Types of fire retardant
The WPA classifies fire retardant products according to their sensitivity to humidity or water – there are three different types:
The choice of flame retardant treatment depends upon many different factors; the principal ones being the standard of performance required and the conditions in which the treated product is to be used.
NOTE: WPA FR Types align with draft CEN Standard: Durability of reaction to fire performance - classes of fire retardant treated wood products in interior and exterior end use applications.
WPA Type INT1 (dry interior applications)
Type INT1 products are for dry interior applications. They are based on inorganic salts. Timber or boards treated with a Type INT1 product are sensitive to high humidity where prolonged exposure results in salt efflorescence and/or migration. They should only be used for interior environments where humidity does not exceed 75%.
Examples of applications include: Thin plywood for exhibition work, scenery, interior hoardings and dry interior structures such as drywall linings, shop fitting materials.
WPA Type INT2 (humidity resistant)
Type INT2 products are based on blended organic and inorganic chemicals. Treated timber or board product is far less sensitive to high or fluctuating humidity due to the lower solubility in water of the product and a degree of chemical interaction with the wood. Type INT2 products can be used in practically all interior situations and in some cases in certain weather-protected exterior situations.
Examples of applications include: Interior constructions dry and humid, internal and weather protected external e.g. wall linings, structural timbers, veneered panelling, weather protected applications that are coated.
Type EXT (leach resistant)
Type EXT leach resistant products may involve the use of chemicals that are cured by heat after treatment but in all cases treated timber or board products can be used in all interior and exterior situations. Leach resistance is brought about by high temperature curing of the complex chemical system in the treated wood following impregnation and re-drying
Examples of applications include: Full exterior exposure with no finish applied e.g. cedar shingles, exterior cladding unprotected and railway/transport infrastructure