Job-made and manufactured ladders must be capable of supporting their intended loads. A ladder should be selected so its duty rating:

Giải thích

A duty rating is the total load the ladder is built to carry: the worker, plus clothing, tools and anything carried up. The ratings run Type III at 200 pounds, Type II at 225, Type I at 250, Type IA at 300 and Type IAA at 375. Option (b) drops the tools and the material, and that is exactly where the failures happen - a 190-pound worker carrying a 40-pound bundle is over a Type III ladder. Option (c) borrows the four-times factor from the scaffold orders, where section 1637(b) requires a scaffold to support its own weight plus four times the maximum intended working load; a ladder's rating is not a multiple of its own weight. Option (d) fixes on one rating when the right rating depends on the load.