Find Me On:
CONTENTS
1.0) Electrical Hazards, Fuses and Safety Switches
2.0) Burns
3.0) Induction Field Effects
4.0) Ozone, Nitrites, and Vapors
5.0) Ultraviolet Light and X-ray Production
6.0) Radio Frequency Interference
7.0) Fire Hazards
8.0) Chemical Hazards
9.0) Explosion Hazards
10.0) Noise Hazards
11.0) Neighbors, The Spouse, and Children
12.0) Other
1.0) Electrical Hazards, Fuses and Safety Switches
Tesla coils use high voltages, and the risk of death or injury
is significant. The following general guidelines are suggested:
Never adjust tesla coils when the power is
turned on.
High voltage capacitors may hold a charge
long after power is turned off. Always discharge capacitors
before adjusting a primary circuit.
Make sure the metal cases of transformers,
motors, control panels and other items associated with tesla
coils are properly grounded.
Make sure that you are far enough away from
the corona discharge so that it cannot strike you. Do not come
in contact with metal objects which might be subject to a strike
from the secondary.
The low voltage primary circuit is extremely
dangerous! These voltages are especially lethal to humans. Make
sure these circuits are well insulated so users cannot come in
contact with the A.C. line voltage.
A safety key should be used in the low
voltage circuit to prevent unauthorized use.
Use adequate fusing of the primary power
and/or circuit breakers to limit the maximum current to your
control panel. Do NOT count on your home circuit panel to
provide adequate protection!
Never operate a tesla coil in an area where
there is standing water, or where a significant shock hazard
exists.
Do not operate a tesla coil when pets or
small children are present.
Spend some time laying out your circuits. Hot
glue, electrical tape and exposed wiring are quick and easy, but
could be lethal.
Information about electricity and humans
Lightning kills about 300 people each year in the United States,
and injures an additional three to four times this number.
(Sorry, I have no data for the rest of the planet.) More than
one thousand people are killed each year in the U.S. due to
generated electric current, and several thousand more are
injured. (This would include potential tesla coilers.) In the
case of lightning, the voltage and current are extremely high,
but the duration is short. The current tends to flow on the
outside of the body and may cause burns, respiratory arrest
and/or cardiac arrest. Many die from lightning due to
respiratory arrest rather than cardiac arrest. (The portion of
the brain controlling breathing is often severely affected in a
lightning strike.) Power line deaths usually involve lower
voltages and currents, but the duration may be significant.
Often the current flows inside the body, causing deep burns and
cardiac arrest. Frequently, the individual cannot let go of the
power source due to involuntary muscle contraction. The brain
and heart are the most sensitive organs. The dose response for
animal and human data suggest the following: for less than 10 mA
hand to foot of 50-60 cycle line current, the person merely
feels a "funny" sensation; for currents above 10 mA, the person
freezes to the circuit and is unable to let go; For currents of
100 mA to one ampere, the likelihood of sudden death is
greatest. Above one ampere, the heart is thrown into a single
contraction, and internal heating becomes significant. The
individual may be thrown free of the power source, but may go
into respiratory and/or cardiac arrest.
Six factors determine the outcome of human contact with
electrical current: voltage, amperage, resistance, frequency,
duration and pathway. I will discuss each individually.
Voltage
Low voltages generally do not cause sudden death unless the
external resistance is low (so don't fire up your coil in wet
areas). As the voltage is increased, more and more current
passes through the body, possibly causing damage to the brain,
heart, or causing involuntary muscle contractions. Perhaps
100-250 volts A. C. is the most lethal voltage, because it is
high enough to cause significant current flow through the body,
and may cause muscles to contract tightly, rendering the victim
incapable of letting go. Lower voltages often are insufficient
to cause enough current flow, and higher voltages may cause the
victim to be thrown clear of the hazard due to the particularly
fierce involuntary muscle contractions. Arcing may occur with
high voltages, however. Naturally, burns become more severe as
the voltage is increased.
Amperage
Greater amperage means greater damage, especially due to heating
within tissues. As little as 10 microamps of current passing
directly through the heart can cause ventricular fibrillation
(heart muscle fibers beat out of sync, so no blood is pumped)
and cardiac arrest. Because of the air filled lungs, much of the
current passing through the chest may potentially pass through
the heart. The spinal cord may also be affected, altering
respiration control. 100-1000 milliamperes is sufficient to
induce respiratory arrest and/or cardiac arrest. Thermal heating
of tissues increases with the square of the current (I2R), so
high current levels can cause severe burns, which may be
internal.
