Tuesday marks 40 years since a major blast killed 31 miners and injured 13 others at a south Wales pit.
Two factors contributed to the blast at the mine
On 17 May 1965, a methane explosion hit the Pentre seam at the Cambrian Colliery in Tonypandy, Rhondda.
Dr Chris Williams, history professor at the University of Wales, Swansea, described it as "a tremendous tragedy".
The explosion was followed the next year by the Aberfan disaster, which claimed the lives of 144 people - 116 of them children - in October 1966.
Former miner Ron Eveleigh, who was working at another pit at the time, knew some of the men killed.
He also attended a mass funeral held for some of the victims at Trealaw, which the then south Wales secretary of the National Union of Miners also attended.
Mr Eveleigh described exactly what happened at the Cambrian Colliery shortly before 1300 BST on 17 May.
"It was a methane explosion in the coal face," he said.
"There were two factors which contributed - first, there was a short circuit in the ventilation of the air going to the face, so the air was still.
"As the methane was built up, it was not ventilated away.
"Second, there was an electrical breakdown and, in checking the electrical equipment, this caused a spark which ignited the methane gas."
The explosion happened around 300 yards underground and more than one-and-a-half miles from the pithead.
The Aberfan disaster followed the year after the Cambrian Colliery blast
Mr Eveleigh, who was at Lewis Merthyr Colliery, is now a guide at the Rhondda Heritage Park on the same site.
He said the Cambrian disaster had shocked other miners, partly because it was considered to be a modern coalmine.
"Even though it was an old mine, it had been modernised," he added.
Mr Eveleigh said that, after investigations at the coal face, work restarted at Cambrian colliery just days after the tragedy, and it did not stop him working.
"Business would have gone on - they would have shut down but it wasn't a long gap, a matter of days," he said.
"I did not think twice about going into work the next day."
In July 1965, an inquiry into the disaster was held at the law courts in Cardiff. The Cambrian colliery was shut in 1966.
Mr Eveleigh finished working as a miner 22 years after the explosion, in 1987.
Mining historian and Aberavon MP Hywel Francis said: "I remember seeing the list of men who died and what shocked and struck me was they were virtually all within a mile of the pit head, from the communities of Clydach Vale, Blaenclydach, Penrhiwfer, Llwynypia and Trealaw.
"There's going to be an immediate memory for those people but it will be remembered as well historically because it continued that process of people turning away from the mining industry and leaving for cleaner and safer jobs."