The Aberfan disaster was not just the single most appalling event in modern Welsh history.

What happened also represented a multiple betrayal of a whole community.

If the deaths of 116 children and 28 adults had been the result of a tragic and unavoidable accident due to natural forces – what insurance companies refer to as an Act of God – it would still have been a profoundly shocking tragedy.

But the criminal negligence of the National Coal Board (NCB) in failing to remove the tip that collapsed, coupled with the callous post-disaster treatment of the community by political leaders, made the loss of life even more heart-rending.

Unlike the Hillsborough disaster or miscarriage of justice cases that took years of persistent campaigning before the truth was recognised, the negligent conduct of the NCB was quickly exposed.

When he was appointed to chair the tribunal inquiry that investigated the disaster, Lord Justice Edmund Davies stressed that he would not be party to a whitewash – and he was true to his word.

It said: “Blame for the disaster rests upon the NCB.

"This blame is shared (though in varying degrees) among the NCB headquarters, the South Western Divisional Board, and certain individuals.

“There was a total absence of tipping policy and this was the basic cause of the disaster."

It criticised the lack of legislation regulating the safety of tips or guidance from the Inspectorate of Mines.

(Image: Daily Herald)

And it said the "legal liability of the NCB to pay compensation... is incontestable and uncontested".

Its conclusion was this: "... the Aberfan Disaster is a terrifying tale of bungling ineptitude by many men charged with tasks for which they were totally unfitted, of failure to heed clear warnings, and of total lack of direction from above.

"Not villains but decent men, led astray by foolishness or by ignorance or by both in combination, are responsible for what happened at Aberfan."

But what made the negligence even worse is that from the time the tips began to accumulate there were compelling signs that they posed a significant danger.

In the years before the Aberfan disaster, complaints had been made to the NCB by local residents and by the local Merthyr Tydfil Borough Council.

A research project by historians Martin Johnes and Iain McLean records four letters detailing those concerns.

Three years earlier, July 1963

On July 24, 1963 – more than three years before the disaster – a letter was sent by DCW Jones, the council’s Borough and Waterworks Engineer, to his colleague T Ritchie, the District Public Works Superintendent.

The letter was headed “Danger from Coal Slurry being tipped at the rear of the Pantglas School”.

It stated: “Councillor Mrs Williams has advised me that the NCB appear to be taking slurry similar to that which was deposited and gave so much trouble in the quarry at Merthyr Vale, up on to the existing tip at the rear of the Pantglas Schools.

(Image: Daily Herald)

“If this is a true statement of the position then I regard it as extremely serious, as the slurry is so fluid and the gradient so steep that it could not possibly stay in position in the winter time or during periods of heavy rain.

“Before writing to the NCB I thought it would be advisable if you called to see the position for yourself and I will leave it to you to decide whether you call at the Merthyr Vale Colliery to see the manager before you pay the visit.

"If you do this it may be a good thing as the manager would probably decide to go with you and show you exactly what they are doing.”

A month later he raised the same concerns with the NCB

Mr Jones' second letter was to D Roberts, Area Chief Mechanical Engineer for the NCB.

The letter carried the same heading and said that the Public Works Superintendent had been in touch with the Merthyr Vale Colliery manager Mr Wynne about the tipping.

He wrote: “I am very apprehensive about this matter and this apprehension is also in the minds of the local councillors and the residents in this area.

"They have previously experienced, during periods of heavy rain, the movement of the slurry to the danger and detriment of people and property adjoining the site of the tips.

“I understand that Mr Wynne has told my Superintendent that the slurry is 40% dewatered before being tipped but he agrees of course, that this would not be a solution to the movement of the slurry in the winter time due to the absorption of storm water.

“You are no doubt well aware that the tips at Merthyr Vale tower above the Pantglas area and if they were to move a very serious position would accrue.”

The NCB failed to take urgent action

The NCB’s failure to take urgent action was made clear in two letters sent by Mr Roberts, its Area Chief Mechanical Engineer.

The first, to Merthyr Town Clerk TS Evans, was dated January 28 1964 and said: “Thank you for your letters of December 16 1963 and January 24 1964.

“I regret not having replied to your letter of December 16, but I have been busy trying to find ways and means of disposing of the tailings [mine waste] and what can be done to prevent any being washed down the culvert.

It goes on to discuss the culvert in more detail but concludes: "A satisfactory and suitable place other than the tip to dispose of the tailings eludes me at the moment, and causes me great concern.

“I would suggest that I meet your Engineer on this matter, and perhaps he could let me have suitable dates after February 9 1964.”

But a second letter did acknowledge the risk posed by the tip

A second letter from Mr Roberts was sent on March 13, 1964.

