While PVC insulation is a mainstay of the wire and cable industry because of its mechanical and electrical properties and its low cost, it presents environmental issues due to its halogen content. Halogens are elements such as fluorine, chlorine, bromine, and iodine. Common cable insulation, such as PVC, contain high amounts of halogens. PVC contains about 29% chlorine by weight. Halogens, under normal circumstances, are very stable and present no danger. However, problems arise when they burn. A halogen-containing plastic can release hydrogen chloride, hydrogen fluoride, and other dangerous gases when burned. Because of this, many legislative bodies (such as the EU) are attempting to eventually phase out PVC-based plastics.