You should have a group prearranged so when things fall down you know where to go and who to let in. I consider a group of eight healthy adults to be the minimum needed. Add another healthy adult for every three children, disabled or elderly person.
During the time following the recent earthquake in Chile the outgoing president refused to send in the army to maintain order. In the first week there was a lot of looting and lawlessness. By the second week the neighborhoods had organized, set guard patrols and when the signal was given people would pour out of their homes armed with whatever they could find to protect their area.
If you have your group prearranged you can skip the week of unpleasantness and move right into the "beat the looters to a bloody pulp" phase which is far more fun.
Bingo, already getting that set up in my neighborhood.
Lots of elderly, or 3-1 ratio not too good.