0886-7798(93)E0001-L Life Safety in Large Underground Buildings: Principles and Examples John Carmody, Olivier Huet and Raymond Sterling Abstract--This article presents the main life safety problems inherent in underground structures; identifies general design patterns related to life safety in underground facilities; and discusses how life safety issues have been addressed in the design of two representative complex occupied underground facilities. Pdsumd--L'article pr~sente les principaux probl~mes de s~curit~ humaine inh~rents aux ouvrages souterrains; il identifie les schemas g~n~raux concernant la s~curit~ humaine clans les ~quipements souterrains; il examine enfin comment les questions de s~curit~ humaine ont dt~ priees en compte darts la conception de deux ouv rages souterrains complexes et repr~sentatifs, occupds en permanence. Design Issues and Problems L ife safetyis frequently mentioned as an important design issue related to placing people in un- derground facilities. One reason is that most underground buildings present some physical constraints that require special design features to en- sure basic safety in an emergency. A second reason is that fear of entrap- ment from fire, flood, or other disaster represents an underlying negative as- sociation with underground space. Thus, the perception ofsafetyis impor- tant to ensure the occupants' sense of well-being and overall acceptance of an underground facility. Generally, the natural and man- made disasters to be considered in de- sign are fire, explosions, earthquakes, and floods, with fire being by far the danger of greatest concern in most un- derground buffdings. Allbuildings must be designed so that unsafe conditions are avoided, emergencies are detected, unsafe conditions (i.e., fireor flood)are alleviatedassoon as pessible, and people are evacuated to places of safety within Present address: John Carmody and Raymond Sterling, Underground Space Center, University of Minnesota, 500 Pillsbury Drive S.E., Minneapolis, MN 55455, U.S.A.; Olivier Huet, 212 Rue Marcadet, Paris 74018, France. The material for this article originally appeared in Underground Space Design, published by Van Nostrand Reinhold (1993), and is reprinted herein with permission. The book may be ordered from the Underground Space Center (see address above) for $US59.95, plus postage. Tumtelhnga'~ul Underground SpaceTechnology, Vo|. 9, No. 1, Elsevier Science Ltd Printed in Great Britain. All rights reserved I1886-7798/94 $6.00 + .00 a reasonable period of time. While the detection and nature of various types of emergencies differ, the fundamental design problem of efficiently evacuat- ing people to places of safety is present in all types of disasters. This paper presents the main life safety problems inherent in under- ground structures, identifies general design objectives, and presents pos- sible design responses in the form of patterns. These design solutions are drawn from researchers attempting to develop standards in this evolving area (Degenkolb 1981; Wise and Wise 1984; Sterling et al. 1988; Tong 1990; Littlechild 1989). The discussion fo- cuses on fire safety and the evacuation of people. Structural design for earth- quakes, as well as waterproofing and drainage design to prevent flooding, are beyond the scope of this paper. The specific life safety features of two occupied underground facilities are presented in the last section. The following key problems are as- sociated with emergencies, particularly fire, in underground facilities: 1. The underground is generally associated with fear of entrapment in a fire, flood, or earthquake (see Fig. 1). 2. Underground facilities do not have windows and may have layout patterns and egress systems that are unfamiliar, resulting in longer evacua- tion times, and may engender fear and anxiety about escape. 3. Without windows, there is nei- ther daylight to provide light in a power failure, nor any view outwards to main- tain orientation and guide an escape during an emergency. 4. To evacuate an underground facility, people must travel up rather pp. 19-29, 1994 Pergamon than down stairways. The evacuation process therefore requires considerably more exertion than downward travel, slowing exit speeds, and the direction of travel is into the rising smoke rather than away from it. 5. To offset a sense of confinement, as well as to provide orientation and stimulation in underground facilities, interconnected and open interior spaces with glass partitions are desirable. This openness tends to conflict with using major entrance and circulation areas as compartmentalized, fireproof corri- dors and egress routes. 6. Because underground buildings are largely not visible and have no windows, fire fighting is difficult. Fire fighters cannot see the fire, nor can they see people to rescue through win- dows. Windows and doors cannot be broken to ventilate the fire or enter the building. 7. Because of the enclosed, win- dowless nature of underground build- ings, positive pressure builds during a fire. This pressure build-up can reduce the fire-resistant capabilities of con- struction materials. 8. In a fire in an enclosed under- ground space, oxygen levels can be depletedin the vicinity ofthe fire. Ifair suddenly reaches the fire area, an ex- plosive "blow-back" can occur as par- tially burned materials ignite. This problem may be exacerbated by an "exhaust only~ smoke removal system. 9. Because underground spaces are below grade, flooding from natural causes or sprinklers activated in a fire cannot drain naturally out of the building. 10. In some site conditions, com- bustible gases can collect around un- 19