Conclusion from R1 Evaluation

Because R1 = 4.08 x 10-5 is greater than the tolerable value RT = 10-5, lightning protection for the structure is necessary
 
Selection of protection measures
 
Table -12: Composition of risk R1components according to Zones (value x 10-5)
Symbol Z1

Entrance area

Z2 Garden Z3 Archive Z4 Offices Z5 Computer centre Structure
RD 0.002 0 2.21 0.177 0.016 2.405
RI 0 0 1.542 0.123 0.01 1.673
TOTAL 0.002 0 3.752 0.3 0.026 4.08
RS 0.002 0 H 0 H 0 H 0 0.002
RF 0 0 3.752 0.3 0.026 4.08
RO 0 0 0 0 H 0 0
TOTAL 0.002 0 3.752 0.3 0.026 4.08
Where
RD= RA+ RB+ RC; RI= RM+ RU+ RV+ RW+ RZ
RS= RA+ RU; RF= RB+ RV; RO= RM+ RC+ RW
And RD - risk due to flashes striking the structure; RI – risk due to flashes influencing the structure; RS – risk due to injury to living beings; RF risk due to physical damage; RO – risk due to failure of internal systems

The composition shows that the risk for the structure is mainly due to physical damage in the zone Z3 caused by lightning striking the structure or the connected lines; the risk of the fire (physical damage) in the zone Z3 is 92 % of the total risk.
 
According to Table -12, the primary contributing factors to the value of risk R1 in zone Z3 are due to
 
- component RB
(lightning flash to structure) for 54 %
- component RV (power line)
(lightning flash to power line) for 9 %
- component RV (tele line)
 (lightning flash to tele line) for 29 %
To reduce the risk to the tolerable value, the following protective measures could be adopted.
 
    • protect the building with a Class IV LPS conforming to IEC 62305 – 3 to reduce component RB.
      • PB = 0.2
      • PU = PV = 0.03 (due to SPDs on incoming lines)
    • install in the archive (zone Z3) an automatic fire detection system, to reduce component RB and RV in this zone and SPDs of LPL IV at the entrance point in the building on both the power and tele lines.Parameters in the Tables 2, 3 and 6 will change as follows:
      • rp = 0.2 only for zone Z3
      • PU= PV = 0.03 (due to SPDs on incoming lines
The changes in the values of risk for each zone are given in the Table– 13
 
Table – 13: Values of risk R1 according to solution chosen (values x 10-5)
Solution Z1

Entrance area

Z2 Garden Z3 Archive Z4 Offices Z5 Computer centre TOTAL
Solution a) 0.002 0 0.488 0.039 0.003 0.532
Solution b) 0.002 0 0.451 0.18 0.0158 0.649
Both solutions reduce the risk below the tolerable value
 
The solution to be adopted is subject to both the best technical criteria and the most cost effective solutions.