General information

General information

Durability in the context of fire retardant treatments is an often overlooked area. It is easy to just look at the initial properties that a product provides while not considering what might happen when, for example, a facade cladding is exposed to varying weather conditions for longer periods of time.

When it comes to durability, there is a big difference between a good product and a bad product. To take a familiar example of clothing, a dark sweater that is poorly constructed or improperly dyed can look decent when worn indoors or before it has been washed; however, after a day in the sun or after a turn in the washing machine, unwanted signs of wear and tear may begin to appear.

The same principle applies to fire retardant treated wood; it is important to choose the right product for the right purpose. Products are divided into three different DRF classes (Durability of Reaction to Fire) according to the EN 16755:

INT-1 = To be used indoors.
INT-2 = To be used indoors and in weather-protected environments as well as environments that may experience a more varying or higher ambient humidity ratio than that of a normal indoor climate, such as attic spaces or cold storages.
EXT = To be used outdoors ( e.g. wood facades with verified durability of reaction to fire properties).

Consequences of incorrect choices in different DRF-classes

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EXT is the toughest DRF class where a product must be able to withstand permanent use in an exterior environment (e.g. on facade claddings). One of the most common mistakes when it comes to this class, is to only look at the reaction to fire properties of the new construction and thereby forgetting to take into account the prolonged wear and tear caused by rain, UV rays, temperature differences and wind that a facade may be exposed to.

In the worst case, the results can be devastating — partly because the durability deteriorates at an unauthorized rate, and partly because the aesthetics of beautiful wood facades may be ruined completely. All of this can result in enormous costs for everyone involved.

The EXT classification includes fire tests where the input parameter is compared with the output parameter; the deviation must not exceed 20%. These requirements apply to all types of treatments, and the test results cannot be linked to the EN13501-1, EN13823 as the THR measurement value.

Image: The image shows a facade that has been treated with a fire impregnation not approved for this purpose. The current facade paint does not have the properties required to ensure proper weather protection for the fire impregnation agent.

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INT 1 is the least restrictive of the DRF classes and is intended for products that are to be used exclusively indoors. One of the common errors for this class is when wood panels are treated with fireproofing paint and impregnation that have negative hygroscopic properties, which can for example contribute to mold growth.

The INT 1 class does not include fire testing of the material, but it is a prerequisite for any EXT classification.

Image: The image shows a dissolved ammonium impregnation that promotes mold growth.

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INT 2 is more restrictive than the INT 1 class and is intended for products that are to be used indoors and in weather protected environments, as well as in environments that may experience a more varying or higher ambient humidity ratio than that of a normal indoor climate; two examples of such environments are attic spaces and cold storages. A common problem in this class is that the product does not withstand environmental changes. Moisture infestations can for example result in mold growth, paint flaking and leaching. This can cause health problems if mold spores are spread within the property, and may also cause large remediation costs.

The INT 2 class does not include fire testing of the material, but it is a prerequisite for any EXT classification.

Image: The image shows how the ambient environment is causing the fire impregnation agent to seep out of the wood panel.