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 near

Chesterfield Chesterfield may refer to: Places Canada * Rural Municipality of Chesterfield No. 261, Saskatchewan * Chesterfield Inlet, Nunavut United Kingdom *Chesterfield, Derbyshire, a market town in England ** Chesterfield (UK Parliament constituen ...

Derbyshire Derbyshire ( ) is a ceremonial county in the East Midlands of England. It borders Greater Manchester, West Yorkshire, and South Yorkshire to the north, Nottinghamshire to the east, Leicestershire to the south-east, Staffordshire to the south a ...

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

1973 accident

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 (mining), face; cutt ...

were killed 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 ...

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

fatigue Fatigue is a state of tiredness (which is not sleepiness), exhaustion or loss of energy. It is a signs and symptoms, symptom of any of various diseases; it is not a disease in itself. Fatigue (in the medical sense) is sometimes associated wit ...

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 striation (fatigue), striati ...

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

Accident investigation

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 or potential energy into a form that can be either used immediately or stored until needed. Typically, regenerativ ...

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

brake shoes A railway brake is a type of brake used on the cars of railway trains to enable deceleration, control acceleration (downhill) or to keep them immobile when parked. While the basic principle is similar to that on road vehicle usage, operational ...

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 cuts 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 the "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.

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 Deformation (mechanics)#Strain, 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 Electrical in ...

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-lubr ...

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 "ve ...

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.

1938 explosion

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 the 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. Fundraising continued until October 2022 when the last figures were installed, completing the commemoration of the 106 men lost.

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