Evaluation of a mathematical model for estimating solvent exposures in the workplace

In the context of risk management or occupational exposure assessment, the need often arises to estimate occupational exposures to airborne chemicals. This has traditionally been accomplished by means of air monitoring, however if sufficient information on chemical use plus the physical and environmental factors is available, mathematical models can be used as a means of estimating exposures. Model evaluation, a series of steps through which a model developer or user assesses a model's performance for selected situations,1 is an important means to understanding the uncertainty associated with a particular model's outcome and to refine the exposure assessment process. This work evaluated the performance of the near field-far field (NF-FF) mathematical model over a range of conditions by comparing predictions made using the model with measured airborne solvent concentrations obtained from two different process evaluations. The first process (Process #1) evaluated the application of a penetrating solvent to an iron-body gate valve under three different environmental test conditions. The second process (Process #2) was evaluated over a consecutive three-day period during the use of a solvent parts washer for cleaning metal parts. Mean concentration estimates obtained from the modeling process were within a multiplicative range of zero to 1.6 times the arithmetic mean of the actual air sample results from both process evaluations. The general agreement between the predicted and measured concentrations suggests that the construct presented herein sufficiently describes the environmental conditions under which the study was performed. The data provided valuable insight on how the model can predict room concentrations under a range of varied parameters.