Unit 5: Fire Safety Installations

Transcription

1 Unit 5: Fire Safety Installations 5.1 Basic Fire Science Definition of Fire: A process of combustion accompanied by a rapid release of heat and light in varying quantities. i By products of fire: Gas and smoke. These products can impede oxygen levels as well as causing visual impairment, leading to asphyxiation as well as inhibiting swift evacuation from building. ii Triangle of Fire: Combustion requires 3 elements in order to take place: a) Fuel: Combustible solids, liquids or gases; b) Heat: c) Oxygen: Makes up approx. 21% of Earth s atmosphere. ii Triangle of Fire Classes of Fires: a) Class A Fires: Ordinary, combustible materials, e.g Paper, wood, etc; b) Class B Fires: Flammable or combustible liquids, liquids or gases, such as petroleum related products; c) Class C Fires: Energized electrical equipment (e Electrical Fires); d) Class D Fires: Combustible Metals, e.g Potassium, sodium, titanium, etc. 1

2 5.2 How Fires are Extinguished Fires can be extinguished by removing any one element from the triangle of fire: Cutting off the oxygen supply to the fire, e.g Using a blanket to smother the fire; Removing fuel supply to the fire, e.g cutting off the gas supply to the stove will cut off the stove fire; Removing heat supply the fire via cooling, e.g spraying water into the fire. Types of Fire Fighting Systems i Automatic fire fighting system: Includes sprinklers, foams, FM200; ii Manual Fire Fighting equipment: Includes water hose reels, hydrants, fire extinguishers; iv. Fire Alarm Systems: Designed to alert nearest fire station as well as inhouse fire fighting team to fight fire. 5.3 Manual Fire Fighting Systems Fire Extinguishers: Common Types of Extinguishing Agents for Portable Fire Extinguishers: Water; Carbon Dioxide (CO2); Halon; Powder; Foam. i All extinguishers in buildings must be charged, tested and maintained in accordance to locality s code of practice (SS: CP 55 in Singapore); ii Construction of Extinguishers in conformance to COP of locality (SS232 for Singapore). 2

3 iv. Types of Extinguishers a) Water: Extinguishing method: Removing heat source (Cooling); Removing oxygen source (Smothering); Can be discharged from: Portable Extinguishers; Water hose reels (Connected to a main water supply line) or other forms of water sprays; Fire Hydrants; Dry/Wet risers. Advantages: Easily available as long as there is a consistent water supply; Cheap; High Specific Heat Capacity (4.2kJ/kg at atmospheric pressure) and High latent heat of vaporization: (225kJ/kg at atmospheric pressure): Able to cool effectively through high heat absorption; When vaporized, water expands up to 1600 times its original volume. This allows it to displace oxygen in the air, hence the smothering effect. Disadvantages: Water is an excellent conductor of electricity, hence unsuitable for Class C electrical fires; Not suitable for Combustible Metals (Class D fires); Not suitable for continuous use on radioactive substances; Tends to damage properties when used to extinguish fires. Suitable classes of fire for water: Class A and Class B Fires. 3

4 b) Carbon Dioxide (CO2): Extinguishing method: Removing oxygen source (Smothering); Advantages: Non-combustible; Does not conduct electricity, hence suitable for all electrical fires; Easily liquefied and bottled; Low Boiling Point: Once discharged, it immediately vaporizes and displaces the oxygen in the air, hence achieving the smothering effect on the fire; Since CO2 is a gas, it dissipates into the atmosphere readily, leaving no traces behind and hence no damage to property; Can penetrate to all areas due to its gaseous form. Disadvantages: CO2 is limited in putting out fires due to its readiness to dissipate into the environment and low cooling capacity; Requires large quantities to put out large or deep seated fires; May create suffocating atmosphere in enclosed areas due to its ability to displace oxygen; Should only be used when there is a nearby escape route for occupants to evacuate before discharge. Suitable Classes of Fire for CO2: Classes A, B, C and D fires. 4

