60. Tests of the Lilly Controller before it was altered after the overwind showed that it was not able to prevent the winding engine from moving the cages at a maximum speed of about 63 feet per second. This was a far higher speed than the management expected from the results obtained by their method of testing. The speed was dangerously high when persons were being carried because the stopping distance that was provided for by the Controller was much less than the distance in which a cage moving at that speed could be stopped by the application of the regenerative and mechanical braking.

61. After the Lilly Controller was altered it was able to prevent the winding engine from moving the cages at a speed exceeding 54 feet per second when winding mineral and 40 feet per second when winding persons. This reduction in the maximum speed at which persons could be carried has effected a great improvement in the standard of safety because the stopping distance for a cage is directly proportional to the square of the speed at which it is moving when the brakes are applied by the action of the Controller. Consequently the stopping distance required for a speed of 40 feet per second is only two fifths of that required for a speed of 63 feet per second.

62. This overwind and the investigation thereof show quite clearly that every automatic contrivance to prevent overwinding in accordance with the statutory Regulation should restrict the speed of winding persons so as to ensure that when the brakes are applied by the actions of the contrivance they will reduce the speed of the cage to a safe speed within the stopping distance provided for by the contrivance. This is but one of the fundamental precautions against overwinding which have been considered in several publications, especially in two papers* that were presented in 1946 and 1951. There is no doubt that dangerous overwinding of persons could not occur if the winding apparatus at every mine was constructed, operated, maintained and tested in accordance with those fundamentals.

63. The brake engine and ancillary apparatus included some features and aspects that were either unsatisfactory or not as good as they might have been. The Iversen Valve had not been properly lubricated, examined, tested and maintained. The air escape valve could not be opened in the "Fast Braking Zone" by the emergency solenoid in the circumstances which have been described earlier. The throttling valve in the cataract system which provided slow braking was not constructed to ensure that it had a minimum aperture through which the fluid could pass. Thus there was a danger that incorrect adjustment of the linkage that operated the valve or the failure thereof might greatly delay or even prevent the application of the brake. This dead weight type braking system was arranged so that slow braking was enforced during the major part of the wind where normally the cages move quickly. This was done to reduce the undesirable stresses on the winding apparatus which are inherent disadvantages produced by the momentum acquired when the dead weight falls to apply the brakes rapidly. For this and other good reasons modern braking systems do not use dead weights except where they are required as a safeguard against the failure of any fluid medium that is normally used to apply the brakes.

64. The method of testing the automatic contrivance that was used until October, 1955, was not as satisfactory as it might have been because it failed to reveal, amongst other things, the maximum speed at which the cages could be moved in the shaft. The method of testing used between that date and the overwind, however, was unsatisfactory as it did not show that the Iversen Valve was defective and that the automatic contrivance could not prevent overwinding in some circumstances. The method of testing should be designed so as to try and defeat the automatic contrivance, because it is only by this means that the testing engineer may prove whether the automatic contrivance can prevent overwinding. The reports of the results of the tests that were made were not circulated to all the officials who should have received them.

65. The winding engine was not fitted with the accelerating and decelerating cams that form part of the normal cam gear to control a Ward Leonard winder that was manufactured some years ago. Although the control system of the engine was such that accelerating cams were not necessary, the decelerating cams would automatically have provided some regenerative braking and returned the power control lever at the same position of the cages in the shaft and thus warned the engineman if he had not taken the appropriate action to control the engine properly. Thus the primary safeguard of a Ward Leonard winder had not been fitted in this case.

66. The emergency push button, by which the winding engineman could operate the safety devices and bring the engine to rest was beyond his reach and was therefore not readily available in an emergency as it should have been.

67. A winding engineman said that on one occasion some five years ago grease or rope oil had got on to the brake paths and caused the drum to slip through the brakes. He thought the grease might have dropped from two plates that were used to prevent sunlight from dazzling the engineman. There was no evidence, however, to show that this had occurred recently.

68. The safety catches in the headframe were provided with linkages by which they could be manually actuated for testing purposes from the top of the headframe. This was a most inconvenient and unsuitable position which obviously resulted in a complete lack of regular testing and contributed to the rusting and inadequate maintenance of the catches. Consequently the catches did not operate properly during the overwind, the cage was tilted and it bent one set of catches that was not sufficiently supported.

69. The breakdown in communications which caused the delay in notifying the colliery manager of the occurrence might have had more serious consequences in other circumstances such as a fire or explosion.

70. In recent years the number of serious casualties caused by overwinding accidents has been very small in relation to the one half million or so persons carried through the shafts every working day. Notwithstanding this apparently satisfactory position, there is no doubt that a violent overwind may result in a far greater disaster than any recent underground fire or explosion. The potential hazards of overwinding are increasing in these days of reorganisation, concentration, deeper shafts and high unit outputs. Formerly the maximum number of persons at risk at one time in a shaft at some of the larger mines was 128. but before long the number may be 240 and in the future it may even be 480. where there are four large cages in a shaft. Although a winding engineman rarely makes a mistake, he is human and therefore liable to do so or to lose control of the engine at any time. It follows, therefore, that some other means of bringing the engine to rest safely must be provided. An additional engineman is not adequate for this purpose and consequently it is imperative to have an automatic contrivance and ancillary apparatus that are designed, constructed, tested and maintained so that they will perform this function. The overwinding and other hazards of raising and lowering persons in shafts are so great that they demand the use of winding apparatus which conforms to the highest standards of mechanical, electrical and civil engineering practice.