hey Andrej Jagar,
you can acheive this effect with the extract tool.
> select the object
> got to face mode
> select all the faces for which you want to create this effect for.
> go to mesh menu --> extract
> once you have applied the extract tool go the settings in the inputs (it will be by the name polyChipOff1)
> in that, first keep faces together - off ( you can do that by keeping the value to 0)
> the play with the local Translate z to give the amount by which the faces should move in z
> you can also use the random option which will give you a cool blast kind of effect for object.
just play with the settings..