"In these times of terror attacks and the threat of war, building owners and tenants are learning how to hunker down without living in bunkers... Some security measures, available mainly in new construction, are invisible to tenants and visitors. For example, reinforced walls and stairwells provide for a "progressive collapse" in the event of a major blast. That way, even if some of the structure is blown away, other parts will remain standing.Other measures are apparent, including security cameras, checkpoints with metal- and chemical-detectors, guard patrols, and card-key or biometric scanners that limit access."
Thanks to Laura Kranz