Question “Is Annex A of NFPA 72 explanatory information or optional requirements?”
Annex A of NFPA 72 is one of several “usability annexes” in NFPA 72 designed to enhance our understanding and application of NFPA 72. Annex A is arguably the most important annex in NFPA 72 because it is referred to multiple times in the heart of the Code.
Code reference numbers in NFPA 72 with have an asterisk (*) after them indicate that explanatory material can be found in Annex A under that same reference number preceded by an “A.” For example, 220.127.116.11.3.1 describes the proper mounting location of spot-type heat detectors (on the ceiling, not less than 4 inches of the sidewall, or on the wall between 4 and 12 inches from the ceiling).
The asterisk (*) at the end of the reference indicates that explanatory material can be found in Annex A in A.18.104.22.168.3.1. When you go to A.22.214.171.124.3.1 it refers to Figure A.126.96.36.199.3.1 which illustrates the proper mounting for heat detectors.
The italic text below the title of the Annex A section is not part of the requirements of the code but is included for information purposes only. Based on this, Annex A is technically “explanatory” not “optional.”
However, one very important thing to consider when dealing with NFPA 72 is the Authority Having Jurisdiction (AHJ). NFPA 72, Chapter 3 defines enforcement of a code as part of the responsibilities of the AHJ. Part of enforcement is interpreting requirements and deciding what to enforce.
Some AHJs consider Annex A to be code requirements, others consider it a recommendation.
Another thing to consider is the terms “shall” and “should”, which are defined in Chapter 3 and used in NFPA 72. Shall indicates a mandatory requirement, and the heart of the code uses “shall” when describing requirements. Should indicates a recommendation, and Annex A uses “should” frequently when describing applications.
Because the “shoulds” in Annex A improve the life safety of the building, some AHJs decide to enforce these recommendation as requirements.
For example, 188.8.131.52 states detectors SHALL not be located when airflow prevents operation of the detector but does not state any specific requirements. Annex A (A.184.108.40.206) states detectors SHOULD not be located closes than 36 inches from an air supply or return.
While locating a detector closer than 36 inches from an air supply or return can cause problems with detection (turbulence, high air movement, etc), there is nothing specifically in the code the prevents it from being done. The minimum 36 inches from the supply or return give additional assurance that the detector will not be affected by potential airflow issues.