160, 162, and 282, and its Report of of the explosive and the color of its Investigations No. 3337.1 wrapper are observed and recorded.

against the main charge with the | drum the rate of detonation of the excharged end of cap pointing toward the plosive is computed. charge of explosive, and the charge is then fired without stemming.

(4) Gaseous products of explosion. To determine these products a charge consisting of 200 grams of explosive from 14-inch-diameter cartridges weighed free of the wrapper, together with the proportionate quantity of original wrapper, is fired in a 15-liter Bichel gage from which the air has been evacuated. The charge is fired by means of a No. 6 electric blasting cap. Five minutes after the shot is fired the pressure is observed and recorded. A sample of gases is drawn from the gage for a chemical analysis, and the average percentage of each gas present is computed from two shots. The volume of the poisonous gases must not exceed 158 liters per 11⁄2 pounds of explosives for a permissible explosive.

If the detonation of the entire file is not complete in any trial that diameter and all smaller diameters shall be deemed nonpermissible.

(6) Pendulum-friction test. This test is made with the pendulum-friction device, which consists of a steel anvil (on which a 7-gram charge of explosive is placed) and a swinging shoe, which is attached to the lower end of a rigid, steel pendulum rod. In testing an explosive for permissibility, a steel shoe or a hardfiber-faced shoe is used. This shoe, which can be dropped from different heights above the anvil, passes over the anvil a number of times. The device is adjusted so that it swings across the face of the anvil 18±1 times before coming to rest when there is no explosive on the anvil. Ten separate trials are made. In order to pass the test a permissible explosive must not show in any trial using the hard-fiber-faced shoe dropped from a height of 1.5 meters, a result more unfavorable than an almost indistinguishable local crackling. A field sample of a permissible explosive must pass the same test, except that in the retests the height of fall of the shoe shall be 1.35 meters.

(5) Rate of detonation. The rate of detonation is determined with the Mettegang recorder. The explosive to be tested is placed in a thin sheet-iron tube 42 inches in length and one-fourth inch larger in exterior diameter than the cartridge being tested. The tube is perforated transversely at two places by holes % inch in diameter. The first hole is 2 inches from the cap end of the tube, and (7) Explosion-by-influence tests. The the centers of the two holes are exactly halved-cartridge method is employed. In 1 meter apart. These holes are covered this method a hole for embedding a No. 6 with friction tape wrapped around the electric blasting cap is made in the centube. The ends of the cartridges are cutter of one end of a 14- by 8-inch caroff, but the explosive is otherwise main-tridge. Before the cap is inserted the cartained in its original wrapper and the tube is charged as a continuous file. Through the explosive at the center of each hole there is passed a 4-inch piece of double cotton-covered copper wire (B. & S. gage No. 28).

The assembled tube is suspended in the bombproof, and two pieces of wire are then attached to complete two separate electrical circuits from the Mettegang recorder. A No. 6 electric blasting cap is embedded centrally in one end of the file of explosive so that the charged end of the cap is one-half inch from the first wire through the explosive. The legs of the cap are then connected to the firing line. After the charge is fired the readings on the sooted drum of the Mettegang recorder are made. From these readings and the known speed of rotation of the

tridge is cut in the middle at right angles to its axis; the two cut ends are placed facing each other with their axes in line. The two halves are spaced the required distance apart by rolling them in paper. The tube thus formed is held in place by carpet tacks. Just prior to firing, the

detonator is inserted in the outer end of one of the half-cartridges.

The greatest distance between the halves of the cartridge at which both halves detonate in four shots without any failures is termed the "sensitiveness" of the explosive. The minimum distance at which no explosion occurs in four shots is also determined.

(8) Large impact test. This test is made on a 1-inch length of a 11⁄4-inchdiameter cartridge, cut from the center of the cartridge. This 1-inch length of

(6) That the shot is not fired in the presence of a dangerous percentage of firedamp.

(7) That the shot is not a dependent shot, is not bored into the solid, and does not have a burden so heavy that the shot obviously is liable to blow out.

