Sampling Guide for Air Contaminants in the Workplace - Irsst

24 IRSST – Sampling Guide for Air Contaminants in the Workplace
in solution. It should be emphasized that this process applies to aerosols as well as to gases and vapours.
2.2.3.6 Blank sample
For each sampling series, a blank must be provided. The recommended number of blanks is 10% of the total
number of samples. However, in the case of asbestos sampling, a minimum of two blanks must be provided or
10% of the total samples, whichever is greater. The blank undergoes the same procedures as the samples
(opening, sealing and transport) except that it is not used for sampling. It must be from the same lot as the
samples.
2.3 Aerosols
2.3.1 General definitions
An aerosol can be defined as a suspension of solid or liquid particles in a gaseous medium. These particles
can be formed by the mechanical fractionation of a starting material (wood, ore, etc.), by condensation, or by
chemical reaction between gaseous pollutants. Fumes are aerosols that result from the condensation of metal
vapours or the incomplete combustion of organic compounds (welding fumes, soot, etc.).
The substances making up the particles of an aerosol can enter the body directly by inhalation, but also
indirectly by ingestion or skin absorption by means of several mechanisms, such as dissolution. In addition,
these particles can act on the body in many ways, producing allergenic or irritant effects. The potential health
risks of aerosols therefore depend on the toxicity of their particles, their size, their concentration, as well as
their mechanical, chemical or biological properties.
2.3.1.1 Solid aerosols (dusts and fumes)
Dusts can be classified into two general groups: dusts with adverse health effects and dusts with no known
toxic effects (nuisance dusts or particulates not otherwise classified). The latter are not biologically inert. They
can interfere with the mechanisms of clearing of airways (10). According to the ROHS, a TWAEV of
10 mg/m³ (total dust) applies to these "nuisance dusts." The ACGIH ® recommends two values for these dusts:
3 mg/m³ (respirable fraction) and 10 mg/m 3 (inhalable fraction) to prevent these pulmonary effects.
Dusts with adverse effects are divided into fibrogenic, toxic and carcinogenic dusts. These dusts undergo
specific sampling and analysis due to the nature of the standards governing them.
Welding fumes cannot be easily classified. Their composition depends on the materials to be welded, the
electrodes, and the processes used. According to the ROHS, a TWAEV of 5 mg/m³ applies if there are no
toxic components present in the welding rod, in the metals to be welded, or in their coatings. When welding
fumes contain components with a toxicity greater than that of iron oxide (in terms of TWAEV), a complete
analysis must be done on the toxic components likely to be present, applying the standards specific to each of
these products individually.
2.3.1.2 Liquid aerosols
Aerosols whose particles are liquid rather than solid can be present in a work environment. For example, oils
or acids that are not very volatile can be found suspended in the air, forming a mist. They are collected on a
filtering membrane by means of a sampling pump. Occasionally, this filter must be placed as quickly as
possible in a stabilizing solution, as is the case for isocyanate oligomers.
2.3.2 Experimental definitions
The locations in the respiratory tract where aerosol particles are deposited generally depend on the aerosol's
aerodynamic diameter. The health effects of particles that enter the body by inhalation therefore depend
mainly on this parameter, but also on the material of which they are made, the amount of this material, and the
characteristics of the respiratory tract where they are deposited. After several years of debate, different
committees and institutions have agreed about the quantification of an aerosol's potential health risks by
establishing three fractions for evaluating the quantity of material likely to be deposited in specific regions of