What if the dust is radioactive?

Then you have much, much bigger problems. Cover yourself in as much protective material, and as many layers, as possible; it is imperative not to let it enter your body. Regardless, seek specialized medical attention immediately. Once the storm abates, strip off and dispose of all exposed material if possible, and make sure that any exposed skin is scoured as clean as possible. It cannot be stressed enough how bad radioactive particulates are for your body. Assume that you have taken a lethal dose of radiation and will begin to exhibit symptoms of radiation sickness imminently. Assume that without advanced medical intervention immediately, you will die. Anything better is a bonus.