SBE2113-SIE3013 Chapter 3.pdf

Chapter 3 Fire Precautions in Buildings Singapore Institute of Technology Dr. An Hui DID: 6592 2074 E-mail: [email protected] Fire Enginee...

Chapter 3 Fire Precautions in Buildings Singapore Institute of Technology Dr. An Hui DID: 6592 2074 E-mail: [email protected] Fire Engineering Fundamentals Chapter 3  SIT Internal LEARNING OUTCOMES At the end of this lesson, you will be able to: 1. Explain the components of fire dynamics 2. Explain the importance and definition of fire resistance 3. Explain the factors affecting the fire severity in building fires Fire Engineering Fundamentals Chapter 3 2  SIT Internal CHAPTER OUTLINE 1. Passive and Active Fire Protection 2. Stages of Compartment Fire Development 3. Heat Release Rate of Fuels in Free and Enclosure Burning 4. Fire Resisting Compartmentation 5. Fire Severity in Building Fires 6. Classification of Building into Purpose Groups Fire Engineering Fundamentals Chapter 3 3  SIT Internal 1. PASSIVE AND ACTIVE FIRE PROTECTION Fire Protection o Include both Passive and Active control measures Passive Active Passive fire protection (PFP) is Active fire protection (AFP) is an integral component of the an integral part of fire components of structural fire protection. protection and fire safety in a It is characterized by items building. and/or systems, which require a PFP attempts to contain fires or certain amount of motion and slow the spread, through use of response in order to actively fire-resistant walls, floors, put out or slow the fire doors, and other examples Fire Engineering Fundamentals Chapter 3 4  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT Fire Development in a Compartment Ceiling jet Hot smoke layer Hot gases out Plume Entrained air Cool lower layer Outdoor air in Fire Fire Engineering Fundamentals Chapter 3 5  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT Typical Development of a Compartment Fire Flashover Heat release rate Fully Developed Decay Growth Incipient Time 1) Incipient 3) Fully Developed 2) Growth 4) Decay Fire Engineering Fundamentals Chapter 3 6  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.1 Incipient Stage ▪ Ignition – 3 elements of fire triangle ▪ Flames are small and aren’t widespread ▪ Occupants can safely escape and the fire could be safely extinguished with portable extinguisher or small hoseline ▪ Transition from incipient to growth can occur quite quickly Fire Engineering Fundamentals Chapter 3 7  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.2 Growth Stage ▪ Fire grows and begins to influence environment within compartment ▪ Thermal layering – Tendency of gases to form into layers according to temperature ▪ The burning rate is primarily influenced by the fuel properties and orientation (Fuel controlled) ▪ The growth rate is typically modelled with a t2 rate of growth ▪ Smoke may be visible from the exterior Fire Engineering Fundamentals Chapter 3 8  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.2 Growth Stage Positive Pressure Neutral Plane Negative Pressure Fire Engineering Fundamentals Chapter 3 9  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.2.1 Growth Stage - Flashover ▪ Flashover – rapid transition of fire growth to a fully developed compartment fire Everything in the compartment ignites at once Gas temperatures near ceiling level: 500-600 ˚C Radiation heat flux at floor level: 15-20 kW/m2 500-600 ˚C 15-20 kW/m2 Fire Engineering Fundamentals Chapter 3 10  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.2.1 Growth Stage - Flashover Flashover Demonstration Source: https://www.youtube.com/watch?v=BtMmymOxdjc&t=3s Fire Engineering Fundamentals Chapter 3 11  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.3 Fully Developed Stage ▪ All combustible materials in compartment are burning ▪ Energy release is at its greatest, and is generally limited by the availability of oxygen (Ventilation controlled) ▪ Average gas temperature: 700 -1200 ˚C Fire Engineering Fundamentals Chapter 3 12  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.4 Decay Stage ▪ Fire will decay as fuel is consumed or if oxygen concentration falls to point (below 16%) where flaming combustion can no longer be supported ▪ The heat release rate reduces, and thus the average gas temperature in the compartment declines ▪ Fire Decay due to reduced oxygen concentration can follow much different path if ventilation profile of compartment changes – Backdraft Fire Engineering Fundamentals Chapter 3 13  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.4 Decay Stage - Backdraft ▪ Explosion that occurs when oxygen is suddenly admitted to a confined area that is very hot & filled with combustible vapors (a) (b) (c) Fire Engineering Fundamentals Chapter 3 14  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.5.1 Ventilation Controlled Burning ▪ The speed of fire development is limited by the availability of atmospheric oxygen provided ▪ In typical compartments, most fully developed fires are ventilation