Lecture Sil Determination

8/11/2019 Lecture Sil Determination

http://slidepdf.com/reader/full/lecture-sil-determination 1/51

http://www.ntnu.no/~lundteig



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Logic solver

Final elementsInput elements

http://www.puffer.com/

Example:




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LT

PT

PT

GD

GD

LT

Logic unit

GD

Logic unit

SIF

An emergency

shutdown system

A fire and gassystem

SIF




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≥ 10−5

≤ 10−4 ≥ 10000

≤ 100000

≥ 10−4

≤ 10−3 ≥ 1000

≤ 10000

≥ 10−3

≤ 10−2 ≥ 100 ≤ 1000

≥ 10−2

≤ 10−1 ≥ 10

≤ 100




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Increasing risk

EUC risk Tolerable

risk

Residual

risk

Risk reduction by

other risk reduction

measures

Risk reduction by

other technologysafety-related

systems

Risk reduction by

E/E/PEsafety-related

systems

Necessary risk reduction

Actual risk reduction

(Adapted from IEC 61508-5)




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= 1PFD

Hazardous

event

C2f d

Avoided by SIS*

Yes

No

1-PFD C1

f res

Risk reduction: How many times

that the frequency is reduced

by having the SIF

Accident

f res: Residual frequency

f d: Demand frequency

f tol: Tolerable frequency

No accident

PFD

f d . PFD = f res < f tol*Or more precisely , the SIF




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Logic solver

Voted 1oo3 (for safety)

Failure rate: λ Test interval: τFraction that are common cause failures: β

PFDIE [ (1-β)λτ]3 /4 + βλτ/2≈

PFD PFDIE + PFD LS + PFDFE≈

Example - input elements:




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℄




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℄




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Starting point

for risk reduction estimation

a

b

1

1

2

2

23

3

34

4

C = Consequence parameter

F = Exposure time parameter

P = Probability of avoiding the hazardous event

W = In the absence of the SIF under consideration

a

a

1

--- ---

---

--- = No safety requirements

a = No special safety requirements

b = A single SIF is not sufficient

1, 2, 3, 4 = Safety integrity level

W W W123

C

C

C

C

F

F

P

P

P

A

B

D

C

A

B

FF

P

P

P

A

B A

B

A

B

B

A

A

F

F P

PA

B

B

X

X6

X5

X4

X3

X2

1

Generalized arrangement(in practical implementations

the arrangement is specific to

the applications to be covered

by the risk graph)

Source: (IEC 61511, 2003)




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A

B

C

D




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= 0.1




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A

B




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A

A

B

A

A B




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1

2

3

i

f d




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W i · P F DSIF = f

< f

f

= f

PLLα

f

α




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f tol

B

B

A A

E ∗(N ) = 0.1 · 0.1 · 0.1 = 0.001

f

= IRPAAC

E ∗(N )α




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f tol

f tol




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1 2 3

P F DrequiredSIF = f

W i

i




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Inherently safer design

Control

Supervisory

Preventive

Mitigative

Barrier

Limitation

Response




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Lecture Sil Determination

Documents

Transcript of Lecture Sil Determination