Rung spacing and width
29 CFR 1926.1053(a)(3) requires rungs, cleats and steps on portable and fixed ladders to be spaced not less than 10 in and not more than 14 in apart, center to center.
Other spacings in the same paragraph are the traps:
- Step stools: 8 to 12 in.
- Extension trestle ladders: 8 to 18 in on the base section and 6 to 12 in on the extension section.
1926.1053(a)(4) sets the minimum clear distance between side rails: 11.5 in for portable ladders and 16 in for fixed ladders. Mixing the two widths is the common error. Neither 19 in (the stair or ladder trigger and the guardrail opening) nor 14 in (the maximum rung spacing) is a width.
Load capacity
1926.1053(a)(1) sets capacity as a multiple of the maximum intended load:
- Self-supporting and non-self-supporting portable ladders: at least 4 times.
- Extra-heavy-duty Type 1A metal or plastic ladders: at least 3.3 times.
- Fixed ladders: each rung or step must hold a 250 lb concentrated load.
Worked case: a Type 1A metal ladder with a 300 lb maximum intended load must support 300 × 3.3 = 990 lb. Trap: using 4x (1,200 lb) for a Type 1A ladder. 300 × 6 = 1,800 lb borrows the scaffold suspension rope factor, and 2x is not a ladder factor at all.
Setting the ladder
For non-self-supporting ladders, 1926.1053(b)(5)(i) sets the foot so the horizontal distance to the top support is about one-quarter of the working length: the 4:1 rule, 4 up for every 1 out.
Job-made wooden ladders with side rails continuous past the top cleat use one-eighth instead (1926.1053(b)(5)(ii)).
Worked case: a 16 ft job-made wooden ladder sets its foot 16 ÷ 8 = 2 ft out. Trap: 16 ÷ 4 = 4 ft applies the 4:1 rule to the wrong ladder type.
The 3 ft extension
A portable ladder reaching an upper landing needs side rails at least 3 ft above the landing (1926.1053(b)(1)). Trap: 3 ft is an extension height, never a setback distance.