Overview
ISO 18921:2008 defines a standardized test method to estimate the life expectancy (LE) of information stored on CD-ROM (including CD audio, excluding recordable media) based solely on the effects of temperature and relative humidity. The standard prescribes accelerated aging experiments, measurement methods and statistical analysis to predict how long data will remain retrievable under typical storage conditions (reference 23 °C / 50 % RH).
Key topics and requirements
- Primary measurement - Block Error Rate (BLER): BLER is measured at the input of the C1 decoder (before error correction) and expressed as erroneous blocks per second. ISO 18921 treats media as having reached end-of-life when the maximum BLER exceeds 220 blocks/s (equivalent to established BLER limits).
- Test specimens and equipment: Test discs must conform to ISO/IEC 10149. Any tester compliant with ISO/IEC 10149 may be used; manufacturers, model/version and software must be reported. Calibration is required before data collection; a control disc must be maintained at ambient conditions and tracked with a control chart (±3σ action limits).
- Accelerated stress plan: The standard calls for accelerated incubation under multiple temperature and RH levels (five stress conditions are specified in the test plan), with stress temperatures up to about 80 °C and RH values up to 85 % where practical. The plan emphasizes assigning the majority of specimens to the lowest stress level to improve precision near usage conditions.
- Statistical models and assumptions: Analysis uses the Eyring acceleration model to relate temperature/RH to degradation and models life with a two-parameter Weibull distribution (shape parameter assumed independent of stress). Key assumptions: the dominant failure mechanism is the same at use and accelerated conditions and is well modelled by the Eyring/Weibull approach.
- Data handling: Procedures for time intervals, survivor analysis, acceleration factors and failure distribution estimation are defined to produce LE and Standard Life Expectancy (SLE) metrics.
Applications and users
ISO 18921:2008 is intended for:
- Optical media manufacturers validating product durability and supporting specifications,
- Quality assurance and test laboratories conducting accelerated ageing and qualification tests,
- Archivists, libraries and preservation programs assessing long-term retrievability of CD-ROM collections,
- Product designers and procurement teams comparing media options for long-term storage.
Practical uses include media qualification, storage policy planning, archival risk assessment, and supplier comparisons.
Related standards
- ISO/IEC 10149 (normative reference) - CD-ROM data interchange and read-only disk specifications.
- IEC 60908 - referenced for BLER criteria and playback limits.
Keywords: ISO 18921:2008, CD-ROM life expectancy, accelerated ageing, block error rate, BLER, temperature and relative humidity, Eyring model, Weibull distribution, optical media testing.
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