FIRE PROOF CONSTRUCTION
INTRODUCTION
Fire safety may be deemed to cover the following aspectsFire prevention and reduction of number of outbreaks of fireSpread of fire, both internally and externallySafe exit of any and all occupants in the event of an out-break of fireFire extinguishing apparatusFIRES ARE CAUSED BY
Careless discarding of lighted ends of cigarettes, cigars, matches and tobaccoSmoking in unauthorized placesIndifferent maintenance of machinery including overloading and under or over lubricating of bearingsGeneral indifference to cleanlinessIncorrect storage of materialsFaulty workmanship and inattention of electrical installationsUn-approved equipment and layoutCarelessness of persons concerned with inspectionInattention of fire safety regulationsTYPES OF FIRE HAZARDS
Possibility of damage or life - Personal hazards
Possibility of fire occurring and spreading inside the building itself - Internal hazard
Possibility of fire spreading from an adjoining building or buildings or from across a street or road - Exposure hazard
FIRE LOAD
Fire load is the amount of heat in Kilocalories (k cal) which is liberated per square metre of floor area of any compartment by the combustion of the contents of the building and any combustible part of the building itself. This amount of heat is used as the basis of grading of occupancies
For example, if a section of a building having an area of 80 sq. metre has 1200 kg of combustible material having a calorific value of 4000 kcal/kg
Fire load = 1200 x 4000/80 = 60000 kcal/m2
FIRE LOAD
Indian standard (IS : 1641 1960) grades the fire loads into the following three classes:
ClassificationFire loadType of buildingsLow fire loadNot exceeding 275000 kcal/m2Domestic buildings, hotels and officesModerate fire loadExceeding 275000 kcal/m2 but not exceeding550000 kcal/m2Trading establishments and factoriesHigh fire loadExceeds 550000 kcal/m2 but does not exceed 1100000 kcal/m2GodownsGRADING OF STRUCTURAL ELEMENTS
Structural elements of buildings are graded, for fire resistance, by the time for which they resist a standard fire of given time
Grade No.Time-in-hoursFire load and class of fire which the structural element can withstandFire load in kcal/m2Class of Fire161100000 and overVery high24500000 - 1100000High32275000 - 500000Medium41Less than 275000Low50.5-Very lowGRADING OF BUILDINGS
TypeAll components haveType 1 construction4 hrs fire resistanceType 1 construction3 hrs fire resistanceType 1 construction2 hrs fire resistanceType 1 construction1 hrs fire resistanceCHARACTERISTICS OF FIRE RESISTING MATERIALS
The material should not disintegrate under the effect of great heatThe expansion of the material due to heat should not be such that it leads to instability of the structure of which it forms a partThe contraction of the material due to sudden cooling with water (during fire exinguition process) after it has been heated to a high temperature should not be rapidFIRE RESISTANCE PROPERTIES OF COMMON BUILDING MATERIALS
Non-combustible materials
Are those which if decomposed by heat will do so with absorption of heat (i.e. endothermically)Do not contribute to the growth or spread of fireBut are damaged or decomposed when high temperature are reachedStones and brick, concrete, clay products, metal, glassFIRE RESISTANCE PROPERTIES OF COMMON BUILDING MATERIALS
Combustible materials
Are those which, during fire, combine exothermically with oxygen, resulting in evolution of lot of heat and giving rise to flame or glowSuch material burn and also contribute to growth or spread of fireWood and wood products, fibre board, staw boardFIRE RESISTANCE PROPERTIES OF COMMON BUILDING MATERIALS
Stone
Non-combustible materialBad conductor of heatDoes not contribute to fireDisintegrate when heated and suddenly cooledGranite- severe heat disintegrate and explodeLime stone-worst performance- crumble under ordinary fireSand stone can withstand moderate fire without serious crackIn general use of stone in a fire-resisting construction should be restricted to a minimumFIRE RESISTANCE PROPERTIES OF COMMON BUILDING MATERIALS
Bricks
Poor conductor of heat Can stand exposure of fire for a considerable time upto a temperature of 1200 oCBrick masonry construction with good mortar and better workmanship, is the most suitable for safeguarding the structure against fire hazardsFIRE RESISTANCE PROPERTIES OF COMMON BUILDING MATERIALS
The behaviour of concrete during exposure to fire varies withThe nature of course aggregate and its densityThe quality of cementThe position of steel in the concreteAggregate expand on heatingConcrete shrink on heatingThese two opposite actions may lead to spalling of concrete surfacePorous aggregate has less tendency to crackFor fire resistance more cover for fire resistanceIn general concrete offer much higher fire resistance than any other building materialsRCC structures can withstand fire lasting for several hours with a temperature of 1000 deg C without serious damageFIRE RESISTANCE PROPERTIES OF COMMON BUILDING MATERIALS
Steel
Very low fire resistanceModulus of elasticity reducesLooses its tensile strength rapidlyYeild stress at 600 deg C is about half at normal temperatureSteel beam sags and column bucklesProtect steel members with some covering insulating materials like Brick concrete etcFIRE RESISTANCE PROPERTIES OF COMMON BUILDING MATERIALS
