Around mast radiators, wooden fences are used to avoid the problem of eddy currents. Railway lines (in the United Kingdom) fixed machinery with dangerous mobile parts (for example at merry go rounds on entertainment parks) Explosive factories and quarry stores Most industrial plants Airfields and airports Military areas Prisons Construction sites Zoos and wildlife parks Pastures containing male breeding animals, notably bulls and stallions. Open-air areas that charge an entry fee Amusement equipment which may pose danger for passers-by Swimming pools and spas