the flanges comprising the joints between parts shall have surfaces with metal-tometal contact, except enclosures requiring glass, in which case glass-to-metal joints are permitted. Gaskets, if adequate, may be used to obtain a firm seat for the glass but not elsewhere. Rubber, putty, and plaster of paris are not acceptable as material for gaskets. For enclosures having an unoccupied volume (air space) of more than 60 cubic inches the width of the joint measured along the shortest flame path from the inside to the outside of the enclosure shall not be less than 1 inch. When the unoccupied volume (air space) is less than 60 cubic inches, this path shall not be less than three-fourths inch.

(b) Locks and seals (lighting attachment). Explosion-proof compartments shall be equipped with seals or locks that prevent unauthorized and unsafe opening of the compartments in a mine.

(c) Locks or seals (battery). The battery shall be enclosed in a locked or sealed container that will prevent exposure of live terminals.

(d) Temperature of lamp. The temperature of the lamp under conditions of use shall not be such that a person may be burned in handling it.

(e) Cable and connection. (1) The cable or cord connecting the lamp to its battery shall be of high-grade design and materials, comparable to the specially recommended trailing cables as listed by the Bureau, and shall be not more than 15 feet in length.

(2) The cable (or cord) shall be adequately protected at the battery end by a fuse in the locked battery box or housing. The cable (or cord) and the fuse shall be considered parts of the lamp, and specifications for them shall be submitted by the lamp manufacturer.

(3) The method of terminating the cable (or cord) at the lamp and at the battery housing shall be adequate, but in no case shall the cable or cord be detachable.

The Bureau reserves the right to make minor changes in the requirements outlined in subparagraphs (1), (2), and (3) of this paragraph (No. 9. class 2 lamps), as experience and service prove to be necessary in the interests of safety.

any of its parts in fulfilling the purposes for which it was designed. These tests include the following:

(a) Safety tests, including tests of safety devices, electrical contacts, and explosionproof features.

(b) Photometric tests.

(c) Tests to demonstrate adequacy of mechanical strength.

(d) Tests of nonspilling features (storagebattery lamps of class 1). (e) Temperature tests.

§ 20.11

Material required for Bureau of Mines records.

In order that the Bureau may know exactly what it has tested and approved, detailed records are kept covering each investigation. These include drawings and actual equipment, as follows:

(a) Drawings. The original drawings submitted with the application for the tests and the final drawings which the manufacturer must submit to the Bureau before approval is granted, to show the details of the lamp as approved, are retained. These drawings are used to identify the lamp and its parts in the approval and as a means of checking the future commercial product of the manufacturer.

(b) Equipment. (1) If the Bureau so desires, parts of the lamps which are used in the tests will be retained as a permanent record of the investigation and of the lamps submitted.

(2) If the lamp is approved, the Bureau will require the manufacturer, as soon as his first manufactured lamps are available, to submit one complete lamp, with the approval plate attached, as a record of his commercial product.

§ 20.12 How approvals are granted.

(a) All approvals are granted by official letter from the Bureau of Mines. A lamp will be approved under this part only when the testing engineers judge that the lamp has met the requirements of this part and after the Bureau's records concerning the lamp are complete, including manufacturer's drawings that show the lamp as it is to be made commercially. No verbal reports of the Bureau's decision concerning the investigation will be given, and no informal approvals will be granted.

(b) As soon as the manufacturer has received the formal approval he shall be free to advertise his lamp as permissible. [Sched. 10C, May 17, 1938, as amended by Supp. 1, 20 F. R. 2719, Apr. 23, 1955]

§ 20.13 Approval plate.

The manufacturer shall attach, stamp, or mold an approval plate on the battery container or housing of each permissible lamp. The plate shall bear the seal of the Bureau of Mines, and be inscribed as follows: "Permissible Lamp. Approval No. issued to the Company." When deemed necessary, an appropriate caution statement shall be added. The size, material, and position of the approval plate shall be satisfactory to the Bureau.

(a) Purpose of approval plate. The approval plate is a label which identifies the lamp so that anyone can tell at a glance whether the lamp is of the permissible type or not. By it the manufacturer can point out that his lamp complies with specifications of the Bureau of Mines and that it has been adjudged safe for use in gassy and dusty mines.

(b) Use of approval plate. Permission to place the Bureau's approval plate on his lamp obligates the manufacturer to maintain the quality of his product and to see that each lamp is constructed according to the drawings which have been accepted by the Bureau for this lamp and which are in the Bureau's filles. Lamps exhibiting changes in design which have not been approved are not permissible lamps and must not bear the Bureau's approval plate.

(c) Withdrawal of approval. The Bureau reserves the right to rescind for cause at any time any approval granted under this part.

§ 20.14 Instructions for handling future changes in lamp design.

