The sampling strategy selected depends on the goal of the sampling program, whether it is to ascertain compliance, provide data for research, or investigate a particular workplace problem. The strategy may seek to evaluate exposures of all workers or a representative worker. Sampling may be conducted to develop an exposure profile (e.g. full shift sampling over several consecutive days), examine the same job on different shifts, or characterize the exposure associated with a specific task. Some strategies evaluate concentrations at the source and extrapolate these results in order to estimate worker exposure. Alternatively, sampling might be conducted to determine the source of exposure where potential “problem areas” have been identified through biological monitoring but where the source of exposure has not been identified.
The development of a sampling protocol which allows hygienists to evaluate exposure to Nicontaining aerosols relative to occupational exposure limits has recently been completed (Rappaport et al., 1995; Lyles and Kupper, 1996). This protocol explicitly recognizes both within- and between-worker sources of exposure variability. Thus, overexposure is defined as the probability that a randomly selected worker would have a mean exposure above the exposure limit, for a particular time period. In addition, this protocol provides guidelines that would allow for the collection of solid and reliable data for future epidemiological studies.
Since operating conditions and individual methods of work can vary enormously, exposure monitoring of the workplace tends to be an inexact science. It is therefore important that the sampling strategy be flexibly designed to account for differences in worker and job variability and to obtain statistically valid results. This may mean that different sampling strategies should be employed in different areas of a plant. Other sources of information on sampling strategies include the aforementioned HSE in the U.K. and OSHA in the U.S., as well as the U.S. National Institute for Occupational Safety and Health (NIOSH).