TOKYO, AP

Japan has ordered safety checks at the country’s 52 nuclear plants and some 800 non-nuclear power stations to prevent the type of accident that killed four people at a reactor this week, government officials said Thursday.

Government investigators kept up searches and questioning Thursday at the plant at Mihama, 320 kilometers (200 miles) west of Tokyo, where a cooling pipe exploded on Monday. The operator, Kansai Electric Power, is under suspicion of negligence.

The Nuclear and Industrial Safety Agency ordered Kansai Electric and six other Japanese utility companies on Wednesday to review inspection records of cooling pipes at nuclear power plants to check for signs of erosion, agency official Koichi Shiraga said Thursday.

The utilities were requested to submit the results by next Wednesday. The agency also ordered operators to check inspection records at their 800 non-nuclear, thermoelectric power stations.

The agency plans to send more officials to investigate Kansai Electric to collect documents related to safety records, Shiraga said.

In Mihama, the dangerously corroded pipe exploded and spewed boiling water and superheated steam on workers, killing four instantly and injuring seven others.

The two of the four victims died of suffocation when the steam burned their windpipes, and the other two apparently died from serious burns, Japanese media reported Thursday.

Kansai Electric acknowledged on Tuesday that the cooling pipe that caused the accident had not been thoroughly checked, despite a warning from inspectors last year that it posed a danger. Kyodo News agency reported that police planned to raid the company’s offices.

Government officials on Thursday acknowledged that they also failed to discover Kansai Electric’s lax safety measures in a 2000 company report that included cooling pipe inspection plans at the Mihama plant, said Yasushi Morishita, another agency official.

In the report, Kansai Electric said it routinely checked the extent of pipe erosion and found no abnormality, and the government had praised the company effort, Morishita said. He added the report was only intended to detail a plan of action and did not have to reflect the actual inspection and its outcome.

“Looking back, the practice at that time was not strict enough,” he said.