Resistance
A heavily callused dry palm may have a resistance of 1 megohm. A
thin, wet palm may register 100 ohms of resistance. Resistance
is lower in children. Different body tissues exhibit a range of
resistances. Nerves, arteries and muscle are low in resistance.
Bone, fat and tendon are relatively high in resistance. Across
the chest of an average adult, the resistance is about 70-100
ohms. Thermal burns due to I2R losses in the body can be
significant, resulting in the loss of life or limb long after
the initial incident. A limb diameter determines the approximate
"cross section" which the current will flow through, (for
moderate voltages and low frequencies). As a result, a current
passing through the arm generates more temperature rise and
causes more thermal damage than when passing through the
abdomen.
Frequency
The "skin effect" also applies to a human conductor, and as the
frequency gets above about 500 kHz or so, little energy passes
through the internal organs. (I unfortunately have little data
in the 50-250 kHz range, where we operate most tesla coils. I'll
check another reference I have at home.) At a given voltage,
50-60 A.C. current has a much greater ability to cause
ventricular fibrillation than D.C. current. In addition, at
50-60 Hz, involuntary muscle contractions may be so severe that
the individual cannot let go of the power source. Higher
frequencies are less able to cause these involuntary
contractions.
Duration
Obviously, the longer the duration, the more severe the internal
heating of tissues. Duration is particularly a problem when
working with 110-240 volts A.C., which can render the individual
incapable of letting go.
Pathway
If the current passes through the brain or heart, the likelihood
of a lethal dose increases significantly. For example, hand to
hand current flow carries a 60% mortality, whereas hand to foot
current flow results in 20% overall mortality. Be aware that
foot to foot conduction can also occur, if a high voltage lead
is inadvertently stepped on or if grounding is inadequate.
Electrical Precautions
Obviously, the A.C. line voltage, the high voltage transformer
and the high voltage R.F. generated by a tesla coil are each
potentially lethal in their own unique ways. One must always
respect this extreme danger and use high voltage shielding,
contactors, safety interlocks, careful R.F. and A.C. grounding,
and safe operating procedures when working with coils. A safety
key to prevent inexperienced operators from energizing a coil is
essential. High voltage capacitors can also retain lethal
energies (especially in the "equidrive" configuration) and
should always be grounded before adjusting a primary. Whenever
possible, have a buddy around to assist you. Place one hand in
your pocket when near electrical components so the current won't
pass through your chest, and use the back of your hand to touch
any electrical components so you can let go if it happens to
bite you. Remember that most deaths are caused by regular 110
A.C. power! Never perform coiling when overtired or under the
influence of mind altering drugs. Watch a tesla video instead!
More Tesla coils electrical danger information
The previous article mentioned some of them in a general
electrical hazard context, while this article will attempt to
discuss the dangers from a tesla coil point of view.
Electrical Dangers
Exposed wiring on transformers. Most transformers have exposed
high voltage lugs.
Most neon sign transformers that I have seen used for tesla coil
usage have exposed lugs. A 15000 volt transformer has a turn
ratio of 125:1 (assuming 120 volts in). If you haven't
disconnected your input power from the source (unplugged your
variac), you may be in for a surprise. A variac that is putting
out two volts will give you a 250 volt shock if you touch the
high voltage outputs of the neon sign transformer!
Pole pigs (also known as distribution transformers, such as the
one that is probably hanging on a utility pole near your home)
have the same dangers as mentioned above, as well as having much
more current available. At the output voltage of a pole pig, the
current that can go through you is not really limited by
anything other than the current regulation that you attached to
the pig.
Once I shocked myself with one end (7500 volts) of a 60 mA. neon
sign transformer. I just brushed against an exposed end, so I
wasn't gripping anything. It was quite painful, much more so
than touching a sparkplug wire. I felt the path of the current
follow my arm, and go down my leg. Keep one hand in your pocket
when working near or with charged items. (Capacitors, secondary
coils, etc.)
