(a) Drilling tests shall be conducted in a test space formed by two curtains suspended across a mine opening in such a manner that the volume of the test space shall be approximately 2,000 cubic feet.

(b) No mechanical ventilation shall be provided in the test space during a drilling test, except such air movement as may be induced by operation of drillingor dust-collecting equipment.

(c) All parts of a unit or system shall be within the test space during a drilling test.

§ 33.32 Determination of dust concentration.

(a) Concentrations of airborne dust in the test space shall be determined by sampling with a midget impinger apparatus, and a light-field microscopic technique shall be employed in determining concentrations of dust in terms of millions of particles (5 microns or less in diameter) per cubic foot of air sampled.

(b) Before a drilling test is started the surfaces of the test space shall be wetted; the test space shall be cleared of airborne dust insofar as practicable by mechanical ventilation or other means; and an atmospheric sample, designated as a control sample, shall be collected during a 5-minute period to determine residual airborne dust in the test space.

(c) A sample of airborne dust, designated as a test sample, shall be collected in the breathing zone of the drill operators during the drilling of each test hole. Time consumed in changing drill steel shall not be considered as drilling time

and sampling shall be discontinued during such periods.

[Sched. 25B, 25 F.R. 6473, July 9, 1960, as amended at 26 F.R. 2599, Mar. 28, 1961] § 33.33 Allowable limits of dust con

centration.

(a) The concentration of dust determined by the control sample shall be subtracted from the average concentration of dust determined by the test samples collected at each drill operator's position, and the difference shall be designated as the net concentration of airborne dust. Calculations of the average concentration of dust determined from the test samples shall be based upon the results of not less than 80 percent of each set of test samples.

(b) Under each prescribed test condition, the net concentration of airborne dust at each drill operator's position shall not exceed 10 million particles (5 microns or less in diameter) per cubic foot of air when determined in accordance with the method given in § 33.32(a). [Sched. 25B, 25 F.R. 6473, July 9, 1960, as amended at 26 F.R. 2599, Mar. 28, 1961] § 33.34 Drilling test.

(a) A drilling test shall consist of drilling a set of 10 test holes, without undue delay, under specified operating conditions. When the test involves the control of dust from more than one drill, all the drills shall be used in the intended manner to complete the set of test holes.

(b) Holes shall be drilled to a depth of 4 feet plus or minus 2 inches and shall be spaced so as not to interfere with adjacent holes. Each hole may be plugged after completion.

(c) Receptacles and filters for collecting drill cuttings shall be emptied and cleaned before each drilling test is started.

(d) Holes designated as "vertical" shall be drilled to incline not more than 10 degrees to the vertical. Holes designated as "angle" shall be drilled to incline not less than 30 and not more than 45 degrees to the vertical. Holes designated as "horizontal" shall be drilled to incline not more than 15 degrees to the horizontal.

[Sched. 25B, 25 F.R. 6473, July 9, 1960, as amended at 26 F.R. 2599, Mar. 28, 1961]

§ 33.35 Methods of drilling; dust-collector unit.

(a) General. All drilling shall be done with conventional, commercial drilling equipment-pneumatic-percussion, hydraulic-rotary, and/or electric-rotary types-in accordance with the applicant's specifications.

(b) Pneumatic-percussion drilling. A stoper-type drill with a piston diameter of 22 to 3 inches shall be used for roof drilling. A hand-held, sinker-type drill with a piston diameter of 22 to 3 inches shall be used for down drilling and also for horizontal drilling, except that the drill shall be supported mechanically. Compressed air for operating the drill shall be supplied at a gage pressure of 85-95 pounds per square inch. Drill bits shall be detachable, cross type with hard inserts, and shall be sharp when starting to drill each set of 10 holes. In roof drilling, 14- and 12-inch diameter drill bits shall be used; in horizontal and down drilling, 134-inch diameter bits shall be used. The drill steel shall be %-inch hexagonal and of hollow type to permit the introduction of compressed air through the drill steel when necessary to clean a hole during drilling.

