A news item last week about the potential role of window frames in fires such as that at Lakanal House in Camberwell may have given a misleading impression of the research it was based on, claims BRE.

The BBC London report highlighted the widespread use of replacement PVC window frames in social housing as presenting an increased risk of fire spread, including a block in Croydon which was destroyed by fire in 2007.

The BBC said: “Safety analysts, the BRE, found wooden frames gave nine minutes more fire resistance than that of PVC.”

BRE says the information was extracted from a report of the work it carried out in 2005 as part of the review of Part B (Fire Safety) of the Building Regulations. The report, “Cavity Barriers: Final Factual Report of the Experimental Programme” investigated the effectiveness of different types of window frame constructions at mitigating the entry of fire into a timber frame cavity. It was not, says BRE, a study to assess the fire resistance performance of glazing systems.

A series of eight ad hoc fire tests were designed to represent a post flashover fire within an enclosure, breaking out through a window opening set in a timber frame cavity wall construction. The tests were carried out using four different window frame systems without any glazing in place: aluminium; PVCu; hardwood and softwood. Each frame system was tested with and without the installation of solid timber cavity closures around the window reveal.

The research focussed on the time taken for fire to enter the timber frame cavity in each test. The times reported are not measures of the fire resistance, explained BRE, as this is a measure of a product’s performance in specific standardised (BS or BS EN) fire test methods.

The results from the work confirmed that when appropriately designed and installed, cavity closures around openings offer a means of delaying entry of fire and smoke into timber cavities. However, the interface between the cavity barrier or closure and the primary structure is of key importance, says the report.

In every case, the timber cavity closures improved the performance by increasing the time to the entry of the fire into the cavity.

A BRE spokesperson said: “It is the responsibility of all users of data to satisfy themselves that they understand the results within the context they are presented. Research and test reports should always be read in their entirety. It is only by reading the full detail that the context, limitations and assumptions surrounding any reported data can be understood and the potential for misinterpretation and misunderstanding can be avoided.”