A confined space is not necessarily a small space and may not always be an enclosed space. The legal definition of a confined space includes any enclosed space in which harm, accident or injury could occur as a result of the lack of or excess of oxygen, the presence of a liquid, hazardous substance, flammable atmosphere or excessive temperature. Some confined spaces can be easily identified - vessels, tanks, containers, vats, silos, hoppers, pipes, sewers, chimneys, wells etc. Others are however, less obvious but equally as dangerous when the hazards listed above are present; they include open topped tanks and vessels, bunds around fixed storage tanks, trenches, enclosed rooms, deep basement rooms, etc. Legislation imposes specific requirements in respect of work in confined spaces. These include assessing the hazards and risks of each entry into a confined space, taking action to eliminate or control risks, using permit to work systems, providing personal protective equipment, task specific training and emergency arrangements. See also: Permits to Work.