In a phased (rather than full) building evacuation, the typical pattern is:

Explanation

Phased evacuation, used in tall buildings where total evacuation could overwhelm stairwells and impede fire-department access, evacuates the fire floor first and then the floors immediately above and below as the highest-risk areas. Additional zones evacuate as the situation develops. Total simultaneous evacuation (b) can paradoxically delay egress and trap occupants; floor-only evacuation (c) ignores the rapid vertical spread of smoke and heat; waiting for verbal clearance (d) delays life-safety action when seconds matter.