Calculate Lightning Protection for Building
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| Fig-1-Conventional Type Lightning Arrester |
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| Fig-2- Conventional Type Lightning Arrester installed to the particular building |
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) = 70 Meter.
- Width of Building ( W ) = 30 Meter.
- Height of Building (H) = 25 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 =0.00001
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Reference
Table As per IS:2309
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|
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Thunder
Storm Days / Year
|
Lightning
Flash Density (Flashes
to Ground /km2/year)
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|
5
|
0.2
|
|
10
|
0.5
|
|
20
|
1.1
|
|
30
|
1.9
|
|
40
|
2.8
|
|
50
|
3.7
|
|
60
|
4.7
|
|
80
|
6.9
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|
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
|
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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
|
Weighting Factors
|
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) = (70×30)+2x(70×25)+2x(30×25)+(3.14x25x25)
- Collection Area (Ac) =9063 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)= 9063x69x10–6 No’s / Year
- Probable No of Strikes to Building / Structure (P)= 0.625347 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 x 0.625347
- Overall Risk Factor Calculated (xc)= 0.001350749
Note:
Here we are getting the overall risk factor
> Maximum acceptable risk factor
That is 0.001350749
> 0.00001
Base
Area of Structure (Ab) = (LxW)
- Base Area of Structure (Ab)=70 x 30
- Base Area of Structure (Ab)=2100 Meter2
Perimeter of Structure (P) =2x (L+W)
- Perimeter of Structure (P)=2x(70+30)
- Perimeter of Structure (P)=200 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 0.001350749 > Max Acceptable Overall Risk Factor is 0.00001
- So Lightning Protection is Required for this building
No of Down Conductor
- Down Conductors As per Perimeter of Structure (t)= P/30
- Down Conductors As per Perimeter of Structure (t)= 200/30
- Down Conductors As per Perimeter of Structure (t)= 7 No’s
- Minimum No of Down Conductor is 7 No’s
Results:
- Lightning Protection is Required
- Down Conductors As per Perimeter of Structure (t)= 7 No’s
- Minimum No of Down Conductor is 7 No’s
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| Fig-3- The arrangement of Simple Lightning arrester installation with one down conductor |
