when assesing the dangers of the kind of terrorisme, explosions ranks by far top on the list. You can't really protect yourself from blast injuries. But in the aftermath, they are similair to an accident. Lots of fysical injury's. There is however a danger of more explosives.

Chemical weapons have only been used in a terrorisme attack in japan 1995. The attack was not very effective in killing people, but it was in harming people. Proper protection against gasses are not practical, although these gasses can be detected with PID type meters, they are not placed in the first line of responds. So like biological attack hard to determent, when it actually is happening, untill it's to late.