Characteristics of peaks of inhalation exposure to organic solvents

Objectives: To determine which exposure metrics are sufficient to characterize 'peak' inhalation exposure to organic solvents (OS) during spraying operations. Methods: Personal exposure measurements (n = 27; duration 5-159 min) were collected during application of paints, primers, resins and glues in 15 companies. A MiniRAE Photolonization Detector measured OS concentrations every second. These readings were adjusted for OS composition, which was determined by charcoal tubes. A peak was defined as a period during which exposure exceeded the time-weighted average (TWA) exposure. Five second and 1 and 15 min moving average times were considered in defining a peak. The number of peaks per hour, the duration of a peak, the maximum concentration within a peak, the average concentration within a peak, the ratio between maximum and average concentration within a peak and the average time between two peaks were recorded for each sample. Data were analyzed using factor analysis on 13 variables for the 27 samples: TWA concentration of the task and the six peak characteristics based on the 5 s and 1 min moving averaging time. Results: There were three statistically independent sources of correlation among metrics of peak exposure, explaining 87% of the multiple correlation. The first factor reflected the intensity of peak exposure; it was also associated with the TWA. The second and third factors were related to measures of variability (in frequency and intensity) and duration of peaks, respectively. Conclusions: We present a method for describing peak profiles for inhalation exposure in terms of various distinguishable and independent parameters. Pending development of toxicologically justified peak exposure metrics, such investigations can be of value in identifying exposure metrics for which non-confounded risk estimates can be obtained in epidemiological studies.