Who loves the lightnings?

Prof. Dr.Sc.Techn. Eng. Stefan Iliev, ROSTI Ltd. Bulgaria

 

The threat of striking lightning is greater for Bulgarians, than elsewhere. Bulgaria is a region with powerful lightning activity. This is why lightning frequently strikes cattle and people, and the fires caused by them lead to considerable losses.

 

WHAT IS LIGHTNING

Opposite electric charges are created through induction between clouds and objects on earth. Owing to electrical conductivity of the air and the medium between them an electric arc - lightning - arises, accompanied with a sound - thunder.

Metal objects. Wet trees, the bodies of live creatures attract lightning. The passing of lightning current prefers vertically situated objects with a horizontal orientation, such as for example, fences, thus expanding the range of damage.

Michael Faradey (1791-1867), the English physicist and chemist has proven that in a metal cage the external electromagnetic field, including lightning, did not provoke a devastating effect.

Another fact is that the interval between the lightning and thunder indicates the proximity of the lightning. An interval of 1 second corresponds to about 330 m the place where the lightning struck.

 

WHEN WE ARE TRAVELING

When we are traveling in a car, bus, truck or tractor, the metal body functions as a cage of Faradey and protects the passengers from lightning. Nevertheless the driver may take fright and lose control over the vehicle.

Experience has shown that when there is lightning there may be a threat for the wheels of the car. Rubber is a good insulator, however they could be damaged by the heat of the current from the lightning.

This is why it is recommended that drivers who find themselves in a strong storm to do the following:

• stop and park the vehicle;
• pull in the aerial, as the tallest point of the car;
• not leave the closed space of the car until the storm passes;
• to stop the trip, and afterwards reduce the speed to a minimum.

The lightning might have affected traffic lights, street lights, or warning signalization at level crossings, pylons or trees may have been knocked down.

It is best for cyclists to seek shelter in a house, in some vehicle, under a steel bridge or a concrete bridge, keeping away from the bicycle.

If this is not possible get off the bicycle or motorbike, get away several meters from them and kneel in some hollow.

There have been cases of lightning striking planes in the air or on the ground. Usually there are no consequences. Once again here we have the effect of Faradey's cage. No doubt lightning can damage some electronic instruments on board and affect flying control.

 

WHEN THERE IS A STORM IN THE FIELDS

There are two risks:

• a direct strike from lightning, when the person is at the highest point;
• when the lightning falls near by has an indirect effect on the person, as the current in the earth spreads in all directions and causes what is known as 'foot tension'. This tension between the legs can be a threat up to about 20 meters from the place where the lightning has struck.

 

The current which passes through the human body can cause burns, temporary paralysis or death.

The threat is smaller is one kneels in a hollow, with the hands around the legs, the feet one over the other. In this way 'foot tension' is lowest.

By no means should one lie on the ground.

Cattle, horses and other quadrupeds are much more threatened by indirect lightning than humans as the difference in the tension between the front legs and the hind legs is considerably greater.

This is why one should get off the horse he is riding.

 

DANGEROUS PLACES DURING A STORM ARE THE FOLLOWING:

• the periphery of the forest with tall trees;
• top of mounds and hilltops;
• metal fences, as the earthing may not be sufficient, and they can conduct the current from the lightning over hundreds of meters;
• separate trees, raising with out-spread branches.

 

A storm is a real threat if the time between lightning and the thunder is less than 10 sec. Then one should take shelter:

• in a car (the best possible protection);
• in a building (preferably with an anti-lightning protection);
• in a forest (the distance to the lower part of a tree if possible non-less than 3 m).

 

If a storms sets in by surprise and it is not possible to find shelter, when the time between the lightning and the thunder is less than 5 sec, all we can do is to kneel to the earth.

If there is a group the distance between everyone in the group should be 3-5 meters.

 

IT IS WRONG TO DO THE FOLLOWING:

• running and lying down on the ground;
• staying at the edge of the forest or under separate trees;
• staying at small distances from one another in a group;
• touching metal objects.

 

WHEN HAVING A BATH IN THE BATHROOM

When a lightning strikes it is possible that a minimal part of the current may pass through the metal pipes of the water supply system.

In spite of that there is no risk, when touching the water tap or below the shower, if the water supply system in the building is earthed according to technical requirements.

 

STORMS AT CAMPING SITES

The risk of lightening at camping sites is reduced if the camping site is suitably chosen.

This can be done with the application of small and simple protective measures:

• do not camp close to pylons, forest edges or separate trees;
• it is dangerous to camp on hilltops or open fields;
• camping in suitable in a forest, the distances being minimum 3 m.

 

SUNSHADES AND UMBRELLAS ARE DANGEROUS

As they strongly attract direct lightning. When a storm breaks out both sunshades and other sharp objects should be left on the ground. Lakes and rivers are more dangerous than the sea. Marine water has more salt and less electrical resistance.

 

FIRST AID

If someone has been struck by lightning his heart may stop. In such cases artificial respiration should be undertaken and a massage of the heart.