Cyclone & Fire

7/30/2019 Cyclone & Fire

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Cyclone and Fire

CHIRAG SHARMA

[email protected]


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What are Cyclones?

"Cyclone" is an intense whirl in the atmospherewith very strong winds circulating around it inanti-clockwise direction in the NorthernHemisphere and in clockwise direction in theSouthern Hemisphere.

Word "Cyclone" is derived from the Greek, word"Cyclos" meaning the coils of a snake.

To Henri Peddington, the tropical storms in theBay of Bengal and in the Arabian Sea appearedlike the coiled serpents of the sea and he named

these storms as "Cyclones". known as Hurricane in the Atlantic and Eastem

Pacific, Typhoon in Western Pacific, Willy-Williesin Australian sea, Baguis in the Philippines.


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Cyclones are intense low pressure areas -from the centre of which pressureincreases outwards- The amount of the

pressure drop in the centre and the rate atwhich it increases outwards gives theintensity of the cyclones and the strengthof winds.


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Criteria followed to classify cyclones

As adopted byMeteorologicalDepartment of India

S.No. Disturbance Wind Speed (Knots)

1. Low Less than 17.

2. Depression 17-27(32-50 km/h)

3. Deep Depression 28-33 (51-62 km/h)4. Cyclonic storm 34-47 (63-88 km/h)

5.Severe cyclonic storm with

a core of Hurricane

winds

48-63-(89-118 km/h)

1 knot - 1.85 km per hour


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Once the cyclones reach higher latitudes they often changetheir direction and move north and then north-east (southand south east hemisphere). The process is known asrecurreature.

Before it recurves, the speed decreases and the system

remains stationary for a day or so. When two cyclones existnear to each other, they inter-act

and move anti-clockwise with respect to each other.

In the Atlantic, tracks often execute a parabola.

In India, when cyclones recur they get broken up over the

Himalayas and their further eastward movement ceases.

Mechanism of cyclones


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Naming of cyclone Cyclones derive their names through a systematic procedure laid

down by the World Meteorological Organisation (WMO) and theUnited Nations Economic and Social Commission for Asia and thePacific (ESCAP).

naming of cyclones began in September 2004

Eight north Indian Ocean countries - Bangladesh, India, theMaldives, Myanmar, Oman, Pakistan, Sri Lanka and Thailand -have prepared a list of 64 names.

Since 2004, the eight countries have faced 20 cyclones.

The countries take turns in naming the cyclones. The last sixwere: Nargis (Pakistan), Rashmi (Sri Lanka), Khai-Muk (Thailand),Nisha (Bangladesh), Bijli (India) and Aila (Maldives).


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Cyclone Map of India


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The principal dangers of a cyclone

Gales and strong winds damage installations, dwellings, communication

systems, trees., etc. resulting in loss of life andproperty.

Torrential rain may cause river floods

Storm surges or high tidal waves A storm surge is an abnormal rise of sea level near

the coast caused by a severe tropical cyclone

as a result, sea water inundates low lying areas ofcoastal regions drowning human beings and live-stock, eroding beaches and embankments, destroyingvegetation and reducing soil fertility.


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What is Storm Surge?


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How high will the Storm Surge be?

Every cyclone that affects the coast produces a stormsurge. But not all storm surges rise to dangerous levels.The height of the surge depends on: The intensity of the cyclone - as the winds increase, the sea

water is piled higher and the waves on top of the surge aretaller.

The forward speed of the cyclone - the faster the cyclonecrosses the coast, the more quickly the surge builds up andthe more powerfully it strikes.

The angle at which the cyclone crosses the coast - local zonesof enhanced surge in areas such as narrow inlets and bays.

The shape of the sea floor - the surge builds up more stronglyif the slope of the sea bed at the coast is shallow.

