Three separate fires in Oakland claimed the lives of six people, including five children, during a 12-hour period described by one fire official as the worst rash of fatalities he could remember. The children and an 85-year-old man were killed in the fires, officials said. Three children died and a fourth was hospitalized in critical condition after a cigarette or match ignited a couch in their first-floor apartment, officials said. The apartment fire left about 40 people temporarily homeless. In a second blaze, two youngsters who had been left alone in an apartment died after an aluminum skillet melted on a stove and ignited a wall. A cigarette was also the likely cause of the third fire, which killed the 85-year-old man who died in his basement apartment, officials said. They estimated total property damage at about $110,000.