Lightning Facts
The maximum distance you can hear thunder is as short as two (2) miles and seldom exceeds twelve
(12) miles. Many factors contribute to this wide range, some of which are wind speed, wind direction, terrain, ambient noise
and the origin of the return stroke.
Sound is generated along the length of the lightning channel as the atmosphere is heated by the electrical discharge
to the order of 55,000 degrees F (5 times the temperature of the surface of the sun). This compresses the surrounding
air producing a shock wave, which rapidly decays to a sound pressure wave as it propagates away from the lightning channel.
The average lightning bolt is 6-8 miles long and can easily travel 25 to 40 miles horizontally prior to turning
downward toward the ground. In October 2001, the visual lightning detection system measured a single bolt that traveled
from Waco to Fort Worth and then Dallas, Texas – a total distance of more than 110 miles
It is almost soothing to hear the low rumble of thunder off in the distance as a storm approaches, yet the very sound
of thunder indicates that you are in immediate danger. The forward and backward reach of lightning far outruns your ability
to hear its thunder. When you hear thunder (even faint thunder) you are in danger of a lightning strike. When
the leading edge of a thunderstorm is within 10 miles you are at immediate risk due to lightning's out reach. In fact, many
lightning deaths and injuries occur with clear skies directly overhead. Example
Many cloud-to-ground lightning flashes have forked or multiple attachment points to earth. Tests carried out in the US
and Japan verify this finding in at least half of negative flashes and more than 70% of positive flashes. Many lightning detectors
cannot acquire accurate information about these multiple ground lightning attachments.
Lightning can travel over the surface of the ground and through the ground. The ground surface can be lethal for up to
60 feet radius or more from the point of contact. This also includes a ground rod as the point of contact. In
water, the lethal radius is about 600 feet from point of contact.
The temperature of lightning's return stroke is (5) five times hotter than the surface of the sun. It can reach about
55,000 degrees Fahrenheit in contrast to about 10,000 degrees Fahrenheit for the surface of the sun. This high temperature
will immediately turn water or water vapor into high pressure superheated steam. This high pressure steam can explode the
clothes off your body, explode the bark from a tree, explode concrete, drywall, wood or any material containing even small
amounts of moisture.
WARNING 30 Second / 30 Minute Rule - A popular warning method that has been widely used for many years
is the "Flash-To-Bang" method that resulted in the creation of half of the 30 second /30 minute rule. The method suggest
that when you see a lightning flash, count the seconds to the bang of thunder, then divide the number of seconds by five (sound
travels one mile in five seconds) to give the distance in miles from you to the lightning. For example: you hear thunder 30
seconds after you see lightning, the distance is may be 6 miles. Thus the reason for the first number of the 30/30 rule.
The accuracy of this method depends on your ability to measure the distance between a witnessed lighting strike and your
observing location and is unreliable for a number of reasons. One reason is the maximum distance you can hear thunder
is as short as two (2) miles and seldom exceeds twelve (12) miles. Many factors contribute to this wide range, some of which
are wind speed, wind direction, terrain, ambient noise and the origin of the return stroke. It is quite possible to have a
close lightning strike and never hear any thunder, rendering this method useless. A second reason is that lightning
can travel much further than 6 miles.
Unfortunately, the "Flash-To-Bang" method this was never a good method to adequately provide a safe warning of a pending
unsafe condition and should not be used today as a warning methodology. Lightning can easily travel further than
you can see. If you see lighting you are already in danger and should seek a safe location. If you hear thunder you are in
immediate danger and should seek a safe location immediately.
The second number of the 30/30 rule ask you to remain in a safe location for 30 minutes after the last sight of lightning
or the sound of thunder. This remains as good advice. 50% of the fatalities occur after the storm has passed because
people resumed activities to soon after the storm.
About 20 million cloud-to-ground lightning strikes occur annually in the USA. That's just under one per second for the
USA and about 100 per second world wide
Typically, more than 2,000 thunderstorms are active throughout the world at a given moment, producing on the order of
100 flashes per second.
A lightning flash is composed of a series of strokes from about 3 to 20, with an average of about four. The duration
of each lightning stroke can vary, but typically average about 30 microseconds. (The average peak power per stroke is about
1012 watts.
