It was 9:15 on a Friday morning when a towering mound of mine waste collapsed at the Merthyr Vale Colliery in the Welsh town of Aberfan, sending millions of tons of sludge crashing down onto Pantglas Junior School in the valley below as classes were beginning for the day.

The wave of rubble killed 116 children, many entombed at their desks, and 28 adults. The school and 18 homes were destroyed. The tragedy, which took place 50 years ago Friday, remains one of the United Kingdom's worst disasters involving children.

Aberfan led to tougher rules on safety and demands for corporate responsibility. The state-owned National Coal Board lied about the causes of the disaster and then tried to cover up its mistakes. A tribunal was convened to investigate — and only then did the truth emerge.

The ability of a tribunal to get at the truth still feeds into policy making — with the aggrieved calling for independent investigations into other national traumas, such as Britain's involvement in the Iraq War and a national sex-abuse scandal.

The Aberfan disaster led to a national admiration for one small coal-mining village in Wales which kept fighting for justice and compensation even after public officials abandoned them. The community had to fight to have the rubble cleared and to have the other tips removed — at one point having to pay for the cleanup themselves. The trauma of the day stayed with many all of their lives.

"Aside from the horrible things that happened on the day, it was the terrible things that happened afterward" that scarred the community, said Iain McLean, a professor of politics at Oxford University who wrote a book about the disaster. "The question is whether collectively society has gotten any better at seeing this through and stopping it from happening?"

In 1966, coal dominated the economy of south Wales and the mines were owned by the National Coal Board, created when the Labour government nationalized the industry after World War II.

Mine waste from Merthyr Vale Colliery was dumped on Merthyr Mountain above Aberfan in massive piles known as tips. The newest, Tip No. 7, was built over streams and springs, which over the years turned the waste to slurry.

Villagers had long complained about water and sludge that slid down the hillside during winter storms, blocking sewers and roads near Pantglas School. A few miles away in 1939, a slide sent 180,000 tons of waste crashing into the valley below, altering the course of the River Taff.

The warnings were ignored.

On the morning of the disaster, Jeff Edwards was sitting at his desk when he heard a rumbling sound.

"The lights started to shake — they were on corded wire — back and forth. It got louder and louder again, and the teacher kept saying it was thunder," Edwards, now 58, told Britain's Press Association. "The next thing I remember is waking up covered in all this material that had been washed over from the other side of the classroom to my side."

Slurry had thundered down the hillside and into the school. More than a hundred children and four teachers managed to scramble out the wreckage, mostly from the younger classes.

Parents and neighbors were first on the scene, searching through the rubble brick by brick as they started to search for survivors. The local fire brigade, mine safety crews and miners joined the effort, and were able to pull some children from the wreckage alive.

The Coal Board said abnormal rainfall had caused the coal waste to slip. The public inquiry ruled that the board had been negligent in allowing water to collect in the piles of rubble.

When the community demanded that the remaining tips be removed for fear of another avalanche, the Coal Board and local authorities once again resisted. The community eventually had to contribute 150,000 pounds from disaster relief funds donated to the people of Aberfan to help fund the work.

The money was eventually repaid, and then in 1997 the Welsh government donated 1.5 million pounds (then equivalent to about $2.4 million) to the Aberfan memorial charity to compensate for lost interest and inflation.

Fifty years after Tip No. 7 gave way, reminders of those events are all around.

A memorial stands at the site of Pantglas School. A group of young women who banded together after the disaster continue to meet.

Edwards said he has felt a "huge feeling of guilt" because he survived and so many of his peers did not.

"A whole generation was wiped out," he said. "There was very few of us that survived, and we had to grow up really quickly. ... We lost a lot of our childhood simply because we had no one to play with, most of the children had died."