Overview
ISO 558:1980, published by ISO/TC 12.5, provides vocabulary and definitions for standard atmospheres used in conditioning and testing of materials, components and equipment. The standard recognizes that measured properties often depend on external influences - principally temperature, relative humidity and pressure - and therefore specifies agreed ambient conditions to achieve reproducible and comparable results.
The document emphasizes the need to re-establish identical ambient conditions when: (a) bringing samples into contact with a conditioning atmosphere prior to testing and (b) carrying out tests in a standard test atmosphere. It also notes that many tests may be performed under conditions close to ordinary ambient values and refers to ISO 554 for standardization of such ordinary ambient conditions.
Key Topics
- Core parameters: temperature, relative humidity and pressure are the parameters that define an atmosphere and are kept within prescribed tolerances.
- Defined terms: the standard provides precise definitions for several essential concepts, including:
- atmosphere: ambient conditions defined by one or more parameters (temperature, relative humidity, pressure);
- conditioning atmosphere: the atmosphere in which a sample is kept before testing, characterized by specified parameter values and tolerances for a given period or until equilibrium;
- test atmosphere: the atmosphere to which a sample is exposed throughout a test and which is maintained within prescribed tolerances;
- reference atmosphere: an agreed atmosphere used as the basis for correcting test results obtained in other atmospheres when suitable correlation data exist.
- Three types: the International Standard specifies three types of standard atmosphere used for conditioning and testing (the standard itself distinguishes and defines the types and their intended use).
- Practical notes: the standard clarifies that conditioning may be performed in a dedicated conditioning chamber, in a test chamber, or in the laboratory depending on the specimen and test.
Applications
ISO 558:1980 is valuable for laboratories, test houses and manufacturers that need:
- Reproducible test conditions to compare material properties across samples and laboratories.
- Controlled pre-test conditioning to ensure specimens reach equilibrium before measurement.
- Investigation of climatic effects, including studies of extreme conditions where atmospheres differ greatly from ordinary ambient environments.
Benefits include improved comparability of data, reduced variability due to uncontrolled ambient factors, and clearer traceability of test conditions.
Related Standards
- ISO 554 - referenced in ISO 558 for standardization of ordinary ambient conditions.
- ISO Recommendation R 558-1967 - the earlier recommendation cancelled and replaced by ISO 558:1980.
Keywords: standard atmospheres, conditioning, test atmosphere, temperature, relative humidity, pressure, conditioning chamber, test chamber, reproducible testing, laboratory comparison.