Richard Hull's "Tesla Coil Primer" tape has some excellent
safety suggestions in it, is entertaining, informative, and well
worth the money. One of his best suggestions is the one of
holding the power plug to the power transformer in your hand
whenever you are putting your hands around the circuit.
The transmission line between your high voltage transformer and
your tesla coil is another potential source of electrocution.
This should be constructed using neon sign wiring (rated to 40
kV) or thick coaxial cable like RG-8A/U or RG-11A/U. If using
coaxial cable, use the inner conductor for the high voltage, and
strip back the outer braid about 6-12 inches from each end.
Connect one end of the braid to your RF ground. Leave the other
end unconnected so it does not form a current loop. Some coilers
also place their high voltage cables inside a plastic conduit,
which is laid on the floor. This also protects the cable
somewhat from strikes.
Charged capacitors
"Equidrive" systems will almost always have a residual charge
remaining on the capacitor when the system is turned off. The
"equidrive" system uses two capacitors in the primary coil
circuit. The gap is across the transformer, and the capacitors
extend from the gap to each side of the primary coil. Even with
the gap shorted, the capacitors can hold a lethal voltage. If
you use this configuration, make yourself a shorting rod using a
piece of copper tubing or wire with an insulating handle
attached, and always short out each capacitor at the end of each
run, and again each time you plan to touch the primary system.
Capacitors can also build up a residual charge from
electrostatic sources.
Capacitors have been known to accumulate a charge from various
sources such as static electricity and electric fields. IF YOU
STORE A CAPACITOR, STORE IT WITH A WIRE ACROSS THE TERMINALS.
(MAKE SURE YOU DISCHARGE THE CAPACITOR BEFORE PUTTING THE WIRE
ON!!!)
Capacitors can "regain" charge from dielectric "memory". The
dielectric in a capacitor is put under electrical stress during
use. During operation, this stress may cause the molecules in
the dielectric to orient themselves in such a manner that they
store this charge in their structure. The charge remains after
the capacitor has been discharged. Later the molecules return to
their original states and the charge that they "captured" ends
up on the plates of the capacitor. This charge is then available
to shock you.
Other sources of danger
You are literally playing Russian Roulette when you stick a hand
held metal rod into the output streamer of your coil running at
3kvA, while standing on a concrete floor!!! When you start
running these kind of power levels (or even less) some coils
have a tendency to form a corona or even send a streamer down to
their own primaries every once in a while. A grounded strike
ring is often added around the primary to try to prevent this
self striking streamer from hitting the primary coil and thus
introducing a high voltage pulse into the 'bottom end
electronics' where it could do damage to components. These
strike rails are not 100% effective. The streamer can still, and
sometimes does strike a point downstairs that is part of the
LETHAL high voltage 60 Hz circuitry. When such a contact is
made, any person also connected to a corona/streamer link to the
secondary at the same time will, via the ionized air path,
become connected to lethal 60 Hz mains current. You could try
the trick you described standing on the cement floor in your
tennis shoes half a dozen times and live, or be killed the very
next time you try it. The fact that the bottom of your secondary
is tied to ground will not save you!
If you isolate your own body well away from the floor and any
other potentially conductive objects in the vicinity, such as
sitting or standing on an elevated insulated platform (I would
NOT consider a plastic milk crate adequate!), then you will
probably survive if 60 Hz is introduced into the streamer you
are in contact with by the mechanism described above. However,
in setting up this insulated platform you must consider the path
that may be taken from streamers that will re-emerge from your
body and head off looking for other targets, which could result
in direct contact with earth ground again.
In a safety warning I have about the potential hazards of Tesla
coils mention is made of a stage lecturer while demonstrating
how he could cause long sparks to come out of his fingers (by
standing on a specially constructed coil), was electrocuted when
the discharge created an ionized path to grounded overhead pipes
supporting stage back drops, and the lower voltage but far more
deadly 60 cycle current passed through his body along that path.
The name of this lecturer is believed to be Transtrom.
I was dinking around once with a vacuum tube coil drawing 15
inch streamers to a hand-held, 10 megohm metal film porcelain
resistor about a foot long while standing on a carpeted,
elevated wooden floor in composition rubber soled dry shoes. I
inadvertently got the resistor too close to the primary tank
coil (the top end directly connected to the 3 kilovolt output of
the plate supply transformer) and the high voltage RF closed a
path to the primary. I felt an uncomfortable 60 Hz shock through
my entire body. Had that resistor been a solid metal rod I would
have experienced a very painful jolt or worse, and had I been
standing on a cement floor, I'd probably be 'worm food'.
