The old edition of ISO 12944-2 standard was issued in year 1998. Below are the explanations of the corrosivity categories and durability ranges.

Atmospheric corrosivity categories and examples of typical environments

C1 - Very Low:

  • Interior refers to heated buildings with clean atmospheres, e.g.  offices, shops, schools, hotels 
  • Not for exterior

C2 – Low:

  • Interior refers to unheated buildings where condensation can occur, e.g. depots, sports halls
  • Exterior refers to atmospheres with low level of pollution: mostly rural areas

C3 - Medium                     

  • Interior refers to production rooms with high humidity and some air pollution, e.g. food-processing plants, laundires, breweries, dairies
  • Exterior refers to urban and industrial atmospheres, moderate sulfur dioxide pollution; coastal areas with low salinity

C4 - High

  • Interior refers to chemical plants, swimming pools, coastal ship- and boatyards
  • Exterior refers to industrial areas and coastal areas with moderate salinity

C5 - Very High (industrial)

  • Interior refers to buildings or areas with almost permanent condensation and with high pollution.
  • Exterior refers to industrial areas with high humidity and aggressive atmosphere.

C5-M – Very High (marine)

  • Interior refers to buildings or areas with almost permanent condensation and with high pollution.
  • Exterior refers to coastal and offshore areas with high salinity.

Categories for structures immersed in water or buried in soil 


  • Fresh water, refers to river installations, hydro-electric power plants


  • Sea or brackish water, refers to immersed structures without cathodic protection (e.g. harbor areas with structures  like sluice gates, locks or jetties)


  • Soil, refers to buried tanks, steel piles, steel pipes

Durability classes

Low - durability between 2 - 5 years
Medium - durability between 5 – 15 years
High - durability over 15 years

Durability is expected life of a protective paint system to the first major maintenance painting. The durability range is not a guarantee time. Durability is a technical consideration/planning parameter that can help the owner set up a maintenance programme.