Overview
ISO 13909-8:2016 - "Hard coal and coke - Mechanical sampling - Part 8: Methods of testing for bias" defines principles and procedures for testing sampling bias of test samples of hard coal or coke taken in accordance with the ISO 13909 series. The standard specifies how to plan, conduct and analyse bias tests so that mechanical sampling systems reliably represent the feedstock for key analytical parameters (notably moisture and ash on a dry basis).
Key topics and requirements
- Scope and terminology: Applies to samples of hard coal and coke; the term fuel is used where appropriate to cover both.
- Pre-test inspection: A thorough inspection of the sampling system (see ISO 21398) is required before bias testing to identify system deficiencies that could introduce bias.
- Reference methods and paired design:
- Bias testing compares system samples with reference samples taken from a stopped belt or other reference method.
- Two common experimental designs: paired-increment (individual primary increments paired) and paired-batch (compounded increments paired). Paired-batch is preferred to minimize operational disruption.
- Parameters to test: The standard recommends at minimum moisture and ash (dry basis); additional variables may be included but can reduce statistical sensitivity.
- Sample size: Minimum 30 paired samples is recommended; fewer may be acceptable if bias is detected. Statistical confidence regions guide whether more samples are needed.
- Sample handling and preparation: Detailed protocols for collection, weighing, preparation and transport are required to avoid introducing bias-special precautions for moisture samples to prevent moisture change.
- Statistical analysis and reporting: Differences between paired results are subjected to statistical analysis; calculations, interpretation and a formal test report are required. The standard includes example calculations and documentation requirements.
Applications and users
ISO 13909-8:2016 is used to:
- Validate and verify mechanical sampling systems in coal mines, coke plants, power stations and fuel terminals.
- Diagnose and quantify sampling bias that affects contractual quality (ash, moisture) and laboratory results.
- Support quality assurance, regulatory compliance and dispute resolution where representative sampling is critical.
Typical users:
- Sampling engineers and laboratory managers
- QA/QC professionals in coal/coke supply chains
- Plant operators, power utilities and coke producers
- Standards bodies and auditors
Related standards
- ISO 13909-1, -2, -4, -5, -6, -7 (other parts of the mechanical sampling series)
- ISO 21398:2007 (Guide to inspection of mechanical sampling systems)
Keywords: ISO 13909-8:2016, mechanical sampling, hard coal, coke, sampling bias, paired samples, reference method, moisture testing, ash content, statistical analysis.