I think the danger of electrocution is just as real by making
contact with a hand held florescent lamp tube, as any solid
conducting metal object.
I cringe when I hear of some body contact stunts proposed by
people on this list! The potential (no pun intended) for death
is very real. Be EXTREMELY careful!
Another viewpoint
The 60 cycle side of things is where electrocution can happen.
Keep well away from any 60 cycle leads, use grounds and cages as
appropriate. Bear in mind that if a radio frequency arc starts
from a place which also has 60 cycles on it (one side of a
primary circuit, for example) there is the possibility of
high-current 60 cycle conduction along the ionized path. That
could be deadly.....
2.0) Burns
Tesla coils can cause burns, especially due to RF discharges
from the secondary. Stay out of the immediate vicinity of a
tesla coil. Remember, if you do get zapped by a large coil
system, the heating effects may be mostly internal, causing
lasting damage! Also remember that spark gaps and rotaries get
hot and are a potential source of burns.
3.0) Induction Field Effects
Tesla coils operate in a pulsed mode, and strong electric and
magnetic fields are locally produced. In addition, significant
amounts of RF may be produced if the grounding is poor, or
before spark breakout. This can result in induced currents in
other conductors, like test equipment, nearby computers and
electronics, and metal structures in the facility. The end
result is generally bad. Turn off computers and sensitive test
equipment, and move it away from the vicinity of your coils. If
you foolishly choose to use your house electrical ground as your
RF ground, you are asking for trouble. Currents may be induced
anywhere in the building, and voltage standing waves along the
wiring may destroy electronics far from the coil location.
Construct a dedicated RF ground, and make sure it is properly
connected before firing any coil of substantial size.
Fire from other induced currents.
Tesla coils are good at inducing currents. Beware of metal
things that are connected to the same ground as a tesla coil.
For example, I run my coil in my garage, which has a wooden door
on metal tracks. The tracks are against the concrete floor, and
near the strap that serves as a ground for my coil. When the
coil operates, it causes sparks to jump between the running
hardware of the door and the tracks.
Static charges
During the operation of the tesla coil, significant static
charges can build up on the secondary. If you need to move the
secondary (say you are adjusting the coupling), you may get a
nasty zap right across your chest when you pick it up with both
hands. Before you touch the secondary, wipe it lightly with a
grounded wire. You can sometimes hear the crackling as you do
so. Besides the shock hazard, there is the physical hazard
caused by the shock. You will likely drop the secondary or jump
onto something that isn't soft.
Hazards to electronics
Strikes to house electrical ground -- also goes to power(?) A
tesla coil must be connected to a ground that is separate from
the house ground or water pipes. Connecting your coil to either
of these grounds is a recipe for disaster. Notice that your
stereo, computer, VCR, etc., have three prong plugs. Also, note
where your telephone box is grounded. It is likely grounded to
the water pipes.
Consider what happens when your coil strikes the grounded strike
rail, or an unexpectedly long spark that hits an electrical
receptacle. That enormous voltage at high frequency will now be
connected to the grounds of all your electronic goodies or your
telephone. Furthermore, a spark is a conducting path in the
atmosphere. By creating this path, you open your electrical
system up to connections among the 120/220v house system and
ground.
Strikes to garage door opener rails. Since many people do their
coiling in the garage, this topic deserves individual
consideration. If you have a garage door opener, or are
installing one, you should put in a mechanism, such as a switch
or plug and socket, that allows you to disconnect the opener
from the house power.
My garage door got zapped by my coil. The door is connected to
the opener track so the opener got zapped too. The strike caused
the opener to attempt to open the already open door. Since the
door couldn't go any further, the opener started binding. I was
able to unplug the opener and keep the thing from smoking.
More than one person on the list has replaced their opener as a
result of their coiling activity. Be warned of the dangers to
the equipment. An untested suggestion is to put a grounded wire
underneath the rail and opener to draw the sparks to the wire.
Electric fields inducing currents and killing sensitive meters.
