(a) Bolts, screws, or studs shall be used for fastening adjoining
parts to prevent the escape of flame from an enclosure. Hinge pins or clamps
will be acceptable for this purpose provided MSHA determines them to be
equally effective.
(b) Lockwashers shall be provided for all bolts, screws, and studs
that secure parts of explosion-proof enclosures. Special fastenings designed
to prevent loosening will be acceptable in lieu of lockwashers, provided MSHA
determines them to be equally effective.
(c) Fastenings shall be as uniform in size as practicable to preclude
improper assembly.
(d) Holes for fastenings shall not penetrate to the interior of an
explosion-proof enclosure, except as provided in paragraph (a)(9) of §18.34, and shall be threaded to
insure that a specified bolt or screw will not bottom even if its lockwasher
is omitted.
(e) A minimum of 1/8-inch of stock shall be left at the center of the
bottom of each hole drilled for fastenings.
(f) Fastenings used for joints on explosion-proof enclosures shall
not be used for attaching nonessential parts or for making electrical
connections.
(g) The acceptable sizes for and spacings of fastenings shall be
determined by the size of the enclosure, as indicated in §18.31.
(h) MSHA reserves the right to conduct explosion tests with standard
bolts, nuts, cap screws, or studs substituted for any special high-tensile
strength fastening(s) specified by the applicant.
(i) Coil-thread inserts, if used in holes for fastenings, shall meet
the following:
(1) The inserts shall have internal screw threads.
(2) The holes for the inserts shall be drilled and tapped
consistent with the insert manufacturer's specifications.
(3) The inserts shall be installed consistent with the
insert manufacturer's specifications.
(4) The insert shall be of sufficient length to ensure the
minimum thread engagement of fastening specified in §18.31(a)(6) of this part.
