The accuracy of three passive dosimeters as compared to charcoal tubes

Abstract

Passive monitors have become increasingly popular for monitoring airborne contaminants because they are lightweight, inexpensive, and easy to use. A passive or diffusive sampler is a device which is capable of taking samples of gas or vapor pollutants from the atmosphere at a rate controlled by a physical process, such as diffusion through a static air layer, but which does not involve the active movement of air through a sampler (1). These dosimeters, although well within the National Institute of Occupational Safety and Health (NIOSH) accuracy standard of +/-25% at the 95% confidence level, are thought by some to yield inferior results to standard pump and sorbent tube samplers. Previous research on passive dosimeters dealt primarily with the accuracy of the 3M 3500 Organic Vapor Monitor (OVM). It has been found to be well within the NIOSH accuracy standard of +/-25% at the 95% confidence level (1-12). However, there are several new brands of passive dosimeters on the market today that may prove to be more precise than the 3M 3500 OVM when comparing the results to charcoal tubes. This project compared the accuracy of three different brands of passive dosimeters: the 3M 3500 OVM, the SKC Series 575-001, and the Gilian Traceair OVM-2 to charcoal tubes. The four devices were placed side-by-side on workers at a Gulf Coast oil refinery and were worn for approximate eight hour shifts. This experiment was replicated twenty-four times for a total of twenty-five groups of samples. The badges and tubes were sent to an American Industrial Hygiene Association (AIHA) accredited laboratory and analyzed for benzene, toluene, xylene, normal hexane (n-hexane), and total organic vapors (TOV). A statistical analysis of the reported data was conducted to determine if there were significant differences between the passive badges and the charcoal tube for the five analytes of concern. Scatter plots were utilized to estimate how closely the results of the passive monitors mirrored the results of the charcoal tube. These analyses show that passive badges tend to yield higher outcomes than the charcoal tube for the analytes studied here. More extensive research is recommended in this area to further investigate the accuracy of passive dosimeters. Sampling with the various monitors should next be conducted in a controlled laboratory environment using known concentrations of contaminants. The results yielded would indicate the true accuracy of each monitor, not just a relative comparison of the precision.