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APPLICA TIONS GUIDE
System
Smoke Detectors
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APPLICA TIONS GUIDE System Smoke Detectors Contents Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Section 4 – Proper Detector Applications, Placement and Spacing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Where To Place Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Secti
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APPLICA TIONS GUIDE: SYSTEM SMOKE DETECTORS The purpose of this guide is installers should find the contents both educational and Introduction to provide information con- informative. cerning the proper application of smoke detectors used in conjunction with fire alarm systems. It outlines basic prin- Though this information is based upon industry expertise ciples that should be considered in the application of early and many years of experience, it is intended to be used warning fire and smoke
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SYSTEM SENSOR Industry Publications Manufacturer’s Publications NEMA Guide for Proper Use of Smoke Detectors in Duct The manufacturer of the smoke detectors being used Applications should be contacted for any published information on their NEMA Training Manual on Fire Alarm Systems products. NEMA Guide to Code Requirements for Fire Protective Signaling and Detection Systems NEMA Guide for proper Use of System Smoke Detectors Section 2 There are two basic types of Electronic circuitry monitors bo
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APPLICA TIONS GUIDE: SYSTEM SMOKE DETECTORS Photoelectric Light Obscuration Smoke Detector Photoelectric Smoke Detector Operation Another type of photoelectric detector, the light obscura- Smoke produced by a fire affects the intensity of a light tion detector, employs a light source and a photosensitive beam passing through air. The smoke can block or obscure receiving device, such as a photodiode (see Figure 8). the beam. It can also cause the light to scatter due to reflec- When smoke particl
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SYSTEM SENSOR For more information, see NFPA 72-1999, paragraphs A-2- save more in the future. Nevertheless, smoke detectors do 3.6.1.2, A-2-3.6.1.1, A-2-3.6.1.2(a), and A-2-3.6.1.2(b). have limitations. They may not provide early warning of a fire developing on another level of a building. A first floor NFPA 72 requirements also dictate that alarm notification detector, for example, may not detect a second floor fire. appliances (including smoke detectors with built-in For this reason, detector
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APPLICA TIONS GUIDE: SYSTEM SMOKE DETECTORS Class A Circuits Class A circuits also differentiate between short circuits across the loop and opens on the loop. Supervision is accomplished by monitoring the level of current passing through the installation wiring and the end-of-line resistor, which in a Class A circuit is an integral part of the fire alarm control panel. Class A wiring must return to and be terminated in the control panel. This technique requires a TYPICAL INITIATING minimum of fo
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SYSTEM SENSOR A manufacturer’s installation wiring drawing routes wires Smoke Detector “A” and shows connections in a certain manner to accommo- date supervision requirements. Any variance from the manufacturer’s drawings might cause a portion of a circuit to be unsupervised and, if an open or short circuit fault occurred, it could prevent the circuit from being able to perform its intended function without giving the required trouble indication. The rules of supervision are not very complex. Ho
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APPLICA TIONS GUIDE: SYSTEM SMOKE DETECTORS Figure 16 is an example of properly connected may require more power than the initiating device cir- Wire Nut smoke detectors provided with pigtails. This cuit can supply. This could result in the inability of the method of termination supervises all wiring to relay to control auxiliary equipment to which it is con- the point at which it connects to the detector. nected. • When using wireless detectors, follow the manufactur- Smoke Figure 17 shows an i
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SYSTEM SENSOR be mounted on the wall. Wall-mounted detectors should be 4 in. (10 cm) located not less than 4 inches nor more than 12 inches from the ceiling to the top of the detector, and at least 4 Ceiling inches (10 cm) from any corner wall junction. (See Figure 18.) When air supply and/or air return ducts are present in a room or space, the detector(s) should not be placed in the path of the air flow supply or return duct (NFPA 72, 1999 Edition). Smoke tests are helpful in determining proper
