30 CFR § 27.20 Quality of material, workmanship, and design.
(a) MSHA will test only equipment that, in its opinion, is
constructed of suitable materials, is of good workmanship, is based on sound
engineering principles, and is safe for its intended use. Since all possible
designs, arrangements, or combinations of components cannot be foreseen, MSHA
reserves the right to modify the construction and design requirements of
components or subassemblies and the tests to obtain the degree of protection
intended by the tests described in Subpart C of this part.
(b) Unless otherwise noted, the requirements stated in this part
shall apply to explosion-proof enclosures and intrinsically safe
(c) All components, subassemblies, and assemblies shall be designed
and constructed in a manner that will not create an explosion or fire
(d) All assemblies or enclosures--explosion-proof or intrinsically
safe--shall be so designed that the temperatures of the external surfaces,
during continuous operation, do not exceed 150° C. (302° F.) at any point.
(e) Lenses or globes shall be protected against damage by guards or
(f) If MSHA determines that an explosion hazard can be created by
breakage of a bulb having an incandescent filament, the bulb mounting shall
be so constructed that the bulb will be ejected if the bulb glass enclosing
the filament is broken.
Note: Other methods that provide equivalent protection against explosion
hazards from incandescent filaments may be considered satisfactory at the
discretion of MSHA.