All approvals are granted with the understanding that the manufacturer will make his lamp according to the drawings which he has submitted to the Bureau and which have been considered and included in the approval. Therefore, when he desires to make any change in the design of the lamp, he should first of all obtain an extension of the original approval to cover the change. The procedure is as follows:

(a) The manufacturer shall write to the Central Experiment Station, Bureau of Mines, 4800 Forbes Street, Pittsburgh 13, Pa., requesting an extension of his original approval and describing the change or changes proposed. With this letter he should submit a revised drawing or drawings showing the changes in detail, and one of each of the changed lamp parts.

(b) The Bureau will consider the application and inspect the drawings and parts to determine whether it will be necessary to make any tests.

(c) If no tests are necessary, the applicant will be advised of the acceptance or rejection of the proposed change by letter from the Bureau of Mines.

(d) If tests are judged necessary, the applicant will be advised of the material that will be required and of the necessary deposit to cover the fee for the test.

[Sched. 10C, May 17, 1938, as amended by Supp. 1, 20 F. R. 2719, Apr. 23, 1955]

(a) The purpose of investigations under this part is to make available flame lamps that may be safely used for detecting the presence of methane and deficiency of oxygen in mine atmospheres. Lists of such lamps will be published from time to time in order that State mine-inspection departments, compensation bureaus, mine operators, miners, and others interested in safe equipment for the mines may have information regarding permissible flame safety lamps. This part supersedes Schedule 7B, issued September 19, 1922, and goes into effect August 30, 1935.

(b) Any flame safety lamp that meets the requirements of this part will be termed permissible by the Bureau of Mines and if actively marketed will be listed as such in publications relating to permissible mining equipment.

(Approvals under this part are given only to equipment for use in gassy and dusty mines.)

(b) Adequate. Adequate means appropriate and sufficient as determined by mutual agreement between the manufacturer and the U. S. Bureau of Mines. [Sched. 7C, Aug. 30, 1935, as amended by Supp. 1, 20 F. R. 2961, May 3, 1955]

§ 21.3 Fees.

(a) Detailed inspection_.

(b) Mechanical tests of complete lamp: 1. Dropping test.

2. Impact test with 5# weight__ 3. Tension test with 10# weight_ 4. Bonnet test (pendulum impact)

5. Temperature of external parts

(c) Mechanical tests of glasses:

1. Impact test with 1# weight_ 2. Temperature test_-_.

(d) Safety tests-moving and still mixtures

(e) Safety tests-igniter. (f) Time of burning-.

(g) Detection of methane and deficiency of oxygen-

(h) Final examination and recording of drawings and specifications requisite to issuing an approval. (i) Examining and recording drawings and specifications requisite to issuing an extension of approval

(1) Tests to assist an applicant in evaluating equipment intended for certification may be made at the discretion of the Bureau. Written requests for such tests shall be directed to the Chief, Branch of Electrical-Mechanical Testing. A deposit of $200 shall be paid in advance when such tests have been authorized. The fees charged shall be in amounts proportionate to the work performed based on normal charges. Any surplus will be refunded at the completion of the work, or applied to future work, as directed by the applicant. [Sched. 7C, 30 F.R. 3755, Mar. 23, 1965]

§ 21.4 Applications.

Before the Bureau of Mines will undertake the active investigation leading to approval of any lamp, the manufacturer shall make application by letter for an investigation of his lamp. This application in duplicate, accompanied by a check, bank draft, or money order, payable to the United States Bureau of Mines, to cover all the necessary fees, shall be sent to the Central Experiment

66-067 0-67-9

(a) One complete lamp, with drawings that show the construction of the lamp and the materials of which it is made, together with a set of operating instructions, should be forwarded prepaid to the Central Experiment Station, at the time the application for tests is made.

(b) When these have been inspected by the Bureau's engineers the applicant will be notified as to the amount of material that will be required for the tests. The applicant will be notified also of the date on which the tests will be started and will be given an opportunity to witness the tests.

(c) 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 approval for permissibility 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 granting approval for permissibility, the Bureau will announce that such approval has been granted to the device and may thereafter conduct, from time to time in its discretion, public demonstrations of the tests conducted on the approved device. 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.

[Sched. 7C, Aug. 30, 1935, as amended by Supp. 1, 20 F. R. 2961, May 3, 1955]

§ 21.6

General requirements. (a) Safety in gaseous atmospheres. (1) Lamps shall be so constructed that they will not cause external ignitions when tested in gassy or dusty atmospheres, such as may be found in coal mines.

(2) Special tests will be made to determine the safety of the igniter device as follows:

(1) To determine whether external ignition is possible when the igniter is operated within the lamp in still mixtures of Pittsburgh natural gas and air.