5 c) Halon Extinguishing method: Removing oxygen source (Smothering). Halon is a form of hydrocarbon: One of the hydrogen atoms replaced by flourine, bromine, chlorine or Iodine. Can be discharged from: Total flooding systems; Portable Fire Extinguishers. Advantages: Non-flammable; Does not conduct electricity, hence suitable for all electrical fires; Does not leave behind messy residues; Does not damage sensitive electronic equipment; Suitable for server rooms. Suitable Classes of Fire for Halon: Classes A, B and C fires. Disadvantages: Expensive; Toxic: Evacuate occupants before usage. Limitations in exposure time and concentration levels; Environmental Issue 1: Depletion of Ozone in Earth s Upper Atmosphere; Environmental Issue 2: Creates Greenhouse Effect by trapping heat in Earth s atmosphere; Limits of quantities used by Montreal Protocol. In Singapore, installation of Halon Systems have ceased since 1990; Not suitable for the following fires: 5

6 d) Dry Powder Extinguishing method: Removing oxygen source (Smothering); Removing heat source (Cooling). How it works: Uses chemical particles to extinguish fire; Forms a barrier to reduce oxygen required for combustion; Crust forms over burning material as heat reacts with the powder, further smothering the fire via cooling. Usually discharged from Portable Fire Extinguishers. Advantages: Good for normal combustibles involving surface fires, as it puts out fire rapidly; Chemical cloud provides effective screen against flame flashback, allowing user to close in on fire safely to put out fire more effectively; Forms radiant heat barrier (Crusting). Disadvantages: Leaves behind messy residue. Will cause damage to electronic equipment; Does not leave behind lasting inert atmosphere on surface. If ignition is expected, dry powder is not adequate; Toxic: May be detrimental to health. Suitable classes of fire for Dry Powder: Classes AB or BC (Class D is available as well, but rare). 6

7 e) Foam Extinguishing method: Removing oxygen source (Smothering); Removing heat source (Cooling). How it works: Special liquid agents mixed with air (sometimes a inert gas) to create foam concentrate; Ability to expand: In liquid form, it blankets fire and forms layer over burning material to smother fire; Vaporized vapor inhibits oxygen from feeding fire; Some foam mixtures can form vapor seal to blanket over burning material. Defined by their ability to expand: Advantages: Effective for fuel-related fires; When doused over fuel spills, fuel is rendered safe from combustion; Because it is in liquid and/or vapor form, it can be used to spray into small spaces where there is suspected fuel residues; In vapor form, it can be used to disperse fuel vapors and reduce oxygen levels via steam displacement. Disadvantages: Water based, so foams are excellent conductors of electricity and cannot be used for electrical fires; Due to its water based nature, foam is unstable and it can easily be broken down and dispersed. Large volumes required to put out fire; Easily diverted away from fire areas under strong winds. Suitable classes of fire for Dry Powder: Classes A and B fires. 7

8 v. How Fire Extinguishers Work Activating the fire extinguisher Gas Cartridge Type a) Pull the safety pin. This will unlock the lever; b) Aim nozzle at base of the fire and press the lever; c) When lever is depressed, actuating rod pushes down and activates the spring-mounted valve; d) End of actuating rod is a needle which activates the gas release valve connected to the gas cartridge; e) Gas is released from the cartridge and the suppressant/extinguishing agent is released from the fire extinguisher. Components of the Gas Cartridge Fire Extinguisher Activating the fire extinguisher Stored Pressure Type a) Similar in operation to gas cartridge type; b) Nozzle may be replaced by extended hose and horn type nozzle; c) Triggering the lever will siphon the suppressant through the syphon tube all the way to the horn to be expelled. 8

