(a) Quality of material, workmanship, and design. The Bureau of Mines reserves the right to refuse to test any equipment that, in the opinion of qualified representatives of that Bureau, is not constructed of suitable materials, or that gives evidence of faulty workmanship, or that is not designed upon sound engineering principles. This right shall apply to all parts of the equipment, and to the design thereof, whether or not the points in question are covered specifically by the requirements of this part.

(b) Type of engine considered for approval. Only locomotives equipped with engines of the compression-ignition type will be considered for approval. Such engines shall be designed to operate only on liquid fuel of flash point not less than 150° F. The starting mechanism shall consist of an explosion-proof electric motor or other device considered safe; engines using gasoline or other volatile fuel for starting will not be considered.

(c) Fuel injection. The fuel-injection system of the engine shall be so constructed that the mechanism controlling maximum fuel injection may be fixed definitely, permitting adjustment only by breaking a seal on a locked compartment, or by altering design. Provision shall be made in the fuel-injection system to permit suitable adjustment in maximum fuel injection for engine operation at different barometric pressures.

(d) Engine intake system-(1) Construction of engine intake system. The intake system of the engine (exclusive of the air cleaner) shall be of such construction that it will withstand internal pressures of 125 pounds per square inch, or such internal pressures as may be developed within it in explosion tests with gas-air mixtures, whichever is the greater. All joints in the intake system shall be formed by flanged metal-tometal contacts designed in accordance with requirements for other types of explosion-proof equipment as outlined in paragraph (i) (6) (ii) of this section.

(2) Intake flame arrester. (i) The intake system of the engine shall be equipped with a flame arrester to prevent propagation of flame from the system to a surrounding inflammable atmosphere. The flame arrester shall be so designed and attached to the intake system that it may be removed readily for inspection, repair, replacement, or cleaning. The flame arrester shall be so constructed

that it may be cleaned readily. The flame arrester shall be of sufficiently rugged construction to withstand use in its intended application and shall be so situated in the locomotive assembly that it is protected from damage.

(ii) The component parts of any flame arrester must be positively positioned. If a flame arrester of the spaced-plate type is used, the thickness of the plates must be at least 0.125 inch; the space between plates must be no greater than 0.02 inch; and the width of plates must be at least 1 inch. The unsupported length of the plates shall be such that deformation in the intended application shall not exceed 0.002 inch. Plates shall be of material not subject to corrosion in the intended application.

(3) Air shut-off valve in engine intake. A valve shall be provided in the engine intake system so that the supply of air to the engine may be shut off. This valve shall be operable from the driver's compartment and shall be so arranged that it may be actuated only when the fuel supply to the engine is shut off.

(4) Air cleaner on engine intake. An air cleaner of automotive type shall be included in the engine intake system. The air cleaner shall be situated in the intake system so that the intake air shall pass through the cleaner before entering the intake flame arrester. size and design of the air cleaner shall be such that resistance to air flow will not increase rapidly in dusty atmospheres.

The

(5) Attachment of gage to engine intake system. A vacuum gage shall be attached to the engine intake system at a point suitable for indicating total pressure drop through that system. The gage shall be graduated in inches of water and shall be situated in the driver's compartment.

(e) Engine exhaust system-(1) Construction of engine exhaust system. The exhaust system of the engine shall be of such construction that it will withstand internal pressures of 125 pounds per square inch or such internal pressures as may be developed within it in explosion tests with gas-air mixtures, whichever pressure is the greater. All joints in the exhaust system shall be formed by flanged metal-to-metal contacts designed in accordance with requirements for other types of explosion-proof equipment as outlined in paragraph (i) (6) (ii) of this section.

(i) The

(2) Exhaust flame arrester. exhaust system of the engine shall be provided with a flame arrester to prevent propagation or egress of flame or heated particles from the exhaust system to a surrounding inflammable atmosphere. The flame arrester shall be so designed that it is readily accessible for inspection, repair, replacement, or cleaning. The flame arrester shall be of sufficiently rugged construction to withstand use in its intended application and shall be so situated in the locomotive assembly that it is protected from damage.

(ii) The component parts of any flame arrester must be positively positioned. If a flame arrester of the spaced-plate type is used the thickness of the plates must be at least 0.125 inch; the space between plates must be no greater than 0.02 inch; and the width of plates must be at least 1 inch. The unsupported length of the plates shall be such that deformation in the intended application shall not exceed 0.002 inch. Plates shall be of material not subject to corrosion in the intended application.

