| | Corrosivity category | Corrosivity | Typical environments—examples | | Indoor | Outdoor |
| | C1 | Very low | Heated spaces with low humidity and insignificant pollution, e.g., offices, schools, museums | Dry or cold zone, atmospheric environment with very low pollution and time of wetness, e.g., certain deserts, Central Arctic/Antarctica |
| | C2 | Low | Unheated spaces with varying temperature and relative humidity. Low frequency of condensation and low pollution, e.g., storage, sport halls | Temperate zone, atmospheric environment with low pollution (SO2 < 5 mg/m3), e.g., rural areas, small towns | | Dry or cold zone, atmospheric environment with short time of wetness, e.g., deserts, subarctic areas |
| | C3 | Medium | Spaces with moderate frequency of condensation and moderate pollution from the production process, e.g., food-processing plants, laundries, breweries, and dairies | Temperate zone, atmospheric environment with low pollution (SO2: 5 mg/m3 to 30 mg/m3) or some effects of chlorides, e.g., urban area and coastal area with low deposition of chlorides | | Subtropical and tropical zone, atmosphere with low pollution |
| | C4 | High | Spaces with high frequency of condensation and high pollution from production processing plants, swimming pools | Temperate zone, atmospheric environment with low pollution (SO2: 30 mg/m3 to 90 mg/m3) or substantial effect of chlorides, e.g., polluted urban area, industrial areas, and costal area without spray of salt water or exposure to strong effect of de-icing salts | | Subtropical and tropical zone, atmosphere with medium pollution |
| | C5 | Very high | Spaces with very high frequency of condensation and/or with high pollution from production process, e.g., mines, caverns for industrial purposes, unventilated sheds in subtropical and tropical zones | Temperate and subtropical zone, atmospheric environment with very high pollution (SO2: 90 mg/m3 to 250 mg/m3) and/or significant effect of chlorides, e.g., industrial area, costal area, and sheltered positions on coastline |
| | CX | Extreme | Spaces with almost permanent condensation or extensive humidity effects and/or with high pollution from the production process, e.g., unventilated sheds in humid tropical zones with penetration of outdoor pollution including airborne chlorides and corrosion-simulatingparticulate matter | Subtropical and tropical zones (very high time of wetness), atmospheric environment with very high SO2 pollution (higher than 250 mg/m3) including accompanying and production factors and/or strong effect of chlorides, e.g., extreme industrial areas, costal areas, and offshore areas, occasional contact with salt spray |
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