Mining accidents A mining accident is an accident that occurs during the process of mining minerals or metals. Thousands of miners die from mining accidents each year, especially from underground coal mining, although accidents also occur in hard rock mining. ...

at the Markham Colliery at

Staveley Staveley may refer to: Places * Staveley, Cumbria, village in the former county of Westmorland and now in Cumbria, England ** Staveley railway station * Staveley-in-Cartmel, village formerly in Lancashire, now in Cumbria, England * Staveley, D ...

near

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Derbyshire Derbyshire ( ) is a ceremonial county in the East Midlands, England. It includes much of the Peak District National Park, the southern end of the Pennine range of hills and part of the National Forest. It borders Greater Manchester to the nor ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

Accident in 1973

On 30 July 1973, 18 coal

miners A miner is a person who extracts ore, coal, chalk, clay, or other minerals from the earth through mining. There are two senses in which the term is used. In its narrowest sense, a miner is someone who works at the rock face; cutting, blasting, ...

lost their lives and a further 11 were seriously injured when a descending cage carrying the men failed to slow down as it approached the bottom of the

mine shaft Shaft mining or shaft sinking is the action of excavating a mine shaft from the top down, where there is initially no access to the bottom. Shallow shafts, typically sunk for civil engineering projects, differ greatly in execution method from ...

and 18 miners were killed by the impact. The accident was caused by fracture of the brake-rod, when a slowly growing

fatigue Fatigue describes a state of tiredness that does not resolve with rest or sleep. In general usage, fatigue is synonymous with extreme tiredness or exhaustion that normally follows prolonged physical or mental activity. When it does not resolve ...

crack reached a critical size and the brake-rod parted. Following a thorough investigation it was found that

metal fatigue In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts o ...

failure occurred in the braking mechanism used to slow down the cage as it descended.

Accident investigation using fracture mechanics

Background

The main part of the set up is the winding motor which is driven by the dc motor. Two double deck cages are attached to the two ends of the winding rope. At the start of the winding cycle, power applied to winding motor is gradually increased and mechanical brake released. The cages accelerate then maintain a speed of until the cages approach the ends of the shaft. During deceleration, generator voltage driving the winding motor is reduced to produce

regenerative braking Regenerative braking is an energy recovery mechanism that slows down a moving vehicle or object by converting its kinetic energy into a form that can be either used immediately or stored until needed. In this mechanism, the electric traction mo ...

and it is finally brought to rest by a mechanical brake. Mechanical brake consists of a pair of

brake shoes A brake shoe is the part of a braking system which carries the brake lining in the drum brakes used on automobiles, or the brake block in Brake (railway), train brakes and bicycle brakes. A device that is put on a track to slow down railroad cars ...

applied to the underside of the brake paths by the action of the compressed spring nest operating through a system of levers. Force is transmitted from the spring nest to main lever through a diameter steel rod long. This vertical brake rod is always in tension as the springs are compressed. It also consists of a servospring mechanism which uses the compressed air to counteract the spring force to move the brake shoes away. For the sake of safety there is an automatic controller which cut off the power supply to winder motor and applies mechanical brake. Also there is an emergency stop button which activates the ‘ungabbling gear’ which disengages brake control lever from Iversen type valve and applies mechanical brake.

Accident

On Monday, 30 July 1973 the winding engine man noticed some sparks under the brake cylinder when he started to retard the winding. He immediately increased regenerative braking and simultaneously pulled the brake lever to ON position. As there was no effect, he pressed the emergency stop button. This too had no effect and the cage crashed the bottom wooden landing baulks with enormous force which killed 18 and seriously injured 11 people.

Investigation

All electrical and mechanical components of the winding system were thoroughly investigated to find the cause of accident. Electrical systems were found to be working as supply of compressed air was available above the servo cylinder. However the brake shoes were about clear of the brake paths as the vertical brake rod had broken into two pieces. So the investigation concentrated on the failure of the brake rod. A chemical analysis proved that the material of the brake rod (carbon steel with the designation ''En8'', conforming to British Standard 970:1947) was within the specification demanded at the time of manufacture. Metallurgical examination of the brake rod showed that it failed because of fatigue. There were many secondary cracks around the fracture surface which were detected by magnetic particle technique. To investigate fatigue failure it was necessary to determine the inservice loading of the brake rod. The broken rod was replaced with a new rod and loading conditions were applied. Four

strain gauge A strain gauge (also spelled strain gage) is a device used to measure strain on an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports ...

s were attached at a distance of from the lower end, located 90 degrees apart around the circumference of the rod. Readings were taken during manual release and application of the brake and during emergency application of brake. The results showed that in addition to the expected direct tensile stresses at gauge positions there were substantial stresses due to bending when the brake was operated. The magnitude of stresses varied to such an extent that for the one farthest from the drum there was a change from tension to compression as the brake was released. The rod was not designed for such alternating bending loads. The rod was designed with a factor of safety 6.1 for tensile stress. But when alternative bending stress are induced, failure was inevitable. It was also found that mild steel bearing pad surfaces were badly worn as

lubrication Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubric ...

was not effective at bearings. This was also due to the unexpected bending stress which progressively squeezed the lubricant out of the gap.

Follow up

A National Committee for Safety of Manriding in Shafts and Unwalkable Outlets was formed and first met on 3 December 1973. The Committee produced two reports and an addendum. The

National Coal Board The National Coal Board (NCB) was the statutory corporation created to run the nationalised coal mining industry in the United Kingdom. Set up under the Coal Industry Nationalisation Act 1946, it took over the United Kingdom's collieries on "v ...

carried out a programme to examine the braking and safety systems on all of its mine winders and modified them in accordance with the recommendations of the reports.

Underground explosion in 1938

An underground explosion in 1938 had killed 79 miners and seriously injured 40 others.

Closure of the mine

The mine closed in 1994. In 2013 the Walking Together sculpture by Stephen Broadbent was installed at the site of the former colliery. The walking trail of steel figures is a memorial to the 106 miners who died in mining disasters at Markham Colliery in 1937, 1938 and 1973. Each figure represents an individual dead miner whose name is stamped on the circular bronze tag on the figure's chest. By 2020, 88 figures had been installed with fundraising continuing to add figures of the remaining 18 miners.

References

External links

List of miners killed in 1973

{{coord, 53.244, -1.330, type:event_region:GB, display=title, format=dms 1938 in England 1973 disasters in the United Kingdom 1973 in England 1938 mining disasters 1973 mining disasters Disasters in Derbyshire Coal mining disasters in England Mining in Derbyshire 1930s in Derbyshire 1938 disasters in the United Kingdom 1970s in Derbyshire