MARKHAM. Chesterfield, Derbyshire. 30th. July, 1973.

At the time of the accident the Markham Colliery was one of 14 producing mines in the North Derbyshire Area of the National Coal Board. It was near the village of Duckmanton about 5 miles to the north east of Chesterfield. It produced about 30,000 tons per week of saleable coal and employed 1,870 men below ground and 425 on the surface. There were four shafts at the colliery arranged in pairs with No.1, a downcast and No.4  and upcast near the general offices and No. 2 downcast and No. 3 upcast about 300 yards to the south. Coal winding was confined to Nos. 1 and 2 while Nos 3 and 4 were used for winding men and materials. At the top of the No.3 shaft there was an Aerex radial flow fan which extracted 238,000 cubic feet if air per minute at 9,8 inches water gauge.

The principle officials who held statutory appointments at the colliery including the winding equipment at the No. 3 shaft were Mr, R.B. Dunn, Area Director, Mr., J, H. Northard, Deputy Director (Mining), Mr. T.W. Peters, Area Chief Mining Engineer, Mr. G. Godfrey, Area Chief Engineer, Mr. J. Rodgers, Colliery General Manager, Mr. W. Fox, Colliery Mechanical engineer and Mr. C.C. Levers, Colliery Electrical engineer. There were two deputy Managers and each held statutory responsibility as Undermanager for a part of the colliery. Mr. D. Hotchkiss was the Senior Deputy Manager who was responsible for the surface and No. 3 shaft. The other officials who had responsibility including the winding equipment at the No. 3 shaft were Mr. A.G. Hartley, Area Mechanical Engineer, Mr. M. Blythe, Area Electrical Engineer and Mr. J.A. Plant, Colliery Chief Engineer.

The No.3 shaft was sunk to the Deep Soft seam in 1886 at a depth of 1,626 feet. Later 189 feet of the pit bottom was filled in which made the shaft 1,407 feet deep which was the Ell Coal seam level. The shaft was 15 feet in diameter and was brick lined throughout. There were two double-deck cages each of which was a capable of carrying 16 people per deck and the cage was attached to a one and one eighth inches diameter locked coil winding rope which was guided down the shaft by four one and half inch diameter half locked coil ropes on the side nearest the shaft wall. There were two rubbing ropes between the cages and these together with the guide ropes were suspended from white metal swivel glands in the headframe and tensioned by weights in the shaft sump. In the pit bottom the cages landed on wooden baulks set into the shaft walls. On the north side a platform gave access to the top deck so that simultaneous loading or unloading of men could take place. At the top of the shaft a circular brick tower formed an air lock and supported the steel frame from the detaching bells and the headgear which had back stays to ground level. Steel tie rods from the frame to the brick tower gave additional stability. Access to an overwound cage suspended from the detaching bell was provided but there was no headframe catches to support a cage in that position. Either cage could ascend 15 feet 9 inches above the normal decking before it was detached from the winding rope.

The winding engine was a 440 h.p. Ward Leonard supplied by the British Houston Company Limited of Rugby. The mechanical parts were designed and manufactured by Markham and Company Limited of Chesterfield. The engine was installed at the Do Well Colliery which was owned by the Staveley Coal and Iron Company Limited in 1921 and transferred to the Markham No. 2 shaft about 1830. In 1945 a cylindrical drum was fitted with a centre ring and in 1949 a replacement automatic contrivance of the torque controller type was installed and commissioned by Tudor Auto Services Limited which at the time of the accident was called Blacks Equipment Limited. In 1952 the original deadweight brake was replaced by a servo-spring brake unit which was in use at the time of the accident. At the same time a Lockheed hydraulic impulse brake tripping system was installed but this was replaced in 1960 a Blacks high pressure oil tripping system. In the same year the 30 hertz alternating current apparatus was converted to operate from a 50 hertz power supply. In 1961 the number of men permitted to ride in the cage was increased from 24 to 32. Thicker barrel plates and anew centre ring were fitted to the drum in 1663 and the cast iron brake shoes and fulcrum brackets were replace by mild steel parts the following year.

