These activities which result in an output which is separately identified in national accounts, by reference to the ISIC classification. Main external protection activity is ISIC 90 “sewage, and refuse disposal, sanitation and similar activities”. Other environmental protection activities may be found in ISIC 37 (recycling), 45 (construction), 51 (for example wholesaling of waste materials and scrap including sorting), 73 (research and development), 75 (general administration), etc.