(c) Rotary drilling. A hydraulicrotary drill with a rated drilling speed of 18 feet per minute free lift, capable of rotating drill steel at 900 revolutions per minute with 100 foot-pounds torque, and having a feed force of 7,000 pounds, shall be used for roof drilling. An electricrotary drill, supported by a post mounting, with a rated drilling speed of 30 inches per minute and powered by a 2.25 horsepower motor, shall be used for horizontal drilling. For roof drilling, the bits shall be hard-tipped, 1% and 11⁄2 inches outside diameter, and 14-inch auger-type drill steel shall be used. For horizontal drilling, the bits shall be hardtipped, 2 inches outside diameter, and 14-inch auger-type drill steel shall be used. Drill bits shall be sharp when starting to drill each set of 10 holes. § 33.36 Method of drilling; combination unit or dust-collecting system.

Drilling shall be conducted in accordance with the applicant's specifications and operating instructions. If special drill bits or drill steel are required, they shall be furnished to the Bureau by the applicant. Otherwise the drill bit and

drill steel requirements stated in paragraphs (b) and (c) of § 33.35 shall be complied with for all types of combination units or dust-collecting systems. § 33.37 Test procedure.

(a) Roof drilling: Drilling shall be done in friable strata, similar to the roof in the Bureau's Experimental Mine, which tends to produce large scale-like cuttings.

(b) Horizontal drilling: Drilling shall be done in strata comparable in hardness to that of coal-mine draw slate. Holes shall be started near the roof of the test space under conditions simulating the drilling of draw slate in coal mining.

(c) Down drilling: Drilling shall be done in typical mine floor strata with a pneumatic percussion-type drill. Five holes shall be drilled vertically and five holes shall be drilled at an angle.

(d) At the Bureau's discretion drilling in "on site" strata may be acceptable in lieu of strata requirements in paragraphs (a), (b), and (c) of this section. (See § 33.20(a).)

§ 33.38 Electrical parts.

(a) Units with electrical parts and designed to operate as electric face equipment (see definition, § 45.44-1 of this chapter) in gassy coal mines shall meet the requirements of Part 18 of Subchapter D of this chapter (Bureau of Mines Schedule 2, revised, the current revision of which is Schedule 2F), and the examination and testing of the electrical parts shall be entirely separate from the examination and testing of dust-collecting equipment as such.

(b) Units with electrical parts designed to operate only outby the last open crosscut in a gassy coal-mine entry, room, or other opening (including electric-drive units with their controls and push buttons) are not required to comply with the provisions of Part 18 of Subchapter D of this chapter (Bureau of Mines Schedule 2, revised, the current revision of which is Schedule 2F).

(c) Units with electrical parts and designed for operation only in nongassy coal mines are not required to comply with the provisions of Part 18 of Subchapter D of this chapter (Bureau of Mines Schedule 2, revised, the current revision of which is Schedule 2F). See § 33.11(b).)

(a) Fire-resistant conveyor belt. A conveyor belt that is identical in all respects to the sample of the conveyor belt designated as acceptable under this part.

(b) Sample. That portion of a conveyor belt submitted to the Bureau by a manufacturer for acceptance testing.

(c) Specimen. A specific portion of a sample prepared for testing purposes.

(d) Acceptance. Written official notification by the Bureau of Mines that a conveyor belt has met satisfactorily the requirements of this part.

(e) Acceptance marking. An identifying mark indicating that the conveyor belt has been accepted for listing by the Bureau of Mines as fire-resistant.

§ 34.2 Scope of this part.

The regulations in this part define the fire-resistant properties, methods of testing to determine such properties, the manner in which samples should be submitted and specimens prepared for tests, and the manufacturer's identification and markings to denote acceptance when the results of tests are satisfactory. Other requirements, such as strength, resistance to wear, and flexibility, are not covered by the regulations in this part.

§ 34.3 Preliminary consultation.

Manufacturers or their representatives may visit or communicate with the Central Experiment Station, Bureau of Mines, 4800 Forbes Avenue, Pittsburgh, Pa., 15213, to discuss the requirements or regulations in this part in connection with a belt to be submitted for test. No charge is made for such consultation, and no formal report will be submitted to the manufacturer.

