5

Question 1

Process safety

Answer 1

Process safety is concerned with the control of those accidents which are special and characteristic of the process industries.

Uses a blend of engineering , management and leadership skills

Focused on preventing major accidents; particularly explosions, fires and toxic releases
3 key aspects:
* Plant (hardware)
* Process (systems)
* People

Question 2

Safety

Answer 2

Prevention of accidents by
identification and elimination
of hazards

Question 3

Hazard

Answer 3

Condition that has potential to
cause harm to people,
property or environment

Question 4

Risk

Answer 4

Measure of harm in terms of
incident likelihood and
magnitude of damage

Question 5

TYPICAL INITIATING CAUSES

Answer 5

1-Sudden failure – unplanned reactions, blockage

2- Weakened containment – gasket or seal failure, fabrication defects

3- External energy – lightning, floods, extreme temperature fluctuations

4- Gradual failure – erosion, creep, fatigue, friction

5- Accidental release – incorrect operation of sample points, drains, filling operations

Question 6

Factors which determine magnitude of incident

Answer 6

Time:
rate of release and time for emergency action

Inventory:
the larger the inventory, the greater the potential for loss

Materials:
the hazards of the particular materials

Energy:
the higher the energy, the larger any flammable toxic vapour cloud is likely to be

Exposure:
the number of people that could be exposed

Question 7

To improve safety we use barriers to block the pathway

Answer 7

These barriers are known as
layers of protection or lines of defence

Question 8

Risk reduction measures

Answer 8

Elimination:
if a hazard isn t present it can t cause a problem!

Prevention:
measures to stop an event from happening

Control:
measures to prevent a hazardous event escalating into major event

Mitigation:
measures to protect people, environment and property from consequences of incident

Emergency:
measure to reduce the effects of hazardous event and prevent escalation

Question 9

Types of barriers/strategy

Answer 9

Inherent
Passive
Active
Administrative

Question 10

Inherent

Answer 10

*Eliminate or
reduce hazards
rather than
developing add
on protective
system
*Examples: Use
technology with
lower operating
temperature

Question 11

Passive

Answer 11

*Don t require
action by a
person or device
*Examples: Fire
resistant coatings
to vessels or
steelwork, bunds,
blast walls, flame
arrestors

Question 12

Active

Answer 12

*Require detection
of a hazardous
condition and
some kind of
action to prevent
or mitigate
consequences
*Examples: High
pressure trip
which shuts down
reactor, sprinkler
system

Question 13

Administrative

Answer 13

*Procedural safety
features
implemented or
carried out by
people
*Examples:
operational
control
procedure,
emergency
response
procedure

Question 14

Barrier integrity

Answer 14

No barrier is perfect

All have weaknesses or holes

The number of barriers required depends on:
Extent of the
consequences
Barrier vulnerability

Question 15

Barrier & asset integrity
Barriers

Answer 15

slide 13

Question 16

reduce these to lower likelihood

Answer 16

*Sudden failure
*Weakened
containment
*External energy
*Gradual failure
*Accidental
release

Question 17

reduce these to lower consequences

Answer 17

*Materials
*Inventory
*Energy
*Time
*Exposure

Question 18

Definition : hazard and examples

Answer 18

A hazard is something with the potential to cause harm

Examples:
- Driving a car is a hazard because you could crash
- Electricity is a hazard because it can electrocute people of cause a fire
- Acid is a hazard because it is corrosive
- Working at height is a hazard because you could fall
- Kettles are a hazard because they are hot
- Process operating at high pressure because the tank could rupture
- A wet floor as people may slip

Question 19

Process hazards

Answer 19

Pressure
Temperature
Noise
Loss of containment
Fire
Explosion
Humans

Question 20

PRESSURE

Answer 20

Overpressure – pressure exceeding the design conditions of the plant is one of the most dangerous hazards in process plant operation. If pressure exceeds the design pressure, then failure of the vessel can occur, usually at a joint or flange.

