This document determines the fuel quality classes and specifications of graded hog fuel and wood chips for industrial use. It covers only hog fuel and wood chips produced from the following raw materials (see ISO 17225-1:–, Table 1): – 1.1 forest, plantation and other virgin wood; – 1.2 by-products and residues from wood processing industry; – 1.3.1 chemically untreated used wood; – 1.4 blends and mixtures. This document covers hog fuel, which is produced with blunt tools, and wood chips, which are produced with sharp tools. NOTE 1 – 1.2.2 By-products and residues from wood processing industry, which can include chemically treated material (e.g. glued, painted, laminated) are not allowed include halogenated organic compounds or heavy metals at levels higher than those in typical virgin material values (see Annex B in ISO 17225-1) or higher than typical values of the country of origin. NOTE 2 – If class I4 includes chemically treated used wood (1.3.2), it can be only used in the installations permitted to use 1.3.2.