| Case Name |
Methane gas explosion hazard during construction of headrace tunnel for agriculture. |
| Pictograph |
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| Date |
June 28, 1978 |
| Place |
Motoki, Negiwa, Yamanobe Town, Higashimurayama District, Yamagata Prefecture. |
| Location |
In the tunnel bored to 2400m from the entrance of the tunnel. |
| Overview |
The methane gas exploded in the tunnel bored to 2400m from the entrance of the tunnel, and 9 people who were engaged in excavation and concrete placing died, and 2 people who walked near the entrance of the tunnel were blown away by the blast, and they got injured. |
| Incident |
The methane gas which arose during the excavation of the tunnel from the underground exploded by a fire source, and 9 people under work in the tunnel died, and 2 people got injured. |
| Sequence |
When the accident occurred, 9 workers ( 1 person was a staff member ) worked in the tunnel. A party of 4 people prepared the concrete placing, and a train which had 6 tons of loading capacity and was coupled with the concrete transit lorry with concrete placer was arranged about 1600m from the entrance of the tunnel. And, the other party of 4 people did the work of excavation and loading, and the 6 ton train was coupled with shovel loader, and the muck car made up of 6 cars was arranged near the face.
A gush of the methane gas and the danger had been recognized, and electrical equipment which was within 100m of the face had the explosion-proof specification form.
About the measurement of the methane gas, the measurement staffs who were full time workers always measured it by the portable measuring instrument, and the stationary type detector with the alarm were arranged in 2 places: one was in the working face and the other was 300m afterwards from it. If the gas was thicker than the given concentration, the alarm was sounded and the tunnel power supply would be cut off .
At around 8 a.m. on that day, the detector was set so that the alarm sounded in the case of more than 1%
concentration of the site rear 300m away from the face, issued the alarm, but the alarm was judged to be
for the trouble of the detector, because power supply in the tunnel was not cut off. And setting of the
detector was changed from 1% to 4.5% in the setting standard concentration.
It exploded at around 5:10 p.m.. |
| Cause |
When the gas detector of stationary type was judged out of order, the setting concentration standard was changed from 1% to 4.5% without taking measures such as an investigation of the causes, ventilation countermeasure, and repair. And it was left as it was.
The danger had been so underestimated that they did not escape when the alarm sounded on the morning.
The stationary type gas detector had been installed in only 2 places of the site, which consisted of the face and the place 300m from it, and the measures for partial blowout of gas from the place except for the face was insufficient. |
| Response |
* The rescue crew who belonged to the mine in Yamagata and Akita were asked to rescue the victims.
* A supervisor of Sendai Mine Safety and Inspection Department directed the rescue crew.
* It was possible to go without mask by natural ventilation from the entrance of the tunnel to the shaft.
* The rescue base was established 30m before the shaft.
* The approach without mask was impossible, because the high-dense methane gas had filled the back from the length pit. Therefore they installed the ventilation fan and removed the inner gas steadily as they extended the air pipe. And the work without mask was possible.
* With the air pipe extension work, the reinforcement work by props was also carried out for the prevention of falling rock, etc..
* Unexpected situations such as air pipe extension, obstruction removal, timbering, and the trouble of the machine in addition, etc., occurred like this, and the necessity for the urgent supply of the equipment and the material also occurred. Because of this, the progress was remarkably delayed, and the work ran into difficulties. However,
fortunately, at 15:30 on July fourth, 6 days after the accident, the carrying out of all victims ended without
accident. |
| Countermeasures |
* The person in charge of measurement is decided, and the methane gas is measured at defined frequencies.
* The scheme of execution is changed according to the result of the measurement.
* The automatic alarm device is installed, when there is the fear that the explosion might be generated.
* Measures in the case of working of automatic alarm device are decided, and it is communicated to the parties concerned.
* All the members is made to take refuge, when it is confirmed that the concentration of methane gas is over 30% of the explosion threshold.
* Ventilation is carried out according to the plan .
* Having the ignition ingredient is banned.
* The use of fire and the like in a tunnel is banned.
* The electric installation of the explosion-proof is used as the need arises. |
| Knowledge Comment |
* All over the country, the many stratum which contains methane gases such as oil fields and gas fields exist.
* The deeper the place is, the more the danger of the methane gas increases.
* The countermeasure of methane gas is sufficiently examined, before the construction is undertaken. |
| Background |
The construction zone was located around Sagae gas field and consists of the hard mudstone which was the country rock of Akita oil field, and the methane gas was contained in its anticline, fault, and crack. About the ventilating installation, it had been equipped with the shaft for ventilation 1200m away from the entrance of the tunnel, and the exhaust fan had been installed. Air was supplied to the face by in-line ( the φ 600 air pipe ) 4 fans including the axial fan installed from the shaft to the entrance of the tunnel. The electrical equipment which was within 100m of the face had the explosion-proof specification form. |
| Incidental Discussion |
Methane gas explosion hazard is the fearful disaster which is generated when people neglect the ventilation and the countermeasure which is necessary for explosion prevention such as measurement, and not being off guard because of its rareness.
The carelessness of methane gas is the taboo . |
| Scenario |
| Primary Scenario
|
Insufficient Analysis or Research, Insufficient Environment Study, Organizational Problems, Poor Management, Insufficient Analysis or Research, Insufficient Environment Study, Misjudgment, Misunderstanding, Malicious Act, Rule Violation, Incorrect Reaction, Self Protection, Bad Event, Chemical Phenomenon, Failure, Large-Scale Damage, Bodily Harm, Death, Loss to Organization, Economic Loss
|
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| Sources |
Japan Construction Safety and Health Association, newspaper article.
|
| Number of Deaths |
9 |
| Number of Injuries |
2 |
| Field |
Civil Engineering
|
| Author |
KITAJIMA, Munekazu (TEKKEN CORPORATION)
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