TABLE OF CONTENTS Event We returned to the origin of developing a remote safety system in the hazardous area of Mt Usu. We were forced to overturn our concept of safety systems through our thorough checking.
Course:
| March: | On March 31, 2000, Mt Usu erupted after 23 years dormant. New craters opened near the hot-spring town of Lake Toya. |
| April: | Volcanic mudflow from Mt Usu drifted into the town. We had to save the town from disaster. |
| May: | Started "Mt Usu Unmanned Construction Project." The construction work took place at the close range of 300m to 700m from the erupted craters. We sent unmanned remote control machines into the hazardous area. Figure 5.1 shows the layout of the construction site. Removing the mudflow and securing channels to guide it were the urgent tasks. |
| June: | The control was frequently lost for minutes on end due to control signals getting mixed up. |
Motive Failure of the unmanned machines could have destroyed the entire construction work, and therefore, we had to come up with appropriate measures as soon as possible to minimize the harms.
Action We investigated the unmanned machine radio system extensively, searching for the cause of the problem and the solution. The construction work was a 7-days-a-week operation, and the sites were closed for the night. These factors made it impossible to perform operational tests...
