Abstract
Results of further studies on the use of small carbon-filled glass tubes, referred to as respirator carbon tubes (RCTs), for predicting the service lives of organic-vapor respirator cartridges, are presented. Organic vapors are drawn through the RCT using a personal sampling pump until breakthrough is detected. This breakthrough time is then used in conjunction with a bed-residence adsorption model to predict the breakthrough time of a cartridge containing carbon identical to that in the RCT. Previous work demonstrated that accurate prediction of cartridge breakthrough time was possible for exposure to carbon tetrachloride in dry air. This report examines the effects of relative humidity (RH) and prehumidification of the RCT and cartridge carbon beds on the predictive accuracy of the method. The effect of varying the flow rate through the RCT is also examined. The RCT method predicted cartridge breakthrough times to an accuracy of ±9% at the 95% confidence level for moderate and high humidity conditions and to an accuracy of ±20% for prehumidified carbon beds. Flow rate had no effect on the performance of the bed-residence model over a range of values corresponding to breathing rates typical of respirator users. Estimates of both the kinetic adsorption rate and kinetic adsorption capacity constants were statistically similar for cartridges and RCTs under all test conditions. A linear relationship was found between RHn and the inverse of the relative breakthrough time normalized to 50% RH, consistent with results reported by other researchers.