Chemical Engineering July 2016 - 44

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tem itself and the distributed control system
(DCS), of which the safety system may be a
part. This is one reason why so many safety
experts call not only for the physical separation
of safety instrumented system (SIS) and
DCS components, but also for different engineering
staffs or vendors to be responsible
for each.
To answer the other questions, we need
to highlight two other standards. One is the
international standard IeC 61511 for SIS
in the process industries. Whether independent
or integrated into an overall basic
process control system (BPCS), the SIS is a
fundamental component of every industrial
process facility.
In this model, the industrial process is surFigure
1. Under a model
put forth under IEC standard
61511, an industrial process
is surrounded by a series of
risk-reduction layers that act
together to lower risk
the relationship between cybersecurity and
plant safety:
1.Can the " insecurity " of integrated control
systems influence the functional safety of
a plant?
2.What needs to be protected?
3. Can the principles developed for functional
safety be applied to security?
This article considers these questions and
includes operational examples and specific
recommendations for improving security and
safety at industrial facilities.
Safety and security standards
The International electrotechnical Commission
(IeC; Geneva, Switzerland; www.iec.ch)
standard IeC 61508 is the international standard
of rules for functional safety of electrical,
electronic and programmable electronic
safety-related systems. According to IeC
61508, functional safety is " part of the overall
safety that depends on functional and physical
units operating correctly in response to
their inputs. "
By this definition, the answer to the first
question posed earlier - Can the " insecurity "
of integrated control systems influence
the functional safety of a plant? - has to be
" yes. " In the examples cited above, vulnerabilities
to people and facilities were introduced.
Clearly, functional safety was compromised,
and while security breaches may
not have led to deaths or injuries, there is
no evidence to suggest that such a situation
could not occur in the future.
even ruling out malicious threats, the fact
remains that IT security-based vulnerabilities
can be found in all kinds of automation systems.
This includes the safety-related sys44
rounded
by different risk-reduction layers,
which collectively lower the risk to an acceptable
level (Figure 1). The risk reduction
claim for the safety layer is set by the safety
integrity level (SIL).
The first line of protection for any plant is
the control and monitoring layer, which includes
the BPCS. By successfully carrying
out its dedicated function, the BPCS reduces
the risk of an unwanted event occurring.
Typically, IeC 61511 stipulates that the risk
reduction claim of a BPCS must be larger
than 1 and smaller than 10. A risk-reduction
capability of 10 corresponds to SIL 1.
The cyberattack and IT vulnerability prevention
layer includes the SIS. The hardware
and software in this level perform individual
safety instrumented functions (SIFs). During
the risk and hazard analyses carried out as
part of the basic design process of every
plant, the risk-reduction factor to be achieved
by the protection layer is determined.
In most critical industrial processes, the
SIS must be rated SIL 3, indicating a riskreduction
factor of 1,000, to bring the overall
risk to an acceptable level.
At the mitigation layer, technical systems
are allocated, allowing mitigation of damages
in case the inner layers of protection
fail. In many cases, mitigation systems are
not encountered as being part of the safety
system, as they are only activated after an
event (that should have been prevented)
happens. However, in cases where the mitigation
system is credited as part of defining
additional measures, it may be covered by
the safety evaluation as well.
now consider the IeC standard for cybersecurity.
IeC 62443 covers the safe security
techniques necessary to stop cyber attacks
involving networks and systems at industrial
facilities.
ChemiCal engineering www.Chemengonline.Com July 2016
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Chemical Engineering July 2016

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