Uncontrolled waste fires burn at much lower and inconsistent temperatures, which means combustion is incomplete. This releases substances from the waste and creates new ones as molecules are decomposed and reformed in the flames. Dioxins and related compounds are often formed when PVC is burned in open fires. At least 30 of these types of compound are considered harmful to human health. They can persist in the environment for years and in the human body for perhaps a decade or more. There is evidence they can damage the brain and disrupt hormones.