Evaluation of DEGADIS 2.1 

Using Advisory Bulletin ADB-10-07 

Cooperating Agency: 

U.S. Department of Transportation, 

Pipeline and Hazardous Materials 

Safety Administration 

Washington, DC 20426

Federal Energy

Regulatory

Commission

Office of 

Energy Projects

July 2011 
EVALUATION OF DEGADIS 2.1 

USING ADVISORY BULLETIN ADB-10-07 

TABLE OF CONTENTS 

Page

1.0 Introduction .........................................................................................................................1 

1.1 Background...................................................................................................................1 

1.1.1 Model Evaluation Protocol.....................................................................................1 

1.1.2 PHMSA Advisory Bulletin ADB-10-07 ................................................................2 

1.2 Project Scope ................................................................................................................3 

2.0 Results of the 2007 Partial DEGADIS Evaluation..............................................................4 

2.1 Scientific Assessment and Verification ........................................................................4 

2.2 Application of the Full Validation Database to DEGADIS..........................................4 

2.2.1 Validation Cases Modeled (MER Section 6.2.1) ...................................................4 

2.2.2 Model Performance for Key Statistical Evaluation Parameters (MER 

Section 6.2.2)..........................................................................................................5 

2.2.3 Evaluation Against Quantitative Assessment Criteria (MER Section 6.2.3) .........6 

2.2.4 Additional Comments (MER Section 6.2.4) ..........................................................7 

3.0 Application of PHMSA Advisory Bulletin ADB-10-07 ...................................................17 

3.1 Source Geometry Handled by the Dispersion Model (MER Section 

2.1.1.2; ADB-10-07 Section 1.a-d).............................................................................17 

3.2 Wind Field (MER Section 2.2.2.1; ADB-10-07 Section 2)........................................17 

3.3 Stratification (MER Section 2.2.2.3; ADB-10-07 Section 3) .....................................17 

3.4 Terrain Types Available (MER section 2.2.3.1; ADB-10-07 Section 4) & 

Complex Effects (MER section 2.3.1.2; ADB-10-07 Section 4)................................18 

3.5 Obstacle Types Available (MER Section 2.2.4.1; ADB-10-07 Section 5) & Complex 

Effects (MER Section 2.4.3.1; ADB-10-07 Section 5)...............................................18 

3.6 Turbulence Modeling (MER Section 2.3.1.5; ADB-10-07 Section 6) .......................18 

3.7 Boundary Conditions (MER Section 2.3.1.7; ADB-10-07 Section 7)........................19 

3.8 Complex Effects: Aerosols (MER Section 2.3.1.1; ADB-10-07 Section 8)...............19 

3.9 Computational Mesh (MER Section 2.4.3.1; ADB-10-07 Section 9).........................20 

3.10 Discretization Methods (MER Section 2.4.2.3; ADB-10-07 Section 10)...................20 

3.11 Sources of Model Uncertainty (MER Section 2.6; ADB-10-07, Section 11).............20 

3.12 Sensitivity to Input (MER Section 2.6.4; ADB-10-07 Section 12).............................20 

3.13 Limits of Applicability (MER Section 2.7; ADB-10-07 Section 13) .........................22 
EVALUATION OF DEGADIS 2.1 

USING ADVISORY BULLETIN ADB-10-07 

TABLE OF CONTENTS (cont’d) 

Page

ii

3.14 Evaluation Against the MEP Quantitative Assessment Criteria (MER 

Section 6.2.4; ADB-10-07 Section 14) .......................................................................23 

3.14.1 Uncertainty Analysis of Model Input...................................................................23 

3.14.2 Uncertainty Analysis of Model Output ................................................................38 

3.14.3 Uncertainty Analysis of Experimental Data.........................................................42 

3.14.4 Uncertainty Analysis Results ...............................................................................46 

3.14.5 Additional Specific Performance Measures .........................................................46 

3.14.6 Individual Specific Performance Measures..........................................................46 

3.14.7 Model Input/Output Results .................................................................................46 

3.14.8 Specific Performance Measures Results ..............................................................47 

3.14.9 Input and Output Files..........................................................................................47 

4.0 Conclusions .......................................................................................................................48 

4.1 Scientific Assessment .................................................................................................48 

4.2 Verification .................................................................................................................50 

4.3 Validation....................................................................................................................51 

4.4 Sensitivity Analyses....................................................................................................54 

4.5 Model Suitability and Limitations ..............................................................................55 

APPENDIX A SENSITIVITY CASE RESULTS 

APPENDIX B REFERENCES 

APPENDIX C LIST OF PREPARERS 
EVALUATION OF DEGADIS 2.1 

USING ADVISORY BULLETIN ADB-10-07 

TABLE OF CONTENTS (cont’d) 

Page

iii

LIST OF TABLES 

2.2-1 SPM Evaluation against Quantitative Assessment Criteria: Overall Trial 

Average.........................................................................................................................6 

2.2-2 SPM Evaluation against Quantitative Assessment Criteria: Individual Trial 

Average................................................................................................................... 8-11 

3.12-1 Sensitivity Case Designations.....................................................................................21 

3.14-1 Pool Diameters as a Function of Vaporization Rate...................................................24 

3.14-2 Distance to LFL Uncertainty Due to Pool Spread Velocity and Vaporization 

Rate .............................................................................................................................25 

3.14-3 Distance to LFL Uncertainty Due To Surface Roughness Length: Maplin 

Sands...........................................................................................................................28 

3.14-4 Distance to LFL Uncertainty Due To Surface Roughness Length: 

Burro & Coyote ..........................................................................................................29 

3.14-5 Concentration Uncertainty Due To Surface Roughness Length: Thorney Island.......30 

3.14-6 Sensitivity Case Inputs................................................................................................33 

3.14-7 Sensitivity of the Water Transfer Sub-Model.............................................................34 

3.14-8 Effect of Time-Average on the Maximum Arc-wise Concentration .................... 35-36 

3.14-9 Effect of Time-Average on the Plume Width .............................................................37 

3.14-10 Comparison of Interpolation / Extrapolation Methodologies: Experiment 

Results.........................................................................................................................39 

3.14-11 Comparison of Interpolation / Extrapolation Methodologies: Model Results ............40 

3.14-12 Experimental and Model Results for Lower Flammability Limits .............................41 

3.14-13 Interpolation and Extrapolation of the Experimental and Model Results...................41 

3.14-14 Uncertainty in the Sensor Measurement of Gas Concentration............................ 43-45 
EVALUATION OF DEGADIS 2.1 

USING ADVISORY BULLETIN ADB-10-07 

TABLE OF CONTENTS (cont’d) 

Page

iv

LIST OF FIGURES 

2.2-1 Short Time Average Measured and Predicted Concentrations ...................................13 

2.2-2 Long Time Average Measured and Predicted Concentrations ...................................13 

2.2-3 Short Time Average Measured and Predicted Distance to LFL .................................15 

2.2-4 Short Time Average MG and VG...............................................................................16 

2.2-5 Long Time Average MG and VG ...............................................................................16 

4.3-1 Predicted Concentration against Measured Concentration .........................................52 
ACRONYMS & ABBREVIATIONS 

v

ABS American Bureau of Shipping 

Advisory Bulletin Pipeline and Hazardous Materials Safety Administration 

Advisory Bulletin ADB-10-07 

cm centimeter 

C.F.R. Code of Federal Regulations 

CSF concentration safety factor 

CSF_LFL concentration safety factor at the lower flammability limit 

DSF distance safety factor 

DSF_LFL distance safety factor to the lower flammability limit 

FAC2 factor of 2 

FERC or Commission Federal Energy Regulatory Commission 

FPRF Fire Protection Research Foundation 

km kilometer 

LFL lower flammability limit 

LNG liquefied natural gas 

m meter 

m/s meters per second 

MDA Modeler’s Data Archive 

MEP Model Evaluation Protocol 

MER Model Evaluation Report 

MG geometric mean bias 

MRB mean relative bias 

MRSE mean relative square error 

NASFM National Association of State Fire Marshals 

NFPA National Fire Protection Association 

PHMSA Pipelines and Hazardous Materials Safety Administration 

of the U.S. Department of Transportation 

SPM statistical performance measure 

VG geometric variance 
1.0 INTRODUCTION 

1.1 BACKGROUND 

In the United States, Title 49, Code of Federal Regulations (C.F.R.), Part 193 

prescribes the federal safety standards for liquefied natural gas (LNG) facilities. The 

siting requirements in Subpart B specify that each LNG container and LNG transfer 

system must have vapor-gas dispersion exclusion zones calculated in accordance with 

§193.2059. The regulation specifically approves the use of two models for performing 

these calculations, DEGADIS and FEM3A, but also allows the use of alternative models 

approved by the U.S. Department of Transportation. 

