Sampling Guide for Air Contaminants in the Workplace - Irsst

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16 IRSST – Sampling Guide for Air Contaminants in the Workplace Figure 8- Example of excursion limit being exceeded with total time Figure 9- Example of excursion limit being exceeded by increase in concentration
IRSST – Sampling Guide for Air Contaminants in the Workplace 17 Part 2: Sampling equipment and techniques Introduction Once the measurement strategy for the chemical substances or biological agents in the workplace has been chosen, measuring equipment, techniques and methods for meeting the objective must be selected. Measurements can be direct, using portable instruments, or indirect, by sampling on a collecting medium and subsequent laboratory analysis. These direct or indirect techniques are described briefly in relation to the type of contaminant: gases and vapours, aerosols (liquids, dusts and fumes), and microorganisms. The list of equipment required for sampling or analysis is presented in Part 3. Other sections complete this part of the guide by providing information about process samples and sampling using pumps. 2.1 Concentration units for PEVs in the ROHS (ppm and mg/m³) The objective in using sampling equipment and techniques is to compare the concentration measurement results for an air contaminant to a reference value, mainly the PEVs in the ROHS. It is therefore important that the result of a measurement, whether expressed in ppm, mg/m 3 or in fibre/cm 3 , be comparable to the value of the PEV in the ROHS and be consistent with the definition of the units. For this, the definitions in the Definitions and Notes section of Schedule I of the ROHS are: "mg/m³: milligram per cubic meter (milligram of substance per cubic meter of air) ppm: parts per million (parts of gas or vapour per million parts of airborne contaminants per volume measured at 25°C and 101.3 kPa)." Consequently, one must conclude that the PEV values expressed in ppm are established for specific conditions of temperature and pressure while the PEV values when expressed in mg/m³ or in fibres/cm³ in the ROHS are invariable in relation to environmental conditions. This reasoning is based on two premises described in greater detail by Stephenson et al. (9), and by the ACGIH ® in 2012 (10): • The volume of air breathed in by a worker during his work day is not significantly different in relation to moderate variations in the ambient conditions of temperature and pressure; • Absorption of a gas or vapour is related to the partial pressure of the substance involved (11). This approach is also used by other organizations proposing reference values, such as OSHA's Permissible Exposure Limits (PELs) (12), the ACGIH's ® Threshold Limit Values (TLVs ® ) (10), and NIOSH's Recommended Exposure Limits (RELs) (13). The aim of this approach is to limit the quantity of contaminant that can be inhaled by a worker, and is therefore similar to a permissible dose approach. It is important to emphasize that some countries such as Belgium (14) and Australia (15) have PEVs based on a permissible concentration approach. The reader must therefore be careful when comparing the literature from different countries because the manner in which compliance with a standard is verified may be different and lead to different conclusions. To expose a worker, inhaling a certain volume of air for a certain period of time at a given dose and under different conditions, the PEVs in ppm must be adjusted in relation to the molar volume under the conditions of the site where the worker is located, or as a corollary, the concentrations in ppm for conditions other than NTP (normal temperature and pressure) must be corrected to "ppm at NTP" units before comparing them to the PEV expressed in ppm. In Québec, for the very great majority of workplaces, the molar fraction that compares the molar volume under certain conditions to the molar volume at NTP (24.45 L) is close to unity. In this case, the permitted ppm concentrations will be practically equivalent to those at NTP. However, for extreme and rather rare conditions (for example for depth work in mines), the molar fraction can differ significantly from unity. The following guidelines must be applied to verify compliance with PEVs:
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Sampling Guide for Air Contaminants in the Workplace - Irsst

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