A comparison study using a mathematical model and actual exposure monitoring for estimating solvent exposures during the disassembly of metal parts

The objective of this research was to compare the airborne solvent concentrations measured during the disassembly of solvent-coated metal parts with concentrations predicted by a mathematical model. The study involved three test simulations where cyclohexane, used as a penetrating solvent, was squirted onto a gate valve while the valve was subsequently disassembled. Three test simulations were performed to evaluate the effect of varying the speed of random air movement in the work area. For statistical considerations, six replicate solvent application trials were conducted for each simulation. Area and personal air samples were collected during the trials performed under each test simulation. Cyclohexane was applied to the valve at a consistent rate to obtain, to the greatest extent possible, a constant generation rate of solvent vapors. The Near Field-Far Field (NF-FF) model, applied using a constant solvent generation rate, was selected to predict the solvent vapor concentrations, and Monte Carlo analysis was used to quantify uncertainty in the input parameters of the model. Solvent concentration predictions obtained from the modeling process were within a multiplicative factor of 0.1 to 1.5 of the arithmetic mean of the actual air sample results for all three NF and FF conditions in each simulation. Application of the NF-FF model under the conditions described suggests there is a reasonable degree of reliability in forecasting airborne contaminant levels in the workplace environment. Given the limited resources faced today by many industrial hygienists, exposure modeling can serve as a valuable tool for generating the information needed to make informed decisions about employee exposure.