ISO TC 238: A Year of Robust Activity

ISO TC 238 is the International Standards Organization’s Technical Committee through which numerous countries around the world are working together to develop standards for solid biofuels. While the efforts of ISO TC 238 are ongoing, historically, they have been most robust during the annual plenary and working group meetings held in the spring of each year. Last year’s plenary was cancelled due to COVID-19, and this year’s meeting is now planned as a virtual event in June. While ISO TC 238 has not met in person since May 2019, we have found new efficiency in using video conferencing platforms such as Zoom and Microsoft Teams. To date, ISO TC 238 has published 44 methods with 12 methods currently under development. The following is an update as to which projects are currently in motion.

A U.S.-led project of interest is ISO 23343-1, determination of water sorption and its effect on durability in thermally treated biomass fuel pellets. For biomass thermal treatment technology initiatives, a common selling point is that the material becomes water resistant and can be stored outside. This test method is designed to determine how much water sorption occurs in thermally treated biomass fuel pellets when immersed in water, and also assesses the durability of the product before and after immersion. This project is in its final stages of publication and has been unanimously approved by all participating countries.

Another standard of significant interest is ISO 5370—Determination of Fines Content in Pellets. In prior years, an issue was raised with ISO 18846 (the current method for determining fines content in pellets) whereby it was found that for samples with larger amounts of fines, the method was not sufficient to fully remove the fines from the pellet sample. During the past couple years, a research initiative was conducted to determine how much sieving is necessary to properly remove fines from various types of pelletized materials. The sieving technique was evaluated to better standardize this manual technique, and a validation study was conducted to prove that the new method can be performed in repeatable fashion. As a result, ISO 5370 will soon be released as a committee draft for further development by the international community. When published, ISO 5370 will replace ISO 18846. One of the major differences includes using 20 sieve rotations for samples where fines are expected to be higher than 1% (e.g., 10 rotations still useable for residential pellet markets, but 20 rotations used for industrial markets).

In addition to new methods, previously published methods come up for systematic review every five years. This past year has been very busy with these systematic review projects. In particular, several of the previously published specifications and classes documents (ISO 17225-1 through 7) are in the process of systematic review, all of which have had varying levels of modification. If you are currently relying on any of these documents for determining fuel quality, it would be wise to review the updated documents when published. Additionally, ISO TS 17225-8 (specifications and classes for thermally treated solid biofuels) is also up for systematic review. This technical specification is currently being considered for, and will likely be converted to, an international standard. This process is still in very early stages, so anyone producing or planning to produce thermally treated solid biofuels would be wise to engage with the U.S. Technical Advisory Group to review and provide feedback on the up-and-coming changes to this document.

Finally, there are also several physical test methods up for systematic review, including those for ash, moisture, volatile matter, length, diameter, bulk density, durability and particle size distribution. Most of these documents will see minor revisions to update method references, alignment with other documents published since their initial adoption, and clarification of language that has proven confusing to method users. Two of these methods—bulk density and length—will have substantial modifications. The bulk density method was inherently flawed in that method users have adopted a wide range of techniques for how this method is conducted. The length method is flawed in that it does not provide clear definition for what constitutes the measuring point at each end of the pellet, and when used to assess the percent of overlength pellets, the samples size is far too small to provide a representative result. These issues will be addressed in the revised versions of these methods.

The U.S. TAG currently has approximately 50 members and is administered by the American Society of Agricultural and Biological Engineers. We are always looking for individuals to join our efforts to review these standards as they are developed, ensuring they are well thought out and reflective of U.S. interests in the global solid biofuels industry. If you would like to join the U.S. TAG, please contact Scott Cedarquist at ASABE (

Author: Chris Wiberg
VP of Laboratories, Timber Products Inspection/Biomass Energy Lab

Printed in Issue 2, 2021 of Pellet Mill Magazine

By Chris Wiberg | May 17, 2021

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