wall plate, and the cage was held until the steel bent and released the cage, which then jumped about 20 feet. The cager was thrown against the wall of the shaft and was decapitated and crushed between the cage deck and the wall plates. No doors were in use on the cage. The shift boss had grasped the handhold on the cage and was able to maintain his grip so that he was uninjured.

Properly fitted doors on the cage might have prevented the accident. Cages should be designed so that doors or gates can be left in place at all times. However, when cages are used from which the gates must be removed to handle cars, the gates should be replaced before men are permitted to ride. Many companies prohibit men from riding a moving cage with tools or equipment.

Moreover, tools or materials that cannot be laid on the cage deck should be securely lashed in position so that they cannot possibly project beyond the confines of the cage.

9. In a 50° inclined-shaft mine the ore body was overlaid by a bed of lignite, which if exposed to air sometimes fired spontaneously. Several places in the mine were so exposed and, in the past, men had been made sick by smoke and possibly carbon monoxide. To leave or enter this mine during the working shift, men rode the bail or ridge of a 1-ton steel skip and held onto the hoisting cable. There was a sharp curve in the inclined shaft; as the skip passed this point, it gave a sudden jerk. A miner who had become sick was riding the skip bail out of the mine. When the skip came to the curve it gave the usual jerk, causing the man to lose his grip on the cable, and he fell down the shaft and was killed.

The fatal injury is a result of an apparent combination of unsafe conditions and practices.

10. In a 60° inclined-shaft mine, the 12-ton ore skip was converted into a man-skip by placing a wooden platform on top of it. As the third shift was leaving the mine, the shift boss got the water keg, put it on the skip platform, and sat on it as the skip ascended the shaft. A chute lip on a level above extended in the shaft and had to be dodged by those on the man-skip every time it was passed. The shift boss failed to dodge this chute lip while he was sitting on the water keg and was struck by it and knocked down the shaft. When the men were able to get to him at the shaft bottom, he was dead.

It is not known whether the blow or the fall or a combination of the two caused the death of the shift boss; if the platform had been placed inside the skip, at least 42 inches below the top, he might have been struck by the chute but would not have fallen down the shaft.

The

11. A new double-drum hoist had been installed at a new location. changeover to the new hoisting equipment was made before overspeed and overwind controls had been installed. Both men and ore were transported in 10-ton skips operating in a steeply inclined shaft. Ore was being hoisted from a lower level during the second shift. For reasons unexplained, the hoistman failed to cut off the power, and a loaded skip was pulled through the headframe and into the abutting mill structure. Fortunately no one was injured; property damage was extensive.

The accident could have occurred when men were being hoisted and shows the fallacy of depending solely upon human reactions and alertness.

12. A timberman was fatally injured. Before beginning work in a stope between No. 3 and No. 2 levels the timberman and his helper were going to repair a leaking waterline in the raise heading to the stope. The timberman had his helper hoist him up the raise on a timber skip, which is powered by a small airhoist, equipped with a 3-inch wire rope. He was hoisted up the raise, stopping at 3 or 4 places to work on the pipe. When he was up about 60 feet he again stopped, and then he gave the signal (3 bells) to be hoisted farther. It was then that the cable broke about 5 feet from the bail, and the skip fell to the drift. He was given first aid, removed to the hospital, and died in less than an hour.

The timberman should not have used the skip for repair work, an unsafe though frequent practice. However, there was lack of inspection and maintenance of the brakes and rope, even for hoisting timber.

Some hoisting safety problems are difficult to solve because replacement of the original shaft and the hoist installations is not feasible. In these cases special methods should be devised to guard against recognized dangers. Insofar as possible, dependence should not be placed on care by the individual while riding into and out of the mine or from place to place underground.

HOISTS AND SAFETY DEVICES

Certain standards of safe operation apply to all uses of hoists, regardless of the material handled and the type of opening through which it is handled. Experience has shown that these standards must be met in one form or another to give protection from serious accidents. Where some of the safety equipment mentioned in the following paragraphs is not provided, the alertness and skill of the hoistman are the only assurance against disaster. In many instances of failure of some part of the equipment, the hoistman would be powerless. Wherever possible, the fullest protection should be given men who are transported into and out of the mine by these hoists.

A detailed Bureau of Mines 5 study of safe practices in hoisting gives as needed standards:

1. Hoists should be of standard design. The use of makeshift equipment should not be permitted.

2. Hoists should have enough power to hoist the loaded cage, skip, or cars and should be equipped with brakes adequate to stop and hold the full load at any point in the shaft or slope.

3. An accurate and reliable indicator of the position of the cage, skip, or cars should be in easy view of the hoistman. Marking the hoist rope should not supplant use of the indicator.

4. The hoist should be provided with automatic overwind and overspeed devices, with the possible exception of hoists at shallow workings where the hoistman has a clear view of the movement of the cage or skip. These devices should be kept in effective operating condition at all times and tested at regular intervals.

