The criteria for a guard having to be used on a machine primarily focus on protecting the operator and other employees from hazards such as point of operation, ingoing nip points, rotating parts, flying chips, and sparks. According to OSHA standard 29 CFR 1910.212(a)(1), any machine that poses these hazards must be equipped with at least one method of machine guarding. This can include physical barriers, electronic safety systems, or two-hand tripping devices. The guard must be secure, prevent physical contact with hazardous parts, create no new hazards, allow safe lubrication, and protect from falling objects. Additional OSHA criteria specify that the point of operation, where the actual work is done and injury risk is highest, must be guarded. Machines should also be anchored in place, and exposed blades require physical guards. Guards must allow free movement without impairing worker navigation, be free of burrs or sharp edges, and be designed for easy maintenance. European regulations, such as the Machinery Directive, emphasize that if risks cannot be minimized by design, moving parts must be fitted with guards or protective devices to prevent accidents. In summary, guards are required whenever machinery parts pose a risk of injury due to movement, sharp edges, projections, or hazardous points of operation, and the guard must effectively prevent contact without introducing new risks or interfering unduly with operations.