Optical density of testing aerosol and fire smoke in a road tunnel with longitudinal ventilation: comparison by FDS6

Specific testing aerosol is used for road tunnel ventilation tests to represent steady-state movement of fire smoke downstream of the fire and to avoid the damage of the tunnel. This study investigates the spread of aerosol in 240 m long section of a road tunnel by computer simulation using the well-known FDS simulation system and compares it with the fire smoke spread. Conditions under which optical density for both cases is similar are determined, mainly the mass flux of aerosol needed to represent the smoke produced by fire and the distance at which steady-state flow of smoke is formed. The influence of the fire HRR and air flow velocity on the determined aerosol mass flux is studied as well. The determined value of mass flux increases with increasing flow velocity and decreases with increasing fire HRR. The results indicate that the aerosol can be used to represent the optical density of steady-state fire smoke spread downstream of the fire in tunnel ventilation tests. (paper)