The integral model DEGADIS was developed for the Gas Research Institute and 

the U.S. Coast Guard specifically to account for effects such as gravity spreading, 

negative or positive buoyancy effects on air entrainment, surface to cloud heat transfer, 

and phase change energy effects associated with air humidity in modeling dispersion of 

dense gases. The theoretical and experimental basis for the model was described in Gas 

Research Institute Report No. 89/0242, LNG Vapor Dispersion Prediction with the 

DEGADIS Dense Gas Dispersion Model. Extensive vapor dispersion experimental and 

analytical work, beginning in 1982, was also conducted prior to adoption of DEGADIS 

into the federal regulations in 1997 (RSPA, 1997). 

1.1.1 Model Evaluation Protocol 

In 2006, the Fire Protection Research Foundation (FPRF), at the request of the 

National Fire Protection Association (NFPA), began to develop guidance to be used in 

assessing vapor dispersion models in analyzing LNG facilities. The main focus of this 

effort was to develop a means to review dispersion models based on their scientific basis 

and through comparison with experimental data. The result of this study, released in 

2007, was a Model Evaluation Protocol (MEP) that could be applied to determine the 

suitability of any dispersion model to simulate dispersion of LNG spills on land (Ivings et 

al., 2007). In 2009, the NFPA LNG Technical Committee revised the 2009 edition of 

NFPA 59A, Standard for the Production, Storage, and Handling of Liquefied Natural 

Gas, to remove the prescription of DEGADIS and require that a model be acceptable to 

the Authority Having Jurisdiction based on an evaluation using the MEP. 

The MEP is based on the European Union Scientific Model Evaluation of Dense 

Gas Dispersion Models, known as the SMEDIS protocol, which is in turn based on 

criteria set by the Council of European Communities Model Evaluation Group on Heavy 

Gas Dispersion. The MEP consists of three stages: scientific assessment; verification; and 

validation. Initially, the physical, mathematical and numerical basis of the model is 

reviewed (i.e., scientific assessment). Then, the model developer provides evidence 

demonstrating that the model correctly implements the bases identified during scientific 

assessment (i.e. verification). Finally, various simulations are performed with the model 
2 

and compared to a database of experimental results from wind tunnel and field trial tests 

(i.e. validation) (Ivings et al., 2007). 

Results of the scientific assessment, model verification, and validation are 

contained in the Model Evaluation Report (MER). Ivings et al. (2007) specifies that the 

MER is composed of eight sections: 

 Section 0. Evaluation information; 

 Section 1. General model description; 

 Section 2. Scientific basis of model; 

 Section 3. User-orientated basis of model; 

 Section 4. Verification performed; 

 Section 5. Evaluation against MEP qualitative assessment criteria; 

 Section 6. Validation performed and evaluation against MEP quantitative 

assessment criteria; and 

 Section 7. Conclusions 

The results of application of the MEP to a specific model, as summarized in these 

seven sections of the MER, can then be used as a basis for establishing the limitations 

and safety margins of the dispersion model. 

As part of the protocol development, the MEP was partly applied to both 

DEGADIS and FEM3A. Based on the scientific assessment and model verification, the 

limits of applicability of both models were described and an assessment of previous 

validations were given. However, the lack of a standard validation database prevented 

application of the full MEP from being within the scope of that report (Ivings et al., 

2007). In February 2009, the FPRF completed and released both the validation database 

and the “Guide to the LNG Model Validation Database,” with subsequent revisions in 

September 2009 and May 2010 (Coldrick et al., 2010). Validation of DEGADIS or 

FEM3A against the database was not performed as application of the remaining portions 

of the MEP was not within the scope of that effort. 

1.1.2 PHMSA Advisory Bulletin ADB-10-07 

In 2009, the National Association of State Fire Marshals (NASFM) released an 

independent review of the MEP. The goal of NASFM’s report, “Final Report: Review of 

the LNG Vapor Dispersion Model Evaluation Protocol,” was to ensure that hazard 

models evaluated with the MEP process were suitable for the specific situations in which 

LNG facilities were being planned (AcuTech, 2009). The panelists for the NASFM 

effort suggested improvements to the MEP and also identified difficulties in using this 

approach in a regulatory setting. 
3 

After reviewing the MEP report and validation database issued by the FPRF in 

2007 and 2010, as well as the NASFM study, the U.S. Department of Transportation’s 

Pipelines and Hazardous Materials Safety Administration (PHMSA) issued Advisory 

Bulletin ADB-10-07 (Advisory Bulletin) to provide guidance on obtaining approval of 

alternative vapor-gas dispersion models under Subpart B of 49 C.F.R. Part 193 (PHMSA, 

2010). The approach is based on the scientific assessment, verification, and validation of 

the MEP with adjustments to address the concerns raised by NASFM, as well as by staff 

of the Federal Energy Regulatory Commission (FERC or Commission). 

1.2 PROJECT SCOPE 

This document provides the complete MEP, as adjusted by modifications from the 

PHMSA Advisory Bulletin, to the DEGADIS dense gas vapor dispersion model specified 

in 49 C.F.R. § 193.2059. This serves two purposes: (1) completing the MEP for 

DEGADIS partially done by Ivings et al. (2007); and (2) illustrating the appropriate level 

of information requested by the Advisory Bulletin for obtaining PHMSA approval of an 

alternative vapor-gas dispersion model as allowed by §193.2059(a). 

The document is intended for developers/evaluators who are going to submit a 

request to PHMSA for an alternative model approval under 49 C.F.R. § 193.2059(a). 

Sections 2.0 and 3.0, as well as the validation database, provide an example of the level 

of detail requested by ABD-10-7. Section 4.0 provides an example of the suitability and 

limitation descriptions which would be included in a public PHMSA approval. 

Completion of the MEP and the DEGADIS validation work was performed by 

FERC staff. The validation work which accompanies this report is included in the Excel 

spreadsheet, entitled “DEGADIS Validation Database.xls,” being issued concurrently 

with this document. Review of the MEP results and limitations for the suitable use of the 

DEGADIS model in exclusion zone calculations was done by staff of the PHMSA. 
4 

2.0 RESULTS OF THE 2007 PARTIAL DEGADIS EVALUATION 

2.1 SCIENTIFIC ASSESSMENT AND VERIFICATION 

Appendix B 10.2 of Ivings et al., (2007) addressed all of the sections of the MEP 

guidance, except for Section 6.2, “Evaluation against MEP quantitative assessment 

criteria.” The conclusions of Appendix B are available upon request from the FPRF and 

are not repeated in this document. Certain sections of the scientific assessment that were 

addressed did not provide enough detail to thoroughly evaluate the limitations of the 

model. As discussed in the following sections, the Advisory Bulletin was used to address 

those areas. 