Past history indicates that loss of life is significant whensurge magnitude is 3 metres or more and catastrophicwhen 5 metres and above


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Surge prone coasts of India Vulnerability to storm surges is not uniform along Indian

coasts.

east coast of India are most vulnerable to high surges

i) North Orissa, and West Bengal coasts.

ii) Andhra Pradesh coast between Ongole and Machilipatnam.

iii) Tamil Nadu coast, south of Nagapatnam.

The West coast of India is less vulnerable to storm surges i) Maharashtra coast, north of Harnai and adjoining south

Gujarat coast and the coastal belt around theGulf of Bombay.

ii) The coastal belt around the Gulf of Kutch.


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Cyclone Accounts The oldest and the worst cyclone on record is that of

October 1737: hit Calcutta and took a toll of 3,00,000lives in the deltaic region. It was accompanied by a 12metre high surge.

Midnapore Cyclone of October 1942 was accompanied by

gale wind speed of 225 kmph Rameswaram Cyclone of 17th to 24th December 1964

wiped out Dhanuskodi in Rameswaran Island from themap. A passenger train which left Rameswaram Roadstation near about the midnight of 22nd was washed offby the storm surges sometimes later, nearly allpassengers traveling in the train meeting water graves.


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Bangla Desh Cyclone of 8-13 November 1970which crossed Bangla Desh coast in the night of12th was one of the worst in recent times, withstorm surges of 4 to 5 metres height at the

time of high tides, and with 25 cm of rain in theareas, the inundation took toll of about3,00,000 people.

Andhra Cyclone of 14-20 November 1977 thatcrossed coast near Nizampatnam in the evening

of 19th, took a toll of about 10,000 lives.

Cyclone Accounts


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How to avoid the catastrophe?

Effective Cyclone Disaster Preventionand Mitigation Plan requires: A Cyclone Forecast - and Warning Service.

Rapid dissemination of warnings to theGovernment Agencies, Marine interests like thePorts, Fisheries and Shipping and to GeneralPublic.

Organisations to construct Cyclone Shelters in

the cyclone-prone areas and ready machineryfor evacuation of people to safer areas.

Community preparedness at all levels to meetthe exigencies.


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Cyclone warning

"Two Stage Warning Scheme

The first stage warning known as the "Cyclone Alert" isissued 48 hours in advance of the expectedcommencement of the adverse weather over the coastal

areas. The second stage warning known as the "Cyclone

Warning" is issued 24 hours in advance.

Both cyclone "Alert" and "Warning" messages arepassed to the AIR stations for repeated broadcast.


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Vulnerable Communities vulnerability of a human settlement to a cyclone is

determined by its siting, the probability that a cyclone willoccur, and the degree to which its structures can bedamaged by it.

most vulnerable to cyclones are

Light weight structures with wood frames, especially olderbuildings where wood has deteriorated and weakened thewalls

Houses made of unreinforced or poorly-constructed concreteblock

Buildings in low- lying coastal areas or river floodplains

Furthermore, the degree of exposure of land and buildings willaffect the velocity of the cyclone wind at ground level,

Certain settlement patterns may create a "funnel effect" thatincreases the wind speed between buildings, leading to evengreater damage.


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How High Winds Damage Buildings

Contrary to popular belief, few houses are blown over.Instead, they are pulled apart by winds moving swiftlyaround and over the building. This lowers the pressure onthe outside and creates suction on the walls and roof,effectively causing the equivalent of an explosion.

Whether or not a building will be able to resist the effects ofwind is dependent not so much upon the materials that areused but the manner in which they are used.

common belief: that heavier buildings, such as those madeof concrete block, are safer.

Truth: well-built and properly-engineered masonry houseoffers a better margin of safety than other types ofbuildings


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Catastrophic Failures

Foundations The uplift forces from

cyclone winds cansometimes pull buildingscompletely out of theground.

In contrast to designingfor gravity loads, thelighter the building thelarger (or heavier) thefoundation needs to be incycloneresistant

design.


