ISO 21660-3:2021

Overview

ISO 21660-3:2021 specifies the oven dry method for determining moisture content in the general analysis sample of solid recovered fuels (SRF). Published in parallel as EN 21660-3, it is intended for all SRF types prepared as a general analysis sample (particle size ≤ 1 mm) and aligns with CEN/TS 15414‑1. The method reports moisture as a mass fraction (%) based on the loss of mass on drying and includes guidance on atmosphere, apparatus and reporting.

Key topics and technical requirements

• Scope: Applicable to all solid recovered fuels; special guidance when large oil fractions are present.
• Sample preparation: Use the general analysis sample (≤1 mm) prepared according to ISO 21646; mix thoroughly before testing.
• Drying conditions: Standard drying at (105 ± 2) °C in an oven with 3–5 air changes per hour. If sample oxidizes at 105 °C, dry under nitrogen. For oil‑rich materials, consider the Karl‑Fischer method (e.g. ISO 760) or a lower temperature (e.g. 50 °C ± 10 °C) with longer drying until constant mass.
• Apparatus: Temperature‑controlled drying oven, weighing dishes (glass or corrosion‑resistant), balance with 0.1 mg resolution, desiccator with desiccant.
• Procedure: Minimum two determinations per sample; use ≥1 g sample in an even layer; achieve constant mass (mass change ≤ 1 mg over a further 60 min of heating); cool in desiccator and weigh rapidly due to high hygroscopicity.
• Calculation & reporting: Moisture calculated from mass loss on drying and reported on an as‑analysed basis. Test reports must identify laboratory, sample, reference to ISO 21660‑3:2021, any deviations, drying atmosphere, results and unusual observations.
• Precision: Repeatability and reproducibility data from interlaboratory testing are provided (see Annex A).

Applications and users

• Who uses it: Analytical laboratories, SRF producers, waste management and recycling facilities, energy‑from‑waste plants, quality assurance/quality control teams, regulatory bodies and environmental consultants.
• Practical uses:
  • Routine moisture determinations for fuel specification and trading.
  • Input data for calorific value and mass/energy calculations.
  • Quality control during SRF production and acceptance testing.
  • Compliance testing where moisture influences combustion behavior, emissions and handling.

Related standards

• ISO 21646 - Solid recovered fuels: Sample preparation
• ISO 21637 - Solid recovered fuels: Vocabulary
• ISO 760 - Karl‑Fischer titration (for materials with significant oil fractions)
• CEN/TS 15414‑1 and EN 21660‑3 (parallel publication/related series)

Keywords: ISO 21660-3:2021, solid recovered fuels, moisture content, oven dry method, general analysis sample, Karl‑Fischer, sample preparation, drying oven, precision, SRF testing.