Unsustainable trends in lightning protection industry

[Trang Bui]

Jaouad....@univ-lille1.fr
Pr. Jaouad ZEMMOURI University of Science and Technology –
Phlam Laboratory
Lille- France

Every single second, 50 to 100 lightning strike the Earth’s surface.
This natural phenomenon has always caused fascination, not only
because of its beauty but also because of its destructive power.
Statistics of damage caused by lightning are rather impressive: around
2 000 people are killed each year, thousands more survive with
sequels, and material damages are estimated in the order of $4-$5
billion in the US only. The widely extended belief that lightning
strike is completely random is actually untrue: shape of the
structures and objects and its conducting properties largely condition
strike probability (for instance, the Empire State building is stroke
between 20 and 25 times each year).


Protection against lightning is widely justified by these facts, and
is nowadays systematically applied to populated areas and industrial
sites. Several standards and technical whitepapers regulate and even
impose the installation of lightning protection systems in all these
sensible areas. As a consequence the industry developed around
lightning protection deals with an increasing business: it is
estimated that this market will amount up to $695.5 million in
2011(1).


Without any doubt, the main milestone in lightning protection is the
use of a single rod as a lightning receptor, by Benjamin Franklin
(around 1750). Ever since, the image of a single lightning rod topping
tall buildings has remained in popular culture as the protection
system. However, other system proposed by Maxwell (in 1876), the so-
called Faraday cage or mesh cage, is also widely applied nowadays. The
working principles of those systems (Single rod and Faraday cage) are
almost antagonists.

[PICTURE]

Figure 1: The Lightning mechanism. In charged clouds, certain not well
known physical processes lead to a descending plasma (electrically
charged) channel. As it approaches the ground, it causes electric
field at the earth’s surface to rise dramatically, causing ionisation
of air. This effect is more pronounced in sharp edges, and takes place
in many different points and objects (picture on the left). Free ions
follow electrical field and therefore progress towards the descending
plasma channel, forming ascending channels. When one of these channels
contacts the descending one, a strong electrical discharge takes place
(picture on the right). All other ascending channels are dissipated.


The Single rod takes advantage of the mechanism of lightning itself.
Although very fast for the human timescale, lightning is indeed a
complex process (see Figure 1), in which a plasma channel descending
from the cloud towards the ground causes the apparition of other
plasma channels ascending from the ground (2). When one of these
ascending channels (whose creation is favoured by sharp edges) enters
in contact with the descending one, a strong electrical current is
established, giving place to the characteristic light flash and shock
wave (thunder) that we all identify as the lightning strike. Single
rods are placed in high spots, seeking to ensure that the ascending
plasma channel originated at the rod is the one that will establish
contact with the descending one in first place. The electrical
discharge is then guided to the ground through a metallic guide.

Mesh cages do not take account of the nature of lighting, but only of
the simple fact that electromagnetic fields do not propagate inside
cages formed by electrical conductors. A protection system based on
this principle does not aim to attract lightning towards a specific
point, but rather expects it to hit anywhere along a grid of metallic
conductor, which will then guide the discharge towards the ground.
Obviously, for this type of system to be effective, the grid of
conducting wire must be dense enough to avoid lightning striking in
unprotected areas between wires.

There is a remarkable unbalance between the amounts of attention that
the research community has devoted to each of the types of lightning
protection systems. Single rods have been subject of intense research
during the last half century. Part of this activity has focused on the
(still ongoing) assessment of the performance of evolved forms of the
single rods, namely the ESE devices. Another significant part of this
activity has been devoted to develop the so-called electro-geometrical
model and its derived engineering methodology (the most relevant one
being the “Rolling Sphere” method), which allows designing consistent
protection structures. This contrasts with the background behind
Faraday cages, whose installation still relies in the meshwork method,
largely based on accumulated experience, rather than theoretical
deduction (3).

At present, both types of protection systems coexist and are employed
massively. So far there is no scientific evidence that one of these
types of protection will be better than the other, although it is
commonly agreed that poor installation design dramatically decreases
the efficiency of the protection system4. Nevertheless, there is no
discussion around the fact that scientific research is the only way
that will allow developing more efficient lightning protection systems
through a better understanding of the amazingly complex subject of
physics of lightning.

