Four male workers were confirmed dead after falling into a manhole in Gyoda, Saitama Prefecture, on Saturday morning, fire authorities said.
The four, all in their 50s, fell into the manhole around 9:25 a.m. during a sewage pipe inspection. Their bodies were recovered but they were later pronounced dead.
According to the Saitama Prefectural Police, hydrogen sulfide was detected inside the manhole. The police suspect that the workers may have inhaled the gas.
Police and other sources said that, of the seven people involved in the inspection, four fell into the manhole, which is about 60 centimeters in diameter and 12 meters deep.
One of the four fell into the manhole first for an unknown reason, and three workers who tried to rescue him also fell, according to the sources.
Gyoda officials said that the inspection was part of a nationwide special survey of sewage pipes. The central government asked local governments across the country to carry out the survey following a road collapse incident in Saitama's Yashio in January, which was likely caused by a sewage pipe rupture.
The manhole was installed on the sewer line, which was built in fiscal 1981.
The inspection was conducted by a company commissioned to do the work by the Gyoda city government. The company was making preparations to visually check the conditions of sewage pipes when the accident happened.
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