Theory and Rationale of Exposure Measurement
Authors: Lynch Jeremiah R. 
Published: August 2005

This chapter explains why workplace measurements of air contaminants are made, discusses the options available in terms of number, time, and location, and relates these options to the criteria that govern their selection and the consequences of various choices. In addition, this chapter discusses industrial hygiene exposure assessment methods in the broader context of exposure assessment as it is used outside the workplace

A person at work may be exposed to many potentially harmful agents for as long as a working lifetime, upward of 40 years in some cases. These agents occur singly and in mixtures, and their concentration varies with time. Exposure may occur continuously or at regular intervals or in altogether irregular spurts. The worker may inhale the agent or be exposed by skin contact or ingestion. As a result of these exposures and depending on the magnitude of the dose, some harmful effect may occur. All measurements in industrial hygiene ultimately relate to the dose received by the worker and the harm it might do.

Early investigators of the exposure of workers to toxic chemicals encountered obviously unhealthy conditions as evidenced by the existence of frank disease. Quantitative measurements of the work environment to estimate the dose received by the afflicted were not needed to establish cause‐and‐effect relationships and the need for exposure remediation measures. At the same time, the ability of these early industrial hygienists to make measurements was severely limited because convenient sampling equipment did not exist and analytical methods were insensitive. Consequently, few measurements were made, and much judgment was applied to maximize the representativeness of the measurements or even as a substitute for measurement.

Changes in working conditions, in technology, and in society have changed the old methods of measurement. It is now both necessary and possible to examine in far more detail the way in which workers are exposed to harmful chemicals. Personal sampling pumps permit collection of contaminants in the breathing zone of a mobile worker. Pump‐collector combinations are available for long and short sampling periods. Passive dosimeters, which do not require pumps, are available for a wide range of gases and vapors. Systems that do not require the continual attention of the sample taker permit the simultaneous collection of multiple samples. Data loggers can continuously record instrument readings in a form easily transferable to a computer. Automated sampling and analytical systems can collect data continuously. Sorbent‐gas chromatograph techniques permit the simultaneous sampling and analyses of mixtures and, when coupled with mass spectrometers, identify obscure unknowns. Sensitivities have improved to the degree that tens and hundreds of ubiquitous trace materials begin to be noticeable.

At the same time the demands placed on our information gathering systems are greater. Now we must not only answer the question, “Is exposure to this agent likely to harm anyone?” but provide data for many other purposes. Process operators want continuous assurance that contaminant levels are within normal bounds. Management information systems that issue status reports when queried require monitoring of data inputs. Data needs are so pervasive that there is a tendency to monitor without a clear idea of what the data will be used for or whether it will meet the need. An overall purpose of this chapter is to suggest the objectives that need to be considered in an analysis of the value of exposure measurement.