Introduction

There are a number of practical limitations on the size and design of construction elements that can be evaluated by a standard method of test. For example, if these elements are larger or of a modified design or type, it is necessary to be able to confirm that the integrity of the test result would be maintained if such changes to the system were implemented. This can be achieved through the use of standardized rules. This British Standard provides the rules to be applied when assessing the implications of such modifications in relation to systems which have been subjected to tests in accordance with BS 8414‑1:2015+A1 or BS 8414‑2:2015+A1.

BS 8414‑1:2015+A1 and BS 8414‑2:2015+A1 provide test methods for determining the fire performance characteristics of non‑loadbearing external cladding systems, rain-screen over-cladding systems and external wall insulation systems when applied to the face of a building and exposed to an external fire under controlled conditions. The fire exposure is representative of an external fire source or a fully‑developed (post‑flashover) fire in a room, venting through an opening such as a window aperture that exposes the cladding to the effects of external flames.

This British Standard is concerned with evaluating the scope of the results obtained from the BS 8414‑1 and BS 8414‑2 tests, defining the parameters which can or cannot be varied and to what extent. It provides direct application (DIAP) rules for a system which has been subjected to a single BS 8414‑1 or BS 8414‑2 test and interpolation for systems which have been subjected to multiple tests.

This British Standard addresses the nature and extent of any permitted alterations to the system as tested. The number of such changes can vary according to the complexity of the external cladding and the type of construction being considered. However, every component of the external cladding could have an impact on the fire spread performance of the system, and therefore each change needs to be the subject of a separate evaluation when considering extending the scope of the original testing.

This British Standard recognizes that when a construction product is manufactured, the process is controlled to ensure that the properties which categorize the product, such as dimensions, density, thermal performance and mechanical strengths, fall within the bounds of set product manufacturing tolerances. Where a rule is provided for varying such properties, the stated variance is based upon the tested value. If no such rule is provided for a particular characteristic then it is recognized that such properties might vary for the product when placed on the market due to manufacturing tolerances; however, it is expected that the performance for all declared performance characteristics will still be achieved.

Although tests to other standards might not be directly applicable to the evaluation of the fire performance of a BS 8414 test specimen, additional test data may be used to support extended application; for instance, to evaluate the influence of a particular component or aspect of the design, or to establish which design variations affect the performance in the most or least onerous way.

A construction product can be placed on the market with a wide range of variations in properties such as dimensions, density and mechanical strengths. When products are combined into a building system, their fire performance can depend on the underlying substrate or covering, how the products are fixed and what products are used for such fixing. It is not feasible to test all combinations of different products or system characteristics for their reaction to fire or fire resistance performances, although such characteristics can substantially influence a test result.

An external cladding system comprises a number of individual products (cladding, insulation, fixation systems, substrates, cavity barriers, etc.). The external cladding system has a number of different functions and performance requirements, including weather resistance, thermal performance, acoustic performance and aesthetics. The products are combined in such a way that they are effective in resisting the spread of fire when tested as part of a complete system in accordance with BS 8414‑1:2015+A1 or BS 8414‑2:2015+A1. Each of the products and the way they are assembled could potentially influence how the complete external cladding system performs in such fire tests, and therefore it is necessary to evaluate their individual characteristics and how these interact. Rules for conducting this analysis are given in Clause 5.

The number of variables which can affect the outcome of such large-scale fire tests on potentially complex structures such as an insulated building facade, with or without a ventilated cavity, is considerable. Changing one of more of these variables might be possible without endangering the integrity of the tested system, but others might require supplementary testing, through either large or smaller scale fire tests. This is to ensure that any changes do not compromise the integrity of the original test result performed in accordance with BS 8414‑1:2015+A1 or BS 8414‑2:2015+A1.

A result obtained in a fire test is that which is reported. In a separate exercise, it is possible to vary the values of the different product characteristics to extend the field of application of the individual test results. This process of extended application uses rules which are based only on worst-case scenarios and interpolation techniques.

Extended application enables a prediction to be made on the expected fire performance of a system under specified fire conditions if one or more of the components or parameters evaluated as part of the test specimen were to be changed. In the specific case of external cladding systems, such predictions are based upon the need to abide strictly with the fundamental principle that the fire performance of the modified system would be equal or better if it were to be subjected to a BS 8414‑1 or BS 8414‑2 test.

This British Standard relates only to the extension of results of an external facade system which has previously been tested in some form in accordance with BS 8414‑1:2015+A1 or BS 8414‑2:2015+A1. It does not provide a means of assessing external facade constructions which incorporate multiple cladding systems.

BS 9414:2019

Fire performance of external cladding systems. The application of results from BS 8414-1 and BS 8414-2 tests

Current, Under Review

Published:

30 Sep 2019