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Proposed Requirements for
Calculating Emergency Planning
Zones for Sour Wells, Sour
Pipelines and Sour Production
Facilities
Presented by:
Gary Neilson BSc(Hons) P.Phys
Public Safety Implementation Team
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Presentation Outline
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Background
Proposed new requirements
EPZ calculation process
Implications
Future work
• EUBMODELS Structure
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Background
• Project initiated to address issues heard
by Provincial Advisory Committee on
Public Safety and Sour Gas*
• Proposed EPZ calculation requirements
based on assessing the hazard footprint of
a sour gas release using dispersion
modelling
*Provincial Advisory Committee on Public Safety and Sour Gas Findings and
Recommendations Final Report December 2000
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Background
• In the past, disagreement between
experts and public about model
choices and inputs that will lead to
accurate, useful and credible results
• Difficult for EUB to make informed
decisions in the public interest without
full understanding of differences
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Background
• Draft requirements published mid-December 2003
– Early draft February 2002
– Technical workshop & focus groups
– Peer review/EUB testing of EUBMODELS
• Requesting feedback on
– clarity of the requirements/additional requirements
– the supporting EUBMODELS documentation and software
– March 31, 2004 (extended)
• Requirements will be included in future revision of
Guide 71 - Emergency Preparedness and Response
Requirements for the Upstream Petroleum Industry
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Proposed Requirements
• Address suite of PSSG Recommendations (17,18,
19, 58 and 62)
• Define the minimum standards to calculate an EPZ
to protect public SAFETY (protect against fatalities
or serious irreversible health effects)
• Replaces the simple release rate based equations (or
nomographs)
• EPZ derived from new requirements remains first
step. Actual size and shape of the final EPZ must
reflect site-specific features of the area
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Proposed Requirements
• EPZ more realistically calculated
– characterization of the release (representative gas analysis,
source conditions at exit calculated, real gas effects)
– dispersion modelling,
– consequence modelling to a toxic load based endpoint
(concentration AND exposure time important)
• Credit for PRACTICAL mitigation actions (e.g.
limiting release duration through ignition)
• No “reduced” EPZ as presently defined as single EPZ
includes mitigation actions – NO EUB PREAPPROVAL
• Applicable to new applications, ERP updates AND
interventions
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Proposed Requirements
Base Case
MANDATORY
REQUIREMENTS
(Minimum Standards)
Sour Gas Release Rates
Gas composition
Depressurization (REAL GAS EFFECTS)
Release Duration
Dispersion Modelling
Meteorological Conditions
Concentration Fluctuations
EPZ Endpoints
EUBMODELS (Screening
Level EPZ Calculation)
Technical Descriptions
and Formulations
User Guide & Tutorial
Software Package
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Release Rates
• For wells maximum release rates required as
described in Guide 56
• For pipelines mass release rate profile from a
guillotine break must be calculated using the
maximum licenced pressure
– account for the emergency shutdown valve (ESD)
trip set points
– the distance between ESD valves
– mass of gas in adjacent pipeline segments that
escapes before the valves close
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Depressurization - why are real gas
effects important?
• Ideal gas laws under predict EPZ
• Real gases can form liquid aerosol as they
expand and cool
• Well releases are sensitive to wellhead exit
conditions (pressure, temperature, hole
diameter)
• More detailed calculation may result in buoyant
release
• Pipelines usually dense due to pressures
• EUBMODELS Base Case always dense release CONSERVATIVE
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Release Duration
• Duration defines exposure time
• Duration for wells must be realistic for the scenario
(drilling, servicing or producing) and other sitespecific factors
• Duration for pipelines determined by transient mass
release through a guillotine break
• Countermeasures such as ignition that limit the
duration of the sour gas release are permissible
(documented and PRACTICAL)
• For pipelines ignition not allowed as a
countermeasure
– releases not typically long enough for manual
ignition
– self-ignition not guaranteed
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Dispersion Modelling
• Worst case Met conditions assumed
• Dispersion model used must account for
– real gas effects
– dense or buoyant releases
• For dense plumes parallel airflow model is acceptable
because a sour gas release from a well or pipeline
occurs at or near ground level
• Plumes that rise complex terrain model may be required
• EUBMODELS Base Case must still be included in the
documentation supporting an EPZ calculation as well as
the calculation using a complex terrain model for
comparison purposes
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Complex Terrain Criterion - H2S
Releases
• Requirements now address issues of terrain
• Buoyant releases may require complex terrain
modelling
• Compare terrain elevations in EPZ to terrain criteria
defined in EUBMODELS
• Criteria based on EUB Guide 60 (Flaring)
– kinetic energy lift sufficient to overcome temperature
gradient
complex
criterion
parallel
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Toxic Load End Points
• Endpoint described by toxic load criterion
– L=KCnt
– same adverse effect for low concentration over
longer time as high concentration for short time
– concentration weighted (n)
– K accounts for concentration fluctuations
(dispersion models only predict averages)
• Objective of endpoint is to provide
conservatism to protect public safety (i.e. if
level achieved would not expect fatality or
other serious irreversible adverse effect)
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EPZ Calculation Process
EUBMODELS Base
Case (Mandatory)
Acceptable
EPZ pre-approval from
EUB not required
EPZ to be
used for Public
Involvement
EPZ tuned to reflect
site specific features
EUBMODELS BC
Parameters varied
EUB
assessment
ERP
Acceptable
Alternate Methods
EUBMODELS BC must also be
modelled using alternate methods
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Implications
• Anticipate zones will change
• More effort required than previous simplistic
approach
– detailed documentation (explaining mitigation
actions, variation of base case parameters,
alternate methods)
• Responsibility on industry to ensure practical
mitigation measures used
• Operational implications (e.g. ESD valve trip
points)
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Future Work
• Toxic load endpoints need further discussion
– workshop on H2S toxicity
– objective to assist EUB in selecting “safety” endpoint
• Ignition timing lower limit needs to be defined
– workshop planned
• Address stakeholder comments
• Develop implementation strategy with
stakeholders depending on impact compared to
previous methods
• Revise Guide 71 – targeting fall 2004
• EUBRISK and EUBHVP – EUBMODELS can
be adapted possibly undertake in new fiscal year
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EUBMODELS Structure
EUBM ODELS
U S E R IN P U T
S p re a d s h e e t
Excel
USER O UTPUT
S p re a d s h e e t
Runs 54 times
for met matrix
E U B F la s h
E U B S la b
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Summary of PROPOSED Requirements
• Requirements in draft – Requirements in Guide 71
still apply
• No “reduced EPZ” application (size of EPZ
determined by varying parameters) - single EPZ can
be taken forward to communities for discussion and
fine tuning
• EUB review post public involvement as part of ERP
assessment – REALISTIC MITIGATION
• Requirements applicable to new applications, ERP
updates or interventions
• Provide clarity to assist in EUB decisions
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Project Website
www.eub.gov.ab.ca/BBS/new/Projects/sgr.htm
[email protected]
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