(3) Exhaust cooling system. (i) A cooling system shall be provided for the exhaust gas of the engine. The heat-dissipation capacity of this cooling system shall be such that the temperature of the undiluted exhaust gas shall not exceed 160° F. at the point of discharge from the cooling system under any condition of operation. A device shall be provided which shall stop the engine automatically and immediately if the temperature of the exhaust gas reaches 180° F. at the point of discharge from the cooling system.

(ii) Cooling preferably shall be obtained by a water spray entering the exhaust system at a point close to the outlet, of the exhaust manifold or by passing the exhaust gas through water in suitable containers, or by a combination of the two. If a water spray is used, the water shall be delivered to the spray nozzle by a pump, and the water shall pass through a filtering device to protect the spray nozzle from clogging by extraneous material. Provision shall be made for draining and cleaning all exhaust cooling boxes included in the locomotive assembly.

(iii) If cooling equivalent to that obtained by the use of water can be provided by other means, such means will be considered acceptable.

(4) Control of surface temperature of exhaust systems. (i) Provisions shall be made for limiting the temperature attained by the external surfaces of the exhaust system. The temperature of such surfaces shall not exceed 400° F. under any condition of engine operation. If water-jacketed parts are used the jackets shall be integral with the parts in question. Insulating coverings that would absorb oil will not be considered acceptable.

(ii) If a water spray is employed to reduce the temperature of the exhaust gas, as mentioned in subparagraph (3) of this paragraph, the spray shall be situated as closely as possible to the outlet of the exhaust mainfold to aid in reducing surface temperature of this portion of the exhaust system.

(iii) Exterior surfaces of the exhaust system shall be designed to minimize accumulation and lodgment of combustible dusts and to permit ready access to these surfaces for cleaning.

(5) Dilution of exhaust gas. (i) Provision shall be made to dilute the exhaust gas with air before it is discharged from the locomotive into the surrounding atmosphere. The quantity of diluting air shall be such that the discharged mixture of exhaust gas and air shall not contain more than 100 parts per million, by volume, of carbon monoxide; 25 parts per million, by volume, of oxides of nitrogen (as equivalent nitrogen peroxide); or 10 parts per million, by volume, of aldehydes (as equivalent formaldehyde) under any condition of operation.

(ii) The final (diluted) exhaust of the locomotive shall be discharged in such manner that it is not directed toward the locomotive operator's compartment and shall be deflected downward so that persons alongside the locomotive do not encounter the exhaust at breathing level.

(6) Temperature indicator in exhaust system. A temperature-indicating device shall be provided in the exhaust system to indicate the temperature of the undiluted exhaust gas after its final contact with cooling water. The indicating portion of this device shall be situated in the operator's compartment of the locomotive.

(7) Provision for attachment of gage or gas-sampling equipment to exhaust system. A connection shall be provided in the engine exhaust system for tempo

rary attachment of a gage at a point suitable for measuring the total back pressure in that system. This connection shall be suitable also for temporary attachment of gas-sampling equipment to the exhaust system. This opening into the exhaust system shall be provided with a locking closure.

(f) Composition of exhaust gas. Under normal operating conditions, and within the rated power output range, the undiluted exhaust gas of the engine shall not contain more than 0.25 percent, by volume, of carbon monoxide.

(g) Locomotive fuel-supply system(1) Fuel tank. (i) The fuel tank shall be fuel-tight and shall be of metal at least 6 inch thick welded at all seams. The fuel tank shall be provided with a drain plug (not a valve or pet cock) that shall be locked in position when inserted. The fuel tank shall be provided with a vent opening of such design that atmospheric pressure is maintained inside the tank and that discharge of liquid fuel from the vent opening is prevented. Construction of the fuel tank shall be such that fuel may be added to the tank only through a self-closing valve situated at least 1 foot from the exhaust manifold of the engine and preferably below it. The self-closing valve shall constitute a fuel-tight closure when fuel is not being added. Any part of the self-closing valve that would be detached during the addition of fuel shall be secured to the locomotive to prevent loss.

(ii) The fuel tank shall be a built-in unit comprising part of the locomotive assembly, and no provision shall be made for attachment of separate or auxiliary fuel tanks to the locomotive.

(2) Fuel lines. All fuel lines to the engine and its accessory parts shall be installed so that they are not subject to damage in ordinary use and shall be designed to resist breakage from vibration.

(3) Valve in fuel line. A shut-off mechanism, operable from the driver's compartment, shall be provided in the fuel system so that the engine may be stopped immediately in an emergency.

(h) Signal or warning devices. All locomotives shall be equipped with a bell, horn, or other suitable warning device. This device shall not be electrically operated.

