Tesla Coil Hazards and
WARNING - I disclaim all warranty for the
information below, including but not limited to any and all warranties of
completeness of this information! I will *NOT* be responsible if you or anyone
dies, gets hurt, or has any damage to real or personal property if anything goes
wrong. This is regardless of whether or not I warned of whatever goes/went wrong
accurately, inaccurately, or not at all! Build, test, and/or operate Tesla coils
only at your own risk!
In addition to any precuations mentioned or implied below, use common
Although the current is low and the high frequency involved usually does
not shock, things sometimes go a bit wrong. You may draw a spark beginning
near time of a secondary voltage peak and ending at a time that the secondary
instantaneous voltage is near zero, which gives some net DC charge transfer to
you which will shock. This may be worse if you are grounded. The shock from
this is usually minimal, but there is no guarantee of safety, especially
with larger coils. Maybe nobody has ever died from this yet, but there is
the chance the shock may jolt you into bumping something and breaking it, or
contacting more hazardous points such as the primary circuit of a spark gap
If you are near the secondary, you become a small part of a resonant
circuit. The secondary has capacitance to you, and you have capacitance to
ground. If you touch something grounded, you can conduct more current
through that point of contact than is normally available from the top
end of the secondary. I have burned myself with nasty arcs of a kilovolt
or two and currents in the tens of milliamps by touching ground while
being close to the secondary of a solid state Tesla coil.
The sparks, brush discharges and corona produced by Tesla coils can produce
ozone. Ozone is bad to breathe since it can corrode lung tissue. If you are
going to breathe it a few hours a day, it can be unhealthful to breathe even if
the concentration is too weak to smell. Ozone can also oxidize some rubber
objects. If you are having brush discharges or corona, you should operate the
Tesla coil only in a very well ventillated area, or expose youself to the ozone
for no more than a few minutes a day.
Sparks and arcs also produce nitrogen oxides which can also be hard on lung
tissue. Nitrogen oxides can be changed to other nitrogen oxides when mixed with
ozone and enough heat or ultraviolet. The worst one is nitrogen pentoxide (N2O5)
which combines with any moisture to form nitric acid. Some other nitrogen oxides
form acid solutions in contact with moisture to a lesser extent. The most
obvious nitrogen oxide is nitrogen dioxide, which is to some extent corrosive
to lung tissue and maybe rubber objects.
Nitrogen oxides may be formed in very significant quantities by the high current
sparks in the spark gap of spark gap type Tesla coils. You can largely confine
the production of noxious gases by putting the spark gap in a closed container.
This container should be either not perfectly airtight or be capable of
withstanding the pressure when the heat of the spark makes the air expand. If
you put the primary spark in a glass jar, you may see the air turn orangish
brown from the nitrogen dioxide. Production of nitrogen dioxide will stop when
nearly all the oxygen in the jar has combined with nitrogen.
One hazard is the possibility of deep burns. Burns penetrating through the
dermis or affecting internal tissue can take a really long time to heal.
Such burns can easily occur from radio frequency currents since they
usually produce little or no electric shock effect, and people exposed to
these can underestimate the risks of these currents. Furthermore, you may
be able to heat up tissue where there aren't many heat-sensitive nerve
endings and can cook part of yourself before you know it!
One really oddball hazard is any effects of putting your head in a strong
enough radio frequency magnetic field. This is more a hazard of solid state
coils which oscillate continuously, and probably requires being at a close range
(maybe almost having your head inside the secondary). The problem is effects of
a sudden temperature change in your brain. This may cause a seizure; in milder
cases suddenly reduced mental function. In severe cases related to point-blank
exposure to powerful microwave beams from radar transmitters, people have been
known to pass out and stop breathing - obviously dangerous! Severe effects can
occur from a sudden temperature change of only a degree or two.
Solid state Tesla coils often oscillate continuously, or even when
intermittently usually do so at a higher duty cycle than spark gap Tesla coils,
which means much higher average currents and somewhat higher RMS currents
everywhere. The same is true of vacuum tube Tesla coils. This makes corona and
brush discharges more intense, meaning more ozone. This also makes sparks, arcs,
brush discharges and corona more capable of causing burns and starting fires.
The main hazard specific to spark gap Tesla coils is the primary circuit.
This can electrocute you. Neon sign transformers and sometimes oil burner
transformers are often used for these. There is some popular misinformation
around that these won't kill you, but they can. The current is below the
most-deadly range of 100 to 1000 mA, but people sometimes die from getting
shocked by these things. And with capacitors added to this which spark gap
Tesla coils normally have, the effects of getting shocked are worse.
One more thing - although having someone nearby who knows CPR or who has a
defibrillator handy is good, the success rate is less than 100 percent.
You should be well aware that Tesla coils make sparks and arcs that can burn
things and start fires. Sometimes, intense corona can set things on fire, and
this is especially true with solid state Tesla coils. Solid state ones usually
oscillate continuously or nearly continuously, and the capacitance of a puff of
corona or brush discharge can draw enough current for it to quite hot!
Conductive objects in the coil's electric field can make sparks if they
touch or get very close to other conductive objects that are grounded or
unequally exposed to the coil's electric field. These sparks could start
fires. One fear I have is that a stray wire, pipe, pipe support strap, or
a long nail behind a wall could touch some damp wood behind the wall and
make a spark and then a carbonized spot and then start a fire.
Closed loops of fine wire may burn up if they are close enough to the coil
to get enough magnetic field to have a lot of current flowing through.
The strong AC electric field is probably not too good for electronic
equipment, especially if the equipment is running. This is particularly
true with computers! They may "latch up" and have even been reported to
spontaneously reboot when exposed to the electric field of a Tesla coil.
NEWS 7/6/2005 - I have caused an answering machine to falsely detect an
actually nonexistent incoming call when 5 feet (1.6 meters) from a slightly
large size Tesla coil that developed peak voltage of merely 40, maybe 50
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Written by Don Klipstein.
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