controlled ▪ Any increase in the supply of oxygen to the fire will result in an increase in heat release rate Fire Engineering Fundamentals Chapter 3 15  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.5.1 Ventilation Controlled Burning Flames burns as Smoke and hot gases : Fuel if outdoors cannot burn freely and generates large amounts smoke Flames obscured by smoke Ventilation air controls burning rate Fuel Fire Engineering Fundamentals Chapter 3 16  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.5.2 Fuel Controlled Burning ▪ In fuel controlled burning, there is excess air supply for complete combustion of the fuel ▪ The rate of burning is predominantly limited by the fuel availability and characteristics ▪ The rate of burning will be similar to the fuel item burning in open air, with enhancement from radiant feedback from the hot upper layer of gases and hot wall surfaces ▪ Most fire become fuel controlled in the growth and decay stages Fire Engineering Fundamentals Chapter 3 17  SIT Internal 2. STAGES OF COMPARTMENT FIRE DEVELOPMENT 2.5.2 Fuel Controlled Burning Heat Release Rate Less Ventilation = Lower Heat Release Ventilation Controlled Fuel Fuel Controlled Controlled Time Fire Engineering Fundamentals Chapter 3 18  SIT Internal 3. HEAT RELEASE RATE OF FUELS IN FREE AND ENCLOSURE BURNING 3.1 Free Burning o Free burning indicates that the items are burning in the open space without any effects of the enclosure in which the fire takes place o Hot gases are vented away from the fuel and there is no limitation on air supply to the fuel Air Entrainment Fire Engineering Fundamentals Chapter 3 19  SIT Internal 3. HEAT RELEASE RATE OF FUELS IN FREE AND ENCLOSURE BURNING 3.2 Enclosure Burning o Fuel burns inside an enclosure, and the hot gases will collect at the ceiling level and heat the ceiling and the walls. o The enclosure vents such as the windows, doors and leakage areas may restrict the availability of oxygen needed for combustion. Ceiling Air Entrainment Fire Engineering Fundamentals Chapter 3 20  SIT Internal 3. HEAT RELEASE RATE OF FUELS IN FREE AND ENCLOSURE BURNING 3.3 Mass Loss Rate Comparisons m (kg/s) Enclosure burning Free burning Time (s) Fire Engineering Fundamentals Chapter 3 21  SIT Internal 3. HEAT RELEASE RATE OF FUELS IN FREE AND ENCLOSURE BURNING 3.4 Heat Release Rate Comparisons Q (MW) Enclosure burning Free burning Time (s) Fire Engineering Fundamentals Chapter 3 22  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.1 Fire Resisting Compartment ▪ A fire resisting compartment is defined as an area of a building, which is totally separated from the remainder of the building by continuous fire resisting construction ▪ The continuous fire resisting construction serves to form a complete barrier to heat and smoke from the fire Containment of Flames, Heat and Smoke Isolation of Flames, Heat and Smoke Fire Engineering Fundamentals Chapter 3 23  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.1 Fire Resisting Compartment ▪ Internal Fire Spread between Rooms and Floors due to: Through Air Ducts Through Vertical Through Ceiling and Shafts Collapsed Partitions Origin of Fire Through Non-Fire Rated Doors Fire Engineering Fundamentals Chapter 3 24  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.1 Fire Resisting Compartment ▪ External Fire Spread due to: Convection Currents Ignition of Materials Ignition of Materials Ignition of Materials Ignition of Materials Origin of Fire Fire Engineering Fundamentals Chapter 3 25  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.2 SCDF Provisions on Structure Fire Precautions o Compartmentation requirements on: 1. Compartment walls 10. Spray painting room 2. Compartment floors 11. Hotel 3. Atrium design 12. Dormitory 4. HDB multistory car park (MSCP) 13. Store room 5. Basement car park 14. Unprotected openings in external 6. Separation of purpose groups wall 7. Fire command center (FCC) 15. Separation between buildings 8. Kitchen 16. Protected shaft 9. Cinema 17. Protected staircase See SIE3014 Chapter 2 Structure Fire Precaution Fire Engineering Fundamentals Chapter 3 26  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.3 Openings through Fire Resisting Compartment o A fire resisting compartment wall or floor should not have any openings except for the following ▪ Fire Resisting Doors ▪ Fire Protected Shafts, Pipes and Ducts Fire Engineering Fundamentals Chapter 3 27  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.3.1 Fire Resisting Doors ▪ A fire resisting door must have the same fire resistance as the fire resisting compartment wall ▪ Fire resisting doors must be self closing Fire Engineering Fundamentals Chapter 3 28  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.3.2 Fire Protected Shafts, Pipes and Ducts ▪ Fire protected shafts, pipes and ducts must have the same fire resistance as the fire resisting compartment wall which they pass through ▪ Fire protected shafts, pipes and ducts are treated with fire resistant materials such as ceramic boards