I couldn't tell from the article bout Philly if it's going to be voluntary or not. Most likely it won't be compulsory, unless they have a ready-made excuse in the waiting (in this case, some kind of chemical warfare).
It's one thing to remind people to be ready for emergencies. That's fine and good. It's another matter entirely to try to make them use up their preparations on a drill
If I was in Philly, I'd take this "shelter in place" thing as fair warning to, yes, tape up all cracks in my house and make sure I have a month's worth of supplies on hand (not just 3 days). But I would still go about my days as normal, unless I get myself arrested by doing so (I have ids at home to take care of, after al).
"Moderation in temper is always a virtue; but moderation in principle is always a vice." -- Thomas Paine