The energy contained in a single lightning stroke can power a 100 Watt light bulb for 90 days, which is equivalent to
215 kWh (kilo-Watt hours).
About 1% of the energy in a single lightning stroke is converted to electromagnetic energy. This can be thought of as
having about 200,000 clear channel 50 kW radio transmitters all turned on at the same time feeding one antenna. The wave front
can propagate half way around the earth.
U S Department of Agriculture estimates that lightning causes over 80 percent of all accidental livestock deaths.
31 % of beetle infestations over a three-year period were related to individual lightning-strikes of pine trees
(research done in Louisiana)
The US averages about 100,000 thunderstorms each year (LPI)
The danger of lightning is often under publicized and misunderstood because it usually kills people one at a time. Lightning
is one of the most dangerous features of a thunderstorm.
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Good Aspect of Lightning
During a power blackout from a lightning strike, it’s hard to remember that some good does come from the powerful
bursts of electrical energy. When lightning bolts discharge, they ionize the air and produce nitrogen oxide. According to
recent studies, this process could generate more than 50 percent of the usable nitrogen in the atmosphere and soil. Nitrogen
is an essential plant fertilizer. Lightning also plays a critical role in the natural cycle of forests by helping generate
new growth. Areas that are burned by lightning-triggered fires are cleared of dead trees so that seedlings have the space
and soil to take root. The global array of thunderstorms serves as a worldwide circuit of electrical generators. Through the
activity of the lightning they produce, these generators continually maintain and renew the atmosphere’s positive electrical
charge.
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Trivia
Thales, the Greek philosopher, in about 600 B.C., found that a piece of amber when
rubbed briskly with a dry cloth would attract feathers or straw. Wm. Gilbert, the court physician to Queen Elizabeth in the
1500's, repeated this experiment and named the science of studying it vis electrica. The Greek word electra means amber. Our
word for electricity is derived from this.
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Surge Suppressors are safe
FALSE: Surge suppressors can be a fire hazard. Surge suppressors manufactured after January
1998 that have passed the tests in the second edition of Underwriters' Laboratories (UL) Standard 1449 may be safer than earlier
models. Additional details here.
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Underground wiring is safe
FALSE: Recent research discovers that when lightning hits
the ground it has a tendency to seek out any metal in the ground. In particular, buried power lines, phone lines and data
cables seem to be quite vulnerable and do not appear to be much safer than if they were located above ground.
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MYTH: Lightning victims are electrified
FALSE: Lightning victims and the surrounding
ground or the surrounding water carry no electrical charge after the strike and are perfectly safe to touch.
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MYTH: Lightning rods attract
lightning
FALSE: Lightning rods simply provide a conductive path to ground for an electrical charge that is already in
the vicinity and certainly dose not attract lightning. While there are complex factors involved in the path chosen by
a lightning bolt, the actual direction is quite random and not effected by lightning rods at the surface of the earth.
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MYTH: Lightning never strikes
in the same place twice
FALSE: Lightning often strikes the same location several times each year.
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MYTH: Lightning only strikes
very tall objects
(OR) Lightning always strikes the tallest object.
FALSE: Typically the taller the structure the more
often lightning will strike, however there are exceptions based on the actual voltage level of the leader stroke and the step
length of the leader stroke. There are many examples of lightning striking the side of a tower or building. Many
of the early photographs of strikes to the Empire State Building demonstrate this effect and in fact, are responsible for
encouraging much of the early research to investigate this phenomena.
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MYTH: Lightning only strikes
good conductors such as metal
FALSE : With lightning, everything is a conductor but metal is better. Given a choice
between metal and a traditional non conductor, metal provides a better path. However, since this energy is RF
(Radio Frequency) in nature it can easily travel over the surface of a substance (aka skin effect) and traditional non
conductors provide a convenient path in the absence of metal.
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MYTH: Jewelry, shoes with
metal cleats or metal objects such as tripods, golf clubs and umbrellas will attract lightning and make me more susceptible
to a strike.
