Assessment Method Integrating Visibility and Toxic Gas for Road Tunnel Fires Using 2D Maps for Identifying Risks in the Smoke Environment

Abstract

This study proposes an assessment method to quantify the risks of the smoke environment for road tunnel fire safety based on previous studies. The assessment method integrates visibility and toxic gases to address the hazards of smoke distribution more comprehensively. Considering that the hazards of visibility reduction and toxic gases for tunnel users vary with exposure time and location in a fire event, the smoke environment (SE) levels are defined as a function of longitudinal location and time. The SE levels simplify smoke distribution as calculated from 3D computational fluid dynamics (CFDs). For easily identifying SE risks, SE levels are illustrated on a 2D map to analyze the potential hazard by quantifying specific areas and times of smoke exposure. To demonstrate the applicability of the assessment method of this study, cases are carried out using CFD simulation to investigate the risks associated with tunnel fires with various tunnel cross-section types, longitudinal velocities, and gradients. In the analysis of the SE level in different cross-section types and longitudinal velocities under the condition of no vehicle, a velocity of 0.9–1.1 m/s can maintain a less serious SE level both upstream and downstream in a horizontal rectangular tunnel, and 0.3–0.5 m/s in a horizontal horseshoe-shaped tunnel. Both rectangular and horseshoe-shaped tunnels reveal an obvious rise within 10–15 min. In the case of inclined tunnels, for both rectangular and horseshoe-shaped tunnels, the SE level near the fire source obviously deteriorates. Thus, the longitudinal velocity range for the purpose of maintaining a relatively less serious SE level should be slightly reduced for inclined tunnels compared with horizontal tunnels.