Lightning Poses Threat to Residential Electrical Networks, Even from Afar
On June 1, 2011, lightning struck Runyanya Primary School , 225 kilometers from Kampala, the capital of the Central African country of Uganda. Devastating, the electrical discharge killed 18 children and a teacher immediately. One child died from burns the following day and 50 others were injured. The accident became known as the largest number of children killed as a result of a single atmospheric discharge, says professor Hélio Eiji Sueta from the USP Polytechnic School. Since then, June 28th has been remembered as International Lightning Safety Day.
What safety measures can be taken to prevent tragedies like Runyanya from happening again? How can we protect ourselves from very strong electrical discharges, which seem to strike randomly? Professor Carlos Augusto Morales Rodriguez is a meteorologist at the Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG) at USP. He says that lightning is a way for the atmosphere to release the energy it contains: “Clouds have electrical charges and, once these electrical charges separate, they generate an electric field. When we look at water, electrically, it has positive and negative charges, but it is neutral, because the negative and positive charges are together”, explains Morales.
When we look at clouds, what we actually see are countless water droplets in chaotic motion, colliding and increasing in size. When it reaches a certain point, the drop falls in the form of rain or hail, if the weather conditions are right. In these collisions, charge transfer occurs. “And every time you have a collision, whether it’s water or ice, you have load transfer. An outer part of the water droplet is charged with one charge and the outer part of the one that bounces back is charged with another polarity. Two charge centers are created and, once the electric field is high enough to break the air resistance, lightning occurs”, explains the professor.
World champion
Morales is a collaborator on the Starnet system, a set of 12 antennas located in Latin America, Africa and the United States, which are used to monitor storms throughout Latin America using radio waves.
The researcher says that Brazil is the world champion in the number of lightning strikes, with around 78 thousand electrical discharges per year: “This is basically due to its territorial extension, which is within the tropics. The places where the most lightning strikes are in Africa and Venezuela, but they are several smaller countries. Brazil is one of the largest countries in the tropical region, which is why you have electronic activity from Roraima to Rio Grande do Sul and, as it is hot, a lot of rays are produced”, adds the professor and researcher.
The risks of lightning
Atmospheric discharges are of very high intensity: according to the Brazilian Physics Society, lightning can reach 100 million to 1 billion volts. With such strength, electromagnetic discharges pose risks to humans and electrical equipment.
Professor Hélio Eiji Sueta, in addition to Poli, is a member of the lightning protection committee of the Brazilian Association of Technical Standards (ABNT). He says that lightning does not need to strike directly on the house to cause damage, it just needs to strike nearby:
“Lightning generates an electromagnetic field that couples with everything wire and every metallic part, and this generates surges that will burn the equipment. There is also that lightning that falls directly or close to the telephone or power line and takes this outbreak into the house”.
If the electrical installation was not carried out following technical safety parameters, lightning could cause a spark in the house’s electrical network, starting a fire. Precisely because the discharge attaches so easily to metal structures, it is not recommended to use electrical and electronic devices plugged in during a storm.
“Last year alone, we were aware of at least five cases of people who died using their cell phones plugged in, because of lightning. There are also cases of people opening a refrigerator, for example,” says Sueta. Therefore, when you notice a lightning storm approaching, it is worth unplugging your equipment; however, equipment should be turned off well before the storm begins. “We were aware of people removing, for example, the TV plug during rainy periods to protect the equipment and just at that moment lightning struck. It didn’t even have to fall into the house where he is, it could have fallen on the line and he suffered a shock”, concludes Hélio Eiji Sueta.