Mitsubishi Electric MELSEC-QS Series Safety Application Manual page 28

3
RISK ASSESSMENT AND SAFETY LEVEL
3.3 PL
The PL is specified in ISO13849-1.
Determine a required performance level (PLr). The PLr refers to a performance level
required for safety functions to achieve required risk reduction.
Figure 3.4 is a risk graph used to determine a PLr.
PLr selection starting point
3
- 5 3.3 PL
Seriousness of Frequency and/or
the injury exposure time to
(S) the source of risk (F)
F1
Seldom or less
often and/or a brief
S1
Light (usually
temporary) injury
F2
continuous and/or a
long exposure time
F1
Seldom or less often
S2
Severe (usually
permanent) injury
F2
including fatality
continuous and/or
a long exposure time
Figure 3.4 Risk graph
Possibility to
avoid or limit injury
P1
Possible under
special conditions
P2
exposure time
Hardly possible
P1
Possible under
special conditions
Frequent or
P2
Hardly possible
Possible under
special conditions
and/or a brief
P2
exposure time
Hardly possible
P1
Possible under
special conditions
Frequent or
P2
Hardly possible
(P)
PLr
a
b
c
d
e
(Referred to ISO13849-1.)
Low risk
High risk