In considering health care delivery systems, it is certainly important to subject them to analysis, breaking them down into component systems and analyzing each system's vulnerabilities discretely. However, perhaps even more important is the need to subject the multitude of systems that support health care delivery to a thorough process of synthesis, viewing the discrete systems as parts of a larger whole that provides a comprehensive infrastructure environment to support the many operational aspects of health care delivery.
From this perspective of synthesis, it is the examination of the interdependencies among systems that provides the framework for assessing vulnerabilities. Rinaldi, Peerenboom, & Kelly (2001) have laid out a model of interdependencies that will be used as the basis for analysis and synthesis of critical infrastructures for health care delivery systems throughout the rest of this course. Excerpts of text describing their model appear below.
Types of Interdependencies
"Interdependencies vary widely, and each has its own characteristics
and effects on infrastructure agents. In the sections
that follow, we define and examine in detail four principal
classes of interdependencies: physical, cyber, geographic,
and logical. Although each has distinct characteristics, these
classes of interdependencies are not mutually exclusive."
Physical Interdependency
"Two infrastructures are physically interdependent if the state
of each is dependent on the material output(s) of the other. As its name implies, a physical interdependency arises
from a physical linkage between the inputs and outputs of
two agents: a commodity produced or modified by one infrastructure
(an output) is required by another infrastructure
for it to operate (an input). For example, a rail network and a
coal-fired electrical generation plant are physically interdependent,
given that each supplies commodities that the
other requires to function properly.... In this manner, perturbations in
one infrastructure can ripple over to other infrastructures.
Consequently, the risk of failure or deviation from normal operating
conditions in one infrastructure can be a function of
risk in a second infrastructure if the two are interdependent."
Cyber Interdependency
"An infrastructure has a cyber interdependency
if its state depends
on information transmitted
through the information
infrastructure.
Cyber interdependencies are
relatively new and a result of the
pervasive computerization and
automation of infrastructures
over the last several decades. To
a large degree, the reliable operation
of modern infrastructures depends
on computerized control
systems, from SCADA [Supervisory Control And Data Acquisition] systems
that control electric power grids
to computerized systems that
manage the flow of railcars and
goods in the rail industry. In these
cases, the infrastructures require
information transmitted and delivered
by the information infrastructure.
Consequently, the
states of these infrastructures depend
on outputs of the information
infrastructure. Cyber interdependencies
connect infrastructures
to one another via electronic,
informational links; the outputs of the information infrastructure are inputs to the
other infrastructure, and the “commodity” passed between
the infrastructures is information."
Geographic Interdependency
"Infrastructures are geographically interdependent if a local
environmental event can create state changes in all of them.
A geographic interdependency occurs when elements of
multiple infrastructures are in close spatial proximity.
Given this proximity, events such as an explosion or fire
could create correlated disturbances or changes in these
geographically interdependent infrastructures. Such correlated
changes are not due to physical or cyber connections
between infrastructures; rather, they arise from the influence
the event exerts on all the infrastructures simultaneously.
An electrical line and a fiber-optic communications cable slung under a bridge connect (geographically) elements
of the electric power, telecommunications, and
transportation infrastructures. The interdependency in
these cases is simply due to proximity; the state of one infrastructure
does not influence the state of another. Traffic
across the bridge does not influence the transmission of
messages through the optical fiber or the flow of electricity.
Because of the close spatial proximity, however, physical
damage to the bridge could create correlated perturbations
in the electric power, communications, and transportation
infrastructures. Note that more than two infrastructures can be geographically interdependent based on their physical
proximity...."
Logical Interdependency
"Two infrastructures are logically interdependent if the state
of each depends on the state of the other via a mechanism
that is not a physical, cyber, or geographic connection.
Logical interdependencies may be more closely likened to
a control schema that links an agent in one infrastructure to
an agent in another infrastructure without any direct physical,
cyber, or geographic connection.... [An] example
is that summer vacationers may flock to the highways
when gasoline prices are low, resulting in increased
traffic congestion. In this case, the logical interdependency
between the petroleum and transportation infrastructures
is due to human decisions and actions and is not the result
of a physical process."
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