Oddly enough sensitive meters and measuring equipment are just
that -- sensitive. Solid state instruments are much more
susceptible to damage from being near tesla coils than are
vacuum tube items. Consider purchasing a cheap volt-ohmeter
(VOM) with an analog meter movement. If will survive in places
many digital units will not. A used vacuum tube oscilloscope is
also more likely to survive the tesla coil environment and can
be obtained cheaply at hamfests.
Good electrical practice
Place your coil in a location that will prevent the strikes from
hitting electrical outlets, people, animals, and sensitive
electrical equipment. Turn off and unplug computers in your
house.
4.0) Ozone, Nitrites, and Vapors
A sparking tesla coil produces ozone, nitrites, and probably a
host of other potentially toxic substances. Do not operate a
large coil in an enclosed area for long periods of time. Make
sure ventilation is adequate at all times. There have been
anecdotal references to people becoming ill due to ozone
toxicity. The long term bioeffects are unknown. (On the other
hand, it does help out the ozone layer!) When constructing
secondaries, use adequate ventilation when coating coils with
varnish, etc. Some of these materials are also quite toxic. The
flux from solder is also potentially hazardous.
5.0) Ultraviolet Light and X-ray Production
Ultraviolet light may be produced by the spark gap during
operation of a tesla coil. The human eye has no pain sensors
within it, so the bioeffects are felt later, when it is too
late. (Ever look at the sun for a while, or watch a welder at
work?) The light produced in a spark gap is essentially
identical to that produced by an arc welder, containing
substantial amounts of hard ultraviolet light. As any
professional arc welder will tell you "Don't Look At The Arc!"
Spark gaps produce a large amount of UV and visible light. The
visible light is extremely bright, and the ultraviolet light
will damage your eyes, and can cause skin cancer. The arc is so
bright that you couldn't make out any detail anyway, so why
bother? If you must study your spark gap, use welder's glasses.
Generally, it is not too difficult to rig up a piece of plastic,
cardboard, etc. that will shield yourself and others.
X-rays
X-rays can be produced whenever there is a high voltage present.
Although a number of coilers have tested their coils for x-ray
radiation and found none present that is not to say that x-rays
cannot be produced, especially if vacuum tubes, light bulbs, and
other evacuated vessels are placed near a coil. Here is a little
information about X-rays.
X-ray Production
A number of vacuum tubes work pretty well as X-ray tubes, and
several articles have appeared in Scientific American magazine
in the distant past. X-rays are typically produced by slamming
electrons into either the nuclei or inner shell electrons of
atoms. The source electrons are usually boiled off a heated
filament (cathode), and accelerated toward an anode via some
large potential difference, typically 25-150 kV in the medical
world. Basically, any time the voltage gets above 10 kV, there
is a significant risk of X-ray production, and the risk
increases with increasing voltages. You can also get some X-ray
production via field emission, whereby electrons escape a cold
metal due to very high local electric fields (the Schottky
effect). This was probably the type of emission obtained by an
amateur described recently on the list. For the remainder of
this discussion I will limit my comments to conventional X-ray
tubes, using a filament and anode, although most of it applies
to both forms. The target or anode is normally a high atomic
number material like tungsten. X-ray production is relatively
inefficient, so most of the energy is wasted as heat (typically
about 99% with good X-ray tubes). Tungsten works well because of
its high melting point (to absorb all that wasted heat energy).
If the potential difference between the anode and cathode is
+100 kV D.C., a spectrum of X-rays will be produced with
energies from zero to 100 keV. The graph of the number of X-rays
produced (y-axis) versus X-ray energy (x-axis) has a negative
slope with a Y=0 point at x = 100 keV. Hence, many more low
energy X-rays are produced than high energy X-rays. Some of
these low energy photons are absorbed by the tube housing. In a
clinical X-ray machine, the tube is placed in a leaded shield
with a window (hole) in it for the X-rays to escape through.
This window has a piece of aluminum over it to further attenuate
the low energy X-rays. In conventional equipment, the tube,
housing and aluminum filter accounts for about 2.5 - 3.5 mm of
aluminum equivalent material in the exit port. This effectively
knocks out most of the low energy (<10 keV) radiation, which
would be absorbed in the patient and could not contribute to
producing an image anyway.
X-ray Absorption
High atomic number materials readily absorb x-ray radiation.
