Lightning
and the
Diver
Oceans Rarely Hit By
Lightning
NASA
has shown with satellite imaging that the oceans rarely get hit with
lightning.
Apparently the surface water does not heat up enough to cause the
positive
charge needed for lightning to occur. Potentially, lightning is the
biggest
weather danger for divers. Every year, lightning kills more people in
the
US than tornadoes or hurricanes. Only floods are more deadly. During
the
last three decades, floods killed an average of 139 people a year,
lightning
87, tornadoes 82 and hurricanes 27 in the US, according to national
Weather
Service figures.
The question should be "what
cautionaries
should the scuba diver take?" Should he get out of the water? Is he
safer
in the water than in the boat? If shore diving - stay in the water or
go
ashore?
Over the years around ten percent of
the
lightning deaths in the US have been in or near the water-
the statistics don't show how manyvictims
were diving or swimming, how many were on boats and how many were on
beaches.
Lightning is likely to strike the highest thing around, which is why
we're
told not to take shelter under trees during thunderstorms. If you're in
a boat during a thunderstorm, the boat and everyone in it are the
highest
things around; they're prime targets for lightning bolts. While people
on land can take shelter in buildings or vehicles, those aboard a dive
boat that's caught by a thunderstorm far from shore have no place to
take
shelter. Diving underwater may not be an option. Lightning that hits
the
water could be deadly because it's electricity flows through water.
Scientists know
little
about what happens when lightning hits water. The electrical current
probably
spreads in all directions, weakening as it spreads out. Since large
numbers
of dead fish aren't found after thunderstorms move across bodies of
water,
the current probably weakens in short distances.
Still, a diver who
happens
to be underwater when a lightning bolt hits nearby could become part of
an unintended scientific experiment on just how quickly the current
weakens.
I can find nothing about a possible
stand
off distance, probably since a prediction cannot be made regarding the
location of the strike. Assume that it will hit the highest point,
however,
and the answer would be to get out of the boat or stay in the water if
shore diving. We just don't know the answer.
Ron Holle, research meteorologist,
NOAA
National Severe Storms Laboratory, Norman, Okla. has this to say about
lightning and water:
"Large numbers of lightning flashes
strike
oceans, lakes, rivers, and ponds. If there is nothing protruding higher
than a body of water or flat ground, then a flat surface is hit.
The area of a swimming pool is small,
so
it's not usually directly hit. However, the area affecting a pool is
quite
large. This area includes the surrounding power and telephone lines,
and
the plumbing around the pool and inside the bathhouse and other
structures.
These are usually unsafe places during a thunderstorm because the
current
from a lightning strike will travel easily through the standing
water,
showers and other plumbing. Since the pump, lights and other facilities
have power lines linked to the plumbing, a hit to any part of a pool
complex
can affect all of it.
Water does not "attract" lightning.
It
does, however, conduct current very well. It's not clear how far
lightning
travels through water. People have been killed or injured by direct or
indirect strikes while in or on the water, boats, docks, piers, surf,
surfboards,
canoes, while fishing, and so on. In most cases, it appears that the
strike
was within a few tens of yards of the person. But the current can
extend
farther through plumbing or wiring so the distance of influence can be
greater.
In general, there is less lightning
per
area over water than over land. This is due to the fact that water
bodies
are usually cooler than land during summer. For this reason
thunderstorms
are less likely to build or continue to develop over water than over
heated
land.
The current in a lightning bolt is as
high
as 30,000 amperes --- about 150 times more than ordinary house current of 200 amps. It's
easy to see how this much electricity is deadly. Fortunately, many
lightning
victims aren't hit directly, if all the charge doesn't go through them.
This is why about six out of every seven persons hit by lightning
survive,
although sometimes with serious injuries and lasting ill effects.
Lightning will
often
hit something, such as a tree, a wire fence or a boat mast. Most of the
electricity flows through the object that it hits, but some jumps to
hit
a person or people. This is called a 'side flash'. Such side flashes
have
killed people talking on the telephone or taking a shower inside
otherwise
safe buildings, following through phone lines or water pipes after
hitting
the ground. People are also sometimes injures when lightning hits the
ground
and follows it to where they are standing.
