Some people never recover from a major trauma. In the case of the Cambrian Colliery disaster that statement can be said of an entire village.
I grew up in Clydach Vale in the Rhondda. My house overlooked the site where the mine once stood but there was very little left of the colliery that dominated the valley. Some old rusty cables, the odd bit of wire. But what did exist in large quantities was the raw emotion of losing 31 men in a small community.
Mothers lost sons, wives left widowed, children fatherless.
For the survivors the event has been relived day after day in their mind's eye. One of those is Myrddin Pritchard.
A door slamming or a car backfiring brings it all back. He was feet away from the explosion, knocked to the ground by the blast, his lamp blown out by the wind and dust. On the morning it happened he swapped places with a friend who died. He knows it could have been him.
Getting him to talk about his experiences has been difficult. He doesn't like doing it, but for the 50th anniversary he agreed and we took him back to the scene. A memorial now stands there.
If a tragedy like that happened today, professional help would be offered to people like Myrddin. He told me the only thing offered to him was sleeping tablets.
The cause was a build up of gas due to poor ventilation. It shouldn't have happened. The colliery had some of the most advanced equipment available at the time.
After the explosion, television crews from all over the world descended on Clydach, with its steep hills and rows of terraced houses.
This archive news report from the time captures the moment and the aftermath.
The memorial wheel and garden in Clydach Vale doesn't just remember May 1965. There was another accident here in 1905 killing 33 men and just down the road at the Gorky Colliery another 7 men died in 1941. Clydach has had its fair share of tragedy.
On Sunday all will be remembered at special service at the site. The First Minister Carwyn Jones will be among those attending. But this is likely to be the last event of its kind. With the passage of time, memories fade and older generations pass.
History will remember Cambrian Colliery, and the generation that lived though it hope future generations in Clydach Vale won't forget.