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by Dr. Chandima Gomes,Chartered Physicist (UK) & Senior Lecturer in Physics, University of Colombo

Lightning protection has become the talk of the town these days. However very few have a clear idea what lightning protection is.

"Although the first lightning season of the year has started, the most intensive stage is yet to come". This may not be good news for you. Whether you are an owner or administrator of an industry, a maintenance engineer, a military officer or even a simple civilian who owns a few modest household electronic items. Lightning may cause you sleepless nights.

Most importantly lightning cause human casualties. Lightning ignites fires that may bring your entire building or house down to ashes. At a lower degree of damage, the lightning current may destroy your electrical, electronic and communication equipment beyond repair. However one of the most significant loses that lightning may cause as far as industries are concerned is the down time.

A couple of hours of standstill of normal operation or a loss of some important data stored in a computer may cause a company an economical loss of several millions. Thus now, lightning protection has become the talk of the town. However very few have a clear idea of what is lightning protection and how it could be achieved.

What is lightning?

A lightning flash originates inside a cloud, several kilometres above the ground level. Except for ball lightning, which is a very rare phenomenon that we will discuss later, lightning is simply an electric spark between a cloud and ground, between two clouds or between two parts of a cloud. The spark that jumps between the ends of two wires, which are connected to the terminals of a car battery, is a very basic form of lightning.

In the first stage of the lightning strike, a channel of charge flows towards ground from the cloud. When this channel is above 50-100 metres above, earthbound objects in the vicinity (eg. trees, buildings, human beings, animals etc.) start sending upward channels of opposite charge to meet the downward channel from the cloud. One of these upward channels succeeds in meeting the downward channel first. Subsequently a large current will flow through the object, which sent that upward channel. Then we say that the object is lightning struck. If your building is a tall protrusion in a certain landscape it may be the unfortunate object that sends the first upward channel that meets the downward stream of charge from the cloud.

How does lightning cause damages?

Lightning may cause damages to your building and equipment in three ways. When your building attracts a downward lightning leader (direct strike) or attract a part of a lightning flash that hit another structure in the near proximity (side flash) you will get the maximum damage. The lightning current reaches a maximum value of about 30,000 Amperes on average but current in the range of 300,000 Amperes are also reported.

Simply compare this value with the current drawn by your refrigerator, which is about 10 Amperes. The lightning current heats its path to a temperature of about 40,000 Celcius.

Compare this value with the temperature on the surface of the sun, which is about 5000 Celcius. The enormous current involved with the lightning flash may destroy the entire power and communication networks in your building including all the equipment connected to the networks. The high temperature resulted by both the current that flows in the lines and the sparks that jump in between different parts of the building may trigger fires that will completely burn out your installation.

Direct lightning (or side flashes) cause damages at a very rapid rate so that once your building is lightning struck it is very unlikely that you can prevent any of the damages to the equipment and human injuries (still you can prevent the spreading of the fire by acting quickly).

The second mode of getting lightning currents into your installation is through the service lines such as power, communication and cable TV. Once lightning strikes a service line, fractions of the lightning current enter all the nearby buildings and may destroy all the equipments that are plugged into the system.

The lightning current may also injure the users of equipments connected to service lines. This mode of intrusion of the lightning current cause less damages than a direct strike, yet service lines are subjected to lightning strikes much more frequently than buildings themselves.

The lightning current that flows from cloud-to ground is a good emitter of electromagnetic radiations. Thus once a lightning hit a nearby object (say at 500 m) even your building is exposed to a strong dose of electromagnetic radiation. When this radiation passes through electronic equipments such as computers, medical equipments, military equipment etc. the sophisticated parts of them can be destroyed. This may happen even when the equipment are unplugged from service lines. However, the chances of ordinary electrical equipment getting damaged due to such radiation is very slim.

What is lightning protection

The above three modes of lightning threats can be eliminated by three types of lightning protection systems. A person who seeks lightning protection should clearly understand this difference.

In the commercial language a building protection system is referred to a network that is meant to protect a building from direct lightning strikes and side flashes. An ordinary building protection system consists of one or several sharp pointed rods (or a mesh of metal stripes/wires) installed at the roof of the building (called air termination), several metal stripes or metal wires from roof to base (down conductors) and one or several conducting rods buried in the ground (earth conductors).

The down conductor system connects the air termination to the earth conductors. When a downward channel comes from a cloud, the air termination sends an upward channel much faster than the other parts of the building thus the lightning is attracted to one of the rods (or to the metallic mesh). Then the lightning current is safely passed into earth through the rest of the system.

Thus, instead of repelling a lightning channel, a lightning protection system attracts that. However, as the lightning current is safely driven into earth the building will not be damaged. The above system is called the "Frankling Rod System", named after Benjamin Franklin who first proposed lightning rods in 1749.

Whatever building protection you select for your installation you have to make sure that the system follows certain standards. As we do not have proper lightning standards in Sri Lanka yet, we have to depend on some other recognised standard such as International Standards (IEC), British Standards (BS), Australian National Standards, American Standards (NFPA 780) etc. However one would find that implementing a Franklin Rod System according to an international standard is very costly.

