Air monitoring

The methods and procedures to monitor airborne concentrations of and worker exposure to airborne concentrations of designated substances must be included in control programs (subsection 20(2)).  

To fulfil this requirement workplaces should develop an “air monitoring program” that, among other things, specifies when and where to conduct air sampling, how often and the methods to be used. The requirements of section 24 of the regulation must be considered and adhered to in the development of the program.

Air sampling

Air sampling refers to a procedure for determining the concentration of a contaminant in workplace air. It usually involves collecting representative samples of the substance from the air and having them analyzed to determine the quantity of the substance present.

Air sampling assesses a worker’s exposure by inhalation. The methods and procedures to monitor airborne concentrations of and worker exposure to designated substances must be included in control programs.

There are several reasons why air sampling is carried out, including:

  • to determine the extent of exposure to the designated substance
  • to demonstrate compliance with the OELs
  • to evaluate the effectiveness and performance of existing controls
  • t o obtain information that will aid in the selection of additional controls including respirators
  • to ensure that respirators are appropriate for the concentration of the designated substance
  • to record the personal exposure of workers to the designated substance

There are a wide variety of sampling methods. It is important to ensure that the method used, the sampling done and the results analyzed are all done in compliance with the regulation.

Who can conduct air sampling

Air sampling must be performed by, or under the direction of, a person who is qualified because of knowledge, training and experience in industrial hygiene practice* (section 24). An employer may use their own staff if they are qualified or engage outside personnel who are qualified to perform or supervise the work. It is ultimately the employer’s responsibility to ensure that the regulatory requirements are met.

Having air sampling conducted by, or under the supervision of, a qualified person in industrial hygiene can help ensure that sampling is carried out in accordance with the regulation and the results are representative of worker exposures.

*While not a requirement of the regulation, occupational hygiene professionals registered by the Canadian Registration Board of Occupational Hygienists or certified by the American Board of Occupational Hygienists are examples of individuals who may be qualified persons.

Acceptable methods of sampling

The regulation requires air sampling methods to comply with a standard method for workplace air sampling and analysis or another method recognized in industrial hygiene practice (section 24).

A standard method for workplace air sampling and analysis, as defined in the regulation, means a current standard method for measuring a designated substance that is published by either:

  • ASTM International
  • the Health and Safety Executive (U.K.)
  • the Institut de recherche Robert-Sauvé en santé et en sécurité du travail (Québec)
  • the International Organization for Standardization
  • NIOSH
  • Occupational Safety and Health Administration, United States Department of Labor
  • U.S. Environmental Protection Agency

For ease of reference refer to Appendix A for a table of commonly used and recognized sampling methods for each designated substance.  

Other methods recognized in industrial hygiene practice may include the use of direct-reading instruments, such as organic vapour monitors, to immediately detect and provide a measurement of an airborne chemical agent.  A portable Miran SapphIRe Infrared ambient analyzer used in the measurement of mercury is an example.  Where direct-reading instruments are used to determine the airborne concentration of a designated substance, employers must ensure that the instrument is used, calibrated and maintained in accordance with the manufacturer’s instructions (subsection 24(2)).

Schedule 1, Part 1 – airborne measurement and calculation of exposure  

In addition to addressing sampling, section 24 of the regulation requires that the procedures for monitoring, sampling and determining airborne concentrations of and worker exposure to a designated substance comply with the rules set out in Part I of Schedule 1 to this regulation.  It further requires that these procedures are performed by, or under the direction of, a person who is qualified because of knowledge, training and experience in industrial hygiene practice.

More information on the rules set out in Part I of Schedule 1 of the regulation within the context of the requirements for monitoring, sampling and determining airborne concentrations outlined below.

Personal versus area sampling

Part I of Schedule 1 of the regulation requires that the average concentrations of a designated substance to which a worker is exposed be determined from analysis of air samples taken as being representative of the exposure of the worker to the designated substance during work operations.

Monitoring may be performed by using either personal or area sampling. Personal samples are obtained by sampling air as close as possible to the breathing zone of the worker.  Wherever possible, personal sampling should be used for determining the exposure of a worker to the substance.

Area sampling is performed by placing the sampling train at a strategically selected location in the workplace.  If the movement of workers in and out of sampled areas is carefully documented, it may be possible to calculate personal exposure levels from the results of area sampling.  

Duration of sampling

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

When determining the eight-hour TWA exposure sampling is usually conducted for six to eight hours. Where there are day to day variations in airborne concentrations, sampling for more than one work day during a week may be necessary. If operations vary only slightly from day to day, it may be sufficient to base calculations of the 40-hour TWA exposure on full-shift sampling conducted for one day.

Short-term exposures may be determined from a single sample or from a time-weighted average of sequential samples taken during that period. Samples should be taken during time periods when maximum exposure concentrations are expected.

When to conduct sampling

In most workplaces, fluctuations occur in the concentrations of air contaminants. It is important to evaluate operations in order to determine when, and under what conditions, the designated substance may be released and use this information to determine when to conduct air sampling that represents worker exposures to the substance.

Frequency of air monitoring

The frequency with which air monitoring is performed should be based on the exposure conditions in the individual workplace and specified in the control program.

If exposure levels regularly approach or even exceed the exposure limits, air monitoring should be performed at least on a monthly or quarterly basis.  If there are any differences between summer and winter ventilation, air monitoring should be conducted during both seasons.  Where exposure levels are usually much lower than prescribed limits, less frequent monitoring may be permissible.

The frequency of air monitoring may require adjusting following a change to workplace processes, methods and procedures that could result in a significant difference in worker exposure to the designated substance, requiring further assessment under section 22.

