It is the responsibility every employer to ensure employee exposures to chemical hazards be maintained as low as possible, and at minimum, below Occupational Exposure Limits as defined by local law through the application of appropriate controls. In order to confirm whether exposures are exceeding these limits, it is necessary to measure or accurately estimate potential exposures. This is achieved by conducting a formal exposure assessment.

The main objectives of an exposure assessment is to determine:

  1. The hazards to which employees are exposed (i.e. which chemicals)
  2. The route(s) by which the employee may be exposed to these chemicals (i.e. inhalation, skin contact)
  3. The amount of chemicals employees may be exposed to (either through measurement or professional judgement)
  4. The types of controls that may be needed to protect the employee from harmful exposure

Although it is not possible to summarize a comprehensive exposure assessment strategy here, the following guidance is provided to answer general questions regarding the process for measuring the concentrations of airborne chemicals.

What to Sample For?

To determine which substances employees are potentially exposed to, you will need to review the SDS for each of the chemicals they use or that are used in their work areas. The chemical composition section of the SDS will tell you which chemicals may be present in the air. This also applies for dermal or skin exposure.

In the below example SDS, workers would potentially be exposed to methyl ethyl ketone and acetone.

How to Sample?

The type of sampling and method to be used will be dependent on the type of chemical being measured. There is often more than one method for sampling, and local authorities may require specific methodologies be used for regulatory compliance. Common methods of sampling include the use of passive sampling badges or personal sampling vacuum pumps that draw air through a filter or sampling tube which collect the specific airborne contaminant. Samples are collected for varying times based on the objective of the sampling (i.e. TWA or STEL Exposure Limits) and should be collected in the breathing zone of the representative worker as shown below:

How Many Samples to Collect?

The number of measurements required to accurately determine whether workers are overexposed will depend upon several variables including:

  • Number of workers exposed
  • Type of exposure
  • Statistical significance required

Some general guidelines include:

  • Generally, a single sample is not sufficient to determine compliance with an exposure limit
  • 1 in 10 similarly exposed workers (10%) with minimum of 3 and spread of results < 25% will provide reasonable approximation of exposure
  • 6 to 10 samples of similarly exposed workers will provide a reasonable approximation of the exposure profile


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