Semi-natural test methods to evaluate fire safety of wall claddings: Update

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.