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Steel Frames

A common misconception: the loss of cladding relievesthe loads from building frameworks.

Truth: the wind loads on the structural frame increases

substantially with the loss of cladding Usual weakness in steel frames is in the connections.

Thus economising on minor items (bolts) has led to theoverall failure of the major items (columns, beams andrafters)



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Masonry Houses

usually regarded as being safe in cyclones.

There are countless examples where the loss

of roofs has triggered the total destruction ofun-reinforced masonry walls.



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Timber Houses

The key to safe construction of timber housesis the connection details.

The inherent vulnerability of light-weighttimber houses coupled with poor connectionsis a dangerous combination which has oftenled to disaster.



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Reinforced Concrete Frames

The design of reinforced concrete frames isusually controlled by the seismic hazard.

If seismic design is not done, wind analysismust be performed

ignoring this, can lead to disaster.



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Component Failures

Roof Sheeting

This is perhaps thecommonest area offailure in cyclones.

The causes are usually

inadequate fasteningdevices, inadequatesheet thickness andinsufficient frequenciesof fasteners in theknown areas of greaterwind suction.


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Roof Tiles

These were thought to have low vulnerabilityin storms but past cyclones have exposed theproblem of unsatisfactory installation practices.



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Rafters

Of particular interest inrecent cyclones was thelongitudinal splitting ofrafters with the tophalves disappearing andleaving the bottom halvesin place.

The splitting wouldpropagate from holesdrilled horizontallythrough the rafters to

receive holding-downstraps.



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Windows and Doors

After roof sheeting, these are the components mostfrequently damaged in cyclones.

Of course, glass would always be vulnerable to flying

objects. The other area of vulnerability for windows and doors is

the hardware latches, bolts and hinges.

Walls

Cantilevered parapets are most at risk.

But so far walls braced by ring beams and columns haveremained safe.



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Damaging Effects of Cyclone on

Houses

Due to thehigh windpressure and

improperconnection ofthe house tothe footings it

can be blownaway.

D i Eff f C l


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Roofing

materials notanchoredcan be blownaway


Houses

D i Eff f C l


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Lightweightverandah

roofs aremoresusceptibleto damage

due tohigh windspeed.


Houses

D i Eff t f C l


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When cyclonesare accompaniedwith heavy rainfor a long

duration, thebuildings can bedamaged due toflooding also.


Houses


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Design Wind Speed and Pressures

The basic wind speed is reduced or enchanced fordesign of buildings and structures due tofollowing factors:

The risk level of the structure measured in terms of

adopted return period and life ofstructures. Terrain roughness determined by the surrounding

buildings or trees and, height and size of the structure.

Local topography like hills, valleys, cliffs, or ridges, etc.


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On which elements the wind pressure

effect must be considered?

It is considered on various elementsdepends on Aerodynamics of flow around buildings.

The windward vertical faces being subjected topressure.

The leeward and lateral faces getting suctioneffects and

The sloping roofs getting pressures or suctioneffects depending on the slope.


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typical effects of openings in the walls

Wind generatingopening on thewindward side during a

cyclone will increasethe pressure on theinternal surfaces

may be sufficient to

cause the roof to blowoff and the walls toexplode.


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Windward face of the building

collapses under pressure of windforce



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During a cyclone an opening may suddenly occuron the windward side of the house.

The internal pressure which builds up as a resultmay be relieved by providing a correspondingopening on the leeward side.



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If the building is not securely tied to its

foundations, and the walls cannot resistpush/pull forces, the house tends to collapsestarting from the roof with the building leaning

in the direction of the wind.


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Failure of the Wall: Wind forces on the walls ofthe house may produce failure. Wind striking abuilding produces pressure which pushes againstthe building, on the windward side, and suction

which pulls the building on the leeward side andthe roof.


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Overturning is another problem for lightstructures. This occurs when the weight of the house is insufficient

to resist the tendency the house to be blown over.