2.2 APPLICATION OF THE VALIDATION DATABASE TO DEGADIS 

Using the LNG Model Validation Database, the following sections of the MEP 

can now be completed for the DEGADIS model (Coldrick et al., 2010): 

 6.2.1 Validation cases modeled; 

 6.2.2 Model performance for key statistical evaluation parameters; 

 6.2.3 Evaluation against quantitative assessment criteria; and 

 6.2.4 Additional comments. 

2.2.1 Validation Cases Modeled (MER Section 6.2.1) 

The DEGADIS model is limited to dispersion over unobstructed level terrain with 

uniform roughness length specified by the user. Therefore, the current validation study is 

limited to the following field trials and wind tunnel trials conducted at full scale: 

 Maplin Sands 27, 34, 35; 

 Burro 3, 7, 8, 9; 

 Coyote 3, 5, 6; 

 Thorney Island 45, 47; 

 CHRC A; 

 BA-Hamburg DA0120 (Unobstructed), DAT223 (Unobstructed 2); and 

 BA-TNO TUV01, FLS. 

The DEGADIS model is also limited to providing the concentration and 

temperature along the vapor cloud centerline. Parameters are provided to determine the 

concentration at crosswise and vertical locations along the vapor cloud, but similar 

parameters are not provided for the temperature distribution. Therefore, values of 

temperatures are not provided for evaluation. 
5 

2.2.2 Model Performance for Key Statistical Evaluation Parameters (MER 

Section 6.2.2) 

The model results are compared to the experimental measurements to develop the 

following statistical performance measure (SPM) values: mean relative bias (MRB); 

geometric mean bias (MG); mean relative square error (MRSE); geometric variance 

(VG); factor of 2 (FAC2); concentration safety factor (CSF); concentration safety factor 

at the lower flammability limit (CSF_LFL); distance safety factor (DSF); and distance 

safety factor at the lower flammability limit (DSF_LFL). The SPM values are shown in 

Table 2.2-1. Shaded cells indicated where the SPM were not within the MEP acceptance 

criteria. 

Table 2.2-1: 

SPM Evaluation against Quantitative Assessment Criteria: Overall Trial Average 

Quantitative Criteria 

Data Set

-0.4<MRB <0.4 

0.67< MG<1.5 

MRSE<2.3 

VG<3.3 

FAC2 >50% 

0.5<CSF<2 

0.5< CSF_LFL<2 

0.5<DSF<2 

0.5< DSF_LFL<2 

Maximum Arc-wise Gas Concentration 

Field Trials 

(Short Time Avg.) -0.47 0.60 0.49 1.80 58% 1.93 1.80 N/A N/A

Field Trials 

(Long Time Avg.) -0.77 0.41 0.92 3.76 36% 3.13 N/A N/A N/A

Wind-Tunnel Tests 

(Scaled) 0.79 2.43 0.80 2.84 36% 0.47 N/A N/A N/A

Maximum Gas Concentration Arc-wise Distance 

Field Trials 

(Short Time Avg.) -0.32 0.72 0.21 1.25 89% N/A N/A 1.47 1.43

Field Trials 

(Long Time Avg.) -0.29 0.74 0.19 1.23 89% N/A N/A 1.43 N/A

Wind-Tunnel Tests 

(Scaled) 0.50 1.68 0.32 1.42 68% N/A N/A 0.62 N/A
6 

Table 2.2-1 (cont’d): 

SPM Evaluation against Quantitative Assessment Criteria: Overall Trial Average 

Quantitative Criteria 

Data Set

-0.4<MRB <0.4 

0.67< MG<1.5 

MRSE<2.3 

VG<3.3 

FAC2 >50% 

0.5<CSF<2 

0.5< CSF_LFL<2 

0.5<DSF<2 

0.5< DSF_LFL<2 

Maximum Point-wise Gas Concentration 

Field Trials 

(Short Time Avg.) 0.52 3.73 1.28 >1,000 46% 0.91 N/A N/A N/A

Field Trials 

(Long Time Avg.) -0.12 1.28 1.26 >1,000 33% 2.70 N/A N/A N/A

Wind-Tunnel Tests 

(Scaled) 0.24 1.50 0.48 11.92 69% 1.07 N/A N/A N/A

Cloud Width 

Field Trials 

(Short Time Avg.) 0.46 1.61 0.28 1.35 84% N/A N/A 0.64 N/A

Field Trials 

(Long Time Avg.) 0.24 1.28 0.12 1.14 92% N/A N/A 0.81 N/A

Wind-Tunnel Tests 

(Scaled) -0.09 0.91 0.03 1.03 100% N/A N/A 1.11 N/A

2.2.3 Evaluation Against Quantitative Assessment Criteria (MER Section 6.2.3) 

With the exception of the maximum gas concentration arc-wise distance SPM 

values, DEGADIS does not meet the MEP quantitative assessment criteria. The SPM 

values for maximum arc-wise gas concentration indicate DEGADIS may over-predict 

maximum arc-wise concentrations by more than a factor of 2 with a moderate to large 

degree of scatter. The SPM values for the maximum point-wise gas concentration 

indicate DEGADIS may under-predict or over-predict maximum point-wise 

concentrations by more than a factor of 2 with an extremely high degree of scatter. The 

SPM values for plume width indicate DEGADIS may under-predict cloud widths by less 

than a factor of 2 with a low degree of scatter. The results also indicate that DEGADIS is 

more over-predictive and generally shows less scatter for long time averages than short 

time averages. 
7 

2.2.4 Additional Comments (MER Section 6.2.4) 

As stated in the Advisory Bulletin, model predictions outside the quantitative 

assessment criteria do not necessarily mean that the model is unacceptable. However, 

such results may alternatively impact the safety factor associated with the model. 

Based on the MEP groups, it would appear that DEGADIS is generally overpredictive by more than a factor of 2 and therefore additional safety margins may be seen 

as over-burdensome. However, upon examination of individual test and sensor data, 

SPM trends become clearer in the model predictions, as shown in Table 2.2-2. Results of 

the individual tests and sensor data trends are discussed below. 
8 

Table 2.2-2: 

SPM Evaluation against Quantitative Assessment Criteria: Individual Trial Average 

