Soe Kerala v2 Chapter 5

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#& Lightning

State of the Environment Report - 2007 - Vol. II - Natural Hazards

LIGHTNING

5.1. INTRODUCTION:

Lightning is a weather phenomenon. It is essentially an electrical discharge. This is not

a phenomenon peculiar to Kerala. It is part of a global electrical system known as the

�Global Electric Circuit� involving the earth, ionosphere, and the atmosphere in between.

Some where in the world lightning always occur5.

Lightning is a high-energy luminous electrical discharge from a thundercloud accompanied

by thunder. In our atmosphere, three types of discharges take place: one within a

thundercloud (intracloud), the second from one cloud to another (intercloud ) and the third,from cloud to ground (CG). The last type takes a toll on our life and property and so is of

concern to us. An exception to this is the aircraft hit by inter cloud and intracloud11

lightning. Lightning is very fast, takes only about only 1/10th

of a second7. Lightning discharge

occurs at millions of volts with a current of several thousands of amperes. The discharge

creates temperature of about 30,0000C

3within a few tens of milliseconds. Prediction of

lightning as to the precise time and location is very difficult or impossible.

The largest of all types of clouds, namely the Cumulonimbus cloud (Cb) is responsible

for lightning. If more electrified Cbs form, then the lightning will be more. Mainly two types

of processes lead to formation of such clouds. Based on the type of formation they areclassified as �Frontal� or �Convective� thundercloud. Frontal thunderclouds form by the

interaction of cold and warm air masses and so such clouds can form at any time of the

day or night. The convective Cb formation commences in the forenoon with the onset of

convective cycle initiated due to heating by the solar radiation. Usually they mature by the

afternoon. Majority of the lightning strikes from this type occur in the afternoon hours.

Charging mechanisms of the cloud, the number of charged cells formed and the regional

meteorology decide the thundercloud formation in a region. Therefore, the Cb behaviour

varies over regions of the globe. A typical cumulonimbus cloud in the equatorial regions



State of the environment report - 2007 - Vol. II - Natural Hazards

#' Lightning

grows up to tropopause7(15 to 18 km in tropics). A line drawing of a Cb is shown in Figure.

5.1.

HORIZONTAL SPAN (km)

32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2

GROUND

CLOUD (Cb)

CUMULONIMBUS

A L T I T U D E ( k m )

0

2

16

14

12

10

8

6

4

Figure 5.1. Line drawing of a relatively small cumulonimbus cloud which can cover an

area of more than 500 sq. km.

The Cb clouds grow to very large sizes covering an area from a few hundred square kilo

metres to several thousand square kilo metres. The figure shows the horizontal span of a

cloud covering an area of about 500 sq. km. The base of these clouds can be one or two

kilometers above ground and the top can reach an altitude of 17 km. These clouds have

one of the strongest air circulations in them and in attempting to penetrate the tropopauseat 17 km an anvil as shown in the figure develops.

Cb top develops a positive electrical charge, the lower level a negative electrical charge1, 6, 10, 12

. A flow of current between these does not occur, as the air is a poor conductor of

electricity. As a thundercloud passes overhead, positive charge accumulates on all objects

below the cloud. Since these positive charges attempt reaching the negative charge of the

cloud, they tend to accumulate at the top of the highest object in the vicinity. Lightning

results when the difference between +ve & -ve charges, the electrical potential difference,

is enough to overcome the resistance of air to force a conductive path between the cloud

& ground. This potential difference may be as much as 100 million volts10

.

Some Cbs are formed with top negative and bottom positive also.

The heavy electrical discharge happening in a time of about few tens of milliseconds

leaves the air heated to a very high temperature1, of about 30,000

oC. This process invokes

shock waves2,6,7,10

, the propagation of which we hear as thunder. In other words thunder

is purely an acoustic, harmless phenomenon which follows the glowing electrical discharge.

Thunder causes little damage or injury. It helps in estimating the slant distance roughly. It

takes three seconds for thunder (sound) to travel 1 km and so the time (seconds) between



$ Lightning


sighting a lightning flash and hearing sound, divided by 3 gives the slant distance in kilometres.

Further, higher the pitch of sound of thunder, the closer is the lightning.

