04 Risk Assessment

8/10/2019 04 Risk Assessment

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Geoenvironmental EngineeringKaniraj Shenbaga

University Malaysia Sarawak
http://www.unimas.my/


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Risk Assessment


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Often taken as synonymous with hazard. But

risk has the additional implication of the

chanceof a particular hazard occurring.

Hazardis a potential threat to humans and

their welfare. Riskis the probability of a specific hazard

occurrence

What is Risk?


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Involuntary risksVoluntary risks

Risk Types


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Most of the natural hazards are involuntary risks.

Risks not willingly undertaken.

Risks often relatively rare but can have a

catastrophic impact.

Risks may be unknown. Risks if perceived are considered uncontrollable.

Involuntary Risks


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Manmade hazards are in the category of

voluntary risks.

Risks more willingly accepted by people

through their own actions.

Have less catastrophic potential. More susceptible to be controlled.

- Government actions safety regulations, etc.

Voluntary Risks


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Risk cannot be completely eliminated. The only

option is to manage it.

Risk management is:- Reducing threats to life and property posed by hazards

- Simultaneously accepting unmanageable hazards

The first step in risk management is risk

assessment.

Risk Management


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1. Identification of hazards likely to result in disasters

Determine all hazardous events that may occur (Ei).(e.g.landslide)

2. Estimation of the risks of such events

Determine the probability of occurrence of each event (Pi).

(e.g. probability of occurrence of landslide = 5%)3. Evaluations of the consequences of the derived risks

Determine the loss created by each event (Li). (e.g. damage

to property due to landslide = RM200,000)

Steps in Risk Assessment


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R= Risk

p= Probability (varies from 0 to 1)L= Loss (money, death, etc.)

Risk Analysis


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The chance of occurrence of a landslide in a region is 5%

and the estimated damage that it would cause to

property is RM200,000. What is the risk (R) due to the

landslide in terms pf property loss?

p= ?L= ?

R= ?

Risk Analysis Example 1


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The chance of occurrence of a landslide in a region is 5%

and the estimated damage that it would cause toproperty is RM200,000. The risk (R) due to the

landslide in terms pf property loss is:

p= 0.05

L= RM200,00R= 0.05 x 200,000 = RM10,000

Example 1 Answer


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In a region, different events may occur mutually

exclusively.- For example, in a region prone to several natural hazards,

flood may occur at some time, cyclone may occur at some

other time, and volcano may erupt at another time.

From historical database, estimate all the events (E1

Ej

En) likely to occur in a year and their corresponding

probabilities (p1 pj pn) and losses(L1 Lj Ln).

Note: The values of p and L are greater then 0.

Risk Analysis Multiple Events


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Calculate:

Calculate:

p0= probability of events with loss L0= 0


=

=


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Arrange all the events in the order of increasing loss

(L0< L1


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Total probable risk, R

=

Risk due to event

i

robability of risk >

i


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A region is prone to earthquake, volcano and tsunami hazards

every year with respective probabilities of 0.06, 0.08 and 0.025.The corresponding estimated property losses are RM60 million,

RM15 million and RM45 million. The corresponding estimated

number of human death are 220, 20 and 350. Estimate:

Total probable risk in terms of money and lives

Probability of property loss > RM15 million

Probability of no loss of human lives

Risk due to tsunami in terms of money and lives

Risk Analysis Example 2


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Event

Proba-

bility

Loss*

Cumulative probability

E0

E1

E2

E3

?

?

?

?

?

?

?

?

P0=?

P1= ?

P2= ?

P3= ?

Table for Property Loss

E1volcano; E2 tsunami; E3- earthquake

*RM values in million


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Event

Proba-

bility

Loss*


E0

E1

E2

E3

0.835

0.080

0.025

0.060

0

15

45

60

P0=0.835 +0.08 +0.025 + 0.06 = 1

P1= 0.08 +0.025 + 0.06 = 0.165

P2= 0.025 + 0.06 = 0.085

P3= 0.06

Table for Property Loss

E1volcano; E2 tsunami; E3- earthquake

*RM values in million


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Total probable riskRtotal=?

Probability of property loss > RM15

million = ?Risk due to tsunami = ?

Property Loss in Terms of Money


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Total probable risk

Rtotal=(0.835 x 0)+(0.08 x 15)+(0.025 x 45)+

(0.06 x 60) = about RM6 million

Probability of property loss > RM15 million =

P1= 0.165 Risk due to tsunami = p2x L2 = 0.025 x 45 =

RM1.125 million

Property Loss in Terms of Money


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Event

Proba-

bility

Loss*


E0

E1

E2

E3

0.835

0.080

0.060

0.025

?

?

?

?

P0=?

P1= ?

P2= ?

P3= ?

Table for Loss of Lives

E1volcano; E2 earthquake; E3tsunami

*Number of human lives


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Event

Proba-

bility

Loss*


E0

E1

E2

E3

0.835

0.080

0.060

0.025

0

20

220

350

P0=0.835 +0.08 +0.06 + 0.025= 1

P1= 0.08 +0.06 + 0.025= 0.165

P2= 0.06 + 0.025 = 0.085

P3= 0.025

Table for Loss of Lives

E1volcano; E2 earthquake; E3tsunami

*Number of human lives


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Total probable riskRtotal=about how manylives

Probability of no loss of human lives, p0

= ?Risk due to tsunami = how manylives

Loss of Lives


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Total probable risk

Rtotal=(0.835 x 0)+(0.08 x 20)+(0.06 x 220)+

(0.025 x 350) = about 24 lives

Probability of no loss of human lives = p0=

0.835. Risk due to tsunami = p3x L3= 0.025 x 350 = 9

lives

Loss of Lives


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The annual probabilities for earthquake, flood and drought

hazards in a region are 0.01, 0.075 and 0.04, respectively. Thecorresponding number of human casualties are 2,500; 300;

and 1,350. The corresponding property losses are RM120

million, RM350 million and RM245 million. Estimate:

Total probable risk in terms of money and lives

Probability of property loss > RM120 million

Probability of no loss of property

Risk due to flood in terms of money and lives

Exercise


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Risk is the probability of occurrence of a specific

hazard. Risk cannot be eliminated, but should be managed.

The first step in risk management is risk assessment.

The risk assessment is made from the probability and

loss associated with each hazard.

Summary


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04 Risk Assessment

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