Quantitative Criteria 

Data Set

-0.4<MRB <0.4 

0.67< MG<1.5 

MRSE<2.3 

VG<3.3 

FAC2 >50% 

0.5<CSF<2 

0.5< CSF_LFL<2 

0.5<DSF<2 

0.5< DSF_LFL<2 

Maximum Arc-Wise Gas Concentration 

Maplin Sands 27 (short) -0.08 0.93 0.37 1.55 75% 1.29 1.40 N/A N/A

Maplin Sands 34 (short) 0.24 1.28 0.06 1.06 100% 0.78 0.74 N/A N/A

Maplin Sands 35 (short) -0.33 0.71 0.17 1.20 83% 1.45 1.28 N/A N/A

Burro 3 (short) -1.00 0.32 1.05 2.48 0% 3.31 3.37 N/A N/A

Burro 3 (long) -1.37 0.18 1.90 21.49 0% 5.92 N/A N/A N/A

Burro 7 (short) -0.79 0.42 0.78 2.64 33% 2.62 1.86 N/A N/A

Burro 7 (long) -1.09 0.28 1.26 5.61 0% 3.75 N/A N/A N/A

Burro 8 (short) 0.08 1.09 0.21 1.25 75% 1.01 0.77 N/A N/A

Burro 8 (long) -0.09 0.90 0.36 1.50 50% 1.35 N/A N/A N/A

Burro 9 (short) -0.64 0.51 0.46 1.70 67% 2.04 1.95 N/A N/A

Burro 9 (long) -0.80 0.41 0.80 2.89 33% 2.78 N/A N/A N/A

Coyote 3 (short) -0.93 0.36 0.91 3.36 0% 2.88 2.78 N/A N/A

Coyote 3 (long) -1.42 0.17 2.02 25.27 0% 6.30 N/A N/A N/A

Coyote 5 (short) -0.57 0.56 0.33 1.44 75% 1.80 1.77 N/A N/A

Coyote 5 (long) -1.17 0.26 1.40 9.10 0% 4.05 N/A N/A N/A

Coyote 6 (short) -0.68 0.49 0.50 1.48 75% 2.10 2.06 N/A N/A

Coyote 6 (long) -1.03 0.32 1.08 3.69 0% 3.21 N/A N/A N/A

Thorney Island 45 (long) -0.29 0.74 0.20 1.24 89% 1.42 N/A N/A N/A

Thorney Island 47 (long) -0.28 0.75 0.18 1.21 83% 1.42 N/A N/A N/A

CHRC A (scaled) 0.31 1.36 0.10 1.11 100% 0.74 N/A N/A N/A

Hamburg DA0120 (scaled) 1.15 3.81 1.37 6.56 13% 0.28 N/A N/A N/A

Hamburg DAT 223 (scaled) 0.63 1.97 0.56 1.95 33% 0.56 N/A N/A N/A

TNO FLS (scaled) 0.81 2.42 0.75 2.46 17% 0.44 N/A N/A N/A
9 

Table 2.2-2 (cont’d): 

SPM Evaluation against Quantitative Assessment Criteria: Individual Trial Average 

Quantitative Criteria 

Data Set

-0.4<MRB <0.4 

0.67< MG<1.5 

MRSE<2.3 

VG<3.3 

FAC2 >50% 

0.5<CSF<2 

0.5< CSF_LFL<2 

0.5<DSF<2 

0.5< DSF_LFL<2 

Maximum Gas Concentration Arc-Wise Distance 

Maplin Sands 27 (short) -0.08 0.92 0.10 1.11 100% N/A N/A 1.13 1.20

Maplin Sands 34 (short) 0.16 1.18 0.03 1.03 100% N/A N/A 0.85 0.80

Maplin Sands 35 (short) -0.26 0.77 0.11 1.12 100% N/A N/A 1.33 1.19

Burro 3 (short) -0.63 0.52 0.43 1.60 50% N/A N/A 1.96 2.21

Burro 3 (long) -0.55 0.56 0.35 1.47 75% N/A N/A 1.82 N/A

Burro 7 (short) -0.65 0.50 0.56 1.93 33% N/A N/A 2.18 1.52

Burro 7 (long) -0.64 0.50 0.56 1.93 33% N/A N/A 2.17 N/A

Burro 8 (short) 0.05 1.05 0.10 1.11 100% N/A N/A 1.00 0.87

Burro 8 (long) 0.04 1.04 0.11 1.11 100% N/A N/A 1.02 N/A

Burro 9 (short) -0.41 0.66 0.22 1.27 67% N/A N/A 1.57 1.54

Burro 9 (long) -0.36 0.69 0.21 1.25 67% N/A N/A 1.52 N/A

Coyote 3 (short) -0.55 0.57 0.31 1.39 100% N/A N/A 1.77 1.78

Coyote 3 (long) -0.48 0.61 0.24 1.29 100% N/A N/A 1.65 N/A

Coyote 5 (short) -0.36 0.70 0.13 1.15 100% N/A N/A 1.44 1.48

Coyote 5 (long) -0.14 0.87 0.05 1.05 100% N/A N/A 1.17 N/A

Coyote 6 (short) -0.48 0.62 0.23 1.27 100% N/A N/A 1.63 1.67

Coyote 6 (long) -0.45 0.63 0.20 1.23 100% N/A N/A 1.58 N/A

Thorney Island 45 (long) -0.06 0.94 0.08 1.09 100% N/A N/A 1.10 N/A

Thorney Island 47 (long) -0.28 0.74 0.18 1.23 83% N/A N/A 1.44 N/A

CHRC A (scaled) 0.24 1.27 0.07 1.07 100% N/A N/A 0.79 N/A

Hamburg DA0120 (scaled) 0.73 2.17 0.57 1.90 25% N/A N/A 0.47 N/A

Hamburg DAT 223 (scaled) 0.36 1.45 0.19 1.22 100% N/A N/A 0.71 N/A

TNO FLS (scaled) 0.46 1.61 0.26 1.31 83% N/A N/A 0.64 N/A
10 

Table 2.2-2 (cont’d): 

SPM Evaluation against Quantitative Assessment Criteria: Individual Trial Average 

Quantitative Criteria 

Data Set

-0.4<MRB <0.4 

0.67< MG<1.5 

MRSE<2.3 

VG<3.3 

FAC2 >50% 

0.5<CSF<2 

0.5< CSF_LFL<2 

0.5<DSF<2 

0.5< DSF_LFL<2 

Maximum Point-Wise Gas Concentration 

Burro 3 (short) 1.04 16.28 1.95 >1000 45% 0.47 N/A N/A N/A

Burro 3 (long) 0.49 3.87 1.38 >1000 27% 0.97 N/A N/A N/A

Burro 7 (short) 0.42 2.78 1.20 >100 60% 0.96 N/A N/A N/A

Burro 7 (long) -0.24 0.89 1.67 31.6 10% 3.05 N/A N/A N/A

Burro 8 (short) 0.41 4.05 1.10 >1000 52% 0.98 N/A N/A N/A

Burro 8 (long) 0.25 4.10 1.19 >1000 52% 1.25 N/A N/A N/A

Burro 9 (short) 0.38 3.02 1.01 >1000 60% 0.96 N/A N/A N/A

Burro 9 (long) -0.03 1.34 0.91 33.6 40% 1.52 N/A N/A N/A

Coyote 3 (short) 0.80 4.05 1.58 >100 42% 0.65 N/A N/A N/A

Coyote 3 (long) -0.77 0.30 1.73 42.9 25% 8.06 N/A N/A N/A

Coyote 5 (short) 0.60 2.93 1.31 >100 29% 0.92 N/A N/A N/A

Coyote 5 (long) -0.24 0.77 0.93 5.21 43% 2.44 N/A N/A N/A

Coyote 6 (short) 0.13 1.66 0.98 59.0 38% 1.31 N/A N/A N/A

Coyote 6 (long) -0.49 0.64 1.16 8.14 15% 2.51 N/A N/A N/A

CHRC A (scaled) 0.14 1.61 0.58 >100 78% 1.30 N/A N/A N/A

Hamburg DAT 223 (scaled) 0.51 1.72 0.37 1.53 63% 0.62 N/A N/A N/A

BA TNO TUV01 (scaled) -0.08 0.92 0.21 1.25 100% 1.20 N/A N/A N/A

BA TNO FLS (scaled) 0.42 1.59 0.47 1.80 52% 0.76 N/A N/A N/A
11 

Table 2.2-2 (cont’d): 

SPM Evaluation against Quantitative Assessment Criteria: Individual Trial Average 

