Roof Ventilators and Terminals: Fire Performance. CI/SfB (37.9) Uniclass L529 May 2012

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1 Roof Ventilators and Terminals: Fire Performance CI/SfB (37.9) Uniclass L529 May 2012

2 Fire - one of nature s destructive forces There is a view held by some in the industry that roof ventilators are an insignificant part of the roof and can therefore be ignored with regard to fire. History has shown us however that this is not the case and there have been instances of roof ventilators contributing to the spread of fire. Below is a fire underway in a department store in Blackpool. The fire is well established and is being attended by the fire brigade. Fire hoses are being directed not only at the burning building but also onto the roof across the road. Infra red imaging, shown below, allows us to see through the smoke. The snowy effect is hot airborne and burning embers. These show up as white and can be seen collecting in valleys and gutters. Such embers would also collect behind roof protrusions such as chimneys and roof tile ventilators. If such products are not fire rated there is a risk that they could catch alight, thereby propagating a fire on that roof. Below, again in infra red, we see the roof opposite the fire source as red. Steam coming from this roof can clearly be seen showing the extent of the temperature build up from the heat radiation from the fire on the opposite side of the road. This shows the temperature of this roof slope due to the radiant heat from the fire. Regulations Requirements The above shows why Building Regulations control roof materials to prevent fire spread (see page 3). The National Federation of Roofing Contractors Technical Bulletin 20 also clearly states The materials used in the manufacture of roof ventilation terminals should not significantly increase the risk of fire spread or penetration of the external roof envelope and comply with current Building Regulations. It will also be necessary to consider the number of roof ventilation terminals used in the roof. 2

3 Buildings Regulations Building Regulations Approved Document B Building Regulations Approved Document B4 External fire spread Requirement states that: The roof of the building shall adequately resist the spread of fire over the roof and from one building to another, having regard to the use and position of the building. This applies to roofs, the roof covering material and parts of roofs, which would include accessories such as tile and slate ventilators and terminals. Note: Approved Document B Volume 1 covers dwellinghouses, Volume 2 covers buildings other than dwellinghouses. Table 5 of Approved Document B (reproduced below) sets minimum distances of roofs from site boundaries or adjoining buildings, according to their fire classification. It shows that roofs and parts of roofs with a fire designation of AA, AB or AC can be used without restriction, ie with no minimum distances between buildings or to boundaries on a particular site. Fire Classifications So what do the two letters of the fire classifications mean and where do they come from? The British Standard which describes the fire tests for roofs and defines the classifications is BS 476-3: 2004 (amd 2007) Fire tests on building materials and structures - Part 3: Classification and method of test for external fire exposure to roofs. The test consists of a preliminary ignition test, followed by two main tests for flame spread and fire penetration. The results for the main tests give designations A-D, and the combination of two letters gives the overall classification AA, AB etc. Next we look at the tests in more detail. 3

4 BS Fire Test BS defines test conditions which simulate radiation from a fire, burning brands, and wind effect. These test conditions can be regarded for example as representing the effects on a roof 7.6 metres above ground level from a fire 13.7 metres away in a building with a façade 15.2 x 15.2 metres and 50% window openings. The test specimens are mounted at 45 for sloping roofs or horizontally for flat roofs. 15.2m 7.6m 13.7m The test is in three stages using different specimens for each stage: Preliminary ignition test A test flame, representing burning brands, is applied for 60 seconds. Spread of flame test The roof is exposed to radiant heat and to the test flame (burning brand) for 3 minutes. Fire penetration test The roof is exposed to radiated heat, with reduced pressure on the underside to simulate wind. After 5 minutes the flame (burning brand) is applied for 60 seconds. The radiant heat is continued for up to 1 hour. The test results generate the performance designations as follows: Fire penetration (first letter) A Those specimens that have not been penetrated within 1 hour. B Those specimens that are penetrated in not less than 30 minutes. C Those specimens that are penetrated in less than 30 minutes. D Those specimens that are penetrated in the preliminary ignition test. Spread of flame (second letter) A Those specimens on which there is no spread of flame. B Those specimens on which the spread of flame is less than or equal to 533mm. C Those specimens on which the spread of flame is greater than 533mm. D Those specimens that continue to burn for five minutes after the withdrawal of the test flame or spread more than 381mm across the region of burning in the preliminary test. For a full classification the prefix EXT.S. or EXT.F. is added to the two-letter classification to indicate whether sloping or flat specimens were tested, eg EXT.S.AA. However, Approved Document B4 refers only to the two-letter classifications. A suffix X is added if during the test there was dripping of molten droplets from the underside of the specimens, or the development of holes or mechanical failure 4

5 Fire Tests on Ventilators Glidevale ventilator test A Glidevale roof ventilator is exposed to radiant heat and the test flame simulating burning brands. Unrated ventilator test The specimen is subjected to radiant heat and the test flame (burning brand) is applied for 3 minutes. As the test progresses the material of the specimen is itself propagating fire, and molten material is dripping from the ventilator onto the roof underlay. This in turn catches alight, resulting in complete failure of the specimen before the test flame is removed. At the end of the test the Glidevale ventilator is intact and shows no ignition or flaming. Hence the Glidevale ventilator achieves an AA rating. Glidevale ventilators are made from a specially formulated fire-retarded polymer and are selfextinguishing. The roof is now well alight even though the adjacent roof tiles have not been affected. 5

6 The Glidevale Solution All Glidevale ventilators and terminals have been independently tested by the Loss Prevention Council (now BRE) to BS and have been awarded an AA classification - the highest possible. Thus they can be used without restriction on any roof. For further advice or detailed information regarding a specific project please contact our Technical Services Team on A CPD seminar on Correct Specification and Detailing for Slate/Tile and Ridge Ventilators fire performance can be provided on request, subject to numbers. Please contact our Marketing Team for further information. References BS 476-3:2004 (amd 2007) National Federation of Roofing Contractors Technical Bulletin 20 Building Regulations Approved Document B4 Glidevale Limited, 2 Brooklands Road, Sale, Cheshire M33 3SS Tel: Fax: info@glidevale.com