With an increasingly dense urban structure and wider use of energy-efficient and combustible materials, the requirements on fire separation distances are becoming an actual topic. In the Czech Republic, separation distances are determined according to the “fire openness” categorisation of external walls. In line with the Czech Fire Standards, combustible external walls must be considered as unprotected areas (fire opened areas) until the opposite is proven. This classification might be a crucial element in building design and for the location of an object on a plot. This paper introduces a project on fire safety evaluation of a load-bearing straw-bale construction and focuses on the experimental determination of fire openness of combustible external walls with the incombustible surface (A1/A2 reaction to fire class). To assess fire risk and a contribution to fire growth and flame spread of the walls, a full-scale fire test of an experimental straw-bale house was carried out in September 2017. The experimental object was designed as a mock-up of a residential house, single-storey, stand-alone building with ground floor dimensions of 4.0 × 6.0 m and a height of 3.5 m with two symmetrical connected rooms. The observations and measurements showed that the experimental wall composition, even though it was not certified as a construction with specific fire resistance, did not contribute to the fire propagation and could be assumed as a fire closed area, whereas unprotected areas are considered only windows. In the case of the evaluated object, this classification leads to a reduction in separation distances of almost 4 meters. According to the results can be concluded that a different approach to evaluating fire openness could be desirable to establish.
Authors: Hejtmánek, Petr; Najmanová, Hana; Váchal, Tomáš, Nov 2018
