72. The frames of electric tools intended to be held in the hands while being operated shall be grounded. Trailing Cables 73. Installation: Trailing cables for portable machines must be flexible and adequately insulated. The trailing cable shall be clamped securely to the machine in such a manner as to protect the cable from injury and to prevent any strain being borne by the electrical connec tion to the machine. 74. Trailing cables on portable equipment shall be protected by a fuse or circuit breaker. 75. Inspection: The machine operator shall examine daily for abrasion and other defects each trailing cable in use, and he shall also be required to observe carefully the trailing cable while in use. If a trailing cable breaks down in service or causes a person to receive a shock, it shall be put out of service at once and shall not be used until it has been repaired and tested by an authorized person. 76. Trailing cables shall be inspected once daily during the period of their use. Trolley and Storage-Battery Locomotives 77. Locomotives (reel-type): Gathering locomotives may be operated with a single-conductor trailing cable if the track is adequately bonded; otherwise, double-conductor trailing cable shall be used. The trailing cable of such locomotives shall be provided with an approved insulating hook or other device for making connection to the feed wire, also a device for connecting to the return wire if doubleconductor cable is used. 78. Storage-battery locomotives: The batteries of storage-battery locomotives shall be insulated from the battery box on all sides and the cells and trays kept free from accumulation of moisture, dust, and electrolyte. 79. Locomotive wiring: The wiring of all types of locomotives shall be of ample size to carry the current and shall be insulated and guarded with special reference to the service required and shall meet the minimum requirements of the National Electrical Code. 80. Battery rooms: Smoking or the use of open flames, or of tools which may generate sparks, should be avoided except when cells are not actively gassing and when prior ventilation has been ample. Sparks from frictional or static electricity should be avoided as they may ignite the gas at its source, as at the vent of a sealed-type cell during overcharging. Storage-battery electrolyte is corrosive, and contact with body or clothes should be avoided. A small battery-charging station in a western copper mine is shown in figure 18. CONCLUSIONS Electrical installations at a majority of metal mines do not follow established standards of safety. The danger of fire from poorly installed and poorly maintained electrical equipment is greater than is generally believed. The hazards of death and injury to mine workers from these same causes are great enough to warrant adoption and careful observance of standards at least equal to those outlined in this section of the accident-prevention course. New types of electrical equipment should be developed for mine use; they should be designed to withstand the necessary hard usage and extreme conditions of this work and to be free of shock and fire hazards with a minimum of care. Until equipment of this description is generally installed in and about mines and plants, all employees who may come into contact with electric conductors should be fully informed as to the actual hazards and the practices by which they can be avoided. 1. Is electric shock more dangerous from direct or alternating current? 3. What methods can be used to remove a victim safely from contact with a live conductor? 4. What method should be used to resuscitate a person unconscious from electric shock? 5. What are some unsafe practices sometimes found in surface electrical installations? 6. What are some of those commonly found underground? 7. What precautions should be taken when making repairs, renewals, or extensions of electrical apparatus and circuits? 8. What fire protection should be provided around underground electrical equipment? 9. How may fires be started by electrical equipment? 10. How often should underground electric circuits, substations, motors, or appliances be inspected? 11. Should trolley wires be guarded their entire length? 12. When and how should underground electrical equipment be grounded? 13. When should surface equipment be grounded? 14. What are the advantages of having all electrical equipment properly fused and provided with cut-off switches? 15. Should all underground electrical equipment be installed and operated in accordance with national electrical standards or company rules? 16. What are the State laws regarding: a. Power and light circuits and trailing cables. b. Grounding and bonding. c. Electric locomotives and motors. d. Switches, fuses, and circuit breakers. e. Underground transformers and substations. f. Report of defective equipment. g. Guarding of trolley and power wires. PART II. PREVENTION OF MECHANICAL ACCIDENTS STATISTICS ON MECHANICAL ACCIDENTS Accidents in which any kind of mechanical equipment is involved are in a way mechanical accidents. In this sense a great portion of mine accidents would fall under this classification, but as accidents from hoisting and haulage equipment and from electricity are considered under those headings, the group is restricted to accidents related to certain types of mechanical equipment. In the accident reports published by the Bureau of Mines these accidents are classed as those from machinery, hand tools, drills, power shovels, and falls of derricks and cranes. The number of accidents of these types over a 10-year period from 1934 to 1943 are shown in table 4, with the percentages of the deaths and injuries from all causes presented by these mechanical accidents. The fatal accidents from these causes amounted to 4.4 percent of all the fatalities, while the nonfatal accidents were 21.2 percent of the total. At the underground mines the fatal accidents from machinery, drilling, and hand tools were 3.5 percent of the total, and the nonfatal injuries were 21.0 percent. At open-cut mines the accidents from machinery, hand tools, power shovels, and falling cranes and derricks were charged with 13.0 percent of the fatalities and 25.0 percent of the nonfatal injuries. The fatal accidents were preponderantly those from machinery, but the bulk of the nonfatal injuries occurred when drilling and when using hand tools. The frequency rates of accidents in metal mines from hand tools, drilling, and machinery are shown graphically in figures 19, 20, and 21. These charts indicate that accidents from hand tools and drilling are occurring less frequently in recent years. The trend in respect to accidents from machinery is not so favorable. The steadily growing use of machinery in mining, as in other industries, has brought new hazards of injury to mine and plant employees. This trend continues; therefore, still different hazards are to be expected as changes in method continue. Use of more machinery and new machinery may, however, eliminate or reduce some of the older hazards, and the accidents caused by machinery are not necessarily more frequent with increased mechanization, since safety of operation is an important item in the selection of mechanical equip ment. 1936 1937 1938 1939 1940 1941 1933 1934 1935 1942 1943 FIGURE 19. Frequency rates, nonfatal accidents from hand tools at underground and open-cut metal mines, 1933-43. 1935 1936 1937 1938 1939 1940 1941 1942 1943 1933 1934 FIGURE 20.-Frequency rates, nonfatal drilling accidents in underground metal mines, 1933-43. FIGURE 21.--Frequency rates, accidents from machinery at metal mines, 1922-43. 1 Compiled from Bureau of Mines bulletins of accidents in metal and nonmetal mines. The accidents charged to machinery cause only about 2.5 percent of the fatalities and less than 5 percent of the nonfatal injuries in underground mines. At open-cut mines these accidents were respon |