EIACP (PC-RP) on Environmental Problems of Mining

West Chirimiri Colliery

The accident occurred in the Main Seam in the splitting district of 9 and 10 Inclines. This seam, 4 m thick and inclined at 1 in 45, had been developed along the floor with pillars 23 m x 23 m and galleries 3.6 m wide x 2.1 m high. The cover over the area varied from 50 m to 90 m and at the maximum depth, the cover comprised a 45 m thick dolerite sill and 45 m of sandstones. Permission had been granted for splitting of the pillars as final operation leaving 30% of coal in-situ in the form of stooks and restricting the height of extraction to 3.8 m. After 14 pillars had been split, an inspection revealed that the stooks being left were too small for their stability. The management was therefore directed to leave stooks of 6.75 m x 6.75 m.

Upto the time of the accident, out of 125 pillars in the panel, 70 pillars had been split covering an area of 213 m x 183 m. Systematic Timbering Rules had been framed and enforced in the panel.

On 11.4.1968 work in the afternoon shift had started as usual at 3 p.m. and 64 persons were engaged in the splitting panel. After blasting operations were completed by about 5 p.m., the goaf started “talking” more prominently -the sound of strata movement in the goaf kept on increasing in intensity. There was also a small fall of roof in the goaf resulting in a mild air-blast and thereafter the workers started running outbye.

It took some time for the supervisory staff to contact the manager who instructed them to withdraw all persons from the mine. At about 6 p.m. when some of the workers were going out through the haulage and travelling roadways, a scouring air-blast took place and these persons were caught in the air-blast. 8 of them died on the spot and 6 others died subsequently. 16 were seriously injured and 27 received minor injuries.

One of the factors that contributed to the high number of fatalities was fitting of heavy steel doors in two preparatory stoppings. These doors were unhinged and thrown over a distance of 80 to 90 m by the air-blast, hitting the fleeing workers on their way. The volume of air displaced was about 95000 m3 and this air passed through 3 openings which had a total area of cross-section of about 14 m2 only. Most of the blast passed through the two intake roadways.

Cause of the accident

The stooks left in the initial stages of depillaring were of much smaller dimensions than prescribed and these were gradually getting attenuated due to the pressure of the massive roof. When some of these stooks ultimately gave way, a general movement in the goaf started, finally resulting in the total collapse of the roof right upto the edges of the split pillars. The fall of roof did not occur all on a sudden but at the final stage a fairly large area had collapsed which pushed out a large volume of air from the goaf to the outbye workings.

There were definite indications of roof movement in the goaf since one hour before the accident occurred. Although the supervisory staff did withdraw persons from the active workings, they did not know what further action was called for. Had they ensured complete withdrawal from the mine, the loss of life and physical injuries could have been avoided.

Design of support pillars

In situations where support to the ground overlying excavated areas has to be provided by a system of pillars, the support pillars must be designed in such a way that they do not fail, regardless of the extent of mining. In the last thirty years or so, considerable amount of research work has been done in the design of pillars and it can be claimed that now pillar workings can be designed to yield optimum recovery commensurate with the long term stability of the pillars. It is hoped that accidents due to pillar collapses should now become a thing of the past.