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LIGHTNING KILLS because it is a high voltage electric current. It lasts
for only a short time, but it can shock, burn and otherwise damage a human
body. Yet although lightning has not changed, you are now far less likely
to be killed by it than ever before. Official statistics for England and
Wales indicate that the number of people killed by direct lightning strikes
each year has fallen dramatically. Since 1960, lightning has killed an average
of only five people each year, compared with 20 people per year in the late
1800s. In the US, lightning strikes now kill about 95 people each year,
down from around 300 deaths per year in the 1890s.

Why is lightning now less of a killer? Thunderstorms are not less frequent:
there are between about 1500 and 2000 thunderstorms throughout the world
at any moment, with lightning strikes about 6000 times every minute. The
change in people’s occupations in Britain and the US helps to explain the
decline in casualties. Because lightning usually seeks out the highest object,
tall or isolated trees, telegraph poles and exposed hill tops are dangerous
places to be in a thunderstorm. There are now far fewer people who work
outdoors, especially in farming: farm labourers were once the prime target
for lightning. In towns and cities people are protected by tall buildings
and structures that conduct electricity more readily than the human body.
Today, people enjoying themselves out-of-doors such as fell-walkers and
golfers seem to face the greatest risk. Water sports are especially dangerous,
because anyone on or in water forms the highest point in their immediate
area.

Men are at higher risk than women. Since 1852, when the authorities
began to collect data systematically, nearly 1800 people have been killed
by lightning in England and Wales. Of these, only 15 per cent were women.
So, because more men have outdoor jobs and play outdoor sports, they are
six times more likely to be killed by lightning in Britain as women. In
some developing countries, where a higher proportion of women work outdoors,
this figure may be reversed.

Lightning kills people directly or by striking nearby trees or the ground.
The current may peak at between 10 000 and 40 000 amperes, although the
sustained current is typically hundreds of amperes. The current comes from
the build-up of electric charge on a cloud during the thunderstorm. Lightning
discharges from cloud to ground are not as common as those between clouds
but (apart from possible aircraft strikes) they obviously pose the greater
threat to people. The lightning discharge, or the heat it generates, can
stop the heart, damage the lungs, brain or other vital organs and cause
serious burns. Even so, only about a quarter of those people struck by lightning
are killed. Many suffer badly from burns and shock but recover completely.

Whether a lightning strike kills depends upon which organs the current
passes through. If the heart stops, people may be able to revive a victim
as long as the strike does not seriously affect other vital organs. A 10-year-old
boy playing with a golf club near his home in Lochgelly, Fife, was struck
by lightning in May 1976. His heart stopped but neighbours gave him the
‘kiss of life’, and he revived.

Metal is dangerous in thunderstorms. Metal fences, pipelines and railway
tracks can conduct lightning that has struck some distance away. In July
1955, at Royal Ascot races, lightning ripped along metal railings in a series
of blue sparks that knocked people several feet into the air; 47 people
were injured and two killed. Touching an unearthed metal fence, roof or
clothesline after a thunderstorm can be dangerous. The storm may have gathered
a lethal electric charge even in metal that has not been struck. Even such
small pieces of metal as jewellery can be a hazard in a thunderstorm. Lightning
seems to strike crucifixes and medallions around people’s necks, and often
leaves a burn shaped like the medal. St Christopher may not always be a
help.

Lightning can also kill people indoors, especially if they are near
water pipes and electrical circuits. Wiring from television aerials is a
particular problem. Lightning frequently strikes the aerials and the cable
conducts the current into homes. If you disconnect the television, there
is less risk of it exploding and starting a fire. The large voltages of
lightning surging through the electric power circuit of a house may also
generate sparks along the wiring, or in appliances, causing dangerous fires.

People tend to underestimate the dangers of telephoning during a thunderstorm.
Jayne Bradshaw, of Stannington near Sheffield, telephoned her husband for
reassurance during a violent thunderstorm in August 1988. Suddenly there
was a loud bang and she felt a pain in her ear. Lightning had struck the
telephone wires and passed through her body. She was treated for shock and
for burns on her ear and thigh.

Try to avoid holding a metal object during a thunderstorm – whether
it is an umbrella, golf club, telephone, garden fork, rifle, window frame
or even tea strainer. Lightning through a window struck the steel tea strainer
held by a woman as she poured a cup of tea for an elderly neighbour at Maidenhead,
Berkshire, in July 1982. She was hurled across the kitchen but escaped with
shock, a numb arm and no permanent injuries. For those people using guns
or golf clubs, the safest action to take is to throw them away. Fishermen
are at risk because their rods, whether made of metal or not, are tall and
pointed, and make a good target for lightning. Golfers should also remove
their shoes if they have metal studs.

