What type of ventilation is most effective to prevent the horizontal spread of fire in a long, narrow building?

Trench ventilation is specifically designed to control the spread of fire in long, narrow buildings by creating a firebreak that limits lateral fire spread. This technique involves cutting a trench in the roof to allow smoke and hot gases to escape, while also introducing fresh air into the structure. The trench effectively channels the heat and smoke upward and allows for better visibility for firefighting teams, which is crucial in long, narrow spaces where the fire can quickly spread from one end of the building to the other.

In contrast, vertical ventilation primarily allows heat and smoke to escape vertically, which may not be as effective in preventing horizontal spread. Natural ventilation relies on existing air flow and might not adequately control fire spread in confined spaces. Positive pressure ventilation uses fans to push air into the space, potentially disturbing the thermal layers, but may not effectively address the lateral movement of fire in longer structures. Therefore, trench ventilation is the most strategic approach in this scenario, aimed at preventing the fire from spreading horizontally across the building.