There is an energy dependence here, as high energy X-rays are
more penetrating than low energy x-rays. For example, the
percentage of radiation which will pass through 10 cm (about 4
inches) of water is 0.04% at 20 keV, 10% at 50 keV and 18% at
100 keV. Compare this with 1 mm of lead (about 0.04 inches),
which transmits 0.02% at 50 keV and 0.14% at 100 keV. The human
body absorbs X-rays pretty readily (similar to water), but
becomes more transparent as the energy of the X-ray increases.
That is why we use 50-150 keV for many clinical procedures. The
low energy X-rays are filtered out of the spectrum before they
enter the patient, usually through the use of an aluminum
filter, which lets the high energy X-rays pass through with
little attenuation (except possibly to give you enough contrast
to see what you want). Most of the x-rays are absorbed in the
patient, with 1-5% exiting the patient typically. Low energy
X-rays (0-15 keV) are totally absorbed in human skin near the
skin surface, and would contribute substantially to patient dose
if allowed to reach the patient. This is to be avoided in
general!
Shielding
The best materials are lead or depleted (nonradioactive)
uranium. Concrete and steel also work pretty well. Aluminum is a
poor absorber of radiation, unless the radiation is very low in
energy. Most plastics are similar to water in attenuating
properties (quite poor).
Hazards
X-rays are capable of producing ionizations, which means that
the electrons can be stripped off of atoms when an x-ray is
absorbed in a material. This results in the production of
chemically reactive free radicals, and the direct disruption of
chemical bonds. This is generally bad in humans, causing cancer,
leukemia cataracts, etc. However, due to natural background
radiation levels, humans have built in radiation repair
mechanisms and can handle low doses of radiation quite well.
Bio-effects are not generally observed for doses of less than 25
rem. Skin reddening occurs with doses of around 300 rem or so.
Natural background radiation levels typically contribute 0.2 -
0.5 rem per year. Most regulatory agencies recommend no more
than 0.5 rem per year above background radiation levels for the
general public. Occupational radiation workers can get 5 rem per
year above background. The radiation from a well designed X-ray
tube can be as high as 10-50 rem per minute of exposure, at a
distance of 1/2 meter. The radiation source acts like a light
bulb, decreasing in intensity via the square law with distance.
Hence, don't stand close to a possible radiation source, use
adequate shielding and minimize the exposure time. Incidentally
produced radiation from metal objects other than X-ray tubes
will generally be at much lower production levels, but should be
avoided, nonetheless.
Regulations
In the U.S. the individual states regulate X-ray machines. They
generally keep close tabs on clinical and industrial X-ray
machines and aren't too impressed to see them in the hands of
people without the appropriate licenses. If you happen across an
old X-ray tube, you might consider releasing the high vacuum
inside (very carefully, please) so that it is inoperable, and a
little safer to handle for show and tell (and much more
acceptable to the regulators). This can be done by making a
small hole in the glass envelope with a file, keeping the tube
wrapped in a large quantity of towels for implosion protection
during the process. (It goes without saying that you should
always have your favorite towel handy anyway [for you Doug Adams
fans]).
Monitoring
At this point I presume you are wondering how to tell if that
great apparatus in your basement or garage is producing X-rays.
There are several ways to tell. First, go look for a surplus
Geiger-Mueller counter at your local hamfest or make friends
with someone in your local fire department, since many fire
departments have radiation survey meters at their stations (in
case we have a nearby nuclear explosion, etc.). (Don't bother
with the fire department if your apparatus is likely to upset
them!) In addition, nearly every hospital has a radiation safety
officer who is likely to be more than willing to take a look at
your toys, and will bring a radiation survey meter along. The
standard method for monitoring radiation dose is via film badge
and/or thermoluminescent dosimetry monitors, but these are not
all that useful to the experimenter since they must be mailed
back to the dosimetry lab for reading. In general, film is quite
insensitive to radiation, and is of limited value in the
experimenters setting unless you can leave the equipment on for
a long time to get adequate exposure. Cloud chambers are great
fun and can detect a variety of radiation particles, but get
easily overwhelmed by devices that put out even low radiation
levels. If you don't expect any radiation but still want to
check, a cloud chamber can be used. Buy a thorium doped lantern
mantle at your local camping store to use as a radiation check
source to make sure your chamber is working okay before you
power up your equipment. Another possibility is to construct an
electroscope and place it near your apparatus. An electroscope
measures the amount of charge using two thin metal foils which
are charged up to a high potential, causing them to swing apart
due to repulsion of like charges. Radiation ionizes the air in
the electroscope chamber, causing a loss of charge on the foils.
