Fire professionals use seconds as the unit of time for suggesting evacuation times from buildings.^1,2 Fires grow rapidly, and smoke — the primary killer — spreads much faster than fire. The logical response to a fire is to flee. However, it is difficult to flee quickly from large-volume buildings, tall buildings, transit tunnels, and underground buildings. Flight can be impossible for physically disabled people, penal inmates, some hospital patients (e.g., critically ill or undergoing surgery), and security personnel at sensitive installations. For these types of buildings and occupants, smoke-control systems provide an added measure of protection.