The engine was used to wind only men, materials and limited quantities of stone and as this did not require a constant winding cycle, it was left to the enginemen to regulate the speed and rates of acceleration. The ropes were attached to the drum by means of white metal swords capels which were bolted to the drum sides next to brake paths and were double layered when they were fully wound on. A new rope had about 11 “dead” coils to allow for recapping. The drum was connected by a slid coupling to a direct current winder motor which had separately excited field windings and an open loop control system. The armature was supplied by the generator of a Ward Leonard motor generator set which was driven by an alternating current slip-ring induction motor housed with the associated control equipment in a separate building adjacent to the winding engine house.

The speed and the direction of rotation of the winder motor were controlled by the engineman’s control lever within a quadrant which had a middle “off” position. Forward or backward movement of this level operated electrical contacts which determined the polarity of the generator field and thus the direction of rotation of the winder motor. The lever also operated a rheostat which varied the generator field strength and hence the output voltage of the generator. Except at low speeds the winder motor speed was proportional to the voltage for a particular load but for each change in the load these proportionally altered.

One of the winding enginemen described a normal wind with equal number of men in each cage said that after receiving the necessary signals, he moved the control level in the appropriate direction from the “off” position, gradually applying power to the winder motor and slowly releasing the mechanical brake. The voltage applied to the motor was the increased to accelerate the winding drum until the voltage reached 300 to 320 which gave a drum speed of about 20 feet per second (13.6 miles per hour). This speed was maintained until the position of the cages in the shaft corresponded to about 10 drum revolutions (283 feet) from the end of the wind when the generator voltage was gradually reduced by moving the control level towards the “off” position to increase braking. This regenerative braking was available to reduce speed during a wind and if there was a descending out-of-balance load, to maintain a selected speed. During this regenerative braking, the winder motor, which was then being driven by the load, became a generator with an output voltage higher that that of the Ward Leonard generator. This caused the generator to drive the alternating current motor which in turn became a induction generator feeding power back into the colliery supply system which thus produce a braking effect on the winding engine. The engineman continued this braking as the wind continued by progressively reducing the voltage to about 200 at 6 drum revolutions (184) feet from the end of the wind, when a warning bell rang. He continued to decrease the voltage and the speed of the cages by gradually bringing the level to the “off” position. At about four revolutions (113 feet) from the end of the wind he progressively applied the mechanical brake until the cages come to rest. With a heavy out-of-balance load descending, the engine was controlled in a similar manner but the mechanical brake was applied earlier.

The engineman estimated the loads in the cages from readings of the winder motor current on a centre zero ammeter which was connected in the main direct current loop. When loads in the two cages were similar the starting current was about 800 amps and this reduced to zero as the cages approached mid-point of the shaft. As the weight of the descending ropes became predominant, the motor current automatically reversed to produce the regenerative braking. The value of the current was indicated on the opposite side of the ammeter scale. With a minimum out-of-balance load descending the starting current was lower, regenerative braking developed earlier and the magnitude of the braking current was greater that that obtained with equal loads in the cages. Although the regenerative braking provided and efficient means of reducing the speed of the Ward Leonard winding engine, it was available in the No. 3 winding engine only when the electrical systems were operating normally. There was no regenerative braking if the power supply failed, if any of the safety devices operated or if the emergency stop button was pressed.

At the time of the disaster a Burns Cradle type brake was in use. It consisted of a pair of Ferodo lined brake shoes applied to the underside of the brake paths by the action of a compressed spring nest operating through a system of levers. The brake was released by using compressed air to counteract the force of the spring nest and move the brake shoes away from the drum brake path. During normal braking the winding engineman’s brake lever operated an Iversen type valve which controlled the flow of compressed air to a servo-cylinder. The force from the spring nest was transmitted to the main level of the brake system by a 2 inch diameter steel rod 8 feet 11 inches long which was located in the centre of the nest, constrained by a plate at the top and connected by a crosshead trunnion to the main lever at the bottom. The piston of the servo-cylinder was connected to the free end of the main lever and when compressed air was admitted to the cylinder this lever was forced down and the brake released.

