Chimney accumulation refers to the buildup of SOOT and SMUT in a chimney. SOOT is a black or dark gray powdery or flaky substance made up of tiny particles of carbon that is produced when something is burned. SMUT is a black or dark gray powdery or flaky substance made up of tiny particles of ash, dirt, and other debris that accumulates in a chimney. Both SOOT and SMUT can be hazardous to health if inhaled, and can cause respiratory problems.