The corrosion classes below describe - with examples - under which conditions treatments for iron and metal are providing sufficient corrosion protection.
| ISO 12944 | Impact | Interior | Exterior |
| C1 | Very low | Heated buildings with clean air, such as offices, shops, schools, hotels, etc. | None |
| C2 | Low | Buildings not heated, where condensation may occur, such as warehouses and sports halls. | Atmosphere with low pollution. For example in the country. |
| C3 | Middle | Buildings for production with high atmospheric humidity and some air pollution such as food manufacturers, breweries, dairies and laundries. | Urban and industrial areas, moderate sulphur dioxide pollution. Coastal areas with low salt content. |
| C4 | High | Chemical manufacturers, swimming baths and ship- and boatyards by the sea. | Industrial areas and coastal areas with moderate salt impact. |
| C5-I | Very high - Industry |
Buildings or areas with almost permanent condensation and with high pollution. | Industrial areas with high humidity and aggressive atmosphere. |
| C5-M | Very high | Buildings or areas with almost permanent condensation and with high pollution. | Coast and offshore areas with high salt content. |
Comment( DS Manual 124:2000)
Corrosion categories C1 og C2 do not exist in Denmark. Due to the prevailing wind conditions at the Danish west coast, corrosion category C5-M may occur as far as 25 km inside the country.