- 6 -
LIFE-CYCLE ACTIVITIES
Application Scope
Definition of the Application Target
The process equipment shall be described in order to define
clearly the application target with its hazard potential.
Applicable LAWS and Standards
All applicable general Laws and Standards related to the
allowed operations of the equipment, as EU-Directives shall
be collected. The plant owner shall produce a Regulatory
Requirements List document.
Definition of the Application Scope
The scope for the safety-related application shall be fully
described in order to produce the following documentation:
- Safety Integrity Level classification;
- Functional safety requirements of the equipment under
control
Necessary steps for the definition of the above listed documents
are:
- Detailed investigation about which potential hazards of the
process equipment have been reduced by design or an
independent layer of protection.
- Checking of the necessary functional requirements required
by the applicable laws and Standards.
- Determination of the Safety Integrity Level with a specific risk
reduction method.
- Specification of each functional risk reduction by its physical
risk, properties to be measured, its safe action to be performed
Functional Safety Requirements of the Target
Equipment
Safety Functions
The documents:
- Safety Requirement Specification;
- Piping and Instrument Diagram;
Shall be produced in order to fully define the safety functions
of the Safety Instrumented System. Necessary steps for the
definition of the above listed documents are:
- Definition of the required Safety Functions.
- List of all the process conditions under which the safe action
is required.
- Investigation of the effect of common cause failures.
- Specification of the actions required for the process
measurement failures which are not covered by the Safety
Functions.
- Identification if the required safe actions are dependent on
operating states or are effective under all operating states.
- Transformation of the verbal functional requirements into a
graphical form.
Process Interface
The documents:
- Functional Requirement Specification;
- Piping and Instrument Diagram;
- Functional Diagram
Shall be produced in order to fully describe the process
interface and connections. Necessary steps for the definition
of the above listed documents are:
- Definition of the Process Interface requirements.
- Identification of the instrumentation for every physical risk
property (input) and define their fail safe signal.
- Definition of the required amount of instruments and
certifications according the SIL requirements
- dentification of the type of actuator and definition of their fail
safe position for the required safe action
- Definition of the required redundancy and certification
- Completion of the functional diagram with instrumentation
details
- Definition of the necessity of a regulatory body approval;
System Safety Requirement Assignment
I/O System Response Time
The total system response time is determined by the following
elements:
- Sensor detection time,
- Logic solver time;
- Actuator response time;
The total system response time must be less than the process
safety time. To ensure a safe operation of the system, the scan
rate of each section of the logic solver multiplied by the number
of channels must be less than the safety time less actuator and
sensor response time.
I/O System Selection
The I/O system selection is mainly dictated by the required
logic solver time. Appropriate selection procedures and analysis
shall be used.
System Structure
System configuration drawings shall be available to describe
the equipment and interfaces required for a complete
operational system. The system must be fully operational
before start-up.
Safety Requirement Allocation
Each safety function, with its associated safety integrity
requirement, shall be allocated to the designated safety-
related systems taking into account the risk reductions achieved
by the other technology safety-related systems and external
risk reduction facilities, so the necessary risk reduction for that
safety function is achieved. The allocation indicated shall be
done in such a way that all safety functions are allocated and
the safety integrity requirements are met for each safety
function.
Programming Environment
Computer system which provides the necessary software to
program, compile, and load an application shall be separated.
Safety Routines
Safety additional requirements may be defined in order to
ensure the correct functionality of sequences in the Safety
Instrumented System.
Safety Templates
Safety Templates must be followed for particular applications.
(e.g. SIL 2 and burner management applications have certified
"Templates" that adhere to all the rules spelled out by the
applicable regulations).
Separation of Safety Functions
Each safety function shall be separated in a different
programming section.
