Performance profiles of exterior fire protective building envelopes

The fire protective envelope of any building consists of multiple elements with widely differing properties relating to a fire, such as glass, roof tiles and sheathings, wood cladding, gaps and openings. Where resistance to an exterior fire is required, all elements should be verified to provide a comparable risk of burn-through. Elements are rated by either the material response to fire or fire resistance. In Europe, cladding sheets and wall membranes can be rated by K classes, which effectively include a measure of the time to burn through. A determination of burn-through time of each element of a specific building envelope should be obtained. A design tool to verify the performance of a building's fire protective envelope has been developed. In this paper, a general description of passive elements of the envelope, which should be included in a risk assessment tool such as an index method, is presented. An illustrative approach to visualise the profiles for areas densely spaced structures where an exterior fire may trigger building-to-building fire spread is also included. The research is based on the hypothesis that a relatively subtle and pointed upgrading of an exterior building envelope will severely reduce the speed of building-to-building fire spread, thus allowing firefighting efforts to get on top of the situation. For a burning structure to expose other buildings to fire, the fire has to settle, which leads to a burn-through to the inside. Once inside, an enclosure fire needs to develop and burn through the roof or break one or more large window panes. It is estimated that a 5–10 min delay for a structure to expose other structures to fire can be sufficient to avoid loss of multiple structures. A 10–50 min burn-through time allows for an extended intervention by the fire brigade, which is significant in rural areas. A fire protective envelope may prevent an exterior fire from penetrating the protective envelope at all and the structure can be saved