(ii) To determine whether the residue left in the lamp after working the igniter device is a source of danger in the subsequent use of the lamp.

(iii) To determine the nature of the materials of the sparking material.

(b) Construction involving safety, operation, and maintenance. Lamps will be examined with special reference to their mechanical construction, strength, size, and weight, the replacement of parts, the ease of inspection, and the attention required to maintain proper operation. The construction shall be such that the omission or incorrect placing of any part when assembling the lamp may be readily noticed. Provision shall be made for the protection of glass chimneys against breakage by expansion or by shock.

(1) Lock. Lamps shall be provided with a magnetic lock that is adequate to prevent the loosening or removal, from the locked lamp, of any part vital to safety.

(2) Gauzes. If gauzes are used they shall be adequate for the safety required. Adequacy will be determined by tests in moving and still mixtures of Pittsburgh natural gas and air, and by inspection of the gauzes relative to the following:

(1) The material of which the gauzes are made.

(ii) The gauze mesh.

(iii) The fabrication of the gauzes, particularly as to uniformity and distortion at seams.

(iv) The relative dimensions of inner and outer gauzes.

(3) Glasses. The adequacy of the glasses will be based upon the following:

(i) The quality and form of the glass. The glasses shall have smooth surfaces throughout and should be clear. Their ends should be parallel and at right angles to the axis of the glass.

(ii) Resistance to breakage. The glasses will be tested to show their resistance to mechanical blows, both alone and when assembled in the lamp, and to sudden temperature changes, such as being sprayed by water at a temperature 85° C. lower than that of the heated glasses.

(iii) Identification. The glasses shall be marked distinctly and permanently by a name or design, by which they are to be designated commercially.

(iv) Protection of the glass against breakage. Standards or other means used for protection of the glass should protect the glass from breakage except under a direct blow against the glass.

(4) Bonnet. (i) The lamp shall be equipped with a bonnet to shield the gauze from the direct action of air currents. The adequacy of the bonnet will be determined as follows:

(ii) The completely assembled lamp will be suspended as a pendulum, the point of suspension being 6 feet above the center of the bonnet. The lamp will be withdrawn 45 degrees from the vertical and allowed to swing freely against the edge of a rigid, flat steel bar one-fourth inch thick, the edge being vertically under the point of suspension. Inward deformation of the bonnet from its normal shape or position shall be not greater than 10 percent of the original outside diameter of the lamp bonnet. The lower openings of the bonnet shall not be materially distorted by this test. (5) Performance. The lamp shall give the following performance:

(i) It shall give positive evidence of the presence of methane and of deficiency of oxygen in mine atmospheres, either through observation of the flame or by a suitable attachment, showing a definite indication in concentrations as low as 1 percent methane.

(ii) It shall have a free-burning, steady flame, sufficient fuel capacity to give 12 hours burning per filling with its normal flame, and a wick adjustment that is simple and dependable. § 21.7 Material required for Bureau of

Mines records.

In order that the Bureau may know exactly what it has tested and approved,

detailed records are kept covering each investigation. These include drawings and actual equipment, as follows:

(a) Drawings. The original drawings submitted with the application for tests and the final drawings which the manufacturer must submit to the Bureau before the approval is granted, to show the details of the lamp as approved. These drawings are used to identify the lamp in the approval and as a means of checking the future commercial product of the manufacturer.

(b) Actual equipment. (1) If the Bureau so desires, parts of the lamps which are used in tests will be retained as a permanent record of the investigation and of the lamps submitted.

(2) If the lamp is approved, the Bureau will require the manufacturer, as soon as his first manufactured lamps are available, to submit one complete lamp, with the approval plate attached, as a record of his commercial product. § 21.8 How approvals are granted.

(a) All approvals are granted by official letter from the Bureau of Mines. A lamp will be approved under this part only when the testing engineers judge that the lamp has met the requirements of the schedule and the Bureau's records concerning the lamp are complete, including drawings from the manufacturer that show the lamp as it is to be made commercially. No verbal reports of the Bureau's decisions concerning the investigation will be given, and no informal approvals will be granted.

(b) As soon as the manufacturer has received the formal approval he shall be free to advertise his lamp as permissible. [Sched. 7C, Aug. 30, 1935, as amended by Supp. 1, 20 F. R. 2961, May 3, 1955]

The manufacturer shall attach, stamp, or mold an approval plate on each permissible lamp. The plate shall bear the seal of the Bureau of Mines, and be inscribed as follows: "Permissible Flame Safety Lamp. Approval No. issued to the Company." When deemed necessary, an appropriate caution statement shall be added. The size and position of the approval plate shall be satisfactory to the Bureau.

(a) Purpose of approval plate. The approval plate is a label which identifies the lamp so that anyone can tell at a glance whether the lamp is or is