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Fire Alarm System Initiating Devices

Chapter 12

Page 357

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Objectives• List and compare the available types of

manually operated fire alarm devices• Discuss the methodology used to increase

the reliability of a fire alarm system• Evaluate the differences between the

available types of heat detectors• Compare the capabilities of the various

types of smoke detectors2

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Objectives

• Define stratification and explain how it can be predicted

• Propose a methodology for detecting a fire where stratification is predicted

• Discuss the “pressure sandwich,” and explain how this principle is accomplished by a fire detection system

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Objectives

• Compare and contrast flame detectors and their applications

• Give examples of where gas detectors and pressure detectors are appropriate for use

• List and discuss the fire protection system supervisory functions that can be provided by a fire alarm system 4

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Manually Operated Devices

• Manually operated fire alarm devices: require the action of an individual to initiate a fire alarm signal

• Manual pull stations: used by building occupants to electronically notify others of a fire

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Manually Operated Devices

• Coded manual stations: send a set of unique time-pulsed signals to the fire alarm control unit three or more times, indicating location of the manual station

• Non-coded manual stations: do not deliver a distinctive signal– Grouped on a circuit so the control unit can

indicate activation

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Manually Operated Devices

• Presignal and General Alarm Manual Stations

• Single-Action and Double-Action Manual Stations

• Breakglass and Nonbreakglass Manual Stations

• Addressable Manual Stations7

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Automatic Fire Detectors• Reliability Methodology for Detectors• Methods of ensuring the reliability of an

automatic fire detection system:– Protection– Wiring– Support– Ceiling jet interaction– Testing accessibility

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Automatic Fire Detectors (con’t.)

Figure 12-2. Detection system support

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Automatic Fire Detectors (con’t.)

• Methods of ensuring the reliability of an automatic fire detection system (con’t.):– Enclosure evaluation– Specific points of hazard– Anticipated fire– Detection zones

• Addressable Detectors

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Automatic Fire Detector Overview and Comparison

• Automatic fire detectors are composed of– Heat-sensing fire detectors– Smoke-sensing fire detectors– Flame-sensing radiant energy fire detectors– Gas-sensing detectors– Pressure detectors– Non-fire detectors (cold detectors, video

surveillance systems)11

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Automatic Fire Detector Overview and Comparison

(con’t.)

Table 12-1. Comparison of automatic fire detectors

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Spot-Type Heat-Sensing Fire Detectors

• Spot-Type Pneumatic Rate-of-Rise Heat Detectors

• Spot-Type Thermocouple Rate-of-Rise Heat Detectors

• Spot-Type Fixed Temperature Heat Detectors

• Spot-Type Rate-Compensated Heat Detectors 1

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Spot-Type Heat-Sensing Fire Detectors (con’t.)

Figure 12-5. Spot-type pneumatic rate-of-rise heat detector

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Spot-Type Heat-Sensing Fire Detectors (con’t.)

Figure 12-6. Bimetallic fixed temperature heat detectors

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Spot-Type Heat-Sensing Fire Detectors

• Spot-Type Electronic Thermistor Heat Detectors

• Spot-Type Analog Heat Detectors• Spot-Type Combination Heat Detectors

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Line-Type Heat-Sensing Devices

• Electric or pneumatic • Can be selected to detect either a fixed-

temperature or rate-of-temperature rise anywhere along the length of the detector

• Well suited for linear or elongated hazards such as conveyors and electric cable trays

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Smoke-Sensing Fire Detectors• Spot-Type Ionization Smoke Detectors• Spot-Type Photoelectric Light-Scattering

Detectors• Spot-Type Photoelectric Light Obscuration

Smoke Detectors• Air-Sampling or Air-Aspirated Smoke

Detectors• Laser-Based Air Sampling Smoke

Detectors 18

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Smoke-Sensing Fire Detectors

Figure 12-10. Line-type heat-sensing device: applications (Note: These detectors are ideal for linear or elongated hazards such as conveyors

and cable trays) 19

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Smoke-Sensing Fire Detectors

• Linear Beam Smoke Detectors

• Air-Duct Smoke Detectors• Analog Smoke Detectors

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Flame-Sensing Radiant Fire Detectors

• Ultraviolet (UV) Flame Detectors• Infrared (IR) Flame Detectors• Combination Ultraviolet/Infrared (UV/IR)

Detectors• Selecting a Flame Detection System• Radiation Spectrum for Flame Detectors• Inverse Square Law for Flame Detectors• Spark/Ember Detectors 2

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Flame-Sensing Radiant Fire Detectors (con’t.)

Figure 12-22. Radiation spectrum

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Multi-Sensor Detectors

• Multi-sensor detectors: increases reliability by combining heat and smoke sensing, heat and carbon monoxide sensing, heat/co/smoke sensing, or ionization plus photoelectric sensing

• Multi-sensor detectors contain algorithms for discerning sources of nuisance alarms

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Gas-Sensing Detectors

• A gas-sensing detector can be chosen to detect the release of a flammable gas before it reaches ignitable concentration

• Gas-sensing detectors: detect the release of a flammable gas before it reaches ignitable concentration

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Pressure-Sensing Fire Detectors

• In tightly enclosed rooms or enclosures where personnel are not present, a fire increases the pressure in the enclosure

• Pressure-sensing fire detector: plate that depresses when the enclosure pressure increases to a predetermined level and activates a signal to the FACU

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Fire Protection System Flow And Supervisory Switches

• Sprinkler System Waterflow Switches• Fire Suppression System Releasing

Switches• Fire Suppression System Supervisory

Switches

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Summary

• Initiating devices on a fire alarm system are watchdogs that supervise essential equipment and report fire conditions to the fire alarm control unit (FACU)

• Initiating devices must be– Protected– Properly wired and supported– Placed within the ceiling jet boundary

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Summary

• Initiating devices must (con’t.):– Tested frequently and suitable in the

enclosure conditions to which it is exposed– Installed for specific points of hazard– Selected correctly for the anticipated fire– Zoned wisely

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Summary

• Detectors types– Heat-sensing– Smoke-sensing– Particle-sensing– Flame-sensing– Gas-sensing– Pressure-sensing

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