Unconventional-weapons threat

All Data Flows to the Information HQ

Experts suggest placing the main emergency-ops center on the ground floor, in a fortified room linked to fire-safe stairs. At least one other command center should be located off-site, in case the main one is destroyed. Freedom Tower designers are not revealing the centers´ locations.

Someday, sensors embedded in walls, floors, elevator shafts, ventilation and mechanical systems-even in bricks, steel and concrete-will take the pulse of a building, monitoring everything from temperature to structural integrity and streaming that information to the command center. Sensor data could also be invaluable to emergency workers. The Sensor-Driven Fire Model, a prototype being developed by the National Institute of Standards and Technology, uses signals from embedded heat, smoke and gas sensors to predict the size and growth pattern of a fire and streams that information to firefighters so they can anticipate conditions and the projected path of the blaze. Other sensors in floors, doors and stairways could relay the location of trapped occupants.

In a skyscraper with a traditional ventilation system, an airborne agent released in a single location could infect the entire building in about 20 minutes. The solution: small, independent heating, ventilation and air-conditioning systems. The Freedom Tower is to have two such units on every floor. In an emergency they will take in air rather than blowing it out, to contain the threat.

Firefighters carry 70 pounds of gear, and they feel it when hiking up hundreds of stairs. Then 30 minutes later they have to head down to refill their tanks. Not in the plans: The Rescue Air System, a pipe that runs vertically through a building, provides stations where responders can get compressed air.

The Freedom Tower will have two sprinkler systems operating on each floor, both housed within concrete structures for fire protection. Not in the plans: Security experts laud such redundancy but suggest an added layer of defense: self-contained water-mist units-sprinklers that release an intense fog of water droplets. Because these units require minimal water, they can be fitted with their own tanks, to ensure that the failure of one system won´t affect the others.


When a harmful agent is found in a building, experts say, managers should shut down the ventilation system, release stored, purified air, and evacuate if necessary. But detection tech is still not advanced enough to make a skyscraper completely immune to attacks by chemical and biological weapons or a dirty bomb. Here, some of the most cutting-edge current solutions:

RADIATION: Detectors made of zinc sulfide and silver send an alert when levels of alpha radiation (the most dangerous kind) register at more than 10 times the background level.

CHEMICAL WEAPONS: Ion mobility spectroscopy sniffs out sarin, mustard gas and other chemical agents within 15 seconds by giving the air samples an electrical charge; suspect contaminants are then identified based on the rate at which they travel through an electromagnetic field. The units are costly ($35,000 or more) and not yet capable of spotting all potentially harmful chemicals.

GERM WEAPONS: Ultraviolet lamps are used in hospitals to irradiate and kill microorganisms, but they aren´t strong enough to eliminate a large quantity of germs introduced all at once, so skyscraper engineers rely on detection. One state-of-the-art technology is a fluorescent particle counter. A laser shines on air samples; if particles fluoresce, that indicates that living organisms may be present. The organisms are quickly filtered out, but determining whether they are harmful takes 30 minutes or more-too long for those at risk.

The Freedom Tower´s designers say they will put biological and chemical filters in the ventilation units on each floor but have not been specific about which variety they plan to use.