and vermiculite in achieving the required fire resistance ▪ The edges of the shaft, pipe or duct must be fire stopped to resist the passage of fire Fire Engineering Fundamentals Chapter 3 29  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.3.2 Fire Protected Shafts, Pipes and Ducts Air flow Air duct treated with fire resisting Fire stopping material to same rating as wall Automatic around all duct- Door closer wall interface Fire resisting door with same resistance as compartment wall Fire resisting walls, floor and ceiling Fire Engineering Fundamentals Chapter 3 30  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.3.3 Fire Stopping ▪ To ensure the integrity of the fire resisting compartment, every opening through its walls, floor and ceiling must be fire stopped to prevent the passage of flames, heat and smoke from a fire Fire stopping using pipe o Cement mortar non-combustible o Gypsum based plaster materials o Mineral wool Compartment floor Fire Engineering Fundamentals Chapter 3 31  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.3.4 Fire Dampers ▪ The air distribution duct system must be installed with fire dampers when it passes through a fire resisting compartment wall or floor ▪ A fire damper is an automatic shutter which closes automatically to prevent the passage of flames, heat and smoke when a fire occurs ▪ It is normally held open by a fusible link which will melt at the required temperature Fire Engineering Fundamentals Chapter 3 32  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.3.4 Fire Dampers Typical multi-blade fire damper Fire damper in open position Fire damper in close position Fire Engineering Fundamentals Chapter 3 33  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.3.4 Fire Dampers Example of motorized fire smoke damper Fire Engineering Fundamentals Chapter 3 34  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.4 Fire Resistance of Elements of Building Structure 4.4.1 Fire Resistance Elements o Walls o Doors o Floors o Columns o Beams Fire Engineering Fundamentals Chapter 3 35  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.4.2 Fire Resistance Definition o The fire resistance of an element of structure refers to its ability to satisfy the three criteria of stability, integrity and insulation and still perform its required function over a period of time STRUCTURE STABILITY INTEGRITY INSULATION The ability to maintain The ability to resist the The ability to ensure it does adequate load bearing passage of flames and hot not allow excessive rise of capacity as gases temperature on the determined unexposed side by the code Fire Engineering Fundamentals Chapter 3 36  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.4.2 Fire Resistance Definition Stability, Integrity and Insulation Integrity : No smoke Stability : Load- passes through wall or bearing wall does not floor above fail Insulation : Materials stored on other side of wall are not affected by heat transferred through wall Fire Engineering Fundamentals Chapter 3 37  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.4.3 Criteria of Fire Resistance for Various Elements of Structure Fire Engineering Fundamentals Chapter 3 38  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.4.4 Fire Resistance Rating o A fire resistance rating is the measurement of fire resistance assigned to an element of building structure on the basis of a test o Fire resistance ratings are assigned in terms of whole numbers of hours or parts of hours o The Fire Code specifies minimum fire resistance ratings for elements of structures for different types of building occupancies and space usage Fire Engineering Fundamentals Chapter 3 39  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.4.4 Fire Resistance Rating Table 3.1 Fire Resistance of Elements of Structure for Different Occupancies Fire Engineering Fundamentals Chapter 3 40  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.4.4 Fire Resistance Rating Table 3.1 Fire Resistance of Elements of Structure for Different Occupancies Fire Engineering Fundamentals Chapter 3 41  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.4.5 Fire Resistance Test o Specimens of each element of building structure are tested in a furnace fire following a standard temperature-time curve Fire Engineering Fundamentals Chapter 3 42  SIT Internal 4. FIRE RESISTING COMPARTMENTATION 4.4.5 Fire Resistance Test Table 3.2 Three failure criteria for fire resistance testing Failure Criteria Conditions An element of structure must perform its load Stability bearing function and carry applied loads for the duration of the test, without structural collapse The test specimen must not develop any cracks Integrity or holes which allow smoke or hot gases to pass through the assembly The temperature increasement on the cold side of the test specimen must not exceed a specified Insulation value, usually an average increase of 140 ˚C and a maximum of 180 ˚C at a single point Fire Engineering Fundamentals Chapter 3 43  SIT