Industrial air monitoring – Worker exposure
Occupational exposure to hazardous chemicals
By their very nature, many industrial and manufacturing processes involve the use of hazardous volatile organic compounds (VOCs). In the absence of appropriate safety procedures or protective equipment, workers can suffer from negative health effects as a result.
As a consequence, since the early 1980s, monitoring personal exposure to toxic chemicals in the workplace has been a focus of study for the analytical community, and in many countries is now enshrined in workplace health & safety regulations.
However, personal exposure levels still frequently fall above safe limits in some developing countries. In addition, a deeper understanding of hazards posed by long-term low-level exposure to certain chemicals has led to the reduction of many limit levels. This has driven a need to monitor personal exposure at ever-lower concentrations.
What Markes can offer
Pumped and diffusive sampling onto sorbent tubes
|Thermal desorption vs. solvent extraction || |
Use of pumped sampling onto glass tubes packed with charcoal, followed by carbon disulfide (CS2) extraction and gas chromatography (GC) analysis, was developed as an air monitoring method for volatile organic compounds (VOCs) in the 1970s.
It is still used today for personal monitoring (and indeed is covered in standard methods such as EN 14662-2), but the laborious and hazardous sample preparation, together with its relatively low sensitivity, mean that it is increasingly being superseded by TD–GC methods (such as EN 14662-1).
For a more detailed comparison of thermal desorption and solvent extraction, see Application Note 046.
|Time-weighted-average monitoring || |
Time-weighted-average (TWA) monitoring is used to assess the average exposure of a worker to one or more chemicals over a specified period of time – usually a standard eight-hour shift.
This is conveniently carried out using diffusive or pumped sampling, but does mean that, for limited periods, a worker may be exposed to concentrations higher than the threshold limit value (TLV).
For this reason (and because differences in behaviour between individuals result in a wide range of exposures), best practice typically requires TWA values to be a fraction (e.g. one tenth) of the TLV, so that it can be safely assumed that no workers are being exposed to hazardous levels.
Workplace monitoring of personal exposure was one of the very first applications of thermal desorption, and used badge-type samplers. Today, samples are typically collected by pumped or diffusive (passive) collection of air onto sorbent tubes, according to any of a number of national and international standard methods (see Further information).
Sorbent tubes used for personal monitoring are typically attached to the upper part of the worker’s clothing (in order to be representative of the air breathed in), and air collected diffusively or using a pump.
- Diffusive (passive) sampling employs a single-bed sorbent tube with an end-cap to prevent ingress of larger particulates, clothing fibres, etc.
- Pumped sampling is easily achieved using a portable pump such as Markes’ ACTI-VOC, and, because more than one sorbent bed can be used, has the benefit of significantly extending the analyte range.
Whichever method is used, the samples collected onto sorbent tubes are analysed by thermal desorption (TD)–GC (for example, using Markes’ UNITY-xr or TD100-xr thermal desorbers), to obtain a time-weighted-average value. These are then assessed against threshold limit values (TLVs), sometimes called ‘occupational exposure limits’ (OELs), to check compliance.
Another method of assessing personal exposure is by biological monitoring. This involves measuring chemical concentrations in the blood, urine, or breath of workers, to provide a more accurate idea of the chemicals that are actually present in the body (whether ingested, absorbed through the skin, or inhaled). This is useful both for assessing exposure to chemicals in the workplace, and also more recently for disease diagnosis.
For occupational exposure monitoring, breath monitoring (for example using Markes’ Bio-VOC™), is less invasive than other techniques, and doesn’t require trained medical personnel. Results are typically interpreted in relative terms – for example, to make sure exposure levels don’t increase over time, or to identify if PPE is effective in protecting workers.
- Relevant methods for monitoring using sorbent tubes include:
ISO 16017 (Part 1), MDHS 72 and NIOSH 2549 for pumped monitoring.
ISO 16017 (Part 2) and MDHS 80 for diffusive monitoring.
ASTM D6196-3 for pumped and diffusive monitoring.
- For a listing of workplace limit levels, see Application Note 038.
- For a study into the correlation between VOC analysis using pumped sampling onto sorbent tubes and biological samples taken using Markes’ Bio-VOC, see: J. Caro and M. Gallego, Environmental and biological monitoring of volatile organic compounds in the workplace, Chemosphere, 2009, 77: 426–433.
- For a study describing the use of diffusive sampling and Markes’ UNITY thermal desorber to analyse hazardous compounds in a variety of (non-industrial) working environments, see: P. Bruno, M. Caselli, G. de Gennaro, S. Iacobellis and M. Tutino, Monitoring of volatile organic compounds in non-residential indoor environments, Indoor Air, 2008, 18: 250–256.