The Rohn emergency scale[1] is a scale on which the magnitude (intensity)[2] 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.[3] The idea was further refined later that year.[4] The need for such a scale was ratified in two later independent publications.[5] [6] 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.
1805 Beaufort scale[7]
1931 Modified Mercalli intensity scale[8]
1935 Richter magnitude scale[9] (superseded by the Moment magnitude scale)
1971 Fujita scale[11] (superseded by Enhanced Fujita scale in 2007[12])
1982 Volcanic explosivity index
1990 International Nuclear Event Scale[13]
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,[1] as depicted on the Emergency Scale Website.[15]
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 percentage 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.
A topographical change means a measurable and noticeable change in land characteristics, in terms of elevation, slope, orientation, and land coverage. These could be either natural (e.g., trees) or artificial (e.g., houses).Non-topographical emergencies are situations where the emergency is non-physical in nature. The collapse of the New York stock market in 1929 is such an example, and the global liquidity crisis of August 2007[16] is another example.The model treats topographical change as a continuum ranging between 0 and 1 that gives the estimated visual fractional change in the environment.
An emergency is typified by a departure from normal state of affairs. The scale uses the change of the number of victims over time and economical losses over time to calculate a rate of change that is of utmost importance to society (e.g., life and a proxy for quality of life).
The scale is a normalized function whose variables are scope (S), topography (T), and rate of change (D), expressed as
E=Emergency=f(S,T,D)
\hbox{Scope}=\tfrac{\hbox{RawScope}}{\hbox{MaxScope}}
where
\hbox{RawScope}=\left(\tfrac{\hbox{Victims}}{\hbox{Population}}+\tfrac{\hbox{MonetaryLosses}}{\hbox{GNP}}\right)W
where
W=\left(\tfrac{ln(\hbox{Victims})}{ln(\hbox{MonetaryLosses})}\right)\beta
β is a coefficient which the model creator calculated to be 1.26 ± 0.03,
and
\hbox{MaxScope}=\left(\tfrac{0.7*\hbox{Population}}{\hbox{Population}}+\tfrac{0.5*\hbox{GNP}}{\hbox{GNP}}\right)V
where
V=\tfrac{ln(\hbox{Victims})}{ln(\hbox{MonetaryLosses})}
The model loosely assumes that a society whose majority of the population (70% in this model) is affected and half of its GNP is drained as a result of a calamity reaches a breaking point of disintegration. Sociologists and economists may come up with a better estimate.
\tfrac{\hbox{Volumebeforetheevent}}{\hbox{Volumeaftertheevent}}
\tfrac{d(\hbox{Victims})}{d(\hbox{Time})}
\tfrac{d(\hbox{Losses})}{d(\hbox{Time})}
In some instances, it may be preferable to have an integral scale to more simply and dramatically convey the extent of an emergency, with a range, say, from 1 to 10, and 10 representing the direst emergency. This can be obtained from the function above in any number of ways. One of them is the ceiling function. Another one is a single number representing the volume under the 3D emergency scale.