Chap4 Risk Assessment Assumptions

Question 1

Name the 2 types of models used in aiding decision-making on risk

Answer 1

Probabilistic

Deterministic

Question 2

It is vital to consider what when doing either probabilistic or deterministic risk modelling?

Answer 2

Sensitivity considerations

Question 3

What is a basic problem with risk assessments?

Answer 3

We don’t know what we have not thought of. It is virtually certain that there will always be something that has not been thought of

Question 4

What are the 2 types of model in which all possible outcomes are known?

Answer 4

“Closed world” and “Open World”

In the real world it is important to have an open world approach

Question 5

Name 2 possible characteristics of things that have not been taken into account in a risk assessment

Answer 5

They may not be incredible, or

they may not be quantitatively negligible

Question 6

What does the curve of an F-N Diagram represent?

Answer 6

The Frequency (F) of N Fatalities per year.
The curve may be used to represent an 'acceptable' line; a case which is above the line is not 'acceptable'. A high consequence accident would only be acceptable if the frequency associated with it were suitably low

Question 7

How does the example of passenger death/injury/illness associated with air travel demonstrate that the probability of the Top Event can change (potentially quite significantly) due to unknown sequences?

Answer 7

Say 10 years ago it is likely that an Event Tree would identify Crash or Fire as causes of death/injury/illness
Now the Event Tree would also likely identify
Crash/fire/Deep Vein Thrombosis, Cross-infection as possible causes

Question 8

What is the ‘Triplet’ definition of risk?

Answer 8

A set of risk scenarios should be:

1. Complete
2. Finite
3. Disjoint

Question 9

What is the Completeness Problem?

Answer 9

In most, if not all cases, real-world decision-making on risk will not know every possible scenario within a system.

Question 10

Give a tunnel example demonstrating how the ‘Incredible’ may happen

Answer 10

A train, seen to be on fire entering a tunnel. Since 1995 there have been at least 3 instances of this happening:
1995 Baku, Azerbaijan (289 deaths)
1996 Channel Tunnel (13 HGV carrier wagons destroyed, no deaths)
2000 Kaprun tunnel, Austria (150 deaths)

Question 11

Give a Policing example of why models created of the real world must not be fixed and dogmatically held

Answer 11

Yorkshire Ripper investigation in late 1970’s.
Police had it fixed in mind that the murder had a North-East England accent. This view held for at least 2 years, despite explicit evidence to the contrary. The person finally convicted did not have a North-East England accent.

Question 12

Give an Escape From Aircraft example of why models created of the real world must not be fixed and dogmatically held

Answer 12

54 people died in a Boeing 737 fire on the tarmac at Manchester airport in 1985. The design guidance said that everyone should have been able to evacuate safely within 90seconds. That guidance didn’t take account of what people actually do in real-world situations.

Question 13

What is the value of looking at near misses w.r.t. risk assessment scenarios?

Answer 13

They provide clues into how a system might fail. In general, Near Misses are a common occurrence. We need to be able to incorporate information derived from near misses into our risk assessments.

Question 14

What is the significance of ‘Buried Research’ w.r.t. risk management?

Answer 14

There is often research results (with considerable relevance to a particular case) in the literature, but the results are not noticed or are ignored.
e.g. 1971 paper about ‘slope effect’ which was very relevant to the 1987 Kings Cross Station fire after which the similar ‘trench effect’ of fire propagation was recognised

Question 15

What is the Precautionary Principle?

Answer 15

Came from the 1992 Rio Environmental Conference. The principle says “Lack of full scientific certainty should not be used as a reason for postponing cost-effective measures to prevent environmental degradation”.

Question 16

Why is the Precautionary Principle important in risk management?

Answer 16

It provides a way of attempting to overcome, in a practical way, the difficulty presented by the incompleteness problem.

Question 17

Give an example of the Precautionary Principle in use

Answer 17

In 2000 a study showed there was currently no evidence that mobile phone use harms users, but some studies showed that cell phones do have some sort of biological effect on the brain. If you have a developing nervous system, it’s known to be more susceptible. It therefore would be precautionary to limit phone use by children (who’s nervous systems are still developing)

Question 18

What do we mean by socio-Economic Factors w.r.t. risk management?

Answer 18

It’s when a particular sequence is known to be a possibility but nothing is really done about it for socio-economic reasons.

Question 19

Give an oil & gas example where socio-economic factors played a part in risk management

Answer 19

The UK CIMAH Regulations (Control of Industrial Major Accident Hazards) were setup in 1984 after the 1974 Flixborough & 1976 Seveso disasters. The regulations didn’t apply to offshore oil & gas installations, even though offshore installations:
1. shortage of space so things are crammed together
2. being surrounded by sea makes escape difficult
3. being surrounded by sea makes fire brigade access very difficult or impossible
It wasn’t until 1988 after the Piper Alpha disaster that Safety Case regulations were mandated for offshore installations.

Question 20

Give an example of Organisational Pressure adversely affecting risk management

Answer 20

Challenger Shuttle disaster Jan 1986:
In Jan 1985 after launch #15, Morton Thiokol (MT) engineer discovered evidence booster tank o-ring had failed. That launch had been the coldest (11degC).
No effective response to this came from NASA or MT.
NASA planned 12 launches in 1986. 24th flight delayed 6 times.