FALSE / TRUE: This is a tricky area and you need to be careful here. Certainly these objects will
not attract lightning from the clouds. However, if the charge field is sufficient for the leader stroke to be near by
then the simple act of holding a cell phone to your head or raising an umbrella above your head may be sufficient to cause
a ground streamer to begin with you.
If you are directly hit with lightning then there is a chance that metal
worn on the body can be heated to a temperature sufficient to cause burns and in some cases severe burns. If the
metal is in the form of a closed circle such as a necklace, a bracelet, a watch band or similar closed circle, then it becomes
a magnetic loop receiver and can receive the magnetic energy from the lightning strike. This energy level can be quite
high and can cause the circle of metal to turn red hot and even vaporize, causing removal by surgery necessary.
Just recently I had a situation where an aircraft took a lightning hit and the necklace around the pilots neck heated
to the level necessary to cause sever burns. Even thought the aircraft acts like a Faraday Cage and protects the occupants
from the electric field, it provides no protection from the magnetic field.
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MYTH: Lightning rods 'discharge'
a cloud and prevent a lightning strike
FALSE: Lightning rods simply provide a conductive path to ground for an electrical
charge that is already in the vicinity. While there are complex factors involved in the path chosen by a lightning bolt,
the actual direction is quite random and not effected by lightning rods at the surface of the earth.
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MYTH: Surge protectors
provide protection against a direct lightning strike
FALSE / TRUE: This area has many variables and the answer depends
on what you are attempting to protect. Depending on what you are trying to protect, some surge protectors can and
some can't. Depending on the distance between the source of the strike and the device to be protected some can and some
can't. Certainly in many instances you can achieve excellent protection from a direct strike. There are
numerous applications where the site receives many direct hit each year and no damage results. See the "Protection Page"
for additional details
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MYTH: Lightning doesn't
strike water
FALSE: Lightning does indeed strike the water and often. Not only are the oceans a good location
for lightning hits but inland lakes are too. Michigan is number two in lightning injuries in the USA and caused mostly
by injuries from being on the water during a lightning storm.
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MYTH: Lightning could be
used as a power source
FALSE: As attractive as this concept can be, it just is not practical with today's technology
to capture and store this short burst of high energy.
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MYTH: Rubber shoes or boots
insulate and protect against a lightning strike
FALSE: A few inches or a few feet of rubber provide no protection
to a person hit with lightning.
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MYTH: 'Heat Lightning'
is a strange phenomenon caused by hot weather
FALSE: There is no such thing as lightning cause just by heat.
To generate lightning you generally need a heat source, a moisture source and an unstable atmosphere. Heat lightning
is simply normal lightning that has occurred at a distance to far for the sound of thunder to reach you. Often it is
at a distance where you can not see the direct lightning bolt but can see the reflect light from the clouds.
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A metal Vehicle is safe
because of the rubber tires
FALSE: Inside a metal vehicle like a car, airplane, train, bus or tractor cab is generally
safe because it diverts the lightning around you and not through you. The metal vehicle acts as a "Faraday Cage" where
it allows the lightning to travel over the surface of the vehicle and down to ground by jumping over the rubber tires from
the metal wheels. Rubber tires have nothing to do with protecting you from lightning. To achieve good protection inside
a metal vehicle it is important to move to the center of a vehicle, close all windows and refrain from touching any metal.
If you have two-way radio, stay off the radio.
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Mouth Lightning
FALSE:
You may have seen the following claim regarding small sparks emanating from the breaking of lifesavers in a person's mouth.
I have tested many of these lifesavers and have observed no evidence that this effect occurs.
The claim:
"You will need: "wint-o- green" or "pep-o-mint" lifesavers and a dark room. Enter a really dark room and
wait a few moments until your eyes get accustomed to the darkness. Then insert a "wint-o- green" or "pep-o-mint" lifesaver
into your mouth. Keeping your mouth open, break up the lifesaver with your teeth and look for sparks. If you do it right,
you should see little bluish flashes of light.
The claimed explanation:
When you break
the candy apart, you're breaking apart sugars inside the candy the sugars release little electrical charges into the air.
These charges attract oppositely charged nitrogen in the air and when the two meet, they react in a tiny spark that you can
see."
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