Is it safe to touch 8 volts?
8 V is too low to send lethal currents through you, unless you implant electrodes under your skin near your heart (don't do that). In fact most authorities round the world reckon that somewhere in the 40 V to 60 V range is safe to touch.

8 V is high enough to send very large currents through metal wires. The heat generated by this could burn you or start fires. 

A re-purposed microwave oven transformer is heavy enough to break toes, if dropped.