l110.16 Flash Protection.

Electrical equipment, such as switchboards, panelboards, industrial control panels, meter socket enclosures, and motor control centers,that are in other than dwelling occupancies, and are likely to require examination, adjustment, servicing, or maintenance while energized shall be field marked to warn qualified persons before examination, adjustment, servicing, or maintenance of the equipment.

FPN No. 1: NFPA 70E 2004, Standard for Electrical Safety in   the Workplace, provides assistance in determining severity of   potential exposure, planning safe work practices, and selecting   personal protective equipment.