Data on spatial and temporal distribution of lightning in the national level is sparse. Atpresent, we neither have an isokeraunic chart (contour maps of thunderstorm days) or a

map of real time lightning distribution. However, satellite detection systems using Lightning

Image Sensor (LIS) and Optical Transient Detector (OTD) have provided data on spatial

distribution of lightning for the whole world4. These data give an indication of the lightning

distribution in India.

The LIS and OTD data indicate that there are about three locations in India where

lightning incidence is relatively high. Kerala is one of the places of high lightning incidence

in India with the region near Kashmir having the highest incidence. Hence Kerala is one of

the regions in India requiring special consideration for the abatement of lightning hazard.

5.2. FRAME WORK FOR REPORTING

The DPSIR frame work as discussed in section 1.3 is used for analysis of the lightning

hazard. Figure. 5.2 depicts the use of the frame work as a flow chart. The different

elements of the hazard and their inter dependence are indicated in the flow chart.

5.3 DRIVING FORCES

5.3.1. Western Ghats influencing Cb formation

As mentioned earlier lightning is produced by Cb. Therefore for Kerala to have morelightning incidence the number of Cbs that form should be more. This leads to the deduction

that the condition for Cb formation in Kerala exist more frequently in terms of space and

time. Regions close to mountains are known to be favourable for Cb formation. Kerala is

bounded in the west by the western ghats. For Cb to form large amounts of water vapour

also is required. The proximity of the sea satisfies this requirement too. The presence of

western ghats and the weather systems together create a condition just right for Cbs to

form and grow. Solar radiation heats the ground and in turn makes the air get heated up.

Because of the slope there is differential heating between the plains and mountain regions.

By about 1200 h sea breeze is able to bring moisture rich air from the sea to the mountain

regions. The mountain foot hills are less than 40 km distant from the coast. Moist air uponreaching the mountain slope rises because of the mountain and the cold air over it. Upon

rising it cools and expands too. In the presence of sufficient condensation nuclei, cumulus

clouds form. If the water vapour supply is continued the cumulus can grow to become a

Cb. Once it grows beyond the height of the mountain which has height of about 2000 m it

starts moving towards the west coast as the predominant wind direction is North East.

The sea breeze which continues will supply water vapour to the cloud during it transit to

west. Hence it can be seen that the state of weather and the western ghats together

create conditions conducive for Cbs to form. In other words there exist a set of elements




$ Lightning

FORMATION.

CESS WEB SITE. MOVIE BY ILM.

WORK SHOPS BY REGIONAL ENERGY

DWEATHER.

PRESENCE OF WESTERN GHATS.HIGH POPULATION DENSITY.HIGH VEGETATION DENSITY.LACK OF AWARENESS.

RELATIVELY MORE EXPOSURE.

RELATIVELY MORE CLOUDP

GROUND CONDUCTION.

5 DISTRICTS ARE BAD.1500 h TO 1900 h ACTIVE TIME.

ARE 'SEASON' MONTHS.APRIL, MAY, OCTOBER & NOVEMBERMID LAND & LOW LAND MORE.

GROUND CONDUCTION.

S

INTERNET, CABLE TV, POWER ETC.ALL NETWORKS LIKE LAND PHONE,

SECTOR IN 2002.Rs.2 CRORES LOSS TO LANDPHONE188 TOTAL ACCIDENTS PER ANUM.

71 DEATHS, 112 INJURIES &I

CENTRE, AN NGO,TVPM.

AWARENES CAMPS BY CESS.BROCHURE ON LIGHTNING BY CESS.

R

AFFECTED.

LESS PREPAREDNESS.

BY A DIFFERENT MODE.LIKELYHOOD OF EXPOSURE

STATE ELECTRICAL INSPECTORATE.IS 2309.

Figure 5.2. Flow chart of the state of environment of lightning hazard in Kerala. Different

elements and their inter dependence are shown.

which are favourable for formation of Cb in Kerala. This is the reason for Kerala to have a

higher lightning incidence compared to most of the other places in our country.

5.3.2 Population Density and Vegetation Density

Kerala is a place of relatively high population density as well as vegetation density. The

population density of Kerala is about 819/km2compared to national average of 325/km

2.

Kerala has a forest cover of about 26% and an average vegetation cover of more than

50% inclusive of mixed cultivation. This indicates the relatively higher probability of the

lightning causing injury or loss of property on account of greater exposure. In other words

cross section for injury and property loss from lightning is relatively high in Kerala.



