Comparison of exposure measurements to near field–far field modeled results for benzene and base solvents during a cleaning process using plain or 0.1% benzene spiked toluene and xylene

Abstract

It has been reported that the presence of ≤0.1% benzene in base solvents often used for cleaning is likely to result in exposure concentrations above the current OSHA PEL. This prediction was based upon calculations that depend largely on the concentration of benzene assumed to be present in a solvent mixture. Measurements of exposure during work simulations and more comprehensive modeling studies show that many factors other than the benzene content of the bulk solvent influence personal and area vapor concentrations. This study examines benzene exposure due to trace amounts of benzene in solvents available recently, and whether exposure in excess of the OSHA benzene standard occurs when 10 and 50 mL of base solvents containing up to 0.1% benzene are used during a manual cleaning process in a poorly ventilated room. Breathing zone (BZ) concentrations were measured for benzene, toluene and xylene during repetitions of a cleaning procedure using a small cloth to wipe a metal paint tray with 10 and 50 mL of consumer-grade toluene and xylene alone and toluene spiked with 0.1% benzene. Air samples were collected in the breathing zone (BZ) for 15 min to determine the short-term exposure. Separate 2 hr samples were collected in the BZ and general area to obtain time-weighted average (TWA) exposure concentrations. All samples were analyzed with a GC–FID utilizing NIOSH Method 1501. A near field–far field (NF–FF) model was used in conjunction with Monte Carlo simulation to predict airborne benzene, toluene, and xylene concentrations and to quantify uncertainty in the input parameters of the model. Variables including solvent evaporation time and air movement around the worker during the work activity were analyzed over a range of possible values. The result after 105 iterations of Monte Carlo simulation was a range of possible outcomes and the likelihood that each would occur; these outcomes are compared to the measured airborne concentrations. Cleaning the metal pan with 10–50 mL of toluene or xylene with or without 0.1% benzene did not result in benzene exposures in excess of either the OSHA PEL 8-hr TWA (1.0 ppm) or action level (0.5 ppm). The ratio of predicted or modeled to measured benzene concentration ranged from 0.42 to 2.1. The ratio of predicted or modeled to measured xylene and toluene concentration ranged from 0.92 to 3.7. Application of the NF–FF model under the conditions studied indicates a reasonable degree of reliability in forecasting airborne solvent concentrations under the conditions studied.