Ali Ardalan - Assistant Professor, Health Emergency & Disaster Division (HE&DD), Institute of Public Health Research, Tehran University of Medical ciences, IRAN

A disaster is a result of a vast ecological breakdown in the relation between humans and their environment, a serious or sudden event on such a scale that the stricken community needs extraordinary efforts to cope with it, often with outside help or international aid. The term “disaster” describes an event defined in space and time (e.g., a hurricane or earthquake), in combination with its damaging effects (e.g., the loss of life or destruction of buildings). It carries the following concepts: hazard, vulnerability of the affected community and non-manageability of the event itself. “Hazard” refers to the event (earthquake, terrorism attack, etc), “vulnerability” to the susceptibility of a population or system (e.g., a hospital, water supply and sewage system, or aspects of infrastructure) to the effects of the hazard and "emergency" describes a managerial state, demanding decision and follow-up in terms of extra-ordinary measures. Emergency is declared by somebody in authority, who, at a certain moment, will also be called to suspend it. The probability that a particular system or population will be affected by hazards is known as the “risk" that is a function of the vulnerability, hazard and resiliency, and is expressed as follows: Risk = (Vulnerability × Hazard) / Resiliency. It means that the risk of a hazard is decreased in a community with lower vulnerability and higher resiliency and vice versa. Disasters and emergencies can be categorized to two general groups: Natural and Man-made, while, more specifically, we can classify them to Natural, Technological, Terrorism, Pandemics and Transportation. This classification refers to the different sources of aetiology, consequences and managerial issues, which are specific for each type of aforementioned disasters. The nature of disasters makes all of them unique in term of their effects on the community regarding different levels of vulnerability, social, health, and economic conditions. In spite of this fact, there are still similarities between disasters. If recognized, these common factors can be used to optimize the management of health humanitarian assistance and use of resources. Disaster management cycle, or in the comprehensive approach, disaster risk management cycle includes Preparedness, Response, Rehabilitation, Recovery and Mitigation (Figure 1).