The importance of the scientific debate has overshadowed some other
issues which have nevertheless become crucial in the dawn of the 21st
century. Last decade has seen the economical rise of countries like
China or India, which enormous populations concentrating into large
cities and developing large industrial sites. The acceleration of
consumption has made obvious that it is impossible to conceive a
highly developed society at a global scale without focusing into
industrial production schemes that are sustainable. However, this is
not the case of some of the models proposed by the lightning
protection industry. Both types of protection systems, single rods and
Faraday cages, are mainly composed of metal, particularly copper, in
the form of large section wire. Although copper has been known and
used since at least 10 000 years, 95% of the overall amount has been
mined in the 20th century. Price of copper has multiplied by 5 in the
period 1999- 2006 only.


In the case of single rods, two wires are used to guide the discharge
from the rod itself towards the ground, so the amount of wire used is
roughly equivalent to twice the height at which the rod is placed. In
the case of Faraday cages, a much larger amount of copper wire is
needed in order to build the grid which wraps around the whole
structure to be protected. Figure 2 shows a comparison of the amount
of copper needed to protect a medium-size basement following current
standards. This example illustrates how a protection based in a
Faraday cage type of system does not fall at all into a sustainable
logic. It may be argued that such type of systems is only to be used
in high risk sites, and not as a general use protection system.
However, as it has been already discussed, there is no proof that the
Faraday cages will perform better than a consistently constructed
single rods structure, which will be much less consuming of natural
resources.


All the facts listed concern a situation which is amazingly complex,
and precisely because of this very vulnerable to abuse. The search for
protection against a powerful and destructive natural phenomenon is
legitimate. The fear against lightning is as old as humanity itself
and therefore plenty of prejudices and myths, some of them senseless.
Care should be taken that the irrational part of this fear does not
interfere both with the scientific debate and the common sense of good
resource management. The need of protection has allowed the
development of some industry which cannot face the current needs of
sustainability and management of natural resources. This situation
strikingly contrasts with the general political and social trend,
which is forcing industry and consumers to adopt responsible aptitudes
through regulation and policy making (a recent example of this could
be the interdiction of manufacturing and sales of incandescent bulbs
for lighting in the EU, in 2009). As it is yet to be proved that these
resource consuming systems offer better protection than other existing
technologies, it is time to take these important socio-economical
factors into account and proceed accordingly.

[PICTURE]

Figure 2 - The schematic representations above correspond to lightning
protection systems of single rod type (left side) and mesh cage type
(right side), designed to protect a basement measuring 40 meters long,
20 meters wide and 10 meters high. It is assumed that the building has
a poor conducting structure, as wood. The systems have been designed
following the specifications of standard 62 305-3, to achieve
protection of level II. The red lines represent the copper wiring with
section of 50 mm2. Taking into account the lengths of wire and the
density of copper (8920 kg/m3) we can estimate the amount of copper
used in the installations, which is approximately 22 kg in the Single
rod type, and 217 kg in the Faraday cage


The impracticality of the Faraday approach becomes evident as soon as
calculation is applied to a group of basements, like those which could
be found in almost any neighbourhood or industrial area. The red
region shown in the left picture contains a group of 52 buildings,
each one with dimensions similar to the example calculated above.
Protection against lightning of the basements will require 11.3 tons
of copper, using mesh cage systems. The large green field appearing
the top right of the picture cannot be protected. In contrast, the
whole area could be protected using two single rod system, which will
need of 1,1 kilos of copper. Single rod type allows improving
protection over wide open spaces such as the green field of the
picture. The region protected is still a minuscule fraction of a
populated area, in this case Metropolitan London (pictured on the
right).

1 See « World Lightning Protection Technologies (LPT) Markets, by
Frost & Sullivan, June 28, 2005.
2 In purity, this is only one possible mechanism (the most commonly
found in nature). The other situation, with first plasma channel
moving
from the ground towards the cloud, can also be observed.
3 See « A Discussion of ‘Faraday cage’ lightning protection and
application to real building structures » by M. Szczerbinski; J.
Electrostatics, 48, 145-
154 (2000).
4 For an updated study, see « New guidelines regarding the positioning
of prospective air terminations on structures using e-field modelling
techniques ». F. D’Alessandro, J. Electrostatics, 67, 501-506 (2009).

For the article with pictures, please visit: http://www.intlpa.org/ilpa.html
or: http://intlpa.blogspot.com/2010/06/unsustainable-trends-in-lightning.html