When using an angle grinder to cut metal, which safety precaution is MOST critical?

ANGLE GRINDER SAFETY is critical because grinders are one of the most dangerous workshop tools — disc failures at 10,000-12,000 RPM are catastrophic. DISC SELECTION: Cutting discs are thin (typically 1-3 mm); grinding discs are thick (5-6 mm); never use a cutting disc for grinding (it will shatter from lateral force); disc must be rated for higher RPM than the grinder's maximum; GUARD POSITION: The guard protects the operator from the explosion direction if a disc shatters; it must face the operator; never remove it; PERSONAL PROTECTIVE EQUIPMENT: Face shield (full face protection from sparks and shrapnel); safety glasses underneath (sparks penetrate around shield edges); hearing protection (angle grinders exceed 100 dB); NO GLOVES on rotating operations — they can catch the disc; leather or cut-resistant gloves for handling metal after cutting; WORKPIECE: Clamp securely — the grinder will try to walk; PROPER GRIP: Two-hand grip on the handle and body at all times; control the tool, don't let it control you; DISC INSPECTION: Check for cracks or chips before mounting; discard damaged discs; SPARKS: Angle grinders produce large volumes of sparks; clear the area of flammable materials; fire watch if welding/grinding near combustibles.