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3 RISK ASSESSMENT AND SAFETY LEVEL
3.3 PL
3.3 PL
The performance level (PL) is specified in ISO13849-1: 2006. Assess the risks of machines without undergoing risk reduction
measures by the safety system first, and then select a required performance level (PLr) for the safety systems. The following
shows a risk graph to be used for the PLr selection.
(For details, refer to ISO13849-1: 2006)
To ensure the establishment of PLr for the PL of the safety system, establish a safety system by selecting a method and
technique for the safety system.
Select PL based on (1) category, (2) average diagnostic coverage (DCavg), (3) mean time to dangerous failure (MTTFd), and
(4) common cause failure (CCF).
F1
F2
S1
S2
P2
P1
P2
PLr
a
P1
F1
F2
P2
P1
P1
P2
b
c
d
e
Scarcely possible
Possible under
specific conditions
Seldom-to-less-often
and/or exposure time
is short
Frequent-to-continuous
and/or exposure time
is long
Slight (normally
reversible injury)
Severity of injury
(S)
Frequency and/or
exposure to hazard
(F)
Possibility of avoiding
hazard or limiting harm
(P)
Serious (normally
irreversible injury
or death)
Scarcely possible
Possible under
specific conditions
Scarcely possible
Possible under
specific conditions
Seldom-to-less-often
and/or exposure time
is short
Frequent-to-continuous
and/or exposure time
is long
Scarcely possible
Possible under
specific conditions
High
Low
Starting point for
risk reduction
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