It was the eerie sound every mining community dreaded. The alarm which signalled an accident underground and summoned miners from their homes to join rescue teams.
Just before dawn on a Tuesday morning, this was no routine test. This was a real emergency.
The people of Easington knew they had a tragedy in their midst. As the long day progressed they would come to realise that it was a tragedy of immense proportions.
At 4.20am on May 29, 1951, a mechanical coal cutter was working in the Duck Bill district of the Five Quarter seam 900 feet below the surface of Easington Colliery, one of the most modern and productive mines in western Europe.
Easington Colliery, May 1951
Sparks from the cutter as it struck pyrites ignited firedamp, causing a massive explosion which brought down 120 yards of roof. Entombed were 81 men.
The explosion couldn't have happened at a worse time. It was between shifts. In the Duck Bill were the 43 men of the fore shift, about to take over from the 38 stone shift men coming to the end of their overnight stint.
As soon as the signal went out, rescue operations manned by off-duty Easington miners anxious to reach their friends and work mates, began.
Help also came from miners from neighbouring collieries in the Durham Coalfield.
As the first rescuers went underground, wives, mothers and loved ones of those trapped underground gathered to begin a pithead vigil. A vigil that for some was to last three days, and end in heartache for every one of them.
Of the 81 men in Duck Bill, only one was rescued. He died from his injuries in Ryhope Hospital a few hours after being stretchered out of the pit cage.
Two rescuers were also killed, taking the death toll of the Easington Pit Disaster to 83.
It was the second biggest disaster in the history of the Durham Coalfield. The explosion at West Stanley in 1909 claimed 168 lives.
By the end of a grim day it was apparent that there would be no survivors.
On its front page the following morning, The Northern Echo's headline read: "Hope Recedes in Stricken Pit". On an inside page it listed the names and addresses of those whose bodies had been pulled out or those who were missing.
The Echo reported that the women of Easington wept as, at 10pm, more than 15 hours after the explosion, Durham Miners secretary Sam Watson read out the list of the missing or dead.
Rescuers told reporters of the devastation they had confronted underground. One said it was as if an atomic bomb had been dropped.
From the King and Queen came a message of "heartfelt sympathy" to the people of Easington. Lord Beveridge, architect of the Welfare State and chairman of the newly-created Peterlee Development Corporation, joined the vigil. The first resident of the new town was among the dead.
But there could be little comfort for a community, where there was hardly a family untouched by the tragedy.
In its editorial, the Echo said the sympathy of the whole nation centred on Easington Colliery. "The Durham miner is a man of sterling qualities," said the paper.
"He brings to his colliery not only his skill, but also the determination and the grit which have made him formidable on the world battlefields of two wars." It said all efforts should be concentrated on the rescue operation, in the vain hope that some of the miners may still be alive.
But once that was over, questions had to be answered. The Echo concluded: "Later the nation which owns the mines must make it a national concern to see that whatever can be done to lessen the frequency of such disasters and their magnitude is done, swiftly and thoroughly."
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