Hydrogen sulphide exposure in waste water treatment

Background: The aims of this study was to assess exposure to hydrogen sulphide (H2S) among waste water treatment workers (WWWs), and achieve a better measure of the risks of H2S exposure than only using the eight-hour average value and the ceiling value because the exposure pattern of H2S for WWWs is dominated by short-term peaks. Methods: Ninety-three measurements of H2S from 56 WWWs in three cities and three rural areas were collected. All exposure measurements were carried out from the start of the day until lunch time (sampling time 4–5 h) when most of the practical work was performed. The type of tasks and extent of flushing were registered. H2S was measured using direct-reading instruments with logging: OdaLog L2/LL, Dräger X-am 5000 and Dräger Pac 7000 (0.1–200 ppm). Number and duration of peaks for different work tasks, seasons, places and extent of flushing were combined in an exposure index (IN), and evaluated in a mixed-model analysis, building a model aimed to predict exposure for different job tasks. Results: Nine Percent (8 of 93) of all H2S measurements have peaks above 10 ppm; in addition, 15% (14 of 93) have peaks of 5–10 ppm, 35% (33 of 93) have peaks of...