ISO 21645:2021

Overview

ISO 21645:2021 - Solid recovered fuels - Methods for sampling - defines standardized methods for taking representative samples of solid recovered fuels (SRF). The standard covers manual and mechanical sampling from production plants, deliveries or stock, including dewatered sludge, but excludes fuels formed by liquid or sludge. ISO 21645:2021 guides users in preparing and implementing a sampling plan to ensure reliable laboratory testing and consistent quality assessment of SRF.

Key Topics

• Scope and applicability: Sampling procedures for SRF in various situations (material flows, static lots, vehicles, ships); dewatered sludge included; liquid/sludge-formed fuels excluded.
• Sampling plan development: Defining objectives, identifying a lot, determining lot size, selecting sampling procedures and frequency. (See Annex A - normative procedure for plan development.)
• Increment and sample mass: Rules to determine the number of increments, minimum increment mass, and minimum composite/sample mass required for analyses (Annexes E–J provide normative methods and examples).
• Distribution of increments: Guidance on how to distribute increments across a lot - from material flows, conveyors, vehicles, static stockpiles and ships.
• Sampling equipment and implementation: Manual and mechanical sampling tools, handling steps before/during/after sampling, storage and transport of samples (Annex D on equipment; Annexes H–I on implementation).
• Material-specific considerations: Addressing heterogeneity of SRF (including fibrous-like materials) and the need for additional statistical adjustments such as a shape factor (f) when applying sampling statistics.
• Precision and quality control: Procedures to estimate sampling precision, use of duplicate samples, and examples of stratified and stratified‑random sampling (Annexes K–L).

Applications

ISO 21645:2021 is intended for practical use by:

• Laboratories performing chemical and physical analyses of SRF.
• Producers and suppliers who must demonstrate consistent fuel quality and prepare compliant shipments.
• Purchasers and utilities using SRF for energy recovery and needing reliable sampling for contract verification.
• Authorities and inspection bodies that enforce environmental and trade requirements.

Typical applications include sampling from conveyor belts, drop flows, lorries, bulk stockpiles and ships to produce representative composite samples for calorific value, moisture, ash, elemental and trace‑element testing.

Related Standards

ISO 21645:2021 references and complements other SRF standards, including:

• ISO 21637 - Terminology for SRF
• ISO 21644 - Biomass content determination
• ISO 21654 - Calorific value
• ISO 21656 - Ash content
• ISO 21663 - C, H, N determination
• EN/ISO methods for elemental and particle-size analyses

Using ISO 21645:2021 together with these standards ensures a complete, traceable testing program for solid recovered fuels and supports robust quality assurance and regulatory compliance.