An expert panel has concluded that a sinkhole that swallowed a truck in Yashio, Saitama Prefecture, in January was created due to corrosion of a sewer pipe by hydrogen sulfide.
In an interim report released Thursday, the fact-finding panel set up by the prefectural government said soil is believed to have leaked into the sewer pipe through small gaps on chemically corroded upper portions of the pipe and created a hollow space above. The underground space grew to eventually cause a prefectural road to collapse at an intersection in the city, on Jan. 28.
Hydrogen sulfide was detected in corroded concrete fragments recovered from the accident site.
Meanwhile, the panel did not publish a conclusion on whether the pipe ruptured before or after the road's collapse, mentioning both possibilities. It is expected to draw up a final report by the end of the year.
After receiving the interim report, Saitama Gov. Motohiro Ono said in a statement that the prefectural government will continue to ask the central government to play an active role in tackling issues revealed by the accident, adding that he will strive to secure the safety of the prefecture's sewer system.
In the accident, the truck's cab was left in the pipe. Its driver was confirmed dead after he was recovered from the cab on May 2.
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