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hazardous wood, requiring further testing [35]. Potentially treated wood that pre-dates 2007 is typically assessed to reflect the withdrawal of CCA from sale in 2006. Clean, sorted demolition wood features quite high up in the waste wood hierarchy, in Category B. Strict limits are set on the amount of coated and treated timber that is allowable in the timber mix. If it includes wood that is deemed treated hazardous, i.e., is likely to exceed the limits on preservatives, the timber is downgraded to Category D timber. It is then handled as hazardous waste with specialist disposal. A Regulatory Position Statement (RPS 250) was in place until 2023 for construction and demolition waste, and a new RPS 291 covers ‘amber waste’ in England. This allows temporary storage of this waste wood while it undergoes the WRA testing mentioned above. One concern at waste handling hubs is the flammability of wood chip piles, if stored for prolonged periods. This is due to microbial action within the chip pile, leading to a build-up of heat. As a result, both the Environment Agency and the local Health and Safety Executive are very strict about the size of wood waste piles. One reason for such piles having developed is the fluctuation of wood waste prices; in order to achieve the best possible prices in the wood industry some storage is needed. In other cases, the market for Category C and D wood has been poor, leading to a backlog of low-quality material when a given operator ceases trading. 3.2. Industry-Adopted Regulations It is common for many industries to specify the quality requirements for their feed- stock materials, and this is also the case for waste wood entering the panel mills. The panel industry (primarily particleboard) uses a significant amount of waste wood in their manu- facturing process; however, the wood has to be clean and free from chemical contamination before it enters the factory. A clear picture emerged early on about the acceptable levels of heavy metals and contaminants that might relate to existing wood treatment agents from the first use of a product [27]. Other aspects of the specification may include the size and form of the timber, the grit content, and the moisture content. Work in this area started in 2000, when the Wood Panel Industries Federation (WPIF) in the UK recognised the increased use of waste wood in manufacturing wood-based panels. They developed an industry standard (WPIF/UKFPA/1-2000) which was based around the strictest European Standard to consider allowable metals content at the time, BS EN 71 or ‘The Toy Standard’ [36]. This standard prescribed the heavy metal content limits for materials used in the manufacture of toys. In 2004, a Publicly Available Specification (PAS 104, [37]) was published, governing contaminant levels, followed by an updated WPIF guidance document in 2005 to cover the manufacture of particleboard, MDF, and OSB in the UK. The limits have been incorporated into the PAS 111 standard for processing waste wood, with an additional restriction on the total heavy metal compound content of 4000 mg/kg dry matter [31]. The WPIF standard was also adopted by the European Panels Federation, as shown in Table 2, with revisions over the past 15 years [38]. Whilst the standard was written to protect the panel board industry’s interests and ensure that panels were able to supply to all industries, it initially prevented the use of most demolition waste wood streams and instigated the sector’s dependence on clean waste wood. Since this time, much work has been undertaken to analyse timber waste streams and demonstrate the decrease in heavy metal content with the transition from older-generation to new-generation timber preservative treatments [34]. The clear but stringent specification on contaminants has led to excellent quality control of waste wood intake for the industry and driven development of best practice in segregation. As a result, there have been many innovations in the processing steps for recycled timber as it enters the panel manufacturers.
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