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.

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 this size are imperceptible to the naked eye.⁷ Most dust particles settle with time as the result of gravity; however, in a wind-blown environment or an explosion, they can be blown through the air and contaminate mucous membranes or be inhaled. Dust particles between 2.5 and 6.0 μm in diameter deposit in the bronchial mucosa, whereas particles smaller than 2.5 μm can reach the alveoli. Fumes are fine, solid particles created by either combustion or condensation and are smaller than 1 μm in diameter. Chemicals may adhere to fumes or dusts and be deposited in the lungs through inhalation.

Liquids have a fixed volume, but their shape conforms to both gravitation and container shape. They will flow downhill and can accumulate in clothing and shoes. A liquid forced through a small orifice under pressure can be aerosolized into fine liquid droplets (i.e., aerosols). Aerosols, like dust, will settle with gravity over time. A vapor may be a dispersion of a liquid or a volatile solid, like mercury. Vapors and aerosols may penetrate clothing, causing contact injury by soaking the underlying skin or reacting with moisture in mucous membranes.

A gas has a variable shape and volume and will diffuse to fill an enclosed space once released. Many compressed gases are stored as liquids in cylinders and are converted to a gas upon their release. Hazardous risk analysis should take into consideration misuse or theft of these compressed gas cylinders. An endothermic reaction may occur during release of a compressed gas, causing hypothermic skin injury. Gases can be inhaled into the lungs and cause local reaction, systemic toxicity, or, in some cases, delayed reactions deep in the pulmonary tree.

How deeply in the lungs a gas or vapor exerts its effects depends on its degree of water solubility. Highly water-soluble compounds react with water in our mucous membranes and can irritate the eyes and upper airway.⁶ Examples of agents with this property includes ammonia and hydrogen chloride. These agents have good warning properties, allowing an awake and ambulatory individual to leave the area of exposure. Low water-soluble compounds may be less irritating, allowing greater duration of exposure and, therefore, greater pulmonary penetration. Phosgene is an example of a low-solubility gas; it has a pleasant smell like new-mown hay and penetrates deep into the alveoli where it slowly is converted to hydrochloric acid.

All liquids at temperatures between their freezing point and their boiling point are in equilibrium between the liquid itself and some amount of gas vaporized into the atmosphere. Below their freezing point, liquids become a solid and pose little risk of vaporization. Above their boiling point, they become a gas, and their vapor pressure equals the atmospheric pressure.⁶ The higher the vapor pressure is for a substance, the more likely it is to volatilize into a gas. It is possible to calculate the concentration of a chemical as a vapor knowing its vapor pressure and the atmospheric pressure. This vapor concentration may be used to predict risk of toxicity based on established exposure limit guidelines.

Several agencies have created exposure guidelines used for different purposes, of which a few may be useful in assessing health risks during an exposure. The American Conference of Governmental Industrial Hygienists has created threshold limit values for many substances.⁸ This value is the maximum allowable airborne concentration of a substance that a worker can be exposed to for an 8-hour workday. Concentrations below this should be regarded as acceptable and safe.^6,8 The American Conference of Governmental Industrial Hygienists has also established a short-term exposure limit for substances to which an individual should not be exposed for >15 minutes.⁸ The National Institute for Occupational Safety and Health has established an acute exposure limit called the immediately dangerous to life or health limit. This is the maximum environmental air concentration of a substance from which a person without protective equipment could escape within 30 minutes and not sustain irreversible health effects.⁶ This applies only to acute health effects and does not take into account chronic health effects or carcinogenicity. The immediately dangerous to life or health level is meant to apply to the work environment and not a chemical accident, where the level of a substance measured in an environment is usually unavailable during an actual disaster and may change over time.

The Environmental Protection Agency created a three-tiered Acute Exposure Guideline Level (AEGL) that is applied to nonoccupational, one-time exposures in the general population.⁹ AEGL-1 levels cause discomfort only; AEGL-2 levels cause irreversible, long-lasting effects; and AEGL-3 levels cause serious disease or death. Each level is further rated by time exposure for concentrations of exposure for 10 minutes, 30 minutes, 60 minutes, and 4 and 8 hours.

Exposures at or less than AEGL-1 limits require public health and emergency response agency efforts to educate the public about the minor effects expected to help minimize ED and physician visits. Access to areas with levels higher than AEGL-1 limits should be restricted. Levels between AEGL-2 and AEGL-3 require accurate and specific information to be given to the public and generally would require people to shelter in place, seal their homes, and perform self-decontamination.⁹ Highly susceptible individuals, such as the elderly, those with lung disease, or the very young, may need priority evacuation and evaluation. Levels anticipated at or greater than AEGL-3 require evacuation, field decontamination, and triage.

