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IMPACT OF LIGHTNING ON BUILDINGS AND ITS REMEDIAL
MEASURES
1. INTRODUCTION
1.1. The Phenomenon of Lightning
Thunderstorms develop when ground heat creates a hot rising
current of air. This air gradually cools until it condenses into
small cumulus clouds. The cumulus continues to grow vertically
until it eventually becomes a storm cloud or cumulonimbus.
These atmospheric conditions lead to the creation of electric
charges resulting from collisions between water, hail and ice
particles of different sizes. There are charges separation inside
the cloud, with a negative charge at the bottom of the cloud
and a positive charge at the top.
The centre of the negative charges is usually at the base of the
cloud due to the movement of electrons through the heavier
droplets and hailstones, whilst the centre of the positive
charges moves up to the top of the cloud carried by convection
currents, which can easily lift the light positively charged
particles. The effect produces a similar change at the earth's
surface due to the charge repulsion, of about the same
magnitude but opposite polarity.
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The potential inside the cloud is usually of the order of several
million volts and electric field may exceed 5 kV/m at ground
level, which gives the creation of the upwards leaders rising
from surface irregularities or metallic structures. (Fig.2 a).
Electrical field is so strong that small discharges are produced
from the cloud, known as step leaders. As these step leaders
get closer to ground level, the upward leaders rise up to meetthem. When the step leader and the upward leader meet, the
circuit is completed creating a short circuit, the lightning strike,
with discharges current from 10 to 200 kA (Fig. 2c).
The energy carried by a lightning strike can easily reach 20
GW.
The most common lightning strikes are from the cloud to
ground (in 80% of cases), and are named negative discharges,
but when the discharge is positive in the downward direction,
the intensity is extremely high.
1.2. Statistics
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were damaged. The copper circuits between building became a
path for the equalisation current. The correct application of
surge protection could have prevented the resulting damage.
This is why an effective lightning protection system will include
protection against the direct strike (i.e. an external lightning
protection system), and protection against the indirect strike
(i.e. an internal lightning protection system using Surge
Protection).
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2. LIGHTNING PROTECTION AND ITS WORKING
Lightning protection creates a preferred point for lightning to
strike (avoiding strikes to sensitive rooftop equipment) using
an air termination network, then conducts the energy to ground
using down conductor(s) and injects the energy into a purpose
designed earthing system.
In some cases, existing structure materials can be used as part
of the lightning protection system, such as using reinforcingsteel as down conductors. The items are referred to as natural
components. The use of existing structure items is most
applicable to situations where the lightning protection is
included in the initial design and construction. For buildings
where lightning protection is retrofitted, it is often difficult to
use natural components.
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There are many possible designs for air termination networks,
and final selection is based on efficiency of performance, ease
of installation/maintenance, cost, visual impact and
compatibility with existing building materials. While the
traditional lightning rod is well known, horizontal conductors,
handrails, parapet flashings and conductive roofing materials
may also be used.
Down conductors are selected to route the energy to ground
and reduce the risk of side-flashing to nearby items. Routes areselected to reduce electromagnetic radiation and control risk of
dangerous touch potentials being developed. The size and
interconnection method of down conductors reduces the risk of
heating and resultant structure fire during a lightning strike.
For new concrete construction, the reinforcing steel within the
building may be utilised.
The earthing system is designed to inject the energy into
ground and reduce the risk of voltage-ground-potential-rise
(step and touch potentials). Various positioning and layout
options are evaluated to select the best choice.
Lightning protection systems are designed to:
Reduce the presence of dangerous voltages (reduce step
and touch potentials)
Reduce the risk of flash-overs (reducing the risk of the
building catching fire)
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Reduce physical damage to buildings (stop holes being
punctured in roofs, stop chucks of building materials being
knocked out)
Reduce the risk of equipment damage
2.1. Protection zone
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To aid in the design of the lightning and surge protection
system, the concepts of zones is used. For example zones
are classified based on:
Is the area vulnerable to a direct strike?
Is the area exposed to the full or partial lightning current?
