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or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
SII'S UN ZARtlH ITI HININ
I.M.Pellls,Exlenslon Saelly Leader
Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
Tips on Safety Lightning
A. M. Pettis
Extension Safety Leader
Florida Cooperative Extension Service
Lightning is one of the most destructive forces
of nature and it is especially dangerous and costly
in rural areas. It is estimated that some 1800
thunderstorms are in progress over the earth's
surface at any given time and that lightning
strikes the earth 100 times each second.
Each year lightning kills a reported 150 per-
sons in the U.S. and injures another 250 persons.
The actual number killed is probably higher. In
Florida an estimated 20 people a year die from
lightning. About 80 percent of all human deaths
or injuries from lightning occur in rural areas.
Lightning has been referred to as nature's ar-
tillery. It has the power and is accompanied by
the noise that makes it equal to the destructive
potential and properties of man's most advanced
Lightning is an electric discharge with a tre-
mendous amount of voltage and amperage. It
comes in several forms. Streak lightning, a single
or multiple line from cloud to ground is the form
seen most frequently. Sheet lightning is lightning
inside a cloud and we see the scattered light.
Heat lightning is seen along the horizon during
hot weather and it is just like sheet lightning-
intra-cloud discharges illuminating clouds from
within. Ribbon lightning is streak lightning
whose conductive channel is moved by high winds,
making successive strokes seem to parallel one
Lightning is a major cause of rural fires. Dam-
age to rural homes and other buildings, livestock
deaths and injuries, forest fires, disruption of
electromagnetic transmissions and other effects
is estimated at more than $100 million annually.
In 1752 during a thunderstorm, Benjamin
Franklin flew his famous kite and when sparks
jumped to his hand from a key tied to the end of
the kite string, his theory, that lightning and
electricity were the same thing, was verified.
Franklin did an awfully dangerous thing and it's
a wonder he wasn't killed! Any would be experi-
enters should take heed and not try to repeat
the kite experiment.
Franklin's experiment led to the use of metal
conductors called lightning rods to protect build-
ings from lightning. In recent years scientists
have improved grounding methods and materials
to give buildings a large degree of protection from
All important rural buildings should be pro-
tected against lightning. Other less valuable
buildings, trees and wire fences may require pro-
Lightning can enter a building in several ways
(a) by direct stroke to the building or TV an-
tenna, etc. (b) by striking a nearby object such
as a tree and leaping to the building and (c) by
striking a power line and following it into the
For protection a building needs a lightning pro-
tection system. The only parts that are usually
visible are small inconspicuous terminal points.
The most common system is semiconcealed and
it is installed on existing buildings. Of course,
it also has terminal points. The conductors are
placed behind downspouts and other building com-
ponents to conceal them as much as possible. In
addition to terminals or rods and conductors, a
lightning protection system consists of grounding
and lightning arrestors. The grounding part of
the system is one of the most important parts.
If a homeowner contracts for a lighting pro-
tection system to be installed he should insist on
a "Master Label" system. This is his assurance
that the system is installed properly of approved
materials. Many homeowners have paid too much
for a lightning protection system because through
ignorance or intention the system was overde-
signed or not properly designed. A person with
mechanical know-how and the proper set of in-
structions might be able to install a system cor-
If a home does not have a complete lightning
protection system, including lightning rods, the
next best thing is to have all grounds tied to-
gether. For example, the neutral on the electric
system, the telephone ground and the TV antenna
mast should all be grounded on the cold water
pipe. Driven ground rods may vary in their re-
distance. Bonding all grounds together on the
cold water pipe will help protect a home if a
lightning bolt strikes nearby.
The average person is more likely to have
electrical equipment damaged from lightning sur-
ges coming in over the electric line, than to have
buildings damaged by bolts of lightning. Manu-
facturers have designed a special type of variable
resistor that acts as a lightning arrestor when
surges come in on the lines. It is mounted at the
main electrical load center in the building or at
the service entrance.
Any home electrical equipment can be damaged
by lightning surges but probably the most often
damaged equipment will be the electric water
heater, air conditioner or pool pump. Bonding
the neutral conductor to the cold water pipe and
installing an arrestor as explained above will help
protect electrical equipment.