One of the most famous golfers struck by lighting is Lee Trevino. Rain
delayed play as Trevino reached the 13th green of the Western Open in Chicago
on 27 June 1975. Together with Jerry Heard, he sat on the edge of the green
by a lake, leaning against his golf bag. Suddenly, lightning threw him into
the air and he blacked out. He came to, but had difficulty breathing and
no feeling in his left side. There were four burn spots on his left shoulder
where the lightning had left his body. Heard was shocked but unhurt. Trevino
was taken to hospital for two days where they explained that the electric
shock had disrupted the muscle tone in his body and dissolved the lubricant
between the discs in his vertebrae. Evidently, the lightning had flashed
off the lake, shot through the metal golf club shafts in his bag and passed
up his back. Though his back continued to give pain for several years he
returned to winning form in July 1977 in the Canadian Open.

Golfers need reminding not to replace one potentially dangerous metal
object, a golf club, with another, an umbrella. David Brooks, chief weather
forecaster for Anglia television, should have known this. As he sheltered
during a round of golf at Cambridge in April 1979, lightning struck the
umbrella he was holding, but he was not seriously injured.

The effects of a lightning strike can be so devastating that people
often talk of a ‘thunderbolt’, as if something solid had struck the ground.
This misconception probably came from the notion of divine weapons used
by the gods or, in part, from confusion with meteorites. There is no solid
object involved. The air through which a lightning flash passes is intensely
heated. The large electric current raises the temperatures in the lightning
channel to as much as 30 000 Degree C in a millisecond or less. The hot
air expands suddenly, creating a shock wave with pressures of between 10
and 30 atmospheres. People within a metre or so of this shock wave can be
thrown into the air. In some cases, the shock wave does not move the victims,
but strips off their clothes. This reportedly happened to 10 French and
West German tourists as they hid under a bush during a thunderstorm, at
Trento in Italy in August 1970. They were left naked but, amazingly, uninjured.

If lightning strikes an object with moisture in it, the moisture can
boil instantaneously. This sudden vaporisation can cause the object to expand
explosively, whether it is a tree, a road, soil or a brick wall. The resulting
explosion is sometimes said to be equivalent to 250 kilograms of TNT. In
July 1974, an 11-year-old schoolgirl died from a fractured skull when lightning
exploded an oak tree at Basildon, Essex. The lightning had run inside the
bark of the tree and vaporised the sap. She was hit by a flying piece of
bark. This victim did not count as a fatality caused by a direct lightning
strike and highlights the fact that for every person killed directly by
lightning, several may die from accidents and fires that follow. One of
the worst death tolls due indirectly to lightning happened in Italy in 1769
when the arsenal at Brescia was struck by lightning. One-sixth of the city
was destroyed and 3000 people killed.

Fortunately, rapid heating and expansion only rarely affect victims
struck by lightning. A golfer was struck at Baltray, north of Dublin, on
7 April 1984, as he carried a bag of golf clubs on his shoulder. His clothes
and metal-studded shoes were completely burnt and the furled umbrella he
was holding shot into the ground like a missile. He had severe wounds to
his right hand and foot, extensive burns, ruptured eardrums and internal
injuries that doctors could only attribute to his bowels having suddenly
expanded. An operation revealed half-a-dozen perforations of his bowels,
that is, peritonitis. Surgeons suggested that as the lightning current passed
through the bowels, the gas inside expanded rapidly, bursting the bowels
in six places. A brass buckle on the victim’s trouser belt had provided
a point of entry for the current into the abdomen. After extensive surgery,
the victim was back playing golf in just six months.

The hazards of lightning are greater around trees, especially if they
stand alone. As many as one-quarter of people killed by lightning were sheltering
under a tree. When lightning strikes a tree, the electrical resistance offered
by it may be sufficient to cause sideflashes or a spark from the tree to
a sheltering person. A sideflash often happens when lightning strikes a
building or a tree. Instead of the current travelling straight down to the
ground, it flashes across to a better conductor nearby. This better electrical
conductor could well be human. John White, a Tottenham Hotspur footballer,
was killed by lightning while playing golf on 21 July 1966 at Enfield, Middlesex.
He had taken shelter under an oak tree during a thunderstorm and was killed
by a sideflash. Oaks appear to be struck more frequently than other trees
as they are often very tall, solitary specimens. Traditionally, farmers
planted an oak near their house so as to divert any lightning strike away
from the building. There are, however, precautions against lightning that
take a lot less time than this.

When lightning strikes a tree or the ground, it creates large voltage
gradients on the ground surface as the current propagates outward. If you
are standing nearby, this can cause a momentary difference of several thousand
volts between your feet, which may induce a fatal surge of current through
your body. The wider apart your feet, the greater and more dangerous the
current. Four-legged animals, whose legs span a greater distance, experience
a greater voltage gradient. Many die because of this effect. So, in a thunderstorm,
you should avoid lying flat on the ground as this increases the difference
in voltage along your body if lightning strikes nearby. Keeping your feet
together and crouching as low as possible with your hands on your knees
is the best advice.