Is the area exposed to the full or partial electromagnetic
field?
ZoneLightning
FlashCurrent Field
LPZ 0a Yes Full Full
LPZ 0b No Partial Full
LPZ 1 No Limited Partial
LPZ 2 No Reduced Reduced
By identifying the various zones around and within a structure,
protection can be applied appropriately. For example, electrical
services passing through a LPZ 0 zone will require surge
protection where they enter into a LPZ 1 zone. Note that zones
may not necessarily be physical boundaries of the structure
2.2. Isolated lightning protection system
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Lightning protection systems may be isolated or non-isolated.
Non-isolated systems electrically bond all conductive building
materials together so they rise and fall at the same potential,
eliminating potential differences and the risk of flash-overs.
This is the traditional lightning protection method.
However, with modern facilities containing a large amount of
electronic equipment, and more critically, rooftop equipment
(air handling units, lift motors, TV aerials and communication
equipment), non-isolated systems can be difficult and costly to
implement.
Isolated systems use special methods to capture the lightningstrike and conduct this to ground without it contacting the
structure. Isolated conductors are the main methods to achieve
this. Isolated systems are ideal for:
Highly flammable structures (grass/straw roofs)
Locations with a high concentration of electronic
equipment (communication towers)
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Structures where the cost of bonding all metallic items
would be prohibitive
Isolated systems are ideal to keep the dangerous lightningenergy away from:
Rooftop communication equipment
Solar cells and other electrical/electronic equipment
Explosion or gas hazard areas
2.3. Surge protection and its working
Surge protection devices are non-linear voltage dependent
devices that transition from high impedance state to low
impedance state to divert over voltages and over current safely
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to ground. They are similar to a safety pressure value that
stops dangerous pressures being built up in pressure vessels.
The correct selection and installation of surge protection isessential for reliable performance. Unfortunately there are a
number of people selling these products with little knowledge
of these issues. HV Power have specialist application
knowledge to guide you.
It is important that:
The right ratings are installed at the right locations
That electrical safety is maintained by having the correct
backup over current protection
That devices are installed in such a manner to ease
inspection and replacement
That the location and wiring to the SPDs does notcompromise the possible protection
That surge protection is properly coordinate
2.4. Coordinated protection
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With surge protection designs, the normal approach to apply a
large lightning rated surge protection device on the main
service entrance. This stops energy entering the facility via the
Z0/Z1 boundary. These are referred to as Lightning Current
Arrestors (IEC 61643-11 Type 1).
Secondary coordinated protection is then installed closer to the
sensitive equipment to be protected. According to IEC 61643-
11 these SPDs are Type II devices, or Surge Arrestors. You
cannot rely on a Surge Protection Device (SPD) mounted in the
main switchboard to protect equipment 10-100s of metres
away, especially when other loads in your facility may also be
generating transient voltages. Having two SPDs ensures the
massive lightning current/voltage is suitably reduced so as not
to damage sensitive equipment. The term "coordinated-
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protection" is used as these two devices must be selected to
work in a coordinated fashion.
This first of this two-pronged approach diverts the bulk of theenergy away from the point-of-entry to the facility, thus:
Stopping energy from entering into building and
radiating/coupling into nearby low voltage
data/communication circuits
Stopping damage to electrical distribution boards (so
power is not disrupted!)
Providing effective protection to robust downstream
equipment such as heating and lights
The second of this two pronged approach, provides fine
protection to the sensitive electronic equipment, thus:
Protecting sensitive equipment to a suitable low voltage
Providing backup if the point-of-entry protection is
damaged
Protecting equipment from internally generated transients
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electronic equipment that it might contain. It is common for
lightning strikes several kilometers away to cause damaging
electrical surges. And even in Newport, Rhode Island, where
there are only about 20 thunderstorms a year, each square
kilometer is struck an average of twice a year. This is enough
to be of concern to facilities where damage can result in
expensive downtime, the loss of important data or the potential
to lose control over hazardous processes - not to mention the
actual damage to costly electronic hardware.
3.2. lightning effect on a building
Direct and indirect effects are the two broad categories. Direct
effects include the physical damage produced by lightning.
