LAUSR

Passive or diffusion samplers have become standard tools for exposure and compliance testing despite their limited accuracy of 25-30%. Passive samplers have several advantages over active/pumped samplers, notably ease of use, low cost and inherent explosion safety. EN 838 advises their use for personal sampling at up to 4 m/s, but with a minimum of 0.1 m/s. Considerable underestimations were found in a set of passive sampler results compared to pumped samplers for BTEX. A literature review of laboratory and field studies was performed to investigate theoretical explanations for the discrepancies found. Based on results published in journals an underestimation of concentration by passive samplers is not uncommon, although usually the difference is within an acceptable range. Temperature and relative humidity have known, quantifiable effects, which are fairly small. High wind speed theoretically causes increased, not decreased, uptake due to smaller diffusion distances. This effect was confirmed experimentally, both in wind tunnels and in field studies, according to literature. Real-time monitoring in company operations shows that personal exposure in outdoor scenarios often fluctuates strongly with short peaks over periods of seconds rather than minutes. Theoretically this may influence uptake by diffusion samplers depending on their design and some researchers do report that passive samplers work less well under such conditions. Further research into passive sampler performance in fast fluctuating conditions as found in the field appears necessary.