Introduction to Risk and Reliability concepts Flashcards
Risk definition
The probability/possibility of incurring loss
Calculating risk
Risk = Consequence * Frequency
Categories of risk
- community risk
- occupational risk
- economic risk
Community risk
The three types of risk
- Unavoidable - without any compensating benefits
- In principle avoidable but have direct compensating benefits. In practise, unavoidable in modern society
- Avoidable - people expose at will
Farmer Curve
- Below the line - acceptable
- Above the line - unacceptable
ALARP
- As Low As Reasonably Practicable
4 basic stages of Quantitative Risk Assessment(QRA)
- identification of potential safety hazawrds
- estiamtion of the consequences of each hazard
- estimation of the probability of occurence of each hazard
- comparison of the results of the analysis against the acceptability criteria
Qualitative risk assessment tools
- Checklists
- used to identify hazards
- HAZOP
- applies a set of guidewords to determine the consequences of operating outside the design intention
- FMEA
- step by step procedure for the systematic evaluation of the severity of potential failure modes in a system
Quantitative Reliability Tools
The most appropriate tool is chosen depending on the characterisitics of the system
Definition of Reliability
- Reliability of a component or system = R(t)
- It is defined as the probability that the component or system remains operating from time 0 to time t, given that it was operating at time 0.
Definition of Unreliability
- Unreliability of a component or system = F(t)
- It is defined as the probability that the component or system has failed once or more times from time zero to time t, given that it was operating at time zero
- R(t) + F(t) = 1
Definition of Availability
- Availability of a component or system = A(t)
- It is defined as the probability that the component or system operating at time t given that it was operating at time zero.
Definition of Unavailability
- Unavailability of a component or system = Q(t)
- It is defined as the probability that the component or system is not operating at time t, given that it was operating at time zero
- A(t) + Q(t) = 1
Qualitative methods in risk assessment
- applied during feasability and conceptual phases
- identify and rank by importance the potential hazards, equipment types, operating/maintenance procedures which may critically affect safety or reliability
- significant reductions in risks and improved reliabiliyu
- provide input into more detailed quantitative studies
3 key stages of risk management
- Risk identification
- Risk analysis
- Risk evaluation
Qualitative methods
- HAZOP
- FMEA
Other
- PHA
- HAZAN/ID
- rapid ranking
- checklists
PHA
- Preliminary hazard analysis
Method
- form a team
- identify hazards
- determine accident scenarios
- determine consequences
- determine likelihood
- evaluate risk
PFHA
- preliminary functional hazard analysis
- separates systems into functions
- compares functions and sub-functions with hazard checklist
- expand hazards and assess the consequences and effects on environment
Rapid ranking
- list of risks ordered accroding to severity and frequency
- relatively quick method
- easy to identify high risks and prioritise resources
HAZID
- used to identify the possible hazards
- flexible method applicable to any type of installation
- hazards revealed at early stage
HAZAN
- process of analysing the outcome of a hazard
- estimating frequency of incident
- estimating consequences
- comparing results to decide if action is needed
Define failure
Deviation from normal design intent or operating standard
Define hazard
a situation with the potential to cause death, injury, damage,losses or liabilities
Accident
an unplanned, uncontrolled event giving rise to death, injury, ill health, damage or loss
Consequences
an outcome resulting from an accident
Severities
a measure of the outcome
