Failure Tracing Methodologies

Question 1

What is meant by probability?

Answer 1

Probability is the chance something will happen.

Question 2

What is meant by frequency?

Answer 2

Frequency takes account of the exposure

Question 3

Who are usually involved in Hazard and Operability Studies?

Answer 3

Study Leader - Should not be closely involved with the project but should have good experience of HAZOP and can keep the team focused.

Recorder - Documents the proceedings

Designer - Explains how the system should work

User - Such as a production manager

Other who MAY contribute

Maintenance Engineer
Software Specialist
Safety Expert
Instrument Engineer

Question 4

List the steps of a HAZOP

Answer 4

Divide the system into parts

For each part, define the design intention i.e. what is meant to occur when it is operating normally

Apply a number of ‘guide words’ to the statement of intention, so that every possible deviation from the required intention is considered.

Question 5

Explain the main guide words used in a HAZOP

Answer 5

NO or NOT
Negation of intention e.g. No Flow

MORE
Quantitative increase e.g. high pressure

LESS
Quantitative decrease e.g. low temp

AS WELL AS
Qualitative increase e.g. impurity present

PART OF
Qualitative decrease e.g. only one of two components present

REVERSE
Logical opposite of intention e.g. backflow

OTHER THAN
Complete substitution e.g. flow of wrong material