Some of the more dramatic incidents involve teams playing football,
hockey and cricket. When lightning strikes, the voltage differential in
the ground throws many of the players to the ground. People fall because
of the pressure wave if they are very close to the strike. At greater distances,
it may be the shock of the current through their leg muscles that makes
them collapse. Further, if one person is struck by lightning, sideflashes
from that person may affect other players nearby. Nine cricketers were injured
and one killed during a match at Isleworth, West London, in August 1987.
Lightning felled 11 soccer players near Newport, in Gwent, on 8 April 1979.
One player, who was standing nearest to a metal post at the edge of the
field, suffered severe burns and stopped breathing, but was revived. Four
others had slight burns and the rest were treated for shock.

You can do things to lower the risk of a current passing through your
body. Getting wet can give some protection. Wet clothes are a better conductor
of electricity than the human body whereas dry clothes are poorer than both.
Wet clothes will conduct most of the current over your body rather than
through it. You may get burnt, but the current bypasses your heart and other
vital internal organs.

Rubber insulation between your body and the ground can offer some degree
of safety, whether it is rubber-soled boots and shoes or rubber tyres on
a vehicle. When lightning strikes a vehicle, the current flows safely around
the occupant through the metal of the bodywork before earthing to the ground
through the tyres, which may contain steel wire and are usually wet from
the thunderstorm. The tyres may be damaged as the current arcs across the
final few centimetres to earth. When lightning struck a truck in Texas in
1979, three passengers sitting in the open back were killed; the three inside
the cab were uninjured.

Farmers out in the open on tractors, especially on older vehicles without
closed metal cabs, have to be particularly careful. Though they may feel
protected by the large rubber wheels, they may have metal ploughs in the
ground when lightning strikes. In upper New York State in 1985, an ambulance
was called to attend to a farmer injured by lightning while he was driving
a tractor and ploughing his field. (An hour later, on his way to hospital,
the ambulance was struck by lightning. It crashed and he was killed.)

Avoiding a lightning strike seems to be a mixture of sensible precautions
and good luck. You may get a few seconds warning that you are about to be
struck by lightning if your hair stands on end. Metal objects such as a
camera or fence may start buzzing or crackling. This is caused by positive
electrical charges forming at the ground and spreading up towards the negative
charge or ‘leader’ propagating downwards from the thundercloud. Lightning
does not always follow, as not all upward discharges make contact with the
leader, but it is best to move away if you notice it. Fishermen who were
on a 10-metre boat about six miles from Whitby, off the North Yorkshire
coast, in July 1980, counted themselves very lucky. For 20 minutes every
strand of their exposed hair, including moustaches and the hair on their
forearms, stood upright. Then a sudden violent thunderstorm began. Lightning
missed the boat by a few metres, striking the sea, and at that moment their
hair fell flat. In California, a few years ago, two brothers and their sister
were standing on an observation point overlooking Sequoia National Park
when their hair began to stand on end. They took photographs of each other.
Five minutes later, after they had left, lightning struck the platform on
which they had been standing. One person was killed and seven others were
injured. Be warned.

Don’t believe in the old saying ‘lightning never strikes twice in the
same place’. It may strike tall buildings many times during the same thunderstorm
and as often as 500 times a year. Despite this, towns and cities are usually
safer than the open countryside, as the high buildings and power lines attract
most of the flashes. Lightning can even strike the same person more than
once. During a thunderstorm in the late evening of 22 June 1978, a motorist
returning home from Wisbech, Cambridgeshire, was struck twice by lightning
in the space of about six kilometres. The only man to survive being struck
by lightning seven times was an ex-Park Ranger of Virginia, Roy Sullivan.
He was first struck in 1942 when he lost a big toe nail, then again in 1969
when his eyebrows were burned, in 1970 with a seared left shoulder, in 1972
when his hair was set on fire, in 1973 when his regrown hair was set alight,
in 1976 with an injured ankle, and in 1977 with chest and stomach burns.

Lightning is not all bad news. On rare occasions, its victims have welcomed
strikes. In 1782, a paralysed member of the household of the Duke of Kent
was struck by lightning. He survived, with his paralysis cured. Edwin Robinson,
a resident of Falmouth, Massachusetts, had been blind and deaf for nine
years following a road accident. Then, as he sheltered beneath a tree during
a storm on 4 June 1980, he was struck by lightning. He lay unconscious for
20 minutes with his hearing aid shattered. When he awoke, his sight and
hearing began to return. But this type of strike is very much the exception.
The rule is that lightning is dangerous.

