To comply with this requirement to reduce exposure so far as is reasonably practicable, employers will need to implement a programme of air monitoring to ensure that workers are not exposed to substances to an extent which exceeds the workplace exposure limit. This will be necessary unless the risk assessment shows the exposure is unlikely to ever exceed the limit.
Airborne concentrations of hazardous substances should be measured in all places of work where this is necessary to ensure the safety and health of workers against inhalation risks. Measurements of airborne contaminants are necessary if other techniques do not suffice to provide a valid estimate of the risk of exposure and to assess the existing control measures.
Because of variations in plant, process, work and other conditions it is difficult to draw conclusions about long-term exposure patterns on the basis of a single measurement of exposure at one point in time.
Exposure monitoring should be carried out on at least an annual basis depending on the risk identified from your initial assessments. The frequency will vary and should depend on how close the measured exposure is to the workplace exposure limit, significant or highly significant exposure scenarios should be measured more frequently.
A regular monitoring program is required for the following reasons:
to ensure that the health of the workers is efficiently protected;
to ensure that the preventive actions which have been taken are still effective;
to ensure that the levels, as measured previously, remain unchanged or fall;
to ensure that any changes made in manufacturing processes or work practices will not lead to an excessive exposure to hazardous substances;
to promote the implementation of more efficient preventive measures.
for insurance purposes
Employers must keep a record of monitoring carried out for at least 5 years, or for 40 years for personal exposures of identifiable employees.
What Is Personal Exposure Monitoring?
Personal monitoring should be used to evaluate the risk of exposure to the individual worker. Air samples should be collected in the workers breathing zone by means of personal samplers. Sampling should be carried out while the work activity is in operation.
Where concentrations vary from one work operation or phase to another, personal sampling should be done in such a manner that the averages and in any case the maximum, level of exposure of each individual worker can be determined.
Personal sampling should measure exposure, or allow assessment of exposure throughout the work shift. The exposure should be compared to legal exposure limit values, which are usually quoted for an eight-hour period or, for short-term limits, 15 minutes. The measurement may be continuous over the whole shift or intermittent, so long as this allows a valid calculation of the average exposure and where necessary is supplemented by short-term sampling during periods of peak emission.
Exposure profiles of particular jobs or occupational categories should be constructed from the air-sampling data of different operations and from the workers' exposure time in these jobs.
What Is Background (static) Monitoring?
If static monitoring is carried out it should only be used to determine the distribution of airborne substances throughout the general atmosphere of the working area and to identify problems and priorities. This form of sampling can not be used to compare exposures against legal exposure limits.
Static air samples should be taken:
close to sources of emission in order to evaluate concentrations or the standard of engineering controls;
at various places in the working area to assess the extent of the substances general distribution; and
from working areas which represent typical exposure.
How Many Staff Should be Monitored?
Taking one or a few samples on one day will not provide you with sufficient information on which to base conclusions about long-term exposures. In reality the number of samples that you can take is usually constrained by the resources available to you. You need to use your judgement when deciding on sample size, especially when small groups are concerned.
For worst-case monitoring, as a rule of thumb, at least one employee in five needs to be monitored from a properly selected similar exposure group (SEG), unless a smaller number can be justified.
What Is A Similar Exposure Group (SEG)?
A SEG is a group of workers whose exposure profile is similar enough to be characterised by a representative set of samples. Workers may be readily categorised by job task or job description, process, craft, exposure to a specific substance, or the control measures available to them. To form SEG's in your workplace look for workers who:
Perform similar types of tasks at a similar frequency.
Use the same materials or processes to complete tasks.
Perform their tasks using the same procedures.
Perform job tasks near the same emission source.
Depending on the substances being monitored, workers may fall into more than one SEG.