nopsa.gov.au
National Offshore Petroleum Safety Authority
Independent and professional regulators of Australian offshore petroleum health and safety
March 2011
Technical Safety Bulletin:
FUNCTIONAL SAFETY
IN THE AUSTRALIAN
OFFSHORE PETROLEUM INDUSTRY
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Technical Safety Bulletin
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FUNCTIONAL SAFETY IN THE AUSTRALIAN OFFSHORE
PETROLEUM INDUSTRY
Following a number of issues where the use of control systems containing programmable devices or
software was identified as a possible cause of a dangerous event, NOPSA published Safety Alert 45
outlining the issue and giving preliminary advice to Operators on a way forward.
This technical bulletin is intended as a more detailed supplement to Safety Alert 45, offering more in-
depth analysis of the issues and legal duties imposed by the Offshore Petroleum and Greenhouse Gas
Storage Act 2006. This document provides duty holders with guidance on possible methods for
reducing risks from functional safety issues to as low as is reasonably practicable (ALARP).
FUNCTIONAL SAFETY IN THE AUSTRALIAN
OFFSHORE PETROLEUM INDUSTRY ................................................................... 1
INTRODUCTION ...................................................................................................... 2
What is functional safety? ......................................................................................... 2
Programmable systems ............................................................................................ 2
Goal-setting regulation .............................................................................................. 4
LEGAL DUTIES ....................................................................................................... 4
Operators ................................................................................................................. 4
Persons in control of parts of a facility or particular work, and employers ................. 5
Manufacturers ........................................................................................................... 5
Suppliers .................................................................................................................. 5
Persons .................................................................................................................... 6
Functional safety in Safety Cases ............................................................................. 6
AS LOW AS REASONABLY PRACTICABLE (ALARP) .......................................... 7
The need for demonstration ...................................................................................... 7
The role of standards ................................................................................................ 7
Any other equally effective means .......................................................................... 10
REFERENCES ....................................................................................................... 10
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INTRODUCTION
This section introduces some key concepts that support understanding of how functional safety relates
to the occupational health and safety regulations in the Australian offshore petroleum industry.
What is functional safety?
While some hazards are created by the physical implementation of control systems, such as noise and
high-pressure fluid in hydraulic systems, or electric shocks from relay logic, instances of harm from
these sources are comparatively rare.
Control systems implemented in software are „virtual‟ in that they usually consist of a series of magnetic
signals, and cannot directly cause physical harm.
Control systems can cause harm when they fail to carry out their function correctly, such as:
an unsolicited movement of a crane hook could cause a dogman to be crushed by a
heavy load;
the failure of a dynamic positioning system could lead to a diving support vessel
dragging a diver into a hazardous situation; or
the failure of a pressure sensor or logic solver could cause a hydrocarbon leak due to
an overpressure in a pipe, leading to a burst.
Functional safety is sometimes described as relating to the failure of a control system to operate
reliably. There have, however, been incidents where a system component has operated correctly, and
in accordance with its design intent, but with unintended consequences. The failure in such cases is in
the design and implementation process rather than being a matter of unreliability in the control system
itself, which could theoretically produce hazardous outputs with high degrees of reliability.
The IEC standard 61508-0
(1)
avoids this issue by defining functional safety as, “part of the overall safety
that depends on a system or equipment operating correctly in response to its inputs.”
This leads to a further definition of a safety-related control system as one which is able to cause a
hazard if it does not respond to its inputs correctly.
These two definitions highlight why it is so important to identify all hazards associated with the control
system: without doing a thorough job of hazard analysis, it is impossible to correctly specify the correct
system response.
Programmable systems
Software is increasingly being used in safety-related applications ranging from smart instrumentation to
programmable logic controllers. Active, computer-based safety management systems are being
employed for such significant applications as electronic permit-to-work packages.
Software‟s unique inherent properties require approaches and treatments quite different from traditional
engineering activities such as mechanical or structural engineering.
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The UK‟s Health and Safety Commission 1998 report, The use of computers in safety-critical
applications, describes the issue as “the essentially discontinuous behaviour of discrete logic, and in
particular of software.”
(2)
Control systems process inputs to produce desired outputs. The nature of software is such that, if a
system gives a correct output for a given input, it cannot be assumed that even a slightly different input
will also give a satisfactory result.
Since testing every possible combination of inputs to ensure none will produce a hazardous set of
outputs is unviable, steps need to be taken to mitigate the risks involved.
Consider Figure 1, which shows a simple example based on a 32-bit microprocessor programmed to
add two numbers represented as strings of 32-bit binary digits. The total possible number of input
combinations is 2
64
.
If one million combinations were tested every second, it would take over five hundred thousand years
to test them all. For very complex systems involving a typical processor running an operating system
and several programme packages, the inherent complexity renders exhaustive software testing
effectively impossible.
