Any equipment and installations with input and/or output voltages greater than 50VAC RMS and/or 75VDC are considered hazardous. If you're running an amp that can provide around 600W into a 4 Ohm load or 300W into an 8 Ohm load, you're working with hazardous voltages.

A-LFR/1000-8 & 2/500v4x2
Air Force, Freedom
had v2