Failure Knowledge Database / 100 Selected Cases

Coal dust explosion at Mitsui Miike coal mine
November 9, 1963.In the tunnels at Mitsui Miike in Omuta, Fukuoka
Masayuki Nakao (Institute of Engineering Innovation, School of Engineering, The University of Tokyo)

An explosion occurred in a m ine tunnel at Mi tsui Miike coal m ine (Figure 1) roughly 500
meters below the m ine ground-level entrance. T he blast and fla me caused roof fall in m any
areas in the tunnels, which then quickly filled wi th carbon monoxide. 458 people were killedand 555 people were injured. It was the worst
postwar m ine disaster . Lack of safety
provisions was the prim al cause. Figure 2 indicates the cross-section of the accident site. The
coal beds at Mitsui Miike sloped towards Ariake Sea, and mine openings had also shifted overtime towards the se a ( to the lef t in the f igure) f rom m ountainside. At the tim e, coal beds
roughly 350 to 450 meters below the sea level were being mined.
SagaOmuta
AriakeSea

Mitsui MiikeIsahaya
ShimabaraPeninsula

Nagasaki

Kumamoto

Figure 1: Location of Mitsui Miike Coal Mine

1Failure Knowledge Database / 100 Selected Cases

Mitsui Miike Mine

Ariake Sea

1st sloped mine
2nd sloped mine

Location where the roof fell

300m horizontal run

Location of original explosion
450m horizontal run

Tunnel with severe explosion

Mine dust pump

Figure 2: Cross section of the accident site [1]1. EventAn explosion occurred in a tunnel at Mitsui Miike coal m ine roughly 500 m eters below themine entrance. The blast and fla me collapsed th e roof at multiple lo cations in th e tunnels
which filled with carbon monoxide. The accident killed 458 people and injured 555 others. It
was the worst postwar mine disaster.
2.

Course(1) The industry shifted its prim ary energy source from coal to oil during the period of1959 to 1960 and Mitsui Mining was forced to reorganize itself with mass layoffs.
(2) Labor dispute took place between the work ers and corporate m anagement, however,the labor side lost the battle and the work force was reduced.
(3) The num ber of e mployees dropped to 10,000 from 15,000, whereas, productionincreased to 15,000 tons per day fro m 8,000. The per cap ita efficiency multiplied by
2.8.
(4) The efforts to cut production cost forced less safety personnel.
(5) On Nove mber 9, 1963, an explosion occu rred roughly 500 m eters below the m ine
entrance. T he blast an d fla me collapsed th e roof and carbon m onoxide filled th etunnels. As a result, 458 people were killed and 555 others injured.

3. Cause
The explosion was the so-called “coal dust e xplosion”. A technique to prevent coal dust
explosion had been established over 50 years before the accident and there had been no m ajor
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coal dust explosion accidents since the Taisho era (1912-1926), and not even minor ones after
world war 2. Coal dust was dangerous, howev er, manageable and it was common knowledgethen that maintaining the site clean and making the area moist by watering could prevent such
explosions. These easy preventative measures had been in place on a routine basis before thelabor dispute. However, after the dispute, the insuf ficient number of safety personnel, causedby the em ployer’s productivity-first policy, failed to take those m easures. Furthermore, theunion, which was supposed to be the or ganizational checking system , knowingly ignored thefacts of neglecting the explosi on preventative m easures because of their peace accord withmanagement (Employees were paid extra in lieu of staying out of strikes).
4. Immediate Action
After the explosion, rescue ef forts took place imme diately. Investigation of the cause of theaccident began. The mining operation was suspended.
5. Countermeasure
After the investigation of the cause of the accident, the management improved the emergency
procedures of the security measures resumed the mine operation -- until March of 1997, whenthe mine was abandoned.
6. Summary
The coal dust explosion at Mitsui M iike was a d irect result of neglecting the safety measures
under productivity-first policy during the energy revolution.
7.

Knowledge(1) Keep in m ind that rationaliz ation f rom the managem ent perspective can dam age
safety factors, and such ill-conditioned
operations can le ad to trag edies. It isimportant to m ake sure that or ganizational checking system s function properly inorder to prevent accidents.
(2) Fine powder of flammable material is the same as flammable gas when the powder isdense. Even wheat flour can cause expl osion. This phenom enon is called “dustexplosion”. Dust does not explode by dire
ctly catching fla me, however , sm allparticles of dust in the air, when th ey bu ild up to a certa in density, ar e f lammablewith the norm al oxygen density and can easily catch fire. Coal dust explosion is aform of dust explosion.

8. Background
The industry shift from coal to oil forced restructuring in the coal industry. Mitsui Mining,
who mined for coal, executed lar ge layoffs during the period of 1959-1960. W orkers such as
Miike Labor Union went on strikes, attractin g nationwide support from other labor unions,and the dispute continued for 313 days. This
was the “Mitsui Miike Labor Dispute”.
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Eventually the com pany prevailed and the m ass rationalization took place. The number ofworkers dropped from 15,000 to 10,000. On the ot her hand, the capacity was increased fro m
8,000 ton a day to 15,0 00. Productivity per person multiplied by 2.8. In order to reduce th e
production cost, the number of safety personn el was reduced. The coal dust explosion took
place under these circumstances.
9. On the side
Series of large-scale accidents at large-scale enterprises occurred in October of 2003, such as
explosion/inflame of coke oven gas tank at Nippon S teel Corporation’s Nagoya W orks andfire at Brid gestone’s T ochigi facto ry. Thes e acciden ts m ay have had direct caus es, withbackground factors like on-going im plementation of facility m aintenance outsourcing acrossthe industrial arena, aging faci lities and reduction of expe rienced workers by corporate
restructuring. I, however , would con clude th at these cas es, includ ing th e accident at Miike
Mine, shared the same problem of neglecting safety, which had been a human factor.
<References>[1] The Practice of Machine Design Book 3,
Learning from Failure, Y otao Hatamura ed.,Practice of Machine Design Research Group, The Nikken Kigyo Shimbun, Ltd.

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