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Placing the detonator_

Size of drill hole_-_.

Firing a double charge of permissible explosive in the same hole...

Making charges..

Size of cartridges___.

Detonator should fit tightly in cartridge_.

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Detonation

Imperfect detonation by using laced fuse.

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Tampers and tamping-

Harmful gases

Limit charge----

Danger from powder and permissible explosives in the same hole_-_

Loose charges should not be used__

Shots on the solid...

Blasting with permissible explosives..

Firing with detonating squibs--

Firing with fuse---

Firing with electricity.

Defective insulation__.

Defective connections--

Electric fuses_

Frozen explosives_

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Ignition

Dry-cell batteries without safety contact buttons..

Shooting from the trolley wire..

Time for shot firing--

Special shot firers for permissible explosives-

Delay in returning after firing--

Classes of permissible explosives---

Class 1, ammonium nitrate explosives....

Class 2, hydrated explosives-

Class 3, organic nitrate explosives_

Class 4, nitroglycerin explosives-

Black blasting powder----

Opening kegs of powder

Paper powder kegs.

Making cartridges----

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Danger from use of loose powder_.

Explosive force of black blasting powder..

Charging black powder and dynamite in same hole__.
Carrying and storing powder in mines___

Tamping

Limit charge

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FIGURE 1. Arrangement of a double charge in the same hole, electric deto- Page.

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4. Details of two adjacent shots fired at the same time with
fatal results----

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5. A hole with a dead end; a dangerous shot; and a properly
placed shot_____.

6. Plan view of a poorly balanced shot---.

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7. Plan view illustrating a safe method of shooting the shot shown
in figure 6----

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8. A badly placed shot hole_-.

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Both directly and indirectly, one of the important causes of injury and death in coal mines is the misuse of explosives or the use of explosives that ought not to be used. The Bureau of Mines has therefore prepared this circular in the hope that it will be of service to the coal miner in avoiding accidents. It is divided into two parts. The first part treats of permissible explosives-dynamite and other "high" explosives-and the precautions to be observed in using them; the second part treats of black powder and the precautions to be observed in using it, because large quantities of this explosive are still used in coal mining.

The object in the development of the permissible explosives was to reduce the danger of disastrous explosions in mines where inflammable gas or dust is found. The flame from the explosion of black powder lasts 2,500 to 3,000 times longer than the flame from these permissible explosives; it also is hotter, and is therefore more likely to ignite gas or dust.

In addition to lessening the risk of fire and explosion, permissible explosives have other advantages. Among them are less damage to roof, cleaner ribs, fewer blown-out shots, less scattering of coal, fewer air blasts and windy shots, and the absence of smoke. The investigations of the Bureau of Mines show that in many mines where miners have stopped using black blasting powder and dynamite and have used permissible explosives in the proper manner they have found their work more agreeable as well as safer.

Several times within the past year mine disasters have awakened the operator and the miner to the need of earnest cooperation in an effort for greater safety. The miner can do little alone-nor by himself can the operator accomplish much-but by working hand in hand the operator and the miner in other countries have greatly reduced accidents. That accomplishment has required wise laws and regulations, based on fact and experience, and strict discipline in the mine.

To reduce the accidents due to the misuse of explosives these things are important: (1) The use of the proper permissible explosives; (2) the entire handling and firing of these explosives by shot firers who have been carefully selected and trained; and (3) strict rules for these men and careful supervision of their work.

J. A. HOLMES.

By J. J. RUTLEDGE.

PERMISSIBLE EXPLOSIVES.

PRECAUTIONS TO BE TAKEN IN THEIR USE.

As permissible explosives have been in use in the United States only a few years and miners have not had the opportunity to become as familiar with them as with black blasting powder, the bureau calls attention to the following general precautions:

Never take more than one day's supply of permissible explosives into the mine at one time.

Never leave permissible explosives in the mine over night.

Never purchase permissible explosives not suited to the coal bed.
Never use weak detonators.

Never fire a charge until it has been completely and carefully tamped. Never put black blasting powder and permissible explosives together in the same drill hole.

Never break the covering of a cartridge of a permissible explosive until ready to charge.

Never expect permissible explosives to yield entirely satisfactory results when coal is blasted off the solid.

Never expect the first blast with permissible explosives in a newly opened coal bed to be satisfactory. Several trials are often required before satisfactory results are obtained.

Never forget that permissible explosives are different from dynamite and entirely unlike black blasting powder.

Never use fuse to fire permissible explosives when it is possible to use electric firing.

PROPERTIES OF PERMISSIBLE EXPLOSIVES.

Permissible explosives give short and relatively cool flames, and are therefore not apt to set fire to or explode mixtures of dust or gas with air. They differ from black powder in many respects, but, like all other explosives, they must be handled with care. The paper wrapper should not be removed from a cartridge of a permissible explosive, and care should be taken not to break the paraffin coating

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