Calculate Lightning Protection for Building

Calculate Lightning Protection for Building

Fig-1-Conventional Type Lightning Arrester

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

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

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

Fig-3- The arrangement of Simple Lightning arrester installation with one down conductor