
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)= 7389x69x10–6 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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