Thunder and lightning

Thunder and lightning are unavoidable natural disasters.Thunder and lightning are active at any time on the earth.Thunder and lightnings disaster is one of the ten most serious natural disasters announced by the United Nations International Decade for Disaster Reduction.Lightning brings about countless losses in both lives and property,resulting in frequent accidents such as fires, explosions, building destruction and so on every year in the world;from satellites, communications, navigation, computer networks to household appliances in every household are seriously threatened by lightning disasters.

Summary of thunder and lightning

What are thunder and lightning?

Thunder and lightning are discharge phenomena in thunderstorm clouds.When thunderstorm clouds are close to the earth, opposite charges are induced on the ground, when charges accumulate to a certain extent, discharges between clouds and clouds, and between clouds and the earth, bursting out light and sound.

The formation of thunder and lightning

Lightning is called thunderstorm in meteorology. The cumulonimbus clouds forming thunderstorms are high and dense with many ice crystals on the top of clouds,thermal convection in the vertical direction of clouds develops vigorously, and electrification and discharge (lightning) phenomena occur continuously, the mechanism is very complex.

Types of thunder and lightning

According to the different characteristics of lightning generation and hazard, which can be divided into the following four types:

(1)Direct lighting

Direct lightning strike means that lightning strikes buildings, other objects, the earth or lightning protection devices directly, which produces electromagnetic, thermal and mechanical effects.It is formed by discharges between charged thunderclouds in the air and objects on the ground.Direct lightning can kill people and animals in an instant.The hundreds of thousands to millions of volts of impulse voltage generated by direct lightning will destroy the insulation of electrical equipment such as generators and power transformers, burn off wires or split poles and cause large-scale power outages, insulation damage may lead to short-circuit and fire or explosion accidents.For example, at 13:00 noon on July 27, 1970, a direct lightning struck down 10 tourists in Tiananmen Square, Beijing, two of them died because of the ineffective rescue of electric current through their bodies.

In addition, the huge lightning current of direct lightning converts into a large amount of heat energy in a very short time through the lightning objects, which causes the combustion of flammable materials or metal melting splash and causes fire.For example, on August 12, 1989, the No. 5 oil tank of Huangdao Oil Depot in Qingdao City was struck and exploded by lightning, the fire burned for 60 hours, the flame was 300m high, 40,000tons of crude oil were burned, 10 fire engines were burned, 19 people were killed, 74 people were injured, and 630 tons of crude oil flowed into the sea.

(2)Spherical thunder

Spherical glowing air masses occasionally appear in thunderstorm season, which can roll along the ground or float in the air， when they float away from open windows, the release of energy can easily injure people.The mechanism of this kind of spherical thunder has not been clearly studied. The spherical thunder has the habit of following the wind, that is, following the airflow.When a person encounters a spherical thunder, if he pulls out his legs and runs, the spherical thunder will follow closely. The best way to avoid danger is to immediately hold your head in both hands and squat with your feet together.On the evening of August 17, 1978, the former Soviet mountaineering team camped on the Caucasus hillside, five members were sleeping soundly in their sleeping bags, suddenly, a big yellow tennis ball burst into the tent, floated 1m above the ground, and crashed into the sleeping bag with a brush, the stench of roasting meat came in a flash, the ball jumped in and out of five sleeping bags in turn, and finally disappeared, resulting in one person was burned to death and four seriously burned.

(3)Induction lightning

When direct lightning is discharged, due to the large gradient of lightning current variation, alternating magnetic field is generated around it, which makes the surrounding metal components produce larger induction electromotive force and form spark discharge, which is induction lightning. Induction thunder is very easy to cause fire. For example, on June 22, 1992, a land thunder fell on the top of the National Meteorological Center building in Beijing, although lightning rods were installed in the building, the huge induction lightning broke six domestic synchronous lines and one international synchronous line in the building, which interrupted the computer system for 46 hours and caused direct economic losses of hundreds of thousands of yuan.

