--- title: "Fire detection and extinguishing systems" subject: "Building Technology" chapter: 12 key: "semester_6/building_technology:fire-detection-extinguishing" source: https://www.bctengineer.com/q/semester_6/building_technology/fire-detection-extinguishing site: BCT Engineering --- # Fire detection and extinguishing systems Building Technology · Chapter 12: Other services in building - Asked in: 2076 Baisakh, 8 marks - Video: [How does firefighting system in a building work?](https://www.youtube.com/watch?v=_yCllHMvQ_0) — Engineering Motive - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/fire-detection-extinguishing - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-12 ## Question Explain briefly various methods of fire detection systems and also explain about fire extinguishing systems. ## Short answer Fire detection methods include heat (fixed-temperature/rate-of-rise), smoke (ionisation/photoelectric), flame, gas detectors, and manual call points. Extinguishing systems range from portable extinguishers (water, foam, CO2, dry powder) and hose reels to wet/dry risers, automatic sprinklers with heat-sensitive bulbs, and gaseous or foam flooding for special hazards. ## Answer #### Fire detection systems Early detection allows escape and quick action. Types of detectors: 1. **Heat detectors:** fixed-temperature (fusible link, bimetallic) or rate-of-rise types; respond to temperature increase; used in kitchens, boiler rooms. 2. **Smoke detectors:** *ionisation* type (good for flaming fires) and *optical/photoelectric* type (good for smouldering fires); used in rooms, corridors, offices. 3. **Flame detectors:** infrared or ultraviolet sensors for hazardous areas. 4. **Gas detectors:** detect combustible gases and CO. 5. **Manual call points:** break-glass push buttons. 6. All connect to a **fire alarm panel** with bells/sirens and indicator zones. #### Fire extinguishing systems 1. **Portable extinguishers:** water (Class A), foam (A, B), CO2 (B, C, electrical), dry chemical powder (A, B, C), wet chemical (kitchen oils). 2. **Hose reels and hydrants:** pipes with hoses on each floor and outside hydrants. 3. **Wet riser / dry riser:** vertical pipe to supply water to floors in tall buildings (wet riser always charged, dry riser charged by fire brigade). 4. **Automatic sprinkler system:** pipe network with heat-sensitive bulbs (about 68 degrees C glass bulb) that burst and spray water over the fire. 5. **Gaseous / foam systems:** CO2, inert gas, or foam flooding for server rooms, stores and oil hazards. 6. **Water storage:** underground static tank and terrace tank with pumps (main, jockey, standby). ```text Terrace tank | riser ---[hose reel] floor 3 |-----[hose reel] floor 2 |-----[hose reel] floor 1 pump <- underground tank ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How do heat detectors work and where are they used? A. They sense smoke particles; used in corridors B. They respond to temperature rise (fixed-temperature or rate-of-rise); used in kitchens and boiler rooms C. They detect gases; used in bedrooms D. They sense infrared flame; used in offices only Answer: B. Heat detectors respond to a temperature increase, suiting places like kitchens and boiler rooms where smoke detectors would false-alarm. (Key point: Heat detectors) 2. Which smoke detector type is better for smouldering fires? A. Ionisation type B. Optical (photoelectric) type C. Fusible link type D. Break-glass type Answer: B. Ionisation detectors suit flaming fires, whereas optical/photoelectric detectors suit smouldering fires. (Key point: Smoke detector types) 3. Which extinguisher is suitable for electrical fires? A. Water B. Foam C. CO2 or dry chemical powder D. Wet chemical Answer: C. CO2 and dry powder are non-conductive and suit electrical fires; water must never be used. (Key point: Extinguisher agents) 4. What is the difference between a wet riser and a dry riser? A. A wet riser is always charged with water; a dry riser is charged by the fire brigade when needed B. A dry riser is always charged; a wet riser is empty C. Both are only for ground floors D. A wet riser uses foam only Answer: A. A wet riser is permanently filled with water, while a dry riser is empty until the fire brigade pumps water in. (Key point: Wet and dry riser) 5. How does an automatic sprinkler system operate? A. A manual valve is opened by occupants B. Heat-sensitive bulbs (glass bulb about 68 degrees C) burst and spray water over the fire C. Smoke detectors trigger a CO2 flood D. A float valve opens when the tank is full Answer: B. Each sprinkler has a heat-sensitive bulb which bursts at its rated temperature and releases water in the pipe network. (Key point: Sprinkler operation) 6. What do all detectors and manual call points connect to? A. The overhead water tank B. A fire alarm panel with bells/sirens and indicator zones C. The energy meter D. The hose reel Answer: B. All detection devices feed a fire alarm panel that sounds alarms and shows the zone of the fire. (Key point: Alarm panel) ## Related in other subjects - [Detection gain of SSB-SC vs DSB-SC](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adetection-gain-ssbsc-dsbsc) — Communication Systems, chapter 9, asked 2× - [Phase error in synchronous DSB-SC detection; synchronized receiver](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aphase-error-dsbsc-costas) — Communication Systems, chapter 2 - [DSB-AM, DSB-SC and SSB spectra; synchronous detection](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Adsbam-dsbsc-ssb-spectrum-synchronous) — Communication Systems, chapter 2 - [Phase error in coherent DSB-SC detection; AM demodulation by PLL](https://www.bctengineer.com/question.md?key=semester_6%2Fcommunication_systems%3Aphase-error-dsbsc-am-pll) — Communication Systems, chapter 2