Does anyone here have any tales to tell about safety hazards involving
tabletop VandeGraaff generators? Parents are leery about the 300,000
volts produced by some of these, so I wrote up a page on VDG safety.
Leyden jars and medical implants are the biggies. Are there other hazards
I should mention? (see below)
Tabletop Vandegraaff machines are very safe. They've been used in
classrooms and Science Museums for decades with little difficulty. I've
not encountered any literature on hazards associated with VDG machines, so
I've put together a bit here.
NOTE: I am not an expert regarding electrical safety. This
page is for your information only. For accurate information,
consult an expert in electrical shock hazards.
VOLTAGE: electric potential or electrostatic fields by themselves cannot
harm humans. Rubbing a balloon upon dry fur can produce potentials
approaching those of a tabletop VDG generator: 20,000 volts. The high
voltage produced by a tabletop VandeGraaff generator is about as dangerous
as an electrified balloon.
DC CURRENT: a tabletop VDG produces an electric current below 100uA
(microamperes), which is about ten times smaller than a human is able to
feel. If you lick your fingertips and touch them to the terminals of a 9v
radio battery, the level of current in your fingers will be much higher
than that produced by a VDG machine. As far as constant currents go, a 9v
battery is more dangerous than a VDG.
SPARKS AND IMPULSE CURRENT: here is where there is possible danger. The
peak current during the spark from a VDG machine can be as high as 10,000
amperes. However, at this amperage the current lasts for less than a
millionth of a second. At a more moderate discharge current of 10mA, the
discharge might last up to a millisecond. This is near the threshold of
human perception of current, and indeed, if you allow the spark to jump to
a metal object held in your hand, you sometimes can feel a small twitch in
the muscles of your arm. The pain from sparks mostly comes from the high
current density and microscopic region of burned skin where the spark
enters your skin. Small sparks might be slightly painful, but there is
far more danger from the suprise they can cause when they happen
unexpectedly.
POSSIBLE HAZARDS
* A person suprised by the small shock might stumble and fall,
especially while standing on a rickety chair during the usual
"hair raise" demonstration.
* If you use your VDG to electrify a large Leyden Jar, you can build
up dangerous energy levels and create an electrocution hazard. If
you touch the wrong parts of the leyden jar, the discharge through
your body can violently tense your muscles, causing you to crash
into nearby furniture. The discharge might knock you unconscious
so you fall and hit your head. It may even stop your heart. Don't
use Leyden Jars unless you are trained in dealing with hazardous
high voltage. Never let kids experiment with VandeGraaff machines
and Leyden jars together.
* Medical implants could be damaged. A person with a cochlear
implant, a portable external defibrillator, or other sensitive
device must steer clear of radio transmitters, microwave ovens,
cellular phones, electrified balloons, and VDG machines.
* The small spark from a VDG could cause a heart attack in a person
having a serious undiagnosed heart condition. Needless to say,
this possibility gives nightmares to public science demonstrators.
It doesn't matter if that person would have had a heart attack
within a day, if YOUR device triggered it, who will be blamed?
* If a person has flammable liquids on their skin or clothing, a
spark from a VDG might trigger a fire. The classic hazard is
butane from a leaking cigarette lighter in an inside pocket in a
jumpsuit.
* Some older VDG machines contain a high voltage power supply. This
supply presents an electrocution hazard if the generator's case is
opened or if the charged lower comb is touched. Also, if the belt
becomes conductive from built up dirt, and if both combs touch the
belt, the generator's upper sphere will present an electrocution
hazard.
* And last: If you operate a VDG next to a computer, and the
computer circuitry gets trashed, the owner of the computer might
kill you! ;)
Created and maintained by Bill Beaty. Mail me at: billb@eskimo.com.
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