OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 4 Chemical Hazards, Biological Hazards and Harmful Substances

Section 20 Airborne concentration measurements

NIOSH and alternate methods

The measurement of exposure concentrations at the workplace is important since compliance with the OELs is based on comparing measured levels with those specified in the OHS Code. The adoption of OELs by the OHS Code reflects the fact that there are valid, tested and reproducible methods for the collection and analysis of the substances involved. Small errors or departures from accepted methods can have a large impact on worker exposures and the costs of compliance.

Revisions to this section of the OHS Code allow for the use of methods developed by seven agencies:

(1) National Institute of Occupational Safety and Health – NIOSH
(2) Occupational Safety and Health Administration (United States) – OSHA
(3) Health and Safety Executive (Great Britain) – HSE
(4) Environmental Protection Agency (United States) – EPA
(5) Institut de Recherché Robert-Sauvé en Santé et en Sécurité du Travail (Quebec) – IRRSST
(6) International Organization for Standardization (Technical Committee TC146) – ISO
(7) Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (Germany) – Deutsche Forschungsgemeinschaft

More information, and in some cases the actual methods, can be found at the following:

  HSE Methods for the Determination of Hazardous Substances Guidance

  OSHA Sampling and Analytical Methods

  US EPA Test Methods

IRRSST Workplace Air Contamination Sampling Guide
8th edition, French language only

Deutshe Forschungsgeminschaft Analyses of Hazardous Substances in Air (must be obtained through a library or purchased)

If there is no specific method for a particular substance, or if the employer wishes to use an alternative analytical method, the method used must be acceptable to a Director of Occupational Hygiene. The Director may accept alternative methods through approval of individual applications or publication of a Safety Bulletin. To obtain approval from the Director, the employer must show:

(a) the precision and accuracy of the method;
(b) who has previously developed and evaluated the method. For example, has the method been developed by a recognized independent source;
(c) the quality assurance and quality control measures that will be used;
(d) interferences with the method i.e. other substances that could affect the results; and
(e) biases with the method i.e. will the method tend to give higher or lower values, false positives or false negatives.

Users of the analytical methods must be sure to look at the detection limits and limits of quantification of the methods. When reporting results, these limits must be used and values reported with the correct number of significant digits.

When measurements are made, conditions at the workplace on the day the measurements were taken should be recorded. This will include

(a) environmental conditions such as temperature, pressure and humidity,
(b) time and date,
(c) production levels,
(d) ventilation levels and air circulation,
(e) location of the sample and a description of the area around the sample, and
(f) type of sample such as area or personal.

In addition, the person collecting the samples should state the reasons for the number and location of samples collected.

Use of a direct reading instrument

In some cases, a direct reading instrument may be more appropriate for monitoring worker exposure, but there are no specified methods. An example of such a compound is hydrogen sulphide.

If an employer uses a direct-reading instrument to measure exposure to a substance, the employer must ensure that the instrument is used, calibrated and maintained according to the manufacturer’s specifications. This means that the employer must ensure that

(a) factory calibrations are done according to the manufacturer’s recommendations,
(b) the instrument should be field calibrated on a daily basis,
(c) workers need to be trained in the proper operation and field calibration of the instrument,
(d) the instrument is used properly, and
(e) someone is responsible for tracking the instrument and making sure that it is properly maintained.

The OHS Code requires that the person who conducts airborne exposure measurements be competent to do so. This means that the person must have specific training and experience in this area. Examples of persons who may have suitable qualifications include Certified Industrial Hygienists and Registered Occupational Hygienists, as well as other professionals with training in the areas of occupational health and safety.

NIOSH Method 7400

NIOSH Method 7400 (Asbestos and Other Fibres by PCM) provides rules for counting fibres to determine the fibre concentration in a sample. Only fibres meeting the criteria specified in the definition of “fibre” may be counted (see Part 1).

When using NIOSH Method 7400 (Asbestos and Other Fibres by PCM), the limit of detection is approximately 2,700 fibres per filter and the range is 100 to 1,300 fibres per square millimetre of filter area. Results from this method, in fibres per cubic centimetre, must be reported to two decimal places and take significant digits into account e.g. 0.01, not 0.014.

For more information

NIOSH Manual of Analytical Methods (NMAM)
4th edition