Under pressure – vessels should also be protected from under pressure or vacuum – as this can lead to buckling and collapse of vessels.

Question 21

TEMPERATURE DEVIATION

Answer 21

Excessively high temperature, above design levels, can cause structural failure and initiate an accident. High temperatures can result from loss of control of reactors and heaters, and externally from fires.

Extremely low temperatures can also be hazardous. This can be caused by ambient conditions, cryogenic processes, flashing of liquids and endothermic reactions., it can cause stress cracking and embrittlement.

Question 22

NOISE

Answer 22

Excessive noise is a hazard to health and safety. Prolonged exposure can cause permanent hearing loss. Excessive noise can also lead to complaints from locals. When I worked at the paper mill, we had to wear ear defenders, and our ears were assessed every year

Question 23

LOSS OF CONTAINMENT

Answer 23

The primary means to protect people from exposure to harmful chemicals is the plant itself. Loss of containment can occur due to:

• Pressure relief events
• Operator error – leaving a drain open
• Poor maintenance procedures – isolation failure

Question 24

FIRE

Answer 24

The intervention of well-trained operators is a vital layer of process safety, as it is usually the last opportunity to restore safe conditions. But there is always the possibility for human error. The likelihood is increased if operating procedures are not documented and followed or there are lapses in training.

Question 25

What is a major accident hazard?

Answer 25

Concerns the potential for a major accident event
What is

Question 26

What is a major accident event?

Answer 26

“
major emission, fire, or explosion resulting from uncontrolled developments in the course of operation of any installation, and leading to serious danger to human health or the environment

Question 27

Hazard effect

Answer 27

A hazard can lead to several different consequences and each will have a different severity

Question 28

Definitions: risk
The factors that influence the extent of the risk:

Answer 28

Risk is the chance or probability that a person will be harmed if
exposed to the hazard

The factors that influence the extent of the risk:
- The likelihood or probability of the harm occurring
- The consequence and severity of the harm

(For common risks e.g. risk of crashes from driving your car, the risk may be obtained from statistics
For less common risks, the risk needs to be estimated)

Question 29

Examples of risk

Answer 29

• The risk of dying in a plane crash is around one in 125 million
• The risk of being struck by lightening in the US is 1 in 700,000

In process engineering we can estimate risk for things like:

• Loss of cooling water to exothermic reaction, resulting in
  explosion
• Extreme weather causing a helicopter to crash into an offshore platform
• Multiple fatalities from release of toxic gas that drifts over a village

Question 30

Probability & frequency

Answer 30

Probability is the likelihood and is dimensionless

Frequency is not dimensionless

It is the probability that an event will happen per unit time

Question 31

Hazard identification & evaluation tools

Answer 31

Risk assessments
Bow tie diagrams
Check lists
What if analysis
HAZOP

Question 32

Check lists

Answer 32

A list of questions and checks on a particular aspect of a project/task.

• Generated and used in every phase of a process from design to commissioning
• Should be comprehensive and used systematically
• Should include learning from previous projects/problems
• Response is often yes/no , with space for additional comments
  where necessary
• Response may sometimes need specific information e.g. final temperature
• Intended to promote thought and raise questions

Question 33

What if analysis

Answer 33

Widely used method
Brainstorming technique in which group of experienced people familiar with the process ask questions and voice concerns about possible hazards
Typically 4 6 people
Focus on a defined section of the process using a layout drawing, P&IDs and other relevant documents
The team work logically thought the process following the sequence or stream

Can be unstructured
Often use guidance based on initial review of process or checklist of questions and areas of concern
More structure version SWIFT (structured what if technique)

Question 34

Bow tie diagram

Answer 34

The knot in the middle represents the hazardous event or risk
A number of initiating causes can lead to this event
There will be barriers that reduce the likelihood of the event happening (LHS of diagram)
If the event does occur there may be more than one consequence
If the event occurs there will be barriers to prevent or reduce the severity of the consequences (RHS of diagram)
Each barrier may block one or more of the accident pathways

