Why does wood need Flame Retardant protection?
All building materials experience negative impacts from exposure to fire: steel buckles, concrete spalls and wood burns. Wood has good thermal insulation properties, high structural strength and slow charring rate, so its general behaviour in a fire situation is fairly predictable.
However, in areas where there is a higher than average risk of fire, for example in public buildings such as cinemas, theatres, libraries, schools, offices, hotels and hospitals, building regulations are in place governing the use of performance rated, flame retardant building products.
Flame Retardants (FR) generally work by reducing the surface spread of flame, heat and smoke release, providing vital extra time for a safe escape. Factory application of a flame retardant treatment prior to installation ensures all faces of the timber or board product can be protected, offering a safer, low maintenance solution.
Because of this, the application of flame retardant products on the construction site, by brush or spray is NOT APPROVED by the WPA as quality control is almost impossible to assure.
Service Environment and Treatment Types
Once you have established the Euroclass rating required of your project material, you also have to consider where and how it is being used in order to specify the appropriate treatment. Three service classes are defined in the structural design code BS EN 1995-1-1.
To correspond with these codes, the WPA categorises flame retardant products into three types:
INT1 (formerly DI: Dry Interior) for dry interior applications
INT2 (formerly HR: Humidity Resistant) for humid interior or fully covered exterior applications
EXT (formerly LR: Leach Resistant) for all interior and exterior applications.
These products will be more commonly known under their respective brand names - listed in the WPA Benchmark Approved Formulations. If you have a preference for a specific product (ie. in terms of suitability for species or component) you can add this at specification.
NOTE WPA FR Types use the same framework as those found in BS EN16755: Durability of reaction to fire performance - classes of fire retardant treated wood products in interior and exterior end use applications.
WPA Flame Retardant Specification Manual – all you need to know
For all the specification information you need please download the full manual. This detailed and comprehensive reference document covers all species types, applications and everything you may need to know about industrial flame retardant treatment. It also provides model specification phrases that can be used to define the specific treatment in contractual documents.
3 easy steps to ensure flame retardant timber treatments are fit for purpose.
Specify the Fundamentals
What fire performance is required - Euroclass B or C?
What is the service environment / treatment type?
Internal dry (INT 1)
Internal humid (INT 2)
or External (EXT)
Specify a named product if desired.
Verify Product Performance
What fire performance properties are claimed by the product manufacturers being considered?
All performance claims should be independently verified.
Such data can be found in the certificate for each WPA Approved flame retardant.
The Audit Trail
Make sure you get what you specified - ask for the following:
Classification Report(s) from a Notified Body in accordance with BS EN 13501
CE Mark & Declaration of Performance
The most widely used process for treating both solid wood components and panel products with flame retardants is vacuum-pressure impregnation. This is carried out by specialist companies in large pressure autoclaves under factory controlled conditions.
For panel products such as OSB particle board, plywood and medium density fibreboard (MDF) a WPA approved flame retardant can be incorporated as an integral part of their manufacture.
Formulations for surface application are only approved by the WPA when they are applied in a factory under third-party quality assured processes to achieve the performance set out in fire test Classification Reports.
The application of flame retardant products on the construction site, by brush or spray is NOT APPROVED by the WPA as quality control is almost impossible to assure.
Find out more in the Application Technologies section