Rockwell Automation AADvance Controller Safety Manual User Manual
Page 27
Document: 553630
ICSTT-RM446K-EN-P Issue: 10
_C
2-3
The second objective is to determine the event sequences that may
lead to a hazardous event.
The third objective is to determine the risks associated with the
hazardous event.
This risk analysis will provide basic information for identifying the safety-
related requirements to mitigate risks.
System Functional and Safety Requirements
A set of system functions and their timing requirements will be specified.
Where possible, the functions should be allocated to defined modes of
operation of the process. For each function, it will be necessary to
identify the process interfaces. Similarly, where the function involves data
interchange with third party equipment, the data and interface should be
clearly identified. Where non-standard field devices, communications
interfaces or communications protocols are required, it is especially
important that detailed requirements for these interfaces are established
and documented at this stage.
The client should provide the functional requirements, where this
information is not supplied the System Integrator should define the
requirements and agree them with the client. It is, however, necessary to
collate these requirements into a document, including any clarification of
the requirements. It is recommended that logic diagrams be used to
represent the required functionality and highly recommended that all
requirements are reviewed, clarified where required and approved by the
client.
During the system safety requirements stage the functional requirements
are analyzed to determine their safety relevance. Where necessary,
additional safety requirements shall be identified and documented to
ensure that the plant will fail-safe in the case of failures of the plant,
safety-related system, external equipment or communications, or if the
safety-related system's environment exceeds the required operating
conditions.
The appropriate safety integrity level and safety-related timing
requirements shall be defined for each safety-related function. For each
function the required safety failure mode shall be determined. The client
should supply this information or it should be defined and agreed with the
client as part of this phase. The System Integrator shall ensure that the
client approves the resulting safety requirements.
System Engineering
The system engineering stage realizes the design of the safety-related
system. It is recommended that the engineering be divided into two
distinct stages, the first defining the overall system architecture, and the
second detailing the engineering of the individual architectural blocks.