If the emergency power supply failed or any of the safety devices operated, or the emergency button was pressed, the emergency brake solenoid was de-energised and the “un-grabbing” gear immediately disengaged the engineman’s brake control level from the Iversen valve and caused the mechanical brake to be applied. The “un-grabbing” gear could not be reset until the brake control level was returned to the “brakes on” position and the safety circuits energised.

The automatic safety equipment was a Black’s controller driven from the drum shaft through a system of gears which also drove a vertical pillar type depth indicator which showed the position of the cages in the shaft. It was designed to cut off the power supply to the winder motor and cause the mechanical brake to be applied to prevent the cages, reaching an excessive speed in the acceleration, constant speed of retardation zones, being landed on the baulks at a speed exceeding five feet per second and travelling beyond a predetermined position above the highest landing. The controller had a centrifugal governor, dial mounted cams and over-speed and over-wind switches which operated in conjunction with back-out switches and two electrical safety circuits.

One of the circuits, which included the brake solenoid and all the protective features provided by the automatic safety equipment was interlocked with the pilot safety circuit which had two contactors in parallel. These contactors could be tripped by various safety devices including the winding engineman’s emergency stop button, and over-wind switch on the depth indicator, the Ward Leonard over-current relay and the slack rope and brake wear switches. The pilot safety connectors had contacts in series with two parallel connected main safety contactors which controlled the supply of electricity to the winder motor and the brake solenoid. Visual indicators in the engineman’s cabin showed correct or incorrect operation of the pilot and main safety contactors.

Before the winding engineman operated a lever which, through a linkage, altered the position of one of the cams on the automatic safety contrivance to enforce lower winding speeds. A switch on the lever gave a visual indication to the banksman, onsetter and the winding engine man that the lever was set for “man winding” but did not positively prove the position of the cam on the automatic contrivance. A rope speed indicator was installed in the engineman’s cabin next to the ammeter about 13 years before but the associated tach-generator was not fitted and the indicator never operated.

At about 5.335 a.m. on Monday 30th July 1973, the day shift winding engine man R.W. Kennan, arrived at the No.3 winding engine house as the last of the night shift men were being wound to the surface. Some 20 minutes later Kennan operated the winding engine to wind the first day shift men into the mine and by about 6.20 a.m. 105 persons had been lowered. The overlap rope cage o the Bolsover side was then loaded at the surface with 15 men on the top deck and 14 on the bottom. The underlap cage on the Roadway side was empty. The wind proceeded normally until the cages had passed the mid point of the shaft when Kennan began to retard the engine and out of the corner of his eye saw sparks under the brake cylinder and heard a bang. He immediately moved the control level towards the “off” position to increase the breaking effect and simultaneously pulled the brake lever towards the “on” position. The operation of the brake level felt the same as “picking up a pen” and had no effect on the speed of the winding drum. Kennan continued moving the control lever towards the “off” position but it appeared to him that this had little effect on the drum speed so he pressed the emergency “stop” button. He expected to see the drum brought to a sudden stop but nothing happened and as a last resort he switched off the motor for the hydraulic pump which supplied the “ungrabbing” gear. This had no effect on the winding engine and the next thing Kennan remembered was bricks falling around him.

The ascending cage was detached from the underlap rope by the operation of the detaching hook in the headframe bell but continued to ascend until it struck the roof girders of the airlock structure where it broke the surrounding concrete and brickwork. As there were no shaft catches in the headframe the cage the dropped back until it was hanging by its suspension chains from the detaching hook. The descending cage carrying the men crashed into on the pit bottom with such force that it fractured nine of the 17 wooden landing baulks. Although the power had been cut off before the crash, the momentum of the winding system unwound spare coils of overlap rope and the sword capel with part of the drum side and brake path was torn away. The rope and capel were pulled over the headgear pulley and then it fell down the shaft on top and alongside the cage containing the men. The drum continued to rotate and the flailing capel of the underlap rope seriously damaged the winding engine house and an adjoining workshop.

It was immediately obvious to the men at the bottom of the shaft that a serious accident had occurred and the onsetter entered his cabin to telephone the surface the winding rope was still falling down the shaft. He was unable to obtain an answer to his emergency call on the automatic telephone but spoke to the surface operator on a a magneto phone. The mine emergency organisations were brought into operation with a control centre at the surface.

