17.3.4 Lightning protection measures
17.3.4.1 External lightning protection
When lightning strikes an OOI, the lightning currents and the spurious signal generated
interact with the equipment by a variety of mechanisms: capacitive, magnetic
and conductive coupling, direct arc-over and potential rise. The primary effects of
direct lightning strikes on OOIs are shown in Figure 17.3. As can be observed,
direct damage to equipment, containers and electrical systems occurs. In addition,
there might be a loss of production, risk of fire and explosion, generation of spurious
signals, and so on. Damage can be reduced or avoided through the installation of
an ELPS.
The International Electrotechnical Commission (IEC) is the recognized entity in
many countries around the world for lightning protection standards. Thus, IEC standards
and others [10–12,15–17,22,24,25] give sound guidance on lightning protection
and on the philosophies underlying the general principles. However, there is a lack
of information concerning OOIs and other special installations.
In dealing with lightning protection of OOIs, two key assumptions are made: (i) it is
a very risky installation and (ii) its structure is generally metallic. The first implies
that a risk assessment is irrelevant as lightning protection should be provided to
ensure that the maximum level of protection is given. The latter implies that much
of the equipment and many devices could already be protected against direct lightning
incidence by the metallic structure itself (which provides a ‘natural’ air terminal).