Ignition of fires is a clear example caused by contact of the
20,000C lightning channel. Other direct effects include
shattering of wood, windows, masonry and other poorly
conductive materials. Direct effects also include the burnout of
electrical power and distribution equipment caused when
lightning injects high currents and voltages into a power
distribution line. A common example of this is the explosion of
power distribution transformers.
Lightning also causes a variety of indirect effects. These result
from earth-voltage rises caused when the flash dumps
thousands of amperes into the earth and from the
electromagnetic fields generated by the lightning stroke
currents. These induce voltage and current surges in electric
power and signal circuits, which may, in turn, burn out
electrical equipment connected by these circuits. Solid-state
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electronics are especially vulnerable to these surges unless
properly protected. Of particular concern are facilities with
several buildings or installations that are interconnected with
above or below ground cables. These cables can experience
significant induced transients. Power, telephone, data and even
underground plumbing have the potential to transfer damaging
lightning surges into a building. Even some fiber-optic cables
can be susceptible to damage from lightning. Although the
fiber-optic signal lines themselves are nonconductive, the
cables are often constructed with a conductive metal sheath
for strength purposes. Fiber-optic cable sheathes can attract
lightning and its blast pressures may crush optical fibers.
3.3. Protection of buildings from direct effects
Since the time of Ben Franklin, the lightning rod, or air
terminal, has been the front line of defense against lightning.
Its basic concept is to provide a preferential terminal for
lightning that would have otherwise hit a vulnerable part of the
structure. An air terminal only will protect a portion of a
building, so most structures will have several lightning
terminals. The spacing and position of air terminals has been
well understood for many years and the proper configuration
and installation of air terminals is detailed in well-known
standards, such as NFPA 780 (National Fire Protection
Association). Basic direct-effects protection also includes a
system of down conductors connecting the air terminals to the
grounding system.
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The configuration of the grounding system is very important
and depends upon soil conditions, building construction and the
presence of other underground conductors. Grounding systems
can be created with driven ground rods, plates and possibly a
counterpoise, which is a buried cable encircling the site. A
counterpoise adds greatly to the protection from earth voltage
rises that may injure people standing on the ground.
The interconnection (bonding) of other metallic items in the
building is important to prevent sparkover from a lightningconductor to other conductive items, such as water pipes, roof
edgings, vent stacks or HVAC equipment, depending on their
locations.
3.4. Protection of buildings protected from indirect
effects
Lightning can cause damaging transient voltages and current
surges in equipment through a direct strike to a wire, through
earth voltage rise and through magnetic field and capacitive
coupling.
There are four engineering concepts that, when properly
applied, can comprise a total lightning protection plan, whether
for a single piece of equipment or a complex of buildings.
These concepts are grounding, bonding, shielding and surge
suppression.
There is no magic bullet for lightning protection. Protection is
achieved only through a careful investigation to identify allsensitive components and all possible paths for lightning
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currents and voltages, followed by the design, specification,
installation and maintenance of a protection system.
Grounding and bonding improvements are made to provideadditional paths for lightning currents to flow to earth, thereby
minimizing surges. These improvements usually involve
interconecting adjacent conductors, such as structural steel,
conduits and ground conductors. Commonly overlooked
grounding problems include conduits, metal equipment
cabinets and individual components within computer rooms.
Shielding of cables helps to reduce surges by providing a
preferential path for lightning currents rather than the actual
circuits. To be most effective, shielding must be completely
continuous, and grounded or terminated to equipment
housings at both ends.
In some cases, grounding, bonding and shielding provide a
sufficient reduction in indirect effects. However, critical
sensitive equipment, and any equipment interconnected by
cables over long distances, requires the installation of surge
suppressers. There are many types and many manufacturers of
surge-suppression equipment. Care must be taken to select themost cost-effective device that will handle the currents and
voltages expected from a severe strike. Surge suppressors
should be installed where they readily can be inspected and
replaced when damaged by a severe strike. In many cases, the
most expensive surge suppressors turn out to be the least
effective or appropriate for a particular application.
