In harsh environments like offshore areas, coastal regions, and industrial facilities, lighting fixtures face a constant threat - corrosion. This silent killer can lead to rust, oxidation, and premature failure, compromising the performance and longevity of lighting fixtures. To combat the destructive effects of corrosion, it’s crucial to understand and select the appropriate corrosion classes.
Atmospheric environments are classified into distinct corrosivity categories (C1 through CX) by ISO 9223 based on mass-loss testing of reference metals and atmospheric harshness. ISO 12944-2 adopts this classification system to help engineers select appropriate protective paint and coating systems for those environments.
What is corrosion?
Corrosion is the gradual degradation of materials due to chemical or electrochemical reactions with their environment. In lighting fixtures, corrosion can be caused by exposure to moisture, humidity, condensation, chemicals, and pollutants. Additionally, galvanic corrosion can occur when dissimilar metals are in contact with each other in the presence of an electrolyte.
Although ISO 12944 formally applies only to structural carbon steel, the lighting industry widely adopts its C1–CX environmental corrosivity tiers as a practical design benchmark for evaluating protective finishes on die-cast aluminum enclosures.
What are corrosion classes?
Atmospheric environments are classified into distinct corrosivity categories (C1 through CX) by ISO 9223 based on mass-loss testing of reference metals and atmospheric harshness.
(Note: The major 2017/2018 ISO revision removed the legacy "C5-M" marine designation, incorporating heavy onshore coastal areas under C5 and introducing CX for extreme marine and offshore environments.)
Atmospheric environments
| Corrosivity Category | Environment Level | Exterior Examples | Interior Examples |
| C1 | Very Low | Clean atmospheres | Heated buildings (offices, schools, hotels) |
| C2 | Low | Low pollution, rural areas | Unheated depots, sports halls |
| C3 | Medium | Urban/industrial with moderate SO2; low-salinity coastal | High-humidity rooms (breweries, food plants) |
| C4 | High | Industrial zones and coastal areas with moderate salinity | Chemical plants, indoor swimming pools |
| C5 | Very High | Industrial areas with high humidity; heavy coastal zones | Buildings with near-permanent condensation |
| CX (Newest) | Extreme | Offshore platforms, high-salinity splash zones, extreme industrial | Extreme industrial atmospheres with severe pollutants |
Underwater or underground structures (water and soil)
The ISO 12944 standard also covers underwater and underground structures, with categories ranging from Im1 (fresh water) to Im4 (sea or brackish water with cathodic protection).
|
Category |
Environment |
Examples of environments and structures |
|
Im1 |
Fresh water |
River installations, hydro-electric plants |
|
Im2 |
Sea or brackish water |
Immersed structure without cathodic protection. Such as harbour areas |
|
Im3 |
Soil |
Buried tanks, steel piles, steel pipes |
|
Im4 |
Sea or brackish water |
Immersed structures with cathodic protection, such as offshore structures |
How Are Environments Classified and Products Tested for Corrosion?
Determining how a lighting fixture will survive in the field involves two distinct processes: establishing the environmental corrosivity category (per ISO 9223), and verifying the coating's durability (per ISO 12944 or equivalent industry standards)
Field Exposure and Environmental Classification
An environment’s baseline corrosivity class (C1 through CX) is formally determined according to ISO 9223 and ISO 9226.
This is accomplished by exposing standardized metal coupons (such as carbon steel and zinc) outdoors for one full year and measuring their mass loss, or by calculating the local Time of Wetness (TOW) alongside airborne salinity and sulfur dioxide levels.
Long-term field exposure racks also serve to validate the real-world performance of finished products against these established conditions.
Accelerated Laboratory Durability Testing
Because multi-year outdoor testing is impractical for product development, manufacturers use accelerated laboratory protocols to qualify protective coating systems:
-
Cyclic Corrosion Testing (ISO 12944-6 / ISO 16701): Recreates real atmospheric mechanics by cycling test specimens through alternating phases of salt fog, UV exposure, drying phases, and humidity. This is the required method for qualifying high-durability coatings for severe C4, C5, and CX atmospheres.
-
Continuous Neutral Salt Spray (ASTM B117 / ISO 9227): A legacy chamber test widely utilized for factory quality assurance and screening gross coating defects. While standard for batch verification, salt spray hours do not directly convert into years of outdoor service life.
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Condensation & Humidity Exposure (ASTM D4585 / ISO 6270): Evaluates moisture permeation, blistering resistance, and film adhesion under constant, high-humidity conditions.
How to choose the right corrosion class?
Selecting the lighting fixture with the right corrosion class is critical.
First of all, you should assess the environment. The indoor or outdoor environment is the primary distinction. C1 is sufficient for a dry indoor environment. Outdoor environments require higher classes (C2 to CX) depending on harshness.
Then, consider the specific location. Rural areas with low pollution can typically use C2 class lighting. Urban or industrial areas call for a C3 class or higher for extended lifespans. In coastal areas, however, the salinity environment might require C4 or higher class lighting.
Last, consider special conditions. Areas with constant moisture exposure might benefit from a higher corrosion class than the base recommendation. Coastal areas with constant exposure to sea spray should prioritize C4 or C5 class lighting.
Remember, corrosion class is just one factor to consider. Materials selection and protective coatings also play a vital role in ensuring the longevity of lighting fixtures. High-grade stainless steel or aluminum with a powder coat finish generally offers superior corrosion resistance compared to standard steel. Lighting fixtures with additional protective coatings like epoxy resin or galvanization can further enhance corrosion resistance within a specific class.
AGC corrosion-resistant lighting solutions
At AGC, we understand the importance of corrosion protection for lighting fixtures. Our corrosion-resistant lighting fixtures are engineered and tested to withstand harsh C4 and C5 environments. They have passed the 1000-hour salt spray test. This ensures reliable and efficient illumination in corrosive environments.
Here are some of our products.
For more details or a quote, contact us.