$ Lightning


5.3.3. Increased Accidents to People Due to Lack of Awareness

In addition to the higher cross section there is another aspect which causes more

personal injury. This is the lack of awareness on dos and don�ts during lightning activity. Inother words if people were aware of the ways of protecting themselves many a personal

accident could have been avoided. Also the most effective method for reducing personal

injury is to create awareness. This is what is practiced elsewhere in the world also.

Studies have indicated that the lack of awareness about dos and don�ts during lightning has

resulted in more people getting involved in lightning accidents.

5.3.4. Accident by Ground Conduction - A Special Feature Of Kerala

Quite a large percentage of accidents in Kerala have been found to have happened

inside the dwellings, irrespective of whether they are RCC roof or not. This happens because

of conduction of energy through ground. Such conducted energy enters buildings even if it

has a RCC roof. Lightning falls on a tree near to a building and by ground conduction it

involves people and equipment inside dwellings. Ground conduction from trees as distant

as 50 metres away has been found to have caused fatal injury. As the vegetation density

is high in Kerala almost all dwellings have trees near them and so the number of such

ground conducted accidents are significantly high.

5.4 PRESSURE:

The conditions conducive for formation of Cbs have been explained in section 5.3.1. In

Kerala, these conditions exist almost all along the length of the state. This is because thestate is bounded by the Western ghats on the western side and these mountains help in

formation of Cb clouds. Therefore clouds form at a frequency much higher than most of the

other places in the country. In other words the state has conditions conducive for relatively

much higher frequency of Cb formation. Because more Cbs are formed lightning frequency

is high. This is the main pressure of the lightning hazard in Kerala.

In addition to the high frequency of lightning the state has more population density. This

increases the probability of more people getting involved in lightning. This results in more

injury and death. A similar situation exists for destruction of plants and trees also. Like

population density the vegetation density is also relatively high in the state. This increases

the probability of lightning strike resulting in more destruction of trees and other plants.

In Kerala awareness about lightning is same as else where and in absolute sense it is

bad. The public neither knows what is lightning nor how to escape from a lightning accident.

Knowledge about protective devices and equipment are also low. In addition people believe

that some places are lightning prone and some places do not have lightning occurrence. In

fact there have been several cases of accidents happening after a gap of 10 to 15 years.

In such cases the wrong belief that lightning will not occur in the area has resulted in injury




$! Lightning

and destruction. This lack of awareness is one of the pressures which results in more

injury and death.

Since lightning is a phenomenon associated with weather the location and intensity isnot always predictable. Collection of data and integrating them in space and time has been

absent. Therefore all lightning strikes remain a mystery to most including the state

administration. The result is that some places are still reported as �lightning prone�. Such a

classification comes about due to reaction of the people there to a few accidents and not

by the statistics. Requests for special treatment and installation of lightning conductor for

a whole district or taluk keep coming in. Special treatment for a district or taluk is not the

answer and installation of lightning conductors for a large area is not practicable. Hence

the lack of awareness results in less preparedness and causes more damage or destruction.

In addition to all the pressures discussed above Kerala has a special feature which

increases the likely hood of exposure. Unlike what happens in other regions of the country,

in several cases in Kerala, several people have been affected by lightning inside their

dwellings by ground conduction, as explained in 5.3.4. Such events have added more

uncertainty to the picture.

5.5 STATE:

5.5.1 Distribution of Incidence in the State

Real time monitoring of lightning only can give the true picture of the spatial and temporal

distribution of incidence and the risk involved. This data is absent. However, presently

some data on spatial and temporal distribution of lightning incidence is available with CESS,Thiruvananthapuram. The data is based on felt reports available with village offices and old

news papers for 17 years between 1986 and 20028. That is, when an event of injury or

loss of property is reported it becomes one datum. The degree of destruction seen in the

data is an under estimate because destruction of some property like house hold objects

and trees goes unreported. The magnitude of the problem as seen from this felt report data

is presented in a plot of incidence on a map of Kerala shown in Figure. 5.3.

It can be seen that there is a relative void in incidents in an area west of the Palakkad.

The same incidents have been plotted on a physiographical map and presented in Figure.

5.4 also shows the void.