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3.5. Protection of home and small business computers
from lightning
By far the best way to protect your computer from lightning isto disconnect it from both the power line and telephone line at
the approach of a thunderstorm. Commonly available surge
strips do provide protection against some of the surges caused
by lightning, specifically voltages induced between the positive
and negative lines of the power supply. Surge strips do not
always protect against voltages that arise between the powerline and house, or system ground or the telephone lines. The
larger concern, at least for any one capable of reading this
FAQ, is the modem. Simply stated, your computer effectively
forms a circuit between your local power company and your
local telephone company. The interface between these two
widely distributed networks is your computer. Lightning
commonly causes serious voltages to arise between circuits at
different distances from the strike and/or referenced to earth
ground at different locations. These voltages appear at the
interfaces between these systems - your computer. It is a
misconception to think that the lightning voltages are carried
down the telephone lines to your computer. Rather, the
voltages appear between the components of your computer.
That is why a surge suppressor designed for a modem would be
ineffective in most cases. This effect can be mitigated by
providing a common ground reference for every device
connected to your computer. In such a system, everything that
is connected to the computer that has its own power or
telephone connection is first connected to a device that
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provides a single ground path. This device is based on the
concept of an equipotential plane, commonly used for lightning
protection of aircraft and other advanced systems.
3.6. Lightning in golf courses
Because public safety is the highest concern in any lightning
protection program, the most important installation for a golf
course is an early warning system. Early warning systems can
include dedicated systems installed at the golf course or
connections to realtime lightning data from a commercial
network. In addition, strategically placed shelters should be
designed and constructed to withstand all lightning effects.
Please see our article on golf shelters available on this web
site.
Golf courses often have sophisticated irrigation systems withelectronic controls. Because these systems have power and
control cables distributed over many acres, they are highly
susceptible to lightning-induced surges. Careful grounding and
shielding and the installation of surge suppression devices can
protect these systems.
There are devices being marketed with claims that they
actually reduce the likelihood of a lightning strike and others
with claims to provide increased effectiveness as air terminals.
What are the merits of these devices?
Lightning Technologies, Inc. has no firsthand experience with
these devices. Most such items are not available for purchaseor installation other than directly through manufacturers and
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their licensees, often making it difficult for independent
evaluation. Moreover, LTI has had very good success with
commonly available conventional parts and materials, and so
has not found it necessary or useful to use expensive,
unproven and sometimes controversial proprietary protection
devices. To our knowledge, no independent studies have
yielded any conclusive evidence of the effectiveness of many
of these devices. Total lightning protection can be achieved
with the proper planning and installation of conventional
lightning-protection hardware and improvements to grounding,
bonding, shielding, circuit design and surge suppression.
Conventional lightning-protection hardware is relatively
inexpensive.
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4. LIGHTNING STROKE IMPACTS IN A BUILDING
Lightning strokes can affect the electrical (and/or electronic)
systems of a building in two ways:
by direct impact of the lightning stroke on the building
(seeFig. 5 a);
by indirect impact of the lightning stroke on the building:
- A lightning stroke can fall on an overhead electric
power line supplying a building (see Fig. 5 b). The
overcurrent and overvoltage can spread several
kilometres from the point of impact.
A lightning stroke can fall near an electric power line
(see Fig. 5 c). It is the electromagnetic radiation of the
lightning current that
produces a high current and an overvoltage on the
electric power supply network.
In the latter two cases, the hazardous currents and
voltages are transmitted by the power supply network.
A lightning stroke can fall near a building (see Fig. 5 d).
The earth potential around the point of impact rises
dangerously.
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Fig. 5: Various types of lightning impact
In all cases, the consequences for electrical installations and
loads can be dramatic.
4.1. Lightning falls on an unprotected building.
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The lightning current flows to earth via the more or less
conductive structures of the building with very destructive
effects:
thermal effects: Very violent overheating of materials,
causing fire,
mechanical effects: Structural deformation,
thermal flashover: Extremely dangerous phenomenon in
the presence of flammable or explosive materials
(hydrocarbons, dust, etc.)