Software, therefore, cannot be tested in the same way as, say, a mechanical or structural system. If a
bridge can safely take a ten-tonne load, then it can usually be assumed that a lighter load will be
acceptable. In software, the concept of a „lighter load‟ does not exist.
Similarly, if a mechanical component in a machine fails, replacing it with a stronger, but otherwise
identical component allows a claim to be made that the machine will be at least as reliable as it was
beforehand. The same cannot be said of software, and there are numerous cases of additional bugs
being introduced as a result of attempts to correct previously identified programming errors.
If the corruption by means of computer virus, voltage spike, or powerful radiation, is ignored, software,
unlike mechanical components, does not suffer from degradation due to wear or stress. For this
reason, all errors in software can reasonably be assumed to be design faults.
It is also for this reason that management of risks caused by software focus on the rigorous
methodologies required to limit the number and consequence of design faults. This is discussed further
in the section on standards.
32-bit integer 1
32-bit integer 2
Figure 1 a simple software operation
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Goal-setting regulation
The philosophy behind the safety regulation of the offshore petroleum industry in Australia highlights
that those creating hazards are responsible for making sure the risk of harm from that hazard is as low
as reasonably practicable (ALARP)
(3)
. This means that safety legislation does not set out a list of
prescriptive measures for managing risk, but puts the onus on Operators to identify the best way of
approaching risk reduction.
Following the July 1988 Piper Alpha disaster in the UK, the subsequent Cullen Public Inquiry report was
clear that prescription stifled continuous improvement in safety and diverted responsibility from those
who were creating the risk. It was also clear that those creating the risk were in the best position to fully
understand it and therefore best placed to identify appropriate control measures.
Although there are no explicit regulations that point Operators towards designing, installing, testing,
operating and maintaining control systems, they are significant issues and Australian law requires them
to be properly managed in a goal-setting framework that reduces any residual risk to ALARP.
LEGAL DUTIES
This section looks at the relevant portions of the legislation that apply to functional safety in the offshore
Australian petroleum industry.
In general terms, the law requires that any safety-related control system is designed, installed, tested,
maintained and operated in such a way as to reduce risks to ALARP. As is often the case with goal-
setting regulations most of these duties are general in nature; they do not have to specifically mention
control systems for the law to apply, nor do they specify exactly what must be done to comply.
For this reason, the discussion is based on the duties of various parties specified in the regulations, and
what this implies in terms of functional safety.
The word „plant‟ in the regulations refers to any machinery, equipment tool or component, including
software.
Operators
The overriding duty of Operators of offshore petroleum and greenhouse gas facilities is covered in
Clause 9 of the Offshore Petroleum and Greenhouse Gas Storage Act 2006.
Clause 9(1) is a general duty to take all reasonably practicable steps to ensure that the facility is safe,
and that all work and other activities are carried out in a safe manner.
These general duties are supplemented by a number of specific duties including: Clause 9(2) (c), “to
take all reasonably practicable steps to ensure that any plant, equipment… are safe”; 9(2) (e) “to take
all reasonably practicable steps to implement and maintain appropriate procedures and equipment for
the control of, and response to, emergencies at the facility.”
These duties imply that if control systems are used, then they must be designed in a way that will
reduce risks to ALARP.
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The duties apply to all safety-related control systems, the implication being that Operators should be
aware which, if any, of their control systems are safety related and take all reasonably practicable steps
to make them safe, including adequate testing and maintenance.
Persons in control of parts of a facility or particular work, and employers
As outlined in relevant sections of Clauses 10 and 11 of the Offshore Petroleum and Greenhouse Gas
Storage Act 2006, it is not only employers of people working on a facility who have very similar duties to
Operators. Anyone given responsibility or control of a part of a facility, or of any particular work carried
out at a facility, is subject to the same duties.
This extends the duty of care to include, among others, diving supervisors, contract labour, operators of
remotely controlled vehicles, and those in control of mobile drill rigs located temporarily on fixed
platforms.
Manufacturers
Clause 12(1) of the Offshore Petroleum and Greenhouse Gas Storage Act 2006 is relevant to anyone
who manufactures plant that they ought reasonably to expect will be used by members of the workforce
of a facility. It would be applicable, for example, to developers of electronic permit-to-work systems as
well as to manufacturers of automated pipe handling systems, gas detection and shutdown systems,
and dynamic positioning systems.
The manufacturers‟ duties differ from those placed on Operators, employers and persons in control of
parts of the facility or particular work in that it includes a requirement to carry out all reasonably
practicable research and testing necessary to discover and eliminate or minimise any risk, and make
the plant safe.
