The best protection from a so-called "dirty bomb" is to simply stay indoors -- get under cover, limit your exposure. The radioactives available ARE dangerous, but the quantity such a device could spread is very limited, even if wind drift is used. Now, a full-blown nuke is another story -- consider what would happen if (and this is known to the movers and shakers of both sides) a small, artillery-shell-sized warhead was loaded into the hold of a tanker and anchored in a port -- say, Seattle or San Diego or Baltimore or Boston. The shell is exploded -- not much damage (compared to the Big Bombs) is done, but the oil becomes radioactive and....

The dirty bomb will kill more by panic than by either blast or radiation because people are ignorant about radiation and have been fed, well, crap, about it for a long time. The other scenario will kill by blast, but moreso by radiation.

Biological warfare is stupid -- you WILL kill your people along with the enemy. Think instead of the release of a bacteria genetically altered to devour petroleum.... Whoops! That already exists and is in use.

Besides, how would stop these things? With a treaty?