Many studies have addressed fires in tunnels. For the most part, these previous studies have addressed fires that might occur during operation of the tunnel, when the tunnel has openings at both ends. During construction of a tunnel, the tunnel has only one opening as the tunnel is being bored. Analysis of fire conditions that might develop during construction of a tunnel is addressed here. A number of analyses are presented to assess tenability conditions in a closed-end subsurface environment as a result of different postulated fire scenarios. The purpose of these analyses is to develop fire tenability criteria for use in evaluating subsurface life and fire safety.