(4) Lightning wave intrusion

Lightning wave intrusion is caused by lightning strike on overhead lines or metal pipelines in the air, resulting in the rapid propagation of lightning voltage along the lines or pipelines.Its transmission speed is 3X108m/s.Lightning wave intrusion can destroy the insulation of electrical equipment, make high voltage into low voltage, and cause serious electric shock accident.Many lightning accidents caused by lightning wave intruders, which account for about 70% of the total lightning accidents in low voltage systems.For example, in thunderstorm days, the sudden explosion of indoor electrical equipment, fire or damage, and the sudden death of people by electric shock while using electrical appliances or making telephone calls in the house are all such accidents, another example is, at about 1:00 a.m. on June 10, 1991, over Mudanjiang city, Heilongjiang province,the lightning flashed and thunder crashed, and deafening land lighting woke up sleeping residents, the lights in the whole area turned on and went out instantaneously, causing damage to more than 20 color TV sets.

Damage of thunder and lightning

The places where lightning are easy to occur：

(1) Lack of lightning protection equipment or unqualified tall buildings, tanks, etc.

(2) No metal roof with good grounding.

(3) Buildings and trees in wet or open areas.

(4) Chimneys are particularly vulnerable to lightning strikes due to the conductivity of flue gas.

(5)Buildings with radio and no lightning arresters and no good grounding.

Damage of thunder and lightning

Lightning can cause harm to people or other objects under certain conditions.When the conditions are suitable, thunderstorm clouds may discharge to buildings or trees, and huge discharge current will flow to the earth along the discharge path of buildings or trees.Discharge current in the discharge circuit, will produce a great deal of energy and form a destructive effect, such as destroying buildings, splitting trees, causing fire, etc,then,if the human body becomes a discharge circuit or close to the discharge circuit, it will be electric shock or electric cauterization and cause casualties.

Land thunder are the most harmful to human beings,the huge current, hot temperature, electromagnetic radiation and concomitant shock wave caused by land thunder have great destructive power, which can cause human casualties and damage to buildings.

The main hazards of thunder and lightning are:

(1) The high-voltage effect of thunder and lightning current can produce impulse voltage up to tens of thousands of volts or even hundreds of thousands of volts, such a huge voltage can impact electrical equipment instantaneously enough to break through insulation equipment and short circuit, resulting in direct disasters such as combustion and explosion.

(2) The high heat effect of thunder and lightning current will emit tens to thousands of amperes of strong current and generate a lot of heat energy, the heat at the lightning strike point will be very high, which can lead to metal melting, fire and explosion.

(3)The mechanical effects of thunder and lightning current are mainly manifested in the phenomena of explosion, distortion, collapse and tearing of objects struck by lightning, resulting in property losses and casualties.

(4)The electrostatic induction of thunder and lightning current can make the stricken conductor generate a large number of charges contrary to the nature of lightning, when lightning disappears before it can disperse, it will produce a high voltage discharge phenomenon, which will lead to fire.

(5) The electromagnetic induction of thunder and lightning current will produce strong alternating electromagnetic field around the lightning strike point, and the induced current can cause local overheating of the transformer and lead to fire.

(6) The intrusion of thunder and lightning wave and the high voltage of lightning protection device will also cause the break-off of distribution device or electric line, which will lead to fire.

Protection of thunder and lightning

Franklin and lightning rods

As a powerful natural force, there is no effective way to prevent the emergence of lightning at present, the most promising thing is to make accurate lightning forecast in time so as to take corresponding countermeasures to avoid lightning strike and to avoid casualties and losses to the greatest extent.The main thing people can do is to prevent and limit its destructiveness,the most important measure is to install lightning protection devices such as lightning rods.The inventor of lightning rod was Benjamin Franklin, an 18th century American businessman, scientist, social activist, thinker and diplomat. Franklin first revealed to people the secret of lightning as an atmospheric spark discharge phenomenon through a series of experiments, such as the famous kite experiment.He first put forward the idea of lightning rod, and the lightning rod made from it avoided the disaster of lightning strike and broke the superstition.

The protection principle of lightning rod: When the thundercloud discharge is close to the ground, it distorts the ground electric field, at the top of the lightning rod, it forms a space where the local electric field intensity concentrates, so as to influence the development direction of the lightning pilot discharge, guide the lightning to discharge to the lightning rod, and then lead the lightning current into the earth through the grounding lead and grounding device, so as to protect the protected object from lightning strike.

The term “lightning rod” is just used to mean that it can avoid lightning damage to the protected object, but on the contrary, it is “lightning”upper body.

Early warning signals of thunder and lightning

Early warning signals of thunder and lightning are divided into three levels, which are yellow, orange and red, respectively. Shown in table 6-7.

