At 8.10am on the morning of October 14, 1913, Evan James and Charles Brown were starting their mining shift 2,000ft beneath a green valley in South Wales.
They were hauliers, directing the teams of dray horses that dragged tubs of coal from the face to the mine shaft to be winched up to the surface.
As they bent to their back-breaking task, there was an ear-splitting boom. The spark from an electric bell had ignited a dangerous mix of methane gas and coal dust, known to miners as “firedamp”.
The ensuing fireball ripped through the deep pit in Senghenydd, near Caerphilly. A river of flame engulfed everything in its path.
Evan, 41, and Charles, 31, stood no chance. Their bodies were incinerated within seconds as they became two of the 439 miners who lost their lives in the worst mining disaster in British history.
The explosion 100 years ago this week was so fierce it made the Welsh valleys shudder. Those not burned to death at once were suffocated by the noxious gases left behind.
On Monday, Hilary Barbrook, granddaughter of both Evan and Charles, will join thousands of people at a memorial service to honour the men and boys who died that day.
Of the dead, 63 were teenagers including 23 aged 14-16. Another 162 were in their 20s The disaster left 542 children fatherless and made widows of more than 200 women. Ten members of the town’s rugby team were killed.
One woman had eight coffins in her house with the bodies of her husband, three brothers and four sons.
During the service, at the exact hour of the blast, a horn like the one that called the miners to work will sound across the hills. For locals who lost relatives it will be a moment charged with emotion.
“There were about 1,000 of them down there. Most didn’t stand a chance,” says gran-of-four Hilary, 73.
“The rescuers found the bodies of a father and son still huddled together. It’s impossible to imagine how horrible it must have been.”
Pointing down to the long terraced row of two-bedroom miners’ cottages, she dabs at a tear and adds: “This was only a small village. Not a single house was unaffected.
"Growing up here, all of us had lost a member of our family.” Today nothing remains of the mine that produced endless tonnes of coal to fuel the British empire.
The machinery is long gone, the shaft was filled in. But Senghenydd is a town which has lived in the shadow of the disaster ever since.
“As children we ran about in the ruins,” she adds. “The older children would say that if you look up to the mine at night you would see the dead miners coming down to haunt you. It would scare us.”
The body of Evan, Hilary’s maternal grandfather, was recovered but charred beyond recognition. The body of Charles, her father’s father, was never found.
Miraculously 18 men were rescued from beyond the wall of fire thanks to an air pocket. In all, 489 miners were brought out alive. It was a catastrophe that could have been avoided had the pit’s wealthy owners taken precautions already ordered by Act of Parliament.
Following an earlier fatal explosion the Universal Colliery all mine owners were ordered to control electrical equipment to prevent sparking, to water dusty areas, and to have reversible fans so clean air could be provided in emergencies.
None of that happened.
The inaction of mine manager Edward Shaw created the perfect conditions for an inferno. There was not even any water on hand to douse the flames. For his guilty role Shaw was fined just £24 – less than 6p per life lost. Incredibly, the pit owners were fined only £10 on one charge – not having a reversible fan.
Joyce Slade, 75, is the daughter of the young girl holding a baby on a hill above the mine entrance in our main picture. That teenager, Agnes Webber, carried her baby sister Gwyneth wrapped in a blanket and waited helplessly for news.
The iconic image was published all around the world.
“My grandfather used to drive a horse and trap,” says Joyce. “Thankfully he was not down the mine.
"But virtually all the families down the street had men down there. Nearly all died. My mother went up to wait because that is all anyone could do.”
On Monday local schoolchildren will unveil a monument which features stone plaques for each of the men who died. Engraved paving stones pay tribute to the victims of 150 other pit accidents.
Welsh rock band the Manic Street Preachers, who grew up nearby, have made a donation.
Songwriter Nicky Wire says: “We know only too well the devastating impact that mining disasters have had. It is so important that those who lost their lives are remembered.”
“I don’t think there will be a dry eye at the service,” Hilary says. “At last the lives of my grandfathers are being properly commemorated.”
For 100 years the catastrophe of Senghenydd has been a forgotten footnote of history, a blip just before the horrors of the First World War. Now its victims will finally get the tribute they deserve.