On the north side of the pit bottom some of the tangled winding rope had to be moved and there was difficulty in opening the cage gates because their vertical rods had been distorted in the crash but once the gate were open, the removal of the casualties proceeded quickly. Morphia injections were given to the very seriously injured as they lay in the pit bottom before they were transported to the surface. Some were brought out through the nearby No.2 shaft and to minimise the delay others were carried out down a steep drift to No.4 shaft about 700 yards away. The last casualties arrived at the medical centre about two hours after the accident.

In the early stages of the recovery there was some delay in getting the injured to hospital but the situation improved as the County Authority sent more ambulances. The mobile emergency winding engine from the Mansfield Rescue Station was in position alongside the No.3 shaft about 80 minutes after the disaster. During the rescue operations, one of the workers was badly injured. J. Maxwell who had started work at the pit only that morning was the pit bottom at the time of the accident and was seriously injured when he fell from the top deck platform while assisting in the recovery.

Those who died:

  • Joseph Birkin aged 60 years, faceworker,
  • Clarence Briggs aged 52 years, deputy,
  • Joseph William Brocklehurst aged 58 years, deputy,
  • Clifford Brooks aged 58 years, deputy,
  • Henry Chapman aged 48 years, deputy,
  • George Richard Cooper aged 30 years development worker,
  • George Eyre aged 60 years, gearhead attendant,
  • Michael Kilroy aged 53 years, development worker,
  • Jan Kiminsky aged 58 years, development worker,
  • Lucjam Plewinsky aged 59 years, general worker,
  • Frederick Reddish aged 52 years, development worker,
  • Wilfred Rodgers aged 59 years, face worker,
  • Charles Leonard Sissons aged 43 years, road repairer,
  • Frank Stone aged 53 years road, repairer,
  • Charles Richard Turner aged 60 years, deputy,
  • Albert Tyler aged 64 years, back repairer,
  • Alfred White aged 57 years, deputy and
  • William Yates aged 62 years, development worker.

Those who were seriously injured:

  • Dennis Brothwell aged 44 years, development worker,
  • Frank Cowley aged 43 years, development worker,
  • Malcolm Joseph Cowley aged 29 years development worker,
  • James Reddish aged 25 years, development worker,
  • Graham Richardson aged 34 years, heavy supplies worker,
  • George Dennis Stone aged 41 years, overman,
  • Harry Taylor aged 47 years, development worker,
  • Terence Thornley aged 18 years, face trainee,
  • Terence Graham Vaughn aged 38 years, development worker,
  • William Henry Watson aged 47 years, face worker and
  • Richard Wrobels aged 44 years, faceworker.

Seriously injured in the rescue operation:

  • John Maxwell aged 35 years, reserve face worker.

The inquiry into the cause of and the circumstances attending the overwinding accident that occurred at Markham Colliery, Derbyshire on 30th July 1973, was held  by J.W. Calder, C.B., O.B.E., B.Sc., C. Eng., F.I.Min.E., H.M. Chief Inspector of Mines and Quarries, at Chesterfield Town Hall on 10th October 1973 and lasted for six days. All interested parties were represented and the report was presented on the 6th March 1974, to The Right Honourable Eric Graham Varley, M.P., Secretary of State for Energy.

There was full investigation of all the winding system at the colliery. The indications were that there had been a complete failure of the winding engine brake and it was found that the centre rod in the spring nest had broken. A short length of this rod was found under the brake engine. The bottom deck of the cage which had landed on the baulks was severely distorted but there was little damage to the top deck. The speed of impact was established to be 27 miles per hour. The top of the airlock was damaged did not affect the ventilation of the mine and inspection of the shaft by hoppet revealed no serious damage to the shaft. The repairs were made to the shaft and the engine house before the investigation could proceed.

