Many buildings have large open lobbies that provide entry and exit points. These lobbies may have separate ventilation systems that can be enhanced to provide pressurization to prevent the entry of potentially contaminated outside air. Higher levels of air cleaning can also be provided for lobby ventilation systems to protect occupants against contaminants, thereby creating a buffer zone with respect to the rest of the building. This buffer zone may protect against outside air releases of bioweapon agents or naturally occurring biocontaminants such as fungal spores. It will also offer improved protection against indoor releases in the lobby area. Although not, by itself, a complete solution, the buffer zone concept can enhance the level of protection for any building and effectively provide a sheltering zone under many conditions.