everthing about cyclones + fire

Cyclone and Fire

Shushant TyagiStudent

Gurukul the school

What are Cyclones? "Cyclone" is an intense whirl in the atmosphere

with very strong winds circulating around it in anti-clockwise direction in the Northern Hemisphere and in clockwise direction in the Southern Hemisphere.

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

To Henri Peddington, the tropical storms in the Bay of Bengal and in the Arabian Sea appeared like 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-Willies in Australian sea, Baguis in the Philippines.

Cyclones are intense low pressure areas - from the centre of which pressure increases outwards- The amount of the pressure drop in the centre and the rate at which it increases outwards gives the intensity of the cyclones and the strength of winds.

Criteria followed to classify cyclones As adopted by

Meteorological Department 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

Mechanism of cyclones

A full-grown cyclone is a violent whirl in the atmosphere 150 to 1000 km across, 10 to 15 km high.

The central calm region of the storm is called the "Eye". The diameter of the eye varies between 30 and 50 km and is a region free of clouds and has light winds.

Around this calm and clear eye, there is the "Wall Cloud Region" of the storm about 5O km in extent, where the gale winds, thick clouds with torrential rain, thunder and lightning prevail.

Away from the "Wall Cloud Region", the wind speed gradually decreases.

The gales give rise to a confused sea with waves as high as 20 metres, swells that travel a thousand miles. Torrential rains, occasional thunder and lightning flashes - join these

Through these churned chaotic sea and atmosphere, the cyclone moves 300 to 500 km, in a day to hit or skirt along a coast, bringing with it strome surges


Once the cyclones reach higher latitudes they often change their direction and move north and then north-east (south and south east hemisphere). The process is known as recurreature.

Before it recurves, the speed decreases and the system remains stationary for a day or so.

When two cyclones exist near 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.


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

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

naming of cyclones began in September 2004

Eight north Indian Ocean countries - Bangladesh, India, the Maldives, 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 six were: Nargis (Pakistan), Rashmi (Sri Lanka), Khai-Muk (Thailand), Nisha (Bangladesh), Bijli (India) and Aila (Maldives).

Cyclone Map of India

The principal dangers of a cyclone Gales and strong winds

damage installations, dwellings, communication systems, trees., etc. resulting in loss of life and property.

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 of

coastal regions drowning human beings and live- stock, eroding beaches and embankments, destroying vegetation and reducing soil fertility.

What is Storm Surge?

How high will the Storm Surge be?

Every cyclone that affects the coast produces a storm surge. 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 are taller.

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

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

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

Past history indicates that loss of life is significant when surge magnitude is 3 metres or more and catastrophic when 5 metres and above

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 the Gulf of Bombay.

ii) The coastal belt around the Gulf of Kutch.

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

October 1737: hit Calcutta and took a toll of 3,00,000 lives in the deltaic region. It was accompanied by a 12 metre 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 the map. A passenger train which left Rameswaram Road station near about the midnight of 22nd was washed off by the storm surges sometimes later, nearly all passengers traveling in the train meeting water graves.

Bangla Desh Cyclone of 8-13 November 1970 which crossed Bangla Desh coast in the night of 12th was one of the worst in recent times, with storm surges of 4 to 5 metres height at the time of high tides, and with 25 cm of rain in the areas, the inundation took toll of about 3,00,000 people.

Andhra Cyclone of 14-20 November 1977 that crossed coast near Nizampatnam in the evening of 19th, took a toll of about 10,000 lives.

Cyclone Accounts

How to avoid the catastrophe? Effective Cyclone Disaster Prevention

and Mitigation Plan requires: A Cyclone Forecast - and Warning Service. Rapid dissemination of warnings to the

Government Agencies, Marine interests like the Ports, Fisheries and Shipping and to General Public.

Organisations to construct Cyclone Shelters in the cyclone-prone areas and ready machinery for evacuation of people to safer areas.

Community preparedness at all levels to meet the exigencies.

Cyclone warning "Two Stage Warning Scheme“

The first stage warning known as the "Cyclone Alert" is issued 48 hours in advance of the expected commencement 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 are passed to the AIR stations for repeated broadcast.

Vulnerable Communities vulnerability of a human settlement to a cyclone is

determined by its siting, the probability that a cyclone will occur, and the degree to which its structures can be damaged by it.

most vulnerable to cyclones are Light weight structures with wood frames, especially older

buildings where wood has deteriorated and weakened the walls

Houses made of unreinforced or poorly-constructed concrete block

Buildings in low- lying coastal areas or river floodplains Furthermore, the degree of exposure of land and buildings will

affect the velocity of the cyclone wind at ground level, Certain settlement patterns may create a "funnel effect" that

increases the wind speed between buildings, leading to even greater damage.

How High Winds Damage Buildings Contrary to popular belief, few houses are blown over.

Instead, they are pulled apart by winds moving swiftly around and over the building. This lowers the pressure on the 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 of wind is dependent not so much upon the materials that are used but the manner in which they are used.