§ 34.4 Application, fee, and sample.

(a) An application for investigation under this part shall be in duplicate, addressed to the Central Experiment Station, Bureau of Mines, 4800 Forbes Street, Pittsburgh 13, Pennsylvania, and shall include:

(1) Description and specifications of the conveyor belt, which may be supplemented by descriptive literature. Specifications shall include: Trade name of the conveyor belt; thickness of covers; designation of the compounds used in the manufacture of the covers, friction, and skim coats; number of plies; type and weight of ply materials; a designation of breaker strip or floated ply; and any other features deemed significant by the applicant.

(2) A statement that the conveyor belt is completely developed and ready for market.

(3) A statement that the conveyor belt has been subjected to a flame test, the nature of the test, and results obtained.

(4) A request that the necessary tests leading to acceptance be made.

(b) Each application shall be accompanied by a check, draft, or money order, payable to the United States Bureau of Mines, to cover the cost of tests (see § 34.5).

(c) Two samples of the conveyor belt to be tested, each 6-feet long by 9-inches wide and having open edges, shall be delivered without charge to the Central Experiment Station, Bureau of Mines, 4800 Forbes Avenue, Pittsburgh, Pennsylvania, 15213. A conveyor belt will not be accepted for testing under this part unless the samples submitted are constructed in the form in which the belt is to be marketed. On receipt of this application, fee, and samples to be tested, the Bureau will act on the application.

(c) Fees for unusual tests, or tests not included in this list, which might be necessary, will be based on actual costs of testing, and will be determined in advance by the Bureau. The applicant will be notified accordingly, and the fee shall be paid before such tests are begun. [Sched. 28, 30 F.R. 3757, Mar. 23, 1965] § 34.6

$25

90

Termination of investigation; disposal of fee and material.

(a) Upon request by an applicant that the Bureau terminate its investigation of the conveyor belt, the Bureau will terminate the investigation, and will return to the applicant the fees paid by him, less such portion thereof as the Bureau determines is applicable to the testing already done.

(b) The Bureau of Mines may retain as its own, for record, all or any part of the material submitted. Any material not retained by the Bureau for record will be returned to the applicant at his expense upon receipt of written request and shipping instructions within one year from the termination or completion of the tests; and thereafter may be disposed of by the Bureau as it sees fit. [22 F. R. 9867, Dec. 10, 1957] § 34.7

Date of tests.

Tests will be made in the order in which samples are received by the Bureau after applications have been filed and accepted; however, not more than three belts will be tested consecutively for any one manufacturer, if applications are on file from other manufacturers. The applicant will be notified of the date on which tests will be started. If a conveyor belt fails to meet any of the requirements set forth in this part, it shall lose its order of test precedence. Tests will be made on resubmitted samples following completion of other test work which is in progress at the time both the request and the materials for retesting are received. Exceptions to the provisions of this section may be made only for minor tests that may be performed simultaneously with other work in the laboratory.

§ 34.8 Observers at formal investigations and demonstrations.

No one shall be present during any part of the formal investigation conducted by the Bureau which leads to acceptability except the necessary Government personnel, representatives of the applicant, and such other persons as may be mutually agreed upon by the applicant and the Bureau. Upon accepting a conveyor belt for listing as fire-resistant, the Bureau will announce that such acceptability has been granted and may thereafter conduct from time to time in its discretion public demonstrations of the tests conducted on the accepted conveyor belt. Those who attend any part of the investigation, or any public demonstration, shall be present solely as observers; the conduct of the investigation and of any public demonstration shall be controlled wholly by the Bureau's personnel. Results of chemical analyses of material and all information contained in the drawings, specifications, and instructions shall be deemed confidential and their disclosure will be appropriately safeguarded by the Bureau.

(a) Size of test specimens. Specimens of conveyor belts 6 inches long by 1⁄2 inch wide by belt thickness shall be cut by Bureau test personnel from the belt sample submitted for testing to provide four test specimens, two of which will be cut parallel to the warp and two of which will be cut parallel to the weft.

