My charger says it draws 1.7 Amps. If I plug in all of the devices at once, and they all are in desperate need of a charge, the chargers will be running at full capacity.
Now, if the circuit is a common 15 Amp circuit, and nothing else is plugged in along the line from the breaker box to the computers, then 15/1.7 = 8 chargers.
IF you are in a modern building, and IF it is wired correctly, you will burn out a fuse or "pop" a breaker switch before you start an electrical fire.
If you can plug in all of your devices without tripping the fuse or breaker switch, then you are good to go. I am in a North American school, and we have 95 chargers plugged into one outlet (chargers are plugged into power bars in the backs of the carts that are plugged into a heavy duty power bar that is then plugged into the wall). Students take computers and bring them back all day long, so all 95 have probably never been plugged in all at once in an almost dead battery condition.
We do not have any problems with breaker switches "popping".