More specifically the region west of Palakkad namely the region near Thrisur has less

incidence. This is because the mountain range has a gap in Palakkad and so the absence of

mountain results in less Cb formation and lightning incidence. The two figures indicate that

the mid land of Kerala has more lightning. The high lands have the least of incidence and the

frequency and distribution in the low lands falls between the other two.

5.5.2. District Wise Distribution of Accidents

District wise distribution of lightning taken from the same data is given in Figure. 5.5.



$" Lightning


The bar graph gives a picture of the relative distribution of incidence in different parts of

the state. The proximity of a mountain in forming a Cb to cause lightning seems to be the

reason for the difference in incidence in different districts.

5.5.3. Month wise Distribution of Incidents

The Cb clouds usually form and produce lightning in, so to say, two seasons in an year.

The first season comprises of months April and May and the second is for the two months

of October and November. This is seen depicted in the bar graph of month wise fraction

shown in Figure. 5.6.

Analysis of the 17 year�s data yielded the most probable time for lightning to occur in

a day also. Of the cases where time was available it was found that 83% of the events

have happened between 1500 h and 1900 h8.

Figure 5.3. Spatial distribution of Lightning in Kerala between 1986 and 2002 8. Thedots indicate that lightning has occurred in that location. There are numerousoverlaps of dots in the plot.




$# Lightning

Figure 5.4. Lightning incidents on a physiographical map (red dots) of Kerala 8.



$$ Lightning


LIGHTN ING - DISTRICT W ISE

159

257

51

218

92

125104

36

83

242 249

19

353

108

0

50

100

150

200

250300

350

400

T r i v a n d r u m

K o l l a m

A l a p p u z h a

K o t t a y a m

I d d u k i

P a

t h a n a m t h i t t a

E r n a k u l a m

T h r i s s u r

P a l a k k a d

K

o z h i k k o d e

M

a l a p p u r a m

W a y a n a d

K a n n u r

K a s a r a g o d

District (Na me)

E v e n t s ,

D

e a t h &

I n

j u r y

(

Death

Injury

Evets

Figure 5.5. District wise distribution of lightning incidence in Kerala 8.

M onth - wise Fraction of Total Incidence

1

45

21 22

7

31

4

19

10

2

0

5

10

15

20

Jan Feb Mar Apr May Jun July Aug Sep Oct Nov Dec

Months (Name )

F r a c t i o n ( %

Figure 5.6. Plot of month wise fraction of lightning incidents to show the distribution over a

year 8. The plot is a result of analysis of the 17 year�s data discussed in thetext.





$& Lightning


5.6 IMPACT:

5.6.1 Statistics of Deaths, Injuries and Property Loss

The death injury and number of events per anum statistics derived from the felt report

data of 17 years is given in Table 5.1. The total number of events shown includes the death

and injury.

Deaths Injuries Events

______________________________________________________________

Average/ year 71 112 188

Table. 5.1. Lightning death, injury statistics from felt report data8

As the data is collected either from reports of news value or from reports filed for the

purpose of compensation claim to the revenue department of government the number of

incidents where property loss is reported is very less. This is true especially for trees and

house hold electrical equipment.

The events listed in the table includes deaths, injuries and a few reports of property

damage. As can be deduced the lightning accidents with property loss alone reported areonly 5 in number.

Economic Loss

Lightning causes destruction to equipment especially those having networks like power,

land telephone, TV cable service, internet, airport net works and the like. Given below in

Table. 5.2 is a sample data obtained from telecom on damage caused to land telephone

equipment. SDCA is the acronym for Short Distance Calling Area comprising

Thiruvananthapuram and Nedumangad taluks. All these equipments had lightning protecting

devices like gas discharge tube lightning arrestor installed in the network. The loss or

damage has happened in spite of the presence of such protective devices. From the sampledata obtained from Telecom on cost of damage to telephone systems, a calculation, taking

into account the lightning distribution and telephone density was done. The result showed

that the loss for the year 2002 for Kerala could be about Rs. 2 crores8.

The revenue loss due to other things like loss life, injury to personnel, cattle, trees etc

have not been worked out. Total loss may work out to an equivalent of several crores of

Rupees per anum. Instances of several coconut trees having been destroyed in one lightning

discharge have come to the notice but have not been recorded. It may be noted that the




$' Lightning

available data is not a real time data and so the loss in consideration can only be an under

estimate.

