Well that post by OBG seems to sum up sum up all I've learned about NBC theory in a good few years of training. If only someone had given me this 16 years ago it would have made life so much easier. Like most who served throughout the cold war I was terrified by the thought of clouds of chemicals and fallout coming my way. The training prior to the Gulf War tended to focus the mind that a chemical attack was survivable and helped to put some of the gremlins to sleep and to see the results of the Tokyo attack confirmed one point in my mind most of all. To be effective a chemical agent has to be employed in the correct manner. As far as I know no-one short of major armed forces have access to delivery systems capable of doing this. Yes a couple of nutters in a crop sprayer could be capable of doing this, but would they have access to enough agent to make this a viable proposal. I believe you can just about do away with the idea of a bio attack, you're not talking about "the Andromeda Strain" or genetically modified Ebola as in "Outbreak" The agents that may be used are known by medical authorities and like Beachdoc said a potential exists for the agent to get back to the terrorists families, countries or leaders. The point is no-one likes friendly fire in any way shape or form.
The major problem as I see it is ignorance, of the effects and capabilities of WMD. The only way to put these fears to bed is by education, not blind panic as has been seen in the past few weeks.
This is my little rattle from this side of the pond, hope it doesn't rattle on too much.

Johno