On-site examinations and fire simulation were carried out to speculate on causes of the fire at an indoor shooting range in Busan. An experiment on the ignitability of unburned gunpowder was also conducted. Cigarette was the most likely source of ignition for the fire, while impact of a stray bullet failed to ignite the unburned gunpowder. The explosion in the shooting area was presumed to be caused by violent combustion of the polyurethane foam and unburned gunpowder accumulated on it. Fire safety measures include prohibit of use of profile polyurethane foam, complete clean-up of unburned gunpowder, and removal of steel components from the bullet trap.