I don't know SFC Thomas, but his information is entirely correct, based upon US military training and doctrine. However, he assumes a level of training (and familiarity) that most civilians won't have.

Chemical and biological agents aren't "weapons of mass destruction", in the sense that they don't destroy anything physical, but they certainly fit into the category of "mass casualty weapons." A widely dispursed aerosol application of a nerve agent such as VX, such as you'd get from a crop duster plane, over a heavily-populated area would be devastating.

You are not in danger if you don't breath it or touch it, but that's hard to do if you are in the open and don't have protective gear. The key to limiting your danger is to get it off you as quickly as possible...blot off (don't rub!) the stuff from bare skin and remove clothing that has been contaminated as soon as possible.