Supplement 2
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SUPPLEMENT 2 Fire Alarm Systems for Life Safety Code Users Robert P. Schifiliti, P.E. Editor’s Note: This supplement is an introduction to fire alarm systems. It explains the various types of systems addressed by the Life Safety Code and describes their components in detail. In this supplement the term fire alarm is intended to include detection systems and systems that provide control functions, such as elevator recall, and alarm information or notification to occupants and emergency forces. Robert P. Schifiliti is the founder of R.P. Schifiliti Associates, Inc., and is chair of the Technical Committee on Notification Appliances for Fire Alarms Systems. Mr. Schifiliti serves as one of several faculty for the NFPA Fire Alarm Workshop and is a licensed fire protection engineer. He received the degree of master of science in fire protection engineering from Worcester Polytechnic Institute. INTRODUCTION cept of Mass Notification Systems used for emer- gency communication and management. This supplement starts with an overview that de- Specific requirements and designs for various oc- scribes how NFPA codes and standards categorize cupancies are not discussed in this supplement. The the various types of fire detection and alarm systems. occupancy chapters of the Life Safety Code should be A section on fire signatures reviews the sensible or consulted for specific requirements. The additional detectable physical and environmental changes that commentary contained in other chapters of this hand- take place during a fire. A review of fire detection book provides a good explanation of the require- devices emphasizes proper selection in order to meet ments and the philosophy behind their intent. This fire safety goals and to reduce the likelihood of false supplement provides an introduction to the opera- and nuisance alarms. Power sources permitted by tion of required devices and systems. Designers, the Life Safety Code for household smoke alarms are owners, installers, and inspectors will find useful in- discussed in the context of their reliability. The discus- formation to assist them in choosing among options sion of circuit types and allowable wiring methods in- not specifically addressed within the Code. For exam- cludes references to other NFPA codes and standards. ple, a choice might need to be made between using The signaling section describes the goals and methods photoelectric or ionization smoke detectors, or infor- for both occupant notification and off-premises sig- mation might be required on how to reduce the likeli- naling for staff and emergency forces notification. A hood of false and nuisance alarms. review of testing and maintenance needs for fire de- tection andsignaling systems provides thereader with OVERVIEW OF FIRE ALARM SYSTEMS an understanding of how to extend a system’s life, reduce nuisance alarms, and ensure system opera- Four principal types of fire alarm systems are re- tion during a fire emergency. A section new to the quired or recommended by various chapters of the 2006 edition of this supplement introduces the con- Life Safety Code: 1113 1114 Supplement 2 • Fire Alarm Systems for Life Safety Code Users 1. Smoke alarms or household fire alarm equipment more complex systems, initiating devices and notifi- 2. Manual fire alarm systems cation appliances are separate, self-contained units 3. Automatic fire alarm systems connected to a control panel by electrical circuits or 4. Supervisory systems for extinguishing systems or radio waves. In these component systems, power is other fire or building systems usually provided to the input and output devices through the control unit. However, it is also possible Each of these categories can be viewed as consisting for power to be provided directly to those units that of three components, as shown in Exhibit S2.1. Detec- require it. Each of these three principal components tion and initiating devices are either manual or auto- (input, control, and output) is discussed in more de- matic, as shown in the illustration, and are referred tail in later sections of this supplement. to as input devices. Manual initiating devices, such The occupancy chapters of the Life Safety Code as manual fire alarm boxes, are operated by people specify fire alarm requirements where appropriate. and in turn signal the control system. Automatic de- Those sections that contain requirements include tection devices sense a change in the environment or subsections that provide the requirements for initia- equipment that is monitored and signal the control tion and notification. Where initiation is addressed, portion of the system. The control or processing sec- the occupancy chapter refers to either a complete tion receives the incoming signals and initiates out- system or a partial system. In addition, the system put signals. The control system can also supply power will be described as manual, automatic, or both. to and supervise the system’s various components Chapter 9, Building Service and Fire Protection and circuits and provide output signals when a fault Equipment, defines