Evaluation of a sampling method for the measurement of occupational exposures to ethylene

In an effort to assess the scope of occupational exposures to ethylene, the Olefins Panel of the American Chemistry Council designed and conducted a research project to develop and apply a sampling and analytical method to measure workplace exposure. The method uses packed Carbosieve S-III thermal desorption tubes (Supelco, Bellefonte, Pa.) with a low sample collection flow rate. The tubes were analyzed by thermal desorption gas chromatography. The methodology was validated for both 15-min short-term exposure limit and 8-hr time-weighted average (TWA) samples in the laboratory prior to the field study. The effects of varying sampling flow rate (2, 5, 10, and 25 mL/min) and temperature (25 and 35 degrees C) on sample breakthrough time were assessed at a constant relative humidity of 90%. Breakthrough times decreased linearly with sampling flow rate and temperature. The optimal sampling flow rate and temperature at 90% relative humidity were 2 mL/ min and 25 degrees C. A full-shift TWA sample can be collected using two tubes for up to 4 hours each at a flow rate of 2 mL/min, while a STEL sample can be collected at 25 mL/min flow rate. The evaluation indicated samples can be stored under ambient conditions for a period up to 14 days without significant sample loss. Field measurements were performed at 14 petrochemical facilities within North America. The mean 8-hour TWA ethylene concentration (71 sample pairs) was 2.6 ppm (range: <0.05 to 2100 ppm). Significant ethylene concentrations were observed for only two of the 73 TWA sample pairs. Each of these two samples was obtained from the same facility, and only one tube of the sample pairs showed a high ethylene concentration (3200 ppm and 4200 ppm, respectively) for the 1600 ppm and 2100 ppm TWA sample. The first tube of each of these two sample pairs showed no detectable levels. Further, 69 of 71 sample pairs had TWA concentrations below 13 ppm. The mean of 26 short-term exposure limit samples was 16 ppm (range: <0.05 to 63 ppm), with only one sample above 50 ppm. The results of this study indicate that airborne concentrations of ethylene can be effectively measured using Carbosieve S-III packed thermal desorption tubes under typical workplace conditions.