Wh h i i f h


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When choosing a site for your house,

consider the following Though cyclonic storms always approach from the direction of the sea

towards the coast, the wind velocity and direction relative to a buildingremain random due to the rotating motion of the high velocity winds.

In non-cyclonic region where the predominant strong wind direction is wellestablished, the area behind a mound or a hillock should be preferred

Similarly a row of trees planted upwind will act as a shield. The influence of such a shield will be over a limited distance, only for 8

10 times the height of the trees. A tree broken close to the house may damage the house also hence

distance of tree from the house may be kept 1.5 times the height of thetree.

When choosing a site for your


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No shielding from high wind due toabsence of barriers

Shielding from high wind bypermeable barriers such as strongtrees


house, consider the following



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In hilly regions,

construction along ridges should be avoidedsince they experience an increase of windvelocity

whereas valley experiences lower speeds ingeneral





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In cyclonic regions close to the coast, a site above the likelyinundation level should be chosen. In case of nonavailability of high level natural ground, construction shouldbe done on stilts with no masonry or cross bracings up tomaximum surge level, or on raised earthen mounds toavoid flooding/inundation but knee bracing may be used.




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Shape of the House

Shape is the most important single factor in determiningthe performance of buildings in cyclones.

Simple, compact, symmetrical shapes are best.

The square plan is better than the rectangle since it allowshigh winds to go around them.

The rectangle is better than the L-shaped plan. This is not to say that all buildings must be square. But it is

to say that one must be aware of the implications of designdecisions and take appropriate action to counter negativefeatures.

The best shape to resist high winds is a square.


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If other shapes are desired, efforts should be made to strengthen thecorners.

If longer shapes are used, they must be designed to withstand the forces of

the wind.

Most houses are rectangular and the best layout is when the length is not

more than three (3) times the width.

Shape of the House


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In case of construction of group ofbuildings, a cluster arrangement can befollowed in preference to row type.


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Roofs

Lightweight flat roofs are easily blown offin high winds.

In order to lessen the effect of the

uplifting forces on the roof, the roof Pitchshould not be less than 22.

Hip roofs are best


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General Design Considerations Avoid a low pitched roof, use a hip roof or a

high pitched gable roof.

Avoid overhanging roofs. If overhangs or

canopies are desired, they should be braced byties held to the main structures.

Avoid openings which cannot be securelyclosed during a cyclone

Roofs


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Overhangs, verandahs

Avoid large overhangs as high wind forcebuild up under them.

Overhangs should not be more than 18inches at verges or eaves.

Build verandah and patio roofs as

separate structures rather than extensionsof the main building.


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Securing the Ridge

If the rafters are not secure, the ridge can fall apart when

strong wind passes over the roof.


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The ridge can be secured by using:-

COLLAR TIES - Timbers connecting the rafters.Nail them to the side of the rafters

Securing the Ridge


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GUSSETS - Usually made ofsteel/plywood. This is used at the ridge.

Securing the Ridge


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METAL STRAPS over the top of the rafters

Securing the Ridge

Securing the corrugated galvanized


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Securing the corrugated galvanized

sheets

The sheets are gauged by numbers. TheHigher the number the thinner thematerial. Example 24 gauge galvanizedsheet is superior to 28 gauge.

Failure in roofs If the sheeting is too thin or there are too few

fittings, the nails or screws may tear throughthe sheet.

If galvanized sheets are used, 24 gauge isrecommended.

Securing the corrugated


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How to secure sheeting to the roofstructure, use

Fixings every two (2) corrugation at ridges,eaves and overhangs.

Fixings every three (3) corrugation. Maximumspacing at all other locations

Securing the corrugated

galvanized sheets


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Fixings for sheetings

Screws Use proper drive crews for corrugated galvanized roof

sheets. Be sure that the screws go into the purlins at least fifty

(50) mm.

use large washers under the screw heads to prevent theroof sheets from tearing

Nails Nails do not hold as well as screws. Use nails with wide heads and long enough to bend over

below the lath. Galvanized coated nails are better than ordinary wire

nails.