Quantitative Criteria 

Data Set

-0.4<MRB <0.4 

0.67< MG<1.5 

MRSE<2.3 

VG<3.3 

FAC2 >50% 

0.5<CSF<2 

0.5< CSF_LFL<2 

0.5<DSF<2 

0.5< DSF_LFL<2 

Cloud Width 

Burro 3 (short) 0.78 2.30 0.65 2.11 33% N/A N/A 0.45 N/A

Burro 3 (long) 0.51 1.69 0.28 1.35 67% N/A N/A 0.60 N/A

Burro 7 (short) 0.43 1.55 0.20 1.24 100% N/A N/A 0.65 N/A

Burro 7 (long) 0.25 1.28 0.07 1.07 100% N/A N/A 0.78 N/A

Burro 8 (short) 0.34 1.42 0.21 1.25 75% N/A N/A 0.74 N/A

Burro 8 (long) 0.38 1.48 0.22 1.27 75% N/A N/A 0.71 N/A

Burro 9 (short) 0.49 1.65 0.25 1.31 100% N/A N/A 0.61 N/A

Burro 9 (long) 0.24 1.27 0.06 1.06 100% N/A N/A 0.79 N/A

Coyote 3 (short) 0.59 1.85 0.39 1.55 67% N/A N/A 0.56 N/A

Coyote 3 (long) -0.18 0.83 0.08 1.08 100% N/A N/A 1.23 N/A

Coyote 5 (short) 0.49 1.65 0.22 1.29 100% N/A N/A 0.61 N/A

Coyote 5 (long) 0.34 1.41 0.11 1.13 100% N/A N/A 0.71 N/A

Coyote 6 (short) 0.22 1.25 0.09 1.10 100% N/A N/A 0.81 N/A

Coyote 6 (long) 0.11 1.12 0.02 1.02 100% N/A N/A 0.90 N/A

CHRC A (scaled) -0.04 0.96 0.04 1.04 100% N/A N/A 1.06 N/A

BA TNO FLS (scaled) -0.13 0.88 0.02 1.02 100% N/A N/A 1.14 N/A

DEGADIS generally over-predicts maximum arc-wise concentrations for field 

trials by approximately a factor of 2. Approximately 69% of the data were overpredicted (CSF>1) with approximately 40% being over-predicted by more than a factor 

of 2 contributing to the reason DEGADIS did not meet the MEP quantitative acceptance 

criteria for MRB, MG, and FAC2. The over-prediction is more severe for field trials 

with long time averages compared to field trials with short time averages. The higher 

over-prediction for longer time averages can be attributed to the little sensitivity the 

model shows to longer time averages compared to the sensitivity the experimental data 

exhibits. 
12 

DEGADIS generally under-predicts concentrations for wind tunnel tests by 

approximately a factor of 2. All of the scaled data were under-predicted (CSF<1) with 

approximately 64% of the scaled data being under-predicted by more than a factor of 2 

(CSF<0.5). The longer time averages associated with the wind-tunnel tests are not as 

likely to affect the concentrations, since the wind-tunnel tests had near steady state 

releases. 

 All the data sets met the quantitative acceptance criteria for MRSE, since 

generally the field trials and wind-tunnel tests showed similar trends resulting in less 

scatter about the mean (i.e., over-predictive of field tests and under-predictive of wind 

tunnel tests). Since the field trials and wind-tunnel trials had opposite trends, the VG for 

the trial average was higher than the MEP acceptance criteria. The larger VG attributed 

to field trials with long time averages is a result of some sensors being more sensitive to 

the longer time averages than others, resulting in some data points being over-predicted 

by significant margins compared to others. 

DEGADIS tends to over-predict concentrations in the near field where 

concentrations are still high and under-predict concentrations in the far field where 

concentrations become low, as shown in Figure 2.2-1 and Figure 2.2-2, which compare 

the measured and predicted concentrations (with ideal solid line and factor of 2 dotted 

lines). The transition from over-predictive to under-predictive happens near the lower 

flammability limit (LFL) concentration (5%). 
13 

0.10

1.00

10.00

100.00

0.10 1.00 10.00 100.00

measured concentration (mol%)

predicted concentration (mol%)

Maplin Sands 27 short

Maplin Sands 34 short

Maplin Sands 35 short

Burro 3 short

Burro 7 short

Burro 8 short

Burro 9 short

Coyote 3 short

Coyote 5 short

Coyote 6 short

ideal

+FAC2

-FAC2

Figure 2.2-1: Short Time Average Measured and Predicted Concentrations 

0.10

1.00

10.00

100.00

0.10 1.00 10.00 100.00

measured concentration (mol%)

predicted concentration (mol%)

Burro 3 long

Burro 7 long

Burro 8 long

Burro 9 long

TI 45 long

TI 47 long

Coyote 3 long

Coyote 5 long

Coyote 6 long

CHRC A scaled

BA Hamburg DA0120 scaled

BA Hamburg DAT223 scaled

BA Hamburg DAT647 scaled

BA Hamburg DAT631 scaled

BA Hamburg DAT632 scaled

BA Hamburg DAT637 scaled

TNO FLS scaled

ideal

+FAC2

-FAC2

Figure 2.2-2: Long Time Average Measured and Predicted Concentrations 
14 

DEGADIS generally meets all the MEP quantitative acceptance criteria for the 

maximum gas concentration arc-wise distance with the exception of the wind-tunnel 

tests. The reason for the better results compared to the maximum arc-wise gas 

concentrations is two-fold. The large over-prediction of gas concentration in the near 

field is mitigated by the large drop off in concentration in the near field, and the large 

over-prediction of gas concentration in the far field is mitigated by the smaller change in 

concentration in the far field. For these reasons, the distance safety factor may not be 

affected by seemingly large concentration discrepancies that are actually small 

differences in distance. 

DEGADIS generally over-predicts the distance to a given concentration for field 

trials by approximately a factor of 1.5. Approximately 89% of the field data is predicted 

with a factor of 2. The over-prediction is similar for short time averages and large time 

averages. This can be explained by the experimental gas concentration data in the near 

field being affected more by longer time averaging compared to the distances to the gas 

concentration in the near field. DEGADIS under-predicts the distance to a given 

concentration for wind-tunnel tests by a factor of 1.5. Approximately 68% of the windtunnel data is within a factor of 2. 

 DEGADIS predicts the maximum point-wise gas concentrations with a wide 

degree of scatter. DEGADIS generally seems to over-predict point-wise gas 

concentrations that are located closer to the cloud centerline where the maximum arcwise concentration often occurred, and under-predict point-wise gas concentrations that 

are located farther from the cloud centerline. In addition, DEGADIS generally seems to 

under-predict short time averages and over-predict long time averages with a difference 

of a factor of 2 or more between them. The wide degree of scatter and inability of the 

DEGADIS crosswind gas concentration similarity profile to model bifurcation of clouds 

may make it unreliable to model point-wise gas concentrations. 

DEGADIS generally meets all the MEP quantitative acceptance criteria for cloud 

width. DEGADIS generally over-predicts the distance to a given concentration for field 

trials by approximately a factor of 1.5. Approximately 84-92% of the field data is 

predicted with a factor of 2. DEGADIS shows better agreement with scaled wind-tunnel 

tests with all data within a factor of 2. 

Anomalies

As shown in Figure 2.2-3, DEGADIS under-predicts the distance to the LFL for 

Burro 8 and Maplin Sands 34, but is well within a factor of 2. 
15 

0

50

100

150

200

250

300

350

400

450

500

0 100 200 300 400 500

measured distance to LFL (m)

predicted distance to LFL (m)

Maplin Sands 27 short

Maplin Sands 34 short

Maplin Sands 35 short

Burro 3 short

Burro 7 short

Burro 8 short

Burro 9 short

Coyote 3 short

Coyote 5 short

Coyote 6 short

ideal

+FAC2

-FAC2

Figure 2.2-3 Short Time Average Measured and Predicted Distance to LFL 

As shown in Figure 2.2-4, Maplin Sands data comparisons indicate that the model 

may be less conservative for dispersion over water. The inclusion of the water transfer 

sub-model had negligible effect on the gas concentration, raising some question as to the 

validity of the water transfer sub-model. The Maplin Sands 34 is the only other LNG 

field trial to show under-prediction, but this is partly due to the larger amount of data 

points taken in the far-field, in which the model tends to be more under-predictive. 

