User Manual

SAFETY
Safety handbook page - 9-
PNSPO
Selecting Parameter S: Severity of injury S1 and S2
In estimating the risk arising from a fault(s) in the safety-related parts of a control
system only slight injuries (normally reversible) and serious injuries (normally
irreversible including death) are considered.
To make a decision the usual consequences of accidents and normal healing
processes should be taken into account in determining S1 and S2, e.g. bruising and/or
lacerations without complications would be classified as S1 whereas an amputation or
death would be classified as S2.
Selecting Parameter F: Frequency and/or exposure time to the hazard F1 and F2
A generally valid time period when parameter F1 or when parameter F2 should be
selected cannot be specified. However, the following explanation can facilitate making
the right decision in cases of doubt.
F2 should be selected if a person is frequently or continuously exposed to the hazard. lt
is irrelevant whether the same or different persons are exposed to the hazard on
successive exposures, e.g. for the use of lifts.
The period of exposure to the hazard should be evaluated on the basis of an average
value which can be seen in relation to the total period of time in which the equipment is
used. For example, if it is necessary to reach regularly between the tools of the
machine during cyclic operation in order to feed and move work pieces, then F2 should
be selected. If access is only required from time to time, then F1 can be selected.
Selecting Parameter P: Possibility of avoiding the hazard P1 and P2
When a hazard arises it is important to know if it can be recognised and whether it can
be avoided before it leads to an accident. For example, an important consideration is
whether the hazard can be directly identified by its physical characteristics, or whether
it can only be recognised by technical means, e.g. indicators. Other important aspects
which influence the selection of parameter P include, e.g.:
- operation with or without supervision;
- operation by experts or non-professionals;
- speed with which the hazard arises, e.g. quickly or slowly;
- possibilities for hazard avoidance,
- practical safety experiences relating to the process.
When a hazardous situation occurs P1 should only be selected if there is a realistic
chance of avoiding an accident or of significantly reducing its effect. P2 should be
selected if there is almost no chance of avoiding the hazard.
P
P
1
1
F2
F1
S
S
2
2
S
S
1
1
Cate
g
or
y
4
B
1 2 3
P
P
1
1
P
P
2
2
P
P
2
2
Risk graph
Preferred categories
for reference points
Possible categories,
which can require
additional measures
Measures, which can
be over dimensioned
for the relevant risk