INTRODUCTION AND EPIDEMIOLOGY
Although the term "agents of mass destruction" is often used in planning for terrorist events, in reality, few chemicals can be delivered by terrorists in the appropriate fashion to create large numbers of deaths.1 However, chemical mass casualty events do occur. The setting may involve the release of industrial chemicals, such as the 1984 industrial accident in Bhopal, India, that caused more than 2500 deaths and 200,000 injuries from a methyl isocyanate release,2 or a natural chemical incident, such as the emission of carbon dioxide in Lake Nyos, Cameroon, that was responsible for 1700 chemical asphyxiant deaths. Chemical terrorism may also occur through acts of willful deployment, as with the sarin release in the Tokyo subway in 1995 in which 12 people died and 5500 sought medical attention.
The emergency physician is most likely to encounter the accidental release of a chemical from a fixed industrial site or transportation accident. In 2005, a freight train collision in Graniteville, South Carolina, caused the release of chlorine gas that resulted in nine deaths and 511 ED visits.2,3 Environmental contamination, even without injuries, may affect an entire community, including local emergency departments. In 2014, a previously little-known chemical named 4-methylcyclohexane methanol that was used in coal washing leaked into the Elk River in West Virginia, in proximity to the intake area for the water supply for nine counties that served 300,000 people. Although there were no injuries, emergency planners needed to supply clean water to the affected population. Providing risk management advice based on limited data on this chemical and the chemical's strong black licorice odor despite levels below the toxic concentration made it challenging to convince the citizens that the water was safe to use again.4
What has been learned from these incidents is that when chemicals are released, the agents create a penumbra effect, in which true chemical emergencies occur in the epicenter and a larger surrounding area of fear and panic arises in individuals with lower, usually nontoxic levels of exposure. Planning for chemical disasters must take into account both the chemical emergency occurring near the center of any chemical release and the chaos that can ensue through fear of exposure.2,3 What makes these events overwhelming for an individual ED is the larger number of victims who are ambulatory, frightened, and make their own way to the hospital, bypassing any scene triage or decontamination.5 Appropriate planning for management of this large, self-extricated population is paramount to the concept of disaster preparedness for chemical emergencies and perhaps even more important than specific antidotes for rare agents that might be encountered.
PRINCIPLES OF PHYSICS: SOLIDS, LIQUIDS, AND GASES
Solids have a fixed volume and shape and can be bulk solids, powders, dusts, or fumes.6 Dust particles are visible if they are >100 μm in diameter; particles smaller than ...