TimberTimber is a combustible materialIgnites and get rapidly destroyed during fireIf timber is used in thick section, it possesses the properties of self-insulation and slow burningDuring exposure to fire, timber surface gets charred, the charred portion act as a protective coating to the inner portionIf temperature are higher than 500 deg C timber gets dehydrated under continued exposure, giving rise to combustible volatile gases which readily catch fireFIRE RESISTANCE PROPERTIES OF COMMON BUILDING MATERIALS
Timber
Timber is made fire resistant by
Using thicker sectionReducing number of corners and reducing surface areaCoating timber structure with chemical like ammoniumphosphate and sulphate, borax and boric acid, zinc chloride
Painting timber surface with asbestos paintsOil paints should not be used as these paints catch fireFIRE RESISTANCE PROPERTIES OF COMMON BUILDING MATERIALS
Cast-iron and wrought iron
Rarely used in fire resistance constructionOn cooling sudden contraction , breaks in to piecesFailure is suddenCover it by brick or concrete for higher resistanceAsbestos cement good fire resistance property
Aluminium poor fire resistance
FIRE RESISTANCE PROPERTIES OF COMMON BUILDING MATERIALS
GlassPoor conductor of heatThermal expansion is lessWhen suddenly cooled cracks are formedCracks minimised by steel reinforcing- reinforced glass is more fire resistantAnd therefore used in fire-resisting doors, windows etcFIRE RESISTANCE PROPERTIES OF COMMON BUILDING MATERIALS
Plaster or mortarPlaster is non-combustibleUsed as a protective coating against fire riskCement plaster is better than lime plasterLime plaster is likely to be calcined during fireReinforced with metal mesh for more fire resistanceGENERAL FIRE SAFETY REQUIREMENTS FOR BUILDINGS
Electrical and/or mechanical lifts may not always reliable during fireBuildings having more than one storey shall be provided with safe fire proof exits and escapesExits shall be so placed that they are always immediately accessible and of having capacity to take all persons of that floorEscape routes shall be well-ventilated as persons using the escapes are likely to be facing smoke problems during fireFire proof doors and the building components should be of grade as per the codeEasily operable doors and windowsStairways/ lifts should be fire resistant constructionGENERAL FIRE SAFETY REQUIREMENTS FOR BUILDINGS
Construction of false ceiling should be given special attention to prevent total or early collapse in the event of fireIt is essential that fire resistance of the basement shall conform to the highest order and all columns for supporting the upper structures shall have a grading not less than laid down in grade 1 to 3Unobstructed smoke extracts, distributed locations, location should be easily identifiable from inside and out side of the building, easily breakable cover for smoke extracts, properly isolated from adjacent rooms by fire proof construction materials are must for basement floors for smoke extractionFIRE PROOF CONSRUCTION : WALLS AND COLUMNS
Made of thicker section so that they can withstand the fire for longer timeThey can also act as barrier against spread of fire to adjoining areasFor walls bricks are preferred than stonesFor framed construction RCC should be preferred than steelSteel if used should be encased with concrete or bricksThicker cover for reinforcementsPartition wall should be of fire resistant material, concrete hollow blocks, bricks, reinforced glass, asbestos sheets, metal wire mesh with plaster coveringCavity wall construction has better fire resistanceFIRE PROOF CONSRUCTION : FLOORS AND ROOFS
Flat roof (RCC) is preferable than pitched /sloping roofFor pitched roof, truss in RCC or encased in fire proofing materialsFloors concrete floor or steel floor encased in concrete is betterTimber beams is of thicker sections without sharp cornersFalse ceiling is of fire resistant materials like asbestos cement sheetsFIRE PROOF CONSRUCTION : WALL OPENINGS AND FIRE ESCAPES
Minimum opening to reduce fire spread but considering the escapes alsoEscapes should be properly fire protectedReinforced glass are better for glazingsTiber doors thickness of the shutters and frame should be increasedFire escapes specificationsFIRE ALARMS
Manual and automatic
FIRE EXTINGUISHING EQUIPMENTS
Manual
As soon as the fire startsNot useful once the fire has spreadPortable carbon dioxide typeFoam generation typeBuckets of water and sand installed at convenient locationsAutomatic sprinklers
Network of pipes 20 mm dia fixed to the ceiling of the roomsSpacing 3 m centre to centreHeat actuated sprinkler heads with fusible plug are fixed to these pipes at regular intervalsFuse melts, water rushes out and fire brought under control in a short periodFire hydrants
Water pressure 3.5 to 4 kg/cm2
Based on density of population and importance to the area
One hydrant per 4000 to 10 000 m2
Post hydrant or sunk/flush hydrant
FIRE EXTINGUISHING EQUIPMENTS
FIRE EXTINGUISHING EQUIPMENTS
Wet riser system
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