It also includes the duty to ensure that the plant is so designed and constructed as to be safe when
properly used so far as is reasonably practicable. For manufacturers of plant, the functional safety
aspects of this duty could relate to identifying possible methods of preventing the defeating of safety
devices, such as interlocks, and that manufacturers should be clear as to what comprises the intended
use of the plant they have manufactured.
Finally, the legal duty includes making available adequate written information about the use for which
the plant has been designed and tested, details of its design and construction, and any conditions
necessary to ensure that it will be safe when employed for its intended purpose (the use for which it
was designed and tested).
This implies that manufacturers of plant should provide information on inspection, testing and
maintenance and any other information necessary to meet the required legal duty.
Suppliers
Suppliers of plant are covered by Clause 13 of the Offshore Petroleum and Greenhouse Gas Storage
Act 2006. This requires suppliers to ensure that, so far as is reasonably practicable, at the time of
supply, the plant is in such condition as to be safe when properly used.
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It also requires suppliers to ensure that research, testing and examination are done to discover,
eliminate or minimise any risk to health or safety that may arise from the condition of the plant.
As for other duty holders, suppliers are obliged to make available adequate written or recorded
information in connection with the use of the plant. This information includes:
the condition of the plant at the time of supply;
any risk posed to the health and safety of personnel at the facility from the condition of
the plant and its usage; and
the steps required in order to eliminate such risk.
Persons
Clause 15 of the Offshore Petroleum and Greenhouse Gas Storage Act 2006 requires a worker at a
facility to take all reasonably practicable steps to ensure that no act or omission creates a risk or
increases an existing risk. Personnel are also duty-bound to cooperate with the facility Operator to meet
obligations imposed on them. The requirement specifically directs anyone on a facility to use equipment
“in accordance with any instructions given by the equipment supplier, consistent with the safe and
proper use of the equipment.”
These obligations would be relevant in cases where users of control systems deliberately defeat safety
systems such a guard interlocks.
Functional safety in Safety Cases
As discussed in the introductory remarks about goal-setting legislation, it is open to Operators of
facilities to specify the standards they use when reducing risks to ALARP.
Regulation 2.7 of the Offshore Petroleum (Safety) Regulations 2009 requires Operators to specify in
their Safety Case “all Australian and international standards that have been applied or will be applied in
relation to the facility or plant used on the facility”.
This implies that the standards used in the design, testing, operation and maintenance of control
systems must be included in the Safety Case for any facility that has safety-related control systems.
Control systems are specifically mentioned in Regulation 2.19 of the Offshore Petroleum (Safety)
Regulations 2009.
This regulation sets out a requirement on Operators to ensure that the Safety Case contains “adequate
provision for the facility, in the event of an emergency, in respect of: back-up power supply, lighting,
alarm systems, ballast control and emergency shut-down systems.”
Before an Operator can submit a Safety Case, a scope of validation may be agreed upon with NOPSA.
Validation activities may include functional safety aspects.
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AS LOW AS REASONABLY PRACTICABLE (ALARP)
The preceding sections contain references to the phrases „so far as is reasonably practicable‟ and „as
low as reasonably practicable‟. This is legal recognition that it is not always possible to completely
eliminate risk. A balanced decision needs to be made to determine the amount of sacrifice needed in
terms of time, resources and funding that it is reasonable to commit to achieve a given amount of risk
reduction.
If risks have been reduced so far as is reasonably practicable, then the residual risk is said to be as low
as reasonably practicable, usually referred to by the acronym ALARP.
This section attempts to tie up the various themes covered in previous paragraphs by giving guidance
on how to approach the concept of functional safety in control systems to ensure that all risks
associated with their use are ALARP.
The need for demonstration
As has been noted above, Operators are expected to detail in their Safety Cases that adequate
provision has been made with respect to shut-down systems. Operators should also be in a position to
demonstrate that they have done everything required to reduce risks from all hazards to ALARP.
It is possible that NOSPA inspectors will also ask for adequate demonstration that control system and
functional safety have been addressed on facilities, either during an inspection, or as a part of the
validation process relating to Safety Case submissions.
The role of standards
The introductory text in most Australian standards describes them as „living documents which reflect
progress in science, technology and systems‟. Standards therefore form a useful reference source
when identifying benchmarks for good practice, and in determining what is reasonably practicable.
Historically, there has been a slight difference in approach between standards aimed at machinery
safety, which tend to use qualitative, risk-graph approaches, and those originating in the process
industries that have traditionally favoured the use of quantitative approaches and Safety Integrity Levels
(SILs).
It is generally recognised that the risk-graph approach, while fine for simple components, does not deal
adequately with programmable systems and components. ISO 13849-2:2003 states, for example,
“this…standard does not give complete validation requirements for programmable electronic systems
and therefore can require the use of other standards.”