(i) Electrical equipment-(1) Classification of electrical parts. The electrical

parts of a locomotive that may cause ignition of mine gas and coal dust are classified as follows:

(i) Class 1. Class 1 shall include motors, starting switches, fuses and all their parts that may produce sparks or flashes as the result of normal operation. Headlights, motors, rheostats, electromagnets, and similar parts which may become dangerous because of failure of electrical circuits in them are also included in this class. Parts in this classification shall be enclosed in explosion-proof casings.

(ii) Class 2. Class 2 shall include all parts, such as batteries and external connections and wiring between enclosures. that do not produce sparks or flashes as the result of normal operation but may do so as the result of accident. Parts in this classification shall have adequate shields or guards of a strength and character proportionate to the risk of injury, or else they shall be enclosed in explosion-proof casings.

(iii) Class 3. Class 3 shall include all parts such as plugs and receptacles that may produce sparks or flashes in normal operation, but are not of necessity operated while the locomotive is in a gassy place. Parts in this classification shall be enclosed in explosion-proof or adequately locked casings. If locked casings are used, they shall have adequate mechanical strength.

(2) Type of electrical system. The electrical system on the locomotives shall be completely insulated from the chassis, the engine, and all other metal parts.

(3) Automatic protection of electrical circuits and equipment. (i) On locomotives using storage batteries for starting of engines, each electrical conductor from the battery to the starting motor shall be protected against short circuit by fuses or other suitable automatic circuitinterrupting devices placed at the battery unless conductors of adequate size are provided.

(ii) Fuses or other automatic circuitinterrupting devices shall be inserted at the point where branch circuits are connected to the main circuit between the charging generator and battery. Headlight circuits and circuits for instruments and instrument-panel lights are construed as being branch circuits.

(iii) Fuses shall be enclosed in explosion-proof casings with locked or sealed covers.

(4) Conductors, conduits, and wiring. (1) Every conductor shall have adequate insulation from "ground" and from conductors of opposite polarity. Insulation shall be selected with special reference to its ability to resist deterioration from engine heat and oil.

(ii) It is recommended that all conductors have a carrying capacity of not less than 110 percent of the total current rating of the motor or other load connected to them. The basis for determining such carrying capacity shall be that given by the National Electrical Code for "allowable carrying capacities of wires."

(iii) All wiring, particularly that outside of locked or explosion-proof enclosures, shall have adequate mechanical and electrical protection to minimize gas-ignition hazards as well as fire hazards. If for any reason rigid conduit is unsuitable or undesirable a good grade of rubber air hose or equivalent may be construed as meeting the requirement for mechanical protection if used where it will not be damaged by engine heat and oil. Flexible metal conduit is not acceptable. All conduit ends must be adequately clamped or otherwise secured to prevent their being pulled out. Inserts should be used to prevent collapse of hose conduit ends that are secured by external clamps.

(iv) Sharp edges and corners shall be removed at all points where there is possibility of damaging the insulation of wires, cables, or conduits by cutting or abrasion.

(v) Wiring and conduits shall be wellcleated or otherwise held to prevent vibration and displacement.

(vi) The ends and terminal lugs of wires and cables shall be held or clamped in a manner that will minimize the possibility of the ends and lugs coming loose from their connections and swinging against sides of enclosing casings or against parts of opposite polarity.

(5) Electrical clearances and insulation. The clearance between live parts and casings of electrical equipment shall be such as to minimize the possibility of arcs striking to the casings, or if space is limited the casings shall be lined with adequate insulation.

(6) Detailed requirements for class 1 electrical parts; enclosure casings-(i) Materials and construction. The casings forming the enclosure for class 1 parts shall be of suitable material and espe

cially durable in order that, with proper care and maintenance, the explosionproof qualities will remain unimpaired not only when subjected to pressures developed during explosion tests, but also under the severe conditions imposed by mining service. Sheet metal used in the fabrication of explosion-proof casings shall be at least 4 inch thick for any wall or cover having an area of 216 square inches or more (12 by 18), unless adequate reinforcing ribs, or their equivalent, are used to prevent deformation. Less than 16-inch thickness is not recommended. If welding is employed to join the side and wall pieces, the joints shall be continuously welded gas tight both inside and out.

Casings may be either of the totally enclosed type, in which no provision is made for ventilation of the interior, or else the type having provision for ventilation or relief of pressure from internal explosions. Totally enclosed construction, however, is recommended by the Bureau. Complicated castings and fabricated housings should be pressuretested at the factory to reveal blowholes and other weaknesses.

