NFPA Journal - November/December 2012 - (Page 36)
ALARM + DETECTION SYSTEMS
wayne d. moore, p.e., fsfpe
One Code, Many Chapters
Why you need to review all of NFPA 72 when planning and installing fire alarm systems
he requirements for fire alarm systems appear in all 15 interrelated chapters of NFPA 72®, National Fire Alarm and Signaling Code. This comes as a surprise to some users of the code, who apparently believe that all the chapters stand alone. Although Chapter 29, “Singleand Multiple-Station Alarms and Household Fire Alarm Systems,” is intended to stand alone, it also refers to the other chapters for guidance. Chapters 12 and 23 illustrate this interrelationship. One would think that Chapter 12, “Circuits and Pathways,” contains all of the code requirements for the pathway classification and operational The chapTers of NFpa 72 are interrelated in many ways. characteristics of fire alarm system circuits. Indeed, we find that Chapter 23, “Protected Premises Fire Alarm Systems,” advises us on the seven critical influences to consider in order to determine the integrity and reliability of fire alarm circuits in a building. Those influences include transmission media used; length of the circuit conductors; total building area covered by, and the quantity of initiating devices and notification appliances connected to, a single circuit; the effect of a fault in the fire alarm system that would hinder the performance objectives of the system that protects the occupants, mission, and property of the protected premises; the nature of hazards present in the protected premises; functional requirements of the system necessary to provide
the level of protection required for the system; and the size and nature of the population of the protected premises. In addition, Chapter 23 requires that the person evaluating these influences on circuit choice include the results in the documentation required in Chapter 7, “Documentation.” Chapter 23 requires that class designations for initiating device circuits, signaling line circuits, and notification appliance circuits be based on their performance capabilities under abnormal (fault) conditions, in accordance with the requirements specified in Chapter 12. It should be obvious when one reads the descriptions of circuit class operation in Chapter 12 that the class of circuit required for a system does not appear in this chapter. The requirements for the class of circuit depend on the owner’s fire protection goals with respect to operational reliability of the circuits. This will guide the designer in choosing the class of circuit. Of course, some jurisdictions have the circuit class requirements in their local fire code. But NFPA 72 does not require a designer to use a specific class of circuit. (Chapter 23 does require the designer to limit the number of addressable devices that could be lost on a circuit with a single fault to not more than 50.) In addition, Chapter 12 requires that the circuit class “be dependent on the pathway (interconnection)
wayne d. moore, p.e., fsfpe, is a principal with Hughes Associates.
NFPA JOURNAL NOVEMBER/DECEMBER 2012
Illustration: Richard A. Goldberg
capability to continue to operate during abnormal conditions,” and that all non-power-limited and power-limited signaling system circuits entering a building be provided with transient protection. The chapter also requires that the installation of all pathway wiring and cable, including all circuits controlled and powered by the fire alarm system and equipment, satisfy the requirements of NFPA 70®, National Electrical Code®, as well as the requirements in the chapter. As you can see, an interrelationship exists between the chapters of NFPA 72. They also incorporate the use of NFPA 70 when reviewing a fire alarm circuit’s installation requirements. As these examples show, users of NFPA 72 need to review the entire code when planning and installing code-compliant fire alarm systems.
Table of Contents for the Digital Edition of NFPA Journal - November/December 2012
NFPA Journal - November/December 2012
In a Flash
Past + Present
Easy Being Green?
2011 Large-Loss Fires
2011 Firefighter Injuries
NFPA Journal - November/December 2012