ISO Standard 12944 specifies corrosion classes described in the table below, with examples. These classes show the situations where iron and other metals are to given 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 | Unheated buildings, 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. |
At the Unit One work space, it has been decided that class C4 offers sufficient protection for products produced and used. This means that from now on, all fastenings must offer class C4 corrosion protection or better.
This weblog post was updated 2021/12/21. to eliminate Needs from the title. This post formed part of a Needs, Seeds and Weeds website that belonged to my daughter, Shelagh. In addition, other things are also out of date, or my opinions have changed. Apart from the title, updating the text to a block format and other minor formatting changes, the text above this paragraph remains as it was before. Any significant content changes are found below this paragraph.