speed of not more than 50 feet per minute. He must inspect one rope at a time, examining it and its connections carefully.

Special attention should be given the rope just above the socket or clamps and the safety clamps if they are used; where the rope rests

FIGURE 1.-Hoisting rope that failed due to inadequate lubrication.

on the sheave; where it leaves the drum when the cage or skip is at the collar of the shaft and the active working level; and at the place where a layer of cable begins to overlap other layers on the drum.

623637°-45-3

The life of a rope under heavy service probably will be estimated by the tonnage hoisted, while a rope used intermittently or on light duty will be estimated by the length of time it has been in use.

Accurate records of the performance of hoisting ropes at a given shaft or slope make possible an accurate forecast of the probable life of ropes of similar construction. Thorough checks of the condition of any rope should be made at intervals determined by the service it is to perform. Such inspections should be more frequent after the rope has been in service for an appreciable part of its estimated life and after any unusual happening that may have damaged the rope.

DISCARDING ROPES

No exact method has been developed to determine when a rope no longer safe for use as a hoisting rope, but the following recommendations are considered to be good practice:

1. For ropes of standard construction, when there are six broken wires in any one rope lay.

2. When wires on the crown are worn to 65 percent of their original diameter. 3. When there is a sudden decrease in the diameter of the rope.

4. When marked corrosion appears.

Whatever practices are adopted, they should always err on the side of safety rather than on the side of long life for the rope.

CAGES, SKIPS, AND BUCKETS

Cages for hoisting or lowering men should be strongly constructed of metal, with fully enclosed sides, and should be equipped with safety gates, handholds, and safety dogs. Gates should be strong metal construction and should extend from the floor to a height of at least 5 feet. Overhead bars should provide each man with an easy and secure handhold. Safety dogs should be strong enough to hold the cage or skip with its maximum load at any point in the shaft if the hoisting rope should break. The safety dogs should be tested regularly with a fully loaded cage and kept in working order at all times (fig. 2).

In vertical shafts, where heavy loads are hoisted from more than one level, chairs should be provided at each level or landing, unless chairs are attached to the cage.

In vertical shafts from which men are hoisted in buckets, the latter should be provided with a steel bonnet of substantial construction. A crosshead traveling on guides should be placed under the bonnet to prevent the bucket from swinging in the shaft. The use of a bucket for hoisting or lowering men is not considered as safe as a properly constructed cage, and its use should be restricted to shaft sinking or similar operations.

Conveyances used for hoisting and lowering men in steeply inclined shafts should be provided with level seats and handholds.

Injuries in connection with skips occur frequently from faulty loadand unloading arrangements and with their use in transporting men. In shafts not equipped with a man cage available at all times during the shift, men are sometimes compelled to travel in the skip. If this is permitted, the proper signal should be given to the hoisting engineer to advise him that men are riding. The same protection, including a

bonnet, should be given to the men as when traveling on a cage. Riding the bail of a skip should be forbidden, and this should include skip tenders, unless special provision is made, such as a small platform with a railing. No one should be allowed to ride on a loaded skip.

6

Grove, G. W., Ash, S. H., and Ristedt, E. J., Some Haulage Safety Devices for Use on Grades, Slopes, and Inclined Shafts: Bureau of Mines Miners' Circ. 43, 1942, 44 pp.

FIGURE 2.-Sliding cage doors and counterweighted shaft gates.

safety devices for transportation equipment on inclines in mines has not progressed with the requirements of the industry, probably owing to the mechanical difficulties involved on inclines of different inclination, the tendency to make shaft openings vertical instead of inclined, and the opinion that, under some conditions, escape from a runaway conveyance on an incline may be possible and often practicable.

The principal measures for preventing haulage accidents on inclines are inspection and proper maintenance of hoists, hoisting cable, and all equipment used.

Cains or safety dogs in general use on cages and skips operating in vertical shafts are applicable also to steep inclines. A mine in Mexico modified the usual scheme by placing the guides under the rails instead of along the sides of the cage or skips. The rails are spiked lengthwise to 4- by 8-inch timbers placed on top of 4- by 6-inch timbers, which are fastened to the cross sills or ties. Only two cams or safety dogs are used; these ride above the guides, and the wheels run along the tops of the guides to keep and the cams from binding or dragging on the guides.

Shoes attached to the axles by angle irons run under the guides at both ends of the combined cage and skip and prevent the skip from being derailed or raised off the guides when the safety dogs are released, as by the breaking of the cable. This combined cage and skip is operated in a shaft that inclines 65° and is used for transporting men, materials, and ore. The capacity of the skip is 60 cubic feet. The safety device has a positive action and is efficient.

The Klasnic car is unique in that when the tension normally exerted by the haulage cable is released the weight of the car on an incline causes the wheels to retract on their cam-type axles into recesses on the sides of the car body until the gear of the car rests on the roadbed and track, and prongs or grip points offer enough resistance to stop the car. These cars can be used only on slopes and have been operated rather successfully for a number of years on inclinations not exceeding 38° to 40° (84 percent).

Devices applicable to grades include various car stops, sprags, brakes, drags, and derail switches. Drags are less suitable on flat grades than on the steeper grades, that is, 10° (17.5 percent).

Slope grades allow a run-away car or train to gain considerable momentum within a very short time. Run-aways on an underground slope usually are confined to haulageways, and with drags or derailing switches the car or train can be turned into a wall or the roof and stopped with little damage other than that to the cars and their

contents.

On slopes of steeper gradient the only satisfactory devices are those of the Klansnic type, Ady-type rail grips, or auxiliary cable grips, such as the Prockter and Hardy-Tynes cars and cams or safety dogs with guides.

The only safety devices of known value for these steep gradients are the guide-and-cam type. In underground shafts these guides can be placed as in vertical shafts, but for surface inclines the method of installing the guides below the rails has many advantages.

Some of the devices discussed have been little used, and it is possible that their basic principles can be utilized in developing a fully practical

device that will benefit mining operations in general. At present the protection of persons from death or serious injury when in run-away cars, trips, or skips on inclines of 15° to 75° is by no means satisfactory. For examples of good hoisting equipment see figures 3,7 4, and 5.

7 Harrington, D., and East, J. H., Jr., Suggested Safe Practices on Hoisting: To be published as a Bureau of Mines miners' circular.

FIGURE 3.-Hoist room.