The U.S. Consumer Product Safety Commission reports that each year over 25,000 residential fires originate in chimneys. Many of the fires are the result of the buildup of a highly combustible material called creosote.
Once the chimney is coated with creosote, there is great potential for a serious chimney fire. At this stage, the flames from a burning newspaper could be sufficient to ignite the creosote. The substance burns rapidly and, as it spreads through the flue, creates a draft that intensifies the fire. As creosote burns, it peels and curls off the inside walls of a chimney, then drips into the flue and literally forms balls of fire that are propelled upward by the updraft. These fireballs shoot onto the roof and can quickly destroy a home. Fires can also occur due to high temperatures that melt mortar, crack tiles, and cause liners to collapse and damage the outer masonry material.