About lightning ...
Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions in the atmosphere or ground temporarily equalize themselves, this phenomenon releases an enormous amount of energy which causes extensive damage to structures and puts people’s lives in danger.
Before to consider setting up a Lightning Protection System (LPS), it is essential to understand how lightning is created to evaluate what is the best solution to protect infrastructure and people.
The following information brings together statistical data and graphical representations to support understanding of lightning phenomenon.
Global total lightning density
Global total lightning density
In 2019, 2,353,476,704 lightning events have been detected.
Lightning activity is different depending on our location, we note that all the countries close to the equator have a very important lightning density, indeed hot and humid regions favor formation of thunderstorms.
Thunderstorm formation
A thunderstorm is formed when the warm, moist air rises into the cold air. The warm air becomes cooler to form small water droplets (condensation) while the cold air has ice crystals.
During the storm, the droplets and crystals bump together and move apart in the air. This rubbing makes static electrical charges in the clouds.
Average data: 24 km diameter and up to 14 km height.
Charge distribution in storm cloud
When the concentration of charges is high it generates the formation of “streamer” also called “leader”, it can be ascending or descending (upward or downward leader).
When two opposing charge leaders meet, it creates a charge transfer (lightning strike) from one region to another.
Lightning facts: A typical lightning strike on a tree
- 100 lightning strikes per second (worldwide)
- Triggering of lightning is generated at 8 Km altitude
- Air temperature around lightning is about 20 000 °C
- 300 million Volts
- Lightning current : 30 000 A (ampere)
- Nasa has recorded strikes until 200 KA
Lightning damages : Direct strike effects
Lightning damages : Indirect strike effects
The 5 lightning mechanisms that cause injury
1 : Ground current
50 -55 % of lightning deaths
The ground current is the most frequent lightning mechanism identified among the injuries and deaths caused by lightning.
When the lightning strike reach the ground, the lightning current is dissipated around the earth surface and can travel several dozens of meters and endanger people who are near the mean impact.
The step voltage between the feet of a person standing near an energized grounded object. It is equal to the difference in voltage, given by the voltage distribution curve, between two points at different distances from the electrode.
2 : Side Flash / sparking
30 -35 % of lightning deaths
3 : Upward leader
10 -15 % of lightning deaths
4 : Contact voltage
3 – 5 % of lightning deaths
5 : Direct strike
3 – 5 % of lightning deaths
We hope that this content which aims to present in a simple way how lightning strike works and which highlights the risk it involves in our daily life has help you to better understand lightning phenomenon.
From these concepts, you will be able to understand how lightning protection technologies works and we will see how to select adapted protection according to your project.
