Airborne corrosivity classification G1–GX for measurement and control equipment (Cu/Ag coupons).
The standard classifies airborne contaminants and biological factors affecting the reliability of industrial process measurement and control equipment, electronic office equipment, and data-center and network equipment. It divides operating environments into four corrosivity severity classes: G1 (Mild), G2 (Moderate), G3 (Harsh) and GX (Severe).
The class is determined by measuring reactivity: the thickness of corrosion-product layers formed on copper and silver coupons during exposure in the environment, normalized to 30 days.
An ISA-71.04 class in a component datasheet describes the environment for which the manufacturer intends the product: G1 means corrosion is not a factor in equipment reliability, G2 that corrosion effects are measurable, G3 that corrosive attack is highly probable, and GX that only specially designed and protected equipment will survive.
The standard classifies the air at the installation location and gives the measurement method; it does not describe a product test or product severity. For relay contacts and connectors, the environmental class indicates the amount of sulfide layer on copper and silver that the product must tolerate without an increase in contact resistance.
Specially prepared pure copper and silver coupons are placed in the environment for about one month. After exposure, they are analyzed by coulometric (cathodic, electrolytic) reduction to determine corrosion-product layer thickness in angstroms; the result is normalized to 30 days.
Classes are assigned by thresholds: G1 – Cu <300 Å/30 days and Ag <200 Å/30 days; G2 – Cu <1000 and Ag <1000 Å/30 days; G3 – Cu <2000 and Ag <2000 Å/30 days; GX – Cu ≥2000 or Ag ≥2000 Å/30 days. The 2013 revision introduced silver reactivity as a required class measure, defined standardized coupons and permitted real-time monitors correlated with coulometric reduction; this change was driven by failures of lead-free electronics following RoHS implementation in 2006.
Check which class (G1/G2/G3/GX) the manufacturer states as the permitted operating environment and whether it references the 2013 edition (with silver criterion) or 1985 (“ISA S71.04”, copper only); if “ISA S71.04” appears without a year, confirm the edition with the manufacturer. The environmental class describes the installation site; resistance of the product itself is demonstrated by IEC 60068-2-60 testing with stated method and duration.
