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Monitoring hazardous substances


Laboratory personnel, even with the greatest of care and with ventilation systems in place can, under certain circumstances, be exposed to small amounts of chemicals such as formaldehyde, glutaraldehyde and xylene when they are at work. If these hazardous substances are not properly monitored and controlled, they may cause ill health if taken into the body through respiration or skin absorption.

With employer responsibility towards employee health and welfare becoming increasingly topical, employers should be aware of their legal responsibilities. Governments have generally set out legal standards and workplace exposure limits for hazardous substances at work and require employers to carry out suitable and sufficient risk assessments including the monitoring of the exposure levels.

Statutory requirements

There are many chemicals listed as toxic substances and these must be controlled below safe legal limits. In the UK for instance, occupational exposure limits (OELs) are included in the Health and Safety Executive Publication EH40, which is updated annually. Under the regulations OELs are defined as workplace exposure limits (WELs) or concentrations of hazardous substances in the air averaged over a specified period of time called a time weighted average (TWA). Two time periods are used: long term (measured over 8 hours) and short term (15 minutes). Short-term exposure limits (STELs) are set to help prevent immediate effects of exposure to harmful substances.

In certain circumstances the exposure must be monitored to ensure that WELs are not exceeded and to check the effectiveness of any control measures put in place. Similar regulations apply in many countries although the actual limits themselves can vary.

Monitoring procedures

The frequency of sampling will depend on the factors considered by a risk assessment, including: the processes and substances present in the workplace, the control measures used, how they are tested and maintained and the concentration of the substance. Where monitoring is required for continuous processes or regular activities, it should be carried out at least once every 12 months, although for some specific substances and processes more frequent monitoring is required. Monitoring should also be carried out when a process changes significantly to ensure that control measures are still effective. For infrequent activities that take place at intervals exceeding 12 months, monitoring should be carried out during the activities concerned.

Where groups of employees are being exposed to similar risks to health, sampling may be carried out on a representative group basis. Exposure to mixtures requires careful assessment of health effects and the appropriateness of control standards as the effects to health can be complex.

Information recorded

For respiratory exposure, methods involving sampling within the breathing zone of the worker are most effective and provide a personal record of actual exposure that can be retained as part of an employee’s personnel records. A record should provide sufficient information to determine:

  • when the monitoring was done and what the results were;
  • what monitoring procedures were adopted, including the duration; and
  • the locations where samples were taken, the operations in progress at the time and, in the case of personal samples, the names of the individuals concerned.

The information should be readily retrievable, easy to interpret, and comparable to any other health records required.

Monitoring badge

The AirChek dosimeter badge from Leica Microsystems was developed as an inexpensive and unobtrusive device to monitor toxic chemicals such as formaldehyde, glutaraldehyde, xylene, toluene and isopropanol. The badge is simply clipped onto the work clothes at a point as close as possible to the breathing zone for the duration of the monitoring period. This will ensure that the TWA occupational exposure will be impregnated onto the badge ‘sensing’ material and the badge can then be returned for analysis.

Within a few days of the badge being returned, a laboratory test result will be forwarded to the employer providing a permanent and personal record of the individual’s exposure. The tests are carried out in accordance with UK Health & Safety Executive recommendations and requirements as well as those for OSHA and NIOSH in the US. The report itself gives clear, concise information that can be easily compared to the published WELs.

The dosimeter badges provide an accurate indication of an individual’s exposure throughout the duration of a working day (8 hours) or during a specific task (15 minutes) and a wide selection of badges is available to monitor a variety of chemical vapours.

Some recent court cases have resulted in employees being awarded substantial damages against their employer because the employer could not offer evidence that adequate precautions had been taken. Dosimeter badges can help to ensure that evidence is available and that the health of staff is protected.

For more information on dosimeter badges, request online at www.labcanada.com/rsc, October 2011 issue, reply card # 18.

This article appeared in the October 2011 issue of Lab Product News.