complete, partial, manual, and occurs or maintenance is needed. The control or proc- automatic systems. Where automatic detection is re- essor interfaces with people and other systems quired, most chapters of the Code specify either par- through output signals. tial or complete smoke detection. If an automatic fire The simplest form of system described in Exhibit detection system is required, but the type of detection S2.1 is a self-contained smoke alarm. This alarm con- is not specified, any automatic units that comply with tains a smoke sensor and a control system, which NFPA 72, National Fire Alarm Code, are permitted includes a power source and a notification system, to be used interchangeably. An occupancy chapter usually a horn, used for occupant notification. In might also require separate smoke detection within dwelling units in addition to any required partial or complete system for the public or tenantless sections of the building. Detection Manual Household fire alarm equipment is intended for Automatic use within dwelling units such as apartments, hotel Alarm Supervisory rooms, dormitory rooms, and one- or two-family dwellings. These devices or systems are intended to detect smoke conditions and alert the occupants of the dwelling units. In occupancies such as hotels, apartment buildings, and dormitories, these devices are not intended to be connected to the overall build- Control/Processing ing fire alarm system. Logic Human interface Within the dwelling unit, household fire alarm Power equipment might be self-contained smoke alarms, or Supervision it might be a small system with detectors, a control panel, and notification appliances such as bells, horns, or strobe lights. The building system can con- sist of manual and automatic initiating devices, extin- guishing system supervisory devices, and notification Signaling appliances that are all connected to a control unit. Occupant notification Therefore, there are two categories of fire alarm: one Off premises that is located within the family dwelling unit and Emergency forces Other systems one that is intended to protect the entire building. In some cases, an occupancy chapter of the Code might require a partial automatic detection system Exhibit S2.1 Overview of components of fire alarm systems. that covers all common spaces. In addition, house- 2006 Life Safety Code Handbook Fire Signatures 1115 hold fire alarm equipment might be required in Ceiling dwelling units. For purposes of occupant notification, the building system would cover all occupiable spaces, including the dwelling units. The household equipment is required to signal only within the dwell- ing unit. Some building fire alarm systems are capa- Physical/chemical Energy Gases Conduction ble of having system-connected smoke detectors in Solid particles Convection the dwelling units programmed to operate like smoke Liquid particles Radiation alarms. In this configuration, they receive power, in- cluding backup power, from the building system and are monitored for faults and sensitivity. When they alarm, these systems provide an alarm signal (audi- ble, visible, or both) only in the dwelling unit. They can also send a supervisory signal to an attended location. Floor In other cases, a complete automatic detection Exhibit S2.2 Fire signatures. system might be required in addition to the require- ments for the dwelling unit. The building system must then provide detection within all spaces, includ- transferred by conduction, convection, and radiation. ing the dwelling units. This detection for the dwelling The second signature group is categorized by the units is not redundant. The intent is for the household physical/chemical changes that take place. This group fire alarm equipment to provide an alarm of smoke is comprised of solids, liquids, and gases produced conditions to the occupants of the dwelling unit. The by the fire. The solid and liquid particles are grouped additional detectors connected to the building system together and called smoke or aerosols. would be heat detectors, which would notify the other Conduction occurs when, during the combustion occupants before a fire in the dwelling unit became a process, some of the energy released is conducted threat to those outside the dwelling unit. This design through the fuel to further the combustion process. concept is described thoroughly in the commentary Any time the temperature of one part of a material of the occupancy chapters in which it is required. differs from another part, heat energy is conducted NFPA 72, National Fire Alarm Code, deals with the from the hotter portion to the cooler portion. application, installation, performance, and mainte- Convection occurs when heat is transferred by nance of fire alarm systems and their components. fluid motion. During combustion, hot fire gases rise, Like this handbook, the National Fire Alarm Code entraining fresh air, which then heats and also rises Handbook contains the text of NFPA 72, along with until the mixture either collects at the ceiling or cools explanatory information. The National Fire Alarm Code to approximately room temperature.