Evacuation

Four Categories of Evacuation

Evacuation can be classified into four categories: emergency protection for short-term, pre-impact response; preventative under long-term, pre-impact [Page 184]conditions; rescue during the short term, immediately after impact; and for reconstruction during the long-term, post-impact phase. Principles and processes of evacuation may be applied on a wide variety of scales, ranging from the egress of people from a burning building to the withdrawal of entire populations from coastal areas threatened by hurricanes. Evacuation can be optional (although it rarely is) or mandatory, and backed up by a legal warrant such as a mayoral ordinance. Although it can be mandated by the power of law, it usually cannot be enforced under the threat of police arrest; in any case, in disasters, resources are not likely to be available for such an endeavor.

The use of pre-impact evacuation is critically dependent on the ability to warn evacuees and on the officials who will guide them to safety. In most cases, evacuation should only be the preferred strategy if there is time to carry it out. Hazard and disaster warnings need systems composed of technical, scientific, organizational, and social components. Scientists will monitor the hazard and decide when it reaches critical levels. Public administrators will determine whether evacuation is the correct response, and the general public will have to respond appropriately to the evacuation order. The whole process needs to be organized into a tried and tested system in which all parties know in advance what their roles and responsibilities are.

The critical points in the warning process are often the linkages between the subsystems. For example, there are questions of how to convey information to people in a useful time interval. There are also issues with potential evacuees' perceptions of warning information. Research suggests that people who react best to warnings are relatively young adults, female, parents with children at home, and those who enjoy the support of kinship networks. They are well-educated, relatively wealthy, well-integrated with local institutions, and fully capable of understanding the risks. They tend not to be members of ethnic, cultural, or religious minorities.

An example of the gross failure of a warning process can be found in the eruption of the Volcano Nevado del Ruíz in Colombia on November 13, 1986. The volcano was heavily instrumented, scientific data was constantly monitored, and an accurate hazard map had been produced, but regardless, 23,000 people died in lahars (volcanic mudflows) that overwhelmed the town of Armero and several neighboring villages. There was a failure of communication between volcanologists and local civil protection authorities. If evacuation was ever ordered, it took place too late to save the local inhabitants.

Army 2nd Lt. Angela Fry hugs a relative after she was evacuated from Hurricane like floodwaters in September 2008

Regardless of the profile of the ideal respondent, during warnings there is much confirmation behavior. This can involve contacting friends, colleagues, relatives, and neighbors—i.e., socializing the knowledge of risk—or getting in touch with local officials. Hence, it is important to make warning messages clear and consistent, and to ensure that they are repeated and transmitted by all appropriate means. To give warnings the status of authority, it is also vital that messages be conveyed to the public by officials such as uniformed police. Warnings should explain what is likely to happen; give a simple, nonscientific indication of the likelihood of the impact; indicate the window of time in which the warning is valid; and explain what mitigating actions are advisable or required. False alarms do not necessarily diminish public confidence in the warning process; they can sensitize people to the existence of risks. On the other hand, warnings tend to lack credibility if there is no evidence of abnormal circumstances that require a public reaction (black clouds, unusual activity on the streets, rising river levels, and so on), due to what is called a normalcy bias, or a tendency for people to believe the most reassuring information they face. [Page 185]The process of evacuation ideally channels people progressively farther away from harm, and does not lead them into danger. Hence, in floods, if there is not sufficient time to complete an evacuation from an area (and verify that it has taken place successfully), it may be better to evacuate people vertically, such as to floors of sturdy buildings above flood level.

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