9 v Maintenance of Fire Extinguishers a) b) Mandated by law. Maintenance of fire extinguishers are focused on three basic elements: Mechanical parts; Extinguishing agent/suppressant; Means of Expulsion. Regular Maintenance (Usually once a year) will include the following check list: Location of the extinguisher at its designated location; Extinguisher is free from obstruction in terms of visibility and accessibility; Operating instructions visible, facing outward; Seal and tamper indicators are still in place; Weighing of extinguisher to ensure suppressant quantity is adequate; Check pressure gauge reading; Check external nozzle for blockage, body of extinguisher free from physical damage and corrosion. c) Under the following circumstances, increase in frequency of inspections should be considered: High frequency of fire hazards in the location; Extinguishers subjected to external damage or losses: Vandalism, theft, abuse due to impact from external forces, etc; Exposure to abnormal atmospheres or temperatures; Presence of physical obstructions; Condition of deteriorating fire extinguishers. e) Schedule for Recharging of Extinguishers: Extinguishers must be recharged after a stipulated time period or immediately after use. d) 9

10 f) Hydrostatic Testing of Extinguishers: To test strength of cylinders as well as detect any leakages in the cylinder. g) Record Keeping Purposes for Fire Extinguisher Maintenance Schedule Necessary to ensure that everything is in order. Maintenance records should include the following: Maintenance date and name of person/agency carrying out maintenance schedule; Date of last recharge and name of person/agency performing the recharge; Hydrostatic re-test day and name of person/agency performing the hydrostatic test; Date of next recharge. 10

11 5.3.2 Hose Reels i ii High pressure hose, connected to a constant water supply (e.g Booster pump system, localized plumbing water supply, etc); Consists of rubber hose and nozzle attached to drum; Drum may be mounted on wall, or portable type designed to be connected to water supply. Wall Mounted Hose Reel Portable Hose Reel iv. Wall Mounted Hose Reel Parts Inspection of Fire Hose Reels: Typically once a month or as per legal requirements; To ensure they are free from leakage, especially valves, nozzles and rubber hose reels; Nozzles should be able to function as per design: Typical nozzles can be tuned for jet streams or cone sprays; Check connecting booster pump systems (if any) for signs of malfunction or leakages; Testing of hose reel to ensure that it should be able to discharge water at a rate of 0.4 Liters/Second; Ensure accessibility of hose reels (not obstructed). 11

12 5.3.3 Dry Riser Mains i ii Used for medium height buildings (In Singapore, it is between 25m 60m). Main vertical pipe rising to upper levels of building for use by fire fighters to suppress fire. Pipes are dry. In the event of fire, water must be pumped into the system before it can be used. iv. Parts of a Dry Riser System: a) Breeching Inlet: Water is pumped into the breeching inlet from a water source, e.g Hydrant or fire truck; b) Riser Pipe: Main pipe directing water to the respective floors; c) Landing Valve: Each level of the building has one landing valve; In the event of fire, fire hose is attached to the landing valve to allow firemen to suppress fire; d) Air release valve: For releasing trapped air in water supply which may cause air lock and hamper fire fighting. 12

13 v. Maintenance: Visual Inspection; Hydrostatic Testing. a) Visual Inspection: b) Hydrostatic Testing Hydrostatic Testing: Changing Dry Riser System to 200 PSI 0r 13.8 bar via Breeching Inlet 13

14 5.3.4 Wet Rising Mains i ii iv. v. Used for high rise buildings (For Singapore, the definition is more than 60m); Similar in design to dry rising main, except that the piping is connected to a water supply system and supplied by a constant water main; Pipes are wet. In the event of fire, fire fighters can proceed to the location of fire and connect the hose reel directly to fight fire without the need to pump water from ground level; If water supply is insufficient or no water supply from the utility services, a breeching inlet for fire service is connected to the water tank for fire services to supply auxiliary water into the system. Maintenance: Visual Inspection of Wet Riser System; Flow test; Pressure test; Testing of Pumping Equipment; Checking of Water Supply and Storage. Pump room of Wet Riser System 14

15 a) b) Visual Inspection: Flow Test: Tested for sufficient flow under gravity and pump operations; Higher flow rates for commercial/non-residential buildings; Usually governed by Code of Practice. CP 29 (Singapore Code of Practice): c) Pressure Test: 15

