In the sinking accident of a sightseeing ship off the Shiretoko Peninsula in Hokkaido, a diver searched the inside of the ship for the first time on the 19th by a method called "saturation diving" that can cope with the water pressure of the deep sea.
What exactly is that "saturation diving"?
What is "saturation diving"?
"Saturation diving" is a method of diving that allows you to work longer in deeper waters than normal diving.
The general procedure is for a diver to first enter a pressurized tank on board and spend a period of time under high pressure to acclimatize to the high water pressure of the deep sea.
This is to prevent abnormalities in the body during diving work.
When ready, the diver heads to the deep sea with a diving capsule.
This time, the capsule will be dropped to the bottom of the sea where the tourist boat sank at a depth of about 120 meters.
Once the target depth is reached, the diver goes out of the capsule and works.
Divers wear special wetsuits to withstand the low water temperatures of the deep sea.
Hot water is sent from the capsule to the diver's special suit with a hose to maintain body temperature.
After finishing the work, return to the pressure tank again and gradually reduce the pressure.
If the water depth is about 120 meters, it will take about 4 to 5 days.
Pressurized tank is an environment where you can live
What kind of environment is the pressurized tank?
We asked Hidetoshi Saito, chairman of the Water Accident Society, who is familiar with saturated diving.
According to Chairman Saito, divers live in pressurized tanks during the period of work on the seabed and the period until the decompression after work is completed.
There are beds and showers in the tank, which means that there is an environment where you can live.
Pressurized tanks and capsules are filled with gases containing oxygen, nitrogen and helium.
What is dangerous when working on the seabed?
At a depth of 120 meters, the pressure on the body is 13 times higher than on the ground.
According to Chairman Saito, the most dangerous thing is "decompression sickness" after finishing work on the high-pressure seabed.
Decompression sickness is a symptom of numbness in the limbs and dyspnea that occurs when nitrogen taken into the body in a high-pressure environment is discharged in the body when the pressure drops and becomes bubbles that clog blood vessels.
In saturated diving, the diver inhales gas containing helium in the capsule to reduce the amount of nitrogen taken into the body and prevent decompression sickness.
In addition, the situation where there is a danger to life if there is something wrong with the equipment is said to be "close to spacewalk".
If hot water is no longer supplied to the dive, the diver will be deprived of his body temperature at once, which is fatal.
Former SDF personnel with experience in saturated diving
We spoke with Kazushi Oshiro (39), a former SDF officer who has dived into the sea at a depth of about 100 meters as a saturated diver.
According to Mr. Oshiro, the image is that a diver inhales concentrated gas and does not come in unless he consciously breathes.
It is sometimes described as "breath like drinking soup."
"The light hardly comes in when going up to 100m. The helmet has a light and a camera because it is supposed to be in a dark and deep place. It can not be seen so far, but it can be seen when approaching."
"It is a dangerous dive because it is deep. However, in reality, the saturated diving system is safe, so I hope that you will proceed so that there are no accidents. "
Search in saturated diving for 20 days
According to the schedule announced by the 1st Regional Coast Guard Headquarters, the search activity will be carried out for about 2 days until the 20th, and the work will be done on the seabed for about 5 hours on the 20th.
The divers will search for the missing person with the highest priority, and then conduct an investigation for the withdrawal of the hull.