ventilation system by injecting an air along the tunnel with certain velocity
(critical velocity) is a vital task as that should justify the criteria of
effective management of fire events. The critical velocity would lead and
control two main phenomena, first the occurrence of the back layering flow
upstream of the fire. Second is the size of the zone with less diluted smoke
(visibility not less than 10 meters) downstream of the fire. However, velocity
lower or higher than the critical velocity would directly change the size zone
of those phenomena.