Naturally, this type of equipment has limited utility in the
direct vicinity of high voltage equipment if electric fields are
significant.
X-rays and Tesla Coils
I have monitored my various tesla coils using a number of
different radiation instruments and have not seen measurable
radiation levels. My coils produce 3 to 5 foot sparks in
magnifier and conventional forms using up to 15 kV input, with
power levels of no more than 1.5 kVA. Obviously, you don't want
to get a survey meter too close to an operating tesla coil.
Finally, always keep safety in mind with all of this equipment.
Humans are not able to sense X-ray and ultraviolet radiation. If
you think you are producing some, use an appropriate instrument
to find out for sure.
6.0) Radio Frequency Interference
Tesla coils are generally inefficient as antennas go, but can
still produce a fair amount of RF, especially if operated with a
large top capacitance, before spark breakout. Significant
quantities of RF can also be produced if the RF grounding is
inadequate. This can cause interference with TV's, radios, and
other electronics. If you note interference, try to improve your
ground first, since that is likely where your problem is. In
addition, every tesla coil should be wired with a power line
conditioner in series with the primary circuit. These are
relatively inexpensive and are very effective in keeping RF out
of the house wiring.
Legal dangers
In the United States, RF transmitters are regulated by the
Federal Communications Commission ( FCC), and they generally
aren't keen on any type of RF interference. They have specific
rules which prohibit the operation of spark gap type damped
oscillators, dating back to the early days of radio. Make sure
you operate your coil with a good RF ground. If interference
still exists, construct a Faraday cage from chicken wire or
similar material, which should eliminate the interference.
Other Comments
When I first got interested in tesla coils, I called the FCC to
ask about the legal aspects of coiling. While the man that I
talked to wasn't too sure about the potential interference, he
did say that modulation of the output is definitely illegal. Of
course, if you shield your coil from emitting RF to the outside
world, you can do anything you like.
Try to be aware that your coil may cause various interference
problems. If you know about any, take care to eliminate them if
possible before they figure out who caused it.
7.0) Fire Hazards
The danger of fires is substantial with tesla coils! Make sure
you have a functional fire extinguisher designed for fighting
electrical fires handy. Fires can be caused by an overheated
spark gap, equipment failure (e.g., shorted transformer), corona
discharge, induced currents, to name a few causes.
Fire starting from sparks to flammable points. The sparks from a
tesla coil are hot. Depending on where they strike, these sparks
can cause a fire. Richard Hull has captured fires caused by
sparks from his coils on video tape. (This was due to a failed
power line conditioner.)
Be sure that when you run your coil, that there are no flammable
substances around. For example, gas cans (e.g., for a
lawnmower), ammunition, sawdust, fireworks, etc. Walls and
ceilings can also be ignited, so keep the fire extinguisher
handy.
Gasoline on premises (mowers, etc.) Without a spark, what's a
tesla coil? What's it take to ignite gasoline? Consider the
location of gas cans, lawnmowers, etc. when operating your coil.
Remember that when you operate your coil, it's usually in the
dark with plenty of exposed high voltage wires. Not a good
combination for fighting a fire in your garage.
In addition, most coilers use polyethylene and other plastics in
constructing their coils, capacitors, and other equipment. These
plastics ignite at relatively low temperatures, and produce
large quantities of toxic smoke.
8.0) Chemical Hazards
Old capacitors and transformers often used PCB oils for
insulation. This oil is a known carcinogen. Similarly, the
materials used to coat coils (e.g., varnish) may contain
hazardous chemicals. Consult a Material Safety Data Sheet (MSDS)
for any materials you have questions about. (Many of these are
available via Internet. Use your favorite Web search engine with
the key word MSDS'.) Some forms of solder contain lead, which is
also generally bad for humans.
9.0) Explosion Hazards
Explosions can and do occur with tesla coils! The rotary gap and
capacitors are the most frequent culprits, but nearby flammables
are also at risk.