It indicates that two more letters had been received raising concerns about the tip above Aberfan and refers to action being taken to deal with a culvert.

It also said: "With regard to disposing of slurries this is, at present, still being disposed of on the tipping site, via the local tramway, but it is our intention to discontinue this and dispose of the slurries mixed with washery shale at Plymouth Colliery [near Merthyr Tydfil] site until such time as a new tipping site can be found.

"As you will appreciate, these tailings are very difficult to handle and we are very careful in disposing of this material, so as not to inconvenience any person or persons and, therefore, we would not like to continue beyond the next 6/8 weeks in tipping it on the mountain side where it is likely to be a source of danger to Pantglas School.”

This letter in particular – written in a numbing and understated bureaucratic English typical of the time – illustrates the disconnect that existed between technical assessments made by NCB officials who understood how dangerous the tip was, and the failure to take any meaningful action to negate the danger.

But this was by no means the whole story.

The negligence went further

(Image: Daily Herald)

Evidence of earlier problems emerging both during the course of the tribunal inquiry and later.

The inquiry heard there had been five incidents at three tip sites between 1939 and 1965: at Cilfynydd Colliery near Pontypridd on December 5 1939; at Aberfan Tip Number 4 on October 27 1944; at Aberfan Tip Number 5 between 1947 and 1951; at Aberfan Tip Number 7 in November 1963; and at the redundant Ty Mawr Colliery in Rhondda on March 29 1965.

Dealing with them had developed the NCB’s experience and expertise on tip stability.

On the basis of these precedents, the inquiry concluded:

However, a rider was put in to the effect that it occurred “not out of wickedness, but of ignorance, ineptitude and a failure in communications”.

Unmentioned at the inquiry was a tip slide that occurred on November 23 1960 at Parc Colliery, on the west side of the Rhondda Fawr.

The South Wales Echo and Rhondda Leader reported at the time that spoil flowed down the hillside, felling a ropeway pylon as lather of waste swirled past it, strongly suggesting a flow-slide into Nant Cwm Parc.

(Image: Rhondda Cynon Taf Library and Museum Service)

The severe effects included a culvert on the Nant blocked with swept-down debris, the colliery surface and railway sidings flooded by water and tip waste, the evacuation of 44 families and restoration work that took 18 months to restore the railway sidings to normal use.

On an unrecorded date in 1965 this tip failed again, with evidence suggesting that a substantial outburst of groundwater probably occurred there, emanating from a buried spring.

So, between one and six years before the Aberfan disaster, the NCB had experienced serious tip failures displaying characteristics very similar to those at Aberfan.

The first incident was managed safely, particularly by the evacuations.

It would also have had a significant impact on the colliery’s capability to produce and export coal for some time, and all this would surely have reached the attention of the NCB’s South West Division at the time.

Almost all the senior managers and engineers at divisional level at the time of the Aberfan disaster had been in post at the time of the Parc Tip failures in 1960 and 1965.

So rather than being subject to “ignorance and ineptitude”, by 1966 this group had gained awareness of and experience of significant tip failures.

(Image: Daily Herald)

We don’t know why the Parc Tip incidents of 1960 and 1965 were not considered at the Aberfan inquiry, and can only speculate whether its conclusions on corporate and personal responsibility would have been the same if they had been.

Some 30 years after the disaster, in 1996, a paper written for the Quarterly Journal of Engineering Geology called Rapid failures of colliery spoil heaps in the South Wales Coalfield identified 21 significant incidents over a period of 67 years to 1965.

The earliest incident – reported in the Western Mail at the time – occurred on November 3 1898, when five houses were demolished in Bailey Street, Wattstown, Rhondda, below the National Colliery tip.

The tip slide happened at 1am, when residents were woken by its noise.

The flow of mine waste was halted temporarily by a high retaining wall, but within a couple of minutes the wall gave way, and with a tremendous roar the huge mass rushed on to the houses.

The residents just managed to escape, but domestic animals and possessions had to be left behind.

With all these precedents, it’s difficult to explain the inertia that seemed endemic in the NCB when it came to the overriding need to safeguard the lives of people living and working beneath the tips.

Perhaps the number of incidents coupled with the lack of fatalities engendered complacency.

Such negligence that led to the loss of so many lives is impossible to excuse.

It would have been unforgiveable if the Aberfan disaster had occurred at a time when the collieries were privately owned, and decisions not to remove the tips were taken for cost-cutting reasons. But that wasn’t the case.

The tips were the responsibility of a nationalised industry which was supposed to be dedicated to the collective good in mining communities which themselves were founded on the finest of humane principles.

In betraying the people of Aberfan, whose lives were cruelly dismissed as insignificant and unworthy of protection, the NCB also trashed the ideal of social solidarity on which the common ownership of the mining industry was built.