Wiktionary
n. all the methods and procedures involved in defending against attack by chemical agents
WordNet
n. procedures involved in taking defensive measures against attacks using chemical agents [syn: chemical defence]
Wikipedia
Usage examples of "chemical defense".
Only some time later did I learn that this was because it had been developed as a potential chemical warfare agent and came via Porton Down (it was originally called BZ, and was much touted by the US Chemical Defense Corps during the Vietnam War period as a disorienting agent which, if sprayed on enemy troops, would cause them to lose their will or ability to fight).
She paused on the bottom step and fumbled in her purse, withdrawing a cylinder that looked like some kind of chemical defense weapon, but even as she did so she looked up in startlement.