The Gresford disaster (Welsh: Trychineb Gresffordd) occurred on 22 September 1934 at Gresford Colliery, near Wrexham, when an explosion and underground fire killed 261 men. Gresford is one of Britain's worst coal mining disasters: a controversial inquiry into the disaster did not conclusively identify a cause, though evidence suggested that failures in safety procedures and poor mine management were contributory factors. Further public controversy was caused by the decision to seal the colliery's damaged sections permanently, meaning that the bodies of only eight of the miners were ever recovered. Two of the three rescue men who died were brought out leaving the third body in situ until recovery operations began the following year.
The Westminster and United Collieries Group began to sink the pit at Gresford in 1908. Two shafts were sunk 50 yd (46 m) apart: the Dennis and the Martin. They were named after Sir Theodore Martin, the company chairman, and Mabel Dennis, wife of the company managing director Henry Dyke Dennis, who had ceremonially cut the first sods for each of the respective shafts in November 1907. Work was completed in 1911. The mine was one of the two deepest in the Denbighshire Coalfield: the Dennis shaft reached depths of about 2,264 ft (690 m) and the Martin shaft about 2,252 ft (686 m).
By 1934, 2,200 coal miners were employed at the colliery, with 1,850 working underground and 350 on the surface. Three coal seams were worked at Gresford across several sections:
Crank (South-East and No. 1 North sections), a 3 ft (0.91 m) seam producing high-quality household coal.
Brassey (South-East and No. 1 North sections), a 4 ft (1.2 m) to 12 ft (3.7 m) seam delivering harder 'steam' coal for commercial use.
Main (Dennis, South-East and No. 1 North sections), a 7 ft (2.1 m) seam that produced softer industrial coal.
Lying east of the Bala Fault, the mine was extremely dry, unlike mines to the west of the fault, and was therefore prone to firedamp. The Main coal in particular, which made up most of Gresford's output, was "of a very gassy nature".
The explosion occurred within the main seam of Dennis. This section, which began more than 1.3 mi (2.1 km) from the shaft bottom, was mined down a shallow gradient following the 1:10 dip of the seam. At the time of the disaster Dennis was divided into six "districts": 20's, 61's, 109's, 14's, 29's, and a very deep area known collectively as the "95's and 24's". Most districts in Dennis were worked by the longwall system where the coal face was mined in single blocks. Gresford was considered a modern pit by standards of the time 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.
Evidence given at the inquiry into the disaster suggested there were a number of adverse conditions in the pit prior to the explosion. Firstly, underground mine ventilation in some districts of Dennis was probably inadequate; in particular, the 14's and 29's districts were notorious for poor air quality. The main return airway for the 109's, 14's and 29's districts was said to be 4 ft (1.2 m) by 4 ft (1.2 m) and far too small to provide adequate ventilation. Secondly, working conditions in the 2,600 ft (790 m) deep 95's and 24's district were always uncomfortably hot. Thirdly, it was alleged, there were also numerous breaches of safety regulations leading to the districts being in an unfit condition to operate.
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. It was revealed that he fired more charges during his shift than a full-time shotfirer could have safely carried out. 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. Henry Dyke Dennis was reputed in the Wrexham district to be a forceful individual who had more control of the pit than the manager. Bonsall was not a trained mining engineer and at Gresford the role of mine agent, which would normally be held by a technically experienced person with authority to stand up to both manager and owners, had for some time been temporarily filled by the company secretary since the retirement of the previous agent Sydney Cockin. Gresford had previously had a good safety record, but there were suggestions that in the two years Bonsall had not had Cockin to help him the pit's management had come under increasing commercial pressure. Bonsall admitted he had spent little time in the Dennis section of the pit in the months before the disaster, as he was overseeing the installation of new machinery in the "Slant", an area in the South-East section. Work on improving the Dennis section ventilation had been halted, and the inquiry's chair later confessed to "an uneasy feeling that Mr. Bonsall was overridden" on the matter.
On Saturday 22 September 1934 at approximately 2:00 am a violent explosion ripped through the Dennis section. The explosion started a fire near 29's district and blocked the main access road, known as "142's Deep", to all the section's other districts. At the time up to 500 men were working underground on the night shift with more than half in the affected areas. The rest were in the Slant district of the South-East section about 2 mi (3.2 km) from the explosion; many there were unaware for some time afterwards that a disaster had occurred.
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. When it cleared he telephoned the surface and told Bonsall, the manager: "something has happened down the Dennis. I think it has fired." Bonsall immediately went into the mine to try to establish what had occurred. 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. Meanwhile, the shift that was working the Slant was ordered to the pit bottom and told to get out of the mine.
Only six men had escaped from the Dennis section, all of whom were working in 29's district: Robert (Ted) Andrews, Cyril Challoner, Thomas Fisher, David Jones (the district's night shift deputy), Albert (Bert) Samuels, and Jack Samuels. Some of the group were sitting taking a mid-shift break about 300 yd (270 m) north of the Clutch when the initial explosion happened. Jack Samuels, in his testimony at the inquest, described hearing a "violent thud [...] followed at once by dust" while at the face and commenting "that's the bloody bottom gone". By the "bottom", Samuels clarified that he meant 14's district, which lay below them. A colleague advised them to leave the district via the "wind road" which was the 29's air return drift. Samuels told a further 30 men working in the 29's district to follow. 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. Jack Samuels described how Jones repeatedly fell back, commenting he was "done", but Samuels told him to "stick it" and shouldered the deputy up a ladder; Samuels was commended at the inquest for his bravery and leadership of the group. After a long and difficult escape up 1:3 gradients, several ladders, and past rockfalls, the six miners eventually rejoined the Dennis main road and met Andrew Williams, the under-manager, who along with Bonsall had immediately descended the Dennis main shaft on being notified of the explosion. Williams took David Jones and went on towards the Clutch, while the remaining five went to the pit bottom and safety.