Sampling Guide for Air Contaminants in the Workplace - Irsst

22 IRSST – Sampling Guide for Air Contaminants in the Workplace
selected in relation to the indications given in the tables in Part 3 of this Guide and the sampling strategy
chosen.
All the information collected during sampling must be noted. The tubes are sealed using plastic plugs and are
stored in a freezer at -4°C until shipment to the laboratory. The storage location must be solvent-free (without
bulk samples or sampling equipment such as jars containing toluene). Shipment to the laboratory in ice must
take place as soon as possible to avoid a loss of adsorbed product.
2.2.3.2 Passive dosimeters
Sampling with a passive dosimeter involves the diffusion process.
It is a phenomenon by which a solute in a fluid (for example
toluene in air) goes from a concentrated region to a less
concentrated region. The concentration gradient is ensured by the
collection of molecules of the substance by an adsorbent located at
the bottom of the dosimeter.
The sampling rate for a solvent is expressed in mL/min. This parameter is both a function of the substance
and the geometric characteristics of the dosimeter. Each solvent therefore has its own specific sampling rate.
Contrary to the use of a pump, contaminants are not collected at the same rate. A constant is used to calculate
the results and it represents the time necessary for the dosimeter to sample a substance contained in one litre
of air. Similar to adsorbent tubes, passive dosimeters can be affected by environmental conditions such as
humidity, temperature and the co-adsorption of different molecules present in a work environment. For
example, a temperature difference of 10°C results in a correction of 1.6%.
Two types of passive dosimeters are available at the IRSST: the 3M monitor for collecting several solvents,
and the SKC UMEX dosimeter for measuring formaldehyde.
The 3M monitor can collect certain solvents. For a list of them, consult the user's guide 2 (in French only).
Furthermore, a computer-based tool 3 ( in French only) is available for calculating the concentration in mg/m 3
equivalent to a non-detected result for these 31 substances.
After sampling, it is important that the dosimeter be hermetically sealed once the diffusion membrane has
been removed. For 3M monitors, the two openings must be tightly sealed. UMEX samplers have a sliding
cover that must be placed over the sampling zone. Subsequently, the plastic end supplied with the 3M monitor
will be used during the analysis; it must be included in the dosimeter box.
Similar to adsorbent tubes, dosimeters are kept in a freezer at -4°C until shipment to the laboratory. The
storage location must be solvent-free (without bulk samples or sampling equipment such as jars containing
toluene). Shipment to the laboratory in ice must take place as soon as possible to avoid a loss of adsorbed
product.
2.2.3.3 Impingers
Impingers are used for sampling a few inorganic acids and organic compounds. The collecting
solution in the impinger is then analyzed to quantify directly the chemical being sampled, or to
quantify a substance resulting from a chemical reaction between the substance and the
collecting solution. Impingers are made of glass or polyethylene; spill-resistant impingers,
inserted into holsters, are also available for personal sampling.
Two types of impingers are used: the midget impinger and the glass fritted tip impinger. The
midget impinger is used to collect contaminants that are very soluble in the collecting solution
or that react very rapidly in it. The glass fritted tip impinger is used for more efficient
collection of compounds that are not very soluble in the collecting solution. In fact, since
fritted glass forms currents of fine and dispersed bubbles, it increases the contact surface
2 http://www.irsst.qc.ca/files/documents/PubIRSST/guide3M.pdf
3 http://www.irsst.qc.ca/files/documents/fr/Utilitaires/VMR-DOS.xls