Calculation Method for Tunnel Fire Smoke Exhaust Volume with Point Smoke Exhaust Mode

Abstract

Objective To address the lack of recognized numerical values and calculation methods for smoke exhaust volume of tunnel fire point smoke exhaust system specialized in GB 50016—2014 ′Code for fire protection design of buildings′, a definition of critical smoke exhaust volume and relevant calculation methods are proposed. Method A force analysis of smoke beneath vent is conducted using the Froude number, which characterizes the relative magnitude of buoyancy force and inertia force, as the theoretical criterion for determining the critical smoke exhaust volume. Based on this criterion, the intrinsic relationship between the relative magnitude of buoyancy and inertia forces, and the smoke gas deviation trajectory is further analyzed. Combined with model test data, a semi-empirical model for the critical smoke exhaust volume is established. Result & Conclusion The Froude number for determining the critical smoke exhaust volume is independent of the spacing between vents and the heat release rate of fire, but is related to the ratio of smoke layer thickness to vent length. When this ratio is greater than 0.67, the Froude number exhibits a power function relationship with the ratio of smoke layer thickness to vent length. Conversely, when this ratio is less than or equal to 0.67, the Froude number is linearly correlated with the ratio of smoke layer thickness to vent length.

Keywords

• tunnel
• point smoke exhaust mode
• critical smoke exhaust volume