Workplace monitoring or exposure assessment

In some cases, the anticipation, recognition and evaluation of a health hazard may need environmental (air) monitoring to establish:

• the substance(s) posing the risk;
• the degree of risk (or severity); and
• who could be at risk of injury (employees and possibly others).

Air monitoring involves the use of a suitable occupational hygiene technique to estimate the amount of employees’ exposure to a hazard. In the case of hazardous substances (e.g. gases, vapours, particles, fumes), the measurement of the airborne contaminant will normally involve collecting a sample of air in the breathing zone using personal equipment. However, in some situations air may be sampled using static (fixed) samples.

Air sampling techniques alone may not give a reliable estimate of exposure where substances can be absorbed through skin or by ingestion. In such cases, biological monitoring should be considered to complement the air monitoring.

Air monitoring often requires special equipment and expertise to fully evaluate the potential risks associated with a particular process. A competent occupational hygienist will be able to provide both of these.

Sampling techniques

Many different types of sampling methods are available for estimating employees’ exposure levels. When sampling, it is important to use a technique which is suitable and recognised by the Health and Safety Executive (HSE). For example, the HSE has published a series of methods called the Methods for the Determination of Hazardous Substances (MDHS) for dealing with airborne pollutants.

Monitoring of exposure levels is usually necessary in the following situations:

• when measurements are needed to demonstrate that occupational exposure limits are not exceeded;
• where failure of control measures could result in serious health effects;
• as an additional check on the effectiveness of controls provided (e.g. ventilation systems); and
• where there are changes in work conditions or practices that could result in control no longer being maintained.

When you have made the decision to monitor exposure, you should establish a suitable programme (sampling strategy) to ensure that the data to be collected is reliable and representative of daily tasks conducted by your employees. The sampling programme should be developed in consultation with individuals with expertise in exposure measurement.

The sampling programme should address the following questions:

• the reason for monitoring exposure;
• who will conduct the monitoring;
• what is to be monitored;
• the measuring and sampling method to be used;
• employees whose exposure is to be monitored;
• the location of the sampler, e.g. personal or static (fixed);
• duration of monitoring, e.g. whole shift or particular tasks;
• activities to be monitored; and
• how the results will be interpreted.

You as the employer should ensure that whoever carries out the monitoring of exposure is competent. In most cases, this will be a qualified occupational hygienist.

The exposure data collected may be used to identify employees at risk or to select suitable controls (e.g. personal protective equipment, engineering controls). Therefore, it is essential that the data collected is reliable and reflects actual work practices and work conditions.