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Overview of Incidents Involving Mass Casualty Weapons

By James Madsen, MD, MPH, U.S. Army Medical Research Institute of Chemical Defense

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Mass casualty weapons are weapons that can produce a mass casualty incident. Mass casualty incidents overwhelm available medical resources because they involve so many injured people (casualties). Mass casualty weapons include a variety of

  • Chemicals

  • Toxins

  • Biological (infectious) agents

  • Radiation sources

  • Explosives

Mass casualty weapons are sometimes called weapons of mass destruction. However, the term weapons of mass destruction is less accurate because it implies significant physical destruction of infrastructure, which occurs predominantly with explosives. The term "weapon" implies intentional use. However, many mass casualty weapons include substances that also can unintentionally cause a mass casualty incident. For example, chemicals or radioactive substances may leak from a factory or power plant, or from a truck or railroad car during transportation. Doctors and public authorities use the same principles to manage intentional and unintentional incidents.

A community's exposure to a mass casualty weapon may be readily apparent, as occurs with an explosion or visible leak or spill, and may even be announced in advance by a perpetrator. However, a community's exposure to radioactive, biological, or chemical weapons may not be so obvious. Such substances may be spread secretly so that the first sign is simply that many people become ill at the same place and time. Doctors may find it difficult to identify or distinguish exposure from an outbreak of natural illness. For example, vomiting and diarrhea caused by a secret exposure to radiation may at first be mistaken for mass food poisoning.

Once in the environment, mass casualty weapons may exist as a combination of solid, liquid, gas, or vapor (the gaseous form of a substance that is liquid at room temperature). Fine dust particles or small liquid droplets may be suspended in the air as aerosols (smokes, fogs, mists, or fumes). When radiation is involved, people may have direct contact with radioactive dust and debris, or they may be exposed to radiation without physical contact with the radiation source (see Radiation Injury). The form of the weapon affects how long it stays in the environment and the potential routes of exposure. Solids and low-volatility liquids tend to remain in the environment for more than a day under usual conditions, and some may persist for weeks. In some cases, such as with radioactive materials, weapons material may persist for years. Gases and high-volatility liquids tend to disperse in less than 24 hours.

The route of exposure is a major factor in how people are affected by a mass casualty weapon. Gases, vapors, and small particles can be inhaled. Inhaled substances usually act very quickly. Solids and liquids can contaminate the skin, from which they may be absorbed or transferred to the mouth and ingested. Skin exposure usually takes longer to cause symptoms. Contaminated objects (for example, debris from an explosion) can penetrate the skin and introduce the substance directly into the body.

Initial Approach

Doctors and emergency personnel typically approach an incident involving mass casualty weapons with the following steps:

  • Preparedness

  • Recognition

  • Assessment and triage

  • Treatment

These steps often overlap. Recognition, assessment, and treatment may be done at the same time when there are many casualties.


Preparedness efforts are crucial. Disaster plans are needed in hospitals and in the community, along with appropriate supplies and equipment to respond to an incident. Disaster preparedness typically includes plans to bring in additional staff and to reassign resources (such as beds, operating rooms, and blood) from routine care to victims of the disaster. Supplies and equipment typically include designated decontamination areas with contained drainage, floor coverings and protective gear to minimize spread of contamination, and stockpiles of antidotes or formal arrangements to obtain them from other sources. Many hospitals regularly hold drills to help familiarize staff with disaster plans, including the location of written procedures, supplies, and equipment (particularly those for decontamination).


Although incidents involving explosives, firearms, and transportation crashes are easy for doctors and first responders to recognize, incidents involving biological or chemical weapons are often much harder to identify.

Recognition of an incident may come via intelligence or announcement by the perpetrators, environmental clues (such as dead or dying animals or unusual odors), or environmental monitors (chemical, biological, or radiation), which may not be widely available. In some cases, the only clue to a possible incident may be a large number of people affected with unusual symptoms or similar symptoms. As they evaluate casualties, doctors may recognize characteristic symptoms and signs that are typical of exposure to a certain substance or infectious organism. Ultimately, doctors may need to send clinical or environmental specimens to a laboratory. However, diagnosis and initial treatment are often urgent, especially for injuries involving certain chemical weapons that act very quickly.

Assessment and triage

Triage is the process of assigning the degree of urgency to injuries. Some people need treatment very quickly, whereas others can safely wait for a period of time. The large number of casualties in an incident involving mass casualty weapons requires that doctors and first responders keep initial encounters with affected people brief so that everyone can be evaluated quickly. Triage can be particularly challenging because people in mass casualty incidents that do not involve explosions or fire may have no visible injuries. In addition, many people at or near an incident who were not exposed to the weapon may have a stress reaction (such as hyperventilation, shaking, nausea, and weakness). Stress reactions may be hard for medical personnel to distinguish from toxic, infectious, or radiological effects.

Medical personnel trained in mass casualty weapons know to set up three zones to help ensure their own safety: a hot zone, a warm zone, and a cold zone.

The hot zone is the area immediately surrounding the release of a mass casualty weapon. Risk to medical personnel is greatest in the hot zone, and normally, only emergency responders with appropriate personal protective equipment are allowed into this zone.

The warm zone (decontamination corridor) borders the hot zone. Thorough, whole-body decontamination is done in this zone. Medical personnel may need to wear protective gear for primary assessment, triage, and initial treatment of casualties, especially people exposed to chemicals.

The cold zone (clean zone) includes hospital emergency departments. Because decontamination should have taken place in the warm zone, medical staff in the cold zone are normally safe with standard precautions. However, hospitals still need decontamination capability because some people may leave the scene on their own and arrive at a hospital without having been decontaminated.


For incidents involving mass casualty weapons, doctors and other responders aim to

  • Protect themselves

  • Stabilize the person's condition

  • Stop exposure to the agent (remove people from the contaminated area, remove contamination from the people)

Doctors typically first stabilize the person's airway. However, people who have been exposed to certain chemicals may need immediate decontamination. Also, for some chemicals (such as nerve agents), an antidote may also be available and needed right away.

What kind of decontamination the person needs depends on the type of weapon. Skin, clothing, or both are typically contaminated in people who have been exposed to aerosols of biological or radiological agents. Because most such agents cannot quickly penetrate intact skin, disrobing and showering usually suffice for decontamination. Certain chemical agents (for example, sulfur mustard and liquid nerve agents) begin penetrating skin upon contact and may start damaging tissue immediately. People exposed to such agents need immediate decontamination to stop ongoing absorption and prevent the spread of contamination. A specially formulated commercial topical skin decontamination product (called Reactive Skin Decontamination Lotion, or RSDL®) inactivates nerve agents and sulfur mustard on the skin (it is not yet approved for use in eyes or wounds). However, soap and water are also effective. Water alone is less effective for oily chemicals but is used when soap is unavailable. A 0.5% solution of sodium hypochlorite (made by diluting standard 5% household bleach in a 1:9 ratio of bleach to water) is also effective but is not used in eyes or wounds. In an emergency, any available product that might soak up the chemical agent (such as paper towels, tissue, talc, clay-rich soil, or bread) can be applied to the affected area for a few seconds and then removed by copious flushing.

Medical personnel inspect wounds and remove all debris. Wounds are then flushed with plain or salt water.


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