Efficiency assessment of façade fire separation distances against the leap‐frog effect

Abstract

Across European countries, different separation distances from 0.6 m to 1.3 m are used to protect façades with openings against leap‐frog fire spread. The aim of all of these separation distances is to delay the fire propagation through adjacent façade openings. According to the literature, the estimated duration of this fire spread process, including the development of the enclosure fire, is about 15 min to 45 min. Based on the earlier full‐scale fire tests dedicated to determining the appropriate separation distance, the efficiency, or in other words, the delay of the fire spread caused by the separation itself cannot be determined precisely. With the numerical modelling of the externally venting flame according to the MSZ 14800‐6 standard, we have an opportunity to measure this delay more precisely and even compare the efficiency of the different separation distances. In this paper, three different internationally used separation distances were compared based on two representative aspects of the phenomenon to clarify the significance and efficiency of separation distances in the current fire safety regulations. Based on the results, the biggest separation distance evidently reduced the risk of leap‐frog fire spread. However, the differences did not seem critical.