11-CS-2 Engineering Communications · December 2017
Question 4 of 7: Fire Detection and Suppression
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
National Exams — December 2017 — 11-CS-2 Engineering in Society: Health and Safety. Closed book; approved calculator permitted. Any five of the seven questions constitute a complete paper; all questions are of equal value. Answers are written in point form but fully, as instructed. Complete answers to all seven questions follow.
Question 4: Fire Detection and Suppression (20 marks: 6/7/7)
(a) Heat detectors — respond to temperature (fixed-temperature or rate-of-rise); reliable, few false alarms, but slower; suit dirty/dusty areas.
(b) Smoke detectors — respond to combustion products (ionization = flaming fires; photoelectric = smouldering); faster early warning but more false alarms in dusty/steamy areas.
(ii) Sprinkler Systems
(a) Wet-pipe — always charged with water; immediate discharge; simplest/most reliable; not for freezing areas.
(b) Dry-pipe — pipes hold pressurized air; water admitted when a head opens; for freezing areas; slight delay.
(c) Deluge — all heads open; a detection system opens the deluge valve so water flows from all heads at once; for high-hazard, rapid, large-area needs.
(iii) Non-Water Suppression Systems
For electronics/flammable liquids: clean agents/gaseous (inert gas/halocarbon—no residue), CO₂ (smother—asphyxiation hazard), dry chemical (interrupt the reaction), foam (blanket flammable-liquid surfaces). Selection depends on fire class, contents and occupant safety.
