A spark from a police officer's gun ignited a small patch of gunpowder residue on the fire-proof rubber floor of the indoor firing range at the Kowloon East police operational base in Siu Yip Street, Ngau Tau Kok, at about 9.40am yesterday. The gunpowder burned brightly, emitting smoke, and an instructor immediately doused it. The flare-up blackened a small patch of the floor, which is cleaned twice a day. An officer said such incidents were very rare and the amount of gunpowder residue was very small.