Outdoor lightning protection

(1) Hide in buildings protected by lightning protection facilities quickly, or in deep caves, the car interior is an ideal place to avoid lightning strikes, but you can't park under trees or poles to shelter from rain.

(2) Do not stay at the top of a mountain, ridge, top of a building, under a chimney of a high building, on a high hill or under an isolated tree, do not avoid thunderstorms under big trees, power poles, billboards and all kinds of iron towers, because the damp branche s of big trees at this time are equivalent to a lightning device, if touch big trees, power poles, billboards and all kinds of iron towers with your hands, you will probably be struck by lightning. absolutely far from the transmission line.

(3) Do not run when there is no time to avoid lightning in the field, you should crouch with your feet together in a low-lying place, put your hands on your knees, bend forward and keep your arms out of touch, be careful not to crowd together or hand in hand.

(4) In the open space, do not play umbrellas, and do not carry metal tools such as hoes, badminton rackets, golf clubs on your shoulders.

(5) Metal objects (tractors, farm tools, motorcycles, bicycles, golf carts, golf clubs, etc.) far from open areas, do not hold metal objects in thunderstorms, because metal objects are conductive materials, which can play a role in thunderstorms. Carried metal articles should be temporarily placed away from 5m, and then retrieved after the lightning activity stops.

(6) Don't swim or engage in water work, don't fish, boat and swim outdoors, don't work outside or work in the ground, leave the water and other open spaces as soon as possible, be quick to avoid lightning in a nearby dry house.

(7) It is inappropriate to drive a motorcycle or ride a bicycle in thunder and lightning weather.

(8) Do not stay near iron gates, iron fences, metal clothesline, overhead metal bodies and railway tracks.

(9) It is better not to ride horses, bicycles, motorcycles or tractors.

(10) Don't answer and dial mobile phones outdoors, because the electromagnetic waves of mobile phones can also cause lightning.

Indoor lightning protection

(1) Must close the doors and windows, as far as possible away from doors and windows, balconies and external walls, prevent direct lightning strike indoor and spherical lightning drift into indoor.

(2) Do not touch any metal pipes in the room.

(3) Household use of computer, color TV, audio, video disc player and other weak electrical equipment should not be close to the outside wall, thunder and lightning weather is best not to use any household appliances, it is recommended to unplug all the power plugs.

(4) In thunder and lightning weather, do not use shower or contact water pipes, because water pipes are connected with lightning grounding, and lightning current can be transmitted through water flow and cause casualties, especially don't use solar water heater for bathing.

(5) When a lightning fire occurs, the power supply should be cut off as soon as possible, special extinguishers such as dry powder extinguishers should be used to extinguish the fire, and “119”or “110” telephone calls should be made to alarm promptly.

(6) Do not touch or close to the grounding wires of lightning-proof leads, water pipes and household appliances in order to avoid touching voltage or lightning strikes and side flashes.

(7)In thunderstorm weather, try not to dial, answer the phone, or use the telephone to access the internet. Pull out the power supply of household appliances, telephone lines and TV feeders, which may lead thunder and lightning into the indoor metal wires.The safe and scientific way is to install power arrester on power supply line, telephone arrester on telephone line, antenna arrester on antenna feeder line, and do a good job of reliable grounding protection measures.

(8) Keep the house dry，when the house leaks, it should be repaired in time.

(9) Do not pull wire to windows or doors for drying clothes, bedding, etc. in order to prevent the wire from triggering thunder.

(10)Don't stay in shelters without lightning protection or in isolated pavilions or straw shacks for a long time. Be careful to avoid the wires, do not stand under the light bulb, it is best to power off or do not use electrical appliances.

How to rescue people injured by lightning

People who are burned or severely shocked by lightning are not electrified.Should be allowed to lie down immediately, extinguish the fire and rescue him.If the injured person has stopped breathing or cardiac arrest, they should be given mouth-to-mouth artificial respiration and cardiac compression promptly and sent to the hospital for first aid.Practice has proved that the more quickly and patiently artificial respiration is performed on the lightning “shock pseudo-death” patients, the more chances of resuscitation are, and some of the wounded can also be resuscitated after 6 hours of artificial respiration. After rescue,the patient can't stand up immediately, should be lifted to bed to rest, return to normal, can let him walk, only before the doctor arrived when the lightning striker appeared stiff, corpse spots can stop rescuing.