What Is Pellet Fines (Screen Testing & Limits)
Pellet fines are small wood particles that pass through a 3.15 mm sieve during a defined test. The result is their mass as a percentage of the test portion. To judge it, use the method and limit specified for the pellet grade and sampling point. A surface handful or an improvised shaking test can give a misleading answer.
A typical customer question is, “My manual says fines must be below a limit. What am I supposed to measure?” The key is that “fines” has a specific meaning in pellet quality control. It is not simply dust you can see, and a valid result depends on how the sample was taken and tested.
Test Basis, Pellet Grade & Sampling-Point Safety Checks
Pellet fines content measures the share of a test portion that passes through a 3.15 mm sieve under the required procedure. Before testing, identify the pellet grade, governing specification, and sampling point. Those details determine which limit applies and help prevent a correct test from being judged against the wrong requirement.
What counts as pellet fines?
In this test, fines are material that passes through the specified 3.15 mm sieve. The result is reported as a percentage by mass, not as a visual estimate of dust or the number of broken pellets.
The test method matters. ISO 18846 covers determination of fines in wood pellets. Sampling and sample preparation are addressed by separate standards, including ISO 18135 and ISO 14780. A purchase contract or certification scheme may require a particular edition or procedure, so check that document rather than assuming all tests are interchangeable.
Fines content is also different from mechanical durability. Durability measures how well pellets resist breaking or abrasion under a specified test. A low fines result does not, by itself, prove that a lot meets requirements for durability, moisture, ash, or heating value.
Which limit should I use?
Common limits associated with ISO 17225-2 and ENplus classes at delivery are shown below. These figures are useful reference points, but the controlling standard edition, certification rules, and contract must be checked before accepting or rejecting a lot.
| Pellet class | Common fines limit at delivery | What to verify |
|---|---|---|
| A1 | ≤1.0% | Applicable edition, scheme, contract, and delivery-point method |
| A2 | ≤1.0% | Applicable edition, scheme, contract, and delivery-point method |
| B | ≤2.0% | Applicable edition, scheme, contract, and delivery-point method |
Do not apply these delivery limits automatically to a sample taken at dispatch, at a plant, or somewhere else in the supply chain. Handling and transport can change the amount and distribution of fines. The contract or scheme must define the relevant sampling point and acceptance basis.
Before testing, write down the grade, the governing specification and edition, the sampling point, and the required test method. If any of these are unknown, resolve them before deciding whether a result passes. That check is the first safeguard against a false acceptance or rejection.
Representative Sampling and Field Sieve-Test Procedure
A sieve test is only as useful as the sample it represents. Collect increments according to the required lot-sampling plan, combine and reduce them without removing fines, then test a portion using the specified method. Do not substitute a surface handful or an improvised shaking routine for the required procedure.
Step 1: Obtain a representative sample
Fines can separate from pellets during handling, transport, and discharge. A sample from the top of one bag or one spot on a pile may contain more or less fines than the lot as a whole. A result from that sample can therefore misrepresent the consignment.
Use the sampling plan specified by the applicable standard, contract, or certification scheme. Depending on the plan, this may require taking increments across a lot or discharge stream. Combine and reduce the sample as directed, taking care not to spill, brush away, or selectively remove small particles.
Keep the sample identified with its lot and sampling point. If the question is whether a delivery meets a delivery limit, collect the sample at the defined delivery point. A result from an earlier point does not automatically establish the condition of the pellets when delivered.
Step 2: Prepare the test portion
Use the sample-preparation procedure required by the selected method. Do not choose a convenient portion by picking intact pellets or shaking loose dust away first. That changes the balance of material being measured.
Make sure the sieve and other equipment are clean and dry. Check that the sieve has the required 3.15 mm aperture and is in suitable condition. Use a balance appropriate for the test and record masses in consistent units.
Step 3: Sieve and weigh
Follow the motion, duration, and handling steps specified by the required edition of ISO 18846 or the procedure named in the contract. There is no safe universal substitute for those instructions: an undocumented shaking time or hand motion can change the result.
After sieving, weigh the material that passed through the sieve and the initial test portion, as required by the method. Keep the fractions separate until their masses have been recorded. If the method requires additional steps, follow them rather than relying on a simplified field routine.
I advise treating a test as a documented measurement, not a quick visual check. The sieve aperture, method, sample point, and both masses let another person understand how the result was produced.
Result Calculation, Acceptance Limits & Quality-Control Checks
Calculate fines as the mass that passes the 3.15 mm sieve divided by the initial test-portion mass, multiplied by 100. Compare that percentage with the limit for the correct grade and sampling point. Record the method and masses so the result can be checked, repeated, or reviewed.
How to calculate fines percentage
Use:
Fines (%) = (mass passing 3.15 mm ÷ initial test-portion mass) × 100
For example, if 8 g passes through the sieve from a 1,000 g test portion, the calculation is (8 ÷ 1,000) × 100 = 0.8% fines. This example shows the arithmetic only; it does not define the required test-portion size or procedure.
Record the measured masses, units, sieve aperture, method and edition, sample point, date, and lot identification. Keep enough detail to show how the percentage was obtained. Report the result at a precision supported by the equipment and required method; do not imply more accuracy than the measurement allows.