As shown in Figure 2.2-4, Burro 8 data comparisons indicate that the model may 

be under-predictive for low wind speed with high atmospheric stabilities, which is a 

larger concern due to its applicability to the 49 C.F.R. § 193.2059 requirements (2 meters 

per second [m/s], F stability). Comparison against longer time averages will tend to 

reduce the concentration of the experiment (but not the model) and make it appear 

conservative. 
16 

0.00

1.00

2.00

3.00

4.00

5.00

0.10 1.00 10.00

MG

VG

Maplin Sands 27

Maplin Sands 34

Maplin Sands 35

Burro 3

Burro 7

Burro 8

Burro 9

Coyote 3

Coyote 5

Coyote 6

FAC2 lower limit

FAC2 upper limit

Parabola

Figure 2.2-4 Short Time Average MG and VG 

As shown in Figure 2.2-5, the only other low wind speed, high stability data 

(Thorney Island 45 and 47) indicated over-prediction. However, it was compiled using 

long time averages and matched closely with the Burro 8 long time average, which makes 

it difficult to comment as to whether under-prediction of low wind speed is a trend or not. 

0.00

1.00

2.00

3.00

4.00

5.00

0.10 1.00 10.00

MG

VG

Burro 3

Burro 7

Burro 8

Burro 9

Coyote 3

Coyote 5

Coyote 6

TI 45

TI 47

CHRC A

FAC2 lower limit

FAC2 upper limit

Parabola

Figure 2.2-5 Long Time Average MG and VG 
17 

3.0 APPLICATION OF PHMSA ADVISORY BULLETIN ADB-10-07 

This section provides a review of the DEGADIS model in accordance with the 

Advisory Bulletin and required supplementary documentation for obtaining approval of 

alternative vapor-gas dispersion models under Subpart B of 49 C.F.R. Part 193 (PHMSA, 

2010) (Coldrick et al., 2010). In each of the following sections, the additional material 

requested by the Advisory Bulletin is reviewed and discussed. 

3.1 SOURCE GEOMETRY HANDLED BY THE DISPERSION MODEL (MER 

SECTION 2.1.1.2; ADB-10-07 SECTION 1.A-D) 

The DEGADIS model is able to simulate the dispersion of vapors emanating from 

ground level with zero momentum (i.e., a vaporizing liquid pool spreading axisymmetrically). The model requires specification of a source radius and vaporization rate 

as a function of time. Source terms of regular geometries (e.g., circles, squares and low 

aspect ratio geometries) may be simplified to a circular area source term of equivalent 

cross-sectional area. Sources with high aspect ratios (e.g., long trenches) or irregular 

geometries cannot be directly inputted and may not be appropriately represented as a 

circular area. Therefore the model is not valid for those scenarios. Multiple source 

locations cannot be modeled. 

DEGADIS is also able to simulate the dispersion of vapors from an elevated, 

vertically oriented gaseous jet source term with vertical momentum for plumes that 

become neutrally buoyant before reaching grade (e.g., vent stack releases and vertical 

pressure relief releases that do not reach grade). Horizontally oriented gaseous source 

terms, gaseous source terms with horizontal momentum, and gaseous source terms that 

may reach grade level where dense gas cloud effects may be applicable may not be 

accurately simulated by this model. 

3.2 WIND FIELD (MER SECTION 2.2.2.1; ADB-10-07 SECTION 2) 

The DEGADIS model is able to simulate steady state wind profiles. The model is 

not able to simulate transient wind speed or direction. Low wind speeds (less than 2 m/s) 

can be modeled, but may not be handled well by the model and may result in underprediction of the hazard distance. 

3.3 STRATIFICATION (MER SECTION 2.2.2.3; ADB-10-07 SECTION 3) 

In the DEGADIS model, the Monin-Obukhov length is calculated automatically 

based on the Pasquill-Gifford category specified (A, B, C, D, E, or F). Specifying a 

different Monin-Obukhov length is also possible and will supersede any calculated value. 

Temperature and/or turbulence profiles cannot be inputted by the user. High atmospheric 

stability (F stability) can be modeled, but may not be handled well by the model and may 

result in under-prediction of the hazard distance. 
18 

3.4 TERRAIN TYPES AVAILABLE (MER SECTION 2.2.3.1; ADB-10-07 

SECTION 4) & COMPLEX EFFECTS (MER SECTION 2.3.1.2; ADB-10-07 

SECTION 4) 

The DEGADIS model is limited to dispersion over unobstructed level terrain with 

uniform roughness length specified by the user. Sloped or varying terrain will affect the 

gravity spreading of a dense gas release. For dense gas releases, such as LNG vapor, the 

cloud will be stretched out as the dense gas plume flows along downward slopes. 

Therefore, for downward slopes, the centerline concentrations may be over-predicted in 

the near field, but under-predicted in the far field. Correspondingly, cross-wise 

concentrations and cloud widths may be over-predicted in the near field, but underpredicted in the far field. In contrast, upward slopes will oppose the movement of the 

dense gas, causing the vapor to accumulate and spread perpendicular to the upward slope. 

Therefore, for upward slopes, the centerline concentrations may be under-predicted in the 

near field, but over-predicted in the far field. Correspondingly, cross-wise concentrations 

and cloud widths may be under-predicted in the near field, but over-predicted in the far 

field. DEGADIS was not validated against sloped terrain tests, since it is not designed to 

simulate those scenarios. 

3.5 OBSTACLE TYPES AVAILABLE (MER SECTION 2.2.4.1; ADB-10-07 

SECTION 5) & COMPLEX EFFECTS (MER SECTION 2.4.3.1; ADB-10-07 

SECTION 5) 

The model is limited to dispersion over unobstructed level terrain with uniform 

roughness length specified by the user. For most instances, downwind concentrations 

assuming unobstructed terrain will be over-predictive. However, there are instances 

where downwind concentrations could be under-predictive due to wind channeling 

effects (Melton & Cornwell, 2009). Wind channeling may occur between adjacent LNG 

storage tanks, buildings, or large structures, which may result in the model being underpredictive for LNG vapor concentrations. 

3.6 TURBULENCE MODELING (MER SECTION 2.3.1.5; ADB-10-07 

SECTION 6) 

The DEGADIS model parameterizes turbulence based on empirical turbulence 

coefficients formed from the user-specified atmospheric parameters (horizontal turbulent 

diffusivity) and Richardson number (vertical turbulent diffusivity). 

The parameterization for horizontal turbulence is based on functions of the 

Pasquill stability category and averaging time. As averaging time increases, different 

empirical coefficients are used. 

For Richardson numbers greater than zero, the parameterization for vertical 

turbulence is based on laboratory scale data for vertical mixing in stable density stratified 
19 

fluid flows reported by Kantha et al (1977), Lofquist (1960), and McQuaid (1976) 

(Havens, Spicer 1990). For Richardson numbers less than zero, the function is taken 

from Colenbrander and Puttock (1983) and modified so the passive limits of the two 

functions agree (Havens, Spicer, 1990). When heat transfer from the surface is present, 

vertical mixing is enhanced by convection turbulence and is parameterized based on work 

by Zeman and Tennekes (1977) (Havens, Spicer, 1990). 

The plume model has separate parameterizations for turbulence caused by jet 

effects. For area source terms, the parameterization of turbulence is a simplification 

based on unobstructed stably stratified flows. Therefore, it would not be appropriate for 

use in situations where obstructions are to be considered or where source terms with high 

momentum (i.e., jet releases) that may result in additional turbulence exist. For jet source 

terms, the parameterization of turbulence is based on jet effects and does not account for 

turbulence associated with impingement of a jet or with a dense vapor cloud reaching 

grade, and therefore would not be appropriate for releases that impinge on surfaces or 

reach grade. 

