Fire ash contains microscopic particles (dust, dirt, soot) that can be deposited on indoor and outdoor surfaces and can also be inhaled if the ash becomes airborne. Unless tested, the ash is not classified as a hazardous waste, however it may contain traces of hazardous chemicals such as metals (lead, cadmium, nickel, and arsenic), asbestos (from older homes or other buildings), perfluorochemicals (from degradation of non-stick cookware), flame retardants, and caustic materials. For these reasons, it is advisable to be cautious and avoid any unnecessary exposure to the ash.

Fire ash may be irritating to the skin, nose, and throat, and may cause coughing and/or nose bleeds. Fine particles can be inhaled deeply into lungs and may aggravate asthma and make it difficult to breathe. If the ash contains asbestos, nickel, arsenic or cadmium, then exposure is a particular concern because these substances can cause cancer. Because the substances in the ash vary, it is always best to be cautious.