Atmospheric corrosivity categories for coating systems selection by ISO 12944
| Corrosivity category | Service environment (Exterior) | Service environment (Interior) |
| C1 very low | Heated buildings with a clean atmosphere | |
| C2 low | Atmosphere contaminated to a small extent, mainly rural regions. | Buildings which are not heated, where condensation may occu |
| C3 medium | Industrial and urban atmosphere with an average sulphur oxide (IV) contamination level. Inshore areas of low salinity. | Production space of high humidity and certain air contamination e.g. foodstuff plants, laundries, breweries, dairies. |
| C4 high | Industrial areas and inshore areas of medium salinity | Chemical plants, swimming pools, ship repair yards. |
| C5-I very high (industrial) | Industrial areas of high humidity and aggressive atmosphere. | Buildings and areas of almost constant condensation and high contamination. |
| C5-M very high (marine) | Inshore areas and offshore areas of high salinity | Buildings and areas of almost constant condensation and high contamination. |
The water and soil corrosivity categories for coating systems selection according to the ISO 12944
| Corrosivity category | Service environment | |
| Im1 | fresh water | River installations, hydroelectric power plants |
| Im2 | sea or brackish water | Seaports with the following structures: sluice gate, locks (water steps), water stilts, piers, offshore structures |
| Im3 | soil | Underground tanks, steel stilts, pipelines |
Digest from Hempel “How to select right paint system: Guidelines for coating protection in accordance with ISO 12944“
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