16 d) Testing of Pumping Equipment e) Water Supply and Storage Fire Hydrants i ii Usually installed outside a building or at the ground floor of the building. Connected to a municipal/localized water source. Provides an instant water supply for fire fighters to plug into with a fire hose via coupling system and suppress fire instantaneously. Female coupling of Fire Hydrant Fire Hydrant Male coupling of fire hose 16

17 iv. How it works: a) Rigging up fire hose male coupling to hydrant s female coupling; b) Hydrant gate valve box chamber cover is removed; c) Using of hydrant key to turn on hydrant gate valve. Hydrant valve is used to turn on and off water but not to adjust water flow; d) Hose reel nozzle is used to control flow rate to suppress fire. v. Maintenance: a) Inspection should be carried out once a year by qualified persons; b) Check for: Any obstruction to fire hydrant (Remove, if any); Fire hydrant gate valve should be in open position at all times. If not, use the hydrant key to open valve; Check for adequate flow rate and pressure. Fire Hydrant key 17

18 5.4 Automatic Fire Fighting Systems Definition of Automatic Fire Fighting System: The ability of the system to control and suppress fire without human intervention. i Automatic fire fighting systems must have the ability to: Detect; Actuate extinguishing medium; Deliver extinguishing medium to suppress fire. ii Types of automatic fire fighting systems: Water sprinkler system; Water spray system; Foam system; Halon System; Carbon Dioxide System; Dry Chemical System Water Sprinkler System i Definition: Thermal Sensitive Devices; Designed to release water when predetermined temperature is reached. Advantages of Water Sprinkler System: Gives advanced warning or alert to fire; Provides early/first line of response to fire; Provides cooling (removal of heat) and reduces smoke at the scene of fire; Reduces potential damage to property in the event of fire; Reduces interruption to activities caused by uncontrolled fire; Causes less considerable damage compared to other manual water systems, such as fire hose reels. Fire Sprinkler 18

19 ii Types of Water Sprinkler Systems a) Wet Pipe Sprinkler System: How it Works: Water piping system is constantly filled with water; When surrounding temperature reaches a pre-determined temperature, sprinkler is activated and water bursts from sprinkler to put out fire. Used for: Used for normal conditions with no special requirements, e.g commercial offices, shopping centres, etc. Not suitable for premises which are undergoing extremely low temperatures, e.g freezers, as water in pipe may freeze and burst. 19

20 b) Dry Pipe Sprinkler Systems: How it Works: Sprinklers attached to pipeline filled with compressed air (Usually Nitrogen; When surrounding temperature reaches a pre-determined temperature, sprinkler is activated and air is released from the sprinkler; Sudden drop in pressure activates the dry pipe valve and releases water into the dry piping system; Used for: Extremely cold conditions, e.g in a chiller room, where water pipe systems are unsuitable due to the problem of freezing. Combined Dry Riser and Wet Riser Sprinkler System 20

21 c) Pre-Action Sprinkler System: Similar to the Dry Sprinkler System; Air fills up dry pipe system. May or may not be pressured air; Fire detection by fire detection system. How it Works: When fire is started, fire detection system first detects the fire; Water Control Valve is opened, water is released into dry pipe; Fire Alarm is triggered; Sprinkler does not open until fire reaches its predetermined temperature (higher than the one set for the fire detection system). Advantages: Can be used for extremely cold conditions due to the dry piping system used; Use for fire detection system, not sprinkler, to release water. Hence water is released faster than dry piping system; Because water is released faster, there is potentially less damage to property. Preaction Sprinkler System 21

22 d) Deluge Sprinkler System: Similar to Pre-action system, except that sprinklers are permanently open; In the event of fire, water is immediately released via control valve into the dry pipe and straight to the scene of fire via the open sprinklers; Used for high hazard areas, e.g fuel storage warehouses Water Spray System Definition: Fixed piped water system connected to a consistent water supply to provide fire protection with water via a series of nozzles over protected area; i Similar to sprinkler systems. May be used in tandem with sprinkler systems, but are generally not used to replaced sprinkler systems. ii Used for: Specialized protection for problematic areas, e.g fuel storage; Providing optimal fire protection and extinguishment. 22

