KANBrief 2/19

Safe storage of wood pellets

Wood pellets have become firmly established on the European market as a heating fuel. Until just a few years ago, it was not widely appreciated that dangerous concentrations of carbon monoxide (CO) may arise in pellet stores. KAN saw a need for action in this area, and since 2014 has either launched or provided expert support for a package of measures intended to increase occupational safety.

Between 2002 and 2011, carbon monoxide poisoning was responsible for 13 documented fatal accidents in ships’ holds, bulk stores, silos, and stores in residential property. Since then, awareness of the need for pellets to be managed safely has risen strongly among all the parties concerned. Requirements concerning adequate ventilation for stores at heating systems have now been set out and implemented in numerous legacy installations. Provisions relating to safe accessing of the stores (CO measurements, warning instructions, etc.) have also been produced.

Two processes may essentially lead to the build-up of CO. Firstly, CO may flow back into the storage area from heating boilers that are not working properly. Secondly, a risk exists in closed storage areas of the unsaturated fatty acids found within the wood reacting with the oxygen in the atmosphere and giving rise to CO concentrations that are harmful or even fatal. The mechanical stress upon the pellets during transport and charging also has a bearing upon the intensity with which CO is formed.

Against this background and based upon a communication by the Institute for Work Design of North Rhine-Westphalia, KAN has since 2013 launched or supported various measures by public agencies and accident insurance institutions and in standardization work. Over the course of several years, a cohesive body of rules has emerged from these measures:

  1. Work on VDI Standard 3464, Storage of wood pellets at the point of end use, which contains rules governing the design of pellet stores and storage arrangements (published in 2015)
  2. Launch of DGUV Expert committee informative publication FBHL 005 (pdf, in german) concerning the occurrence of carbon monoxide during the commercial transport and storage of wood pellets (2017). This publication exploited the results of a study by the German Social Accident Insurance Institution for the trade and distribution industry (BGHW) into the CO concentration at various storage sites
  3. Proposal for requirements concerning the storage of pellets to be added to the German Specimen Firing Installations Ordinance (MFeuV); implementation anticipated in Hesse in 2019 and in Lower Saxony in 2020
  4. Involvement in work on ISO 20023 (2019) and ISO 20024 (publication anticipated for 2020) governing the safety of solid biofuel pellets and containing rules for the design of pellet stores and for handling and storage
  5. Inclusion of the back-flow issue in EN 303-5, Heating boilers for solid fuels (publication anticipated for the end of 2019)

In these very diverse projects at national, European and international level, KAN’s endeavours have been for the hazards on heating boilers and in storage areas that have been revealed by accidents to be tackled specifically by the imposition of safety requirements upon the technology. Supported by the DEPI (website in german), this has included the introduction of comprehensive standards for the design of stores, a final technical inspection prior to the commissioning of new storage areas, and safety instructions for users. Requirements concerning operation of the installations have also been added to several documents in cases where corresponding national provisions did not exist.

Gaps can be found in the regulatory arrangements for pellet stores. Standardization is therefore particularly important in this area. EN ISO 20023 has now acquired particular weight: for example, the requirement in the Firing Installations Ordinance (FeuVO) of the state of Hesse for pellet stores to feature adequate ventilation is based upon the provisions of this standard, and plans are for the relevant parts of the standard to be introduced in Hesse in the form of a technical building regulation (Ordinance amending the Firing Installations Ordinance, Hesse, October 2018, reasoning, Part B, concerning Paragraph 11 [5]). With respect to the heating technology, back-flow of CO from the burner into the store (for example as a result of a technical malfunction or improper operation), in particular, must be prevented by technical measures. This issue has now been included for the first time as part of the risk analysis in the EN 303-5 standard governing heating boilers.

During these steps, KAN’s particular concern was for the bodies of rules of the state authorities, those of the accident insurance institutions and provisions in standards to be aligned, with the aim of providing the user with a body of regulations free of contradictions.

Michael Robert