Going Automatic in California
Effective July 1, 2002, the California Legislature passed a law requiring automatic fire alarm systems in various school construction projects, such as Eureka High School, pictured right. The law is known as the Green Oaks Family Academy Elementary School Fire Protection Act (SB 575). In order to ensure proper long-term operation of an automatic fire alarm system in a school, the system designe...
Effective July 1, 2002, the California Legislature passed a law requiring automatic fire alarm systems in various school construction projects, such as Eureka High School, pictured right. The law is known as the Green Oaks Family Academy Elementary School Fire Protection Act (SB 575).
In order to ensure proper long-term operation of an automatic fire alarm system in a school, the system designer and specifier must pay close attention to all applicable codes as well as suitable design criteria and methods. It is also important that the school's maintenance staff prepare for specific periodic inspection, testing and maintenance requirements of these systems.
Basically, the fire alarm system is used for the purpose of detecting the presence of a fire or potential fire and sounding a local and/or remote alarm. Needless to say, its primary objective is protecting life and property.
Following are important issues that need to be carefully considered.
Fire detection devices
For most school applications, unless specific requirements are dictated for certain areas, ceiling-mounted, spot-type smoke and heat detectors are the commonly used types.
The two major types of smoke detectors are ionization and photoelectric. Different detectors respond to different types of smoke particles. (See Product Comparison on p. 71 for a primer on the pros and cons of various types of smoke detectors.) In an air-handling system, smoke is cooler and more visible because of the growth of sub-micron particles into larger particles due to agglomeration and recombination. For this reason, photoelectric has advantages over ionization detection technology in air-duct system applications.
One way of categorizing heat detectors is as fixed- or rate-of-rise- temperature types. Fixed-temperature detectors respond when their operating element becomes heated to a predetermined level. The most commonly used heat detector temperature ratings are 135°F and 200°F. Per National Fire Protection Assn. (NFPA) Standard 72, the temperature rating of detectors shall be at least 20°F above the maximum expected temperature. Therefore, in locations such as cavities above ceilings and in relatively hot climate zones such as California, 200°F heat detectors are being used. Rate-of-rise heat detectors respond when the temperature rises at a rate exceeding a predetermined amount (typically 15°F/min.)
Detectors are mainly the initiating devices that activate automatic fire alarm systems, making the overall proper operation of an automatic fire alarm system more dependent on detectors than is a manual pull station.
Proper spacing of detectors is imperative. A detector's coverage is not a square but rather a circle whose radius is 0.7 times that of the listed linear spacing. Normally, the listed spacing for heat detectors is 50 ft. and 30 ft. for smoke detectors.
Also, several ceiling conditions factor into detector spacing, including ceiling height and construction. The spacing varies for smooth, solid joist, beam, sloped, shed and peaked-type ceilings. NFPA 72 defines each type of ceiling and provides guidelines for spacing determination.
Smoke detection for HVAC
NFPA 90A and NFPA 72 define where smoke detection in the supply air and/or return-air ducts should be. Upon detection of smoke, the associated HVAC unit shall be shut down to prevent its spread.
Interfacing fire alarm system and elevator control
The relationship between fire alarm systems and elevator controls has evolved over the past decade. All related codes can be found in NFPA 72, NFPA 13, and ANSI/ASME A17.1. These codes are intended to establish the following sequence of operation in case of fire:
A smoke detector would sense smoke and initiate elevator recall.
The elevators would be recalled immediately to the floor of recall, and the doors would open.
Heat buildup would cause the heat detector to actuate, which would initiate elevator power shutdown.
Further heat buildup would cause the sprinkler to fuse and release water.
The above-referenced codes address the requirements of positioning smoke and/or heat detectors in elevator lobbies, machine rooms and hoistways.
Central monitoring systems
NFPA 72 requires central monitoring of all protected premises. This monitoring should take place at a continuously attended location and be operated by a listed company. Normally, a digital alarm communicator transmitter is provided at the fire alarm control panel. This transmitter communicates with a digital alarm communicator receiver located at the central monitoring location.
DACT should be connected to the public switched telephone network upstream of any private telephone system on the protected premises. Special care should be used when connecting a DACT to a digital service such as DSL or ADSL. Filters or other special equipment might be needed to communicate reliably.
Notification appliances such as horns and strobes should be sufficient in quantity, audibility, intelligibility and visibility so as to reliably convey information to the intended recipients. NFPA 72 and the Americans with Disabilities Act set certain guidelines for specification and positioning of these appliances.
Battery/voltage drop calculations
Per NFPA 72, the batteries should have sufficient capacity to operate the fire alarm system under quiescent load (in a non-alarm situation) for a minimum of 24 hours and, at the end of that period, should be capable of operating all alarm notification appliances used for evacuation or to direct aid to the location of an emergency for five minutes.
Notification appliance circuits require special treatment to ensure that the voltage supplied to all connected appliances will be within the limits specified for proper operation of each appliance. Voltage that is below the operating range of the appliance can cause the appliances to produce unacceptable visible signal intensities or sound pressure levels.
It is imperative to consult the manufacturer's cut sheets to ensure the appliances' actual current draws are included in calculations.
Inspection, testing, maintenance
An automatic fire alarm system requires the school's maintenance staff to perform periodic visual inspection, testing and maintenance in accordance with the schedules shown in NFPA 72.
For instance, heat detectors should be inspected semiannually to ensure that there is no mechanical problem or water damage, or that they have not been inadvertently painted. Smoke detectors should be visually inspected, too. Analog addressable smoke detectors can be monitored for contamination by fire alarm control panels that include a drift compensation feature. However, despite this monitoring, obstructions such as covered detectors will not be detected. Often, during special cleaning or renovation projects, the smoke detectors are covered to avoid contamination and possible nuisance alarm. Following the project, a visual inspection will ensure that the covers, bags or tape have been removed.
In addition to visual inspection, reacceptance testing will be required. For instance, smoke detectors require periodic calibrated sensitivity testing. The type and frequency of these tests are described in NFPA 72.
Many existing schools in California use only a manual fire alarm system. As the school modernization projects progress across the state, designers, installers and school maintenance personnel need to get familiar with the requirements of automatic fire alarm systems. These systems should be designed, installed and maintained to provide indication and warning of abnormal fire conditions and summon appropriate aid in time to allow occupants to get out safely.