23 5.4.3 Foam System Production of Foam: a) Proportioning Process: Correct mixture of foam agent, air and water; b) Foam Generation Phase: Generation of foam; c) Distribution Method: Distribution of foam for storage or fire fighting purposes. i Types of Foam Systems: a) Fixed Foam Systems; b) Semi-fixed Foam Systems. ii Fixed Foam Systems Complete installations; Used to protect fixed installations, e.g fuel dumps. Foam is discharged through fixed outlets should the system be activated. Activation of Fixed Foam System Schematic Drawing of Fixed Foam Systems 23

24 iv. Semi-Fixed Foam System How it Works: Similar to fixed foam system; Discharged foam outlet can be linked to mobile vehicle, usually a fire truck; Water supply from hydrant can be linked to fire truck; Foam and water is mixed to allow fire truck to discharge foam mixture on fire. Suitable for: Fuel storage facilities stored over a large area, so much so that fixed foam system installation is impractical. Linking up of fire truck to Semi-fixed Foam System Discharging of Foam from a Fire Truck Dry Powder System Consists of: Dry chemical Supply; Fixed Piping; Actuating mechanism. i Types of Systems: Total Flooding System; Local Application System. ii Total Flooding System: Localized Dry Powder System for Kitchen Entire protected area is covered; Only when protected area is totally enclosed and no re-ignition expected; Pre-determined amount of dry powder is released if system is actuated by fire. iv. Local Application System: Nozzle is directly pointed to fire localized protection only); Only when protected area is totally enclosed and no re-ignition expected; Pre-determined amount of dry powder is released if system is actuated by fire. 24

25 Total Flooding System using Dry Powder Halon System i Consist of: Halon supply (Usually in cylinders); Linked to existing fire alarm system; Halon Cylinders are connected via piping network to various locations designated for protection. Types of Systems: Total Flooding System; Local Application System. Release of Halon Gas via Halon System Halon cylinders stored in secured location 25

26 ii Total Flooding System Used to protect enclosed locations; Cannot be used in places with high human concentration due to toxicity; Halon 1301 used due to higher volatility and lower toxicity. iv. Localized Application System Used to protect enclosed locations over smaller area; Use of Halon 1211 for lower volatility. Total Flooding System FM 200 Usually seen as an alternative to Halon system: Lower toxicity; Not harmful to ozone layer; No harmful residues left behind; Suitable for use where there is sensitive equipment, e.g Server rooms. i How it works: When fire activates fire suppression panel, FM200 is released to the nozzle; Additional nitrogen from nitrogen cylinder is also released under high pressure to create supersaturated mixture for fire suppression. 26

27 5.4.7 CO2 System Total Flooding System Used to protect enclosed locations; Quantity of CO2 must be calculated based on volume of protected space and concentration of CO2 required to extinguish fire of combustible materials; i Localized Application System Used to protect enclosed locations over smaller area; Nozzle pointed directly at localized point of protected space. 5.5 Fire Detection and Alarm Systems i Definition: System designed to detect the presence of fire by monitoring environmental changes associated with combustion. When fire is detected: Fire Alarm is sounded to warn occupants of impending fire for evacuation purposes; Automatic fire suppression methods (E.g FM 200) is activated; Designated fire lifts homed to ground level for use by fire fighting teams; Location of fire source can be identified by system to guide in-house fire fighting team and subsequently the fire fighters; Firefighters from nearest fire fighting precinct can be activated. 27

28 5.5.1 Fire Alarm Components Fire Alarm Panel Central processing unit of the system. May be linked to sub panels at various floors at multiple storey buildings; Receives signal from manual call points and respective automatic detectors and relays it to output devices (Auxillary equipment, alarm, decam); Must have separate emergency power supply (Emergency Battery Operating Supply, or EBOPs) inside panel to provide E-power to alarm system in the event of power failure; Addressable systems: Provides information on: Origins of fire alarm; Which device has been activated; What type of signal is being transmitted. Non-Addressable Systems: Older type. Provides information only on the zone where the signal is being received. Fire Alarm Panel 28

