Lightning is a visible discharge of static electricity that can occur within or between clouds or between the earth and a cloud. It is caused by high electrostatic stresses that ionize the air, allowing discharge between charged clouds and tall structures on the ground. A lightning protection system aims to safely intercept lightning strikes using air terminals, down conductors to direct current to ground terminals buried in the earth. The risk of lightning strikes on a structure is assessed using flash density maps and calculations of the equivalent collective area to determine if protection is required.

2. Lightning is the visible
discharge of static
electricity within a
cloud, between clouds,
or between the earth
and a cloud.

3. Current levels sometimes in
excess of 4000 KA,
Temperatures to 50,000
degrees F (water freezes at 32
degrees Fahrenheit under
normal conditions), and
Speed approaching one third
the speed of light (NLSI).

4. 1. Charged clouds induce
opposite charges on the
apex of tall structures, e.g.
towers, chimneys, trees,
mountains etc.

5. High electrostatic stresses at the
ends of these objects then ionizes
the air, resulting in lowering the
resistance of the path between the
cloud and the object, thus allowing
a discharge to occur between them.
Hence strikes the highest or most
pointed object in the area.

6. 2. Occurs when a sudden
potential difference
between a cloud and the
earth is established
instantly. This is induced
soon after a strike of the
first kind.

7. e.g. if there is a discharge
between cloud 1 and 2, cloud 3
can be suddenly left with
greater potential difference
gradient immediately adjacent
to it than the air can withstand
and a sudden strike to the
earth will occur.

8. Lightning risk assessment
methodology is provided
to assist the building
owner or architect /
engineer in determining
the risk of damage due to
lightning

9. If Nd > Nc lightning protection
should be installed, Where
Nd = Yearly lightning strike
frequency;
Nc = Tolerable lightning
frequency.

10. Nd = (Ng)(Ag)(C1)
Where:
Ng = the yearly average flash
density in the region where the
structure is located.
Ag = the equivalent collective area
of the structure in km2.
C1 = the environmental coefficient.

11. Yearly Flash density is
measured in km2/year, i.e.
flashes/km2/yr.
The data is obtained on flash
density maps.
These are obtained from the
meteorological offices,
e.g. A 10-year flash density
map

12. Refers to the ground area
having the same yearly
direct lightning flash
probability as the structure.
The effects of height and
location are also considered
in the area computations.

14. RECTANGULAR
MODEL

15. This accounts for the
topography of the site of
the structure and any
other objects within a
distance of 3H
Given as follows:

17. This is a measure of the
damage risk to the
structure including factors
affecting risks to the
structure, environment
and the monetary loss.
It is calculated as follows:

23. If Nd > Nc lightning protection
should be installed, Where
Nd = Yearly lightning strike
frequency
Nc = Tolerable lightning
frequency

24. EXAMPLE:
 Lightning flash density (Ng) = 4
 Relative structural location (C1) = 2
 Rectangular structure L = 80m
W = 50m
H = 30m
 Lightning strike frequency (Nd) = 3.93
C2=3, C3=3, C4=1, and C5=5
 Qs: Should the structure be protected
or not?

25. The Primary components:
Air terminals
Down conductor / cable
Ground terminals
Surge protectors

26. These intercept the
lightning discharge
TYPES:
Plain air terminals
Safety air terminals
Flexible air terminals

30. Copper
Aluminum
Class 1
Class 2
Structural steel frames

32. Ground rods
Plain/sectional copper clad
steel, copper, galvanized steel,
stainless steel
Ground plates
Ground mesh
Concrete encased electrodes
Reinforced steel
Copper conductors

34. The lightning protection
system has a zone of
protection.
A single vertical conductor
protects an area in circular
form of the building having
its center at the conductor
and reaching equal to twice
the height of the conductor.

35. It is however better to
provide a protection with a
zone consisting of a cone
with its apex at the top of
the vertical conductor and
a base of radius equal to
the height of the conductor.

36. There are basically three types
of lightning protection system
which are:
1. The simple lightning rod
2. The lightning rod with taut
wires
3. The lightning conductor with
meshed cage

37. 1. The simple lightning rod
The lightning rod is a metallic
capture tip placed at the top
of a building, and is earthed
to the ground by one or more
down-conductors and earth
plates or crow’s feet.

40. 2. Rod with taut wires
The tin plated copper
wires are stretched above
the structure to be
protected.
For special structures e.g.
rocket launching areas,
etc.

42. 3. Meshed cage
This involves fixing numerous
down conductors symmetrically
all round the building.
This type is highly
recommended for highly
exposed buildings with very
sensitive installations like
computer rooms.