	1 f/cc (F)
Glass wool fibres	1 f/cc (F)
Refractory ceramic fibres	0.5 f/cc (F)
Rock wool fibres	1 f/cc (F)
Slag wool fibres	1 f/cc (F)
Special purpose glass fibres	1 f/cc (F)
Synthetic Vitreous Fibres, not otherwise classified (excluding fibrous glass dust and mineral wool fibre)	1 f/cc (F)(d)
Talc [14807-96-6], containing no asbestos	2 mg/m3 (R)(E)
	2 f/cc (K)
Tantalum, metal and oxide (total dust) [7440-25-7]	10 mg/m3
Tellurium hexafluoride [7783-80-4], as Te	0.01 ppm
	0.1 mg/m3
Tetrachlorophathalic anhydride [117-08-8]	0.1 mg/m3
Tetrachlorophenol [25167-83-3]	0.5 mg/m3		Skin
Tetrasodium pyrophosphate [7722-88-5]	5 mg/m3
Tin [7440-31-5], as Sn
Metal	2 mg/m3
Oxide and inorganic compounds, as Sn, except tin hydride	2 mg/m3
Organic compounds, as Sn	0.1 mg/m3		Skin (organic compounds)
o-Tolidine [119-93-7]	(L)		Skin
Triethanolamine [102-71-6]	0.5 ppm
	3.1 mg/m3
Triethylenediamine [280-57-9]	1 ppm		Skin
	4.6 mg/m3
Triethylenetetramine [112-24-3]	0.5 ppm		Skin
	3 mg/m3
Trimethoxyvinylsilane [2768-02-7]		10 ppm
		60 mg/m3
2,4,6-Trinitrotoluene (TNT) [118-96-7]	0.01 ppm	0.02 ppm	Skin
	0.1 mg/m3	0.2 mg/m3
Trixylylphosphate [25155-23-1]	0.1 mg/m3
Vegetable oils (mists) except mists of irritant oils such as oils of castor and cashew nut	10 mg/m3
*Vinyl chloride [75-01-04]	1 ppm
Vinylidene chloride [75-35-4]	1 ppm	20 ppm
	4 mg/m3	80 mg/m3
Wheat flour dust (total dust)	3 mg/m3
Wood dust
Certain hardwoods as beech and oak	1 mg/m3
Softwood	5 mg/m3	10 mg/m3

Endnotes and Abbreviations:

* Denotes a chemical agent listed in Table 1 of Ontario Regulation 490/09 (Designated Substances) made under the Act. See clause 2 (2) (a) of this Regulation.

¹ Means the benzene soluble fraction of total particulate matter of the substances emitted into the atmosphere from metallurgical coke ovens including condensed vapours and solid particulates.

² As sum of components assayed by chromatographic procedure with reference to the bulk sample.

[CAS No.] - CAS Registry Number.

f/cc - Fibres per cubic centimetre of air.

mg/m³ - Milligrams of the agent per cubic metre of air.

ppm - Parts of the agent per million parts of air by volume.

Skin - Danger of cutaneous absorption.

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

(F) Respirable fibres: length > 5µm; aspect ratio ≥3:1, as determined by the membrane filter method at 400-450 times magnification (4-mm objective), using phase-contrast illumination.

(G) As measured by the vertical elutriator, cotton-dust sampler.

(H) Aerosol only.

(I) Inhalable fraction: means that size fraction of the airborne particulate deposited anywhere in the respiratory tract and collected during air sampling with a particle size-selective device that, (a) meets the ACGIH particle size-selective sampling criteria for airborne particulate matter; and (b) has the cut point of 100 µm at 50 per cent collection efficiency.

(K) Should not exceed 2 mg/m³ respirable particulate mass.

(L) Exposure by all routes should be carefully controlled to levels as low as possible.

(R) Respirable fraction: means that size fraction of the airborne particulate deposited in the gas-exchange region of the respiratory tract and collected during air sampling with a particle size-selective device that, (a) meets the ACGIH particle size–selective sampling criteria for airborne particulate matter; and (b) has the cut point of 4 µm at 50 per cent collection efficiency.

(V) Vapour and aerosol.

(a) Asbestos fibres longer than 5 µm in length and less than 3 µm in width and that have a length to width ratio not less than 3:1 as viewed in a phase contrast optical microscope at 400-450 times magnification.

(b) Provided that the total dust contains less than 0.7 per cent vanadium.

(c) For assessing the visibility in a work environment where 1,2-propylene glycol aerosol is present.

(d) A secondary limit of 5 mg/m³ (total dust) is recommended to deal with dusty operations where fibre counts are usually difficult to determine. Where both types of measurements are made simultaneously, the more restrictive limit should be used to assess the exposures.

O. Reg. 491/09, s. 7.

SCHEDULE Revoked: O. Reg. 491/09, s. 8.

SCHEDULE 1
AIRBORNE MEASUREMENT AND CALCULATION OF EXPOSURE

1. Airborne concentrations of a biological or chemical agent are expressed as,

(a) parts of the agent per million parts of air by volume (ppm);

(b) milligrams of the agent per cubic metre of air (mg/m³); or

(c) fibres per cubic centimetre of air (f/cc).

2. Air sampling of the airborne concentrations of the biological or chemical agent is not required for the full period of a work day or a work week if the air sampling is representative of airborne concentrations of the agent likely to be present during the full period.

3. The method of air sampling, the number and volume of the samples and the method of analysis of the samples shall be determined,

(a) according to the nature of the operations or processes and the characteristics of the biological or chemical agent; and

(b) in accordance with recognized industrial hygiene practice.

4. In determining exposure to airborne concentrations of the biological or chemical agent, no regard shall be had to the wearing or use of personal protective equipment.

5. The time-weighted average exposure to an airborne biological or chemical agent in a work day or work week shall be calculated as follows:

1. The cumulative daily or weekly exposure shall be calculated using the following formula:

C₁T₁ + C₂T₂ + ... + C_nT_n

where,

C₁ is the concentration found in an air sample, and

T₁ is the total time in hours to which the worker is taken to be exposed to concentration C₁ in a work day or a work week.

2. The time-weighted average exposure shall be calculated by dividing the cumulative daily exposure by eight and the cumulative weekly exposure by 40 respectively.

6. Short-term exposures to the biological or chemical agent in any 15-minute period are determined from a single sample or from a time-weighted average of sequential samples taken during that period.

7. For mixtures of airborne chemical agents that exert an additive health effect, if analytical results of individual airborne agents are available, the following formula shall be used, subject to section 8 of this Schedule:

E

where,

C₁, C₂, ... , C_n are the concentrations of the individual agents found in the air sample,

L₁, L₂, ... , L_n are the respective exposure limits for the agents determined in accordance with the rules set out in section 4 of the Regulation,

and the sum of these ratios, E, shall not exceed 1.

8. If the agents in a mixture of airborne chemical agents have substantially different health effects,

i. section 7 of this Schedule does not apply, and

ii. exposure to each agent shall be calculated independently.

O. Reg. 491/09, s. 9.