Lightning Protection Calculation
1. Collection Area, Ac (sqm) 1.1. Rectangle Building
Length（m
）
Width
（m）
Height
（m）
Collection Area Ac
(sqm） Formula: Ac=LW+2LH+2WH+лH2
10 10 12 1032.4
1.2. Tower Radius
（m）
Height
（m）
Collection Area Ac
（sqm） Formula: Ac=л(H+R)2
10 30 5026.6
1.3. Sloping Roof (Here pitch ≧45°,if pitch <45°,adopt 1.1) Length（m
）
Height
（m）
Collection Area Ac
（sqm） Formula: Ac=лH2+2LH
20 30 4027.4
2. Flash density, Ng (per/sqkm) Thunderstor
m days per year Td
Flash density, Ng
(per/sqkm) From Curve of Table 6
20 1.10
Note: adopt for north Africa
Calculation for Evaluating Need for Protection - by BS6651
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Lightning Protection Calculation
3. Risk of being struck, p 1.1E-03 Formula: p=Ac×Ng×10-6 4. Overall risk factor
1 2 3 4 5 6 7 8 9
A Use of structure (Table 8)
B Type of
construction (Table 9)
C Contents or consequential
effects (Table 10)
D Degree of
isolation (Table 11)
E Type of country (Table 12)
1.1E-03 0.3 0.4 0.3 1.0 0.3 0.011 1.23E-05
protection recommended Overall risk
factor (product of columns 1
and 7)
Recommendations
Note: Risk less than 1×10-5 do not generally require protection;
risk between 1×10-5 and 1×10-4 protection is recommended;
risk greater than 1×10-4 require protection.
Risk of being struck,
p
Weighting factors
Overall multiplying
factor (product of columns 2 to 6)
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Weighting factors Flash density
Weighting factors Flash density
Curve of Flash density and Thunder day per year
Note: This curve is made from Table 6 of BS 6651
