Asansol, Jan. 16: An explosion at an abandoned coal mine pit ripped through a cluster of houses early this morning and caused cracks along a 700-metre stretch of a national highway which forms part of the Golden Quadrilateral.

The blast, which was accompanied by a tremor, could be heard even a kilometre away. But there were no casualties.

The coal mine pit, ripped open by the explosion. (Below) Some of the residents. Pictures by Sitaram Mukherjee

Chhatarpathar, a colony of working class people, got enveloped in thick grey smoke and water in many of its wells became boiling hot.

Panic-stricken residents ran out of their homes with whatever they could lay their hands on.

Traffic on the Calcutta-Delhi highway — part of the network of roads connecting the four metros — was stopped and diverted through Asansol, about 240 km from Calcutta.

Officials said that the explosion was caused by methane, a coal bed gas, that had accumulated in the abandoned pit over decades.

The mine was abandoned in the early 1960s and the pit was sealed with a concrete slab two years ago after a baby fell into it, but it wasn’t filled with sand, as it should have been.

“I woke up to a deafening explosion and found everything shaking. I panicked and got out of bed with my child in my arms and ran. Outside, there was a blast of hot smoke, thick and grey. It was billowing from the mouth of the old mine,” said Asha Rajvanshi, a housewife.

Asha left for a relative’s place at Kulti, about 25 km away, with her family.

The administration blared requests to vacate the place over the public address system.

Shankar Nath, a professor of IIT Kharagpur’s geology and geophysics department, said methane is highly combustible. “It appears that the gas had filled the void inside the mine over the years. With the accumulation of gas, tremendous pressure had been building up inside. Somewhere in the seams of coal in the abandoned mine, there must be a fire. The gas reached a certain temperature and ignited, leading to the explosion.”

There were cracks on the highway but not so much in the houses that were much nearer to the blast site because the road was built with tightly packed, high-density stone chips and other construction materials. “It became a carrier of high velocity energy,” Nath added.

It would take at least Rs 10 crore to repair the many cracks — horizontal, vertical and diagonal — along the highway, said engineers.

After Asansol choked, unable to bear the burden of around 3,000 cars and 1,000 trucks, the chairman of the Asansol Durgapur Development Authority and MP, Bansagopal Chowdhury, held a meeting that decided to only divert light vehicles through the town.

Trucks were being diverted from Durgapur and Ranigunj. They will hit the highway again near Chas in Jharkhand after travelling via Bankura and Purulia.

Officials of the Eastern Coalfields, the Directorate General of Mine Safety, the National Highway Authority of India and Burdwan district attended the authority’s meeting.

The highway authority said the route could be changed permanently if a study proved that the area was unsafe.