Beware the Siren's Song: Why "Non-Lethal" Incapacitating Chemical Agents are Lethal

A number of events have brought “non-lethal” chemical incapacitating agents into the news recently. Most prominently, their use in the rescue of hostages held in the Moscow theater in October 2002 encouraged advocates of the military development of such weapons, since most of the hostages were rescued. Detractors were alarmed that over 15% of the hostages died of effects of the chemical agent (as well as all of the captors, who were executed by security forces while they were comatose). In this paper we address only the causes of the high level of lethal effects among the captives in Moscow, and ask if that is typical, and whether truly non-lethal chemical weapons are feasible. We conclude that this level of mortality is to be expected, and that genuinely non-lethal chemical weapons are beyond the reach of current science. The model The following simplified analysis illustrates why seemingly non-lethal incapacitating agents may be quite lethal in actual use. The analysis assumes simple equilibrium theory for agents with a single molecular receptor causing incapacitation, and a different single receptor causing lethality. This two-receptor model may, for instance, include the anesthetic ketamine, the discontinued veterinary anesthetic phencyclidine (“angel dust”), and the classical chemical weapon agent BZ (3-quinuclidinyl benzilate), which exert their incapacitating effect via the muscarinic acetylcholine receptor in the central nervous system, but appear to cause death by independent cardiac effects. In this simple model, we assume the fraction of receptor bound to the agent approximately parallels the statistical effect of the chemical agent. If 99% of receptors responsible for incapacitation are bound, there is a very high probability that the victim is incapacitated; and conversely if only 1% of the receptors are bound there is little probability that the victim is incapacitated. In this model, fi is the fraction of receptors bound, and also the approximate fraction of people incapacitated: 4