Question 35

Advantages of bow tie diagrams

Answer 35

Visual representation of causes, outcomes and barriers
Easily understood
May be developed in workshop setting as part of hazard
identification process
Helps to identify pathways with inadequate barriers

Question 36

Hazard and operability
study (HAZOP)

Answer 36

Widely used hazard identification method

Structured analysis of a system,
process or line carried out by multi disciplinary team

Uses guidewords in combination with system parameters to study deviations from the design intention

When a problem found, team
decides whether a change or further investigation required

Question 37

Safeguards

Answer 37

Safeguards help to reduce the occurrence frequency of the
deviation or to mitigate its
consequences. They may already exist in the P&ID (often the case) or may be identified as
requirements following a HAZOP study.

In principle, there are five types of safeguards, that:
1. Identify the deviation
2. Compensate for the deviation
3. Prevent the deviation from occurring
4. Prevent further escalation of the deviation
5. Relieve the process from potential hazardous deviation

Question 38

HAZOP advantages

Answer 38

Due to the structured approach there is a high probability of identifying the hazards Wide range of hazards can be assessed
Method can identify operational problems as well as hazards
New and novel processes can be investigated
Team gains a good understanding of how the process is likely to operate
Can lead to financial payback from faster start up, fewer
operational problems and reliability issues

Question 39

HAZOP disadvantages

Answer 39

High resource requirement (manpower and data)
Need to multidisciplinary team and experienced leader
Needs to be done at the correct time, whilst changes can still be
made to plant design
Doesn’t address spatial issues, such as siting and layout

Question 40

What are the potential impacts of major accident events?

Answer 40

There is no single correct answer here. Students get marks for listing a number of potential impacts from a major accidents, such as loss of life, injury, damage to the environment etc. In an exam, the number of marks allocated to the question will give a clue as to the number of impacts required.

Question 41

Give examples of process safety hazards and the harm that each hazard could cause.

Answer 41

As above, there is no single correct answer here. Students get marks for thinking about the process hazards and giving examples of the harm
e.g. Storage of flammable liquids – potential harm from fire due to loss of containment

Question 42

What is the barrier model and how does it apply to the bow-tie methodology and the management of risk?

Answer 42

In process safety a barrier is used to interrupt the hazard pathway, in order to prevent or mitigate a hazardous event. These barriers are known as layers of protection or lines of defence.
You are then expected to relate this to the bow-tie model – by drawing a diagram indicating where these barriers are placed.
In terms of management of risk you can talk about the Swiss cheese model.

Question 43

What is the difference between prevention and mitigation barriers?

Answer 43

Prevention barrier – measures to stop an event from happening

Mitigation barrier – measures to protect people, environment and property from consequences of incident

Question 44

Give examples of prevention and mitigation barriers and explain how they can stop an accident causal pathway.

Answer 44

As above, there is no single correct answer here. Students get marks for thinking about the examples of prevention and mitigation barriers. E.g. prevention barrier – operate process at lower temperature, stops the pathway to over temperature
Mitigation barrier – fire alarm and evacuation helps to reduce risk to personnel from fire

Question 45

If barriers were categorised as passive, active and administrative which would be the most reliable and which the least? Explain your reasoning.

Answer 45

Most reliable is passive – as it requires no action by a person or device
Least reliable is administrative – as it is carried out by people

Question 46

Why are process alarms not effective barriers?

Answer 46

They only raise an alert, they do not stop or start things from happening

Question 47

Identify the initiation, propagation and termination steps for the following accident. Suggest ways to prevent and contain the accident.

Answer 47

A contractor cuts into a propane line operating at high pressure, at a liquid natural gas storage terminal. A large vapour cloud soon covers 50 acres and is ignited 4-5 minutes later by an unknown source. Liquid products from the storage tanks feed the fire for 7 hours before being blocked in. Both fire water pumps failed because heat damaged the control wiring on one, and a sight glass broke on another spilling diesel and setting the engine on fire.

Here a few answers. There may be more suggestions. T3 table :)