DEPARTMENT OF CHEMICAL ENGINEERING

UNIVERSITY OF MALAYA

SEMESTER 2 (SESSION 2015/2016)

Quantitative Risk Assessment (QRA)

2

Lecturer : Dr. Jegalakshimi JEmail : jegalaxmi24@um.edu.myConsultation : via email / watsapp

Will contact the class rep about class crelated matters and update on spectrum.

Learning Outcomes

Understand the principles of QRAAble to identify the stages of risk assessmentAble to carry out a risk assessment study for

hazardous industry and environmental health.

References

Lees, F.P., Loss Prevention in the Process Industries, 2nd Ed., Butterworth-Jinemann, 1996.

CCPS, Guidelines for Consequence Analysis of Chemical Releases, AIChE, 1999.

CCPS, Guidelines for Evaluating the Characteristics of VCE, Flash Fire and BLEVES, AIChE, 1994.

Crowl, D.A. and Louvar, J.F., Chemical Process Safety: Fundamental with Applications, 3rd Ed., Prentice Hall Publications.

SPECTRUM Account

Notes, assignments, solutions, grades etc. will be posted on SPECTRUM.

http://spectrum.um.edu.my

Assessment

Continous assessment (50%)

Group assignments

Test

30 %

20 %

Examination (50%)

Final examination 50 %

Important Notes

Passing mark is 65% (B)Student with less than 80% attendance will

be barred from examination.

Class Monitor

Notes, assignments etc.Replacement class

Groups

Please form into 10 students per groupAll assignments must be done in groups

An Overview of Quantitative Risk Assessment

Risk assessment is the determination of risk related to a situation and a recognised hazard.

It includes scenario identification and consequence analysis.

Scenario identification describes how an accident occurs and frequently includes the analysis of the probabilities.

Consequence analysis describes the damage expected including the loss of life, damage to the environment or capital equipment and days outage.

Hazard identification procedures include some aspects of risk assessment.

Risk Assessment and Decision Making

Risk vs Hazard

video

Control measure

Risk Ranking/Risk Matrix

Risk ranking is a semi quantitative method of determining risk.

Add-on extra to hazard identification studiesWhen a hazard identification team have identified a

hazard, they need to decide whether the existing risk is acceptable or not.

This is done by considering the likelihood and consequences of the event bearing in mid the safeguards that are normally in place.

During the discussion, a consensus will be reached on whether the risk is acceptable or unacceptable, or the problem will be referred for further analysis.

Risk Ranking/Risk Matrix

Risk ranking can help the team to reach a consensus regarding the risks identified by assigning relative risk ranking numbers.

This enables all of the risk identified within the study to be compared and prioritized.

Risk Ranking Approach

1. Discuss and agree the consequence of the event and then assign a Severity Index.

2. Discuss and agree the likelihood of this event and then assign a Frequency Index.

3. Calculate the resulting Risk Index by multiplying the two numbers.Risk Index = Severity Index x Frequency Index

Risk Ranking Approach

The resulting Risk Index may then be compared with criteria to decide whether the risk is low, medium or high (negligible, tolerable or intolerable). The same approach can be used to determine the effectiveness of the recommendations the team makes by seeing how much they reduce the Risk Index.

Example of a Risk Matrix

Probability Accident Severity Catastrophi

cI

Fatal/Critical

II

Severe/Marginal

III

Minor/Negligible

IVFrequent A A A BProbable A A B COccasional A B C CRemote B C C CImprobable C C C CImplausible C C C C

Risk Classification

Risk Class DefinitionA IntolerableB Undesirable and shall only be accepted by the Project

Safety Committee if risk reduction is impracticableC Tolerable with the endorsement of the Project Safety

Committee

Background to Quantitative Risk Assessment

At the QRA: Alchemy to Acceptability Conference in London (1993) 1980: Major Oil Company Rep.

“QRA is equivalent to counting the number of angels that can stand on the head of a pin.”

1985: International Study Group on Risk Analysis“The whole analytical exercise might be considered to be objective. However, it must be realised that because of the large body of assumptions, estimates, judgements and opinions involved, much of the input information is often subjective.”

1993: Major Oil Company Risk Engineering Standard “QRA is a tool which helps translate hindsighgt (accident) into

foresight (planning)…showing ways and means to prevent the calculated accidents from happening.”

Background to Quantitative Risk Assessment

What can go wrong? Hazard IdentificationHow bad? Consequence ModellingHow often? Frequency EstimationSo what? Risk AssessmentWhat do I do? Risk Management

Stages of QRA

Represented in term of flow diagram.It is very flexible and has been used to guide the

application of risk assessment of many hazardous activities.

1st stage: System description/definition – defining the installation or the activity whose risks are to be analysed.

2nd stage: Hazard identification – consists of qualitative review of possible accidents which may occur, based on previous accident experience or judgment where necessary.

3rd stage: Frequency Analysis and Consequence Modelling are done in parallel.

Flow Diagram of QRA

Strengths of QRA

Limitations of QRA

Standards

Assignment 1• What is risk?• What is risk analysis?• What is risk assessment?• Risk analysis and assessment processes• Risk perceptions• How to measure risk• Hazard• Classification of hazard• Difference between hazard and risk• Strengths of QRA• Limitations of QRA• Standards

Risk

Types of Risk

Risk Perceptions

How to measure Risk?

Hazard

Classification of Hazard

Differences Between Hazard and Risk

- See more at: http://www.izenbridge.com/blog/differentiating-quantitative-risk-analysis-and-qualitative-risk-analysis/#sthash.aEBWb27X.dpuf