29 i Automatic Detectors Primary Function: Detect environmental changes, e.g Smoke in the atmosphere, and send signal to fire panel; Usually mounted at ceiling surfaces or in air ducts; Activated by one or combination of the following conditions: Fire Detection can be classified as follows: Smoke Detector Spot detector: Detection of fire at one point; Line Detector: Detect fire along a continuous line of path. Types of Detectors: Heat Detectors; Smoke Detectors; Flame Detectors; Aspirating Detectors. a) Heat Detectors: Spot detectors; Comes in two prototypes: Fixed Temperature: Activates only when surrounding temperature reaches predetermined temperature; Rate of Rise: Activates when there is a sudden temperature flux (Not suitable for environments where temperature changes are frequent). Detector Types and their Respective Characteristics Heat Detector 29

30 b) Smoke Detectors Three main types: Light scattering; Light Obscuring; Ionization. Smoke Detector Suitable for confined areas where combustible materials produce small smoke particles are expected in the event of fire; Not suitable for locations where smoke is constant, e.g Basement Car Parks. 1. Light Scattering Smoke Detectors: Spot detectors; Operating principle: Dependent on detecting light scattered by smoke particles onto photocell. How Light Scattering Smoke Detector Works 2. Light Obscuring Smoke Detectors: Line Detector; Operating Principle: Light source projected to photocell; When smoke particles enter the smoke detector, light reaching photocell is interrupted; Signal is sent out from detector. Suitable for high ceiling areas, e.g Atriums. 3. Ionization Detectors: Spot Detectors; Operating Principle: Two electrodes charging air inside detector (+ve and ve charges); Current flow caused by charge; Smoke particles entering detector attracts electrodes, reducing current flow. Once current drops below acceptable alarm, signal is sent out from detector. 30

31 c) d) ii Flame Detectors Detects specific portions of flame: Visible and invisible light spectrums; Typically infra red and ultraviolet lights from the flame of the fire: 5 15 Hertz Hz lights are typically identified; Extremely sensitive, used only for high hazard areas, e.g aircraft hangars, petroleum storage facilities, etc; Infra Red Flame Detector Aspiring (Air Sampling) Detector Uses a pump to draw air into unit; Drawn air is sent to lab to test for combustion products. Fire Alarm Devices Two types: Audible Alarm Sounders; Visual Signaling Devices. To warn occupants of impending fire so as to allow for orderly evacuation of premises. a) Audible Alarm Sounders: Generate continuous tone of alarm bell; Should be min. 5 db (Decibels) over ambient noise (Standard ambient noise is 60dB); Should not exceed 120dB; All alarm bells in building should activate simultaneously, unless it is a multi-stage alarm system. b) Visual Signaling Devices: Used in facilities where ambient noise makes alarm sounders ineffective; Additional strobe lights/signaling devices used in conjunction with standard alarm sounders to reinforce announcement. Audible Alarm Sounder Visual Signaling Devices c/w Audible Alarm Sounders 31

32 iv. Manual Call Points Installed for use by occupants to sound emergency alarm should fire or an emergency be detected. Signal is sent to the fire alarm panel; Usually used as secondary back up to automatic detectors, or in locations where detectors are not installed; Manual call points should be free from obstruction. Types available: Break Glass Type: Activation by breaking the glass. This will trigger a switch which then sends signal to fire alarm panel. Glass panel must then be replaced to shut off signal; T-Bar Type: Activation by pulling down the Tbar. This action triggers a switch which then sends signal to fire alarm panel. Reactivation can be done using specialized key. Break Glass Manual Call Point T-Bar Manual Call Point Common Problems Associated with Fire Alarm Systems False Alarms Defined as the unintended activation of alarm devices when there is no actual fire. Inconvenience to building occupants, as well as creating a hazard. If actual fire occurs, occupants may take it for granted that it is another false alarm. Possible causes include: 32

