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
