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Table 5:
Damage and loss in a structure according to point of lightning
strike (IEC/BS EN 62305-1 Table 2)
Source of
Type of
Point of strike
damage
damage
Type of loss
Structure
S1
D1
L1, L4**
D2
L1, L2, L3, L4
D3
L1*, L2, L4
Near a Structure
S2
D3
L1*, L2, L4
Lines connected to
S3
D1
L1, L4**
the structure
D2
L1, L2, L3, L4
D3
L1*, L2, L4
Near a Line
S4
D3
L1*, L2, L4
*Only for structures with risk of explosion and for hospitals or other structures where
failures of internal systems immediately endangers human life
**Only for properties where animals may be lost
Technical reference
IEC/BS EN 62305-1 - General principles
Furthermore, It defines the relationships between damage
and loss that form the basis for the risk assessment
calculations in part 2 of the standard.
Lightning current parameters are defined. These are used
as the basis for the selection and implementation of the
appropriate protection measures detailed in parts 3 and 4
of the standard.
Part 1 of the standard also introduces new concepts for
consideration when preparing a lightning protection
scheme, such as Lightning Protection Zones (LPZs) and
separation distance.
Damage and loss
IEC/BS EN 62305 identifies four main sources of damage:
–
–
S1
Flashes to the structure
–
–
S2
Flashes near to the structure
–
–
S3
Flashes to the lines connected to the structure
–
–
S4
Flashes near the lines connected to the structure
Each source of damage may result in one or more of
three types of damage:
–
–
D1
Injury of living beings by electric shock
–
–
D2
Physical damage (fire, explosion, mechanical
destruction, chemical release) due to lightning current
effects including sparking
–
–
D3
Failure of internal systems due to Lightning
Electromagnetic Impulse (LEMP)
The following types of loss may result from damage
due to lightning:
–
–
L1
Loss of human life (including permanent injury)
–
–
L2
Loss of service to the public
–
–
L3
Loss of cultural heritage
–
–
L4
Loss of economic value (structure, its content, and
loss of activity)
The relationships of all of the above parameters are
summarized in Table 5.
For a more detailed explanation of the general principles
forming part 1 of the BS EN 62305 standard, please refer
to our full reference guide ‘A Guide to IEC/BS EN 62305
Protection Against Lightning’. Although focused on the
BS EN standard, this guide may provide supporting
information of interest to consultants designing to the IEC
equivalent.
Scheme design criteria
The ideal lightning protection for a structure and its connected
services would be to enclose the structure within an earthed
and perfectly conducting metallic shield (box), and in addition
provide adequate bonding of any connected services at
the entrance point into the shield.
This in essence would prevent the penetration of the lightning
current and the induced electromagnetic field into the
structure. However, in practice it is not possible or indeed
cost effective to go to such lengths.
This standard thus sets out a defined set of lightning
current parameters where protection measures, adopted in
accordance with its recommendations, will reduce any
damage and consequential loss as a result of a lightning
strike. This reduction in damage and consequential
loss is valid provided the lightning strike parameters fall
within defined limits, established as Lightning Protection
Levels (LPL).
This opening part of the IEC/BS EN 62305 suite of standards serves as an
introduction to the further parts of the standard. It classifies the sources and types
of damage to be evaluated and introduces the risks or types of loss to be
anticipated as a result of lightning activity.