The building and the installations inside the building are
generally destroyed
4.2. Lightning falls near an overhead line
The lightning current generates overvoltages through
electromagnetic induction in the distribution system. These
over voltages are propagated along the line to the electrical
equipment inside the buildings.
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The electrical installations inside the building are
generally destroyed
4.3. Lightning falls near a building
The lightning stroke generates the same types of overvoltage
as those described opposite. In addition, the lightning currentrises back from the earth to the electrical installation, thus
causing equipment breakdown.
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5. VARIOUS MODES OF PROPAGATION
5.1. Common mode
Common-mode over voltages appear between live conductors
and earth: phase-to-earth or neutral-to-earth (see Fig. 7). They
are dangerous especially for appliances whose frame is
connected to earth due to risks of dielectric breakdown.
Fig. 7: Common mode
5.2. Differential mode
Differential-mode over voltages appear between live
conductors:
phase-to-phase or phase-to-neutral (see Fig. 8). They are
especially dangerous for electronic equipment, sensitive
hardware such as computer systems, etc.
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Fig. 8: Differential mode
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6. PROCEDURE TO PREVENT RISKS OF LIGHTNING STRIKE
The system for protecting a building against the effects of
lightning must include:
protection of structures against direct lightning strokes;
protection of electrical installations against direct and
indirect lightning strokes.
The basic principle for protection of an installation against the
risk of lightning strikes is to prevent the disturbing energy from
reaching sensitive equipment. To achieve this, it is necessary
to:
capture the lightning current and channel it to earth via
the most direct path (avoiding the vicinity of sensitive
equipment);
perform equipotential bonding of the installation;
This equipotential bonding is implemented by bonding
conductors, supplemented by Surge Protection Devices (SPDs)
or spark gaps (e.g., antenna mast spark gap). minimize
induced and indirect effects by installing SPDs and/or filters.
Two protection systems are used to eliminate or limit
overvoltages: they are known as the building protection system(for the outside of buildings) and the electrical installation
protection system (for the inside of buildings).
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7. BUILDING PROTECTION SYSTEM
The role of the building protection system is to protect it
against direct lightning strokes.
The system consists of:
the capture device: the lightning protection system;
down-conductors designed to convey the lightning current
to earth;
"crow's foot" earth leads connected together;
links between all metallic frames (equipotential bonding)
and the earth leads.
When the lightning current flows in a conductor, if potential
differences appear between it and the frames connected to
earth that are located in the vicinity, the latter can cause
destructive flashovers.7.1. The 3 types of lightning protection system
Three types of building protection are used:
7.1.1. The simple lightning rod
The lightning rod is a metallic capture tip placed at the top of
the building. It is earthed by one or more conductors (often
copper strips) (see Fig. 12).
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Fig. 12: Simple lightning rod
7.1.2. The lightning rod with taut wires
These wires are stretched above the structure to be protected.
They are used to protect special structures: rocket launching
areas, military applications and protection of high-voltage
overhead lines (see Fig. 13).
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Fig. 13: Taut wires
7.1.3. The lightning conductor with meshed cage
(Faraday cage)
This protection involves placing numerous down
conductors/tapes symmetrically all around the building.
(see Fig. J14).
This type of lightning protection system is used for highly
exposed buildings housing very sensitive installations such as
computer rooms.
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Fig. 14: Meshed cage (Faraday cage)
7.2. Consequences of building protection for the electrical
installation's equipment
As a consequence, the building protection system does not
protect the electrical installation: it is therefore compulsory to
provide for an electrical installation protection system.
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50% of the lightning current discharged by the building
protection system rises back into the earthing networks of the
electrical installation (see Fig. 15): the potential rise of the
frames very frequently exceeds the insulation withstand
capability of the conductors in the various networks (LV,
telecommunications, video cable, etc.). Moreover, the flow of
current through the down-conductors generates induced
overvoltages in the electrical installation.
Fig. 15: Direct lightning back current
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7.3. Lightning protection - Electrical installation protection
system
The main objective of the electrical installation protection
system is to limit overvoltages to values that are acceptable for
the equipment.
