Abstract: At approximately 10:38 a.m. on December 19, 2006, Employees #1 through #3, all contractors, were running a new multi-conductor conduit to a metal subpanel box prior to its installation. Employees #1 and #2 were using an electric hole drill to cut a 3 to 4 in. diameter knockout hole at the top right on the back frame of the 8 ft 3 in. tall by 3 ft wide by 2 ft 5 in. deep Square D, 2,000 amp/480 volt switchboard panel box, Model QED, Type II Power Style. Employee #2 was drilling from a ladder on the right side while Employee #1 was on a ladder in front of it. When the hole piece drilled out, it fell into the switchboard through a job-made cardboard box held in place to catch it. As it dropped, the piece of metal landed across the busbar, causing an arc flash. Employee #1 sustained burns to the front of his body, including his head, knees, arms, and hands; Employee #2 suffered burns to his arms, face, and abdomen. Subsequent investigation revealed that the employees were working on an energized switchboard without insulation and without appropriate personal protective equipment. There were no host employees working with the contractors, but Employee #3 was nearby when the arc flash occurred. He was blown backward against a metal object, suffering minor injuries to his leg and back.