FIGURE 10.-Steel, rubber-lined explosives car.

Blasting caps and electric blasting caps should be kept separate and apart from other explosives until ready to be used.

It is recommended that primers be made up just before placing in a hole.

Detonators or other explosive materials that are not to be used in the blast should not be permitted to be present or in the vicinity of the loading area.

When drill holes are to be loaded for blasting, the explosives containers should be stacked in piles at least 25 feet, and preferably 50 feet, from the nearest drill hole to be loaded. For a given total amount of explosives in the loading area it is preferable to have a few piles each containing relatively large quantities of explosives rather than to have a large number of piles each containing small quantities. The containers should be opened some distance from the piles as needed and the opened explosives cases carried one at a time to the loading station. This station should be at least 6 feet from the hole to be loaded or from any unstemmed loaded hole and at least 25 feet from the main pile. The quantity of explosives at this point should not exceed 100 pounds. From this station the explosives should

be passed one cartridge or unit at a time for loading into the hole. Empty cases and lining paper should be removed to a waste pile immediately.

Excessively large amounts of explosives should not be delivered to the loading area at one time. If deliveries of explosives are made by truck, the quantity permitted at or near the loading operations should

FIGURE 11.-Mine truck for bringing explosives to a level magazine. be limited to one truckload. Other trucks loaded with explosives should wait or be unloaded in separate safe places away from the loading operations.

When explosives for a blast cannot be delivered to the loading area by truck or railroad and must be carried to the holes by men, the same care should be taken to avoid having excessively large quantities of explosives in one area.

Explosives should be delivered to the holes farthest from the truck first to avoid driving or walking among piles of explosives.

Some serious blasting disasters in quarries or similar operations in recent years have been caused by neglect or violation of these standard procedures, and one explosion due to other causes was made much worse by having piles of explosives too close to danger points.

An open box of primer cartridges was being carried from hole to hole by a blaster in an open-cut mine; the blaster was killed and a helper injured by the explosion of this dynamite. Leg wires of the

FIGURE 12.-Plastic container for carrying electric detonators. electric detonators were not short-circuited and were left trailing outside the box; these wires may have come in contact with an electric charge, some object may have fallen into the open box, or a wire may have been jerked. Similar accidents occurred where fuse was used in making the primers.

A quarry disaster in which 31 men were killed was due to the detonation of approximately 20 tons of dynamite by premature explosion of a hole. The dynamite for charging each hole had been placed about the tops of the holes, which were only 12 feet apart.

USE OF EXPLOSIVES AND DETONATORS

A review of reports of explosives accidents, summarized in table 5, shows that accidents during storage and transportation are relatively infrequent, indicating that the hazard is small or that it has been customary to follow safe methods, perhaps both.

The actual use of explosives is a different matter, as the annual records show a large number of accidents from this source year after year, with many accidents from the same clearly unsafe practices. The unsafe acts responsible for most explosives accidents are committed either through lack of knowledge of the dangers involved, or through carelessness or poor judgment on the part of those doing the blasting.

PRINCIPLES OF SAFE BLASTING

Three fundamental principles underlie safe practice at any blasting operations: That the risks of accident are reduced by having as few men as possible handle explosives, that men employed in blasting

should be careful and should have training and experience in the work they are to do, and that safety regulations must be observed. The number of men engaged in blasting can be curtailed by assigning certain men to these duties and systematizing the operations. At a magazine, one man should be in charge and receive and issue all explosives and detonators. At most mines it has been found advisable to have one man cut, cap, and prepare capped fuse for use; the same man usually issues capped fuse and detonators to miners; the central fuse-capping room where this work is done at a large iron mine is shown in figure 13. In large blasting operations, as in quarries,

tunnels, or long-hole blasting of stopes where crews of men work together, men or groups of men should be given the tasks of bringing explosives, opening boxes, loading, priming, tamping, connecting blasting circuits, and firing. All men in a crew should know the duties of the others, as well as his own, and the procedure to be followed to prevent confusion and interference on any task by persons not given those duties. No unnecessary men should be on any part of the work, and persons not of the loading crew should be excluded from the vicinity. In mining and other operations where blasting at a particular place is done by a crew of only two or three men, the same principles should be applied.

Men who handle explosives should be of a type who will act with caution and good judgment.. They should be men who have knowledge of the use of explosives, who know safe from dangerous practices, and who by experience follow those that are safe. Where crews are used in blasting, supervisors and those designated to skilled duties should have the necessary qualifications. A "green" man should be instructed in the necessary safety regulations before he is allowed to handle explosives, followed by work under the direction of an experienced, careful man until he has shown his fitness for the work. Men experienced in the use of explosives who, through ignorance, carelessness, or recklessness, follow unsafe practices should be trained in safe methods; those who cannot or will not adopt such teaching should not continue to handle or use explosives.

Methods of training that have been used with success are: Posting safety regulations and clearly understandable illustrations of safe methods, distribution of similar material in bulletin form, holding classes or schools, and discussion among the men themselves with instruction of men at work by their immediate supervisors.

The enforcement of safety regulations is of primary importance in preventing explosives accidents because an experience that would prove the wisdom of one or more safety regulations usually comes too late to do the victim of an explosives accident any good; another reason for supervision and enforcement of regulations in blasting is the ease with which omissions and short cuts are adopted. Close supervision must be coupled with the fostering of a sense not only of individual but also of group responsibility for careful observance of safe blasting practices.

WHEN AND BY WHOM SHOTS SHOULD BE FIRED

The problem of restricting the use of explosives in mines to especially qualified men is complicated by the need of blasting at many widely separated places; this introduces the hazard of transporting relatively large amounts of explosives from place to place in the mine if only these special men handle explosives and do the blasting. An alternative method sometimes practiced is to have the holes drilled and loaded by the miners and the actual blasting done by a shooting crew, but this method has little to recommend it in metal mines. In mines where blasting is confined to a centralized area and is so systematized that drilling can be properly done by men who do not do the blasting, it has been found advantageous to have a special blasting crew. Under this system the use of explosives has been more efficient and the hazard of blasting accidents greatly decreased.

Because of the scattered development work ordinarily necessary in metal mining, the difficulties of using a shooting crew usually are too