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EXPERIENCE IN INDUSTRIAL EXPOSURE CONTROL

Industrial hygiene, as we think of it today, began in The Dow Chemical Company in the late 1930's. The technology we used in the beginning was crude by today's standards, but nevertheless the efforts were useful in helping to assess the degree of exposure of workmen. These data were used very early to correlate with medical findings and subjective responses of the people. In the early days, samples were taken by drawing known volumes of workroom air through absorbers containing an appropriate solvent or if particulates were involved, an impinger was used. Most of the equipment we used was handmade except for air pumps and wet test meters. Analyses were by wet chemical methods that left a lot to be desired, both from the qualitative as well as the quantitative points of view. As the years have passed, analytical specificity and sensitivity have gradually increased. At the present time, four methods generally are available for environmental monitoring of air for the presence of vinyl chloride. They are: 1. Gas chromatography, 2. Total hydrocarbon analyzer with flame ionization detector, 3. Combus tion-conductivity , and 4. Infrared spectrophotometry. The most desirable method will depend upon individual plant conditions, particularly interfering substances. Gas chromatography is very specific, but requires about 20 min/ sample. Flame ionization detectors have no specificity; they respond to all carbon-carbon or carbon-hydrogen bonds. However, they are portable and the measurement is instantaneous. The combustion-conductivity method responds to any material which burns to produce ions or any material which produces ions when dissolved in water. It responds rapidly. Infrared analyzers are very specific, respond quickly, and are portable. All of these techniques have adequate sensitivity, detecting concentrations of 1 ppm. The sensitivity achievable through the use of gas chromatography, in particular, can easily be extended to parts per billion. Personnel monitoring is achieved through use of absorption tubes filled with activated carbon. The absorbed chlorinated hydrocarbons are determined by gas chromatography after thermal release or extraction by carbon disulfide. A word of caution is in order here. Activated carbon from different sources and different batches from the same source vary in their capacity to absorb vinyl chloride and to release it. This makes it imperative that one check each batch before use. Another method' that has not been much used for personnel monitoring involves breath analysis. This method was researched some years ago and the data obtained show that there is a direct relationship between the total exposure and the concentration in the expired air at the end of the workday. This method can be very specific and if workmen will cooperate, it can be a very useful tool. At Dow, most of our environmental monitoring has been with combustion-