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Roof cladding

As the corners and the roof edges are zones of higher localwind suctions and the connections of cladding/sheeting tothe truss need to be designed for the increased forces.

following precautions are recommended:- Sheeted roofs:- A reduced spacing of bolts, of that

admissible as per IS:800, recommended. For normal connections, J bolts may be used but for cyclone

resistant connections U bolts are recommended.


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Alternatively, strap may be used at leastalong edges to fix cladding with thepurlins to avoid punching through the

sheet.


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Clay tile roofs:- Because of lower deadweight, these may be unable to resist theuplifting force and thus experience heavy

damage, particularly during cyclones. Anchoring of roof tiles in R.C. strap beams is

recommended for improved cyclone resistance.

As alternative to the bands, a cement mortar

screed, reinforced with galvanized chickenmesh, may be laid over the high suction areasof the tiled roof.


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Foundations

The foundation is the part of the housewhich transfers the weight of the buildingto the ground. It is essential to construct asuitable foundation for a house as the

stability of a building depends primarily onits foundation.

It is desirable that information about soiltype be obtained and estimates of safe

bearing capacity

Parameters need to be properly accounted


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Parameters need to be properly accounted

in the design of foundation

Effect of surge or flooding:- Invariably a cyclonic storm is accompanied by torrential rain

and tidal surge (in coastal areas) resulting into flooding of thelow lying areas.

Flooding causes saturation of soil and thus significantly affectsthe safe bearing capacity of the soil.

In flood prone areas, the safe bearing capacity should betaken as half of that for the dry ground. Also the likelihood of any scour due to receding tidal surge

needs to be taken into account while deciding on the depth offoundation

Buildings on stilts:- Where a building is constructed on stilts it is necessary that

stilts are properly braced in both the principal directions. Knee bracings will be preferable to full diagonal bracing so as

not to obstruct the passage of floating debris during stormsurge.


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main types of foundation

Slab or Raft Foundation

Used on soft soils.

Spread the weight over a wider area


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Strip Foundation

Used for areas where the soil varies.

Most common.

Supports a wall.



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Stepped Foundation

Used on sloping ground.

Is a form of strip foundation.



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Pile Foundation

deep foundations for small or large buildings.

Under reamed piles often used in expansiveclay or alluvial soils.



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Masonry walls


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Strengthening of walls against highwind/cyclones.

Reinforce the walls by means of reinforcedconcrete bands and vertical reinforcing bars asfor earthquake resistance.

Masonry walls


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Wall Openings

general areas of weakness and stressconcentration, but needed essentially for lightand ventilation.

The following are recommended in respect of

openings. Openings in load bearing walls should not be within adistance of h/6 from inner corner for the purpose ofproviding lateral support to cross walls, where h is thestorey height upto eave level.

Openings just below roof level be avoided

Since the failure of any door or window on the wind-ward side may lead to adverse uplift pressures underroof, the openings should have strong holdfasts as wellas closing/locking arrangement.


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Wall Openings


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Glass Panes

Glass windows and doors are, of course, veryvulnerable to flying objects

Use thicker glass panes.

reduce the panel size to smaller dimensions.

Also glass panes can be strengthened by pastingthin film or paper strips


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CYCLONES - Do's & Dont's

Before the Cyclone season: Check the house; secure loose tiles, carry out repair

works for doors and windows

Remove dead woods or dying trees close to the house;anchor removable objects like lumber piles, loose tin

sheds, loose bricks, garbage cans, sign-boards etc.which can fly in strong winds

Keep some wooden boards ready so that glass windowscan be boarded if needed

Demolish condemned buildings

Keep some dry non-perishable food always ready foremergency use


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When the Cyclone starts Listen to the radio about weather warnings Pass on the information to others. Believe in the official

information Remember that a cyclone alert means that the danger is within 24

hours. Stay alert.

