Fault tree analysis - Insulin delivery system

The FTA diagram sample "Fault tree analysis - Insulin delivery system" was redesigned from the illustration of "CMSI 641: Introduction to Software Engineering. Design of Critical Systems. B.J. Johnson. 2005. Loyola Marymount University".
"Another way of assessing hazards is using fault tree analysis. In this process, each of the identified hazards is covered by a detailed analysis to find out what might cause it. Either inductive or deductive reasoning is applied. In the case of software hazards, the usual focus is to determine faults that will cause the system to fail to deliver a system service, such as a monitoring system. A "fault tree" is constructed to link all the possible situations together, to help identify the interrelationships of the failures, which modules may cause them, and what "trickle-down effects" there might be. Here is an example of a fault tree, as applied to the Insulin delivery system from Sommerville...
Note that this tree is only partially complete, since only the potential software faults are shown on the diagram. The potential failures involving hardware, such as low battery, blood monitor or sensor failure, patient over-exertion or inattention, or medical staff failure are noticeable by their absence.
The fault tree and safety specification processes are two ways of helping with system risk assessment tasks. Once the risks are identified, there are other assessments that need to take place. First, the likelihood of the risk occurrance must be assessed. This is often quantifiable, so numbers may be assigned based on things like MTBF, latency effects, and other known entities. There may be other non-quantifiable contributors to the risk likelihood, however, such that these must be assessed and estimated by experts in the domain. (Don't short-change this process when dealing with critical systems!) Finally, the risk assessment must include the severity of the risk, meaning an estimation of the cost to the project in the event the risk item actually does occur. "Cost to the project" means all associated costs, including schedule delays, human injury, damage to hardware, corruption of data, and so on."
[myweb.lmu.edu/ bjohnson/ cmsi641web/ week15-2.html]
The FTA diagram example "Fault tree analysis - Insulin delivery system" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Fault Tree Analysis Diagrams solution from the Engineering area of ConceptDraw Solution Park.

The vector stencils library "Fault tree analysis diagrams" contains 12 symbols for drawing Fault Tree Analysis (FTA) diagrams.
"Fault tree analysis (FTA) is a top down, deductive failure analysis in which an undesired state of a system is analyzed using Boolean logic to combine a series of lower-level events. This analysis method is mainly used in the fields of safety engineering and reliability engineering to understand how systems can fail, to identify the best ways to reduce risk or to determine (or get a feeling for) event rates of a safety accident or a particular system level (functional) failure. FTA is used in the aerospace, nuclear power, chemical and process, pharmaceutical, petrochemical and other high-hazard industries; but is also used in fields as diverse as risk factor identification relating to social service system failure.
In aerospace, the more general term "system Failure Condition" is used for the "undesired state" / Top event of the fault tree. These conditions are classified by the severity of their effects. The most severe conditions require the most extensive fault tree analysis. These "system Failure Conditions" and their classification are often previously determined in the functional Hazard analysis." [Fault tree analysis. Wikipedia]
The shapes example "Fault tree analysis diagrams" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Fault Tree Analysis Diagrams solution from the Engineering area of ConceptDraw Solution Park.

"Fault tree analysis (FTA) ... can be used to:
(1) understand the logic leading to the top event / undesired state.
(2) show compliance with the (input) system safety / reliability requirements.
(3) prioritize the contributors leading to the top event - Creating the Critical Equipment/ Parts/ Events lists for different importance measures.
(4) monitor and control the safety performance of the complex system (e.g., is a particular aircraft safe to fly when fuel valve x malfunctions? For how long is it allowed to fly with the valve malfunction?).
(5) minimize and optimize resources.
(6) assist in designing a system. The FTA can be used as a design tool that helps to create (output / lower level) requirements.
(7) function as a diagnostic tool to identify and correct causes of the top event. It can help with the creation of diagnostic manuals / processes." [Fault tree analysis. Wikipedia]
The fault tree analysis diagram template for the ConceptDraw PRO diagramming and vector drawing software is included in the Fault Tree Analysis Diagrams solution from the Engineering area of ConceptDraw Solution Park.

The accident analysis diagram example "Accident analytic tree" was redesigned from the picture 7-14 from the "DOE Workbook. Conducting Accident Investigations. Revision 2."
"Analytic tree analyses are well defined, useful methods that graphically depict, from beginning to end, the events and conditions preceding and immediately following an accident. An analytic tree is a means of organizing information that helps the investigator conduct a deductive analysis of any system (human, equipment, or environmental) to determine critical paths of success and failure. Results from this analysis identify the details and interrelationships that must be considered to prevent the oversights, errors, and omissions that lead to failures. In accident investigations, this type of analysis can consist of both failure paths and success paths, and can lead to neutral, negative, or positive conclusions regarding accident severity.
TIP.
An analytic tree enables the user to:
(1) Systematically identify the possible paths from events to outcome.
(2) Display a graphical record of the analytical process.
(3) Identify management system weaknesses and strengths."
[homer.ornl.gov/ sesa/ corporatesafety/ aip/ docs/ workbook/ Rev2/ chpt7/ chapt7.htm]
The FTA diagram example "Accident analytic tree" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Fault Tree Analysis Diagrams solution from the Engineering area of ConceptDraw Solution Park.

This example was redesigned from the Wikimedia Commons file: Example of High Level Fault Tree.jpg. [commons.wikimedia.org/ wiki/ File:Example_ of_ High_ Level_ Fault_ Tree.jpg]
"Risk assessment is the determination of quantitative or qualitative value of risk related to a concrete situation and a recognized threat (also called hazard). Quantitative risk assessment requires calculations of two components of risk (R):, the magnitude of the potential loss (L), and the probability (p) that the loss will occur. Acceptable risk is a risk that is understood and tolerated usually because the cost or difficulty of implementing an effective countermeasure for the associated vulnerability exceeds the expectation of loss.
In all types of engineering of complex systems sophisticated risk assessments are often made within Safety engineering and Reliability engineering when it concerns threats to life, environment or machine functioning. The nuclear, aerospace, oil, rail and military industries have a long history of dealing with risk assessment. Also, medical, hospital, social service and food industries control risks and perform risk assessments on a continual basis. Methods for assessment of risk may differ between industries and whether it pertains to general financial decisions or environmental, ecological, or public health risk assessment." [Risk assessment. Wikipedia]
The FTA diagram example "High level fault tree" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Fault Tree Analysis Diagrams solution from the Engineering area of ConceptDraw Solution Park.