[Generation of hydrogen sulfide at excavation sites. I. A survey of job sites in the sewage system construction work].

It has long known that H2S is sometimes encountered during excavation in the Hiroshima delta. In order to secure information necessary to the improvement of working conditions in this area, we investigated the generation of H2S where work was being done on the Hiroshima sewage system. Using the shield method, we measured the concentration of H2S in the air around eight work sites, and we also measured pH, total sulfide, SO4(2-), C1-, Mg2+, and salinity in samples of water collected at the sites and from nearby wells. The ventilation volume was calculated from the measurement value of air movement with reference to ventilator capacity. The past situation of H2S generation at the sites was also investigated. The survey was conducted from August 30 to September 4, 1982, using the shield method. Concentrations of H2S from 0.8 to 7 ppm were detected in the air at four of the eight sites. Total sulfide varying from a trace to 8.5 mg/l was found at six sites, which included the four where H2S was found in the air. SO4(2-), C1-, and Mg2+ were found in high concentration in water in which sulfide was detected, and the same samples tended to have high salinity. At some of the sites, ventilation was implemented up to a maximum of 3,000 m3/h according to the concentration of H2S. At the sewage system construction sites covered in this survey, H2S concentration was kept below the permissible level of 10 ppm, and it may be concluded that adequate safety precautions have been taken.