5. In most instances, electric- and steam-powered hoists should be equipped with devices that will cause automatic application of the brakes in case of power failure. They should permit lowering of the cage, skip, or cars by means of the brakes.

6. Hoists should be placed or housed so that the noise of other machinery, such as a compressor, will not prevent the hoistman from hearing signals.

7. All hoists by which men are handled should be equipped with at least two independent brakes.

8. The hoistman should be physically fit and should undergo yearly examinations to determine his continued fitness.

9. A second engineer should be in attendance at all times while men are being hoisted or lowered unless the hoist is equipped with automatic overwind, overspeed, and stop controls.

5 Harrington, D., and East, J. H., Jr., Safe Practices in Mine Hoisting: Bureau of Mines Miners' Circ. 61, 1946, 55 pp.

341084°-55- -2

ROPES

When selecting hoisting ropes, especially where men are handled, the following factors should be considered:

1. Strength.

2. Flexibility.

3. Resistance to abrasion.

4. Resistance to corrosion.

5. Crushing strength.

6. Preformed construction to twist where guides are not used.

The varying mine conditions, as well as the diverse types of equipment used in hoisting, make selection of a rope to meet specific conditions extremely difficult. Rope manufacturers, with their experience and trained personnel, are in position to advise mining companies regarding the best rope for their requirements.

Ropes used for hoisting men should be of multiple-wire construction of recognized standard character (American Standards Association Pamphlet M-11). The number and arrangement of wires in a rope are usually designated numerically by stating the number of strands and the number of wires per strand. Thus, 6-strand rope with 19 wires per strand is called a 6 by 19 rope, and one of 6 strands of 7 wires per strand is called a 6 by 7 rope.

The minimum safety factor should not be less than is shown in table 4:

TABLE 4.-Safety factors for hoisting ropes for various depths of shafts

The attachment of rope to cage or skip should develop the rope's full strength as nearly as possible. The attachment may be by means of a zinc-filled coned socket, or the rope may be bent back on itself to form an eye containing a thimble, the loose end being fastened by clips or clamps.

When properly done, the socket method develops the full strenth of the rope, but it has several disadvantages. It is much more difficult to make this attachment; poor workmanship is concealed and is revealed only when the rope slips or breaks in the socket; it cannot be inspected readily; the rope is held rigidly in the socket; and the effect of bending is concentrated just above the socket. Á spelter-filled

Ilsley, L. C., and Mosier, McHenry, Inspection and Maintenance of Mine Hoisting Ropes: Bureau of Mines Tech. Paper 602, 1939, 27 pp.

socket for a hoisting rope should be prepared only by an experienced person.

The method of fastening by clips develops approximately 80 percent of the strength of the rope; it can be inspected readily, but it bruises and crushes the strands where the clips are applied and is liable to slip.

After a rope has been attached, it should always be tested by making several trips under a heavy load before men are allowed to ride.

At least 3 full wraps or turns should remain on the drum when the rope is extended its maximum distance; the rope should make at least 1 full wrap on the drumshaft or around the spoke of the drum (in case of a free drum), and the end should be fastened securely, preferably by means of plate clamps (fig. 4).

Plate clamps, grooved to fit the rope, are generally used for attaching bridle or safety chains to rope above a socket. The bolts should be finally tightened after the rope is under tension.

A number of rope manufacturers recommend attaching the rope to cage or skip by means of a coned socket, but here also authorities differ.

the

The following is quoted from a paper presented by C. M. Haas, assistant chief engineer, Bethlehem Steel Co., Williamsport, Pa.: Sometimes the question of socketed connections versus clipped connections is presented to us. We do not favor the use of sockets on shaft hoist ropes. Due to the comparatively large mass of socket any vibration in the rope is arrested quite suddenly at the socket. This condition can cause a fatigue spot where failure may occur. This is the reason some mining codes give definite intervals

for socketing.

A thimble and clipped connection will dissipate the vibration less abruptly, and we recommend their use. Furthermore, this type of connection is susceptible to inspection. Yet even with this connection we strongly recommend that the rope be cut off and reclipped at periodic intervals.

Haas, C. M., Wire Rope-the Sinews of the Iron Range: Proc. Lake Superior Mines Safety Council, May 17-18, 1951, pp. 48-61.

ROPE CLIPS

The clamped attachment is made by bending the end of the rope back over a thimble of the proper size, to which the load is attached; this loose end is then clamped against the long end of the rope with the necessary number of clips (fig. 5).

FIGURE 5.-Correct Application of Crosley-Type Clips.

The Crosby-type U-bolt clip has proved most satisfactory.

The clips should be spaced a distance apart equal to six times the diameter of the rope with the forged-steel saddle or base against the long end or main rope and the U-bolt over the loose end.

The number of clips required to develop approximately 80 percent of the strength of a 6 by 19 plow-steel rope is shown in table 5.

TABLE 5.-Clips required for 6 by 19 plow-steel rope