The gap between these two approaches is narrowing with the publication of standards that deal with the
inclusion of software-based systems. This convergence is illustrated in Figure 2, taken from AS 62061,
which shows the interrelationships between various international standards relating to the functional
safety of machinery.
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It is up to the Operator to select appropriate standards, and make an assessment as to whether or not
following a particular standard will result in a particular control measure being ALARP.
Current international standards on functional safety are based on the hazard identification and risk
assessment approach to designing for safety, and are clear in their requirements for a methodical
approach that limits to ALARP the possibility for systemic failures.
Safety of machinery and systems
AS 4024 Safety of Machinery
(incorporates ISO 12100 Safety of machinery Basic concept,
general principles of design and ISO 14121 Safety of machinery
Principles for risk assessment)
Design of safety-related electrical, electronic and programmable electronic control systems (SRECS) for machinery
Methodology using:
Safety-related control functions
System based approach
- Quantitative index of safety:
integrity level (SIL)
- SIL assignment methodology for SRECS
of machinery
- Architecture orientated
- Requirements for avoidance/control of
systematic failures.
- Index of safety:
Category/performance level
- Category assigned by qualitative risk
graphing
- Architechture oriented
Design objective for the
SRECS
Relevant standards
Electrical safety aspects of machinery
IEC 60204-1, Safety of machinery -
Electrical equipment of machinery
Part 1: General requirements
Design of complex subsystems
to SILs
IEC 61508, Funcrtional safety of
electrical, electronic and programmable
electronic safety-related systems
IEC 62061
Safety of machinery Functional safety
of safety-related electrical, electronic
and programmable electronic control
systems
Design of low complexity
subsystems to categories
ISO 13849-1 and 2 Safety of machinery
Safety related parts of control systems
(SRPCS)
-Part 1: General principles for design and
Part 2: Validation
Non=electrical SRPCS (mechanical,
pneumatic, etc.)
Electrical SRPCS
Figure 2 Interrelationship between AS4024, AS 62061 & ISO 13849
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Duty holder
Operator
Person in
control
Supplier Manufacturer
Process Safety
AS 61508 series
#
X X X
EEMUA Publication
222
X X
Machinery Safety
AS62061 Safety of
machinery *
#
X
X X X
ISO 13849 *
X X X X
AS 4024.1-2006
Series : Safety of
machinery^
X X X X
Bespoke systems
(such as custom-
coded software
systems)
AS 61508 series
#
X X
Notes
# These standards including, AS IEC 61511-2004 : Functional safety - Safety instrumented
systems for the process industry sector, are derived from AS 61508, and share a common
methodology.
* see diagram 1 for inter-relationship.
^ A useful reference for 'traditional' machinery type standards.
Table 2 – Typical functional safety standards and their relevance to duty holders under the
regulations.
These standards clearly define the types of documentation required to assist in the design process,
thus facilitating the legal obligations of duty holders to provide adequate information and enabling them
to make valuable demonstrations when developing Safety Cases.
These standards incorporate guidance on validation, verification and ongoing testing requirements of
control systems that all contribute to meeting various legal requirements.
There are, of course, other sources of guidance than standards, such as The Engineering Equipment
and Materials Users’ Association’s (EEMUA) Publication 222
(4)
.
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Any other equally effective means
Although the standards and approaches described in this document are acknowledged as authoritative
sources of good practice by industry practitioners, they are recommendations only, and are not to be
considered mandatory.
One of the greatest strengths of goal-setting legislation is that it allows innovation in risk reduction. It is
open to all duty holders to investigate different approaches to managing functional safety from those
outlined in this paper, provided they can demonstrate that the alternative solution is at least equally as
effective.
REFERENCES
(1)
Available in Australia as AS 61508.0-2006: Functional safety of electrical/electronic/programmable
electronic safety-related systems - Functional safety and AS 61508. Online overview can be found
at: http://www.iec.ch/functionalsafety/
(2)
The use of computers in safety-critical applications, the final report of the study group on the safety
of operational computer systems. HSE Books.
ISBN 9780717616206.
http://books.hse.gov.uk/hse/public/saleproduct.jsf?catalogueCode=9780717616206
(3)
http://www.nopsa.gov.au/document/Leaflet%20-%20Prescriptions%20and%
20Standards.pdf%20%20
(4)
The Engineering Equipment and Materials Users‟ Association (EEMUA) Publication 222 - Guide to
the Application of IEC 61511 to safety instrumented systems in the UK process industries. ISBN 0
85931 168 6. www.eemua.org.
The information in this technical bulletin is intended as a general guide only. The relevant Acts and Regulations should be
consulted for detailed information. This document should not be relied on as advice on the law or treated as a substitute for
legal advice in any relevant situation.
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