3.7 BOUNDARY CONDITIONS (MER SECTION 2.3.1.7; ADB-10-07 

SECTION 7) 

The model requires the user to specify: the source term as a radius and 

vaporization rate at different time intervals; the wind profile in terms of the PasquillGifford category (or Monin-Obukhov length); and the surface roughness. Zero velocity 

is imposed at the ground boundary condition. No other boundary conditions are able to 

be specified by the user. 

3.8 COMPLEX EFFECTS: AEROSOLS (MER SECTION 2.3.1.1; ADB-10-07 

SECTION 8) 

Using DEGADIS, flashed vapors may be treated as gaseous jet source terms. 

However, for jet source terms, DEGADIS assumes a vertically oriented release with 

vertical momentum. DEGADIS also does not account for turbulence generated from 

plumes that reach grade or releases that impinge onto surfaces. Therefore, jet source 

terms, horizontally oriented gaseous source terms, gaseous source terms with horizontal 

momentum, and gaseous source terms that may reach grade level may not be accurately 

simulated by this model. 

The model is not able to explicitly simulate the formation, vaporization, rainout, or 

subsequent dispersion of aerosol droplets. Hanna, et al. (1993) has attempted to simulate 

the dispersion of evaporated aerosol by specifying a source term based on the density of 

the vapor-aerosol-air mixture and the mole fraction of vapor-aerosol in the cloud (based 

on the corresponding mass concentration of the vapor-aerosol) obtained by assuming 

complete adiabatic mixing. 
20 

3.9 COMPUTATIONAL MESH (MER SECTION 2.4.3.1; ADB-10-07 SECTION 9) 

As use of a computational mesh is not related to integral models such as 

DEGADIS, this section is not applicable. 

3.10 DISCRETIZATION METHODS (MER SECTION 2.4.2.3; ADB-10-07 

SECTION 10) 

DEGADIS solves ordinary differential equations using the Runge-Kutta method 

with a variable step that is 4th order accurate. This is one of the oldest and probably the 

most commonly used numerical method for integral type models. More accurate 

numerical solution methodologies now exist, but are not expected to have a great effect 

on the results. 

3.11 SOURCES OF MODEL UNCERTAINTY (MER SECTION 2.6; ADB-10-07, 

SECTION 11) 

All models contain simplifications to minimize the computational time, which 

causes a certain degree of uncertainty and limits the applicability of the model. The areas 

of uncertainty for the DEGADIS model would be the numerical solver used to discretize 

the space, the source term simplification, the steady state wind profile simplification, and 

the turbulence parameterization. 

3.12 SENSITIVITY TO INPUT (MER SECTION 2.6.4; ADB-10-07 SECTION 12) 

A sensitivity analysis of the DEGADIS model was conducted based on the various 

inputs that could be specified, including source term, wind speed, surface roughness, 

atmospheric stability (and/or Monin-Obukhov Length), ambient temperature, ambient 

pressure, ambient relative humidity, and molecular weight. The sensitivity of the model 

was determined based on respective uncertainties for those values. Each sensitivity case 

is denoted by a corresponding letter and number. The letter corresponds to a different 

source term and the number designates the inputted variables as shown in Table 3.12-1. 

The base case assumes values provided in the MEP, which were verified with the 

original data series reports available (Goldwire et al 1983a), (Goldwire, et al 1983b), 

(Koopman et al 1982a), (Koopman et al 1982b), (Colenbrander et al 1984a), 

(Colenbrander et al 1984b), (Colenbrander et al 1984c), (Johnson, 1985). Notes have 

been provided in the validation database for instances where there were conflicts between 

the MEP and original data series reports. The original data series reports were utilized to 

generate the sensitivity bounds for the inputs into DEGADIS. The lower and upper 

sensitivity bounds were based upon the lower and upper quartiles of the data. Where the 

lower and upper quartiles did not vary by more than 10% from the mean, no sensitivity 

analysis was conducted (e.g., a_10 and a_13). Since the wind tunnel tests were 
21 

conducted under controlled atmospheric conditions, the wind tunnel test data were not 

subject to any sensitivity analyses related to atmospheric conditions. Values for the base 

case and sensitivity analyses are justified in the validation database. 

Table 3.12-1: Sensitivity Case Designations 

Case Designation Description 

a Base case 

b_* Alternative source term 

c_* Alternative source term 

a_1 Averaging time sensitivity 

a_2 Lower wind speed sensitivity 

a_3 Higher wind speed sensitivity 

a_4 Alternative wind speed sensitivity 

a_5 Lower surface roughness sensitivity 

a_6 Higher surface roughness sensitivity 

a_7 Monin-Obukhov Length sensitivity 

a_8 Lower atmospheric stability sensitivity 

a_9 Higher atmospheric stability sensitivity 

a_10 Ambient temperature sensitivity 

a_11 Ambient pressure sensitivity 

a_12 Ambient relative humidity sensitivity 

a_13 Surface temperature sensitivity 

a_14 Water Transfer Submodel sensitivity 

a_15 Molecular weight sensitivity 

The sensitivity cases and results are shown in Appendix A. Highlighted values 

indicate the upper and lower bounds of the calculated concentrations and distance to the 

LFL. 

The ranges in concentrations are also shown in Appendix A with graphical 

depictions (vertical error bars) for each experiment followed by input/output summaries 

for each sensitivity run. The largest uncertainties are due to the specification of the 

surface roughness, wind speed, and molecular weight. As expected, specifying a lower 

surface roughness will generally result in higher concentrations downwind and 
22 

subsequently longer distances to the LFL and vice versa. As expected, specifying a lower 

wind speed will generally result in higher concentrations downwind and subsequently 

longer distances to the LFL and vice versa. Specifying a lighter molecular weight of 

LNG (i.e., as methane) generally will result in higher concentrations downwind and 

subsequently longer distances to the LFL and vice versa. Overall, the concentrations may 

differ by more than a factor of four and downwind dispersion distances to the LFL may 

differ by up to a factor of two, dependant on the uncertainty in the user input and 

sensitivity to that input. 

3.13 LIMITS OF APPLICABILITY (MER SECTION 2.7; ADB-10-07 

SECTION 13) 

The DEGADIS model is limited to dispersion over unobstructed level terrain with 

uniform roughness length specified by the user. The model cannot accurately simulate 

obstructed, sloped or varying terrain or terrain with varying surface roughness length. 

The model does not have a built-in source term model and requires user-input to 

describe the source term. The source terms that can be defined are: (1) a single regularly 

shaped area source term with no momentum with specified equivalent radius and 

vaporization rate with respect to time (i.e., a single steady state or spreading vaporizing 

pool); or (2) an elevated vertically oriented gaseous jet source term with vertical 

momentum for plumes that become neutrally buoyant before reaching grade with 

specified diameter, elevation, release rate, and duration of release (i.e., a single timelimited elevated gaseous jet from a vent stack, pressure relief valve). Flashed vapors may 

be treated as gaseous source terms, where appropriate. Aerosol formation, vaporization, 

rainout, or subsequent dispersion of aerosol droplets cannot be modeled explicitly by the 

model, but alternative approaches may be suitable subject to further evaluation. The 

model cannot model multiple source terms that may occur simultaneously, nor can it 

accurately simulate a single source term with a highly irregular geometry or high aspect 

ratio (e.g., trenches). The model is not able to simulate horizontally oriented gaseous 

source terms, gaseous source terms with horizontal momentum, or gaseous source terms 

that may reach grade level where dense gas cloud effects may be applicable. 
23 

3.14 EVALUATION AGAINST THE MEP QUANTITATIVE ASSESSMENT 

CRITERIA (MER SECTION 6.2.4; ADB-10-07 SECTION 14) 

3.14.1 Uncertainty Analysis of Model Input 

This series of uncertainty analyses accounts for model uncertainty due to 

uncertainty in the assumption of input parameters specified by the user. This subtopic is 

further broken down into seven areas. 

i. Analysis of source term(s)

The DEGADIS model does not have a built-in source term model and requires the 

specification of the source diameter and vaporization rate as a function of time. 