Rotary gaps
During operation, rotary gaps spin at high speeds. The spinning
rotor or disk is subjected to tremendous force. At a modest 3600
RPM, the periphery of a 10" disk is subjected to a force of 1835
G's. A 5 gram (0.011 lb) 1/4-20 brass acorn nut used as an
electrode will exert a force of over 20 pounds. The peripheral
speed of the 10" disk is 107 MPH. At 10000 RPM, the edge of the
disk is running at about 300 MPH!
All these numbers translate into one thing: Danger.
The best way to guard against this danger is to shield the rotor
and build the entire system carefully and take pains to balance
it. The shielding must be nearly bullet proof (literally). Lexan
(polycarbonate) is an excellent plastic for shielding. It is
non-conductive, strong, and tough. Consult with your plastics
dealer to determine what thickness you need.
Capacitors
Capacitors are great at releasing energy very quickly. The
explosion danger in a capacitor occurs when it shorts out and
suddenly produces a large volume of hot vaporized gas. Since
capacitors are usually in an airtight container, the volume of
gas will cause the container to explode, sending pieces of solid
cap guts and oil all over.
One recommended method of shielding capacitors is in an HDPE
(High Density PolyEthylene) pipe. These pipes are used in the
pyrotechnics industry as mortars because of their strength and
the fact that they don't create shrapnel as steel or PVC pipes
do.
Also, avoid storing gasoline or other flammables near a tesla
coil!
10.0) Noise Hazards
Tesla coils produce a lot of noise, and large coils can damage
one's hearing. Go to your local gun shop and buy ear protection
if you operate large coils.
One type of spark gap, the air blast gap, produces a loud noise.
Buy and use a set of ear muffs or ear plugs. There are a wide
variety of types of ear plugs and muffs, so you will likely find
one that works well and is comfortable. I prefer the roll up
foam type myself. If you are on a tight budget (blew all the
$$$'s on the pig), you can wash the foam ear plugs. Just put
them in a pants pocket (one that closes is best) and run the
pants through the wash. Works great.
When a coil is in tune, you will notice a dramatic increase in
the noise level as it sparks. This noise is loud enough that it
can damage hearing. See the warnings in the previous paragraph.
Hearing is important -- how will you tell if your teenager is
mocking you behind your back without it?
11.0) Neighbors, The Spouse, and Children
While the beauty of a tesla coil firing outside is something to
behold, often your neighbors will not see it that way, and your
local police will make a personal house call. Be cognizant of
your possibly unreasonable neighbors, and do your work inside if
possible, or invite them over and explain things before you
start. Attitudes are a lot different if a little common sense is
used first.
Coils are noisy
Please consider your neighbor's sleep habits.
Remember the following:
¨ For new parents, sleep is the most precious commodity that
they have.
¨ Not everyone works 8am to 5pm.
¨ Not everyone is tolerant or nice.
A potential secondary hazard would be from enraged neighbors if
radio or TV interference was generated often enough to be a
nuisance, and said neighbors could trace it to its source. Good
citizenship will solve this problem (or a large building with a
good RF ground and a batch of power line filters).
Kids, small pets
Kids and small pets are quite curious, innocent, and ignorant.
(Note the similarity!) Their judgment isn't the greatest either.
If you have children and they have access to your coil, install
some sort of key lock on your power cabinet, variac, or
whatever. Killing or injuring a child or pet, be it yours or
neighbors, will most likely be the worst thing that will happen
to you in your life.
The Spouse
Another potential hazard is if the spouse thinks one is spending
too much time on his or her hobby. ANY HOBBY!!!! Expect the wife
to not understand!
11) Other
Whenever possible, have a buddy assist you. Most coilers prefer
to operate their coils with the lights off, which is inherently
dangerous. This situation can be improved by having an assistant
around to operate the lights and/or power switch. Also, have
your buddy learn CPR, and post your local emergency telephone
numbers, just to be safe.
The layout of your apparatus is also a safety consideration.
Many coilers throw their systems together using electrical tape,
hot glue, and assorted bits of plastic. If things move around a
bit during firing, the risk of something bad occurring is
increased significantly. Spend a little time to construct
yourself a nice power cabinet with a safety switch, and
construct a safe high voltage transmission line to your coil.
Drinking and coiling can be lethal! If you feel the need to
consume some mind altering drugs, watch a tesla video instead!
Never operate a tesla coil while under the influence! Quaff the
ales later during bragging hour, not when you are actually
working.
