Safety Category - Mitsubishi Electric Melsec-QS Series Safety Application Manual

3
RISK ASSESSMENT AND SAFTY LEVEL

3.2 Safety Category

The safety category is standardized in EN954-1.
The risk graph to be used for the safety category selection is shown in Figure3.3.
Severity of the injury
S1
recoverable) trouble
Safety category
selection starting point
S2
unrecoverable) trouble
Figure3.3 Safety category selection relevant to safety related sections of control system
Risk analysis result
Frequency and time of
exposure to hazard
(S)
Minor (normally
F1
Rare, considerable,
often, or short
time exposures
Major (normally
F2
Frequent to
continuous, or long
time exposures
Definition of symbols:
Possibility of hazard
avoidance
(F) (P)
P1
Available under a
specific condition
P2
Almost impossible
P1
Available under a
specific condition
P2
Almost impossible
Symbol
Safety category which is desirable as a reference
point
Safety category which may be over-specification
— Insufficient safety category
3.2 Safety Category
Safety category selection
Safety category
B 1 2 3 4
Definition
(Referred to EN954-1.)
3
1
2
3
4
5
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