🔥 Sampling of solid biofuels (sawdust, pellets, chips, nut shells, baled straw, large pieces, vegetable and fibrous waste, thermally treated and densified biomass, roundwood) from the place of growth, production plant, deliveries and stock — sampling plan (full and brief), sampling certificate, division of lots into sub-lots (manually up to 2500 t), visual inspection, minimum number of increments nmin = 4Vi/(NSL·PL² − 4VPT) (at least 10 unless otherwise agreed), manual and mechanical methods, PN-EN ISO 18135

Petrochemistry PN-EN ISO 18135

Overview

WHAT THE STANDARD COVERS. Scope from the PKN catalogue card of PN-EN ISO 18135:2017-06 (Polish version), in full (our translation): “This document describes methods for preparing sampling plans and sampling certificates for solid biofuels both from the place where the raw materials grow, from the production plant, from deliveries, e.g. from a lorry, and from stock. The document covers both manual and mechanical methods and applies to solid biofuels which are: - fine-particle materials (particle size up to about 10 mm) of regular shape, which can be sampled with a scoop or probe, e.g. sawdust, olive stones and wood pellets; - coarse-particle materials of irregular shape, particle size up to about 200 mm, which can be sampled with a fork or shovel, e.g. wood chips and nut shells, forest residue chips and straw; - baled materials, e.g. bales of straw or grass; - large pieces (particle size above 200 mm), which are picked manually or automatically; - vegetable waste, fibrous waste from virgin pulp production and from production of paper from dewatered pulp; - roundwood. This document does not apply to airborne dust from solid biofuels. It may be possible to use this document for other solid biofuels. The methods described in this standard may be used, for example, when the samples are tested for: moisture content, ash content, calorific value, density, durability, particle size distribution, ash melting temperature and chemical composition.” The list on the card lacks an item which in the ISO text stands before roundwood: “thermally treated and densified biomass materials”. We read the text of the standard in the preview of ISO 18135:2017 from the cover to the end of 8.5 (page 9); formulae 2, 4 and 7 and the text of pages 7 and 9 were checked on the page image; we do not have Clauses 9–16 (among others sampling methods from stockpiles, conveyors and roundwood) or Annexes A–H — we only know their titles from the table of contents.