33 i Loss of Effectiveness in Fire Alarm Systems When fire alarm panels lose effectiveness, they may not be able to warn occupants of fire; May be caused by: 5.6 Voice Communication Systems Voice communication systems (VCS) are installed in buildings which are designated to have a Fire Command Centre (FCC) by law. i The VCS is designed for the following functions: Allows for communication between occupants or fire fighting members at the scene of incident and the FCC. This allows fire fighters at the FCC to determine the extent of the emergency; Early communication allows for FCC team to strategize and plan for the best strategy to tackle emergency and deploy sufficient manpower to tackle emergency promptly; Broadcasting via speakers allows FCC team to evacuate occupants promptly once the incident is ascertained. ii Two types of VCS (VCS equipment should be firerated): One-way communication system; Two-way communication system. 33

34 a) 1-way Communication System: Basically a network of loudspeakers to provide a one-way communication from FCC to occupants; Speakers are typically located in major areas of access by occupants or members of publics, such as lifts, lift lobbies, staircases, as well as emergency locations such as escape staircases, places of refuge, etc. Consists of: Microphone at FCC; Selector switches allowing for FCC to switch off alarm when announcement is made; Amplifier: Sends signal to FCC indicator board with regards to which speakers have been activated; Loud speakers at various strategic locations for broadcasting purposes. Loudspeaker Microphone and Selector Switches in FCC b) 2-way Communication System: Basically a network of telephone sets to provide a one-way communication between FCC and occupants; Telephone set at FCC should be linked to all telephone sets for 2-way communications; Besides FCC, telephone sets should be placed at equipment laden areas, such as lift motor rooms, lifts, AHU rooms, etc, as well as places of refuge or other high risk locations. Consists of: Telephone sets at FCC; Selector switches allowing for FCC to switch of alarm when announcement is made; Amplifier: Sends signal to FCC indicator board once telephone is activated to indicate location of activation; Telephone sets at various strategic locations May be housed in secure lock boxes if vandalism is a problem. VCS Telephone Set 34

35 5.7 Smoke Control Systems Definition of Smoke: By-products of combustion in rising plume of hot air; Can be in gaseous or solid particles; Consist of burned and unburned portions of fuel, plus other chemical components released from combusted material. Why smoke is dangerous: Most deaths during fires are caused by smoke inhalation. Few people actually burn to death; Smoke reduces visibility, hence impeding escape; When designing fire installations, it should be assumed that all forms of smoke from fires are dangerous, and should be directed away safely from building in the event of a fire. Smoke Control within building proper is to achieve the following objectives: Keep smoke away from designated escape routes; Limit the spread of smoke throughout the building. Methods of Smoke Control: Pressurization (Containment of smoke); Venting (Removal of smoke); Smoke Curtain Pressurization i Pressurization of escape stairways/routes: To prevent smoke from entering escape route when access door is opened; Achieved by keeping the escape route area constantly pressurized by air; Activated by alarm system during fire. How it works: 35

36 ii Use of air-pressurized escape routes mandated by regulations: In Singapore, pressurization is provided for the following: Medium to high rise buildings (Exceeding 24m); Internal exit staircases with no other forms of natural ventilation; Basement staircases (More than 4 storeys). iv. Pressurization Level: v. Air Velocity: Maintain at 1.0 m/s when activated(escape doors opened or closed). v Equipment: Each ventilation system is complete with mechanical ventilation fan, ducting and other Mechanical ventilation accessories; Each ventilation system for each staircase, independent of one another Venting Venting: Direct, method of directing smoke to external environment. i Nature of smoke progression: Smoke tends to rise to the highest point within the building (Ceiling, atrium, etc); As smoke builds up, it gets lower and lower, eventually engulfing whole building and creating hazard for occupants to escape. ii Purpose of Venting: Give sufficient time for occupants to evacuate building; Give sufficient time for fire fighting team to locate fire and extinguish it without being obscured by smoke. Extract smoke to prevent dangerous build up of smoke within building premises. iv. Types of Venting: Natural ventilation; Mechanical Ventilation. Mechanical Smoke Control Fan 36

