© 2008 AcuTech Group, Inc - pscfiles.tamu.edu · © 2008 AcuTech Group, Inc Changes to NFPA 59A (continued) • Technical committee for NFPA 59A has worked to meet the requests of

© 2008 AcuTech Group, Inc

Mary Kay O’Connor Process Safety Center Process Safety Symposium

Making Safety Second Nature October 28-29, 2008

NASFM Project on LNG Vapor Dispersion and Source Term Modeling

David A. MooreBrad Fuller

Lee SalamoneTara Aboyoun

AcuTech Consulting Group2001 North Beauregard Street

Alexandria, VA 22311www.acutech-consulting.com

mailto:[email protected]


Scope and Objectives of the NASFM Project

• A project was initiated in early 2008 by the National Association of State Fire Marshals and funded by DOT. The objectives are:– Provide an independent evaluation and input to the LNG Source

Term and Vapor Dispersion Model Evaluation Protocols and Validation Database referenced by NFPA® 59A Standard for the Production, Storage, and Handling of Liquefied Natural Gas (LNG) 2009 Edition

– Assist NASFM and emergency responders in better understanding the strengths of various models used to understand the hazards of LNG in an onshore setting.

– Ensure tools are available for use by emergency responders participating in the siting of a potential LNG import terminal.


Key Aspects for the Fire Service

• Fire Service is a key stakeholder in the siting of LNG terminals

• This project will help the fire service:– Understand the different types of consequence models that can be

used to evaluate flammable vapor Exclusion Zones– Understand the process for vetting models and selecting models

“fit for purpose” for LNG siting– Applicability, advantages and disadvantages of different models– Impact on the Exclusion Zone distances for the LNG terminal


LNG Terminal Siting

• DOT/PHMSA/OPS regulates the siting and safety of LNG pipeline facilities, including LNG peak-shaving plants, under the Pipeline Safety Act of 1994 (P.L. 102-508) as amended. Implementing regulations for the Act, including provisions on facility siting, are found in 49 CFR 191 – 199.

• Standards for operation, maintenance, fire protection, and security at such facilities are chiefly found in 49 CFR 193 and incorporate National Fire Protection Association (NFPA) 59A standard.

• DOT/PHMSA/OPS also performs construction and operational safety inspections.

• The siting analysis includes:– Verification of LNG dike and impoundment volumes– Equipment spacing– Design spills– Exclusion zone calculations , using specified models historically

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Role of Fire Service in LNG Terminal Siting

• NASFM Publication “Fire Service Guidance for Participating in LNG Terminal Evaluation, Siting, and Operations” released in January 2007.– “Citizens and communities are likely to seek the opinions of public

safety officials about the risks of LNG during the siting review process. The fire service can be influential in the decision process and should be well-informed and involved early in the process.” (pg 21)

– Steps for Fire Service involvement in the LNG siting process


Fire Service has a Role Throughout the Siting Process


Step 3: Safety & Security Analysis, Pre-planning and Needs Assessment

• MEP Project is Directly Related to Step 3– LNG Hazards– Safety/Security Scenarios– Fire and Dispersion Modeling– Exclusion Zone Distances– Gap and Needs

Applicant Process

FERC Process

USCG Process

Fire Service Involvement


Changes to NFPA 59A (continued)

• Technical committee for NFPA 59A has worked to meet the requests of code users for new models to help them determine how far away (Exclusion Zone) to situate a plant from its neighbors to ensure ongoing safety

• Development of New Vapor Dispersion and Source Term Modeling Protocols– The code committee enlisted NFPA's Fire Protection Research

Foundation (FPRF) to develop protocols for evaluating vapor dispersion models, known as model evaluation protocols (MEP).

– The MEP can be used to evaluate future LNG models for LNG siting.

– It also serves as a reference database for models that have been evaluated.

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Changes to NFPA 59A 2009

• 5.3.3.6* The spacing of an LNG tank impoundment to the property line that can be built upon shall be such that, in the event of an LNG spill as specified in 5.3.3.7, an average concentration of methane in air of 50 percent of the lower flammability limit (LFL) does not extend beyond the property line that can be built upon, in accordance with a model that is acceptable for use by the authority having jurisdiction that has been evaluated by an independent body using the Model Evaluation Protocol facilities published by the NFPA Research Foundation report Evaluating Vapor Dispersion Models for Safety Analysis of LNG.

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Release Scenario/Potential Outcomes


Stages in a Release and the Downwind Dispersion Process


Modeling LNG Releases


Source Term Model

• Defines the Parameters of the Release Scenario– Chemical– Inventory for Release– Spill Rate– State (liquid or gas)– Pool Formation and

Vaporization– Duration

• Source Term MEP still being developed by FPRF


Vapor Dispersion Model

• Takes the output of the Source Term model to define the hazard zone.

• Dependant on– Source strength– Ambient conditions– Wind Speed– Wind Direction– Obstacles/Terrain– Concentration

• MEP that NASFM Panel is currently reviewingDownwind

Direction

Source Term

* Illustration Source: Gas Research Institute, LNG Vapor Dispersion Prediction with the DEGADIS Dense Gas Dispersion Model, Topical Report, April 1988 – July 1990.


Examples of Models Available for LNG Dispersion


NFPA 59A – New Model Evaluation Protocols

• The MEP can be used to agree on evaluation criteria for existing and future LNG models for LNG siting.

