Scope

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.

Topography

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.

Speed of change

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).

Scope

${\displaystyle {\hbox{Scope}}={\tfrac {\hbox{RawScope}}{\hbox{MaxScope}}}}$

where

${\displaystyle {\hbox{RawScope}}=\left({\tfrac {\hbox{Victims}}{\hbox{Population}}}+{\tfrac {\hbox{Monetary Losses}}{\hbox{GNP}}}\right)^{W}}$

where

${\displaystyle W=\left({\tfrac {\ln({\hbox{Victims}})}{\ln({\hbox{Monetary Losses}})}}\right)^{\beta }}$

β is a coefficient which the model creator calculated to be 1.26 ± 0.03,

and

${\displaystyle {\hbox{MaxScope}}=\left({\tfrac {0.7*{\hbox{Population}}}{\hbox{Population}}}+{\tfrac {0.5*{\hbox{GNP}}}{\hbox{GNP}}}\right)^{V}}$,

where

${\displaystyle V={\tfrac {\ln({\hbox{Victims}})}{\ln({\hbox{Monetary Losses}})}}}$

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.

Topographical change

${\displaystyle {\tfrac {\hbox{Volume before the event}}{\hbox{Volume after the event}}}}$ or zero for non-topographical events.

Rate of change

${\displaystyle {\tfrac {d({\hbox{Victims}})}{d({\hbox{Time}})}}}$ and ${\displaystyle {\tfrac {d({\hbox{Losses}})}{d({\hbox{Time}})}}}$

comprise the rate of change that is of utmost importance to society and therefore incorporated in the model.