Process Safety Flashcards
What is a hazard?
The potential for harm arising from an intrinsic property of disposition of something to cause detriment.
What is risk?
The chance that someone or something that is valued will be adversely affected in a stipulated way by a hazard.
Give 5 consequences of major accidents.
- Injuries & fatalities
- Environmental damage
- Disruption to communities
- Reputation damage to company/industry
- Impact on business performance
What is the law of diminishing returns.
The decrease in incremental output of a process as a single factor incrementally increases whilst all others are constant.
What is a HAZID?
Hazard Identification Study - given list of hazards and evaluate each.
What is a HAZOP?
Hazard Operability Study - generate deviation and question.
What is a deviation?
A change from the design intent - guide word + property word
What are the 5 stages in a HAZOP?
- Deviation
- Cause
- Consequence
- Safeguards
- Action
What is a node?
A section of a P&ID chosen for analysis.
What is inherent safety?
A method of safety design which reduces amount of a thing that could cause a hazard rather than controlling the hazard itself.
What are the 5 guidewords for inherent safety?
- Eliminate
- Substitute
- Minimise
- Moderate
- Simplify
Define, ‘consequence’.
The potential severity of the outcome in terms of harm to people & environment if an accident occured.
Define, ‘frequency’.
The likelihood which the accident could occur per year.
What are the 4 stages of consequence analysis?
- Define event type
- Determine magnitude & duration of event
- Model effects vs location
- Evaluate impact on target
What is likelihood analysis?
It is sourced from various data sources either from history or synthesis techniques like fault tree or event tree.
What is the difference between fault tree and event tree techniques?
Fault tree - all routes to top event
Event tree - all outcomes from initiating event
How are tree techniques different to historical techniques for likelihood analysis?
- Derive a frequency from no existing data
- Suggest location & specific safety factors.
How do you calculate the frequency/probability of the top event for an OR gate for;
- FA + FB
- PA + FB
- PA + PB
- Frequency = FA + FB
- 0 = PA + FB
- Probability = PA + PB - PAPB
How do you calculate the frequency/probability of the top event for an AND gate for;
- FA + FB
- FA + PB
- PA + PB
- 0 = FA + FB
- Frequency = FAPB
- Probability = PAPB
How do you assign frequency or probability to an event?
Frequency - loss of control will result in top event faster.
Probability - stop or slow the path to top event.
What is revealed failure? How do you calculate the probability?
Has immediate fail eg. control systems.
P = Failure Freq x Repair time
What is unrevealed failure? How do you calculate the probability?
Required action before knowing failure eg. brakes.
P = 0.5 x Failure Freq x Test interval
What is meant by cut sets?
Barriers between single event and top event occurring.
What are the 2 methods to calculate the probability of a top event.
- Boolean method
- Gate-by-gate method
What is a CMF and why is it important?
Common Mode Failure - accounts for numerous things to fail simultaneously.
Can increase probability of top event by a lot by account for 10% CMF.
In a risk matrix, what are the levels in which problems are addressed?
Equipment, unit, site, group.