Lightning can
affect
all parts of the body, but the usual cause of deaths is heart stoppage.
The electrical charge disrupts the heart's rhythm, stopping it.
Usually,
however, the heart will quickly resume beating. The electricity is more
likely to paralyze the brain's respiratory center. The victim will die
from lack of oxygen unless someone nearby can quickly perform
artificial
respiration to get the victim's breathing going again. This may have to
continue for hours before the victim begins to breath normally.
A Lightning Safety
Group,
which met at the 1998 American Meteorolgical Society convention to
update
safety recommendations, noted in it's report: "Generally speaking, if
an
individual can see lightning and/or hear thunder, he or she is already
at risk. Louder or more frequent thunder indicates that lightning
activity
is approaching, increasing the risk for lightning injury or death."
The report also
notes
that "many lightning casualties occur in the beginning, as the storm
approaches
--- Also, many lightning casualties occur after the perceived threat
has
passed." In fact, the danger can persist as long as thirty minutes
after
the storm has passed and the last thunder is heard.
Lightning always
comes
from a thunderstorm cloud, but has been known to hit as far as 20
miles from
the nearest cloud, far from the storm's rain. This is why the group
says
seeing just one lightning bolt or hearing one clap of thunder should be
a warning to get into a safe place.
If you're caught in
a
boat, about all you can do is crouch down in the boat's center and stay
as far away from any metal surfaces, and radios or other electrical
gear
that might be attached to an antenna.
If you see
lightning,
knowing which way the wind is pushing the clouds will make a big
difference.
If the wind is pushing the clouds your way, it's time to head for
shore.
If you see lightning, the flash to bang method can also help determine
whether lightning is moving closer. ( sound travels about one mile
every
five seconds).
If caught at sea
in a
thunderstorm:
-Stay in the center
of
the cabin
--Keep arms and
legs
in the boat - do not dangle in the water.
--Discontinue all
water
activities
--Disconnect and do
not
touch any electronic equipment.
--Lower, remove or
tie
down the radio antenna and other protruding devices if not part of the
lightning protection system
--Avoid making
contact
with any part of the boat connected to the lightning protection system.
Avoid touching two components that are connected to the system at the
same
time, such as the gear lever and spotlight handle.
NOAA has this to say about
lightning and
water:
-Get out of the water, it's a great conductor of electricity.
-Stay
off the beach and out of small boats or canoes.
-If caught in a boat, crouch
down in the center away from metal hardware.
-Swimming, wading, snorkeling
and scuba diving are NOT safe.
-Lightning can strike the water and travel
some distance beneath and away from its point of contact.
-Don't stand in
puddles of water.
The US Navy Manual does not address
the
problem, that I can find.
So-- what to do? If I were
diving
in a thunderstorm, I'd get out of the water. Before diving? I'd not
dive
during and for thirty minutes after the storm.
However, we might want to alter our recommendations considering
this answer to a question to Science Update posed about lightning and
fish kills. This was sent to us by Jeff Wiberg.
"Does lightning fry fish? I'm Bob
Hirshon and this is Science Update.
Today's question comes from
Matthew Dabney of Longmont, Colorado.
Matt:
"Why is it that we're directed to get out of water during a
lightning storm to avoid electrocution? Do fish get electrocuted when the
lightning strikes a lake?"
We asked Don MacGorman, a physicist at the National Severe Storms
Laboratory in Norman, Oklahoma. He says that as long as the fish are underwater,
they're probably okay.
Don:
"Basically lightning stays more on the surface of the water
rather than penetrating it. That's because water is a reasonably good conductor,
and a good conductor keeps most of the current on the surface."
So, when lightning hits the water, the current zips across the surface in
all directions. And if you're swimming anywhere in the vicinity, it'll probably
hit you. But below the surface, most of the electricity is instantly
neutralized. So the fish are generally spared.
Of course, if the fish happen to be surfacing, they're at risk just like
you are. And Dr. MacGorman adds that some electricity does penetrate the water,
right at the strike point.
Don:
"So fish under a lightning strike can be killed, if it's close
enough to the surface. But it has to be much closer than you do on the surface
of the water."
Considering this answer - and if you have diving gear and
adequate air - the best place for you to be would be underwater
(not on the surface swimming).