5.6.2. Destruction to Other Net Works

Loss to other similar sectors like cable TV net work goes unreported. In October 2006

there was a report of a lightning accident in Thiruvananthapuram airport. The landing lights

network of the run way failed because of a lightning hit and flights had to be diverted to

other airports for several hours. At present most of the internet net work is also hard

wired and the failure due to lightning hit is not infrequent.

Power net works and high tension lines have some amount of protection by lightning

conductors and lightning arrestors installed in them. However destruction by lightning do

happen but goes un noticed.

5.7 RESPONSE:

• High rise buildings, installations consuming more than 50 kW of power and other

installations like storage houses of fuel etc have mandatory requirements for installation

of lightning protection systems. IS 23099provides guidelines for these and institutions

like the State Electrical Inspectorate enforces installation of the required equipments.

• For people living in dwellings which do not belong to the above category, and for low

power systems, as mentioned earlier, creating awareness becomes an important

element in reducing personal injury and property loss. Awareness on dos and don�ts

during lightning and times for which one has to be careful to avoid accident, is very

important in reducing personal injury. There is no institutional mechanism for creating

awareness. However the Centre for Earth Science Studies has prepared a brochure in

2002 and had sent it to all village offices of the state in 2003 for display. This was

prepared in Malayalam and was prepared in a simple language for almost any body to

easily understand. The brochure also discusses the special problem of ground

conduction and recommended remedy for it. The brochure has been sent to all news

papers for publication too. The CESS team has visited many an accident spot and

Period of accidents Repair & replacement Subscribers

(between) cost. affected (No.)

12/4/02 & 04/6/02 Rs. 13, 65,237.00 13038.

30/9/02 & 18/11/02 Rs. 4, 47,706.00 4323.

Table. 5.2 Details of sample data from telecom pertaining to Trivandrum SDCA.8






% Lightning

5.9.2. Alleviation of the Hazard by Early Warning

Early warning is a preferred solution of lightning hazard. Neither all Cb clouds are charged

nor the formation of a Cb cloud can be predicted

8

. Further it is not possible to predictwhere a discharge will occur. The possible things are detection of a Cb cloud using Radar

and measurement of its electrical activity with electric field equipment. These two cannot

give a long term and sure warning. Warning regarding electrical activity or magnitude gives

information that a charged cloud is near by or overhead only. Since the area covered by a

Cb can be vary from a few hundred km2to several thousand km

2it is not possible to predict

where the discharge will be initiated. However, once the discharge activity is detected and

the direction of the thunderstorm movement is known a warning of a possible danger can

be provided through electronic media. Installation of a real time lightning monitoring network

is also recommended. Such systems are a bit expensive to acquire. Considering the revenue

loss the expenditure is justified. Further, such net works cover a large area and will be

useful for the whole of south India. Real time data will help in taking correct and cost

effective hazard alleviation measures. The real time data will be helpful in risk analysis

also.

5.9.3. New Studies

Understanding the science behind formation of Cb in causing high lightning incidence in

Kerala is required. A pilot study to understand the process for one region is being done in

CESS. Study on simultaneous formation multiple cloud systems covering larger areas and

regions, like along the Western ghats, should also be taken up.

5.9.4. New Projects Required

The ground propagation and the ring conductor protection require special mention. It

has been found that many people living in the foot hills of the mountains get injured by

ground conduction. Most of them are poor who cannot afford installation of a ring conductor

as per international standards. It is recommended that attempt be made to develop a

cheaper method like using a cheaper ring conductor with a few GI wires etc. A project

seems essential to try this.

5.9.5. Changes in Institutional ArrangementsSecond aspect on the lack of awareness is about the preventive and protective measures

to be adopted. There is an absence of an authority or agency for people to seek advice or

consult regarding lightning protection equipment. For high rise buildings and those consuming

more than 50 kW of power the state Electrical Inspectorate is the authority for sanctioning

license or permission. Installation of lightning protection equipment is mandatory in such

buildings. Further IS 23099provides all details required for lightning protection equipment

installation for such buildings. For individuals and low power consuming dwellings there is



% Lightning


nobody to guide them. The standard is a good guide line for details of installation of lightning

conductor, its specifications and the like for the public. But it does not deal with conditions

under which the lightning rod will not be effective etc. For example near a house if a tree

exists the lightning rod will be effective only if the lightning conductor tip is well above the

tree top. Hence the details and guidelines in IS 2309 are not enough for the public having

independent dwellings of small heights. Even for school buildings, where a large number of

children sit assembled in the afternoons there seems to be not even a guideline regarding

lightning protection equipment. An institutional arrangement for people to consult and

seek advice is necessary.

