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

3
RISK ASSESSMENT AND SAFETY 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 Figure 3.3.
Safety category
selection starting point
Figure 3.3 Safety category selection relevant to safety related sections of control system
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- 3 3.2 Safety Category
Frequency and time of
Severity of the injury
(S)
S1
Minor (normally
recoverable) trouble
S2
Major (normally
unrecoverable) trouble
Definition of symbols:
Risk analysis result
Possibility of hazard
exposure to hazard
(F)
P1
Available under a
F1
Rare, considerable,
often, or short
P2
time exposures
Almost impossible
P1
F2 Available under a
Frequent to
continuous, or long
P2
time exposures
Almost impossible
Symbol
Safety category which is desirable as a reference
point
Safety category which may be over-specification
— Insufficient safety category
Safety category selection
Safety category
avoidance
(P)
B 1
specific condition
specific condition
Definition
(Referred to EN954-1.)
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