Gresford was considered a modern pit by standards of the time[6] and most districts in the Dennis section were mechanised except 20's and 61's, which were farthest from the main shaft (approximately 2.75 mi (4.43 km)) and which were still worked by hand.

[11] The disaster inquiry was told that one of the pit deputies, whose job was to oversee the safety of a district, admitted that he also carried out shotfiring during his shifts, in addition to his other duties.

[12] The colliery had incurred an operating loss in 1933, and the pit manager, William Bonsall, is thought to have been under pressure from the Dennis family to increase profitability.

In Dennis the night overman, Fred Davies, who was on duty at the bottom of the main shaft, heard a crashing sound and was enveloped in a cloud of dust for around 30 seconds.

At approximately 3:30 am the afternoon shift overman, Benjamin Edwards, reported that parts of the Dennis main road were on fire beyond a junction, known as the Clutch, where the haulage motors were located, and that a large number of miners were trapped beyond the blaze.

But as the six-man lead group went ahead attempting to fan the air to mitigate the effects of the deadly afterdamp, they soon realised the other miners had not followed them.

[23] Bonsall later stated that his intent had only been that the team establish the atmosphere in the return:[17] he claimed that his order had been "not to go in until they got definite instructions from me, because what I had in my mind was that it would be charged with carbon monoxide, and I did not want them to go through that because there would not be the slightest chance of getting men back through it.

[25] Despite the fact that the carbon monoxide levels in the 20's return suggested that no one farther inbye could be left alive,[24] rescue efforts became focused on trying to fight the fire at 29's Turn, using sand, stone dust, and extinguishers.

"[27] By early Saturday morning large crowds of concerned relatives and off-duty miners had gathered silently at the pit head awaiting news.

Hopes were raised in the evening when rumours began circulating that the fire in the Dennis main road was being brought under control; families waiting at the surface were told rescue teams would soon be able to reach the miners in the 29's, the nearest district beyond the Clutch.

On 25 September, a surface worker named George Brown became the 265th victim when he was killed by flying debris after one blast blew the cap off the Dennis shaft.

2 rescue team, accompanied by two inspectors and a Ministry of Mines doctor, entered into the 20's return airway to recover the body of John Lewis of Cefn-y-Bedd, one of the members of the No.

[27] By July, a party of men using breathing apparatus had proceeded 700 yards beyond the stoppings into the Dennis section as far as the top of the haulage road of the 142's Deep, though they found no trace of any of the missing miners.

Local interest in the inquiry was enormous: as time went on the colliery officials called as witnesses faced increasing hostility from the public gallery, to the degree the atmosphere began to affect the quality of their evidence.

[34] The blast had ignited a pocket of firedamp which, Cripps suggested, had accumulated in the airway because of inadequate ventilation and the lax attitude of the management to monitoring gas levels, contrary to section 29[35] of the Coal Mines Act 1911 (1 & 2 Geo.

[36] While the regulations also gave individual miners safety responsibility, many said in evidence that they were unwilling to speak out for fear of victimisation at the hands of the deputies, or that they would lose their jobs.

[33] The assessor approved by the miners, Joseph Jones, also theorised that a large quantity of methane gas, which had accumulated at the coal face in the 14's district, might have been ignited through an accident with a safety lamp or from a spark from a mechanised coalcutter.

Jones was sharply critical of the management, stating that 14's was a "veritable gasometer", that there had been "flagrant and persistent breaches of the Coal Mines Act and General Regulations" and that the deputy responsible for ordering the rescue men into 20's airway was "guilty of manslaughter".

Although recovery teams wearing self-contained breathing apparatus re-entered the sealed pit in May 1935, both government inspectors and officials from the Westminster and United Collieries Group would not allow any further attempts to be made to access the Dennis section.

[34] Shawcross suggested that the explosion might have been caused by the spontaneous heating of a pillar of coal, based on reports of a burning smell in the area of the Clutch prior to the disaster.

[34] Shawcross had been able to demonstrate that the evidence of the miners with respect to stone dusting on the main haulage roads was exaggerated or untrue, and used this to cast doubt on their reports of gas and dangerous shotfiring practices at the face.

[42] The assessor chosen by the mine owners, John Brass, also argued that the explosion, judging by the positions in which the bodies of the haulage men were found, had taken place at the Clutch, and that the gas had come from a new drift being driven from there to 29's for ventilation.

Despite being presented with evidence of management failures, a lack of safety measures, bad working practices and poor ventilation in the pit, Walker drew very cautious conclusions about the cause in his final verdict.

[45]Later in 1937, legal proceedings were started in Wrexham's petty sessions court against the pit manager, the under-manager and United & Westminster Collieries Limited, the owners of the mine.

Aside from the evidence of poor working practices, it was discovered that Bonsall had after the accident instructed an assistant surveyor, William Cuffin, to falsify records of ventilation measurements during several weeks when none had actually been taken.

This decision was widely perceived by the public as a deliberate attempt by the mine owners and Inspectorate to cover up any evidence of their culpability in the cause of the explosion.

[47] The miners' unions continued to press for entry into the sealed districts to recover bodies, with Grenfell and senior union officials including Herbert Smith and Joe Hall of the Miners' Federation of Great Britain volunteering to lead the recovery teams personally, but the matter was finally settled when the three Gresford rescue teams themselves said they would follow the Inspectorate's advice in the matter.

[48] Bonsall was portrayed by Cripps and others as a ruthless and cynical manager, but researchers now think that he is more likely to have been a "weak man driven beyond his capabilities"[49] whose evidence was affected by the extreme exhaustion and stress of enduring 4000 questions and 20 hours of cross-examination at the inquiry.

[52] Williams was understood to have recognised the dangerous conditions on taking the job at Gresford and had begun to rectify them: he also had three sons working in the pit, giving him, it was suggested, a personal interest in its safety.

[citation needed] "The Gresford Disaster" is a folk song in 6/8 time which appears to have been published anonymously and distributed as a broadside shortly after the colliery explosion.