Rohn Emergency Scale

The Rohn Emergency Scale is a scale on which the magnitude (intensity) of an emergency is measured. It was first proposed in 2006, and explained in more detail in a peer-reviewed paper presented at a 2007 system sciences conference. The idea was further refined later that year. The need for such a scale was ratified in two later independent publications. It is the first scale that quantifies any emergency based on a mathematical model. The scale can be tailored for use at any geographic level – city, county, state or continent. It can be used to monitor the development of an ongoing emergency event, as well as forecast the probability and nature of a potential developing emergency and in the planning and execution of a National Response Plan.

Scales relating to natural phenomena that may result in an emergency are numerous. This section provides a review of several notable emergency related scales. They concentrate mainly on weather and environmental scales that provide a common understanding and lexicon with which to understand the level of intensity and impact of a crisis. Some scales are used before and/or during a crisis to predict the potential intensity and impact of an event and provide an understanding that is useful for preventative and recovery measures. Other scales are used for post-event classification. Most of these scales are descriptive rather than quantitative, which makes them subjective and ambiguous.

According to the Rohn Emergency Scale, all emergencies can be described by three independent dimensions: (a) scope; (b) topographical change (or lack thereof); and (c) speed of change. The intersection of the three dimensions provides a detailed scale for defining any emergency, as depicted on the Emergency Scale Website.

The scope of an emergency in the Rohn scale is represented as a continuous variable with a lower limit of zero and a theoretical calculable upper limit. The Rohn Emergency Scale use two parameters that form the scope: percent of affected humans out of the entire population, and damages, or loss, as a percentile of a given Gross National Product (GNP). Where applied to a specific locality, this parameter may be represented by a Gross State Product, Gross Regional Product, or any similar measure of economic activity appropriate to the entity under emergency.

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