For different machines or different parts of a machine, the assessment of risk might lead to
different risk levels, it is therefore necessary to establish the level of safety of the measures
to be adopted in proportion to the risk. Standard AS 4024.1501 defines the classes of safety
related parts according to the following parameters:
- Severity of injury (reversible, irreversible, fatal)
- Frequency and duration of exposure to the danger
- Possibility of avoiding danger
The Standard also defines the behaviour of the safety related parts in the event of a failure:
Safety categories for control systems conforming to per. AS 4024.1-2006
Categories |
Summary of requirements |
System behaviour |
Principles to
achieve safety |
B |
The safety related parts of the control system and/or its
protection devices, as well as their components, shall
be designed, constructed, selected, assembled and
combined in accordance with relevant standards, so
that they can withstand the expected influence. |
– The occurrence of a fault can lead to a
loss of the safety function.
– Some faults remain undetected. |
Mainly characterised
by selection of
components |
1 |
Requirements of B shall apply.
Well-tried components and well-tried safety principles
shall be used. |
The occurrence of a fault can lead to
loss of the safety function, but the
probability of occurrence is lower than
for category B. |
2 |
Requirements of B and the use of well-tried safety
principles shall apply.
Safety function shall be checked at suitable intervals
by the machine control system. |
– The occurrence of a fault can lead to
loss of the safety function between
the checks.
– The loss of safety function is
detected. |
Mainly characterised
by structure
The correct selection
of safety components
and principles |
3 |
Requirements of B and the use of well-tried safety
principles shall apply.
Safety-related parts shall be designed so that:
a) A single fault in any of these parts does not lead to
loss of the safety function; and
b) Whenever reasonably practicable the single fault is
detected. |
– When a single fault occurs, the safety
function is always performed.
– Some but no all faults will be detected.
– Accumulation of undetected faults can
lead to loss of the safety function. |
4 |
Requirements of B and the use of well-tried safety
principles shall apply.
Safety-related parts shall be designed so that:
a) A single fault in any of these parts does not lead to
loss of the safety function; and
b) The single fault is detected at or before the next
demand upon the safety function. If this is not possible,
then an accumulation of faults shall not lead to loss of
the safety function. |
– When the faults occur the safety
function is always performed.
– The faults will be detected in time to
prevent loss of the safety function. |
