facilities constructed prior to the effective date of this
volume shall be done, as applicable, in accordance with
the requirements of this volume.
It is not the intent of this volume to require retrofitting
of existing equipment. However, when an item is
being modified, its performance requirement shall be
reviewed relative to the current volume. If the performance
differs substantially, the need to meet the current
requirement shall be evaluated by a qualified person
selected by the owner (user). Recommended changes
shall be made by the owner (user) within I year.
Section V: Mandatory and Advisory Rules
Mandatory rules of this volume are characterized by
use of the word shall. If a provision is of an advisory
nature, it is indicated by use of the word should and
is a recommendation to be considered, the advisability
of which depends on the facts in each situation.
Section VI: Metric Conversions
The values stated in U.S. customary units are to be
regarded as the standard .