Terrorists Attacking via Air Conditioners
From the DHS and the FBI, a great movie-plot threat:
It is possible to introduce chemical or biological agents directly into external air-intakes or internal air-circulation systems. Unless the building has carbon filters (or the equivalent), volatile chemical agents would not be stopped and would enter the building untenanted.
Other scenarios involve the use of helicopters equipped with agricultural spraying equipment to discharge large chemical or biological contaminant clouds near external or roof-mounted air intakes or ventilators.
Terrorists have considered producing a radiological dispersal device (RDD) by burning or exploding a source or sources containing radioactive material. If large quantities of easily dispersed radioactive material were released or exploded near an HVAC intake or circulation system, it is possible that targeted individuals could suffer some adverse health effects.
I’m sure glad my government is working on this stuff.