If provision is not made for pressure relief through special devices, the casing will need to be strong enough to withstand explosion pressures approaching 100 pounds per square inch. However, if a casing communicates with another through a small passage or is itself divided by a partition, the effect of "pressure-piling" may be produced, and pressures considerably in excess of 100 pounds per square inch may be anticipated.

The use of phenolic and other insulating materials that give off highly explosive gases when decomposed by electric arcs should be avoided in mounting live parts within explosion-proof enclosures.

(ii) Joints and machining tolerances. Where an explosion-proof enclosure consists of two or more metal parts that are held together by bolts or other suitable means, the flanges comprising the joints between parts shall have surfaces making metal-to-metal contact. Glassto-metal joints are permitted in casings such as those for headlights and meters. 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 gasket materials.

The surfaces comprising a flange joint need not be all in one plane. For enclosures having an unoccupied volume (air space) of more than 60 cubic inches, the total width of joint measured along the shortest path from inside to outside of the enclosure shall be not less than 1 inch, except as follows:

A rabbet joint having a total width of 34 inch may be accepted if neither the cylindrical nor the plane fit is less than 316 inch wide, with a maximum radial clearance of 0.002 inch for the cylindrical fit. When the unoccupied volume (air space) is less than 60 cubic inches, a minimum width of 34 inch may be accepted for plane joints, but a 1-inch width of plane or rabbet joint is recommended.

The width of blow holes in joint surfaces will be deducted in measuring flange widths. Diameters of holes for bolts or screws required to maintain tight joints will also be deducted in such measurement: (a) If excessive clearance (over 64-inch radial) is allowed for the bolt in its hole, and (b) if the diameter of the bolt hole is more than half of the required metal-to-metal contact. It is recommended that such holes be located so that the shortest distance along the joint from the interior of the enclosure to the edge of the hole is not less than 16 inch. However, less than 4 inch will not be accepted for 1-inch joints, nor less than 6 inch for joints under 1 inch. (Exception may be made for narrow interpoles, in which case the distance from the edge of pole piece to the bolt hole in the motor frame shall not be less than 1⁄2 inch and the diametrical clearance around the bolt shall be as stated in the next paragraph of this subdivision. Furthermore, the pole piece shall seat against the frame surface.)

Bolts and screws shall be close-fitting in holes that cut through joint surfaces. If the edge of a bolt or screw hole is less than 16 inch from the interior of the enclosure, the diametral clearance around the bolt or screw shall not exceed 164 inch and this clearance shall be maintained for a distance of at least 1⁄2 inch as measured from the joint.

When the flanges of a joint cannot be brought into actual contact with each other owing to warping or faulty machining of parts or necessity for sliding fits, the requirement for metal-to-metal contact will be construed as having been met for plane flanges under the following conditions:

1. If the separation does not exceed 0.004 inch at any point.

2. If the 0.004-inch separation does not extend over 6 inches along the joint.

3. Provided the joint does not permit discharge of flame during the explosion tests.

When it is necessary in manufacture to provide for a running fit between cylindrical surfaces other than motor shafts, a shoulder shall be included in the design to provide a change in direction through the flame path between the parts. In joints of this type, the diametral clearance between cylindrical surfaces shall be kept as small as feasible, but in no case shall it exceed 0.01 inch.

Laminated motor frames having end rings assembled as an integral part under high pressure may be considered with less width of contact between the end rings and laminations than that specified in the preceding paragraphs of this subdivision. It is recommended that the metal-to-metal contact be kept as near the 1-inch standard as practical, but less than 1/4 inch will not be accepted. If less than the 1-inch standard width is used for joints of this type, the construction must permanently preclude any separation between the end rings and lamination, and if a 0.0015inch-thickness gage can be inserted % inch at any point, the construction will be considered unsatisfactory. The joint should not open under explosion pres

sures.

(iii) Bolts and similar fastenings. Bolts and similar means of clamping flange joints together shall be generously proportioned to minimize stripping of threads and to give adequate strength. Steel inserts shall be used when it is necessary to thread screws or bolts into aluminum castings. Clamping bolts and screws should be at least 1/4 inch in diameter and preferably not less than 1⁄2 inch.

Unless the design permits especially rigid construction between bolts, spacings greater than 6 inches are not recommended for flange joints.

All bolts, nuts, and screws used in fastening flange joints, as well as those used in holding parts such as pole pieces, brush rigging, and bearing caps, shall be provided with lock washers or other suitable means to prevent loosening. The length of threads in bottomed holes and on bolts, screws, and studs shall be such that the joint can be made tight even though lock washers are omitted.