Process Safety

Question 1

What is a hazard?

Answer 1

The potential for harm arising from an intrinsic property of disposition of something to cause detriment.

Question 2

What is risk?

Answer 2

The chance that someone or something that is valued will be adversely affected in a stipulated way by a hazard.

Question 3

Give 5 consequences of major accidents.

Answer 3

1. Injuries & fatalities
2. Environmental damage
3. Disruption to communities
4. Reputation damage to company/industry
5. Impact on business performance

Question 4

What is the law of diminishing returns.

Answer 4

The decrease in incremental output of a process as a single factor incrementally increases whilst all others are constant.

Question 5

What is a HAZID?

Answer 5

Hazard Identification Study - given list of hazards and evaluate each.

Question 6

What is a HAZOP?

Answer 6

Hazard Operability Study - generate deviation and question.

Question 7

What is a deviation?

Answer 7

A change from the design intent - guide word + property word

Question 8

What are the 5 stages in a HAZOP?

Answer 8

1. Deviation
2. Cause
3. Consequence
4. Safeguards
5. Action

Question 9

What is a node?

Answer 9

A section of a P&ID chosen for analysis.

Question 10

What is inherent safety?

Answer 10

A method of safety design which reduces amount of a thing that could cause a hazard rather than controlling the hazard itself.

Question 11

What are the 5 guidewords for inherent safety?

Answer 11

1. Eliminate
2. Substitute
3. Minimise
4. Moderate
5. Simplify

Question 12

Define, ‘consequence’.

Answer 12

The potential severity of the outcome in terms of harm to people & environment if an accident occured.

Question 13

Define, ‘frequency’.

Answer 13

The likelihood which the accident could occur per year.

Question 14

What are the 4 stages of consequence analysis?

Answer 14

1. Define event type
2. Determine magnitude & duration of event
3. Model effects vs location
4. Evaluate impact on target

Question 15

What is likelihood analysis?

Answer 15

It is sourced from various data sources either from history or synthesis techniques like fault tree or event tree.

Question 16

What is the difference between fault tree and event tree techniques?

Answer 16

Fault tree - all routes to top event

Event tree - all outcomes from initiating event

Question 17

How are tree techniques different to historical techniques for likelihood analysis?

Answer 17

• Derive a frequency from no existing data

- Suggest location & specific safety factors.

Question 18

How do you calculate the frequency/probability of the top event for an OR gate for;

1. FA + FB
2. PA + FB
3. PA + PB

Answer 18

1. Frequency = FA + FB
2. 0 = PA + FB
3. Probability = PA + PB - PAPB

Question 19

How do you calculate the frequency/probability of the top event for an AND gate for;

1. FA + FB
2. FA + PB
3. PA + PB

Answer 19

1. 0 = FA + FB
2. Frequency = FAPB
3. Probability = PAPB

Question 20

How do you assign frequency or probability to an event?

Answer 20

Frequency - loss of control will result in top event faster.

Probability - stop or slow the path to top event.

Question 21

What is revealed failure? How do you calculate the probability?

Answer 21

Has immediate fail eg. control systems.

P = Failure Freq x Repair time

Question 22

What is unrevealed failure? How do you calculate the probability?

Answer 22

Required action before knowing failure eg. brakes.

P = 0.5 x Failure Freq x Test interval

Question 23

What is meant by cut sets?

Answer 23

Barriers between single event and top event occurring.

Question 24

What are the 2 methods to calculate the probability of a top event.

Answer 24

• Boolean method

- Gate-by-gate method

Question 25

What is a CMF and why is it important?

Answer 25

Common Mode Failure - accounts for numerous things to fail simultaneously.
Can increase probability of top event by a lot by account for 10% CMF.

Question 26

In a risk matrix, what are the levels in which problems are addressed?

Answer 26

Equipment, unit, site, group.