Full definition
Physical barriers, devices, and systems that prevent workers from accessing hazardous moving parts of machinery (point of operation, power transmission, and other moving parts), the primary engineering control for mechanical hazards. Types per OSHA 29 CFR 1910.212 and NOM-004-STPS-1999 (Mexico): (1) Fixed guards — permanent enclosures bolted to machine frame; most reliable, no moving parts; cannot be bypassed; for areas not requiring frequent access. (2) Interlocked guards — movable guards with electrical or mechanical interlock switches that stop the machine when the guard is opened; for areas requiring periodic access (e.g., loading). (3) Adjustable guards — guards that can be repositioned for different work setups (drill presses, band saws). (4) Self-adjusting guards — automatically adjust opening size to the workpiece (table saws). (5) Presence-sensing devices — light curtains (AOPD), safety mats, laser scanners — detect worker presence and stop the machine; for operations where physical guards are impractical. (6) Two-hand controls — require both hands on buttons to initiate stroke, keeping hands out of danger zone (presses). Safety requirements: guards must prevent reach-through (ANSI/NFPA 79 safety distance tables), be firmly secured, not create new hazards (sharp edges, pinch points), and not impede maintenance access unnecessarily. Per OSHA 29 CFR 1910.212, NOM-004-STPS-1999, ISO 14120, and ANSI B11 series.