Overview
ISO 483:2005 - "Plastics - Small enclosures for conditioning and testing using aqueous solutions to maintain the humidity at a constant value" - provides guidelines for constructing and using small enclosures (volumes < 200 dm³) to obtain atmospheres of constant relative humidity for conditioning and testing plastics. The standard covers methods using saturated salt solutions, glycerol/water solutions, and sulfuric acid/water solutions to generate reproducible humidity levels at controlled temperatures (0 °C to 70 °C). It is intended for conditioning small quantities of material and tests that can be performed entirely inside a sealed enclosure (for example electrical tests). Enclosures that require frequent opening are excluded.
Key topics and requirements
- Scope and principle
- Enclosures under 200 dm³ using aqueous solutions to establish equilibrium relative humidities.
- Atmospheres produced by saturated salts (Method A), glycerol solutions (Method B) or sulfuric acid solutions (Method C).
- Materials
- Use analytical/reagent-grade chemicals (salts, glycerol, sulfuric acid) and water meeting ISO 3696 Grade 3.
- Apparatus & environmental control
- Temperature control: ovens, baths or conditioned rooms able to maintain ±1 °C.
- Thermometry: internal thermometers readable to ±0.1 °C; record 1 hour after closing and at least every 24 h.
- For Method B: refractometer (range ~1.330–1.470, 0.001 resolution). For Method C: hydrometer accurate to ±0.001 g/ml.
- Air circulation (fans) recommended for hygroscopic materials to ensure uniform RH.
- Procedures
- Precondition enclosure (e.g., place saturated solution 24 h before specimens unless proven faster).
- Maintain excess undissolved salt to keep solutions saturated.
- Limits on specimen load relative to solution surface area (V/S considerations); different allowances with/without air circulation.
- Cleaning/replacement schedule: keep solution and interior surfaces clean; replace solution weekly if conditioning >1 week.
- Tolerances, precision and reporting
- Specifies normal and close tolerances for standard atmospheres, methods to determine equilibrium, and required test-report information.
Applications and users
- Practical for laboratories performing plastics conditioning, humidity-controlled aging, material property testing, and small-scale electrical tests.
- Users: materials test labs, quality assurance engineers, R&D teams in plastics manufacturing, and calibration/standards labs requiring reproducible humidity environments for specimens.
Related standards
- ISO 291 - Plastics: standard atmospheres for conditioning and testing.
- ISO 3696 - Water for analytical laboratory use (Grade 3).
- Useful keywords: ISO 483:2005, small enclosures, humidity control, saturated salt solutions, glycerol solutions, sulfuric acid solutions, plastics testing, conditioning cabinets.