If I might just raise a point related to this, I can tell you in a nutshell why I would object to using the word “agreement”.
Remembering the last such emergency, on October 21, 2014, it would have been extremely difficult as a practical matter, given the fact that communications had broken down and people were locked up for a fair time and then were taken under guard by police. In my case, I didn't get out of here until 11 p.m.