determination of risk, risk classification · 23/04/2018 the acceptability of risk 40 safety risk -...

DETERMINATION OF RISK,

RISK CLASSIFICATION

Lecture 8.

23/04/2018 The Acceptability of Risk 40

Safety Risk - Reminder

• The significance of a hazardous effect in an application is called „safety risk”.

• Safety risk is the combination of the :

• (predicted) frequency or probability,

• and the severity of the consequences or outcomes of

• a hazard.

• The safety risk can be influenced by other risk parameters.

• The risk can be determined by:

• quantitatively,

• or risk classification/qualitatively.

Severity

Frequency

Risk


Summary of Basic Risks


Quantitive Risk Determination, Example - 1

• Failure of a particular component is likely to result in an explosion that could kill 100

people. It is estimated, that this component will fail once in every 10 000 years.

• What is the risk associated with this component?

• 𝑅𝑖𝑠𝑘 = 𝑠𝑒𝑣𝑒𝑟𝑖𝑡𝑦 𝑥 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦

• 𝑅𝑖𝑠𝑘 = 100 𝑑𝑒𝑎𝑡ℎ𝑠 𝑥 0.00011

𝑦𝑒𝑎𝑟

• 𝑅𝑖𝑠𝑘 = 0.01𝑑𝑒𝑎𝑡ℎ

𝑦𝑒𝑎𝑟


Quantitive Risk Determination, Example - 2

• In a country with a population of 50 000 000, approximately 25 people are killed each

year by lightning. What is the risk associated with death from this cause?

• The fraction of the population killed per year is 25/50 000 000= 5x10-7.

• The associated risk may be expressed by saying that each individual has a probability of

5x10-7 of being killed by lightning in any given year in the given country.

• Alternatively we could say that the population as a whole is exposed to a risk of 5x10-7

deaths per person-year.


Damage, Injuries

• transport is a hazardous facility, it endangers thesafety of:

• persons,

• objects,

• environment.

• 𝑣𝑖𝑐𝑡𝑖𝑚𝑠 = 𝑑𝑒𝑎𝑡ℎ𝑠 + 0.1 𝑥 𝑠𝑒𝑟𝑖𝑜𝑢𝑠 𝑖𝑛𝑗𝑢𝑟𝑖𝑒𝑠 +0.01 𝑥 𝑚𝑖𝑛𝑜𝑟 𝑖𝑛𝑗𝑢𝑟𝑖𝑒𝑠

• 1 𝑣𝑖𝑐𝑡𝑖𝑚 = 1 𝑑𝑒𝑎𝑡ℎ = 10 𝑠𝑒𝑟𝑖𝑜𝑢𝑠 𝑖𝑛𝑗𝑢𝑟𝑖𝑒𝑠 == 100 𝑚𝑖𝑛𝑜𝑟 𝑖𝑛𝑗𝑢𝑟𝑖𝑒𝑠

• eg. from an accident insurrance:


Individual Risk

• Example:

• rockfall in a railway section once in 10 years,

• there are 100 trains in a year,

• a train passes trought this hazardous section under 4 sec.

person

death

day

year

trip

tripevent

year

dayyear

eventDaHRRi iii 1

sec606024

100sec

4

36510

1

yearperson

deathRii

6102,1• HRi = hazard rate

• Dai = damage


Collective Risk

• the sum of the individual risks

• Eg.

• in a train, there are 650 passengers:

year

deathRi

yearperson

deathpersonRiRi

o

io

4108,7

6102,1650


Connection between RAMS Components

• D Danger

• H Hazard

• HR Hazard Rate

• Da Damage

• Ri Risk

• S Safety

• R Reliability

• A Availability

• M Maintainibility

• µ Repair Rate

• λ Failure Rate

• t Time

• P Probability

• Riunuzul Unacceptable Risk

Risk Classification


Risk Classification

• In such cases severity and frequency data must be combined in less mechanical way

(severity x frequency).

• The result of this process is a risk classification of the risk associated with a particular

hazard.

• This classification is sometimes called a risk class, a risk level or a risk factor.

• Used and categorized parameters could be:

• severity,

• frequency,

• controllability etc…


Consequence Categories – Severity, Examples, EN 50126

CENELEC EN 50126-1:2017, Railway applications - The Specification and Demonstration of Reliability, Availability, Maintainability and Safety (RAMS) - Part 1: Generic RAMS process


Consequence Categories – Severity, Examples

Software Testing & Analysis (F22ST3) Safety-Critical Systems Andrew Ireland School of Mathematical and Computer Science Heriot-Watt University Edinburgh


Frequency Categories – Examples, EN 50126


Frequency Categories – Examples



Risk Acceptance Categories – Examples, EN 50126


Risk Classification – Examples, EN 50126


Risk Classification – Examples



Severity Categories

(Vehicle Industry, AAAM, ISO 26262)

• AIS 0: no injury

• AIS 1: minor injury (skin damage, muscle pain…)

• AIS 2: moderate injury (deeper cutting damage, less, than 12 hours of loss of

consciousness)

• AIS 3: serious injury (bone fracture [not skull], joint injury…)

• AIS 4: severe injury with probable survival (severe bone injury, less, than 12 hours of

loss of consciousness)

