Options for protection
Fire safety is a critical factor in building design. With the increasing popularity of wood as a low carbon sustainable construction material it is vital that designers are able to specify fire retardant treatments for wood that give long term, predictable performance.
WITH MORE fire protection options for wood on the market than ever before just how does a designer make the right choice? “Verifying a products fitness for purpose is the crucial test” says the Wood Protection Association (WPA), the UK technical and advisory authority on wood preservation, modification and fire protection. The WPA has just issued a nationwide call for building designers to double check the fire performance credentials of all fire retardants before writing specifications.
To help guide designers, the WPA has published a Fire Retardant Specifiers Checklist. This step-by-step checklist, summarised in this article will be included in a new edition of the WPA Fire Retardant Specifiers Manual later this year to reflect a new European Standard, prEN 15912, currently in draft and the WPA’s own fire retardant product approval procedures.
Extended Application Reports supplement Classification Reports and provide the test evidence and assessments that define a fire retardant products application scope or range of substrates and thicknesses to which a Classification Report applies.
Always select a fire retardant with a verifiable performance. If no Extended Application Report is available then choose another treatment that is appropriate to the Application.
Step 1: Check the Specification fundamentals
Before specifying a fire retardant treatment for a specific component, check and verify the specification fundamentals:
1.1 What fire performance is required?
• Euroclass B or C
• BS476 Part 6 or 7 (Typically Class O and Class 1)
1.2 What is the service environment?
• internal dry
• internal humid
• external.
Step 2: Verify performance credentials of the product options
What fire performance properties are claimed by the manufacturers of the treatment options being considered? All performance claims should be independently corroborated.
Check and establish that the claims made by the manufacturer reflect the performance required in Step 1.1 and the end use service environment in Step 1.2. Full guidance about the different standards and service environments is given in WPA Manual on Fire Retardants.
Step 3: Verification of Euroclass B or C performance claims?
If performance in accordance with a European Standard is required (typically Euroclass B or
C), the specifier should check the following:
3.1 Classification Report(s) from a Notified Body
In accordance with BS EN 13501, Classification Reports from a Notified Body state the fire performance of the treated timber eg Euroclass B, s1, d0. In this example, ‘B’ is the class achieved,‘s’ is the smoke rating and ‘d’ is the burning droplets rating.
Classification Reports also specify a field of application to which the classification applies by defining minimum treatment loadings for the fire retardant eg 40kg/m3, the species of timber (eg spruce) and the allowed variation in thickness (eg 12mm to 25mm).
3.2 Reports of tests to BS EN 13823 (Single Burning Item)
Such reports should be available but they can be considered optional information for the specifier as they are referenced in the Classification Report.
Step 4: Verification of Performance to BS476 - Class 1 and Class ‘O’
If performance in accordance with BS 476 Part 7 and/or Part 6 is required (typically Class 1 or Class ‘O’) check the independent test reports that show the performance to the required standard of treated substrate similar to that which it is to be specified.
Class ‘O’ is an artificial class specified in UK Building Regulations requiring a particular performance in both BS 476 Parts 6 and 7. Supplementary reports are sometimes produced to draw together the data from BS 476 Parts 6 and 7 although these are not normally necessary in regulatory terms.
REMEMBER: Euroclass B and C is not equivalent to Class 1 or Class ‘O’ (or indeed any other BS 476 Class) It is important to understand that a fire retardant having a Euroclass rating cannot be taken as being equivalent to Class 1 or Class ‘O’. In the same way, it is wrong to take a BS 476 Class as equivalent to a Euroclass. The two standards have test methods and results interpretation that are entirely different.
Step 5: Check hygroscopicity tests for internal high humidity applications (WPA Type: HR)
Evidence should be provided of compliance with the hygroscopicity test in prEN 15912.
This ensures that in-service exposure to high humidity will not degrade the fire performance or cause surface disfigurement.
Step 6: Check weathering capabilities of external flame retardant treatments (WPA Type: LR)
Where external applications are concerned evidence should be provided of accelerated weathering tests showing adequate performance after weathering. A European standard currently in draft (prEN 15912) indicates the requirements for maintenance of performance after weathering and guidance will be given in the next edition of the WPA Manual.
Step 7: Verify manufacturing and application Quality Assurance
The manufacture of flame retardant products and their application to timber should be under a third party quality assurance scheme, ideally according to ISO 9001. WPA requires that any factory-impregnation flame retardants and processes listed by the Association meet these quality requirements.
Take Caution: Products such as coatings for surface application depend on achieving the manufacturers correct application rates and/or film thicknesses on which laboratory test results were based. When such products are applied by brush or spray on site, fire performance can only be assured when application is carried out under an independent certification and accreditation scheme for installers.
Step 8: If in any doubt, check with the WPA
The WPA publishes detailed specification guidance in its Manual on industrial fire retardant treatments. Designers may also register for the architects help line on the Association’s web site www.wood-protection. org and request specific project or material specifications.
The WPA’s own 21-year fire retardant test programme carried out by leading independent Fire Test Laboratories demonstrates that wood can be used with complete confidence in fire critical applications, with no loss of performance, so long as it has been properly treated with a product appropriate to the application. Further details about this 21-year trial are available on request.
The WPA maintains a list of approved fire retardant products that meet its own product quality and performance procedures which includes the verification of independent test results and reports from accredited bodies.
