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LIGHTNING PROTECTION CALCULATION

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Calculation of  Lightning Protection for Building  / Structure :

Example: Calculate Whether Lightning Protection is required or not for following Building. Calculate No of Down Conductor for Lightning Protection

Area of Building /  Structure:

Length of Building (L) = 60 Meter.

Width of Building ( W ) = 28 Meter.

Height of Building (H) = 23 Meter.

Lightning Stock Flushing  Density:

Number of Thunderstorm (N)= 80.00 Days/Year

Lightning Flash Density (Ng)=69 km2/Year

Application of Structure (A)= Houses & Buildings

Type of Constructions (B)= Steel framed encased without Metal Roof

Contests or Consequential Effects (C)= Domestic / Office Buildings

Degree of Isolation (D)= Structure in a large area having greater height

Type of Country (E)= Flat country at any level

Maximum Acceptable Overall Risk Factor =0.00000001

Reference Table As per IS:2309
Thunder Storm Days / Year
Lightning Flash Density
 (Flashes to Ground /km2/year)
5
0.2
10
0.5
20
1.1
30
1.9
40
2.8
50
3.7
60
4.7
80
6.9
100
9.2
Application of Structure
Factor
Houses & Buildings
0.3
Houses & Buildings with outside aerial
0.7
Factories / workshop/ Laboratories
1
Office blocks / Hotel
1.2
Block of Flats / Residences Building
1.2
Churches/ Hall / Theaters / Museums, Exhibitions
1.3
Departmental stores / Post Offices
1.3
Stations / Airports / Stadium
1.3
Schools / Hospitals / Children’s Home
1.7
Others
1.2
Type of Constructions
Factor
Steel framed encased without Metal Roof
0.2
Reinforced concrete without Metal Roof
0.4
Steel framed encased with Metal Roof
0.8
Reinforced concrete with Metal Roof
1
Brick / Plain concrete or masonry without Metal Roof
1.4
Timber framed or clad without Metal Roof
1.7
Brick / Plain concrete or masonry with Metal Roof
2
Timber framed or clad with Metal Roof

Contests or Consequential Effects
Factor
Domestic / Office Buildings
0.3
Factories / Workshop
0.3
Industrial & Agricultural Buildings
0.8
Power stations / Gas works
1
Telephone exchange / Radio Station
1
Industrial key plants, Ancient monuments
1.3
Historic Buildings / Museums / Art Galleries
1.3
Schools / hospitals / Children Homes
1.7
Degree of Isolation
Factor
Structure in a large area having greater height
0.4
Structure located in a area of the same height
1
Structure completely Isolated
2

 Calculation:

Collection Area (Ac)=(L  x W) + 2 (L x H) + 2(W x H) +(3.14 x H2)

Collection Area (Ac) = (60×28)+2x(60×23)+2x(28×23)+(3.14x23x23)

Collection Area (Ac) =7389 Meter2

Probable No of Strikes  to Building / Structure (P)= Ac  x Ng x 10-6 No’s / Year

Probable No of Strikes to Building / Structure (P)= 7389x69x106 No’s / Year

Probable No of Strikes to Building / Structure (P)= 05098 No’s / Year

Overall Multiplying  Factor (M) =A x B x C x D  x E

Application of Structure (A)= Houses & Buildings as per Table Multiplying Factor = 0.3

Type of Constructions (B)= Steel framed encased without Metal Roof as per Table Multiplying Factor =0.2

Contests or Consequential Effects (C)= Domestic / Office Buildings as per Table Multiplying Factor =0.3

Degree of Isolation (D)= Structure in a large area having greater height as per Table Multiplying Factor =0.4

Type of Country (E)= Flat country at any level so as per Table Multiplying Factor =0.3

Overall Multiplying Factor (M) =0.3×0.2×0.3×0.4×0.3

Overall Multiplying Factor (M) =0.00216

Overall Risk Factor  Calculated (xc)= M x P

Overall Risk Factor Calculated (xc)= 0.00216 x0.05098

Overall Risk Factor Calculated (xc)= 000110127

 Base Area of  Structure (Ab) = (LxW)

Base Area of Structure (Ab)=60×28

Base Area of Structure (Ab)=1680 Meter2

Perimeter of Structure  (P) =2x (L+W)

Perimeter of Structure (P)=2x(60+28)

Perimeter of Structure (P)=176 Meter

Lightning Protection  Required or Not

If Calculated Overall Risk Factor Calculated  > Maximum Acceptable Overall Risk Factor than only Lighting Protection  Required

Here Calculated Overall Risk Factor is 0.000110127 > Max Acceptable Overall Risk Factor is 00000001

Lightning Protection is Required

 No of Down  Conductor

Down Conductors As per Base Area of Structure  (s) =1+(Ab-100)/300

Down Conductors As per Base Area of Structure (s) =1+(1680-100)/300

Down Conductors As per Base Area of Structure (s) =6 No’s

Down Conductors As per Perimeter of Structure  (t)= P/30

Down Conductors As per Perimeter of Structure (t)= 176/30

Down Conductors As per Perimeter of Structure (t)= 6 No’s

Minimum No of Down Conductor is 6 No’s


 Results:

Lightning Protection is Required

Down Conductors As per Base Area of Structure  (s) =6 No’s

Down Conductors As per Perimeter of Structure  (t)= 6 No’s

Minimum No of Down Conductor is 6 No’s



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