A P P L I C A T I O N S G U I D E System Smoke Detectors
A P P L I C A T I O N S G U I D E System Smoke Detectors Contents Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Section 4 – Proper Detector Applications, Placement and Spacing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Where To Place Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A P P L I C A T I O N S G U I D E : S Y S T E M Introduction The purpose of this guide is to provide information concerning the proper application of smoke detectors used in conjunction with fire alarm systems. It outlines basic principles that should be considered in the application of early warning fire and smoke detection devices. Operating characteristics of detectors and environmental factors, which may aid, delay or prevent their operation, are presented.
S Y S T E M S E N S O R Industry Publications Manufacturer’s Publications NEMA Guide for Proper Use of Smoke Detectors in Duct Applications NEMA Training Manual on Fire Alarm Systems NEMA Guide to Code Requirements for Fire Protective Signaling and Detection Systems NEMA Guide for proper Use of System Smoke Detectors The manufacturer of the smoke detectors being used should be contacted for any published information on their products.
A P P L I C A T I O N S G U I D E : S Y S T E M M O K E D E T E C T O R S Photoelectric Smoke Detector Operation Photoelectric Light Obscuration Smoke Detector Smoke produced by a fire affects the intensity of a light beam passing through air. The smoke can block or obscure the beam. It can also cause the light to scatter due to reflection off the smoke particles. Photoelectric smoke detectors are designed to sense smoke by utilizing these effects of smoke on light.
S Y For more information, see NFPA 72-1999, paragraphs A-23.6.1.2, A-2-3.6.1.1, A-2-3.6.1.2(a), and A-2-3.6.1.2(b). NFPA 72 requirements also dictate that alarm notification appliances (including smoke detectors with built-in sounders) produce the 3-pulse temporal pattern fire alarm evacuation signal described in ANSI S3.41. (Audible Emergency Evacuation Signals) S T E M S E N S O R save more in the future. Nevertheless, smoke detectors do have limitations.
A P P L I C A T I O N S G U I D E : S Y S T E M S M O K E D E T E C T O R S 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.
S Y A manufacturer’s installation wiring drawing routes wires and shows connections in a certain manner to accommodate 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.
A P P L I C A T I O N Wire Nut Smoke Detector Figure 16: Pigtail Connections – Correct Wiring Method S G U I D E : S Y S T E M Figure 16 is an example of properly connected smoke detectors provided with pigtails. This method of termination supervises all wiring to the point at which it connects to the detector. Figure 17 shows an incorrect pigtail connection. This is a form of “T-tapping” discussed earlier.
Y be mounted on the wall. Wall-mounted detectors should be located not less than 4 inches nor more than 12 inches from the ceiling to the top of the detector, and at least 4 inches (10 cm) from any corner wall junction. (See Figure 18.) S T E M S E N S O R 4 in. (10 cm) Ceiling 4 in. (10 cm) Minimum S 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).
O N S G U I D E : S Y S T E M Special Application Detectors The guidelines in this document generally apply to standard open-area smoke detectors. System Sensor has a number of advanced technology detectors that are optimized for specific environments and should be considered. Pinnacle™ Laser technology smoke detector is designed for use in areas that require extremely early warning of fire.
S Y S T E M S E N S O R 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 (12.8 meters), one detector can be used under ideal conditions. Figure 21 shows how a length of hallway can be protected by only two detectors under ideal conditions. Rectangles A 10 ft. × 41 ft. = 410 sq. ft. B 15 ft. × 39 ft. = 585 sq. ft. C 20 ft. × 37 ft. = 740 sq. ft. D 25 ft. × 34 ft. = 850 sq. ft. E 30 ft. × 30 ft. = 900 sq. ft.
A P P L I C A T I O N S G U I D E : S Y S T E M • Alternate Detector Mounting. Mounting alternate detectors up to 3 feet (1 m) below the ceiling can increase detection of small or smoldering fires when the possibility of air stratification exists. Figure 23 illustrates such an installation. Specific designs for such an alternate detection should be based upon an engineering survey.
S Y Smoke detectors are designed to be as maintenance free as possible. However, dust, dirt, and other foreign matter can accumulate inside a detector’s sensing elements and change its sensitivity. They can become either more sensitive, which may cause unwanted alarms, or less sensitive, which could reduce the amount of warning time given in case of a fire. Both are undesirable. Therefore, detectors should be tested periodically and maintained at regular intervals.
A P P L I C A T I O N S G U Section 6 Troubleshooting Techniques I D E : S Y S T E M What to Do About Unwanted Alarms No detection system is impervious to unwanted alarms. Statistically, as the system size and the total number of detectors increases, the total number of nuisance alarms per year tends to increase.
S Y NFPA standards require and smoke detector manufacturers recommend that all detectors be visually inspected twice a year. Clean the detectors at least once a year, or more frequently if environmental conditions warrant it. See the section on Detector Testing and Maintenance in this guide for more details.
A P P L I C A T I O N S G U I D E : S Y S T E M If assistance must be sought from the installer or manufacturer, there will be an indication of the tests that have already been done by the owner’s personnel. These services can be provided by qualified outside organizations. The installers of smoke detector equipped alarm systems are responsible for providing the owners with the necessary information and training so that their personnel can maintain the integrity of the alarm system.
S Y Addressable System Smoke Detector System smoke detectors, which, in addition to providing alarm and trouble indications to a control unit, are capable of communicating a unique identification (address). Appendix 1 Glossary of Terms Air Sampling-type Detector A sampling-type detector consists of piping or tubing distribution from the detector unit to the area(s) to be protected. An air pump draws air from the protected area back to the detector through the air sampling ports and piping or tubing.
A P P L I C A T I O N S G U I D E : S Y S T E M M O K E D E T E C T O R S product evaluation, that maintains periodic inspection of listed equipment or materials and whose listing states either that the equipment or material meets appropriate standards or has been tested and found suitable for use in a specified manner.
S Y S T E M S E N S O R Appendix 2 Fire Alarm Log Customer Name: Installation Date: Installing Contractor: Inspection and Test Date: Inspection and Test Performed By: Check one Date Time Recorded By Fire Location Trouble (Bldg, Zone, Det #) Action Taken By Probable Cause Action Taken Name and Date 19
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