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 apparatus

FIRES 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 regulations

TYPES 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/m2Godowns

GRADING 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 low

GRADING OF BUILDINGS

TypeAll components haveType 1 construction4 hrs fire resistanceType 1 construction3 hrs fire resistanceType 1 construction2 hrs fire resistanceType 1 construction1 hrs fire resistance

CHARACTERISTICS 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 rapid

FIRE 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, glass

FIRE 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 board

FIRE 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 minimum

FIRE 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 hazards

FIRE 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 damage

FIRE 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 etc

FIRE 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 fire

FIRE 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 ammonium

phosphate and sulphate, borax and boric acid, zinc chloride

Painting timber surface with asbestos paintsOil paints should not be used as these paints catch fire

FIRE 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 resistance

Asbestos 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 etc

FIRE 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 resistance

GENERAL 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 construction

GENERAL 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 extraction

FIRE 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 resistance

FIRE 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 sheets

FIRE 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 specifications

FIRE 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 locations

Automatic 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 period

Fire 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