Fire performance requirements
The fire performance for all materials used in buildings, including wood and wood based panel products, are set out in Building Regulations. These regulations call for fire performance to be in line with British Standard or European Standard Test Methods.
In the past the principal standard used for assessing the reaction to fire performance of wood and wood based materials was BS 476 'Fire Test Classifiactions' typically Class 0 or Class 1 which are still referenced in UK Building Regulations as alternatives to Euroclass classifications typically Euroclass B or Euroclass C however, FR treated wood with BS476 classifications are being phased out in favour of the Euroclass system and are no longer widely available. Almost all fire testing carried out today is to meet Euroclass reaction to fire performance criteria which is different to BS 476.
BS476 fire test classification requirements are different to the Euroclass system and cannot be used to demonstrate compliance with a European flame retardant Euroclass standard - EN ISO 11925 and EN 13823.
Following the introduction of harmonised European fire test methods, Euroclasses based on performance in these tests. These are known as Euroclass A, B, C, D, E and F. Building Regulations Approved Document B has been revised to include Euroclasses for fire performance alongside the equivalent BS 476 classes.
The EU Construction Products Regulation requires all products demonstrate compliance with harmonised European product standards (where they exist). Marking a product with the CE mark as a declaration of compliance. This is done in conjunction with a Notified Body.
Once a standard is mandatory, then compliance with Building Regulations is shown by use of the European tests alone, however, where no harmonised European standard exists, compliance may be demonstrated by conducting either current national test methods such as BS 476 Part 7, or the European tests. (N.B. most UK manufacturers of FR treatments have adopted the Euroclass system for fire classification testing of materials.)
The final performance of the product is critically dependent upon the care and control exercised by the processor over the factory application process and also upon the quality/efficacy of the flame retardant treatment used.
The WPA operates a quality assurance/independent approval scheme for flame retardant products for wood and also for the processes by which they are applied. The scheme is called the WPA BenchmarkTM of quality.
How to specify
The WPA Flame Retardant Specification Manual provides detailed guidance about the selection of the most appropriate fire retardant treatment or treated panel product. It includes a Checklist to assist specifiers navigate the product selection process and provides model specification phrases that can be used to define the specific treatment in contractual documents.
The WPA FR Manual also defines five Commodity Specifications which cover the most typical situations. They are a simplified method by which the appropriate FR treatment is identified by the suppliers of FR treatments and are referenced widely by other standards setting bodies such as NBS and NHBC.
Model specification phrases
(a) Dry interior constructions (maximum 75% relative humidity): [insert material/species] to be treated to [Class 1 Surface Spread of Flame to BS 476 Part 7 or Class 0 BS 476 Parts 6 & 7, or Euroclass B or Euroclass C], using a * WPA Type DI dry interior process.
(b) Interior constructions (humidity resistant): [insert material/species] to be treated to [Class 1 Surface Spread of Flame to BS 476 Part 7 or Class 0 BS 476 Parts 6 & 7, or Euroclass B or Euroclass C], using a * WPA Type HR humidity resistant process.
(c) Full Exterior Exposure: [insert material/species] to be treated to [Class 1 surface Spread of Flame to BS 476 Part 7 or Class 0 BS 476 Parts 6 & 7, or Euroclass B or Euroclass C], using a * WPA Type LR leach resistant process.
* Where specifiers wish to specify the type or identity of fire retardant to be used, appropriate details can be inserted where an asterisk appears in the above sentences.