Internal 5. FIRE SEVERITY IN BUILDING FIRES 5.1 Fire Severity o In building fires, fire severity is considered as the condition of a fire which is related to ▪ The maximum temperature achieve, and ▪ The duration when the maximum temperature persists Fire Engineering Fundamentals Chapter 3 44  SIT Internal 5. FIRE SEVERITY IN BUILDING FIRES 5.2 Factors Affecting Fire Severity o Combustible Contents in the Compartment ▪ Nature of Fuel ▪ Fire Load Density ▪ Arrangement of Fuel o Design of the Compartment ▪ Size and Height of Window ▪ Size, Depth and Height of Compartment ▪ Thermal Insulation of Walls and Ceiling Fire Engineering Fundamentals Chapter 3 45  SIT Internal 5. FIRE SEVERITY IN BUILDING FIRES 5.2.1 Nature of Fuel ▪ Nature and composition of combustible materials found in buildings vary according to the type of occupancy ▪ To limit fire severity, materials with low heat release rates and high ignition temperatures must be used Fire Engineering Fundamentals Chapter 3 46  SIT Internal 5. FIRE SEVERITY IN BUILDING FIRES 5.2.2 Fire Load Density ▪ Fire load density - amount of combustible materials present in building per unit floor area ▪ A low fire load density limits severity of a fire Fire Load Density Description (kg/m2 of wood equivalent) Flats, apartments 25 Schools, hospitals 25 Office 25 to 50 Factory Up to 150 Cinemas, restaurants 25 to 50 Warehouses Up to 500 Fire Engineering Fundamentals Chapter 3 47  SIT Internal 5. FIRE SEVERITY IN BUILDING FIRES 5.2.3 Arrangement of Fuel ▪ Fire spread rapidly if combustible materials are closely packed ▪ If combustible items are tall, flames reach the ceiling quickly and fire will spread to other items by the radiant heat from the ceiling. ▪ Ratio of the surface area to mass of the material. A high ratio means rapid combustion. ▪ Combustible materials have to be uniformly distributed in large blocks with minimum area exposed to air Fire Engineering Fundamentals Chapter 3 48  SIT Internal 5. FIRE SEVERITY IN BUILDING FIRES 5.2.4 Size and Height of Window ▪ Amount of ventilation air available for combustion in a compartment: QA H (m3 /s) where: A = area of window opening, m2 H = height of window, m ▪ A window with a big area and height will allow in more air for combustion Fire Engineering Fundamentals Chapter 3 49  SIT Internal 5. FIRE SEVERITY IN BUILDING FIRES 5.2.5 Size, Depth and Height of Compartment ▪ Larger compartment area implies greater amount of combustible materials available for burning ▪ Deeper compartment means higher fire temperature because cooling air flowing in and out of the window is unable to affect all the burning materials. ▪ Flames reaches ceiling faster for low ceilings compartments, fire spread to other parts of the compartment. ▪ Tall compartment better than low compartment, but taller compartment has greater volume of smoke generated. ▪ For less fire severity, small volume shallow and moderate height compartment Fire Engineering Fundamentals Chapter 3 50  SIT Internal 5. FIRE SEVERITY IN BUILDING FIRES Conditions to Minimize Fire Severity Nature of Low burning Rate and Fuel Ignition Fuel Amount of As low as Maximum Rate of Fuel possible Temp Burning Reached of Fuel In large blocks Arrangement Keep minimum of Fuel Fire Air area exposed to air Severity Supply Size and Minimum Size Duration Shape of As shallow as Duration of Fuel Room possible at High Temp Burning Window Area Maximum area Loss of and Shape Heat Thermal Insulation As low as possible of Walls & cladding Fire Engineering Fundamentals Chapter 3 51  SIT Internal 6. CLASSIFICATION OF BUILDING INTO PURPOSE GROUPS 6.1 Classification of Buildings into Purpose Groups o Since there are different types of fire hazards and hence fire severity, buildings are classified into different purpose groups o This allows the risk elements to be segregated so that the correct fire protection measures can be provided for each purpose group of buildings Fire Engineering Fundamentals Chapter 3 52  SIT Internal 6. CLASSIFICATION OF BUILDING INTO PURPOSE GROUPS 6.1 Classification of Buildings into Purpose Groups ❑ PG I Small Residential (eg. bungalow, detached house, semi-detached house, terrace house) ❑ PG II Other Residential (residential other than PG I) ❑ PG III Institution ❑ PG IV Office ❑ PG V Shop ❑ PG VI Factory ❑ PG VII Places of public resort ❑ PG VIII Storage Fire Engineering Fundamentals Chapter 3 53  SIT Internal 7 RECAP 1. What are differences between passive and active fire protection systems and give some examples? 2. Describe the typical stages of the fire development. 3. Describe rollover and flashover phenomena. 4. Fuel controlled burning VS ventilation-controlled burning. 5. What is backdraft? 6. Describe the general requirements on fire doors. 7. Describe the general requirements using graphical illustration when Fire Protected Shafts, Pipes and Ducts penetrate the fire resisting compartment wall or floor 8. What are the three (3) failure criteria for fire resistance testing? Fire Engineering Fundamentals Chapter 3 54