ISO 13909-7:2025

Overview

ISO 13909-7:2025 - Coal and coke - Mechanical sampling - Part 7 specifies methods to determine and estimate the precision of mechanical sampling, sample preparation and testing for coal and coke. The third edition updates methods for estimating overall sampling precision, deriving primary increment variance, and checking the variance of sample preparation and analysis. The Standard develops formulae linking factors that contribute to precision (product variability, number of increments, sub-lots and preparation/testing variance).

Key topics and technical requirements

• Precision estimation methods: procedures for estimating overall precision using experimental designs such as replicate and duplicate sampling (Clauses 6–8).
• Primary increment variance (VI): methods to estimate variance of individual primary increments, including direct determination and methods based on precision estimates (Clause 6).
• Formulae for precision: relationships between variables affecting precision - number and mass of increments, sub-lots, and preparation/testing variance - and how to use these formulae to design or adjust a sampling scheme (Clause 5).
• Practical sampling checks: duplicate sampling with twice the number of increments, duplicate sampling during routine operation, alternatives to duplicates, and a precision adjustment procedure (Clause 7).
• Calculation procedures: guidance for calculating precision for both replicate sampling and normal sampling schemes (Clause 8).
• Sample preparation and testing checks: methods to check and partition the variance contributed by on-line and off-line preparation, target variances, procedures for stage-by-stage checks, and interpretation of results (Clause 9).
• Informative methods: annexes include the variogram method and Grubbs’ estimators for determining variance.

Practical applications

• Design and validate mechanical sampling systems to achieve a required coal sampling precision.
• Diagnose and reduce variability sources in sample preparation and testing (on-line and off-line).
• Adjust sampling schemes (number of increments, sample mass) based on measured primary increment variance to meet quality control targets.
• Provide documented, repeatable procedures for auditing sampling performance and demonstrating compliance in procurement, quality assurance, and regulatory reporting.

Who should use this standard

• Sampling engineers and system designers for coal and coke handling facilities.