How do airports handle traffic during emergencies? What does ATC do when there is an emergency? This could be a tower or an ARTCC being evacuated or otherwise unusable.


How do they decide whether to close the airport/airspace?
What do they do with the traffic, whether they do or don't close?


On this related question, it turned out that Newark closed because of smoke in the tower.

Another user posted an interesting anecdote about another tower being evacuated, so I thought it warranted a question.
The facility under duress will declare "ATC Zero" and all traffic will be handed off to other controllers while that facility is offline.  

In the case of a control tower, this means the airport either acts as a non-towered field or as a closed field (depending on the nature of the emergency).  If it is a TRACON, then the ARTCC will assume control of the TRACONs airpsace.  If it is an ARTCC, that might present bigger problems as continuity of radio communications may be impacted and I'm not sure exactly how this would be handled but assume it would be re-routes around the ARTCC.

I've been inbound to IAH when their tower decided to close (I forget why), and the response was to put everyone inbound to IAH into holds and handle diverts when fuel became an issue.