6. PERFORMANCE OF LVL IN FIRE The requirements of reaction to fire classes for different applications are defined in national building regulations. In general, LVL panels and structures may be left exposed in a building under the same conditions as other solid wood products. In the classification, the first letter A-E denotes combustibility, with D being typical for wood products. The second symbol, s1-s3, denotes smoke production and the third symbol, d0-d3, denotes the risk of flaming droplets. The class for LVL is similar to most untreated wood products. Some manufacturers specify for some applications a smoke production class of s1 based on separate testing, which is slightly better than the typical class s2. The flaming droplets class d0 assigned to woodbased products means that no flaming droplets or particles are produced. Although the European system has been in use since the beginning of 2000, national classification systems are still in parallel use in some countries. The reaction to fire classification can be improved by fire retardant treatments or with inorganic surface laminates up to a class B-s1,d0, which is the highest class for combustible materials. The fire retardants are mainly salt-based chemicals that are usually hygroscopic, meaning that they absorb humidity from the surrounding air. It is therefore essential that the durability of the treatment is verified for the intended use class for the whole service life of the product. LVL manufacturers provide fire retardant treatment as an additional service for their products, details of which can be found from their product information material. 6.3 FIRE PROTECTION ABILITY, K-CLASSES OF COVERINGS The encapsulation requirements of fire protection ability classes K10 - K60 of coverings are used in building regulations to Table 6.1. Classes of fire protection ability performance of LVL – laminated veneer lumber according to EN14374. The table has been published as a draft annex of (EC Ref. Ares(2017)2463446 - 15/05/2017) pending formal issuing as a European Commission Delegated Regulation 38. protect underlying products against damage. The classes may be achieved by LVL panels, when the minimum thicknesses are according to the Table 6.1. However, in some applications only non-combustible materials are approved for the encapsulation. Note: the same layer in a structure can give fire protection in accordance with the K-classes and at the same time be taken into account for fire resistance time of the structure. 6.4 FIRE RESISTANCE OF LVL STRUCTURES The fire resistance of LVL structures can be calculated according to the structural fire design specification of Eurocode 5 (EN1995-1-2) and its National annexes. The model of the structural system adopted for design shall reflect the performance of the structure in the fire situation. 6.4.1 Fire resistance design process The fire resistance design process has the following steps: 1. Determination of the charring depth The charring depth is the distance between the outer surface of the original member and the position of the char line. It is calculated using the time of fire exposure and the relevant charring rate which depends on the material of the structure and possible additional protection layers on the structure. The original size reduced by the charring depth on exposed sides is defined as the residual cross section. 2. Determination of the effective cross section Due to the increased temperature, the mechanical properties of wood reduce which is taken into consideration by LVL 06, Table 6.1 Product 1) Product detail 2) Minimum mean density [kg/m3] Minimum thickness of a board [mm] Field of application K Class Laminated veneer lumber products covered by the harmonised standard EN 14374 With and without tongue and groove and a minimum layer thickness of 3 mm 4) 450 15 Wall and ceiling covering K2 10 3) With and without tongue and groove and a minimum layer thickness of 3 mm 5) 450 26 Wall and ceiling covering K2 30 With and without tongue and groove and a minimum layer thickness of 3 mm 6) 450 52 Wall and ceiling covering K2 60 1) Mounted directly on the substrate (particle board 680 kg/m3 according to EN 14135) without an airgap 2) Joints with square edges or tongue and groove profile and with the same thickness as the wood product and without gaps. 3) K110 for substrates ≥ 300 kg/m3 4) Screw length minimum 30 mm and spacing maximum 200 mm 5) Screw length minimum 50 mm and spacing maximum 200 mm 6) Screw length minimum 75 mm and spacing maximum 200 mm 160 LVL Handbook Europe
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