EIACP (PC-RP) on Environmental Problems of Mining

Saunda ‘D’ West Colliery (Opencast) Blasting Accident

Upper Balkudra seam, 8.9 m thick, was being worked by mechanized opencast method using diesel operated machinery. Several seams lying below this seam had been worked by underground methods. Lower Balkudra seam, 2.4 to 3.6 m thick, lying 5.4 m below the upper Balkudra seam, had been depillared by the caving method. Kurse and Nakari Top seams, lying further below, had also been extracted by the year 1978. Other seams upto Sirka seam lying below, were standing on pillars. Depillaring of the lower seams by caving had resulted in subsidence of the surface. Spontaneous heating had taken place in the caved area and hot gases were being emitted from the surface cracks. Blasting was done in overburden as well as in the coal benches. Deep blast-holes, 150 mm in diameter, were charged with either opencast gelignite (OCG) or slurry explosives and were fired with the help of detonating fuse.

On 18.9.1984, 11 holes had been drilled in the overburden bench by about 11 a.m. 56 cartridges of OCG, a reel of detonating fuse, 3 delay-acting detonators and shot-firing tools were brought to the site and 3 to 4 cartridges were placed near each hole. Charging of the holes started at about 1 p.m. and soon afterwards a violent blast occurred which killed all the six persons who were engaged in the charging operation. The violence was so great that the bodies of all the six victims were badly mutilated with the different limbs scattered all around. 18 cartridges of OCG out of the 56 cartridges could not be found.

Next day (19.9.84), the temperature inside the blast-hole was measured using an optical pyrometer. The temperature in one hole was 975°C, in another it was 950°C. These holes were 5.1 m and 4.8 m deep respectively. One of the holes was found completely filled. Another hole was found blocked beyond 0.5 m depth. The remaining holes were found to be intact.

Examination of the OCG cartridges from the batch which detonated as also from other batches in various magazines in the area indicated that several cartridges had deformed within a few months of their manufacture. Many of these deformed cartridges were found to be bigger than the shot-hole diameter.

It was concluded that the overburden in which the shot-hole was being charged had been heated up to a high temperature due to the fire in the seam being worked as well as the goaved out seam about 6 m below and due to the high temperature, the nitroglycerine-based explosive in the hole along with the detonating fuse exploded prematurely causing detonation of 3 lots of explosives stacked near the blast holes.

Based on the research carried out after this accident, the DGMS recommended that the following precautions should be observed while blasting in fire areas:-

This accident brought out interesting details about the working of granite and other similar mines.

1. No explosive other than slurry and emulsion explosives shall be used.
2. Blasting shall be done with detonating fuse down the hole.
3. Temperature inside the blast-holes shall be measured (before filling with water) and if the temperature exceeds 80°C in any hole, such hole shall not be charged. Record of temperature measurements in each hole shall be maintained in a bound paged book.
4. All blast holes shall be kept filled with water. When any hole is traversed by cracks or fissures, such hole shall not be charged unless it is lined with an asbestos pipe and the hole filled with water. In addition, bentonite should be used for sealing any cracks at the, bottom of the hole.
5. Detonating fuse shall not be laid on hot ground without taking suitable precautions which will prevent it from coming in contact with hot strata.
6. The charging and firing of the holes in anyone round shall be completed expeditiously and in any case within two hours.
7. Blasting operations shall be carried out under the direct supervision of an Assistant Manager.