As mentioned earlier the ground conduction of lightning energy into buildings is a relatively

serious problem of the state. By installing a ring conductor around the house or building this

problem can be reduced to a great extent. As on today guidelines on this seems to be not

available. However there are sites which discuss this issue and guidelines are available in

them. A very brief guideline is provided in the brochure published by CESS.

Here again an authority is required to guide people regarding the use of ring conductor

for protection. They may provide advice as to where it is needed.

5.9.6. Creating awareness

Lack of awareness is a major problem in the effort to alleviate the hazard. There are

two components to it. One is lack of awareness on dos and don�ts during lightning. This is

detrimental for personal injury. Most of the injury to people could have been reduced by

knowing dos and don�ts about escaping lightning injury. In fact the data shows that if one

takes care for four months in an year and that too most of the time in the afternoon and

evenings injury to people could have been drastically reduced. Dissemination of information

in this regard requires prime consideration. This is what is done elsewhere in the world

also.

Educating the children, preferably at the plus two level would be a good solution to

creating awareness about lightning and protection. Present level of knowledge about this

subject even among the educated is meagre. Since Kerala happens to be a region of relatively

high lightning activity, introducing the subject to children in detail should be given serious

thought irrespective of its absence in other state�s school syllabi.

5.9.7. New Policies/Changes In Existing Policies

The present policy considers Kerala as any other place in the country regarding lightning

also. A policy change should come about to accept the fact that Kerala is place of relatively

high lightning incidence. This change is required to address and take remedial measures

for many problems related to lightning accidents. The first remedial or alleviation measure

should be in creating awareness among the public about lightning and methods to avoid

accidents. Another aspect is the lack of data. The data discussed here was collected in




%! Lightning

project mode. The policy change should help in making it necessary to collect data on

lightning continuously.

REFERENCES

1. Chalmers, J. A., 1967, Atmospheric electricity, Second edition, Pergamon press,

Oxford, pp 309-311, 341.

2. Golde. R. H. Lightning, 2 Vols, 1977, Academic Press, London, pp 395-405

3. Hart, William. C and Malone, Edgar. W, 1979, Lightning and Lightning Protection in

Multi Volume EMC Encyclopaedia Series, Volume IV, Don White Consultants, Inc.,

Virginia, USA, , p 1.5.

4. Global Hydrology and Climate Center (GHCC), (NASA) Data, 2003, High resolution

full climatology annual flash rate Global Distribution of lightning April 1995 � February

2003 from the combined observations of NASA OTD (4/95-3/00) and LIS (1/98-2/

03) instruments - Internet site.

5. Israel, H., 1971, Atmospheric Electricity, 2 Vols, Israel Program for Scientific

Translations, Jerusalem, p517.

6. Mac Gorman, Donald. R and Rust, W. David, 1998, The Electrical nature of Storms,

Oxford University Press, pp 49-53, 99-100.

7. Magono Choji, 1980, Thunderstorms, Developments in Atmospheric Science,

Elsevier Scientific Publishing Company, New York, pp 20-21, p 158, p176.

8. Murali Das. S, Sampath. S & Mohan Kumar. G. 2004, Understanding Lightning

Accidents To Alleviate The Hazard. CESS, Thiruvananthapuram, Project Report,

Ministry of Home Affairs, Govt. of India.

9. IS 2309:1989, REVISED March 1991, Protection Of Buildings And Allied Structures

Against Lightning- Code Of Practice.

10. Rakov Vladimir. A and Uman Martin. A, 2003, Lightning- Physics And Effects,

Cambridge University Press, pp 68-93, 110, 111, 378.

11. Ruhnke, Other. H and Latham, John, Ed. 1983, Proceedings in Atmospheric

Electricity, A. Deepak Publishing, Virginia, USA, , pp 314-317

12. Uman, Martin. A, 1969, Lightning, McGraw-Hill Book Company, New York, pp3-

5.A recommended site for many an useful information: www.lightningsafety.com

[National Lightning Safety Institute (NLSI)

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