Many men believed it was too dangerous to dig him out. Two of his comrades, however, tore at the coal and dragged him clear, seconds before the whole seam collapsed.
The incident haunts him, but the most crippling legacy of his mining days was from the dust he breathed in. It has left him unable to walk more than a few metres, his lungs devastated by chronic bronchitis and emphysema.
For him to have survived to the age of 79 is no small achievement; many of his friends who worked at Glynhebog and Pentre Mawr collieries in south- west Wales are long dead, their lives shortened by lung disease.
"I took the wrong road," said Mr Morgan. "I should have followed my father into the building trade. Daft I was. I went down the mines with my friends."
Now Mr Morgan - like thousands of former pit men - has to use oxygen to keep alive. His wife, Lilian, has to be with him 24 hours a day. She said: "I don't like to say this in front of you, Derek, but I would prefer you to go - this is no life for you."
Mr Morgan has been designated 100 per cent disabled, but like his colleagues has had to wait a decade for compensation. While pneumoconiosis and silicosis were seen as industrial diseases, it has been difficult to prove to British Coal's satisfaction that chronic bronchitis and emphysema are directly linked to working in the pits.
The principle was established in the late Eighties but British Coal and ministers have been haggling over how much should be paid in compensation.
It has been estimated that since then, former miners have been dying of lung disease at the rate of 200 a week. "Before he died, one oldminer told his wife to be sure the doctors opened him up after his death so they could see what killed him," Mrs Morgan said.
Bill Sutton was X-rayed 18 times before British Coal agreed he was due compensation. Mr Sutton, 65, worked at Lewis-Merthyr and Ynysybwl collieries in the Rhondda, some 20 miles to the east of the anthracite pits that slowly crippled Mr Morgan.
"There was no such thing as dust suppression. They just sprayed our faces with water. My chest isn't as bad as some men. But I'm always wheezing. I've got lungs like a concertina."Reuse content