Mining accidents at the Markham Colliery at Staveley near Chesterfield, Derbyshire, England. Accident in 1973 On 30 July 1973, 18 coal miners 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 and 18 miners were killed by the impact. The accident was caused by fracture of the brake-rod, when a slowly growing fatigue crack reached a critical size and the brake-rod parted. Following a thorough investigation it was found that metal fatigue 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 and it is finally brought to rest by a mechanical brake. Mechanical brake consists of a pair of brake shoes 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