ACCORDING TO THE TEXT OF ISO 18135:2017 (foreword, introduction, Clauses 1–8.5). The standard was prepared by ISO/TC 238 (solid biofuels). Introduction: unambiguous sampling principles as a tool for trade, understanding between seller and buyer, communication with equipment manufacturers, authority procedures and reporting; solid biomass according to ISO 16559 and ISO 17225-1; the standard was developed with significant content from EN 14778:2011. References (2): ISO 13909-8, ISO 14780, ISO 16559, ISO 21398. Definitions (3): bias (relative to a reference method); large stockpile — above 40 t; nominal top size — aperture of the sieve through which at least 95 % by mass passes (for pellets — the diameter); overall precision — includes preparation and analysis (results are accurate only if free from bias). Principle (5): a sample representative of the whole lot — every particle of the lot or sub-lot should have an equal probability of being included in the sample; a sampling plan is needed; a full plan (6.2) is prepared once for repeated or continuous sampling, a brief one (6.3) — for routine use; new material or supplier — checking and updating the plan. Plan (6): model of the full plan in Annex A — completed forms become the certificate; the brief plan contains: reference to the full plan, sample identifier, date and time, supplier, lot or sub-lot number and type of biofuel, and it is worth adding among others the sampler, mass, carrier, storage conditions, sampling technique and location. Division of lots (6.4): for manual sampling a lot is sampled as a whole only up to 2500 t or divided into sub-lots of up to 2500 t; division serves precision, sample integrity (airtight bag — loss of moisture, change of calorific value by biological activity), convenience, lifting capacity, distinguishing components of a mixture and avoiding bias from segregation; for mechanical sampling (large shipments) the sub-lot size is agreed by the parties, e.g. up to 5000 t; Example 1: 140 lorry-loads of chips a month (3500 t) — four weekly sub-lots; Example 2: 46 000 t of pellets — 10 sub-lots of 4600 t mechanically or 19 of 2421 t manually. Visual inspection (7): choice or verification of classification, equipment and method; mixture of different materials or impurities (soil, metal) — in the certificate; strong divergence of type or quality — immediately to the appropriate party. Number of increments (8): the true value is unknown, so precision is estimated — the index of precision is twice the standard deviation; P = 2s = 2√VSPT (Formula 1); VSPT = Vi/(NSL·n) + VPT/NSL (Formula 2); PL = 2√(Vi/(NSL·n) + VPT/NSL) — overall precision for the whole lot at 95 % confidence (Formula 3); when divided, ALL sub-lots are sampled. The primary increment variance Vi (8.2) depends on the type and top size of the fuel, pre-treatment, mixing, the value of the parameter and the increment mass, and differs between parameters — the number of increments is calculated for each parameter and the highest is taken; Vi is determined from at least 30 increments across the whole lot, each analysed separately (preferably ash dry basis and total moisture): Vi = [Σxi² − (Σxi)²/n]/(n − 1) − VPT (Formula 4), or taken from similar materials or from Annex D (preferably verified afterwards). Variance VPT (8.3): at least 20 sub-samples across the whole lot, each divided into a pair at the first division stage and tested as in routine: VPT = Σdi²/(2nP) (Formula 5), or from experience or Annex D. The overall precision PL is agreed by the parties, and without agreement the values of Tables D.1–D.10 are assumed (8.4). Number of increments (8.5): nmin = 4Vi/(NSL·PL² − 4VPT) (Formula 6), rounded up; below 10 it is set to 10 unless otherwise agreed (the parties may agree fewer); increments of extreme content influence the result, especially in segregating materials (fines concentrated in the centre); an infinite or negative nmin means that the preparation and testing errors do not allow the required precision with this number of sub-lots — they must be reduced, a larger PL agreed or the number of sub-lots increased: NSL = 4(Vi + nmp·VPT)/(nmp·PL²) (Formula 7, nmp — maximum practicable number of increments); it is recommended to measure Vi and VPT per type, group or supplier of fuel; for small storages (cellars, silos, bunkers) Annex D is not applicable. From the table of contents: sampling from falling streams, conveyor belts, bucket conveyors, drag conveyors, bucket loaders and grabs (12.3), roundwood including a method for fast moisture determination (12.4), combined and laboratory samples (13), packaging, storage, transport and labelling (15), certificates (16), annexes: model plan and certificate (A), large stockpiles (B), bulk densities (C), reference values of Vi and VPT (D), guidelines on the number of increments (E), quality parameters from BIONORM projects and large pellet shipments (F), single delivery (G) and continuous delivery (H).

STATUS (PKN catalogue cards as of 02.10.2026). The card of PN-EN ISO 18135:2017-06 (Polish version, published 26-10-2020, 62 pages, price group V) has no “Withdrawn” header: Mining Sector, KT 144 Coke and Processed Solid Fuels, ICS 75.160.40, “Introduces: EN ISO 18135:2017 [IDT], ISO 18135:2017 [IDT]”, “Replaces: PN-EN 14778:2011 – English version”. The PKN search for “PN-EN ISO 18135” (02.10.2026) shows the English and Polish versions 2017-06 and PN-EN 18135:2026-08 — a DIFFERENT standard with the same number (product passport for floor coverings, KT 27), unrelated to biofuels. The EVS catalogue (read 02.10.2026) lists ISO 18135:2017 as valid from 30.03.2017.

HOW MANY LABORATORIES AND IN WHAT FORM (copy of the accreditation scope database, data up to 17.09.2026, read 02.10.2026). The number 18135 appears in 10 records at 7 laboratories: AB 053, AB 081, AB 490, AB 687, AB 688, AB 743, AB 949. In the current scopes on the PCA website (read 02.10.2026, issues from 03.12.2025 to 09.09.2026) all give “PN-EN ISO 18135:2017-06”, usually with subclauses: subclauses 8 and 11 (AB 081, mechanical devices), 12.2.3, 12.3.3.2 and Annex B (AB 081), 12.2.3.3 (AB 490, AB 687), 12.3.3.2, 12.2.2 and 12.2.3.3 (AB 743), 12.3.2 (AB 949), “excluding subclause 12.4” (AB 688, two entries) and “excluding subclauses 11.3, 12.3, 12.4” (AB 688, third entry); AB 053 — without subclauses, next to PN-EN ISO 14780:2017-07. The “Laboratories” tab searches for entries STARTING WITH “PN-EN ISO 18135” and shows all 7 laboratories — checked with the tab query on the production server labcoda.pl on 02.10.2026.

