What is Lightning and How to Protect Your Building Against it
Whoever said that lightning does not strike twice is wrong for lightning can strike an object twice especially tall buildings and mountaintops. There are some 100 lightning that strikes the earth every second and each bolt is close to a billion volts of electricity.
What causes lightning? An imbalance between the negative and positive charges in the atmosphere causes lightning. During a storm the rapidly moving particles of ice, rain or snow collide thereby increasing this imbalance that causes storm clouds to charged negatively. Objects down below like trees, people, houses and church spires become positively charged. These negative and positive charges create an imbalance that nature tries to fix - and that is by passing current between the opposing charges.
A stepped leader is a series of negative charges the works its way down to earth coming from the bottom of a storm cloud. Each step is about 46 metres long. When the lowermost step is about 46 metres from the ground or of a positively charged object the negative charge is met by a climbing surge of positively charged electricity called a streamer. The streamer can rise up through any object from the earth. That object could be you.
Lightning is a spectacular phenomenon of nature. However, lightning is dangerous. A reported 2,000 people are killed by lightning each year around the world. There are those who survive strikes but more often than not, symptoms such as memory loss, numbness, weakness, and other life-altering conditions are evident.
Worldwide statistics show that you have a 1 in 3,000 odd of being struck by lightning in your lifetime. Suddenly, 3,000 is not such a large number!
Do You Need Lightning Protection?
In Britain and Wales about 30-60 people are unfortunately struck by lightning each year. On average about three might be killed. In the USA, an average of 75 people is killed by lightning-related incidents. On average there are about 300,000 ground strikes of lightning in the UK yearly. Based on a ten-year period, this statistics could be expressed as one person is struck once every 6,000 strikes and one person is killed every 100,000 strikes. If there is a thunderstorm, 10,000 ground strikes can happen.
Lightning has the ability to directly or indirectly strike a person. Direct hit means the object is the positively charged component. An indirect hit would mean radial currents spreading out from the object that was hit giving someone nearby an electric shock. When lightning strikes a house a very strong current could pass along the wires and cables and metal pipes within the house. If there is a thunderstorm it is best to get off a corded phone, turn off a PC monitor that is directly connected to a phone jack and unplug all electrical appliances.
Every structure needs some form of lightning protection. There are three critical reasons why.
- To reduce the structural damage to buildings - lightning damage can be as slight as a burnt mark on a wall or the complete demolition of a building. Damage to structure could be cause by:
o Thermal damage
o Arch attachment point
o Acoustic shock wave
- To reduce damage to equipment - a direct or indirect hit can generate enough current to damage all electrical equipment and appliances inside the structure.
- To reduce danger to humans and animals - it is not a safety precaution to stay indoors when lightning strikes as it has the capacity to radiate current that could shock anyone nearby. A lightning striking a house also has the capacity to damage and adversely affect the occupants.
How Do You Protect a Building from Lightning?
There are currently companies who are producing and marketing lightning protection systems. For the most parts, the lightning protection systems are the same in principles. Here are the basic systems.
1. Lightning rods are put up on top of buildings to conduct current away from buildings to earth. Currently called "air terminals" are deemed to send streamers up at different distances and times depending to height, shape and other related factors. There are different designs of air terminals for each building type. However, air terminals do not "eliminate" lightning and they do not provide protection for the electronics within the structure.
2. Downconductors should be installed through a known route outside of a building. It is not wise to paint downcondutors because that would increase impedance or its electric resistance. A gradual bend of about 8 inches per radius is advisable to avoid flashover difficulties. You can replace downcondutors with building steel as part of the earth's electrode system.
a. Bonding insures that all the metals have the same electric potential. This means that all metallic conductors such as gas and water pipes, electrical current, phone, cable and internet lines, should be put together electrically to the earth electrode system
b. Shielding could be added to prevent higher frequency electromagnetic noise from blocking or obstructing signals.
3. Grounding should be able to deal with low resistance and low earth impedance. It is required building regulation to have a wire routinely grounded to earth before its entry to a building's main panel board. This could be achieved when all equipment within the structure are connected to a main bus bar that is connected to external grounding.
4. Surge suppressors and transient limiting devices should be installed as regular circuit breakers are incapable of handling lightning -induced transients. These lightning protection devices will protect the entire main AC electrical panel and all its secondary distribution panels, and all plug-in electronic and electrical appliances.
5. Lightning detectors can be useful for early warning. An added feature of this device is when they are connected to the main electrical panel to disengage from the main grid and switch to standby power before a potential lightning hit. These equipments still need "fine tuning" as they do not always obtain pertinent lightning data.
These installations are best done by qualified contractors. Bear in mind that these lightning protection systems will not eliminate lightning but help in limiting damages caused by one.