Emergency preparedness encompasses the planning and response to disasters. A disaster is defined by the World Health Organization (WHO) as a sudden phenomenon of sufficient magnitude to overwhelm the resources of a hospital, region, or location requiring external support.[1] Based on this definition, a disaster could be as massive as the terrorist attacks of September 11, 2001, or as small as a single patient with an infectious disease. Defining a disaster ultimately depends on the type of event, timing, the severity of illness or injuries, local preparedness, and resources available. Disasters are either internal or external disasters. Internal disasters are events that occur within the walls of the hospital itself, such as an active shooter, power outage, or radiation exposure.[2]

External disasters occur at locations separate from the hospital, such as transportation incidents or industrial accidents. Disasters can be both internal and external disasters concomitantly, such as natural disasters that cause mass casualties as well as damage hospital structure. Disasters can be acute or ongoing. Acute disasters have a general time of onset of the time of an event occurring. Acute disasters have a typical patient flow, which produces numerous low acuity patients presenting to the hospital, overwhelming the surge capacity, or the number of patients the facility can care for presenting at a single time. This surge event is followed by the majority of patients presenting by personal transport and later EMS or prehospital transport of the critically ill. Peak volumes in acute disasters are expected at two to three hours post-event. Evolving disasters such as infectious pandemics have a gradual progression to critical populations, but volumes and resource strain remain for extended periods. Disaster types can further subdivide into categories such as natural disasters, chemical disasters, and bioterrorism; each subdivision produces a specific injury or exposure profile and individual strain on resources that can guide emergency preparedness planning and response.

Emergency preparedness encompasses diverse fields within the hospital and regional settings. Planning membership groups should address key aspects across these fields including but not limited to: public safety, facilities, logistics, pharmacy, transportation, clinical patient care, non-clinical patient care, media/public relations, communications, radiation, infection control, and administration. These key members must develop specific plans to address the facility or region they serve to prioritize resources to address the most severe disasters they may face in an ongoing or continual process of evaluation and training.[3]

Emergency preparedness follows three main stages:

1. Emergency Planning
   • Planning/Prevention–focuses on providing protection from disasters on both the domestic and international levels in an attempt to limit the loss of life and reduce the financial impact of disaster response. Planning includes care, evacuation, and environmental planning and response standards. The UN implemented the Sendai Framework in March 2015 which emphasizes “reduction of disaster risks, preventing new risks, limiting existing disaster risks, strengthening community and global disaster resilience.”[4]
   • Risk Assessment–identifies high priority and vulnerability areas and directs mitigation efforts. The goal of risk assessment is the identification of the possible disasters that challenge the area including both internal and external disasters, collecting resource inventory, identifying a facility or region's vulnerabilities based on location and resources, and generating a priorities list. A single facility's risk assessment should indicate both natural disasters that are known to affect the area as well as possible mass casualty events, understand facility capabilities in regards to the patient population, identify vulnerabilities such a specialty coverage or transportation, and focus on priorities such as limiting the loss of life. As a basis for the evaluation of potential hazards, the SMAUG model prioritizes the potential risks associated with various disasters. SMAUG stands for seriousness, manageability, acceptability, urgency, and growth. Each risk has a score of high, medium, or low. Seriousness includes an evaluation of impact both in the financial evaluation as well as the potential for lives lost. Manageability is the ability to mitigate the hazard. Acceptability is the degree of acceptability regarding impact. Urgency is the determination of how crucial it is to address the hazard. Growth is the potential for the hazard to increase in probability.[5]
   • Mitigation–actions performed before the disaster occurs that includes proactive steps to limit vulnerability and address previously identified risks to support the response to a disaster.[6] Mitigation strategies are generally disaster specific. Mitigation measures can be as simple as mounting appliances to the wall in earthquake-prone areas, including an emergency power or natural gas shut off, or as broad-scale as creating floodways or canals in flood-prone areas. In general, mitigation efforts are investments in facilities or regions to limit response from disasters as identified by risk assessment.
   • Preparedness- measures taken to prepare for a disaster. FEMA outlines general preparedness guidelines for facilities that include quantities of nonperishable food, water, and power.
   • Developing a response team–detailing clearly defined leaders, roles, and responsibilities addressing key issues in emergency response.
   • Writing an emergency plan–written emergency response plan details the overall strategy for responding to a disaster once it occurs. The written emergency response plan should be directed to specific types of disasters, detailed procedures, as well as identify leaders and training schedules for the emergency plan to be successfully implemented when the time comes.[7]
2. Emergency Response- The response phase focuses on executing the disaster plan. Emergency response encompasses both facility level as well as a regional and national level planning. The initial primary concern is fulfilling the basic humanitarian needs of the population affected as well as limiting the loss of life. Types of medical care will ultimately depend on the disaster type. A substantial task within the response phase is coordinating efforts between a facility and regional response, particularly when the demand has exceeded the facility's capacity. The National Response Framework is a US government guide for a national response to disasters and explains responsibilities at the local, state, and federal levels which can be integrated into the response process.[8] In general, there are two response tactics:
   • Shelter in place–in the basic form is establishing a safe location within the confines of the facility and remaining in place until the “all clear” is called. At a facility level, this is caring for those injured via immediate resources available.
   • Evacuation–leaving the facility or region affected by the disaster. Depending on the scenario, resources may be left in place or transferred as possible.
3. Salvage and Recovery- The salvage and recovery phase occurs after determination of the initial response, the immediate threat to human life is under control, and efforts begin to return the facility or area to normal operational function as quickly as possible. The most intense circumstances would include ongoing wartime environments or prolonged epidemics which inhibit salvage and recovery for years.

In the United States, the Federal Emergency Management Agency (FEMA), which operates as part of the Department of Homeland Security (DHS), controls emergency management. Initially, management of all disasters is at the local level via facility groups, police, fire, and EMS. Once local authorities become overwhelmed, the disaster management transitions to the state level, with FEMA acting as an assisting agency rather than an authoritative leader. FEMA organizes the nation and its territories into ten regions. The Citizen Corps is a volunteer organization that works to educate and train the public for emergency response. These services are performed locally and organized through DHS.

In the event of a terror-related disaster, the Secretary of Homeland Security starts the National Response Framework (NRF), which integrates federal resources with state and local resources for the management of resources at the lowest possible level.

The Centers for Disease Control and Prevention (CDC) provides education and information regarding specific disaster types, including infectious diseases, chemical and radiation exposure, and natural disaster or weather-related incidents.