In the early stages of the investigation the broken centre rod was removed from the spring nest and sent to the Mines Safety Research Establishment for metallurgical examination. It was found that it had failed through fatigue. After completing the investigation the winding engine was reassembled with nest spring applied calliper type brakes and a high pressure hydraulic system with duplicated brake solenoids all supplied from Blacks Equipment Limited. The drum sides were replaced, barrel plates renewed and a tacho-generator installed to operate the rope speed indicator. a reconditioned automatic contrivance was installed with an independent drive. Commissioning tests were carried out for the previous winding duties and in addition it was demonstrated that the winding system could be brought safely to rest by braking on only one brake path. The representatives of all interested parties agreed that normal winding could be resumed on 1st October 1973.

The inquiry urged immediate action that the centre rods in all spring nests similar to the one involved in the accident be changed and the National Coal Carried out non-destructive tests on winding engine brake components and examined all winding apparatus to identify all “single line” components and assess the stress in brake components. In addition schedules of mechanical and electrical examinations were being reviewed and action taken to ensure compliance with instruction PI 1965/10.

During the inquiry it became evident that there was an urgent need for a committee of engineers to consider all safety aspects of manriding in shafts and unwalkable outlets. Immediately after the inquiry Mr. Calder met representatives of all interested parties who agreed that a committee should be formed and the nation Coal Board agreed to implement any interim decisions of the committee as the work proceeded.

The inquiry came to the following conclusions:

1). The disaster was caused by the complete failure of the mechanical brake of the winding engine because the spring nest centre rod which was a “single lines” component broke. The design of the trunnion did not take account of the high pressures due to the spring nest, and the main level could not rotate freely about the trunnion axle which ad no practicable means of lubrication. Consequently, operation of the brake produced bending forces and induced fluctuating stresses in the rod which could not sustain. Cracks developed in the rod and one of them extended until failure occurred.

2). The cracks which were present in the rod could have been detected before it broke by the magnetic particle method on non-destructive testing.

3). There can be no criticism of R.W. Kennan, the winding engineman who, as a last resort, attempted to stop the engine by pressing the emergency stop button provided for that purpose.

4). It was always necessary to apply the mechanical brake to stop the engine but had regenerative braking been available after the emergency stop button was pressed, there is little doubt that the speed of the cages at the end of the wind would have been significantly reduced.

5). The fatal or serious injuries received by the men in the descending cage were caused by it crashing on to the wooden baulks at the bottom of the shaft. The accident would not have been so serious if, instead of landing baulks, an arresting device had been installed below the lowest landing.

The inspector went on to make the following recommendations:

1). All winding engines be examined and modified as necessary to ensure that the mechanical brakes should always be capable of bringing them safely to rest.

 2). Where possible the operation of winding systems should not rely on “single line” components. If this cannot be achieved the systems should be modified to ensure that “single line” components are designed, operated and maintained to prevent danger.

 3). All winding engine brake components essential for safety be non-destructively treated as necessary and the tests should be repeated at approximate intervals.

 4). A design analysis be made of all winding engine brakes components essential for safety to ensure that all the working stresses can be sustained and to establish definitive life. This analysis should take account of the fluctuation of stress irrespective of the conventional static factors of safety. The use of screwed components should be avoided when ever possible.

 5). The control systems of electric winding engines be reviewed with the object of making electrical braking available after the initiation of an emergency or automatic trip at least until the application of the mechanical brake has been proved.

 6). All solid landings in shafts be replaced by suitable arresting devices below the lowest winding level as soon as possible.

 7). An operating manual be prepared for each winding engine and the training and examination of winding enginemen be reviewed.

 8). Every winding engine which can attain a speed in excess of seven feet per second be provided with a rope speed indicator.

 9). The Coal and Other Mines (Shafts, Outlets and Roads) Regulations 1960 be revised to include additional statutory requirements for the safe winding of persons through shafts and unwalkable outlets.

 

REFERENCES

The report of the causes and the circumstances attending the overwinding accident which occurred at the Markham Colliery, Derbyshire, on the 30th July 1973 by J.W. Calder, C.B., O.B.E., B.Sc., C.Eng., F.I.Min.E.,  H.M. Chief Inspector of Mines and Quarries. C.D. 5557.

Information supplied by Ian Winstanley and the Coal Mining History Resource Centre.

 

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