Question: My knowledge of electrics is very limited, I am planning to buy a Multimeter, but I am confused when it comes to safety. I do not really know what is a danger to life when measuring a circuit with a multimeter. Is it the voltage, current, resistor, capacity, frequenz a combination of some of this or other factors. Could you please explain common conditions in working with an multimeter and when it is safe and when not.

Answer: 
Some general points- of course you should always follow the meter and test probe manufacturer's recommendations.

There is danger from electrocution and from release of high energy (shrapnel, molten metal, vapor) in case of a short. Arc flash is a particular type of high energy fault that can cause fatal injuries, A lesser danger of injury (death is less likely) is from high high current causing burn injuries, which can occur even at low voltage. Some cheap meters have no fuse at all in the high current range and putting the probes across a hefty battery or high current supply will melt or blow the test leads off. Others have a fuse but with woefully inadequate interrupting capacity. 

In all cases using a multimeter with **at least** the minimum safety category for the situation will reduce the risk. A good summary of the categories is in [this](http://www.testequipmentdepot.com/application-notes/pdf/safety/abcs-of-multimeter-safety_an.PDF) Fluke publication- ABCs of Multimeter Safety.

I would recommend CAT III for most mains measurement situations. 

[Here](http://m.ecmweb.com/arc-flash/case-deadly-arc-flash) is an analysis of an incident that killed two people as a result of using cheap multimeter.
I'll skip the fun stuff, like measuring the voltage of a lightning bolt by standing in the middle of a thunderstorm with one DMM probe stuck in the ground while holding the other above your head.

There are two basic areas to be careful of.

First, measuring high voltage (basically, 110 volts or greater). You've got to be careful that you don't inadvertently complete a circuit. This means being careful not to let your fingers touch the metal probe ends, or try it while wet, or get careless about what you touch. A useful technique, if you are worried, is to keep one hand in your pocket. That is, you clip the DMM ground probe to a handy ground point, then use one hand to make the probe connection to the point of interest, while keeping the other hand in your pocket. The very worst thing you can do is to make contact with two voltage sources with both hands - the current path from one hand to another will include your heart, and this is technically known as A Bad Thing. Another thing to consider is to make sure that your contact points are mechanically stable. Do not, under any circumstances, try to use a DMM on a point which is not held firmly in place, such as the end of a wire which is hanging freely.

For voltages of, let's say, 24 volts or less, the above concerns are simply not much of a problem as long as you're not doing it while immersed in water. With dry hands, 24 volts may give you tingle, but nothing more, and lower voltages, such as 5 volts simply won't produce any sensation at all. Under these conditions, you need to worry more about accidentally short-circuiting two adjacent conductors with the metal end of the probe. This can happen, for instance, if your hand slips, or if you have the probe touching one point and turn away (for instance to look at the DMM face), and change the angle of the probe so that it makes contact with two points and short circuits them. This is most likely to just damage the circuit, but if the voltage being shorted can produce currents of many amps you may get spatters of hot metal being thrown off.