While working on his third working fire in a 14 hr. period, a Lieutenant on our department walked around the back of a fully involved structure and stepped on live "downed" power lines. It had been announced by the I/C over the radio that there were power lines down at the rear of the structure. The power company had been called and were in transit. Luck was with us this night. The Lieutenant stepped on the lines approximately 18" from the broken ends on the lines, causing them to ground with the earth and not through him. The light show was spectacular but fortunately no injury. The live lines were carefully moved another 10′ from the house to provide a safety zone. The power company arrived and disconnected the power. This event happened at approximately 0345 in the morning.