Almost all workers, including managers required to deal with accidents, defied orders and fled the Fukushima No. 1 nuclear plant at a critical juncture when the disaster was unfolding in March 2011, documents showed.

Amid fears that a reactor containment vessel had been destroyed, around 650, or 90 percent, of the approximately 720 workers at the plant left the premises despite being told to remain at the site by the plant’s manager, Masao Yoshida.

Tokyo Electric Power Co., the operator of the No. 1 plant, has never mentioned the orders Yoshida issued on March 15, 2011, four days after the Great East Japan Earthquake and tsunami caused the meltdowns of three reactors. The company now says Yoshida’s orders were flexible, and that no breaches of company rules occurred.

Yoshida’s orders were revealed in a document covering exchanges when prosecutors on loan questioned him on behalf of the government’s Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo Electric Power Co.

The Asahi Shimbun obtained a copy of the document, consisting of more than 400 pages.

Yoshida was questioned on 13 separate occasions between July 22, 2011, and Nov. 6, 2011, for a total of 29 hours, 16 minutes, including an hour and eight minutes of breaks.

He died in July 2013 of esophageal cancer.

According to the document, Yoshida was in the emergency command center on the second floor of a quake-proof building on the plant site when he received two reports around 6:15 a.m. on March 15, 2011. One was about the sound of an explosion coming from the direction of the No. 2 reactor. The other described pressure falling to zero in the reactor’s suppression chamber.

Both were signs that the No. 2 reactor containment vessel was damaged or destroyed, which would have been a crisis situation at the plant.

However, Yoshida judged that the containment vessel had not been damaged because radiation levels were not increasing in the emergency command center.

At 6:42 a.m., Yoshida ordered workers to temporarily evacuate to locations at the plant site where radiation levels were comparatively low. He told them to wait in locations from where they could immediately return to their posts.

He added that the workers would be asked to return once confirmation was made that there were no abnormalities.

In the document, Yoshida said he considered areas at the plant where radiation levels were low as the temporary evacuation sites.

According to Yoshida’s testimony to the government panel, some workers around 7 a.m. told drivers of buses waiting outside the command center to head to the Fukushima No. 2 nuclear power plant about 10 kilometers to the south. Other workers hopped into their own vehicles and drove to the No. 2 plant, also operated by TEPCO.

The roads were damaged by the quake and tsunami, and the workers who fled would have to wear and remove protective clothing and face masks when entering and leaving the Fukushima No. 2 plant. That means they would have been unable to follow Yoshida’s order to return immediately to their posts at the No. 1 plant.

Designated group managers, who are required under TEPCO regulations to remain at their posts to provide support in operating and controlling nuclear reactors when a major accident occurs, were among the 650 people who fled to the No. 2 plant.

According to the document, Yoshida told a government panel questioner: “In fact, I never told the workers to go (to the No. 2 plant). I thought I gave an order to temporarily evacuate to a location where radiation levels were low near the Fukushima No. 1 plant and await further instructions.

“After the workers arrived at the No. 2 plant, I contacted them and asked that the group managers be the first to return.”

Yoshida did not seem to blame the rank-and-file workers for fleeing, telling his questioner “it may have been unavoidable.” However, he did express surprise that group managers were among those who had left.

Only 69 workers remained at the No. 1 plant. It was not until around noon on March 15 that other workers returned from the No. 2 plant.

During their absence, white steam was seen spewing out of the No. 2 reactor and a fire occurred at the No. 4 reactor. Radiation levels reached the highest levels near the main gate of the No. 1 plant.

Yoshida’s testimony raises questions about whether utility workers can be depended upon to remain at their posts in the event of an emergency.

TEPCO’s internal documents do not mention Yoshida’s orders for workers to remain near the No. 1 plant. The company’s report on its own investigation into the Fukushima disaster explains that about 650 workers evacuated to the No. 2 plant, but it gives the impression the move was in line with ordinary procedures.

In 2012, TEPCO released videos of teleconferences after the Fukushima nuclear accident started. In one scene, Yoshida is seen giving orders to a large number of workers in the emergency command center. However, it was unclear what Yoshida said at that time because TEPCO said no audio recording had been made.

Even today, TEPCO officials avoid placing blame on those workers, including the group managers, who left for the No. 2 plant.

“Evacuating temporarily to the No. 2 plant was not a violation of regulations because Yoshida’s order left open the possibility of leaving for the No. 2 plant if there were no locations at the No. 1 plant where radiation levels were low,” a TEPCO official said.