As a remedy to this drawback of the conventional Franklin Rod System, during the last few decades a new mechanism is proposed to attract lightning much faster than a conventional air termination. Today we refer the air termination systems that apply this new mechanism as "Early Streamer Emmitters (ESE)". A majority of lightning protection systems available in Sri Lanka are ESE or similar types. There is a hot debate going on at the international level regarding the acceptability of the ESE devices.

Therefore it is worth looking at the present situation of the ESE devices with an academic viewpoint.

The ESE concept was developed, based on a premise that some form of a sophisticated device, connected to the air termination system could launch an answering leader much earlier than the conventional Franklin Rod. Therefore the lightning rod with the ESE device attracts the downwards-lightning leader much fast than any other object would do so.

The first generation of such devices used ionisation properties of radioactive materials as the streamer stimulation mechanism. A couple of decades ago these systems were completely discarded and even banded in many countries not solely for its inability to prove the claimed efficiency but due to the health hazards of radiation as well.

Lightning repeller! Do they work?

One of the new concepts developed in the last decade in lightning protection proposes a device that can repel or neutralise a lightning leader so that it has no harm to the protected site. This radical concept is highly advantageous in the protection of buildings (especially high risk installations) if the claimed performance of the device is true.

Unfortunately still only a very few scientist at the international lightning community accept this concept while the rest strongly oppose it at the fundamental level. None of the national or international standards in the world have adopted this technique so far. Thus, in the present context the theory behind lightning elimination systems is simply a hypothesis to be experimentally proved and justified.

Protection of high-risk installation

It should be clearly understood that the protection of high-risk structures needs special designs in contrast to low-risk structures irrespective of the type of protection system selected.

High-risk structures include explosive industries, industries of toxic chemicals, military bases with ammunition and explosive stores, high voltage lines and power plants, oil refineries, nuclear plants etc. Typically for these high-risk structures, tall masts or overhead grounded shield wires located above the structure to be protected are designed.

Here, the idea is to collect the lightning above the structure, not directly on it so that any risk of interacting the lightning current with the risky areas of the structure or with dangerous substances is completely excluded.

Protection from current surges through service lines

With the above-described systems your building is protected only from direct strikes and probably from side flashes. Still your building can be penetrated by lightning currents that propagate along service lines (power, telecommunication etc.). There are special devices (surge diverters or surge suppressors), which prevent these current impulses from entering your building. A surge diverter is connected at the entrance of the service line to the installation.

At high level of protection they are connected at the power socket of each electrical or electronic equipment as well. Under normal operation the surge diverter does not interfere with the line signals.

In the case of a lightning invasion it provides a convenient path for the lightning current to divert into the earth without permitting it entering into the building or the equipment.

Surge suppressor, which have to be connected to protect power lines, communication lines and data lines, are different from one another. Make sure that you go for a recognised brand of surge suppressor, as the performance of such a device is difficult to be predicted unless it has a proven laboratory test report.

Electro Magnetic Compatibility (EMC)

The sophisticated electronics in your building can also be damaged by radiation, which will be emitted from the lightning flash, electromagnetic radiation propagates in free space. This radiation can be prevented from entering your building by taking suitable protection measures. The typical method of radiation prevention is to screen the building with a conductive material so that the building becomes a "Fraday Cage".

As it is very costly and unnecessary to screen the whole building it is recommended to take safety measures only to compartments of the building where sophisticated electronics are installed (such as computer rooms, medical theatres and scanning rooms, control chambers of power plants, airports, military bases, and communication bases etc.).

Design and implementation of protection systems that prevent the intrusion of undesired electromagnetic impulses through both radiation and conduction is termed Electro Magnetic Compatibility (EMC). This newly emerged concept of electromagnetic protection is a huge business in many developed countries but rather unheard to the Sri Lankans. Hence for an interested entrepreneur a tremendous opportunity is opened in the industry of EMC in Sri Lanka.

Fireballs out of the sky! Is it possible?

Sometimes people have observed balls of fire emerging from the sky in overcast conditions. They are now termed ball lightning. These fireballs are reported as having a size varying from that of a peanut to greater than that of a football. Their colour varies from pale yellow to glittering red. It has been seen that ball lightning moves at walking pace and also travelling along transmission and power lines.

Some people believe that water attracts ball lightning. There are some cases where people have seen fireballs jump into water and vanish with a hiss.

It has also been reported that once a ball lightning passes over some one's body the flesh and skin along the path will be burnt to ash while the person get no feeling of heat.

Despite all these observations, still the scientists have failed to come up with a concrete explanation for ball lightning. There are several theories put forward in this respect. At present, those are being discussed and reviewed by the scientific community. Nobody has yet succeeded in giving ball-lightning-protection at any level.

Few tips for the lightning protection seekers

It is always much less costly to design and implement the lightning protection system as that constructions stage of a building rather than doing so after the building is constructed. It is also advisable to get your entire lightning protection network from one company or consultant to avoid complexities that may arise afterwards. Always keep a blueprint of the lightning protection network so that the future modifications to the building can be done without disturbing the lightning protection system.. Make sure that your lightning protection consultant inspect the system at least once in every six months.

With all these protection systems still nobody can guarantee you 100% protection from lightning.

The company, which provides lightning protection, will give a certain level of protection (by a percentage) related to the system you buy. The cost of the system depends on the level of protection. For an example a nuclear power plant or a store of explosives and ammunitions may need a level of protection of about 99.99% (a highly expensive system) while that of 75% may be acceptable for an ordinary house.

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