Hydrocarbon Processing - June 2022 - GP-14

SPECIAL FOCUS: PIPELINES & TRANSPORT
FIG. 5. The ALARP concept.
are as established on an F-N
curve, as shown in FIG. 4. Societal
risk is typically presented in
the F-N curve, which plots the
cumulative frequency of events
that can cause N + number of
fatalities vs. number of fatalities.
* Guidance on environmental risk
acceptance criteria:
° The broadly acceptable
environmental risk threshold
is 2.4 × 10-2
FIG. 3. Example of engineering assessment document structure.
FIG. 4. CSA Z662:23 proposed societal risk
acceptance criteria.
to a potential pathway forward for demonstrating
margins of safety for existing
pipelines vs. pipeline replacement, the
CSA Z662 Risk Management Task Force
has developed quantitative safety risk and
environmental risk acceptance guidelines
that are proposed for the 2023 standard
(at the time of this publication, this standard
has not yet been approved) as part of
the non-mandatory Risk Assessment Annex
(Annex B) in the CSA Z662 standard.
Note: Non-mandatory reliability-based
targets, as a function of safety and environmental
consequence factors for the
14 MAY/JUNE 2022 | GasProcessingNews.com
design of natural gas and low vapor pressure
(LVP) liquid hydrocarbon pipelines,
respectively, are provided in Annex O of
the current CSA Z662:19 standard. These
risk acceptance thresholds are expected to
be a useful tool in demonstrating pipeline
safety to stakeholders in the context of
both pipeline risk assessments and engineering
assessments. The proposed risk
acceptance criteria are as follows:
* Guidance on safety risk (likelihood
of failure × consequence of failure)
acceptance criteria:
° Individual risk (i.e., the
annual probability of fatality
for an individual situated at
a particular location): The
broadly acceptable individual
risk threshold is 1 × 10-6
/yr,
and the maximum tolerable risk
threshold is 1 × 10-4
/yr.
° Societal risk (i.e., a measure of
the risk where the consequence
considered is a function of the
expected number of fatalities):
The broadly acceptable and
maximum tolerable thresholds
/km-yr (the impactm3/km-yr,
and the
maximum tolerable risk threshold
is 2.4 m3
adjusted release volume). The
impact-adjusted release volume is
estimated with due consideration
of factors, including failure mode
and associate pipe opening,
pipeline diameter, flowrate,
product properties, sectionalizing
valve spacing, release detection,
isolation time and environmental
impact based on location.
With respect to the broadly acceptable
and maximum tolerable risk thresholds
noted in the above criteria, the region between
these two thresholds is considered
tolerable risk if it can be demonstrated to be
as low as reasonably practicable (ALARP),
as shown in FIG. 5. The triangle represents
the decreasing risk and the diminishing
proportional benefit as risk is reduced.
Demonstration of ALARP requires that
the cost of further risk reduction is grossly
disproportionate to the risk reduction
achieved. So, with respect to risk acceptance
thresholds, if it can be demonstrated
that the risk levels satisfy broadly acceptable
or ALARP requirements, a compelling
case for pipeline safety can potentially
be made in the context of a pipeline engi
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Hydrocarbon Processing - June 2022

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