SPOKANE VALLEY — A cigarette that appears extinguished may still pose a serious fire threat, according to the Spokane Valley Fire Department. Over the past two months, investigators have determined that five fires were caused by improperly discarded smoking materials. Two recent incidents involved cigarettes placed in potted plants at apartment complexes, where they smoldered beneath the soil before igniting. The following day, firefighters responded to another apartment fire on East Cataldo, where a discarded cigarette had ignited a flowerpot on a second-floor balcony. Potting soil can insulate heat from a smoldering cigarette, allowing it to continue burning beneath the surface and eventually ignite nearby materials.