Bottom line on chemical weapons (and it's the same if they use industrial chemical spills): They are intended to make you panic, to terrorize you, to herd you like sheep to the wolves. If there is an attack, leave the area and go upwind, or to the sides of the wind stream. You're more likely to be hurt by a drunk driver on any given day than be hurt by one of these attacks. Your odds get better if you leave the area. Soap, water, time, and fresh air really deal this stuff a knock-out-punch. Don't let fear of an isolated attack rule your life. The odds are really on your side.
Up and Atom
Nuclear bombs: These are the only weapons of mass destruction on Earth. The effects of a nuclear bomb are heat, blast, EMP, and radiation. If you see a bright flash of light like the sun, where the sun isn't, fall to the ground! The heat will be over a second. Then there will be two blast waves, one out going, and one on its way back. Don't stand up to see what happened after the first wave. Wait. Everything that's going to happen will have happened in two full minutes.
Any nuclear weapons used by terrorists will be low yield devices and will not level whole cities. If you live through the heat, blast, and initial burst of radiation, you'll probably live for a very very long time. Radiation will not create fifty foot tall women, or giant ants and grasshoppers the size of tanks. These will be at the most 1 kiloton bombs; that's the equivalent of 1,000 tons of TNT.
Here's the real hazard: Flying debris and radiation will kill a lot of exposed (not all)! people within a half mile of the blast. Under perfect conditions this is about a half mile circle of death and destruction, but when it's done it's done.
EMP stands for Electro Magnetic Pulse and it will fry every electronic device for a good distance. It's impossible to say what and how far, but probably not over a couple of miles from ground zero is a good guess. Cars, cell phones, computers, ATMs, you name it, all will be out of order. There are lots of kinds of radiation, but , physically,you only need to worry about three: alpha, beta, and gamma. The others you have lived with for years.
You need to worry about "Ionizing radiation," little sub atomic particles that go whizzing along at the speed of light. They hit individual cells in your body, kill the nucleus and keep on going. That's how you get radiation poisoning: You have so many dead cells in your body that the decaying cells poison you. It's the same as people getting radiation treatments for cancer, only a bigger area gets irradiated.
The good news is you don't have to just sit there and take it, and there are lots you can do rather than panic. First, your skin will stop alpha particles, a page of a news paper or your clothing will stop beta particles. Then you just have to try and avoid inhaling dust that's contaminated with atoms that are emitting these things and you'll be generally safe from them.
Gamma rays are particles that travel like rays (quantum physics makes my brain hurt) and they create the same damage as alpha and beta particles only they keep going and kill lots of cells as they go all the way through your body. It takes a lot to stop these things, lots of dense material. On the other hand it takes a lot of this to kill you.
Your defense is as always to not panic. Basic hygiene and normal preparation are your friends. All canned or frozen food is safe to eat. The radiation poisoning will not affect plants, so fruits and vegetables are OK if there's no dust on them (Rinse them off if there is). If you don't have running water and you need to collect rain water or use water from wherever, just let it sit for thirty minutes and skim off the water gently from the top. The dust with the bad stuff in it will settle and the remaining water can be used for the toilet which will still work if you have a bucket of water to pour in the tank