(a)Construction. The intake system (exclusive of the air
cleaner) shall be designed to withstand an internal pressure equal to 4 times
the maximum pressure observed in explosion tests, which are described in
§36.46, or a pressure of 125 pounds per square inch,
whichever is the lesser. Joints in the intake system shall be formed by metal
flanges fitted with metal or metal-clad gaskets, positively positioned by
through bolts or other suitable means for secure assembly, or shall meet the
requirements for flanged metal-to-metal flame-proof joints as required in
§36.20(b). Either type of joint shall withstand
repeated explosions within the intake system without permanent deformation
and shall prevent the propagation of flame through the joint into a
surrounding flammable mixture.
(b)Intake flame arrester. (1) The intake system shall
include a flame arrester that will prevent an explosion within the system
from propagating to a surrounding flammable mixture. This flame arrester
shall be between the air cleaner and the intake manifold and shall be
attached so that it may be removed for inspecting, cleaning, or repairing.
Its construction shall be such that it may be cleaned readily. The flame
arrester shall be of rugged construction to withstand the effects of
repeated explosions within the intake system, and the material of
construction shall resist deterioration in service. It shall be so mounted
in the equipment assembly that it is protected from accidental external
(2) The parts of any flame arrester shall be positively
positioned to produce a flame path that will arrest the propagation of an
explosion and shall be so designed that improper assembly is impossible. In
flame arresters of the spaced-plate type, the thickness of the plates shall
be at least 0.125 inch; spacing between the plates shall not exceed 0.018
inch; and the plates forming the flame path shall be at least 1 inch wide.
The unsupported length of the plates shall be short enough that deformation
during the explosion tests shall not exceed 0.002 inch. Corrosion-resistant
metal shall be used to construct flame arresters.
(c)Air shutoff valve. The intake system shall include a
valve, operable from the operator's compartment, to shut off the air supply
to the engine. This valve shall be constructed to permit its operation only
after the fuel supply to the engine is shut off. In reverse operation the
valve must open fully before fuel can be supplied to the engine.
(d)Air cleaner. An air cleaner shall be included in the
engine intake system and so arranged that only clean air will enter the flame
arrester. The resistance to airflow shall not increase rapidly in dusty
atmospheres. Filters of the self-cleansing (oil-bath) type will be
considered satisfactory for this application. Provision, satisfactory to
MSHA, shall be made to prevent overfilling the oil-bath air cleaner.
(e)Vacuum-gage connection. A connection shall be provided in
the intake system for temporary attachment of a vacuum gage to indicate the
pressure drop under flow conditions. This opening shall be closed by a plug
or other suitable device that is sealed or locked in place except when a
gage is attached.