A private salvage company's ship, which was requested by the Japan Coast Guard in the sinking accident of a tourist ship that killed 14 people and lost 12 people off the Shiretoko Peninsula in Hokkaido, was sunk at the earliest on the 7th. It is expected that the ship will arrive in the waters of Hokkaido and the investigation of the hull by the unmanned submarine will begin.

On the 23rd of last month, 14 passengers were killed and 12 people are still missing in the accident where the sightseeing boat "KAZU 1" carrying 26 passengers and crew sank off the coast of the Shiretoko Peninsula.

The 1st Regional Coast Guard Headquarters, the Self-Defense Forces, and the police continued to search a wide area around the site sea area, and was there anyone left behind by putting an underwater camera in the "KAZU 1" that was found to be sinking? We are in the process of confirming, but no new clues have been found so far.

On the other hand, the Japan Coast Guard requested a private salvage company specializing in dealing with marine accidents to conduct on-site investigations, keeping in mind that the search would be difficult.

The salvage company's ship is sailing in the Sea of ​​Japan near Hokkaido as of 3:00 pm on the 6th, and is expected to arrive at the site sea area as early as the 7th.

As soon as the ship arrives, the condition of the hull that sank to the seabed at a depth of about 120 meters will be checked with an unmanned submersible.

After that, another work boat will be sent to the site, and a full-scale investigation will be started by diving the diver by a method called "saturation diving" that allows diving into the deeper sea.

What is a "saturation diving" survey?

"Saturation diving" is a method of diving that allows you to work longer in deeper waters than normal diving.

It is adopted by the Maritime Self-Defense Force unit that rescues submarines and private companies that handle the salvage of sunken ships, and it means that it can work even in the deep sea over 100 meters.

We spoke with Jun Abe, a former Maritime Self-Defense Force officer and vice chairman of the Japan Society for Water Accidents, who is investigating water accidents nationwide, about the general procedure for "saturation diving."

According to this, in "saturation diving", the diver first enters a pressurized tank called a "chamber" and spends a certain period of time under high pressure.

It is a preparation to prevent abnormalities in the body due to diving work, and it depends on the diving depth, but when diving to the same water depth of about 120 meters as the accident site this time, it takes half a day to a day in this chamber to deep sea. It means getting used to the high water pressure.

When the preparation is complete, we will lower the diving capsule with the diver into the deep sea.

Then, when the target deep sea is reached, the diver goes out of the capsule and works while receiving hot water and air to maintain body temperature from the hose connected to the capsule.

When the water depth is about 120 meters, the work can be done for about 20 to 30 minutes per person, so we will proceed while taking turns with several divers.

After the work is finished, it will take about 4 to 5 days to return to the "chamber" and gradually reduce the pressure, and if the water depth is about 120 meters, it will take about 4 to 5 days for the body to return to its original state.

Mr. Abe said, "Since detailed work is required for investigation and withdrawal, I think that the method called" saturated diving "that can be done by human hands instead of robots is the best. In addition to being deaf and hard of hearing, divers are also psychologically stressed. "

Maritime Self-Defense Force releases training video of "saturation diving"

The official channel of the Maritime Self-Defense Force's "YouTube" shows a video of the training of "saturation diving".

The video shows a diver going to the deep sea with a capsule for diving after spending time in a narrow pressure tank in advance to dive to a depth of 100 meters.

Then, it is introduced how the divers who came out of the capsule train the work of connecting the hose assuming that air is sent to the submarine on the seabed, and how the members on the ship at sea monitor the work.