Preface This is the fourth edition of CSA Z11, Portable ladders. This Standard supersedes the previous editions published in 1981, CSA Z11-1969, Supplement No. 1 to the 1969 edition published in 1976, and the CSA Tentative Standard Z11-T published in 1967. Scope 1.1 This Standard applies to common types of portable ladders and includes design and performance-related requirements and tests. 1.2 Ladders covered by this Standard are intended for use by only one person at a time under normal conditions of usage, with the exception of trestle ladders, which are designed for use by two persons at the same time. 1.3 This Standard does not specify details on the design and construction of portable ladders. The requirements listed in this Standard are intended to specify certain minimum characteristics of strength and stability deemed necessary for the safe use of portable ladders. 1.4 This Standard covers single-section ladders, multiple-section ladders, and combination ladders but does not cover special-purpose ladders or ladder accessories (e.g., ladder levellers, ladder stabilizers or stand-off devices, ladder jacks, or ladder straps or hooks) that may be installed on, or used in conjunction, with ladders. 1.5 The values given in SI units are the units of record for the purposes of this Standard. The values given in parentheses are for information and comparison only. 1.6 In CSA standards, "shall" is used to express a requirement, i.e., a provision that the user is obliged to satisfy in order to comply with the standard; "should" is used to express a recommendation or that which is advised but not required; and "may" is used to express an option or that which is permissible within the limits of the standard.    Notes accompanying clauses do not include requirements or alternative requirements; the purpose of a note accompanying a clause is to separate from the text explanatory or informative material.    Notes to tables and figures are considered part of the table or figure and may be written as requirements.    Annexes are designated normative (mandatory) or informative (nonmandatory) to define their application.