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© Engineering Safety Consultants Limited
Page 23
Proof
Test
Proof
Test
Proof
Test
Proof
Test
Time t
Probability of failure
Probability of failure with time
•
λ
DU
is the dangerous undetected failure rate per hour;
•
T
p
is the proof test frequency
© Engineering Safety Consultants Limited
Page 24
Configuration
λ
SYS
PFD
1oo1
DU
DU
P
1oo2
λ
DU
2
.T
P
λ
DU
2
.T
P
2
/ 3
2oo2
2.
λ
DU
λ
DU
.T
P
1oo3
λ
DU
3
.T
P
2
λ
DU
3
.T
P
3
/ 4
2oo3
3.
λ
DU
2
.T
P
λ
DU
2
.T
P
2
3oo3
3.
λ
DU
3.
λ
DU
.T
P
/ 2
1oo4
λ
DU
4
.T
P
3
λ
DU
4
.T
P
4
/ 5
2oo4
4.
λ
DU
3
.T
P
2
λ
DU
3
.T
P
3
3oo4
6.
λ
DU
2
.T
P
2.
λ
DU
2
.T
P
2
4oo4
4.
λ
DU
2.
λ
DU
T
P
. T /2
λ
λ
PFD for undetected Failures
The frequency of the
Proof Tests have an
impact of the PFD
achieved for a specified
dangerous undetected
failure rate per hour
(That is:
).
However, the resource
implications and
competence requirements
of undertaking the Proof
Test should be thoroughly
thought out.
λ
DU