With valuable livestock it may be advisable to
install protection for buildings, fences, and trees.
A 2-year study of 3,842 livestock deaths by light-
ning showed 67 percent occurred in buildings, 20
percent under trees, 6 percent along wire fences
and 7 percent in open pasture. Of course it is
not feasible to protect in open pasture.
Trees under which livestock usually congregate
can be fenced off or grounded by installing air
terminals. Grounding a tree in this manner may
not save the animals. When lightning strikes a
metal fence, electrical charges may travel up to
two miles. Danger lurks for humans and live-
stock. To reduce the danger the fence may be
grounded and electrical continuity broken.
If fence posts are made of wood or concrete,
grounds for the fence can be solid copper rods or
1/2-inch galvanized pipe driven into the ground at
intervals of 150 feet and at corners. The rods
should be driven to a depth of eight feet or down
to permanently moist earth. Clamp all strands
of the fence to the ground rods. In addition to
grounding, long stretches of fence should have
their electrical continuity broken. At intervals of
100 feet interrupt the wire by a wooden section
of fence or by using some form of insulator. This
would help limit a lightning stroke on the fence
to prevent it from energizing the entire length of
Fig. 1. Shaded area shows the portion of Florida that
has 100 thunderstorm days per year.
Very often thunderstorms come up suddenly
and people are caught outdoors. If this happens
to you the best thing is to find some protection
quickly. If it's not too far to a building that is
protected from lightning, then head for there.
Second choice would be an automobile. Stay in a
vehicle with a steel roof during a lightning storm
and you are well-protected.
Some don't if you're caught out in the weather
during lightning. Don't go near metal fences or
get close to trees, especially lone trees or trees
higher than surrounding woods. If you're in a
boat or swimming in the water when the lightning
begins, your life is in danger! Get back on land
and find a safer place already mentioned. A per-
son in a boat is the highest object in that vicinity
and thus he is in a dangerous position. While
swimming if a bolt should strike the water even
a distance away, the person may drown from
paralysis caused by the shock.
Certain parts of Florida have 100 thunderstorm
days a year, the highest number found in the U. S.
The state varies from 60 to 100 thunderstorm
days per year with the highest part being a long,
narrow portion of the peninsula of Florida
bounded approximately by Orlando, Lakeland, Ar-
cadia, Immokalee, and Lake Istokpoga.
Here are some lightning safety rules that may
save your life:
1. Stay indoors during a lightning storm.
2. Stay away from open doors and windows,
fireplaces, radiators, heaters, metal pipes,
sinks and portable electrical appliances.
3. Don't use plug-in electrical equipment suet
as hair dryers, electric toothbrushes, or elec-
tric razors during the storm.
4. Avoid using the telephone during the storrr
5. Don't take laundry off the clothesline.
6. Don't work on metal fences, pipelines, tele.
phone lines or electric lines.
7. Refrain from using metal objects like fishing
rods or golf clubs.
8. Don't handle flammable materials in opera
9. Never drive a tractor, especially one pulling
metal equipment. Dismount.
10. Get out of the water and stay off small boats
11. Stay in your automobile when on a trip.
12. A good shelter is in a building.
13. With no shelter avoid the highest object ii
14. Avoid hill tops, metal fences, clotheslines
sheds, and other objects.
15. When you feel the electrical charge-if you:
hair stands on end or your skin tingles, dro]
to the ground immediately.
1. Uman, Martin A. Understanding Lightning. BE]
Technical Publications, Carnegie, Pa., 1971.
2. Lightning. U. S. Department of Commerce
3. Lightning Facts and Figures. Lightning Protectio
4. Lightning Protection For the Farm. FB2136, U. k
Department of Agriculture.
5. Pettis, A. M. Lightning Protection. Mimeograpl
Single copies free to residents of Florida. Bulk rates
available upon request. Please submit details on
request to Chairman, Editorial Department, Institute
of Food and Agricultural Sciences, University of
Florida, Gainesville, Florida 32611.
This public document was promulgated at an annual
cost of $302.15 or $.0302 per copy to inform public
how to protect lives and property from lightning.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30,1914)
Joe N. Busby, Dean