Smoke spread in a ventilation system - Room fire experiments and technical solutions in a prison environment with active ventilation

¹ Brandskyddslaget AB, Stockholm, Sweden
² Bengt Dahlgren Research AB, Mölndal, Sweden
³ Briab, Stockholm, Sweden

^* Corresponding author: hans.nyman@bsl.se

Abstract

This paper presents an overview of results from full-scale tests with a limited amount of combustible material adjusted to the conditions that can be expected in prison cells. The results are combined with theoretical calculations where the ratio between pressure drop across supply and exhaust air devices is studied to achieve an optimal ventilation solution without fire dampers with active ventilation and adequate personal safety. In Sweden, the most common protection method to prevent fire smoke spread in a buildings ventilation system is active ventilation in combination with non-return dampers on the supply air ducts to each fire compartment. In the initial stage of a fire, high pressures can occur due to the thermal expansion. At this stage, the fire room is assumed to be relatively airtight and thus, there is a risk of smoke spreading via openings and the ventilation system due to the increased pressure caused by this expansion. In the later stages of the fire, the fire room is normally depressurized due to glass breakage and thus the fire also has free access to oxygen. In the initial pressure build-up phase of the fire, a stratification will occur in the fire room with a dense smoke-filled upper layer at ceiling and less dense smoke in the lower layer close to the floor. With supply air close to the floor the concentrations of dangerous smoke will decrease.