What is Lightning?

 

Lightning is a sudden electrostatic discharge that occurs during

a weather event such as a thunderstorm. This discharge occurs

between electrically charged regions of a cloud

(called intra-cloud lightning or IC), between two clouds (CC lightning), or

between a cloud and the ground (CG lightning).

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The charged regions in the atmosphere temporarily equalize

themselves through this discharge referred to as a strike

(if it hits an object on the ground), and a flash, (if it occurs within a cloud).

Lightning creates light in the form of black body radiation

from the very hot plasma created by the electron flow, and

sound in the form of thunder. Lightning may be seen and not heard

when it occurs at a distance too great for the sound to carry.

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In order for an electrostatic discharge to occur, two preconditions

are necessary: firstly, a sufficiently high electric potential between two regions of space must exist, and secondly a

high-resistance medium must obstruct the free, unimpeded equalization of the opposite charges. It is well understood

that during a thunderstorm there is charge separation and aggregation in certain regions of the cloud; however the exact

processes by which this occurs are not fully understood. The atmosphere provides the electrical insulation, or barrier,

that prevents free equalization between charged regions of opposite polarity. This is overcome by "lightning", a complex process

referred to as the lightning "flash".

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The electric current within a typical negative CG lightning discharge rises very quickly to its peak value in 1–10 microseconds,

then decays more slowly over 50–200 microseconds. The transient nature of the current within a lightning flash results in several

phenomena that need to be addressed in the effective protection of ground-based structures.

 

The rapidly changing currents also create electromagnetic pulses (EMPs) that radiate outward from the ionic channel. This is a characteristic of all electrical discharges. The radiated pulses rapidly weaken as their distance from the origin increases. However, if they pass over conductive elements such as power lines, communication lines, or metallic pipes, they may induce a current which travels outward to its termination. This is the "surge" that, more often than not, results in the destruction of delicate electronics, electrical appliances, or electric motors. Devices known as surge protectors (SPD) or transient voltage surge suppressors

(TVSS) attached in parallel with these lines can detect the lightning flash's transient irregular current, and, through an alteration of its physical properties, route the spike to an attached earthing ground, thereby protecting the equipment from damage.

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It is well understood that certain parts of the world experience high storm activity and subsequent lightning strikes. What is less well known however is that the randomness of a storm event means that lightning can occur anywhere and anytime given the right conditions. Over the years industry has calculated the risk of lightning

compared to the "average strikes per square kilometer rule". In other

words if a site is situated in a red zone then it is more likely that the site will

require lightning protection equipment. This misconception has led to confusion

and inaction or incorrect specification and design resulting in a lack of site

protection.

 

For instance the rise in ionisation forward of a storm front ( sometimes as much

as 5 km) is capable of damaging sensitive electrical or electronic equipment

regardless of whether that site is directly hit by a lightning strike or not.

 

The other issue is that a site located in a 0-1 to 1 average strikes per square

kilometre per year is often misrepresented as having little to no lightning strikes.

Designers of LP systems do not use actual strike data but rather rely on

the "average strikes per square kilometer rule".

 

Based on the  "average strikes per square kilometer rule" some LP Engineers/ 

Designers have accepted that the area known as "Melbourne/Australia" 

experiences less than 1 to 5 strikes per year per square km. But what does that

actually mean? Does that mean that Melbourne has less than 1strike per km per

year?

 

If we take actual lightning strike data for the period of January 2018 for the area

Melbourne/Australia, there were in fact 23,232 lightning strikes.

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WHAT IS LIGHTNING PROTECTION?

 

A lightning protection system is designed to protect a structure from

damage due to lightning strikes by intercepting such strikes and safely

passing their extremely high currents to earth. A lightning protection

system includes a network of air terminals, bonding conductors, and

ground electrodes designed to provide a low impedance path to earth for potential strikes.

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Lightning protection systems are used to prevent or lessen lightning strike damage to structures. Lightning protection systems mitigate the fire hazard which lightning strikes pose to structures. A lightning protection system provides a low-impedance path for the lightning current to lessen the heating effect of current flowing through flammable structural materials. If lightning travels through porous and water-saturated materials, these materials may literally explode if their water content is flashed to steam by heat produced from the high current. This is why trees are often shattered by lightning strikes.

