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!
In addition to any precuations mentioned or implied below, use common
WARNING - I will *NOT* be responsible
if you or anyone else 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!
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 and intense corona easily produced by Tesla coils can produce
ozone. Ozone is bad to breathe since it can corrode lung tissue. And 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 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
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
more intense, meaning more ozone. This also makes sparks, arcs and even corona
much 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 particularly true with solid state Tesla coils. Solid
state ones usually oscillate continuously or nearly continuously, and the
capacitance of a puff of corona can draw enough current to make the corona
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
Back up to Don's Tesla coil main page.
Back up to Don's home page.
Written by Don Klipstein.
Please read my Copyright and authorship info.
Please read my Disclaimer.