WHAT THE LABORATORIES TEST (PCA entries). Solid fuels — solid biomass, solid biofuel: “Sampling for chemical and physical testing” (AB 053, AB 687, AB 688, AB 743, AB 949, AB 081), “Manual method of sampling from fixed piles” (AB 490); mechanical and automatic devices for sampling solid biomass — “Accuracy of sampling, preparation and analysis of samples” and “Loading of the sampling system” next to PN-ISO 13909-8 (AB 081 — the same for coal according to PN-G-04502 and PN-ISO 13909-7/-8).

WHERE A SEEMINGLY CORRECT RESULT IS EASY TO GET. Number of increments: it is calculated separately for each parameter and the HIGHEST is taken; the minimum of 10 applies unless the parties agreed otherwise. Variances: Vi and VPT taken from Annex D instead of measured on the given fuel are only an assumption — the standard recommends verifying them afterwards, and for small storages Annex D is not applicable. Division: when divided into sub-lots, ALL of them must be sampled; manually a lot above 2500 t must be divided. Integrity: as a reason for dividing lots the standard gives loss of moisture from a standing sample and change of calorific value through biological activity — which is why the sample is enclosed in an airtight bag or container (6.4 b); such changes are not visible in the result itself. Negative or infinite nmin: this signals that the preparation and testing error exceeds the required precision — increasing the number of increments will not fix it. Segregation: fines concentrate in certain places (e.g. in the centre), so increments of extreme content shift the result. Subclauses in scopes: most laboratories cite subclauses of Clause 12 and Annex B, which are not in the part we read — the description of these sampling methods is outside this entry.

WHAT WE DO NOT STATE. We do not have Clauses 9–16 or Annexes A–H: dimensions of tools and minimum increment volumes, specific sampling methods from stockpiles, conveyors, lorries and roundwood, rules for combined and laboratory samples, packaging and labelling, reference values of Vi, VPT and PL from Tables D.1–D.10 — we therefore give none of these figures.

Method principle

A lot (or sub-lots) of biofuel is sampled according to a plan so that every particle has the same chance of being included in the sample; the minimum number of increments is calculated from the primary increment variance Vi, the preparation and testing variance VPT, the number of sub-lots NSL and the required precision PL (nmin = 4Vi/(NSL·PL² − 4VPT), at least 10).

Applications

• Solid biofuels: pellets, chips, sawdust, straw, roundwood — sampling for testing; 7 laboratories in PCA scopes
• Biomass deliveries to power and heating plants — seller–buyer settlements
• Checking mechanical biomass sampling systems (accuracy, system loading)

Key parameters

Standard

Standard number

PN-EN ISO 18135:2017-06 (wersja polska; EN ISO 18135:2017 IDT, ISO 18135:2017 IDT)

Title (PL)

Biopaliwa stałe — Pobieranie próbek

Title (EN)

Solid biofuels — Sampling

Step-by-step procedure

1. Sampling plan

   Full plan (once) according to Annex A or brief plan for routine use: reference to the plan, sample identifier, date and time, supplier, lot/sub-lot number, type of biofuel. PN-EN ISO 18135:2017-06 current (PKN cards as of 02.10.2026).

2. Division of the lot

   Manually up to 2500 t per lot or sub-lot; mechanically by agreement (e.g. 5000 t); when divided, all sub-lots are sampled.

3. Visual inspection

   Verification of classification, equipment and method; mixtures and impurities (soil, metal) — into the certificate; strong divergences — immediately to the appropriate party.

4. Number of increments

   Vi and VPT measured (≥ 30 increments, ≥ 20 pairs) or from Annex D; PL agreed or from Tables D.1–D.10; nmin according to Formula 6, at least 10; for each parameter, take the highest.

5. Sampling and certificate

   Taking increments by the method appropriate to the material and location (Clause 12), combined and laboratory sample, packaging and sampling certificate (Clauses 13–16 — outside the part we read).

Required equipment and apparatus

Health and safety (OHS)

• The standard contains no safety warnings in the part we read; when dividing lots it takes the lifting capacity for samples into account (6.4 d) — other safety rules are set by the laboratory
• TECHNICAL NOTE: the number of increments depends on the measured or assumed variances Vi and VPT; with a negative or infinite nmin, preparation and testing errors must be reduced or the division of the lot changed

Frequently asked questions