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The Grenfell Tower fire has brought the regulatory system that permitted combustible materials on high-rise buildings in England into question. At the heart of that system is the BS 8414 test, and the BR 135 criteria used to demonstrate compliance with the Building Regulations. The test is empirical and the criteria arbitrary: there is no scientific link between test performance and how a building will perform in the event of a fire; nor any detailed analysis of why fires spread through façade systems which have passed the test. Following the Grenfell tragedy, the UK government commissioned a series of tests on Grenfell Tower-type facades, using BS 8414. This paper critically analyses BS 8414, the BR 135 criteria and the government tests. It shows that important aspects of the standard are poorly defined: the heat flux imposed on the façade is not measured and the fire load can vary by at least a factor of 2; the ambient ventilation has a significant impact on the thermal attack but is not adequately controlled; judicious location of the cavity barriers can confer compliance or failure on a façade system. As the vehicle for allowing combustible products on tall buildings, the test does not specify the extent of cavity barrier deployment, while ignoring features present in real buildings, such as windows, vents or other openings, despite a test rig height of more than 8 m. There is no restriction on debris, or molten or burning droplets falling from the façade during the test. The BR 135 criteria only specify that the test must run for the full 60 min duration without flames reaching the top, and the temperature rise at thermocouples 5 m above the fire chamber must only remain below 600°C for the first 15 min. It is unclear how the fire safety of the occupants behind the façade system can be ensured, when the criteria specify such a high temperature for such a short period, so early in the test. There is no direct connection between the façade system in the test and the actual façade system the results deem compliant. Worse, “desktop studies”, using large-scale test data, have been allowed to confer compliance on systems which have never been subject to the test. The UK government tests used heavy-duty welded aluminium “window pods”, preventing flames from entering the cavity within the façade. They also used a disproportionately large number of vertical and horizontal cavity barriers of a higher specification than required by statutory guidance. These aids to meeting the criteria are not proscribed by BS 8414-1 but are not commonly found in actual rainscreen system designs.

External walls and their components are subjected to a number of fire safety requirements. Fire resistance and reaction to fire are the harmonised requirements in the EU. These cover two fire scenarios: contribution of internal wall linings to an intermediate-size developing fire inside a fire compartment, and resistance of external walls to post-flashover fire inside a fire compartment (resistance to an external fire may also be required). The spread of fire along the external surface is not part of this European evaluation system and remains subjected to national fire safety codes and regulations. A number of test methods covering this scenario exist in Europe and North America at national levels as well as at the international level (ISO). These test methods and associated criteria differ in fire size, test duration, test specimen size and configuration. This paper presents principles of major existing test methods and comparison of test results on comparable test specimens where they are available. INTRODUCTION: IMPORTANCE OF FIRE SPREAD The Construction Products Regulation (CPR) (1) provides the regulatory framework for the performance of construction products in Europe. In the CPR, the Basic requirement for construction works no. 2 "Safety in case of fire" requires that the construction works must be designed and built in such a way that in the event of an outbreak of fire: • the load-bearing capacity of the construction can be assumed for a specific period of time; • the generation and spread of fire and smoke within the construction works are limited; • the spread of fire to neighbouring construction works is limited; • occupants can leave the construction works or be rescued by other means; • the safety of rescue teams is taken into consideration. External wall cladding may become a contributing factor in a fire incident in all these aspects! Yet the practical way of evaluating the safety of external wall claddings in case of fire differs a lot from this definition - at least at the level of harmonised approach to construction products in EU. External wall claddings and their components are evaluated for reaction to fire as standalone products and assemblies to EN 13501-1 (2) in a room fire scenario; fire resistance requirements to EN 13501-2 (3) may comprise wall claddings as part of the structure; and spread of fire along the external surface is currently not part of this harmonised system at all. Consequently European member states, which presently regulate for this characteristic, have to rely on national test methods. Therefore it is worthwhile to look at the approaches used in European Member States and overseas. The methods for evaluating the fire spread over external wall claddings are diverse although some similarities can be identified.