Define critical system:
A critical system is a computer, electronic or electromechanical system, the failure of which may have serious consequences.
What are some consequences of a failure of a critical system?
- substantial financial losses
- substantial environmental damage
- injuries or death of human beings
What are the three types of critical systems?
- Safety-critical systems
- Mission-critical systems
- Business-critical systems
What are safety-critical systems?
Systems where failure may cause injury or death to human beings or substantial environmental harm
What are mission-critical systems?
Systems where failure may result in the failure of some goal-directed activity
What are business-critical systems?
Systems where failure may result in the failure of the business using that system
What are some examples of Safety-Critical sytems?
- Medical Devices
- Aerospace
- Chemical industry
- Nuclear power stations
- Traffic control
- Military equipment
What are examples of mission-critical systems?
- Navigation systems
What are examples of business-critical systems?
- Customer account system in a bank
- Online shopping cart
- Areas where secrecy is required
- Areas where personal data are administered.
What types of safety critical software are there?
Primary and secondary safety-critical software
What is primary safety-critical software?
Software embedded as a controller in a system. Malfunction causes hardware malfunction, which results directly in human injury or environmental damage.
What is safety-critical software?
Software indirectly results in injury. E.g. software tools used for developing safety critical systems. Malfunction might cause bugs in critical systems using that tool
What are Preliminary events?
Events which influence the initiating event, without them the accident cannot advance to the next step
What is the initiating event, trigger event?
Mechanism that causes the accident to occur.
What are intermediate events?
Events that may propagate or ameliorate the accident/event.
What are Ameliorating events?
Ameliorating events can prevent the accident or reduce its impact.
What are propagating events?
Propagating events can cause an accident or increase its impact.
What should you avoid when designing a critical system?
Avoid triggering events by adding safeguards.
What are safeguards?
A method to prevent a triggering event from causing an accident or reducing its impact.
What is the three level model to identify the reason behind accidents?
Level 1: Mechanisms, Chain of events
Level 2: Conditions
Level 3: Condition and constraints
Define root causes:
Root causes are weaknesses in general classes of accidents, which contributed to the current accident but might affect future accidents, underlying issues.
What model do we use to identify the real reason behind accidents?
Three-level model
What is Level 1 in the three-level model?
Mechanisms, chain of events leading to an accident
What is Level 2 in the three-level model?
The conditions that allowed the events on level 1 to occur
