Abstract: Two employees were injured while installing footings for a sewer injector in a pit which was about 16 ft and 1 in. deep. The opening had a metal cover which was 6 ft diameter. Both men were connected to a chain hoist for fall protection. Employee #1 was working down in the pit and Employee #2 was working above at the opening. While attempting to mark the footings for cutting with a Krylon flammable spray can, the spray can fell to the ground and was punctured. Interviews indicate that after approximately 15 to 20 minutes of ventilating the confined space, one employee lowered a Logic 600 multi-gas monitor and read levels that were safe to continue work. Employee #1 was beginning to cut out the footings when he triggered the electric rotohammer and an explosion occurred. Employee #1, who was working in the pit, suffered burns to his arms, chest and neck and was hospitalized. Employee #2, who was working above the pit, suffered minor burns and he was treated and released.