Chemical weapons are classified according to their intended target and physiological effects.

Nerve agents-(Sarin, tabun, soman VX)-Structurally related to organophosphate insecticides. All are liquids at room temperature and produce a vapour capable of penetrating the skin, respiratory epithelium, and cornea.  They are irreversible inhibitors of cholinesterase enzymes. Clinical effects occur mainly at peripheral nicotinic and muscarinic receptors, but there are also ill-defined CNS effects.   Exposure results in cholinergic crises. After inhalation of vapour, respiratory symptoms, decreased vision and meiosis occur.  Sweating and fasciculation of local muscle groups follow.  

Blistering agents (vesicants) (mustard gas) are liquids at cold, damp temperatures but evaporate rapidly in a warm dry environment to produce a vapour that penetrates ordinary clothing and causes burns and blistering.  Symptoms may not develop until 12-24 hours after exposure. Systemic manifestations following inhalation include respiratory failure, blindness, vomiting, hypotension, bradycardia, and pancytopenia. Death is usually due to overwhelming infection.

Choking agents (chlorine, phosgene) are highly volatile liquids.  Inhalation of gaseous phase causes respiratory distress and subsequent pulmonary edema. Exposed patients may be free of symptoms for hours.

Blood agents(HCN) inhibit cytochrome oxidases and interrupt cellular metabolism.  Acidosis and tissue hypoxia result.

Toxins (ricin, saxitoxin, botulinum) are biologic products and are the most toxic chemicals known to man.

Tear gas (pepper spray) is a sensory irritant that temporarily incapacitate.

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Donna Seger, M.D.
Medical Director, Middle Tennessee Poison Center