What material needs to be cleaned from air ducts?
Your duct should only contain clean air. This means everything else has to go. Foreign particulates is the term for what gets cleaned from ducts, including but not limited to dust, dirt, allergens, contaminants, mold spores, pet dander and other pollutants. In the event of a structural fire, special cleaning is needed to ensure that all hazardous residues from the fire are removed from the air ducts.