Surveillance and Control of Workplace Exposures in New Zealand: Report to the Minister of Labour
Data Collection Methods for
Workplaces can be surveyed to provide information on exposures of interest. These surveys can involve:
- observing the workplace and the workforce
- taking measurements of personal or area exposures
- developing questionnaires for workers or managers that are delivered by mail, telephone or person-to-person interview
- auditing the presence of particular exposures or control measures.
The resulting information may be qualitative or quantitative.
For example, a survey of solvent use was conducted in a light industrial area in Sydney in the 1990s. Researchers sent a questionnaire to businesses then validated the responses by visiting a sample of the businesses and taking actual measurements.
A similar approach focuses on the worker or the manager rather than the workplace. For example, questionnaires of workers and managers have been used to gather information on exposure to environmental tobacco smoke, and on the presence of workplace smoking bans (a control measure)[7, 8, 9].
The most extensive surveys for exposure surveillance were conducted in the United States by the National Institute of Occupational Safety and Health (NIOSH) in the 1970s and the 1980s, and a third major survey has been proposed. The type and extent of information that can be collected is illustrated in the NIOSH survey goals, which are to:
- estimate the total number of workers exposed to a wide range of specific hazards and the number exposed at varying qualitative levels of exposure
- describe the distribution of hazards with regard to occupation, industry, geography and worker demographics
- describe the nature and extent of hazard controls for reducing worker exposures
- describe the nature and extent of specific occupational safety and health programme components
- identify previously unrecognised groups at risk from known hazards
- identify new and emerging hazards (by comparing data from previous surveys and future surveys).
Personal monitoring is used to obtain information on an individual’s exposure to physical and particularly chemical hazards. Depending on the sampling frequency and the standardisation of the approach, exposure data can be obtained through ad-hoc (grab samples) and continuous monitoring of the exposures of interest.
For many exposures, the risk of the outcome’s occurrence, or the outcome’s severity, is directly related to cumulative exposure over a defined period of time. Valid exposure surveillance requires an ongoing assessment of the cumulative exposure, for example, ionising radiation. While this can be relatively difficult and resource intensive, it may be the only appropriate method, for example, for chemical exposure in agricultural workers.
An example of monitoring applied to ergonomic exposures involves using log books or electronic methods to track long-distance truck drivers’ time while driving, or time without a proper rest break.
Biological monitoring has an uncertain place in exposure surveillance. Strictly speaking, it meets the definition of exposure surveillance as it relates directly to occupational exposures.
Biological monitoring (for example, of blood lead) can provide useful information on the qualitative aspects of exposure. It contrasts with the external exposure measurements that typically form the basis of exposure surveillance, which are used in an attempt to understand the likely internal dose a typical worker will receive. These external exposure measures, whether environmental or personal, are really used as surrogate measures of the internal dose for an individual worker – so it can be argued that biological monitoring provides a better exposure estimate, as it is based on the presence of the substance in body fluid or tissue.
Biological effect monitoring (for example, monitoring red cell cholinesterase in pesticide-exposed workers) is somewhat different, in that it measures not the amount absorbed, but the biological consequences of that absorption. If the measured consequences are not themselves important, and precede the development of more serious consequences, it might be reasonable to use biological effect monitoring in an exposure surveillance programme. However, exposure surveillance aims to identify problem exposures before they occur, while biological effect monitoring measures the effects of exposures after they have occurred.