§ 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:

(i) 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:

(i) 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.