I was thinking of biological weapons as chemical weapons. Biological weapons would not expire because they are viruses and bacteria. Viruses and some bacteria can lay dormant for many many years, maybe even hundreds of years. If we are talking about manufactured chemicals, then, OK, they are likely expired. I don't know any more about chemicals than I had to learn for my nursing degree. But I do know a fair amount about biological weapons. Medical workers have to be ready to handle such an attack, and are trained for it. We also have to be 'fit tested' with a mask that will keep biological and chemical weapons out of our bodies. You put on the mask, and then they spray a stinky something or other. If you can smell it your mask is all wrong. You can't go back to the job until your mask keeps you from smelling the stinky stuff. That way you are safe. But bear in mind, I've been retired for a year. They were still doing this right before I retired.
Biological warfare - Wikipedia, the free encyclopedia
Biological weapons, though, are not without problems. First, there has to be a method of delivery which can be problematic. And of course such weapons
can be degraded by chemicals, weather, sunlight, etc. But they can be very deadly. I have had some very dire scenarios played for me in training to handle casualties in biological warfare.
I would consider it unwise to just blow off the possibility of such warfare should these agents fall into the hands of terrorists.