(8) That the explosive be stored under proper conditions so that it does not undergo change in character.

explosive in its original wrapper is placed on the anvil of the large impact device with the cylindrical axis of the cartridge vertical and the weight of 25 kilograms dropped 10 times from a height of 15 centimeters, fresh charges being used each time. Attached centrally to the lower end of the falling weight is a steel pin 2 inches long and 1% inches in diameter. This steel pin falls directly on the sample under examination. This test is made at the option of the Bureau of Mines when as a result of a review of the chemical analysis of the explosive, or (2) That the permissible conditions of from other cause, any question concern-charging as to thickness of disk, weight ing the sensitiveness to impact of the of heater ingredient, and weight of carexplosive arises. Failure of the explosive bon dioxide charge are met and that on any trial shall constitute a failure the device is properly confined with clay to pass the test, and such failure shall or other incombustible stemming. disqualify an explosive from further testing.*+

§ 15.8 Provisions for the permissibility of explosives and blasting devices. The Bureau reserves the right to rescind for cause, at any time, any approval granted under this part. An explosive or blasting device which has passed all tests necessary to place it on any of the Bureau's permissible lists may, therefore, be omitted from future lists.

An explosive or blasting device is permissible in use only when it satisfies the following requirements:

(a) Permissible explosives. (1) That the explosive is in all respects similar to the sample submitted by the manufacturer for test.

(2) That electric detonators (not fuse and detonators) are used of not less efficiency than No. 6, the detonating charge of which shall consist of a 1-gram mixture of 80 parts of mercury fulminate and 20 parts of potassium chlorate (or their equivalents)—and that the required electric firing must be done by means of a permissible-type blasting unit. (3) That the explosive, if frozen, shall be thawed thoroughly in a safe and suitable manner before use.

(b) Blasting devices. (1) That the device is in all respects similar to the sample submitted for tests.

(3) That the lead wires shall be connected to either type of shell top (end or side connection) only after the shell has been placed in the borehole, and further that the terminal plug when the end-connection shell top is used, shall not be inserted into the shell until these connections are being made.

(4) That the device shall not be fired in the presence of a dangerous percentage of firedamp.

(5) That the device shall not be charged with the heater ingredient and carbon dioxide in the mine.*†

§ 15.9 Wording, purpose, and use of approval plate for permissible blasting devices-(a) Approval plate. Manufacturers shall attach, stamp, or mold an approval plate on each permissible blasting device. The plate shall bear the seal of the Department of the Interior, Bureau of Mines, and be inscribed as follows: "Permissible Blasting Device Approval No. issued to the Company."

cautions shall be added. The size and When deemed necessary, appropriate position of the approval plate shall be satisfactory to the Bureau.

Where the nature of the device is such (4) That the quantity used for a shot that it is not feasible to attach a permadoes not exceed 680 grams (11⁄2 pounds)nent metal approval plate, a paper label and that it is properly confined with clay may be used if permitted by the Bureau or other incombustible stemming.

(5) That the diameter of the cartridge used must be not less than that determined by tests.

of Mines, and in addition there shall be
stamped, etched, or otherwise engraved
on the device the following: "B. M.
No.
This is an abbreviation to

indicate "Bureau of Mines Approval to the basic samples. To govern the inNo. ____." terpretation of such tests the tolerances If the exgiven hereafter are applied.

(b) Purpose. The approval plate or label is an identifying mark which en-plosive or blasting device (including ables any one to tell at a glance that the heater element) does not pass the retests device is of the permissible type. By the or exceeds the tolerances for chemical analysis or physical tests, such failure plate or label the manufacturer shows may be due to either (a) improper manuthat his device complies with the Bu- facture or (b) improper storage. reau's requirements and that it has been approved for use in coal mines.

(c) Use. Permission to place the Bureau's approval plate or label on his device obligates the manufacturer to maintain the quality of his product and to see that each device is constructed according to the drawings that have been accepted by the Bureau and are in the Bureau's files, and further to instruct the user that the device is only permissible when used as the Bureau prescribes. Blasting devices exhibiting changes in design that have not been approved are not permissible and must not bear the Bureau's approval plate or label.*†

The manufacturer is responsible for the first, but the consumer or owner is responsible for the second because the manufacturer has no control over the conditions of storage when the explosive or heater element has once passed from his ownership. The manufacturer should exercise due care that the quality of the raw materials, as well as the weighing and incorporation of them, shall be similar in all respects to those employed in the making of the original sample.