• AIS 5: critical injury, life-threatening injury with uncertain possibility to survive (more,

than 12 hours of loss of consciousness, internal bleeding…)

• AIS 6: maximum injury, fatal injury, death


Severity Categories – ISO 26262

AIS


Severity Classsification – Examples, ISO 26262

• S0: bumps with roadside infrastructure/damage entering or exiting parking space,

• S1: side impact with a narrow stationary object, eg. crashing into a tree with very low

speed/collision with minimal vehicle overlap (10% to 20%),

• S2: side collision with a passenger car (eg. intrudes upon passenger compartment) with

very low speed/pedestrian or bicycle accident while turning (city intersection and

streets),

• S3: side impact with a narrow stationary object, eg. crashing into a tree with medium

speed/ reaor or front collision with another passenger car with medium speed


Frequency – ISO 26262

• Categories: E0, E1, E2, E3, E4

• E0 is assigned to situations which, altough identified during a hazard and risk analysis,

are considered to be unusual or incredible

• eg. a vehicle involved in an accident which includes an aeroplane landing on highway

• remaining levels (E1, E2, E3, E4) are assigned for situations that can become hazardous

depending either the duration of a situation (temporal overlap) or the frequency of

occurrence of a situation


Frequency Categories – ISO 26262

• based on the duration:

• based on the frequency:


Controllability – ISO 26262

• ability to avoid a specified harm or damage through the timely reactions of the persons

involved, possibly with support from external measures

• persons involved can be include the driver, passengers or persons in the vicinity of the vehicle’s

exterior,

• external measure: measure, that is separate an distinct from the item which reduces or mitigates the

risk


Controllability and Hazardous Events – Examples, ISO

26262

• C0 (everybody): unexpected radio volume increase – maintain intended driving path,

• C1 (99%+): faulty adjustment of seat position while driving – brake to slow/stop

vehicle,

• C2 (90%+): failure of ABS during emergency breaking - maintain intended driving path,

• C3 (90%-): failure of brakes - maintain intended driving path, stay in lane.


Risk Classification – ISO 26262

risk categories:

negligible (QM – quality

managemenet needed),

A (very low probability) –

D (high, having resonable

possibility)


Risk Graph – General Scheme (IEC 61508)


Risk Graph - Example

Door Closing System – Inadvertent Operation

C1

C2

F2

P1

P2

P1

P2

F1

F2

C3

C4

F1

–

–

1

2

3

4

5

6 7

6

5

4

3

2

1

–

7

8

6

5

4

3

2

1

W3 W2 W1 Risk parameter Classification

Consequence(Severity)

C1 Minor injury

C2Serious permanent injury to one or more persons;death to one person

C3 Death to several peopleC4 Very many people killed

Frequency of, andexposure time in, the hazardous zone.

F1 Rare to more often exposure in the hazardous zone

F2 Frequent to permanent exposure in the hazardous zone

Possibility of avoidingthe hazardous event.

P1 Possible under certain conditions

P2 Almost impossible

Probability of the unwantedoccurrence.

W1A very slight probability that the unwanted occurrenceswill come to pass and only a few unwanted occurrences are likely

W2A slight probability that the unwanted occurrences will come to pass and few unwanted occurrences are likely

W3A relatively high probability that the unwanted occurrences will come to pass and frequent unwanted occurrences are likely




C1

C2

F2

P1

P2

P1

P2

F1

F2

C3

C4

F1

–

–

1

2

3

4

5

6 7

6

5

4

3

2

1

–

7

8

6

5

4

3

2

1



C1 Minor injury














Example – Vehicle Industry

• the car is stopped on a ramp:

• hill start assist is not working:

• red light, in a ramp,

• parking on a slope,

• etc…


Severity, Frequency

• S0: no injuries,

• S1: light to moderate injuries,

• S2: severe to life-threatening (survival

probable) injuries,

• S3: life-threatening (survival uncertain) to

fatal injuries.

• E0: incredibly unlikely,

• E1: not specified, more, than once a

year,

• E2: <1% of average operating time,

sometimes in a year,

• E3: 1% to 10% of average operating

time, sometimes in a month,

• E4: >10% of average operating time

(often).


Severity, Frequency




probable) injuries,


fatal injuries.



year,






(often).


Controllability

• C0: controllable in general,

• C1: 99% or more of all drivers or other traffic participants are usually able to avoid

harm,

• C2: 90% or more of all drivers or other traffic participants are usually able to avoid

harm,

• C3: less than 90% of all drivers or other traffic participants are usually able, or barely

able to avoid harm.


Controllability


• C1: 99% or more of all drivers or

other traffic participants are usually

able to avoid harm,



able to avoid harm,

• C3: less than 90% of all drivers or


able, or barely able to avoid harm.

• Question:

• Is there a driver in the car?


Controllability

• With a driver:




able to avoid harm,



able to avoid harm,




• Without a driver:




able to avoid harm,



able to avoid harm,





Controllability

• With a driver:




able to avoid harm,



able to avoid harm,








able to avoid harm,



able to avoid harm,





Classification


Classification

without

driver

with driver

End of Lecture 8.

Thank you for your attention!

determination of risk, risk classification · 23/04/2018 the acceptability of risk 40 safety risk -...

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