(b) Flame-test apparatus. The principal parts of the apparatus within and appended to the 21-inch cubical test gallery are:

(1) A support stand with a ring clamp and wire gauze.

(2) A Pittsburgh-Universal Bunsentype burner (inside diameter of burner tube 11 mm.), or equivalent, mounted in

a burner placement guide in such a manner that the burner may be placed beneath the test specimen, or pulled away from it by an external knob on the front panel of the test gallery.

(3) A variable speed electric fan and an ASME flow nozzle (16-82 inches reduction) to attain constant air velocities at any speed between 50-500 feet a minute.

(4) An electric timer or hand-operated stopwatch to measure the duration of the tests.

(5) A mirror mounted inside the test gallery to permit the test specimen to be viewed from the back through the viewing door.

(c) Preparation of test specimen. The specimen shall be clamped in a support with its longitudinal axis horizontal and its transverse axis inclined at 45° to the horizontal. Under the test specimen shall be clamped a piece of 20-mesh ironwire gauze, 5 inches square, in a horizontal position 1⁄4 inch below the pulley cover edge of the specimen and with about 1⁄2 inch of the specimen extending beyond the edge of the gauze.

(d) Procedure for flame test. The procedure for flame tests on conveyor belting is as follows:

(1) The support stand, with the test specimen mounted as described above, shall be positioned in the burner placement guide within the flame-test gallery.

(2) The Bunsen burner shall be adjusted to give a blue flame 3 inches in height when using Pittsburgh natural gas or equivalent as a fuel.

(3) The test specimen shall be inserted into the flame at a distance 1 inch above the top of the burner.

(4) The free end of the specimen shall be centered in the flame.

(5) The observation door of the gallery shall be closed for the entire test.

(6) The burner flame shall be applied to the test specimen for 1 minute in still air.

(7) At the end of one minute, the burner flame shall be removed, the ventilating fan turned on to give an air current having a velocity of 300 feet per minute, and the duration of flame measured.

(8) After the test specimen ceases to flame, it shall remain in the air current for at least 3 minutes to determine the presence and duration of afterglow. If

a glowing specimen bursts into flame within 3 minutes, the duration of flame shall be added to the duration of flame in subparagraph (7) of this paragraph.

(9) The tests of the four specimens cut from any sample shall not result in either duration of flame exceeding an average of 1 minute after removal of the applied flame or afterglow exceeding an average of 3 minutes' duration. [Sched. 28, 20 F. R. 8419, Nov. 10, 1955, as amended at 22 F. R. 9687, Dec. 10, 1957] § 34.11 Drum-friction test.

This test shall be applied only to samples which pass the flame test.

(a) Size of test specimen. A test specimen 5 feet long by 9 inches wide shall be cut from one of the two samples of conveyor belting submitted. test (b) Drum-friction apparatus. The essential parts of the drum-friction test apparatus are:

(1) A suitable clamp for securing the fixed end of belt sample in test position and an adjustable weight clamp for the free end.

(2) Means for measuring accurately the temperature at specified points of the belt sample under test.

(3) Electric drive motor of at least 15 horsepower.

(4) Positive drive to maintain drum speed of 110±10 r. p. m.

(5) Drive pulley of at least 18 inches in diameter.

(6) Where drive pulleys in excess of 13 inches in width are used, insulation shall be provided for the portion of the face in excess of 13 inches and the ends of the drum to reduce heat loss. The test specimen shall cover approximately 180° of the exposed drum surface in test position

(7) Scales, to be installed in the fixed clamp when tension measurement is desired.

(8) Multiple jets of compressed air, issuing from 6-inch-diameter holes on 2-inch centers along the top of a 2inch pipe of the same length as the drum, to maintain an air velocity of 300 feet per minute at the surface of the drum.

(c) Preparation of test specimen. Two steel clamps, 12 inches long by 2 inches wide by 1⁄2 inch thick, shall be bolted onto the specimen approximately 1 inch from each end. One clamp, called the fixed clamp, is fitted with a chain and hook arrangement, while the other