The user should employ only explosives or heater elements which are in first-class condition and freshly manufactured. Explosives or heater elements § 15.10 Instructions on handling fu- should be stored in well-ventilated magture changes in design of a blasting de-azines, and if possible the temperature vice. When the manufacturer desires to make any changes in the design of a blasting device he must first of all obtain the Bureau's approval of the change before making the change.*+

therein should be kept below 90° F. Boxes of explosives should be placed in the magazine so that the cartridges lie horizontally. It is well to purchase explosives or heater elements only in such quantities that they can be used promptly. The explosives or heater elements purchased first should be useful first; accordingly, older explosives or heater elements should not be stored under or behind a fresh consignment.*+

§ 15.13 Tolerances as applied to field or manufacturers' samples; permissible explosives. Tolerances which provide

§ 15.11 Active and inactive lists. The Bureau maintains active and inactive lists of permissible explosives and permissible blasting devices. The active lists are published annually, and the inactive lists include those permissible explosives or blasting devices which have not been manufactured during any calendar year or those placed upon these lists at the request of manufacturers. | for reasonable limits of variation in the The Bureau will transfer an explosive or blasting device from the inactive list to the active list upon the request of the manufacturer, provided the explosive or blasting device meets the regulations then in force.*†

§ 15.12 Field sampling. The Bureau of Mines will from time to time collect and reexamine permissible explosives and blasting devices found in commercial shipments and in the field in order to determine how closely they conform

results of analyses and tests of field samples and manufacturers' samples of permissible explosives were established July 1, 1915, subsequently amended November 15, 1920, and February 26, 1921, and further modified in this section. The tolerances as enumerated below supersede all previous tolerances.

(a) Chemical analysis of field samples-(1) Moisture. The tolerances for moisture shall be in accordance with those shown in Table 1:

IATION (PERCENTAGE OF TOTAL EXPLOSIVE)
FOR VARIOUS QUANTITIES OF CONSTITUENTS

TABLE 1.-TABLE SHOWING THE LIMIT OF Var-1 Table 2.-TABLE SHOWING THE LIMIT OF VAR-
IATION (PERCENTAGE OF TOTAL EXPLOSIVE)
FOR VARIOUS QUANTITIES OF MOISTURE (PER-
CENTAGE) ARRANGED FOR "TOLERANCES" PRO-
MULGATED JULY 1, 1915, BY THE BUREAU OF
MINES

Quantity of constit-
uent (percent)

Limit of
variation
of total
explosive
(percent +)

From

To

1.4

1.0

0.0

6.4

1.3

0.2

1.4

0.6

1.5

11.5

1.8

1.4

17.5

1.8

20.4

2.1

1.8

2.0

1.9

23.5

2.6

26.4

2.0

26.5

3.0

30.4

3.3

2.1

2.3

30.5

3.4

33.5

2.5

37.5

4.2

40.5

4.6

44.5

5.0

47.4

5.3

2.6

2.8

47.5

5.4

51.4

5.7

2.7

2.9

5.8

2.8

54.5

6.2

57.5

6.6

60.0

3.0

(b) Physical tests of field samples. (1) The volume of poisonous gases from 680 grams of the explosive including its wrapper must be less than 158 liters by one trial or the average of two or three trials. The volume of poisonous gases emitted by a field sample must be within a tolerance of ±15 percent of the volume emitted by the basic sample. Where the volume is over 137.3 liters and less than 158 liters then the minus-15-percent tolerance will be the only one applied. (2) Rate of detonation by Mettegang recorder in sheet-steel tubes; ±15 per

(3) Impurities in ammonium nitrate may include ammonium chloride and ammonium sulfate. The tolerance for the sum of the last two items is 4 percent of the sum of all the items included as "commercial ammonium nitrate" (viz, ammonium nitrate, chloride, and sul-cent of that shown by the basic sample. fate).

(4) Other ingredients or their equivalents. For ingredients in quantities of 60 percent or more the tolerance shall be ±3 percent of the total explosive.

For ingredients in quantities not exceeding 60 percent the tolerances shall be in accordance with those shown in Table 2.

(3) Unit deflective charge. Plus or minus 10 percent of that shown by the basic sample.

(4) Grams of wrapper (for any size). Plus or minus 2 grams of that shown by the basic sample.

(5) Apparent specific gravity. Plus or minus 7.5 percent of that shown by the basic sample.