Short-Duration Characterization of Source Emissions for Use in Predictive Software Models to Assess Worker Exposure: A Note of Caution

This article reports on use of advanced Near-Field—Far-Field software for assessing short- versus long-duration data obtained minute-by-minute at two distances from a small source of an evaporating solvent located in an isolated subsurface structure (a type of confined space) accessed through a manhole containing one or two opening(s). The software uses this data to predict worker exposure to airborne chemical substances. Initial flash-off of volatile components was readily visible in graphs prepared from some tests and especially so in initial output from the calibration utility contained in the modelling software. The calibration utility orients the mathematics of the software to measured data. The calibration utility indicated constant magnitude from longer-duration emissions consistent with constant composition. Source characterization of emissions from solvents containing multiple ingredients and constant initial mass deserves careful consideration because initial emissions may not represent overall behavior. This situation indicates the potential to bias predictions of worker and other types of exposure utilizing the same mathematics. This is especially the case during source characterization using measurements of short duration. This study advocates for further investigation to develop guidelines for source characterization during use of modelling software that minimize the potential for error in exposure assessment.