For the naysayers on the bandana/N95...

I was working in engineering dept for a hospital 7-8 blocks from ground zero. We had close to thousand people come in first day when towers fell for dust/debris inhalation issues.
Simple disposable N95, handkerchief or bandana would have alleviated a lot of that.
I carry both in my little EDC bag.

As an aside: First day we had a 2" accumulation of dirt and debris over all our rooftop HVAC equipment. Prior to this one of our mechanics had a great idea to put hospital sheets over all the air handling, prevented clogged filters and helped keep equipment running.