Hazard analysis
Introduction
Class, as you learned this past week, understanding vulnerability and vulnerability assessment is a key part of creating a good, actionable emergency plan. And an important part of understanding vulnerability is understanding the differences in characteristics of physical and social vulnerabilities, hence this week's essay question. Beyond the definition of the terms, which everybody had a great handle on, the book also provided a basic understanding of why the difference between social and physical vulnerabilities matter. If they are both vulnerabilities, why do we care what category the vulnerability fits in to? The answer to this question revolves around the tangibility of physical vulnerabilities versus the intangibility of social vulnerabilities.
A disaster occurs when an extreme event exceeds a community’s ability to cope with that event. Understanding the process by which natural disasters produce community impacts is important for four reasons. First, information from this process is needed to identify the preimpact conditions that make communities vulnerable to disaster impacts. Second, information about the disaster impact process can be used to identify specific segments of each community that will be affected disproportionately (e.g., low income households, ethnic minorities, or specific types of businesses). Third, information about the disaster impact process can be used to identify the event-specific conditions that determine the level of disaster impact. Fourth, an understanding of disaster impact process allows planners to identify suitable emergency management interventions.
The effects of a disaster are determined by three preimpact conditions—hazard exposure, physical vulnerability, and social vulnerability. There also are three event-specific conditions, hazard event characteristics, improvised disaster responses, and improvised disaster recovery. Two of the event-specific conditions, hazard event characteristics and improvised disaster responses, combine with the preimpact conditions to produce a disaster’s physical impacts. The physical impacts, in turn, combine with improvised disaster recovery to produce the disaster’s social impacts. Communities can engage in three types of emergency management interventions to ameliorate disaster impacts. Physical impacts can be reduced by hazard mitigation practices and emergency preparedness practices, whereas social impacts can be reduced by recovery preparedness practices.
Hazard Exposure
Hazard exposure arises from people’s occupancy of geographical areas where they could be affected by specific types of events that threaten their lives or property. For natural hazards, this exposure is caused by living in geographical areas as specific as floodplains that sometimes extend only a few feet beyond the floodway or as broad as the Great Plains of the Midwest where tornadoes can strike anywhere over an area of hundreds of thousands of square miles. For technological hazards, exposure can arise if people move into areas where they could be exposed to explosions or hazardous materials releases.
In principle, hazard exposure can be measured by the probability of occurrence of a given event magnitude, but these exceedance probabilities can be difficult to obtain for hazards about which the historical data are insufficient to reliably estimate the probability of very unusual events. For example, many areas of the US have meteorological and hydrological data that are limited to the past 100 years, so the estimation of extreme floods requires extrapolation from a limited data series. Moreover, urbanization of the watersheds causes the boundaries of the 100-year floodplains to change in ways that may be difficult for local emergency managers to anticipate. Even more difficult to estimate are the probabilities of events, such as chemical and nuclear reactor accidents, for which data are limited because each facility is essentially unique. In such cases, techniques of probabilistic safety analysis are used to model these systems, attach probabilities to the failure of system components, and synthesize probabilities of overall system failure by mathematically combining the probabilities of individual component failure.
The greatest difficulties are encountered in attempting to estimate the probabilities of social hazards such as terrorist attacks because the occurrence of these events is defined by social system dynamics that cannot presently be modeled in the same way as physical systems. That is, the elements of social systems are difficult to define and measure. Moreover, the interactions of the system elements have multiple determinants and involve complex lag and feedback effects that are not well understood, let alone precisely measured. Indeed, there are significant social and political constraints that limit the collection of data on individuals and groups. These constraints further inhibit the ability of scientists to make specific predictions of social system behavior.
