The short answer
EN ISO 21640:2021 is the principal common standard for specifying and classifying solid recovered fuel in Europe. Estonia has adopted it as EVS-EN ISO 21640:2021. It gives producers and users a shared vocabulary for trade, but it does not create one universal commercial grade for every receiving plant.
RDF is a broad market term for combustible material prepared from refuse. There is no equivalent EN or ISO quality-classification system for generic RDF. Material produced from non-hazardous waste and classified and specified under EN ISO 21640 can be designated SRF. Untreated municipal solid waste is not SRF, although it can be an input to an SRF production process.
Three characteristics, three independent classes
The standard classifies SRF using net calorific value, chlorine and mercury. A code such as NCV 2; Cl 2; Hg 1 reports three separate results—not one overall grade. Class 1 is the strongest band for each characteristic and class 5 the lowest class within the system.
NCV and chlorine use mean results. Mercury uses both the median and the 80th percentile; both conditions must be met, so the more restrictive result determines the mercury class. The boundaries are one-sided. For example, NCV class 2 covers a mean from 20 to below 25 MJ/kg, while chlorine class 2 covers a mean above 0.20% and up to 0.60% on a dry-matter basis.
| Characteristic | Measure / basis | Class 1 | Class 2 | Class 3 | Class 4 | Class 5 |
|---|---|---|---|---|---|---|
| NCV | Mean, MJ/kg as received | ≥25 | ≥20 | ≥15 | ≥10 | ≥3 |
| Chlorine | Mean, mass % dry | ≤0.20 | ≤0.60 | ≤1.00 | ≤1.50 | ≤3.00 |
| Mercury | Median, mg/MJ as received | ≤0.020 | ≤0.030 | ≤0.050 | ≤0.100 | ≤0.150 |
| Mercury | 80th percentile, mg/MJ as received | ≤0.040 | ≤0.060 | ≤0.100 | ≤0.200 | ≤0.300 |
The reporting basis changes the meaning
‘As received’ includes the moisture present at delivery; dry or dry-matter basis excludes it. The standard’s NCV class is stated as received, while chlorine is reported on a dry basis. A chlorine result of 0.8% dry is therefore not the same statement as 0.8% as received.
NCV is also called lower heating value or PCI. Gross calorific value—also called higher heating value—is not interchangeable with NCV unless the necessary moisture and hydrogen data are used for conversion. A certificate and contract should always place the unit and basis beside the number.
Classification is not the whole specification
EN ISO 21640 deliberately separates classification from specification. The class code is a compact comparison tool; a traded fuel still needs a fuller description covering origin, form, particle size, moisture, ash, energy values and relevant trace elements. National rules, permits and buyers can add tighter requirements.
Meeting the standard does not automatically give a material end-of-waste status. That legal question depends on EU waste law and any applicable national criteria or decision. A technically classified SRF may therefore remain waste and continue to require the corresponding controls.