Safety Information
Working with tesla coils is very fascinating. Nevertheless you should be aware of the dangers that come around with those devices. These dangers are primarily the electical hazard, but also other effects have to be kept in mind when starting a tesla coil project. Thanks to the web, you can learn very much from other experienced coilers by visiting their web pages. See my links page for a list. Expecially I suggest you to read Chip Atkinsons collection of information about safety with Tesla Coils.
ELECTRICAL HAZARD
Voltages and currents that are used with tesla coils may be lethal and you only should attempt to build a coil, if you are experienced with high voltage. No part of the system should be touched while in operation. Especially the primary circuit is very dangerous, because of high voltages and currents and the low frequency, which does not cause skin effect. Currents at this frequency will directly flow through your body. Currents as small as 50mA can kill you, and currents in the primary unit are 1000 times higher and even more! Although the secondary only contains high frequency, contact with sparks is dangerous, too. First of all, direct contact will burn skin. And, it is possible that the arcs find their way down to the primary, even if you use a strike ring. In this case, a sudden conducting path (remember: the arc is nothing else than this!!!) is created to the low frequency part of the primary tank. This will kill you for sure. But also the switched off unit still contains danger, because capacitors may still contain enough energy to at least cause a nasty shock. Always discharge capacitors. Capactiors should also be stored with their electrodes shorted, as they may charge themselves over time.
FIRE
There exists a danger of fire, too. One rule is always to keep a fire extinguisher rated for electrical fires with you when operating a coil. Fires may be caused by different effects. For example, compontents of your system may overheat, especially the spargap is very stressed. Also short circuits may happen. Sparks may strike flammable materials.
OZONE AND OTHER GASES
The sparks and arcs and the sparkgap ionize the air because of the very high temperature and by this they produce a considerable amount of ozone and oxides of nitrogene. These are toxic gases. They may cause nausea, headache and dizziness. And materials of your coil could get attacked long term, too. When running your coil always be sure to have very good ventilation. I even had a strong smell of ozone with my small coil running outside in the garden. I don't think, I would run it inside.
UV RADIATION
The sparkgap produces hard ultraviolet radiation when running just like an arc welder. Avoid looking into the arcs produced by your sparkgap, and if you want to do, use shields for your eyes.
NOISE
Tesla coils produce a loud noise while in operation. Large coils require an ear protection. This noise is produced by the spargap and by the sparks themselves.
EMV
Tesla coils are high frequency devices producing strong electric and magnetic fields in their environment. Under any circumstances ensure, that nobody wearing a pacemaker is near the tesla coil while in operation. Sensitive electronic equipment may be destroyed by the fields near the coil. This does not only apply to pacemakers, but also to computers for example.

Radio frequency interference is also possible, especially, if spark breakout is prevented by too large top capacitance. But main cause is bad RF grounding. A good RF ground is most important for tesla coil operation.
© 1999 by Herbert Mehlhose