How to calculate the time-weighted average exposure

In accordance with Part I of Schedule 1, the daily or weekly time-weighted average exposure to a designated substance must be calculated in accordance to the following formula:  

Daily or weekly exposure

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

C1T1 + C2T2 + ... + CnTn

Where:

  • C1 is the concentration found in an air sample
  • 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

Time-weighted average exposure

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

Sample calculations

Example 1

This example calculates the time-weighted average exposures over a:

  • 8-hour work day
  • 40-hour work week

Full shift sampling representative of exposure conditions over the course of an 8-hour work day and 40-hour work week were carried out.

A worker is exposed to a solvent containing benzene. The time-weighted average occupational exposure limit for benzene is 0.5 parts per million (ppm). In order to determine the exposure to benzene, a series of five personal air samples were taken during the week.  The results of the sampling and the number of hours the worker was estimated to be exposed are as follows:

Day Concentration (Cn) in ppm Total time in hours in which the worker is taken to be exposed to concentration Cn
Day 1 0.35 ppm (C1) 8(T1)
Day 2 0.25 ppm (C2) 8(T2)
Day 3 0.75 ppm (C3) 8(T3)
Day 4 0.5 ppm (C4) 8(T4)
Day 5 0.1 ppm (C5) 8(T5)

(a) TWA8 = (C1T1 + 0)/8

= (2.8 + 0)/8

= 0. 35 ppm (for Day 1)

(b) TWA40 = (C1 T1 + C2 T2 + C3 T3 + C4 T4 + C5 T5)/40

= (2.8 + 2 + 6 + 4 + 0.8)/40

= 0.39 ppm(for 40-hour work week)

Thus, the worker has an 8-hour time-weighted average exposure to benzene of 0.35 ppm for Day 1 and a time-weighted average exposure of 0.39 ppm for the 40-hour work week.

Example 2

This example calculates the time-weighted average exposures over a:

  • 12-hour work day
  • 48-hour work week

Full shift sampling representative of exposure conditions for the same solvent containing benzene as above example and over the course of a 12-hour work day carried out using two consecutive six-hour samples each day.

In this case the work week consists of four 12-hour work days.

Day Concentration (Cn) in ppm Total time in hours to which the worker is taken to be exposed to concentration Cn
Day 1

0.3 ppm (C1)

0.4 ppm (C2)

6(T1)

6(T2)
Day 2

0.2 ppm (C3)

0.3 ppm (C4)

6(T3)

6(T4)
Day 3

0.7 ppm (C5)

0.8 ppm (C6)

6(T5)

6(T6)
Day 4

0.05 ppm (C7)

0.15 ppm (C8)

6(T7)

6(T8)

Even though the worker was exposed for 12 hours a day and 48 hours a week, the time-weighted average exposure is calculated for an 8-hour and a 40-hour exposure as follows:

TWA8 =(C1T1+C2T2)/8

= (1.8 + 2.4)/8 = 0.53 ppm (for Day 1)

TWA40 = (C1T1+C2T2+C3T3+C4T4+C5T5+C6T6+C7T7+C8T8)/40

= (1.8+2.4+1.2+1.8+4.2+4.8+0.3+0.9)/40

= 0.44 ppm (for a 48-hour work week)

Thus, the worker has an 8-hour time-weighted average exposure of 0.53 ppm and a 40-hour time-weighted average exposure of 0.44 ppm.

Example 3

This example uses an alternative approach to calculating the time-weighted exposure for extended work shifts using methodology set out in Quebec’s IRSST Guide for the Adjustment of Permissible Exposure Values for Unusual Work Schedules (March 2015).

In accordance with Part I of Schedule 1 of the regulation, a determination of the time-weighted average exposure for extended work shifts may be calculated using the methodology set out in the Guide for the Adjustment of Permissible Exposure Values for Unusual Work Schedules (March 2015), published by Quebec’s Institut de recherche Robert-Sauvé en santé et en sécurité du travail (IRSST), using the applicable TWA set out in Table 1 of the regulation.

Determining the personal exposure of workers

The regulation requires the employer to maintain records of the personal exposure of workers to a designated substance at the workplace.  To do this, it may not be necessary to monitor each worker individually. If every worker is not monitored, it is recommended that personal exposures be determined by assigning each worker to an appropriate exposure category within which similar conditions of exposure exist.

Exposure records should also indicate the following:

  • results of air monitoring for all workers sampled
  • calculated time-weighted average exposure levels for all workers sampled
  • the range (lowest and highest) of time-weighted average exposure levels for each exposure category
  • the average (mean) time-weighted average exposure level and standard deviation for each exposure category
  • some indication of past exposures to show trends in exposure levels in recent times

In addition, the following information should be recorded each time air monitoring is performed:

  • date of sampling
  • number of workers sampled in exposure category
  • average (mean) time-weighted average concentration and standard deviation for the exposure category
  • range (highest and lowest) of time-weighted average exposure values for the exposure category
  • results of personal sampling for the individual worker if it has been performed
  • use and type of respirators

Posting of air monitoring results and record-keeping

The regulation requires that the control program include provisions for air monitoring and for maintenance of records showing the personal exposure of workers to the substance.  

The regulation requires the employer to give the results of air monitoring to the JHSC and promptly post them in a conspicuous location(s) where they are most likely to come to the attention of workers who would be affected by them for at least 14 days.  Employers are required to keep air monitoring results for a minimum of five years.

Employers must also furnish a copy of worker personal exposure records to a physician who examines the worker or supervises clinical tests.  The physician must keep these records in a secure place for 40 years from the date such records were first made in the personal exposure record or for 20 years from the date the last of such records was added to the personal exposure record, whichever is longer.  

If the physician is no longer able to keep the records, they must forward them to the Provincial Physician, Ministry of Labour, Training and Skills Development or designate, who will then retain the records in accordance with the same rules set out above.

Refer to Chapter 4 for more information on personal exposure records.