Walking-Working Surfaces and Fall Protection
The Trigger Height
General industry's walking-working surfaces rule (29 CFR 1910 Subpart D) was rewritten in 2016. In general industry, fall protection is required at 4 feet - at unprotected sides and edges, above dangerous equipment, and at hoist areas - and holes 4 feet or deeper must be guarded or covered. Construction (Subpart M) uses 6 feet and scaffolds use 10 feet, which is a favorite distractor. Fixed ladders extending more than 24 feet above a lower level require a ladder safety system or personal fall arrest system.
Guardrails, Covers, and Stairs
A standard guardrail has a top rail 42 inches (±3) above the walking surface, a midrail at 21 inches, and toe boards 3.5 inches high, and must withstand a 200-pound force. Hole covers must be secured, marked "HOLE" or "COVER," and support at least twice the intended load. Stairways with four or more risers need at least one handrail; handrails run 30 to 38 inches above the tread nosing, and risers and treads must be uniform.
Ladders
Portable ladders must extend 3 feet above the landing, be set at a 4:1 angle (about 75 degrees), be secured against displacement, carry one person at a time, and be faced while climbing. The top step or cap is not a step. Inspect ladders before use and remove damaged ones from service.
Traps and a Rule of Thumb
Traps: quoting 6 feet on a general-industry question; calling out 45 inches for a top rail; treating a hole cover as satisfying an edge-protection requirement; ignoring the non-fall provisions of Subpart D (housekeeping, aisle width, floor loading).
Rule of thumb: the 4:1 ladder rule - for every 4 feet of working length up, move the base 1 foot out from the wall.