When evacuation is inappropriate, such as during a chemical or biological attack, occupants can congregate in protected spaces known as refuge areas. In Israel, refuge areas are mandated by law in all buildings erected since 1992, even private homes, and in Asia, entire floors of high-rises must be set aside for the purpose. Refuge areas vary widely in size, design and sophistication. The most advanced ones are independent units with their own ventilation systems and sprinklers, as well as extra fire-proofing, structural reinforcement and blast-resistant doors and windows. Not in the plans: The Freedom Tower's refuge areas will be extremely limited: Stairwell landings will be enlarged to allow people to wait for assistance.