SIS & ESD (IEC 61511, 61508) Training - Safety Life Cycle

XRS Consulting Engineers and Project
Managers 1
Section 4
Safety Instrumented Systems (SIS) & Emergency Shutdown
(IEC 61511 & IEC 61508) and Boiler/Gas Turbine Control
Safety Instrumented Systems
Section 4
Safety Life Cycle

Managers 4
Section 4
The purpose of a safety instrumented system (SIS) is to
reduce risk from a hazardous process to a tolerable
level.
Although selecting a safety integrity level (SIL), which
we will look at later, is vital to this purpose, an
organization must also devote significant effort to
supporting safety activities.
Safety life-cycle (SLC) is an engineering process
designed to optimize the design of the SIS and to
increase safety.
INTRODUCTION
Safety Life Cycle
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Managers 7
Section 4
INTRODUCTION
The SLC is a closed-loop process as described in
several functional safety standards, including IEC61508
and IEC61511.
The Safety Life Cycle process does not end. Its
lifecycle tasks are continuously performed while the
process is in operation, and especially when the
designs are periodically reviewed and process changes
occur.
Safety Life Cycle

Managers 10
Section 4
The IEC 60508 and IEC 61511 / ISA 84 safety life-cycles
are shown schematically in the next slides
Each phase of the overall SLC is divided into
elementary activities, and the scope, inputs and
outputs are specified for each phase
OVERVIEW
Safety Life Cycle

Managers 13
Section 4
The essential details of analyzing, designing, verifying,
and documenting are discussed and defined in all
safety standards.
It is important for an organization to devote extra care
to the essential Safety Life Cycle so as to ensure that
the desired safety level is achieved.
A study of actual causes of industrial accidents,
performed by the Health and Safety Executive in the
United Kingdom, showed that there are a number of
causes.
OVERVIEW
Safety Life Cycle

Managers 16
Section 4
Phases of Safety Life Cycle
Safety Life Cycle

Managers 19
Section 4
Safety Life Cycle
Modify?
Select SIS Technology
Select SIS Architecture
Determine Test Frequency
SIS Detailed Design
SIS Installation
SIS Commissioning
SIS Initial Validation
Conceptual Process Design
Identify Potential Risks
Consequence Analysis
Layer of Protection Analysis
Develop Non -SIS Layers
Determine SIF Target SIL
Document Requirements
Yes
Startup
Operation
Maintenance
Periodic Proof Tests
Modifications
Decommissioning
No
Analysis Realization Operation
Safety Life Cycle – ISA S84.00.01-2004
Modify?
Yes No
How much safety
do I need?
How much safety
do I have
with my design?
How will I keep
it safe?

Managers 22
Section 4
Generally, this step involves conducting a detailed
hazard and risk analysis.
In the process industries a Process Hazards Analysis
(PHA) may range from a screening analysis through to a
complex Hazard and Operability (HAZOP) study,
depending on the complexity of operations and
severity of the risks involved.
Analysis Phase
PHASES OF SAFETY LIFE CYCLE
Safety Life Cycle

Managers 25
Section 4
The latter involves a rigorous detailed process
examination by a multi-disciplinary team comprising
process, instrument, electrical and mechanical engineers,
as well as safety specialists and management
representatives.
Detailed cause and effect scenarios are considered and
risks quantified for all process functions and operations.
If the study determines that the mechanical integrity of a
process and the process control are insufficient to protect
against the potential hazard, a SIS may be required.
Analysis Phase
Safety Life Cycle

Managers 28
Section 4
BASIC TANK LEVEL CONTROL WITH OVER
PRESSURE RELEASE HAZARD
Pump
Discharge valve
Analysis Phase
Safety Life Cycle

Managers 31
Section 4
A key part of this planning step is developing
maintenance and proof-test schedules to ensure any
potential failure in the safety equipment can be found
and repaired before the system is required to act.
Once the conceptual design is completed,the
organisation needs to analyze the prospective system
to confirm it meets the SIL selected and documented
in the SRS.
Realisation Phase
Safety Life Cycle

Managers 34
Section 4
Operations Phase
Safety Life Cycle
Operation & Maintenance
Provide operator and maintenance personnel training
Operate according to operation and maintenance planning and procedures
Proof test and inspect the system according to written proof test procedures for every SIF
Document proof tests and inspections
The SIMATIC Safety Matrix provides built-in mechanisms for implementation
of secure bypasses/overrides and automatically documents all actions in an events log.

Managers 37
Section 4
SAFETY REQUIREMENTS SPECIFICATION
Safety Life Cycle
Safety Requirements Specification (SRS)
Identify and describe safety instrumented functions
Document target SIL
Document functional operation
(e.g. control narrative, cause and effect, etc.)
Document associated parameters – timing, maintenance bypass requirements, etc.
Documentation of the functional operation, cause & effect matrix

Managers 40
Section 4
The effect of the SRS on each of these steps varies.
For a typical grass-roots project, the interaction is
illustrated in the next slide with the initial step being
"feasibility" and continuing clockwise around the
figure.
The important point of this illustration is that the SRS
is central to the design of the SIS. All activities
associated with the SIS either affect or are affected by
the SRS. Therefore, the SRS must be developed and
reviewed by a team of people with process,
equipment, operating, and maintenance experience
and knowledge.
Safety Life Cycle

Managers 43
Section 4
The SRS should include the following requirements:
Description of all the SIF necessary to achieve the
required functional safety
Requirements to identify and take account of common
cause failures
Definition of the safe state of the process for each
identified SIF
Definition of any individually safe process states
which, when occurring concurrently, create a separate
hazard (for example, overload of emergency storage,
multiple relief to flare system)
Safety Life Cycle

Managers 46
Section 4
Maximum allowable spurious trip rate
Failure modes and desired response of the SIS
Any specific procedure requirements for starting up
and restarting the SIS
All interfaces between the SIS and any other system
(including the BPCS and operators)
Description of the modes of operation of the plant and
identification of the safety instrumented functions
required to operate within each mode
The application software safety requirements
Safety Life Cycle

Managers 49
Section 4
Definition of the requirements for any safety instru-
mented function necessary to survive a major accident
event, for example, time required for a valve to
remain operational in the event of a fire.
Safety Life Cycle

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SIS & ESD (IEC 61511, 61508) Training - Safety Life Cycle