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 but this 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 caliper 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 pad. 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 assed 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 had 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 tested 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.