All survivalists, indeed all citizens everywhere, should give proper thought and consideration to the threat posed by Nuclear, Biological, Chemical (NBC) and Radiological agents, particularly chemical agents as they are the most likely to be encountered in dozens of possible situations. It is a fact of life that chemicals are everywhere, be they in surplus military storage depots, the local chemical plant down the road, the chemical laden train moving through the county, the semi hauling a tank filled with chemicals, or the nefarious terrorist who has finally realized that all he needed to make some very nasty blood agents was a basic high-school/college level education in chemistry, some basic lab equipment, and precursor chemicals easily ordered online or common found in any college chemistry class. The main defense against NBC threats is knowledge, knowledge which leads to preparations. You have to understand the potential threats and realize what steps need to be taken to prepare/counter them.