Introduction to Risk and Reliability concepts Flashcards
(26 cards)
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