The electrical installation protection system consists of:
one or more SPDs depending on the building
configuration;
the equipotential bonding: metallic mesh of exposed
conductive parts.
7.3.1. Implementation
The procedure to protect the electrical and electronic systems
of a building is as follows.
7.3.2. Search for information
Identify all sensitive loads and their location in the
building.
Identify the electrical and electronic systems and their
respective points of entry into the building.
Check whether a lightning protection system is present onthe building or in the vicinity.
Become acquainted with the regulations applicable to the
building's location.
Assess the risk of lightning strike according to the
geographic location, type of power supply, lightning strike
density, etc.
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7.3.3. Solution implementation
Install bonding conductors on frames by a mesh.
Install a SPD in the LV incoming switchboard.
Install an additional SPD in each subdistribution board
located in the vicinity of sensitive equipment (see Fig.
16).
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8. CONCLUSIONS
Thunderstorms and Lightning are climate related, highly
localized phenomena in nature known for devastating
consequences. Many scientific experiments have culminated in
inventions for lightning safety, yet the mystery behind lightning
is still unresolved and lightning as a phenomena is not
completely understood The technology of lightning protection
have registered steady improvements but even with all the
known precautions, complete safety is still beyond our grasp.
Creating awareness among the general people could go a long
way in mitigating lightning threats. The Asian countries like
India, Sri Lanka, Bangladesh, Nepal and Bhutan have started
Lightning Awareness Centres and one of their objectives is to
spread awareness among the people. The High Powered
Committee of the Government of India on Disaster
Management too has identified Thunderstorms and Lightning
as natural hazards of great concern. The Bureau of Indian
Standards purveys lightning protection guidance for structures
and the builders are advised to adhere to the prescribed code.
Research and Development programmes are being supported
on lightning protection and many leading Indian institutes and
Laboratories are working on lightning safety. The paper lays
stress on spreading the culture of safety against lightning. It
deals with the issues, Indian standards and methods of
lightning protection, and introduces on going awareness
programmes and research and development needs for
lightning safety in the Indian context.
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Though lightning incidents are less, whenever they strike, they
cause severe damages to life and properties. Casualties due to
Lightning can be easily, efficiently and inexpensively avoided,
and lightning safety can be achieved mainly by creating public
awareness, technical education on Lightning Protections,
educating people on lightning and surge protection. Stringent
steps to ensure adherence of building standards and codes
wherever necessary and promoting research and development
on lightning protection are essential. There is a need to give
lightning its due attention as a natural disaster and give it a
priority in National Disaster Management Programmes.
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9.REFERENCES
1. http://www.weighing-
systems.com/TechnologyCentre/Lightning1.pdf
2. http://www.kerenvis.nic.in/files/pubs/soe_2007/volume2/so
e_kerala_v2_chapter%205.pdf
3. http://www.cirprotec.com/products/lightning-
protection/Externa
http://www.weighing-systems.com/TechnologyCentre/Lightning1.pdfhttp://www.weighing-systems.com/TechnologyCentre/Lightning1.pdfhttp://www.kerenvis.nic.in/files/pubs/soe_2007/volume2/soe_kerala_v2_chapter%205.pdfhttp://www.kerenvis.nic.in/files/pubs/soe_2007/volume2/soe_kerala_v2_chapter%205.pdfhttp://www.cirprotec.com/products/lightning-protection/Externahttp://www.cirprotec.com/products/lightning-protection/Externahttp://www.weighing-systems.com/TechnologyCentre/Lightning1.pdfhttp://www.weighing-systems.com/TechnologyCentre/Lightning1.pdfhttp://www.kerenvis.nic.in/files/pubs/soe_2007/volume2/soe_kerala_v2_chapter%205.pdfhttp://www.kerenvis.nic.in/files/pubs/soe_2007/volume2/soe_kerala_v2_chapter%205.pdfhttp://www.cirprotec.com/products/lightning-protection/Externahttp://www.cirprotec.com/products/lightning-protection/Externa