CONSTRUCTION SPECIFICATIONS
§ 21.31. General.
(a) Sides. Ladders may have either parallel or spreading straight sides unless otherwise specified in this section. Portable ladders may also have the sides flaring at the base to increase their stability and converging at the top where specific uses warrant.
(b) Distance. For ladders exceeding four feet in length, the inside width between side rails shall be not more than 32 inches except for bases flared as permitted in subsection (a) and not less than 10 inches except where rails are converged at the top, in which case this minimum width shall be obtained not more than 4 feet from the top. For ladders not exceeding 4 feet in length the minimum width between side rails shall be not less than 8 inches.
(c) Spacing. A uniform step spacing shall be employed. It is recommended that this spacing be 12 inches except where specific uses require shorter spacing in which case it may not be less than 8 inches.
(d) Fastening. All holes for wood rungs shall either extend through the side rail or be bored to within 3/16 inch of the outside face of the rail. In the former construction the rungs shall extend through to at least flush with the outside rail surface while in the latter the distance between the end of the rung and the outside face of the rail shall not be greater than 5/16 inch.
(e) Holes. All holes for wood rungs shall be located on the center line of the wide face of the side rails. The size of holes shall be such as to insure a driving fit for the rung.
(f) Tenon. The shoulder of round wood rungs shall be forced firmly against the side rail and the tenon secured in place by a nail or the equivalent to prevent turning. Oval rungs shall be secured in place by two nails or equivalent in each rail.
(g) Treads. Wood treads shall be inset in the side rails not less than 1/8 inch, fastened to it by nails or screws, and secured by braces, bolts, tie rods or the equivalent, except when ladders are built entirely of species listed in § 21.61 (relating to group one wood). In this latter case the treads may be fastened by two inch screws or equivalent and secured at intervals not greater than 4 feet apart along the length of the rail by braces, bolts, tie rods or the equivalent.
(h) Cleats. Wood cleats shall be housed into side rails not less than 1/2 inch or equivalent construction. They shall be fastened to each rail by three 10d wire nails or equivalent.
(i) Wood steps. All wood steps 28 inches or more in length shall be reinforced by braces or supported by additional bearings.
(j) Metal rungs. Metal rungs shall be securely fastened to the side rails by riveting, bolting or welding. Their position and method of attachment to the rail shall be such as to distribute uniformly the stresses transmitted to the side rail.
(k) Metal treads. Metal treads shall be flanged downward not less than two inches at each end of tread and secured to each side rail by two bolts or rivets.
(l) Old construction. ‘‘U’’ sections used as steps or rungs, on old construction may be fastened on the outside of the wall by using two 5/8 inch diameter through bolts on each end.
(m) New construction. ‘‘U’’ sections used as steps or rungs on new construction shall be built into the structure a minimum of 8 inches with not less than 3 inches of the inner ends bent at right angles. ‘‘U’’ sections shall not be used on smoke stacks.
(n) Hardware and fittings. All hardware and fittings shall be securely attached by means of rivets, bolts or the equivalent. The bolts or rivets shall make a close fit in the holes prepared to receive them.
(o) Movable parts. The construction and assembly of the movable parts of ladders shall be such that they operate freely without binding or unnecessary play.
(p) Slipping. Portable, extension, and sectional ladders shall be either equipped with approved devices or shall be so placed, fastened or held as to prevent slipping.
(q) Portable ladder hooks. When service conditions warrant, hooks may be attached at or near the top of portable ladders to give added security.
(r) Hooks. Hooks shall be securely bolted or riveted to the side rails or equivalent construction, and shall be of such dimensions as to withstand the loads imposed upon them.
(s) Special ladders. Ladders of special design shall be of an approved type.
Cross References This section cited in 34 Pa. Code § 21.40 (relating to step ladders).
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