Electronics and safety.

Danger!
Electricity can be dangerous: Before dealing with any high voltages, please get proper training and take all necessary precautions. Even if the available current is too low to kill, there are still other possible dangers which could result in serious injury or death.

Warning. It is not always necessary that you touch a supply to get a shock. Some high voltages will leap out and get you if you get too close. Also, if your mains supply uses an earth system (as in the UK), you only need touch one side of a supply to get a shock. All piping (including water supply and heating) will be connected to earth, and so can become the other connection needed to allow current to flow - through you.

The main dangers include:
Electrocution: It only takes a few milliAmps to kill. Death is usually caused by current flowing through the heart, causing it to stop.
Burning: Current flowing, or arcing can generate heat. This heat could cause injury or even start a fire.
Reflex action: A sudden jerk of the hand or body may cause other dangers, such as glass components (tubes, CRTs, etc) breaking and causing injury, touching a lethal supply or falling from a high place.

Basic precautions.
* Ensure that your equipment is maintained correctly. Pay great attention to mains plugs, as these are often poorly wired. Check your equipment regularly.
* Never work when tired.
* Avoid working alone. If an accident does occur, another person being there could save your life. Learn emergency procedures and life saving techniques.
* Ensure that the equipment to be serviced or repaired is safe to connect.

Watch your pockets. Never keep screwdrivers or pens in your shirt or jacket breast pocket! As you lean over the equipment to look inside, those objects can fall in and, if it is switched on, the results can be disastrous.

* When using power supplies, use current limited supplies and set the current correctly. Avoid using car or truck batteries, as the current is only limited by the battery rating and will be several hundred Amps, which is more than enough to start a fire. There may also be dangers associated with the acid used or the battery exploding if shorted.
* When working on earthed system, an isolating transformer can provide good protection against shocks to earth. However, always take other relevant precautions as the transformer may not always be available (such as for field work).
* Work away from metal pipes, and never lean or hold on to metal pipes while working.