A window, panel, or similar opening in which (1) the opening has dimensions of not less than 560 mm (22 in.) in width and 610 mm (24 in.) in height and is unobstructed to allow for ventilation and rescue operations from the exterior, (2) the bottom of the opening is not more than 1120 mm (44 in.) above the floor, (3) the opening is readily identifiable from both the exterior and interior, and (4) the opening is readily openable from both the exterior and interior.