An assessment of the exposure of water reclamation workers to hydrogen sulphide

The paper describes a 4-month study of water reclamation workers in a rural area. Workers were chosen randomly from each of three groups: permanent site workers, mobile workers and tanker drivers. The exposure to H2S of each of these workers was monitored with pumped long-term colorimetric tubes over 4 days. The reclamation sites were visited over the period of the study and monitored with a hand-held H2S-measuring instrument to identify sources of possible exposure. Data on the weather conditions were also collected. Routine exposure to H2S was found to be low; only 14% of exposures were above the minimum detection limit of 0.1 ppm 8-h time-weighted average (TWA). None of the 190 valid samples were above the 8-h TWA occupational exposure standard (OES) of 10 ppm. If all the exposure had occurred in a 10 min period, 6% of exposures would have been above the 10 min TWA limit. The hand-held readings and knowledge of the work pattern suggest that this was unlikely to have been the case. Most of the positive personal exposure measurements were associated with tanker drivers who were not dealing with treated sludge only. There was a statistically significant difference between the likelihood of exposure to H2S occurring in warmer, drier weather and in cooler, wetter weather. Sites and jobs which can result in transient exposure to H2S are identified.