Mitsubishi Electric MELSEC iQ-R Series Safety Manual page 24

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.
Starting point for
risk reduction
(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).
3 RISK ASSESSMENT AND SAFETY LEVEL
22
3.3 PL
Frequency and/or
Severity of injury
exposure to hazard
(S)
(F)
F1
Seldom-to-less-often
and/or exposure time
is short
S1
Slight (normally
reversible injury)
F2
Frequent-to-continuous
and/or exposure time
is long
F1
Seldom-to-less-often
and/or exposure time
is short
S2
Serious (normally
irreversible injury
F2
or death)
Frequent-to-continuous
and/or exposure time
is long
Possibility of avoiding
hazard or limiting harm
(P)
P1
Possible under
specific conditions
P2
Scarcely possible
P1
Possible under
specific conditions
P2
Scarcely possible
P1
Possible under
specific conditions
P2
Scarcely possible
P1
Possible under
specific conditions
P2
Scarcely possible
PLr
Low
a
b
c
d
e
High