This Presentation bout Lightning Accidents.

1. Unit 17
Lightning Accidents
1

2. 2
 Lightning causes loss of human, animal and plant life.
 There are seasons in which the lightning accidents are more frequent.
 The lightning activity is at peak in the months of March-April and October-November.
 Meteorologists call those two periods inter-monsoons.
Nature of the atmosphere during the periods of inter-monsoons.
 Having high temperature close to the Earth.
 Blowing of wind is low.
 The amount of water vapour in the atmosphere is high.
 This water vapour rises up and also gets cooled forming clouds.

3. 3
 Cumulonimbus is the type of cloud that contributes most to lightning.
 Generally, these are located at a height of about 15 000 m from the ground
level.
Cumulonimbus cloud

4. 4 How lightning occurs?
 Clouds contain crystals of snow and tiny droplets of water.
 Insides the clouds, wind blows fast from the bottom to the
top.
 This makes crystals and water droplets rub each other.
Because of this rubbing electrostatic charges are formed in
the crystals and water droplets.
 In a cumulonimbus cloud positive charges
accumulate in the upper region whereas negative
charges get collected in the lower region.

5. 5
 The air in a cloud is an insulator. Hence electrical charges do not flow easily
through air.
 Therefore, a large amount of electrical charges accumulate in the upper and lower
regions of a cloud.
 When, very large amounts of charges are developed like this, a moment will arise
where electricity can flow even through air.
 A jump of electrical charges or an electric discharge is known as lightning.

6. 6
Types of lightning
Depending on the sites between which the charges jump, lightnings are classified
into three types.
1. Cloud to cloud lightning
2. Cloud to air lightning
3. Cloud to ground lightning

7. 7
1. Cloud to cloud lightning
 A jump of charges either
between two regions of a
charged cloud or between
two clouds with different
charges is referred to as a
cloud to cloud lightning.
2. Cloud to air lightning
 Discharging of charges
accumulated in a cloud
occurs to surrounding air.
3. Cloud to ground
lightning
 Discharging of
charges
accumulated in
a cloud to the
earth

8. 8 Lightning and thunder
Information related to cloud to ground
lightning.
The voltage - 10 million
The amount of current – 25 000A
Temperature – 30 000°C
 Due to the high air temperature, around the
lightning current expands instantaneously.
 When air expands at once like this,
first a wave is generated followed by a sound
wave. The result of the sound wave is the
thunder.

9. 9
How lightings get earthed
There are four ways by which lightings get earthed
harming humans and animals and damaging buildings.
1. Direct strikes
2. Side flashes
3. Contact voltages
4. Step potentials

10. 10
How lightings get earthed?
1. Direct strikes
 A strike of a lightning on
a solitary man, tree or a
building standing on a
flat land is known as a
direct strike.
 The lightning current
flows to the Earth
through his/her body.
2. Side flashes
 A bolt of lightning hitting a
tall building or a free passes
into the Earth through it and
during its passage may side-
step from it and get earthed
through the body of a man
standing near by.
3. Contact voltages
 Being struck by a lightning at
a time of its production
because of touching domestic
electrical appliances or using
cellular phones is known as a
contact voltage.

11. 11
4. Step potentials
 When a lightning strikes a building,
a tree or the ground the lightning
current spreads in every direction
from that place.
 Suppose a person or an animal is
standing within such a spread area.
 The lightning current that enter the
body of that man or the animal from
one leg will pass through the other
leg. This phenomenon is called step
potential.
 An ox is hurt more than a human by a step potential.
 It is safer to keep the two feet closer at a time of
lightning.

12. 12
Prevention of lightning accidents
• Fixing lightning conductors for tall buildings and
maintaining them properly.
² Installing earth wires properly in domestic electrical
circuits
² Disconnecting all electrical appliances from the
circuit

13. 13
Ensuring safety from lightning accidents
² Not staying in open areas such as playgrounds, tea
plantations and paddy fields
² Refraining from using equipment such as mamaty and
crowbars
² If it is required to stay in an open area keeping feet
closer and being in squatting position
² Wearing dry shoes or standing on insulator materials
² Not staying on trees or high lands

14. 14
First aid for a person struck by lightning
 If the limbs are benumbed bring them back to normally by
massaging
 If respiration has stopped, give artificial respirations
 If the heart beat has stopped, massage the heart