How to read a result
Compare the calculated percentage with the requirement that applies to the exact pellet class and point in the supply chain. A result below a stated maximum is within that numerical limit only when the sample and test also meet the governing requirements.
| Example result | Possible reading against common delivery limits | Important qualification |
|---|---|---|
| 0.8% | Below the common A1, A2, and B limits | Valid only for the applicable delivery test and specification |
| 1.0% | At the common A1 and A2 limit; below the common B limit | Confirm how the governing document treats rounding and equality |
| 1.6% | Above the common A1 and A2 limits; below the common B limit | Grade and delivery point must still match |
| 2.2% | Above the common limits shown | Check test validity and the controlling document before acting |
These are comparison examples, not alternate acceptance rules. In particular, do not round a borderline value in a way that changes pass or fail unless the governing method or contract tells you how to report it.
If the result is close to the limit or disputed
First check the basics: was the correct grade and sampling point used, was the sample representative, and was the specified sieve procedure followed? A handling mistake or sample taken from only one location can matter as much as the calculation.
If the result is near the limit or challenged, repeat the test with a fresh representative sample under the same applicable procedure. Do not merely re-sieve the same portion and treat it as an independent sample. For a formal dispute, use the sampling and testing route agreed in the contract; an accredited laboratory may be appropriate where required.
Sample Handling, Test-Equipment Care & Records
Good records make a fines result traceable and useful for quality control. Identify the lot and sampling point, preserve the sample as collected, and document the method, sieve, and masses. Keep equipment clean and in good condition, and avoid actions that remove or add fines before testing.
Protect the sample and equipment
Label the sample promptly so it cannot be confused with another lot. Store and handle it as required by the sampling or test procedure. Avoid spilling loose material during transfer: fines are part of the sample, not waste to be discarded before the measurement.
Inspect the sieve for damage, contamination, or blocked openings before use, and clean it using a method that does not alter its aperture. Keep the balance suitable for the measurement and follow its care and calibration instructions. If equipment condition is uncertain, resolve that before reporting a result.
Record a complete test
A useful record includes:
- Lot or consignment identification and pellet grade
- Sampling date, location, and point in the supply chain
- Sampling plan or reference used
- Test method and edition
- Sieve aperture: 3.15 mm
- Initial test-portion mass and mass passing the sieve
- Calculated fines percentage and pass/fail decision
- Operator, equipment identification, and any relevant observations
These details help explain differences between results. For example, a dispatch sample and a delivery sample may differ because they represent different points after handling. That difference does not automatically mean one test is wrong; it means the sampling points must be understood.
Illustrative quality-control scenarios
These examples show how to apply the checks; they are not reports of specific customer cases.
- A bag-top sample appears dusty, but the full lot is in question: Do not treat the handful as representative. Follow the required lot-sampling plan, then test the resulting sample.
- A delivery result exceeds a limit, while a dispatch result did not: Check whether both samples were taken and tested at the points required by the contract. The results are not directly comparable if their sampling points differ.
- A result sits near the limit: Check the recorded masses and procedure, then use a fresh representative sample or the agreed dispute process. Avoid changing the test method to obtain a preferred result.
The practical next step is simple: confirm the acceptance basis before testing, preserve a representative sample, and keep a complete record. Fines content is meaningful only when the grade, method, and sampling point all match the requirement.
Frequently Asked Questions
These quick answers clarify what the fines result can tell you and how to use it. For a formal acceptance decision, the current specification, certification scheme, and purchase contract control. If they differ from a general reference value, follow the document that governs the lot.
What are pellet fines?
Pellet fines are the mass of material that passes through a 3.15 mm sieve during the specified wood-pellet test.
How are pellet fines measured?
They are measured by sieving a prepared test portion under the required procedure, weighing the passing material, and calculating its percentage of the initial test-portion mass.
What is the formula for fines percentage?
Divide the mass that passes the sieve by the initial test-portion mass, then multiply by 100.
What sieve size is used for wood-pellet fines?
The stated aperture is 3.15 mm. Follow the test method and sieve requirements specified by the governing document.
What is the common delivery limit for A1 pellets?
A common ISO 17225-2 and ENplus reference is no more than 1.0% at delivery. Confirm the applicable edition, scheme, and contract before making an acceptance decision.
Are A2 and B limits the same as A1?
Common delivery references are no more than 1.0% for A2 and no more than 2.0% for B. Verify the rules that apply to the specific lot.
Can I use a handful from the top of a bag?
Not as a reliable lot sample unless the required sampling plan says so. Fines can segregate, so a surface handful may not represent the contents or consignment.
Are fines content and mechanical durability the same?
No. Fines content measures material passing the sieve; mechanical durability measures resistance to breakage under a separate test. One result does not establish the other.
Can I use the delivery limit for a sample taken at dispatch?
Not automatically. Use the limit and method specified for that sampling point. Handling between dispatch and delivery can affect fines.
What should I do if the result is close to the limit?
Check the sample, method, sieve, and recorded masses. If needed, test a fresh representative sample or follow the contract’s dispute process, which may involve an accredited laboratory.
(This article was written by one of our staff writers, Evan Bradley. Visit our Meet the Team page.)