37 v. Technical Specifications for Vent Systems Venting via Natural Ventilation Venting via Mechanical Ventilation Smoke Curtains Use for large buildings, such as shopping complexes. i Purpose: To prevent smoke from spreading sideways. ii Designed to work with venting system: Creates smoke reservoir for smoke to be directed out of building via venting system. iv. Designed to be fire rated (Min. as good as the roof structure). Smoke Curtain in Shopping Complex Smoke Curtain being Manually Activated for Testing Purposes 37

38 5.7.4 Fire Dampers Fire dampers: Passive fire protection device installed inside HVAC and ACMV ducts to prevent smoke from spreading inside duct works; i Fire damper must be fire rated (Usually similar to the surrounding wall which its ducting penetrates). ii How it Works: When fire occurs, thermal element melts (e the fusible link), dropping the fire rated door in the damper; Another design would be to connect the damper to the fire alarm to trigger the fire damper, instead of the thermal element. When the door drops, smoke is prevented from spreading. How the fire damper works 5.8 Fire Lifts i In the event of fires, designated fire lifts are designed to function the following roles, even if the main power supply is cut: Ensure that the internal lift lighting and ventilation systems are working via Emergency Battery-Operated Supply (EBOPs); The lift is able to function, so that it can still transport passengers and at the same time home in to ground floor for use by fire fighters. This is achieved using generator and/or battery power; In the event the building has no generator supply (For buildings which are lower than 60m), the lift is actually homed to the nearest floor. This is achieved by a separate battery operated system known as Automatic Rescue Device (ARD). Firemen can manually activate and control lifts via firemen switch (These are usually locked to avoid vandalism, with firemen or authorized crew with the keys to manually control the fire lifts). 38

39 5.8 Emergency & Exit Lights i ii iv. v. Emergency lighting: Placed in strategic locations to direct occupants to the nearest exits in the event of an emergency by providing luminance, particularly when normal lighting has failed due to power failure. Exit signs help to provide instructions to the nearest exit, while other emergency lights help to provide luminance for evacuation purposes. During normal operations, emergency lights are connected to the emergency switch board or, in the case of ARD, normal switchboard power supply; During a power failure, these emergency lights have their own battery packs to last a prescribed duration until power resumes, and/or to give ample time for occupants to evacuate building. Exit and emergency lights are designed such that even in a smoke-filled environment, they can still be highly visible. 39

40 Illustration showing Exit Lighting and Emergency Lighting Placements in a building proper 40

41 Tutorial Questions: 1) i ii iv. 2) i ii iv. v. Basics of Fire Science: Define fire, and identify the by products of fire (4 marks). With the aid of a diagram, indicate the basic elements of fire (4 marks). Identify the classes of fire and indicate the types of fire which these classes denote. Give 1 example for each class of fire (8 marks). Explain the methods whereby fire can be extinguished (4 marks). Dry and Wet Riser Mains are used by fire fighting teams to fight fires in multistorey buildings. Indicate the height prescription for the installation of dry and wet riser mains(2 marks). Indicate the key difference between a wet riser system and a dry riser system (2 marks). Describe the components of a dry riser main system and explain how it can be used by fire fighting teams in the event of an emergency (8 marks). Describe how hydrostatic testing is carried out on the dry riser system and state the criteria for compliance (4 marks). Describe how the wet riser system can be used by fire fighting teams in the even of an emergency (4 marks). 3) i ii The fire alarm system is an integral feature in many buildings. Sketch/draw a simple schematic diagram of the fire alarm system (7 marks). Briefly explain the how the fire alarm system works (5 marks); Explain why false fire alarms can be detrimental to occupants in the building, and list down the possible causes of false fire alarms (8 marks). 4) i ii iv. v. In the event of a fire, smoke is considered to be the most dangerous killer. Briefly describe the nature of smoke and its contents (3 marks). List down the ways smoke can kill in the event of a fire (2 marks). List down the objectives of smoke control techniques (2 marks). List down three methods of smoke control (3 marks). Discuss the use of fire dampers in air ducting systems, including the requirement(s) of fire dampers and how it works (10 marks). 41