* * *

The truth about Thor’s thunderbolts

LIGHTNING is a transient electric discharge with a high current, along
a path many kilometres in length. The mechanisms by which thunderstorms
gain electric charges, and subsequently produce lightning, remain elusive
in spite of major developments in investigative techniques and physical
modelling.

The atmosphere is electrically neutral below the ionosphere, which starts
60 kilometres above the Earth’s surface. The air in which we live does not
normally have an electric charge. In a thunderstorm, lightning has a negative
charge, leaving large parts of the thundercloud positively charged. In order
to understand lightning, scientists must work out how the positive and negative
charges separate.

One hypothesis offered to explain electrification and charge separation
within thunderstorms invokes collisions between particles, droplets and
crystals of different sizes within the cloud. As large falling raindrops,
hailstones and ice pellets (or graupel), together called hydrometeors, collide
with smaller water droplets and ice crystals suspended in the cloud, they
transfer their electrical charges. The larger hydrometeors gain a negative
charge as they fall, while the smaller hydrometeors are left behind in the
upper part of the cloud,with a positive charge. The cloud becomes positively
charged at the top, and negatively charged below. But this hypothesis does
not explain why thunderstorms usually have a small positively charged region
at the base of the cloud. One recent discovery may provide the answer.

Physicists have found that the sign of the charges acquired by falling
ice particles as they collide with smaller ice crystals, in the presence
of droplets of supercooled water, depends upon the temperature of the cloud.
There is a critical temperature of about -15 Degree C at which the charge
passed onto the ice particles changes sign. Throughout much of the cloud,
where temperatures are lower than -15 Degree C, an ice pellet acquires a
negative charge as it falls. But as ice reaches the lowest regions of the
cloud, where it is warmer than the critical temperature, it gains a positive
charge. It is this process that probably forms the small region of positive
charge near the base of a mature thundercloud.

Once the electric charge has built up from impacts between ice particles
and water drops, there is an electric field with a potential difference
of between 1 million and 3 million volts per metre. A typical cloud-to-ground
lightning flash begins with the formation of an intermittent, highly-branched
discharge, called a stepped leader, that spreads downward. The leader carries
a negative charge towards the ground along the tips of the branching discharge
and it leaves a trail of ionised air. As a branch of the stepped leader
comes to within about 100 metres of the ground, the negative charge in the
air attracts a positive charge just above the ground. The electrical field
beneath the leader becomes very large, and one or more discharges form at
the ground and propagate upwards. These discharges or streamers rise until
one or more attach to the leader between 10 and 20 metres above the ground
surface.

When contact is made the first bright return stroke occurs. This is
the start of the lightning strike. The return stroke is a very large pulse
of current that starts at the ground and runs back up the channel of ionised
air into the cloud. The return stroke has a peak current of between 10 000
and 40 000 amperes. After a fractional pause, another leader propagates,
down the ionised channel from the preceding return stroke, and starts off
a second return stroke.

A typical lightning flash consists of three or four leaders and return
strokes, but as many as 40 have been measured. As the human eye cannot resolve
the time intervals of tens of microseconds between these components, we
see lightning flicker. Sometimes, the leader propagates only part of the
way down an existing ionised channel and then forges a different path to
the ground. In such cases we see forked lightning or lightning that strikes
the ground in two places.

A lightning conductor rod protects a building by readily setting up
a discharge whenever a stepped leader approaches within ‘striking distance’.
A lightning conductor is pointed so that it builds up a high density of
positive charge in response to the negative charge of the leader above.
Isolated trees and tall structures are dangerous in the same way because
they are easy targets for a strike. A lightning conductor channels the return
stroke along its cable, keeping the current safely outside the building.
In other words, the conductor simply creates a preferred strike point for
any lightning around an exposed building or structure. Although they can
fail, you are better off with a lightning conductor on your house than without.

* * *

How to dodge thunderbolts

KEEP away from wide open spaces as well as tall or isolated trees. Seek
shelter in a building.

You are safest if you crouch down with both feet close together and
your hands on your knees.

If you get your clothes wet, you will probably avoid serious injury
if you are struck.

If you are swimming, windsurfing or in a boat, get to the shore as quickly
as possible.

Stay inside a car if you can. It will protect you as long as you do
not touch the metal of the car body.

If you are caught outside get rid of umbrellas, fishing rods, golf clubs
and other bits of metal where possible.

In a thunderstorm if your hair stands on end or you hear buzzing from
nearby rocks, metal fences and so on, move away.

Give first aid to anyone struck by lightning; they will probably recover.

Derek Elsom is Principal Lecturer in Geography at Oxford Polytechnic
as well as Director of the Research Centre of the Tornado and Storm Research
Organisation (TORRO).