Anyone have thoughts or (?) knowledge on efficacy, or guidelines on how long the heating should last for decontamination?
I would not think that ordinary ironing would effectively decontaminate letters with anthrax in them. These are tough spores. The only way to really find out what works would be to try the experiment, but they need a lot of heat, so you might need to do a lot of ironing. Irradiation is a much better bet. Better still is a plain old gas mask, or maybe some anthrax vaccine. Oh wait, civilians aren't allowed to have vaccine because safety isn't really the goal here.
The obvious terrorist counter-countermeasure would be to add a heat-activated agent to the weapon.
There is no counter-countermeasure necessary. The goal of the terrorists isn't to take down America by killing Americans. The goal of anthrax is to spread hysteria and terror, and it is doing that with great efficacy. The counter-measure to hysteria is knowledge. There is no counter-measure to knowledge, which is why it's so cool. Unfortunately the US government is contributing to the hysteria by withholding knowledge. Fortunately we have the Internet which lets us find information for ourselves.