Why would a lightning-struck tree glow after being hit?
It is not on fire and does not give off heat, but glows.
It was a dark and stormy night. Chris emails he
was walking in the woods "a little after a thunderstorm" when he
noticed the tree. The tree, shattered by an earlier lightning
stroke, stabbed the night like a broken pike. An eerie glow extended ...
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Everybody out of the
pool!
 Q: Does lightning strike indoor swimming pools? If
the building has lightning rods? Has anyone ever been hurt or killed?
Ann, Oberlin, Ohio
A crawl swimmer, indoors. Photo courtesy of the US Army, Fort Sill
and Wikipedia.
A: Lightning can strike indoor swimming pools. That's why lifeguards yell, "Every body out of the pool!" when lightning gets within six
to eight miles.
Current from a lightning strike can invade
an indoor pool, and hurt people. Here's how: Lightning strikes a power pole
outside the pool building. A surge of current races along the electrical
wires from the hit power pole to the pump in the building. The pump
moves water and, therefore, contains water; water conducts electricity. The
current surge flows from
pump wires into pump water, which conducts the electric current into pool water
and water splashed around the area.
This endangers people in the pool and walking on the wet floors, because the
current then flows through people to ground, along any of various paths: A
person standing in the pool, one climbing on the ladder, another touching the
underwater lights. The huge current could injure or kill all such people.
When lightning is within five miles of an indoor pool, safe practices dictate
leaving the pool, and moving to a dry area of the building — well away from any metal (such as, phone lines, electrical wires or buried pipes).
Metal can conduct a bolt's current.
If the "Flash-To-Bang" delay (length of time in seconds between a lightning
flash and its subsequent thunder) is 30 seconds, the lightning is five miles
away.
Current flowing from a lightning strike is fearsome — averaging about 25,000 amps.
For comparison: a reading lamp shines with only one amp of current. In the year 2000, lightning killed
two boys in an outdoor pool in Florida.
"The enormous power of a lightning bolt does make the kind of precautions you
outlined appropriate, although they may seem extreme to the kid who really wants
to go swimming," emails physicist
Rod Nave, professor at Georgia State University.
"We could find no reports of deaths or injuries in indoor pools related to
lightning causes," says
Richard Kithil of the National Lightning Safety
Institute and Kevin Johnston, a senior consultant. They suspect such
incidents happen, but go unreported. They have observed: a main
circulation pump destroyed, injuries to employees touching electrical panels and
the concrete footing of a water slide blown apart.
"There are many reports of injuries/deaths in bathtubs from lightning. This
is indirect evidence, of course, but it seems reasonable
the same danger exists in (larger) swimming pools," emails Kithil.
Kithil and Johnson conclude: suspend all pool activities (including showers) until 30
minutes after the last observed thunder or lightning.
By the way, over the past 30 years, lightning killed more people in the USA than
tornadoes or hurricanes, according to
John Jensenius of the NOAA and the National Weather Service.
Further Reading
Lightning and aquatics safety: a cautionary perspective for indoor pools by
Richard Kithil and Kevin Johnston, National Lightning Safety Institute
Weather
fatalities, NOAA
Lightning safety,
NOAA
Lightning current by Rod Nave, HyperPhysics
Lightning safety, National Weather Service
Lightning
FAQ, National Severe Storms Laboratory (NSSL)
Reader's Answer
According to the National Severe Storms Laboratory (NSSL),
both indoor and outdoor pools are unsafe during a lightning storm. Reason being
that any part of a home or outdoor facility that is struck by lightening can
affect the entire location. According to this website, there have been no
reported deaths due to swimming indoors during a lightning storm.
Karishma, Kaajal, and Shanya, West Sacramento, California USA
(Answered Oct. 9, 2007)
Readers' Comments:
- Why does the article begin, "Lightning strikes indoor swimming pools", as
if there have been deaths from lightning in indoor swimming pools? The fact
of the matter is that virtually everyone refers to the NLSI article by Kithil,
but never has there been a death in an indoor swimming pool. But there have
been deaths in showers (where many go when forced to leave the pool).
Lightning is virtually impossible to predict, but if no one has ever been
killed in an indoor pool, wouldn't it make sense to actually go get IN the
pool when lightning is in the area. Where would you rather be? In a place
where it has killed, or in a place where it has NEVER killed?
My opinion is that the NLSI piece is a cya piece that pretends to be
scientific, but contains no research other than scouring the internet, only to
find that no deaths have ever been reported in an indoor pool. Wouldn't any
sane person thereby conclude that swimming in an indoor pool when there is
lightning in the area poses no significant risk? What other conclusion could
you come to?
Look, in elementary school they used to instruct us to hide under our desks in
case of an atomic bomb attack? Why don't we do that any more? Because it is
pointless. The same is true for requiring folks to leave an indoor pool when
there is lightning in the area.
When will we act according to facts, as opposed to acting because someone
invented a bogeyman? Lloyd, Austin, Texas,
USA
- Reply: You've got a point,
Lloyd. I've changed the lead to lightning can strike indoor
pools, which it certainly can. Just as it can showers. I would not
go anyplace near metal pipes during a thunderstorm.
-
On an added note, while I suppose it is true that lightning can strike
virtually anywhere, including indoor pools, you might want to take a look at
an article published by Aquatics International here:
You'll note that their conclusion is that, if simple, basic national
building standards have been met, one is just as safe in an indoor pool as
anywhere else, as the statistics bear out.. To me that says that there is
no good scientific reason for clearing indoor pools when lightning is in the
area. In fact, since people often walk into a parking lot to go to their
car to exit a facility when forced to exit an indoor pool, clearing a pool
when lightning is in the area actually exposes more people to increased
danger from lightning. That would make clearing an indoor pool a very poor
and dangerous decision. Wouldn't you agree? Lloyd, Austin, Texas,
USA
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