To maintain the differential air pressure, spectators usually entered and left the seating and concourse areas through revolving doors, since the use of regular doors without an airlock would have caused significant loss of air pressure. The double-walled construction allowed warmed air to circulate beneath the top of the dome, melting accumulated snow. A sophisticated environmental control center in the lower part of the stadium was manned to monitor the weather and make adjustments in air distribution to maintain the roof.