Physical Vulnerability
Human vulnerability. Humans are vulnerable to environmental extremes of temperature, pressure, and chemical exposures that can cause death, injury, and illness. For any hazard agent—water, wind, ionizing radiation, toxic chemicals, infectious agents—there often is variability in the physiological response of the affected population. That is, given the same level of exposure, some people will die, others will be severely injured, still others slightly injured, and the rest will survive unscathed. Typically, the most susceptible to any environmental stressor will be the very young, the very old, and those with weakened immune systems.
Agricultural vulnerability. Like humans, agricultural plants and animals are also vulnerable to environmental extremes of temperature, pressure, chemicals, radiation, and infectious agents. Like humans, there are differences among individuals within each plant and animal population. However, agricultural vulnerability is more complex than human vulnerability because there is a greater number of species to be assessed, each of which has its own characteristic response to each environmental stressor.
Structural vulnerability. Structural vulnerability arises when buildings are constructed using designs and materials that are incapable of resisting extreme stresses (e.g., high wind, hydraulic pressures of water, seismic shaking) or that allow hazardous materials to infiltrate into the building. The construction of most buildings is governed by building codes intended to protect the life safety of building occupants from structural collapse—primarily from the dead load of the building material themselves and the live load of the occupants and furnishings— but do not necessarily provide protection from extreme wind, seismic, or hydraulic loads. Nor do they provide an impermeable barrier to the infiltration of toxic air pollutants.
Almost by definition, physical vulnerabilities are tangible in that they can be identified and quantified. We can see the number of people in a flood plain and we can count the number of lives lost. We can give monetary values to agriculture and structural losses and we can even estimate damages to each portion without an event even occurring. This becomes extremely important when determining how a town should allocate resources in the event of flooding, how a family might mitigate flood damage to their home, and how a business might plan for business continuity once the product on their lower shelves is destroyed by water. (It also becomes important for insurance purposes, but that dilemma is for another day). Also important - physical vulnerabilities tend to vary little across a given geographic area. If one house on the street is vulnerable to flooding, the next faces a similar vulnerability, and so on. If one farm is subject to a tornado, the one next door best realize it may face the same problem.
Social Vulnerability
In contrast, social vulnerability is quite intangible. It is difficult to quantify "coping" or identify "resistance" and, although we have behavioral studies that can help, it is difficult to understand how any given demographic may respond to the same incident. Social vulnerability is highly variable across the same geographic population and develops and changes over time (whereas physical vulnerabilities can usually be identified pretty quickly after an incident). These vulnerabilities are, thus, much more difficult to plan for. As an emergency manager, you can look to plan for councilors and make other social services available, but even then you make no guarantee that you will reach affected populations.
SOVI
Social Vulnerability and Hurricane Katrina
The central point of the social vulnerability perspective is that, just as people’s occupancy of hazard prone areas and the physical vulnerability of the structures in which they live and work are not randomly distributed, neither is social vulnerability randomly distributed—either geographically or demographically. Thus, just as variations in structural vulnerability can increase or decrease the effect of hazard exposure on physical impacts (property damage and casualties), so too can variations in social vulnerability. Social vulnerability varies across communities and also across households within communities. It is the variability in vulnerability that is likely to be of greatest concern to local emergency managers because it requires that they identify the areas within their communities having population segments with the highest levels of social vulnerability.
Summary
Understanding these differences is important to your planning and, fortunately (or unfortunately maybe), past experiences, along with behavioral studies, can help us understand the vulnerabilities in certain geographic areas or to certain populations. During your first, or next vulnerability assessment, be sure to consider all of these vulnerabilities and be sensitive to their differences so that you leave no stone unturned.
References:
Federal Emergency Management Agency (FEMA). Accessed March 14, 2016, from http://training.fema.gov/hiedu/aemrc/booksdownload/fem/
Federal Emergency Management Agency (FEMA). Accessed March 14, 2016, from
http://www.fema.gov/media-library-data/20130726-1828-25045-0014/cpg_101_comprehensive_preparedness_guide_developing_and_maintaining_emergency_operations_plans_2010.pdf
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