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APPLICA TIONS GUIDE: SYSTEM SMOKE DETECTORS to use system detectors and manual fire alarm stations in Special Application Detectors the hallways and common areas of the complex and resi- The guidelines in this document generally apply to stan- dential single station type smoke detectors and heat detec- dard open-area smoke detectors. System Sensor has a num- tors in the individual apartments. The system detectors, ber of advanced technology detectors that are optimized manual stations and heat d
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21 ft. 21 ft. SYSTEM SENSOR In other words, if a diagonal through the center of the room is no greater than the diameter of the circle, or 42.4 feet Rectangles (12.8 meters), one detector can be used under ideal condi- A 10 ft. × 41 ft. = 410 sq. ft. tions. Figure 21 shows how a length of hallway can be pro- B 15 ft. × 39 ft. = 585 sq. ft. tected by only two detectors under ideal conditions. C 20 ft. × 37 ft. = 740 sq. ft. D 25 ft. × 34 ft. = 850 sq. ft. E 30 ft. × 30 ft. = 900 sq. ft. Special S
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APPLICA TIONS GUIDE: SYSTEM SMOKE DETECTORS • Alternate Detector Mounting. Mounting alternate Detectors in Air Handling and Air Conditioning detectors up to 3 feet (1 m) below the ceiling can Systems increase detection of small or smoldering fires when See NEMA Guide for Proper Use of Smoke Detectors in the possibility of air stratification exists. Figure 23 Duct Applications and NFPA 72, National Fire Alarm Code illustrates such an installation. Specific designs for for more specific informatio
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SYSTEM SENSOR Section 5 Smoke detectors are designed If a detector’s sensitivity is within specifications, nothing to be as maintenance free as further needs to be done to the detector. If the detector’s Testing, possible. However, dust, dirt, sensitivity is outside specifications, clean the detector and Maintenance and other foreign matter can retest. If that does not place the sensitivity within the unit and Service of accumulate inside a detector’s specified range then follow the manufacture
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APPLICA TIONS GUIDE: SYSTEM SMOKE DETECTORS Section 6 Make sure that all the detectors in the zone or pinpointed What to Do About device(s) that show an alarm are checked before deciding Troubleshooting Unwanted Alarms that it is a false alarm. If a fire does exist, more than one Techniques No detection system is imper- detector may be in the alarm state, although no signs of fire vious to unwanted alarms. may be evident in the vicinity of the first activated detec- Statistically, as the system
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SYSTEM SENSOR NFPA standards require and smoke detector manufacturers or other dust-producing operations in the vicinity of the recommend that all detectors be visually inspected twice detector heads to prevent false alarms due to the dust get- a year. ting into the detector sensing chambers. In new construc- tion applications drywall dust contamination affects all Clean the detectors at least once a year, or more frequent- types of smoke detectors. To help overcome this problem, it ly if enviro
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APPLICA TIONS GUIDE: SYSTEM SMOKE DETECTORS If assistance must be sought from the installer or man- •Helping the owner set up appropriate Detector ufacturer, there will be an indication of the tests that Maintenance and Alarm Logs for the system. have already been done by the owner’s personnel. •Providing initial instruction and training to the owner’s personnel or outside organization which will These services can be provided by qualified outside be monitoring and maintaining the system. organi
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SYSTEM SENSOR Appendix 1 Addressable System Smoke End of Line Relay Detector Device used to supervise power (for four-wire smoke Glossary of Terms System smoke detectors, detectors) and installed after the last device on the loop. which, in addition to providing alarm and trouble indica- False Alarms tions to a control unit, are capable of communicating a An unwanted alarm caused by non-smoke contaminants unique identification (address). such as dust or insects. Air Sampling-type Detector Fire A
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APPLICA TIONS GUIDE: SYSTEM SMOKE DETECTORS product evaluation, that maintains periodic inspection of Smoothing Algorithms listed equipment or materials and whose listing states A method of “smoothing out” a detector’s interpretation of either that the equipment or material meets appropriate sudden, short-duration increases in obscuration within the standards or has been tested and found suitable for use in sensing chamber, intended to reduce the occurrence of nui- a specified manner. sance alar
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SYSTEM SENSOR Appendix 2 Fire Alarm Log Customer Name: Installation Date: Installing Contractor: Inspection and Test Date: Inspection and Test Performed By: Check one Location Action Taken By Date Time Recorded By Fire Trouble (Bldg, Zone, Det #) Probable Cause Action Taken Name and Date 19
