in a manner to provide protection equal to or greater than
the sheathing and shoring required for the situation.
5. Ladders used as access ways should extend from
the bottom of the trench to not less than 3 feet above the
surface. Lateral travel to an exit ladder should not
exceed 25 feet.
6. Backfilling and removal of trench supports
should progress together from the bottom of the trench.
Jacks or braces should be released slowly and, in
unstable soil, ropes should be used to pull out the jacks
or braces from above after all personnel have cleared the
trench.
7. Minimum size and spacing of timbers for
shoring of trenches should be maintained according to
set standards (table 4-1).
8. Aluminum hydraulic shoring should be installed
according to the manufacturer’s recommendations.
SCAFFOLDING
A scaffold is an elevated working platform for
supporting both men and materials. It is usually
temporary; its main use being in construction work.
Scaffolds should be designed to support at least four
times the anticipated weight of both men and materials
that will use them.
Scaffolding is a structure made of wood (fig. 4-29)
or of metal (fig. 4-30) to support a working platform.
Built-up and suspended scaffolds may be made of
wooden structural members, but steel tubing should be
the first choice. This type of scaffold affords a firm,
solid work platform for use by one or more men. Their
lightness, mobility, and ease of erection make them
most suitable for light-duty to heavy-duty work,
particularly when the equipment must be erected and
dismantled frequently.
Most scaffolds are in one of three primary
categories: tubular, suspended, or rolling. They are
also classified according to their intended use: light
duty (working load must not exceed 25 pounds per
square foot of platform surface), medium duty (50
pounds per square foot), and heavy duty (75 pounds
per square foot).
A tabular scaffold is constructed of tubing that fits
into various positions to form posts, bearers, braces,
ties, and runners. A base assembly supports the posts
Figure 4-29.—Wood scaffold.
and special couplers that serve to connect the uprights
and to join the various members (fig. 4-30).
A suspended scaffold carries a working platform
on beams and ropes that is secured to structural
members or to thrust outs from the structure.
Figure 4-30.—Folding sections with fixed platforms, guard
rails, and built-in stairs.
4-23