If your house is securely built on high ground take shelter in thesafer part of the house. However, if asked to evacuate do nothesitate to leave the place.

Provide strong suitable support for outside doors. Keep torches handy Be sure that a window and door can be opened only on the side

opposite to the one facing the wind. If the centre of the cyclone is passing directly over your house

there will be a lull in the wind and rain lasting for half and hour orso. During this time do not go out; because immediately after thatvery strong winds will blow from the opposite direction.

Switch off electrical mains in your house. Remain calm



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When Evacuation is instructed Pack essentials for yourself and your family to last you a

few days, including medicines, special foods for babiesand children or elders.

Head for the proper shelter or evacuation points

indicated for your area. Do not worry about your property

At the shelter follow instructions of the person in charge.

Remain in the shelter until you have been informed toleave



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Post-cyclone measures You should remain in the shelter until informed

that you can return to your home.

Strictly avoid any loose and dangling wiresfrom the lamp posts.

Clear debris from your premises immediately.

Report the correct loss to appropriateauthorities



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Fire


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Elements of fire protection

Include use of non-combustible building materials,

use of fire-resistive building assemblies,

installation of automatic detection devices andsprinklers,

development of improved fire fightingtechniques


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Fire-resistive construction

A building construction in which thestructural members (including walls,partitions, columns, floors, and roof) areofnoncombustible materials having fire-endurance ratings at least equal to thosespecified by the appropriate authorities
http://www.answers.com/topic/noncombustible-3http://www.answers.com/topic/noncombustible-3


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fire-resistive ratings

"fire resistance rating" is a legal term utilized bymodel codes to regulate building construction.

The fire-resistive ratings of various materials andconstructions are established by laboratory tests

Specified in terms of hours a material orassembly can be expected to withstand exposureto fire.

For exterior walls, floors, and roof of masonry or

fire-resistive material with a fire-resistance ratingof at least 2 hours.


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Fireproofing of Construction Materials

In construction, heavy wood timbers have arelatively high fire resistance, because fire tendsto burn very slowly inward from the surface,leaving enough sound timber in the center toprevent collapse.

Wood framing can also be impregnated withammonium phosphate solution or covered withspecial mastics.

To be classed as fire resistive, buildings must be

made of reinforced concrete or protected steelthat will stand considerable fire with minordamage;

While steel retains its strength up to a very hightemperature, it fails rapidly at temperatures over

1,000F (540C).


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Structural steel may be protected in a number of ways. It can befaced with brick, concrete, or tile; however, construction withthese materials usually adds too much weight to a building.

A protective layer of concrete over all surfaces of a beam or overthe steel bars in reinforced concrete has to be at least 2.5 in. (6.4cm) thick to be effective;

hollow clay tile used to cover beams and girders has to be at least

4 in. (10 cm) thick. most buildings use lightweight fireproofing such as gypsum,

perlite, and vermiculite mixed in plaster; one inch (2.5 cm) ofsuch materials will absorb an equivalent amount of heat as 2.5 in.(6.4 cm) of concrete.

Some recent buildings circulate water inside each column,protecting the structure against meltdown.

In urban areas, buildings must also provide protection against firein neighboring buildings through fireproof exterior walls-preferablywindowless, since windows are fire openings.

Fireproofing of Construction Materials


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How to Build a Fire Resistant House

Frame your home with metal studs. Metal studscannot combust in the same way that wood studscan.

Install GFI (ground fault circuit interrupters) outletsand circuit breakers.. It can, in just 1/30 of a second,trip the internal circuit, effectively cutting off theflow of electricity in the event of a possible short.

Use as much concrete as possible in the structure ofyour home.

Use hard materials for flooring, doors and roofing.Carpet is highly combustible.

Install safety features. Fire alarms


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