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

Truth: well-built and properly-engineered masonry house offers a better margin of safety than other types of buildings

Catastrophic Failures Foundations

The uplift forces from cyclone winds can sometimes pull buildings completely out of the ground.

In contrast to designing for gravity loads, the lighter the building the larger (or heavier) the foundation needs to be in cyclone resistant design.

Steel Frames A common misconception: the loss of cladding relieves

the 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 the overall failure of the major items (columns, beams and rafters)

Catastrophic Failures

Masonry Houses usually regarded as being safe in cyclones. There are countless examples where the loss

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


Timber Houses The key to safe construction of timber houses

is the connection details. The inherent vulnerability of light-weight

timber houses coupled with poor connections is a dangerous combination which has often led to disaster.


Reinforced Concrete Frames The design of reinforced concrete frames is

usually controlled by the seismic hazard. If seismic design is not done, wind analysis

must be performed ignoring this, can lead to disaster.


Component Failures Roof Sheeting

This is perhaps the commonest area of failure in cyclones.

The causes are usually inadequate fastening devices, inadequate sheet thickness and insufficient frequencies of fasteners in the known areas of greater wind suction.

Roof Tiles These were thought to have low vulnerability in

storms but past cyclones have exposed the problem of unsatisfactory installation practices.


Rafters Of particular interest in

recent cyclones was the longitudinal splitting of rafters with the top halves disappearing and leaving the bottom halves in place.

The splitting would propagate from holes drilled horizontally through the rafters to receive holding-down straps.


Windows and Doors After roof sheeting, these are the components most

frequently 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 have

remained safe.


Damaging Effects of Cyclone on Houses Due to the

high wind pressure and improper connection of the house to the footings it can be blown away.

Roofing materials not anchored can be blown away

Damaging Effects of Cyclone on Houses

Light weight verandah roofs are more susceptible to damage due to high wind speed.


When cyclones are accompanied with heavy rain for a long duration, the buildings can be damaged due to flooding also.


Design Wind Speed and Pressures The basic wind speed is reduced or enchanced for

design of buildings and structures due to following factors: The risk level of the structure measured in terms of

adopted return period and life of structures. 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.

On which elements the wind pressure effect must be considered?

It is considered on various elements depends on Aerodynamics of flow around buildings. The windward vertical faces being subjected to

pressure. The leeward and lateral faces getting suction

effects and The sloping roofs getting pressures or suction

effects depending on the slope.

typical effects of openings in the walls Wind generating

opening on the windward side during a cyclone will increase the pressure on the internal surfaces

may be sufficient to cause the roof to blow off and the walls to explode.

Windward face of the building collapses under pressure of wind force

typical effects of openings in the walls

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

The internal pressure which builds up as a result may be relieved by providing a corresponding opening on the leeward side.

typical effects of openings in the walls

If the building is not securely tied to its foundations, and the walls cannot resist

push/pull forces, the house tends to collapse starting from the roof with the building leaning in the direction of the wind.

Failure of the Wall: Wind forces on the walls of the house may produce failure. Wind striking a building produces pressure which pushes against the building, on the windward side, and suction which pulls the building on the leeward side and the roof.

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

to resist the tendency the house to be blown over.

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 building remain random due to the rotating motion of the high velocity winds.

In non-cyclonic region where the predominant strong wind direction is well established, 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 the tree.

No shielding from high wind due to absence of barriers

Shielding from high wind by permeable barriers such as strong trees


In hilly regions, construction along ridges should be avoided

since they experience an increase of wind velocity

whereas valley experiences lower speeds in general


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


Shape of the House Shape is the most important single factor in determining

the performance of buildings in cyclones. Simple, compact, symmetrical shapes are best. The square plan is better than the rectangle since it allows

high 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 design decisions and take appropriate action to counter negative features.

The best shape to resist high winds is a square.

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

In case of construction of group of buildings, a cluster arrangement can be followed in preference to row type.

Roofs Lightweight flat roofs are easily blown off

in high winds. In order to lessen the effect of the uplifting

forces on the roof, the roof Pitch should not be less than 22º.

Hip roofs are best

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 by ties held to the main structures.

Avoid openings which cannot be securely closed during a cyclone

Roofs

Overhangs, verandahs

Avoid large overhangs as high wind force build up under them.

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

Build verandah and patio roofs as separate structures rather than extensions of the main building.

Securing the Ridge

If the rafters are not secure, the ridge can fall apart when strong wind passes over the roof.

The ridge can be secured by using:- COLLAR TIES - Timbers connecting the rafters.

Nail them to the side of the rafters

Securing the Ridge

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

Securing the Ridge

METAL STRAPS over the top of the rafters

Securing the Ridge

Securing the corrugated galvanized sheets The sheets are gauged by numbers. The

Higher the number the thinner the material. Example 24 gauge galvanized sheet 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 through the sheet.

