What 29 CFR 1926.431 requires (plain English)
29 CFR 1926.431 is the maintenance-of-equipment provision within Subpart K (Electrical), addressing electrical equipment installed in hazardous (classified) locations on construction sites: locations where flammable gases or vapors, combustible dusts, or ignitable fibers may be present in quantities sufficient to create a fire or explosion hazard.
The rule is specific and demanding: the employer must ensure that all wiring components and utilization equipment in hazardous locations are maintained in a dust-tight, dust-ignition-proof, or explosion-proof condition, as appropriate. There must be no loose or missing screws, gaskets, threaded connections, seals, or other impairments to a tight condition. In other words, the special enclosures that make equipment safe in a classified location must be kept fully intact, because their protection depends entirely on the enclosure remaining tight.
1926.431 reflects how hazardous-location electrical equipment works. Explosion-proof enclosures do not prevent an internal spark; they CONTAIN it and cool the escaping gases so they cannot ignite the surrounding atmosphere. Dust-ignition-proof and dust-tight enclosures keep combustible dust out and heat in. Every one of these depends on a complete, tight enclosure: the full set of bolts, intact gaskets, and made-up threaded joints. A single missing screw or damaged seal breaks the containment and turns the equipment into an ignition source, which is why maintenance to a tight condition is the whole point of this standard.