LNG Exclusion Zones
LNG Exclusion Zones-Radiant Heat Flux & Vapor Dispersion Modeling
Exclusion zones are established to protect the public from the potential consequences of an unintended release of LNG. Operators are required to legally control all activities in the area surrounding an LNG facility which may be impacted by radiant heat flux from a fire or from vapor dispersion from initial release through formation of a cloud or pool to final dispersion. The endpoint thresholds are prescribed by regulations in 193.2057 and 193.2059.
Operators use hazard analysis software based on failure release scenarios to predict the extent of an exclusion zone. For vapor dispersion modeling purposes, the physical process is typically divided into two phases: source term and atmospheric dispersion. The source term phase describes what occurs immediately after a release where the fluid behavior (LNG and its vapor) is mainly controlled by release conditions. After the source term phase, the atmosphere dominates the vapor dispersion behavior.
PHMSA approves which radiant heat flux and atmospheric dispersion hazard analysis software can be used in determining the extent of an exclusion zone. Petitioners must demonstrate that their hazard modeling software has been validated by experimental test data by using a three-stage process described in the model evaluation protocol (MEP). The MEP is based on three distinct phases: scientific assessment, model verification and model validation. The petitioner submits a Model Evaluation Report (MER) which PHMSA evaluates and issues a Final Decision. The Final Decision provides PHMSA's summary of findings, limitations and conclusions. The Final Decision also provides additional clarifications and information that must be included with model submissions for use in exclusion zone calculations.
The following software is approved for use:
Radiant Heat Flux Models
- LNGFIRE3: A Thermal Radiation Model for LNG Fires
Vapor Dispersion Models and Links to Final Decisions
- LNG Vapor Dispersion Prediction with the DEGADIS 2.1 Dense Gas Dispersion Model
- Evaluation of Mitigation Methods for Accidental LNG Releases. Volume 5: Using FEM3A for LNG Accident Consequence Analyses
- Gexcon's FLACS v9.1r2 https://www.regulations.gov/search?filter=phmsa-2011-0101
- DNV's Process Hazard Analysis Software Tool (Phast) version 6.6/6.7 https://www.regulations.gov/search?filter=phmsa-2011-0075
- DNV's Process Hazard Analysis Software Tool (Phast) version 8.4 https://www.regulations.gov/search?filter=phmsa-2021-0041 and https://www.phmsa.dot.gov/regulatory-compliance/phmsa-guidance/approval-phast-v84-alternate-model-liquefied-natural-gas-lng
Model Evaluation Protocol Documents
- For Modeling Software used to Calculate Source Term
- MEP at: https://primis.phmsa.dot.gov/matrix/FilGet.rdm?fil=17427
- Guide for Model Validation Database (MVD) at: https://primis.phmsa.dot.gov/matrix/FilGet.rdm?fil=19366
- MVD at: https://primis.phmsa.dot.gov/matrix/FilGet.rdm?fil=19388
- MEP at: https://primis.phmsa.dot.gov/matrix/FilGet.rdm?fil=17427
- For Modeling Software used to Predict Flammable Vapor Hazards
- Model Description Questionnaire: https://primis.phmsa.dot.gov/matrix/FilGet.rdm?fil=14581
- MEP at: https://primis.phmsa.dot.gov/matrix/FilGet.rdm?fil=21819
- Guide for MVD at: https://primis.phmsa.dot.gov/matrix/FilGet.rdm?fil=21820
- MVD: https://primis.phmsa.dot.gov/matrix/FilGet.rdm?fil=18635 and https://primis.phmsa.dot.gov/matrix/FilGet.rdm?fil=18634
- Model Description Questionnaire: https://primis.phmsa.dot.gov/matrix/FilGet.rdm?fil=14581
- For Modeling Software used to Predict Toxic Vapor Hazards
- For Modeling Software used to Predict Vapor Cloud Explosion Hazards
- For Modeling Software used to Calculate Boiling Liquid Expanding Vapor Explosion Hazards
Last updated: Thursday, August 7, 2025