Sampling Guide for Air Contaminants in the Workplace - Irsst

IRSST – Sampling Guide for Air Contaminants in the Workplace 33
2.7 Description of the sampling systems
Evaluation of an air contaminant requires a system for collecting a given volume of air, a collecting medium,
and an analytical method. It generally includes the following components: pump, tube, cassette-filter unit,
cyclone, etc. Calibration of a sampling system, meaning the adjustment of the air flow through it requires the
use of a flow meter and will depend on the pump and ambient conditions on the sampling site and calibration
site. The following sections describe the flow meters and pumps most commonly used in industrial hygiene
and discuss the effects of temperature and pressure on their mechanism and on their calibration.
2.7.1 Sampling pumps
Pumps are the devices most commonly used in industrial hygiene for sampling a known volume of air for the
purpose of determining the concentration of the contaminants present. The pumps most used are high flow,
low flow, and very high flow pumps.
2.7.1.1 Personal pumps
Personal sampling pumps are classified in two categories: pumps with low flow rates which generally operate
in the 1 to 500 mL/min range, and high-flow pumps which operate from 1.0 to 5.0 L/min. They operate
independently due to rechargeable batteries, thus ensuring at least 8 consecutive hours of sampling during the
work period.
Use of a pump assumes periodic verification of the flow rate in order to ensure that it remains constant.
Generally, the flow control mechanisms on some pumps are designed to maintain this constant flow despite
the drop in battery voltage and normal clogging of the collecting medium. Flow checks, at least at the start
and end of sampling, are used to determine the average flow and, if need be, to detect poor functioning of the
pump. The difference between these flow measurements must be less than 5% (21).
Utilization temperatures of the main pumps
Manufacturers generally mention a temperature range in which pumps can be used with complete confidence:
Table 5- Temperature range for the use of some personal pumps
2.7.1.2 Very high flow pumps
Manufacturer and model
GilAir, GilAir 5
Gilian HFS 113
SKC PCxr-7 SKC PCxr-8
Interval
-20°C to 45°C
Very high flow pumps are used for sampling in the general ambient environment when a large amount of
material is to be collected for analysis or when a large sampling volume is needed to collect sufficient
contaminant in a context in which the concentrations in the air are very low.
Microorganism samplers and cotton elutriators use pumps able to operate at high air flow rates. The necessary
air flow rate is 28.3 L/min for the Andersen ® sampler, and 7.4 L/min for the cotton elutriator. For the cotton
elutriator, a critical orifice is used to maintain a constant flow.
2.7.2 Flow meters and flow measurement
The precise determination of the flow rate is a key aspect of occupational hygiene sampling. It is measured
using a flow meter. There are several types of flow meters, which use different operating principles. Their
precision, variable from one model to another, is found in the manufacturer's specifications. The four most
common models are the following:
• Bubble flow meter (conventional burette or electronic version), e.g., Gilibrator;
• Piston flow meter, e.g., Drycal;