• It also is a useful repository for information on models that may encourage their improvement and development

• It allows for the introduction of a wider array of models than was presently codified

• However, it does create a new operating environment, i.e.’ a new frontier to embrace and manage


Model Evaluation Protocol

• Assess the suitability of dispersion models for predicting hazard ranges associated with large spills of LNG.

• The protocol is based on that developed by the EU SMEDIS project (Carissimo et al. 2001, Daish et al. 2000) for dense gas dispersion.

• Modified to make the MEP specifically applicable to the dispersion of LNG on land.


FPRF Deliverables

• MEP for LNG Vapor Dispersion Models– Currently only 3 models evaluated with MEP (DEGADIS,

FEM3A, Fluent)

• MEP for LNG Source Term Models– The initial spill (or source term) also needs to be evaluated using

approved models. Source term is the input to the vapor dispersion model, and together define the Exclusion Zone.

– Scheduled for completion December 2008

• Development of the Validation Database– The performance of the models (acceptable or recommended

models) is quantified using a range of data sets and performance measures.

– Scheduled for completion December 2008


Key MEP Elements• Questionnaire

– Detailed information on the model from a standardized Questionnaire that is completed by the ‘model developer’ or a ‘proponent for the model’

• Evaluation Criteria– Quantify the performance (statistical performance measures) of the

model by comparison of its predictions with observations from a Validation Database.

• Validation Database– Models predictions will be compared against

• Suitable datasets• Specific validation cases• Definition of physical comparison parameters

• Model Evaluation Report– Main output following application of the MEP

• Questionnaire (Scientific Assessment and Model Verification)• Reports Validation against evaluation criteria • Addresses model limitations• Contains conclusions


Benefits of Fire Service Participation on NASFM Panel

• Development of the MEP– NASFM Panel providing independent review of Source Term and Vapor

Dispersion MEPs

• Development of Validation Database– NASFM Panel providing independent review of Database and Criteria

• Understanding of the Application of MEP in Future LNG Siting– Panel is providing input to the utility of the MEP from their perspective


Conclusions and Questions

• Areas of particular interest:– Impact on the siting of projects due to flexibility of the

criteria and multiple available models rather than limited number of models used presently

– Ensuring that the MEP considers these effects sufficiently to maintain good siting decisions

– Ensuring that the users (fire marshals, first responders, owners and operators) have an appreciation of the MEP and the different outcomes and decisions that may be made given this performance based approach


NASFM Project Scope and Objectives

• Provide an independent evaluation and input to the LNG Source Term and Vapor Dispersion MEPs and Validation Database.

• Assist NASFM and emergency responders in better understanding the strengths of various models used to understand the hazards of LNG in an onshore setting.

• Ensure tools are available for use by emergency responders facing a potential LNG import terminal in their community.

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Selection of Technical Panel

• Criteria:– Experts in the topic of LNG modeling– Expert in chemical engineering– Academics, users and developers of LNG modeling tools– AHJ who need to be confident that the models used to make

decisions are “fit for purpose”

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Overview of Tasks in Project

• Review of the Model Evaluation Protocol (MEP) developed by the Fire Protection Research Foundation (FPRF)– Suggesting revisions to the MEP process, tools and Validation

criteria– Identify missing or modify validation criteria– Identify additional assessment tools (models) for the current MEP– Give feedback from the perspective of the fire service user– NASFM may incorporate these reports into its existing LNG safety

program, so that emergency responders receive these tools as part of the broader NASFM pipeline/hazardous materials safety projects

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Some conclusions from the review

– The steps of the process are acceptable as the MEP is based on SMEDIS

– Validation Database and Criteria need to be reviewed and aligned with the needs of NFPA 59A and land- based LNG terminal siting

– Conducting MEP and developing MER for a model is not a trivial task

– Source Term and Validation Database are a critical component of overall LNG MEP

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Some conclusions from the review

• Some models may show better performance under particular circumstances, so applicability range needs to be estimated as well to let the user know when to use it and for what purpose.

• A key value is setting validation standards is not only the short term approval or rejection of specific models, but to encourage model developers to enhance their model over a period of time.

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Likely recommendations in report

• Further guidance is needed for application of the MEP which would be helpful for those who are charged with implementation of such an approach – whether the reviewer is the AHJ or an expert consultant working on their behalf

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Further guidance needs to enhance the use of the MEP

• Areas of particular interest:– Impact on the siting of projects due to flexibility of the

criteria and multiple available models rather than limited number of models used presently

– Ensuring that the MEP considers these effects sufficiently to maintain good siting decisions

– Ensuring that the users (fire marshals, first responders, owners and operators) have an appreciation of the MEP and the different outcomes and decisions that may be made given this performance based approach

– Education will be required to explain these issues

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Further guidance needs to enhance the use of the MEP

• Practical guidance on:– the considerable effort required of a reviewer and

developer/proponent of a model when undertaking a full model evaluation

– the likely need for a reviewer to have repeated contact with the developer or proponent of a model over a lengthy period of time

– clarifying the level of verification demanded by the protocol– setting reasonable expectations for the process and outcomes of a

model evaluation– how to interpret these outcomes– the wider value of model evaluation in encouraging model

improvements

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Questions?

David A. MoorePresident & CEO

AcuTech Consulting Group2001 North Beauregard Street

Alexandria, VA [email protected]

mailto:[email protected]

Documents

© 2008 AcuTech Group, Inc - pscfiles.tamu.edu · © 2008 AcuTech Group, Inc Changes to NFPA 59A (continued) • Technical committee for NFPA 59A has worked to meet the requests of