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Because of the high energy and current levels associated with lightning

(currents can be in excess of 150,000 amps), and the very rapid rise time

of a lightning strike, no protection system can guarantee absolute safety

from lightning. Lightning current will divide to follow every conductive path

o ground, and even the divided current can cause damage. Secondary

"side-flashes" can be enough to ignite a fire, blow apart brick, stone, or

concrete, or injure occupants within a structure or building. However,

the benefits of basic lightning protection systems have been evident for

well over a century.

 

Originally, scientists believed that such a lightning protection system of air

terminals and "downleads" directed the current of the lightning down into

the earth to be "dissipated". However, high speed photography has clearly

demonstrated that lightning is actually composed of both a cloud component

and an oppositely charged ground component. During "cloud-to-ground"

lightning, these oppositely charged components usually "meet" somewhere

in the atmosphere well above the earth to equalize previously unbalanced

charges. The heat generated as this electric current flows through flammable

materials is the hazard which lightning protection systems attempt to mitigate

by providing a low-resistance path for the lightning circuit.

 

RISK MITIGATION. No lightning protection system can be relied upon

to "contain" or "control" lightning completely. Nor thus far, to prevent lightning

strikes entirely.

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Steel framed structures can bond the structural members to earth to provide

lightning protection. A metal flagpole with its foundation in the earth is its own

extremely simple lightning protection system. However, the flag(s) flying from

the pole during a lightning strike may be completely incinerated.

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The majority of lightning protection systems in use today are of the traditional Franklin design. The fundamental principle used in Franklin-type lightning protections systems is to provide a sufficiently low impedance path for the lightning to travel through to reach ground without damaging the building.This is accomplished by surrounding the building in a kind of Faraday cage. A system of lightning protection conductors and lightning rods are installed on the roof of the building to intercept any lightning before it strikes the building.

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LIGHTNING PROTECTION IN A HAZARDOUS AREA

 

Whilst simple apparatus such as Franklin Rods are acceptable for use in non-hazardous environments, their use in a hazardous area or near a classified Zone0/1/2/20/21 & 22 should be carefully considered. A Franklin Rod and subsequent copper down conductor positioned near or within a hazardous area, dangerous goods area or classified Zone Zone 0/1/2/20/21 & 22 could introduce an ignition source and result in a fire or explosion.

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The popularity of ESEs for use in hazardous area, dangerous goods area or

classified Zone Zone0/1/2/20/21 & 22 applications has increased over the

last 10 years. However even the use of ESEs in hazardous area, dangerous

goods area or classified Zone Zone0/1/2/20/21 & 22 should be well researched

prior to installation.

 

The electrical earth installed by your electrician is there to protect the internal

workings of the electrical system in your building to accommodate everyday

electricity usage. The electrical earth is not designed to handle the mega

electricity (100 million + volts of power or 200 kA of electrical energy) that a typical

lightning strike can release.

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IT IS CRITICAL THAT YOU UNDERSTAND YOUR RESPONSIBILITY AS THE SITE

OWNER AND THE COMPLIANCE REQUIREMENTS AS SET OUT IN AS/NZS 1768: 2018.

 

LP SYSTEMS ARE COMPLEX AND REQUIRE EXTENSIVE ENGINEERING AND DESIGN.

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HOW CAN WE HELP?

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Our approach is simple: LIGHTNING PROTECTION IN A HAZARDOUS AREA REQUIRES CAREFUL 

CONSIDERATION. THE CONSEQUENCES OF POOR DESIGN OR INCORRECT SPECIFICATION

CAN BE DIRE.

 

AUDIT + TEST + SPECIFICATION = DESIGN & LIGHTNING PROTECTION PLAN

 

Once we have gathered together all of the information required and validated the findings of our audit under test, we work with our engineering team to provide detailed design and drawings, including specification of equipment.

 

If you have been specified lightning protection equipment without conducting the necessary audits and tests, then you may be operating with equipment that is not suitable for the application.