1.1 Firing systems This document applies to atmospheric fluidized-bed and grate firing systems of steam boilers and hot water generators. These systems commence at the fuel bunkers and end at the ash extraction plant. For combination of various firing systems, the individual requirements of each system apply, especially those included in prEN 12952-8:2020 and prEN 12952-9:2020. If several fuels are burnt simultaneously or if a fuel quality varies considerably (e.g. moisture content), additional safety measures may be necessary, especially with respect to limitation of the fuel flow into the firing system and ensuring proper air supply to the individual fuels. Pressurized firing systems may require enhanced safety measures, which are not given in this European Standard. 1.2 Fuels This document covers the use of solid fuels. Pulverized fuel fired in an entrained air flow (burner) system is covered by prEN 12952-9:2020. Solid fuels covered are: " all coal qualities, e.g. lignite or brown coal, sub-bituminous or hard brown coal, bituminous coal or hard coal, pitch coal, anthracite, coke, coal culm, coal sludge; " other fossil solid fuels (e.g. peat, oil shale); " biomass solid fuels (e.g. wood, wood wastes [bark], pellets, energy plants [miscanthus], harvest wastes [straw] and briquettes); " municipal waste solid fuels (e.g. garbage, sewage sludge, refuse derived fuels [RDF]); " industrial waste solid fuels (e.g. petrol coke, soot, tyres, paper wastes, coated wood chips, spent wood, animal product wastes). Fuel blends from two or more groups, or fuels of unconventional or unknown quality may require special safety measures which can be proved either by practical experience gained from comparable fuels, or by suitable tests, e.g. in accordance with EN 14034-2:2006+A1:2011. Such measures specified and documented by the manufacturer. Fuels on which the design is documented in the operating instructions (see 11.2). This includes the fuel data for 100 % input of the basic fuel and the data for any supplementary fuels together with their maximum thermal input percentage. 1.3 Operation The requirements for operational equipment in Clause 4, Clause 5, Clause 6, Clause 7, Clause 8, Clause 9, Clause 10 and Clause 11 apply to steam boilers and hot water generators with permanent supervision by properly trained personnel familiar with the special conditions of the firing systems and the type of fuel.