Each year, there are 15,000 to 19,000 hazardous materials (HAZMAT) events in the United States. Planning for chemical exposure events, whether terrorist or accidental, builds on our existing principles of HAZMAT response. Core concepts of planning are listed in Table 8-1.

The Superfund Amendments and Reauthorization Act, also called the Emergency Planning and Community Right-to-Know Act, requires states to create state-level emergency response commissions and communities to form local emergency planning committees to prepare emergency response plans for chemical accidents. Chemical facilities are required to provide local emergency management agencies and local fire departments with annual inventory reports and information about hazardous chemicals. The Environmental Protection Agency maintains a national database containing a Toxics Release Inventory that mandates certain facilities to annually report the quantities of their emissions of toxic chemicals (http://www.epa.gov/tri and http://www.epa.gov/triexplorer/maps.htm). This information includes the chemical name, an estimate of the maximum amount of the hazardous chemical present at the facility at any time during the preceding calendar year, an estimate of the average daily amount of the hazardous chemical present at the facility during the preceding calendar year, a brief description of the manner of storage of the hazardous chemical, and the location within the facility of the hazardous chemical. Table 8-2 lists the most common chemicals stored in the United States. Appropriate emergency planning would require a laborious review of these databases at each local level and is not often done with any assessment of vulnerability to release. Rather than expect an accurate accounting of local risk, each ED must be knowledgeable in the general principles of HAZMAT decontamination. An awareness of the clinical manifestations of the most common stored chemicals and the availability of just-in-time information sheets can supplement risk assessment in the real world.¹⁰

Most chemical releases are recognized early because many chemicals have early warning properties, including a noxious or unusual odor, or cause eye or upper airway irritation. Toxic exposures may produce rapid death at the site of the release. Sometimes, more subtle clues are present, such as large numbers of dead animals in an outdoor environment.

Most HAZMAT events occur in fixed industrial facilities, and many industries have monitors for leaks of chemicals at nontoxic threshold levels that have no warning properties. For example, the semiconductor manufacturing industry has monitoring sensors for many toxic semiconductor gases, such as arsine, and these are triggered at very low levels. However, these agents are gases and pose no risk of secondary contamination.

The most common agents released in the United States are the pulmonary irritants ammonia and chlorine. There are numerous resources for the identification of which substances are involved in a spill by a transportation accident or industrial site (Table 8-3).

Few of these resources will identify the amount, and none will have treatment recommendations. Although it may be intuitive that an exact identification of a substance is critical to the disaster or HAZMAT process, in reality, it is more important to recognize the clinical syndromic manifestations of the victims. It is not necessary at the scene to know which organophosphate is involved; it is more important to identify that the symptom complex of a cholinergic crisis is occurring. Similarly, early recognition of the pulmonary irritant effects of a highly water-soluble acid is usually more important than the concentration or the specific chemical identified. Ultimately, identification of the exact agent involved will need to be made. HAZMAT teams have several techniques to identify substances and usually have a standard procedure to enter and evaluate a building where an odor is detected. The treating physician should evaluate all presumptive initial identifications of substances with some caution.³ If the symptoms of the patient do not fit the initial chemical identification, then the accuracy of the identification should be called into question. Experience with chemical events has sometimes revealed that the substance involved must be reidentified during the evolution of the incident, and sometimes, the initial determination of the chemical involved in the release is wrong.

Once a suspected chemical release occurs, the EMS response team must establish an incident command system; designation of hot, warm, and cold zones; and an isolation process. The immediate area where the suspected chemicals and victims of exposure are located is designated the hot zone. Only trained personnel in fully encapsulated protective gear should be allowed to enter. Their primary role is rescue of victims by removing them from further exposure. There is substantial risk of secondary contamination and, therefore, toxic effects for any rescuer or bystander who enters the hot zone without the proper protective gear.¹¹

A surrounding corridor through which each victim is washed off and decontaminated is created outside the hot zone and is designated the warm zone (Figure 8-1). Basic treatment, such as opening obstructed airways, may occur simultaneously with decontamination. Once appropriately decontaminated, the patient can be transferred to the cold zone where a lower level of protective equipment is necessary and a very low risk of secondary contamination exists. With less cumbersome protective gear, reevaluation in the cold zone, triage, and initiation of treatment can occur (Figure 8-2).