Which of the following is NOT a common category of chemical agents?

• A. Nerve
• B. Blister
• C. Blood
• D. Psychoactive agents

Answer: (D)

Classifying chemical agents for emergency response is about the mechanism of harm they produce and the response it requires. Nerve agents disrupt the nervous system by inhibiting acetylcholinesterase, leading to a cholinergic crisis that affects breathing, secretions, and muscle control. Blister (vesicant) agents damage the skin and eyes, causing delayed painful lesions. Blood agents interfere with the body's ability to use oxygen at the cellular level, often leading to rapid systemic effects. These categories—nerve, blister, and blood agents—are standard in hazmat and CBRN response because they have well-defined symptoms, decontamination procedures, and medical treatments.

Psychoactive agents, while they can alter mental state or behavior, are not a standard chemical-threat category used in typical EMS/CBRN classifications. They don’t define a common mechanism of toxicity or a unified set of response protocols in the way the other categories do, so they aren’t considered a common category of chemical agents in this context.