Overview - ISO 20492-2:2008 (Chemical fogging tests)
ISO 20492-2:2008 is the International Standard that specifies chemical fogging tests for insulating glass (IG) units used in buildings. It defines two test approaches - Approach 1 (markets such as North America) and Approach 2 (markets such as Europe) - to assess the resistance of pre‑assembled, permanently sealed IG units (or units with intentionally left open capillary tubes) to internal fogging or permanent visual condensation. The standard excludes IG units with spandrel glass coatings and decorative‑only units.
Key topics and technical requirements
- Scope and purpose: Test the sealing system and construction of sealed insulating glass units to help preserve energy performance (U‑value, solar factor), vision, acoustic properties and mechanical safety.
- Two approaches: Approach 1 and Approach 2 use different test methods and pass/fail criteria aligned with regional market practices.
- Acceptance criteria:
- Approach 1 - No visible fog after testing.
- Approach 2 - No permanent visual condensation permitted.
- Test conditions (Approach 1 example):
- Chamber temperature: (50 ± 3) °C with continuous air circulation.
- Chilled cooling plate in contact with glass: (21 ± 2) °C.
- UV source intensity: ≥ 400 µW/cm² measured at ~355 mm.
- Exposure duration: 7 days.
- Specimen geometry and quantity: Standard specimen size 355 × 505 mm; minimum 2 specimens for double glazing or 4 specimens for triple glazing. Glass and airspace thickness tolerances and material types are defined (clear, tinted, coated, annealed/tempered/laminated).
- Apparatus details: Test box with reflective interior (e.g., plywood lined with foil or stainless steel), fan for temperature control, radiation‑shielded thermocouples, conductive cooling plates (nominal 150 mm diameter or equivalent area).
- Special cases: Procedures for units with low‑e coatings, gas‑filled units, units with capillary tubes (open/closed), and internal grids are specified.
Applications and who uses it
ISO 20492-2 is used by:
- Insulating glass manufacturers for product development and quality control.
- Independent test laboratories performing fogging resistance tests.
- Architects, façade engineers and specifiers to verify long‑term visual and thermal performance.
- Curtain wall and window fabricators ensuring edge‑seal durability and compliance.
- Regulatory bodies and certification agencies for product marking and conformity (e.g., CE marking considerations).
Practical benefits include maintaining energy efficiency, visual clarity and occupant health/safety by preventing internal fogging in fenestration, skylights, curtain walls and other glazing applications.
Related standards
- ISO 20492‑1: Durability of edge seals by climate tests
- ISO 20492 Parts 3 & 4: Gas concentration/gas leakage; physical attributes of edge seals
- EN 1279 series, EN 572 series, ASTM C1036 (referenced for glass types and tolerances)
Keywords: ISO 20492-2:2008, chemical fogging tests, insulating glass, IG units, fogging resistance, volatile fog test apparatus, low‑e coatings, edge seals, sealed insulating glass units.
