🕒 3 min read • 🟡 Intermediate • Educational Resource
The Standard:
ANSI B11.0-2023, Section 7.20, addresses mechanical power transmission. ANSI B11.19-2019 (R2024) provides performance requirements for safeguarding, including guard design and construction. These standards support evaluating and reducing exposure to hazardous rotating components.
OSHA 29 CFR 1910.219 provides specific requirements for exposed shafting, projecting shaft ends, unused keyways, projecting keys, set screws, collars, and couplings. The appropriate safeguarding depends on which conditions are present.
Note: The half-diameter rule applies specifically to projecting shaft ends. It does not provide a general exemption for other exposed shafting or eliminate separate requirements for keyways and projecting fasteners.
The Practical Translation:
Start with the shaft end. Its edges and end must be smooth. If it projects more than one-half the shaft diameter, it requires a nonrotating cap or safety sleeve. For a 1-inch-diameter shaft, that projection threshold is ½ inch. Reference: §1910.219(c)(4)(i).
Check the features that can catch. Unused keyways must be filled or covered. Projecting keys, set screws, and similar projections must be removed, made flush, or protected by a metal cover, subject to the regulation’s limited exceptions. References: §1910.219(c)(4)(ii) and §1910.219(h)(1).
Consider the complete assembly. A 1-inch shaft projecting only ⅜ inch meets the projection dimension, but an exposed unused keyway still requires attention. Making a set screw flush also leaves the remaining shaft, collar, and coupling to be evaluated.
Smooth or slow does not mean harmless. Rotating shafts can catch hair or clothing even at low speeds. OSHA generally requires guarding of exposed shafting located 7 feet or less above the floor or working platform, subject to the specified exceptions. Reference: §1910.219(c)(2)–(3).
Ask yourself:
Can someone contact the shaft while it is rotating?
How far does the shaft end project compared with its diameter?
Are unused keyways, protruding keys, set screws, or damaged surfaces exposed?
Does the proposed safeguard address the complete accessible rotating assembly?
The Takeaway:
Evaluate projection, surface features, and access together. Shaft length is one part of the guarding decision.
Correcting a visible projection should be followed by a review of the remaining exposure. The objective is to prevent hazardous contact with the rotating assembly.
Compliance identifies the requirements for the components involved. Practical risk reduction asks whether the completed safeguarding protects people during the work performed around the machine.
