| Case Name |
The tunnel of Kokubugawa River diversion channel was submerged, and all seven workers in it died. |
| Pictograph |
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| Date |
September 19, 1991 |
| Place |
21st century hill - Toyama Cho, Matsudo City, Chiba Prefecture |
| Location |
The Kokubugawa River diversion channel construction site |
| Overview |
Because of the typhoon No.18, Kokubugawa River flooded, and it flowed to the neighboring tunnel construction site. Though the temporary cofferdam had been installed in the tunnel, it collapsed because of the hydraulic pressure of muddy stream, and the seven workers in the tunnel died. |
| Incident |
Since the temporary cofferdam at pit mouth collapsed, the muddy stream flowed to the diversion channel tunnel under construction, and all seven workers in it died. |
| Sequence |
* At about 4:30 p.m., Kokubugawa River flooded because of the typhoon No.18, and the muddy stream overflowed onto the temporary road in the drill site in front of the cofferdam.
* At about 4:52 p.m., the construction staff of S Construction Company called the chief of construction section of Chiba Prefecture, and told him that the muddy stream had overflowed onto the temporary road and the flow was so strong that they it could not be stopped easily.
* At about 4:55 p.m., the construction section chief of T Prefecture told the site agent of T Construction Company over the phone that the bank near the water gate construction site in the upstream had collapsed and the water overflowed to the site, and the staffs of S Construction were piling sandbags.
* The site agent of T Construction Company in charge of tunneling directed the staff of the company to pull the workers out of the tunnel.
* At about 5 p.m., the construction section chief of the prefecture told the site agent of T Construction Company over the phone that he would like the agent to communicate directly with S Construction Company, and he offered to start spraying the working face.
* At about 5 p.m., the site agent of T Construction Company accepted this offer, and he dropped his direction to pull the workers of the tunnel, and he directed the workers to start spraying the working face.
* At about 5:18 p.m., the temporary cofferdam collapsed because of hydraulic pressure of the muddy stream, and the tunnel was submerged. Seven persons such as the employee of T Construction Company who were working in the tunnel died. |
| Cause |
* In spite of the fact that there was the imminent danger, the owner (the prefecture) didn't determine to stop the operation, but directed the workers to carry out the operation (spraying the working face). Once the director of the contractor (the site agent of T Construction Company) directed the workers to stop the operation, he could not go against the instruction of the owner, and he directed them to continue the operation. However the director of the contractor (the site agent of T Construction Company) noticed the danger, and he believed what the section chief of the prefecture told him. If he had sensed danger and considered safety, he should have stopped the operation, even though it was against the indication of the prefecture.
* The temporary cofferdam was not constructed as designed by the designer (the consultant). In other words, the staff of the consultant designed it without understanding the situation of the site. Therefore, the design was changed so that S Construction Company could construct it. However, the strength of the bolt became lower than that of original design. |
| Response |
* T construction and the site agent of this company were sent to the public prosecutor's office for violation of Industrial Safety and Health Law, and the punishment was announced in September, 1994.
* For the construction section chief of T Prefecture, the court has judged that his fault was not directing work continuation, but ignoring an emergency and not telling to leave the site. |
| Countermeasures |
* Under an unusual weather conditions such as typhoons, an abnormal situation may come about. It is necessary to install the system which directs the workers to work stop under an abnormal situation and to deal with it.
* When an abnormal situation comes about, what should be done immediately is pulling the workers out of the site and securing their lives. Even though the work must be carried out, it should not be done until the abnormal situation finishes.
* Though bolts are often used in the design of temporary structures, there are many cases in which the structures built temporarily collapse since the actual conditions in the field does not always meet the design intent (to make it resist by shear stress) and the bending moment would be applied, if it is designed to resist by shear stress. The design of temporary structures such as this cofferdam requires not only accuracy of calculation process, but prudent consideration for safety on the basis of the site situation. |
| Incidental Discussion |
The first trial at Chiba District Court led to a prison sentence of one year and six months for the following reasons. "Section chief of T Prefecture didn't anticipate the danger of collapse of the temporary cofferdam and issued inadequate indication of work continuation. " The defendant appealed against the sentence. However, the second trial at Tokyo High Court judged that "The content of what the defendant talked about on the phone doesn't determine the feasibility of his fault. His fault is not that he indicated the work continuation, but that he didn't tell the workers to leave in an emergency." Then the defendant was given prison sentences of 2 years-imprisonment with suspended sentence 3 of years for the reason that he had paid compensation to the families of the victims. However, the defendant appealed against the sentence once again. |
| Scenario |
| Primary Scenario
|
Unknown Cause, Occurrence of Abnormal Phenomenon, Misjudgment, Misunderstanding, Insufficient Analysis or Research, Insufficient Practice, Insufficient Analysis or Research, Insufficient Prior Research, Incorrect Reaction, Poor Communication, Non-Regular Action, Emergency Action, Misjudgment, Misjudgment of Situation, Non-Regular Action, Change, Failure, Large-Scale Damage, Bodily Harm, Death
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| Sources |
Measures for preventing a recurrence learning from 70 examples of grave accident - construction accident - , Nikkei Construction
|
| Number of Deaths |
7 |
| Number of Injuries |
0 |
| Field |
Civil Engineering
|
| Author |
MAEKAWA, Yukimasa (Japan Engineering Consultants Co., Ltd.)
KITASHIMA, Masayoshi (MAEDA CORPORATION)
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