Fire-induced breakage of modern windows

Ventilation conditions play a key role in determining the fire development in enclosures, and thereby, in how a fire affects the structural elements in the fire room. In general, larger ventilation openings lead to fiercer but shorter fires, whereas
smaller openings lead to milder but longer fires, which leads to higher temperatures in the structural elements [1]. Therefore, an accurate and not overestimated prediction of the ventilation factor is paramount to avoid overestimation of the
structural capacity in fire [1] and possible consequent fire-induced collapses of buildings. Moreover, it can be used to document structural survival through burnout as utilised in e.g., the Norwegian high-rise “Mjøstårnet” and similar tall mass
timber buildings [2]. To predict the actual ventilation factor for a given enclosure, it is necessary to know whether and when the glass panes of the windows in the fire room break and to what extent. Common design practice as well as several studies [3], [4] indicate that breakage and fallout of single pane windows used in old buildings would occur already in the early phases of fire, before flashover. However, the same assumption might not be justified in case of modern energy-efficient windows, made of multiple glass layers, often toughened, laminated, or coated with solar shading or energy saving coatings [5]. Therefore, the use of modern windows might pose a threat to the structural fire safety of both existing and new buildings. This is because decreasing ventilation factors will prolong fires, which in turn will heat structural elements more and could lead to unpredicted collapses if not accounted for. However, based on the current knowledge of the phenomenon, the scale of the threat is not very well-known. The authors have conducted a literature study [6] where several knowledge gaps were identified. This led to the devopment of a roadmap for future studies shown in fig. 1.
In the current study, the fire performance of modern windows is investigated with the aim to provide insights for better assessment of ventilation factors.