If galvanized sheets are used, 24 gauge is recommended.

How to secure sheeting to the roof structure, use Fixings every two (2) corrugation at ridges,

eaves and overhangs. Fixings every three (3) corrugation. Maximum

spacing at all other locations

Securing the corrugated galvanized sheets

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 the roof 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.

Roof cladding As the corners and the roof edges are zones of higher local

wind suctions and the connections of cladding/sheeting to the truss need to be designed for the increased forces.

following precautions are recommended:- Sheeted roofs:- A reduced spacing of bolts, ¾ 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.

Alternatively, strap may be used at least along edges to fix cladding with the purlins to avoid punching through the sheet.

Clay tile roofs:- Because of lower dead weight, these may be unable to resist the uplifting 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 chicken mesh, may be laid over the high suction areas of the tiled roof.

Foundations The foundation is the part of the house

which transfers the weight of the building to the ground. It is essential to construct a suitable foundation for a house as the stability of a building depends primarily on its foundation.

It is desirable that information about soil type be obtained and estimates of safe bearing capacity

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 the low lying areas.

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

In flood prone areas, the safe bearing capacity should be taken 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 of foundation

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 storm surge.

main types of foundation Slab or Raft Foundation

Used on soft soils. Spread the weight over a wider area

Strip Foundation Used for areas where the soil varies. Most common. Supports a wall.

main types of foundation

Stepped Foundation Used on sloping ground. Is a form of strip foundation.


Pile Foundation deep foundations for small or large buildings. Under reamed piles often used in expansive

clay or alluvial soils.


Masonry walls

Strengthening of walls against high wind/cyclones. Reinforce the walls by means of reinforced

concrete bands and vertical reinforcing bars as for earthquake resistance.

Masonry walls

Wall Openings general areas of weakness and stress

concentration, but needed essentially for light and ventilation.

The following are recommended in respect of openings. Openings in load bearing walls should not be within a

distance of h/6 from inner corner for the purpose of providing lateral support to cross walls, where ‘h’ is the storey 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 under roof, the openings should have strong holdfasts as well as closing/locking arrangement.

Wall Openings

Glass Panes Glass windows and doors are, of course, very

vulnerable to flying objects Use thicker glass panes. reduce the panel size to smaller dimensions. Also glass panes can be strengthened by pasting

thin film or paper strips

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 windows can be boarded if needed

Demolish condemned buildings Keep some dry non-perishable food always ready for

emergency use

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 the

safer part of the house. However, if asked to evacuate do not hesitate 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 or so. During this time do not go out; because immediately after that very strong winds will blow from the opposite direction.

Switch off electrical mains in your house. Remain calm

CYCLONES - Do's & Dont's

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

few days, including medicines, special foods for babies and 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 to

leave


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

that you can return to your home. Strictly avoid any loose and dangling wires

from the lamp posts. Clear debris from your premises immediately. Report the correct loss to appropriate

authorities


Fire

Elements of fire protection Include

use of non-combustible building materials, use of fire-resistive building assemblies, installation of automatic detection devices and

sprinklers, development of improved fire fighting

techniques

Fire-resistive construction A building construction in which the

structural members (including walls, partitions, columns, floors, and roof) are of noncombustible materials having fire-endurance ratings at least equal to those specified by the appropriate authorities

fire-resistive ratings "fire resistance rating" is a legal term utilized by

model codes to regulate building construction. The fire-resistive ratings of various materials and

constructions are established by laboratory tests Specified in terms of hours a material or

assembly can be expected to withstand exposure to fire.

For exterior walls, floors, and roof of masonry or fire-resistive material with a fire-resistance rating of at least 2 hours.

Fire-Resistive Assemblies An assembly is a combination of materials

put together in a specific way that achieves the fire resistance rating required in the building code.

For example, gypsum wallboard applied to a steel stud.

Fire-resistance ratings apply only to assemblies in their entirety.

Fireproofing of Construction Materials In construction, heavy wood timbers have a

relatively high fire resistance, because fire tends to burn very slowly inward from the surface, leaving enough sound timber in the center to prevent collapse.

Wood framing can also be impregnated with ammonium phosphate solution or covered with special mastics.

To be classed as fire resistive, buildings must be made of reinforced concrete or protected steel that will stand considerable fire with minor damage;

While steel retains its strength up to a very high temperature, it fails rapidly at temperatures over 1,000°F (540°C).

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

A protective layer of concrete over all surfaces of a beam or over the steel bars in reinforced concrete has to be at least 2.5 in. (6.4 cm) 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) of such 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 fire in neighboring buildings through fireproof exterior walls-preferably windowless, since windows are fire openings.

Fireproofing of Construction Materials

How to Build a Fire Resistant House Frame your home with metal studs. Metal studs

cannot combust in the same way that wood studs can.

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

Use as much concrete as possible in the structure of your home.

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

Install safety features. Fire alarms

Thank You

Education

everthing about cyclones + fire