Visibility

Visibility is very important for evacuation during a fire and, therefore, a very important parameter for fire safety in a tunnel. There are different methods for estimating the visibility in smoke-filled spaces, using mass specific extinction coefficient or the mass optical density. For both methodologies there are experimental values available for some materials of interest. First, the mass extinction coefficient methodology is presented and at the end compared and correlated to the mass optical density methodology. Values of these parameters for selected materials are presented, and conversion of values for one of the parameters into the other is discussed. Finally, the effect on the walking speed during egress is discussed.