For experiments involving LNG spills over water, this model validation study used 

the ABS (American Bureau of Shipping)/FERC LNG pool spread source term model to 

determine pool diameter and vaporization rates as a function of time (FERC, 2004a) 

(FERC, 2004b). The ABS/FERC LNG pool spread model assumes a 0.167 kg/m2

/sec 

vaporization rate based on empirical data for spills over water. For all other experiments 

the specified pool diameters and rates were used and no sensitivity analysis was 

performed. 

For the Thorney Island and wind tunnel trials, the gas was released through a well 

defined opening at ground level that was designed to give a release with negligible 

vertical momentum. The source term was defined based on this information without any 

need for additional sensitivity analyses. This approach is similar to previous validation 

studies (Hanna, et al 1993). 

For experiments involving LNG spills over water, a sensitivity analysis was 

conducted to examine the effect of pool spread velocity. The ABS/FERC model, which 

models the pool spread and specifies a vaporization of 0.167kg/m2

/sec was compared to 

an instantaneously formed steady-state pool (i.e. spreads instantaneously) using the same 

vaporization rate. 

A sensitivity analysis was also conducted to examine the effect of the vaporization 

rate. A source term based on an instantaneously formed steady-state pool using a 

vaporization rate of 0.167 kg/m2

/sec was compared to an instantaneously formed steadystate pool using a vaporization rate of 0.085 kg/m2

/sec. The 0.085 kg/m2/sec vaporization 

rate has been commonly used in previous validation studies, and is based on visual 

observations of the steady-state pool size and spill rate during the Maplin Sands 

experiments (Puttock, 1987). The resultant pool diameters are shown in Table 3.14-1. 
24 

Table 3.14-1: Pool Diameters as a Function of Vaporization Rate 

Test 

Maximum Pool 

Diameter based 

on ABS/FERC 

with 0.167 

kg/m2

/sec 

Steady-State 

Diameter based 

on 0.167 

kg/m2

/sec 

Steady-State 

Diameter based 

on 0.085 

kg/m2

/sec 

Maplin Sands 27 14 m 13 m 19 m 

Maplin Sands 34 14 m 13 m 18 m 

Maplin Sands 35 15 m 14 m 20 m 

Burro 3 26 m 26 m 36 m 

Burro 7 28 m 28 m 39 m 

Burro 8 32 m 30 m 42 m 

Burro 9a 35 m 32 m 45 m 

Coyote 3 30 m 28 m 39 m 

Coyote 5 34 m 31 m 44 m 

Coyote 6 33 m 31 m 43 m 

a. It is noted that the pool diameters (and corresponding vaporization rate) may have greater 

uncertainties than those evaluated. For example, the diameter reported for the Burro 9 experiment 

by an airborne infrared imager was about 10 m in diameter (Koopman et al., 1981). However, this 

should not be considered representative of other experiments since rapid phase transitions 

destroyed the spill plate early in the test, drastically changing the nature of the LNG pool on the 

water surface. 

The concentrations predicted indicate little sensitivity to the pool spread velocity 

and sensitivity to the vaporization rate and resultant steady pool diameter, as shown in 

Appendix A. As shown in Table 3.14-2, the distance to the LFL differs by less than 5%-

10% from the base case, which is well within the overall uncertainty of the experimental 

or modeling results. 
25 

Table 3.14-2: 

Distance to LFL Uncertainty Due to Pool Spread Velocity and 

Vaporization Rate 

Test Arc 

ABS/FERC Pool 

Spread Model 

with 0.167 

kg/m2

/sec 

Steady-State 

Diameter based 

on 0.167 

kg/m2

/sec 

Steady-State 

Diameter based 

on 0.085 

kg/m2

/sec 

Maplin 

Sands 27 204 m to LFL 206 m to LFL 216 m to LFL 

Maplin 

Sands 34 191 m to LFL 191 m to LFL 191 m to LFL 

Maplin 

Sands 35 223 m to LFL 222 m to LFL 202 m to LFL 

Burro 3 405 m to LFL 402 m to LFL 394 m to LFL 

Burro 7 388 m to LFL 387 m to LFL 368 m to LFL 

Burro 8 289 m to LFL 291 m to LFL 308 m to LFL 

Burro 9 492 m to LFL 482 m to LFL 465 m to LFL 

Coyote 3 392 m to LFL 392 m to LFL 385 m to LFL 

Coyote 5 396 to LFL 387 to LFL 358 to LFL 

Coyote 6 457 m to LFL 455 m to LFL 451 m to LFL 
26 

ii. Analysis of boundary conditions

The DEGADIS model requires the user to specify the following items: the inlet 

boundary as a source term radius and vaporization rate at different time intervals (i.e. 

source term); the wind profile based on the Pasquill-Gifford (or Monin-Obukhov length) ; 

and the surface roughness. Zero velocity is imposed at the ground boundary condition. 

No other boundary conditions are specified by the user. The source term and wind 

profile boundary sensitivities are discussed in sections i and iii, respectively. 

iii. Analysis of wind profile. 

The DEGADIS model is only able to simulate steady state wind profiles and 

direction. For all trials, the wind speed used for the base case was defined as the domain 

average wind speeds from the MEP, which were verified to match the domain average 

wind sensor data during the dispersion periods found in the original data series reports, 

where available (Goldwire et al 1983a), (Goldwire, et al 1983b), (Koopman et al 1982a), 

(Koopman et al 1982b), (Colenbrander et al 1984a), (Colenbrander et al 1984b), 

(Colenbrander et al 1984c), (Johnson, 1985). Similarly, the upper and lower bounds for 

the wind speed were based on the upper and lower quartiles of the domain average wind 

sensor data during the dispersion periods found in the original data series reports, where 

available (Goldwire et al 1983a), (Goldwire, et al 1983b), (Koopman et al 1982a), 

(Koopman et al 1982b), (Colenbrander et al 1984a), (Colenbrander et al 1984b), 

(Colenbrander et al 1984c), (Johnson, 1985). Given the little fluctuation and/or 

uncertainty (<10% of mean) in some of the data, certain sensitivity cases were not 

simulated. In Maplin Sands 27, the original data series report (Colenbrander et al 1984a) 

claims that the wind speed sensor at 250 m, -90 deg, 10 m,, which recorded a 6.1 m/s 

mean (270-430 sec), probably represents the environmental conditions best, since the 

plume was blown in the direction of this pontoon. Accordingly, a number of reports list 

6.1 m/s as the mean wind speed, while other reports list 5.5-5.6 m/s as the mean (190-350 

sec) wind speed. Coincidentally, the upper quartile of the domain average wind sensor 

data provided in the original data series reports is 6.2 m/s. For consistency, the base case 

was taken as the 5.6 m/s domain averaged sensor data provided in the original data series 

reports and listed in the MEP. In addition, where the domain average wind sensor data 

reported in the MEP differed from the wind speed provided in the MEP, an additional 

case was simulated (a_4). 

The upper and lower bounds for the stability class were based upon the 

atmospheric conditions (e.g. wind speed, cloud cover, insolation, time of day, etc). Wind 

speed data and atmospheric conditions were used in conjunction with various guidance 

documents, including the DEGADIS 2.1 documentation (Havens, Spicer, 1990), to 

determine the wind stability. 
27 

The surface roughness values for the base case were taken from the MEP 

(Coldrick et al., 2010) (Ivings et al., 2007). For field trials, surface roughness is rarely 

known to better than an order of magnitude (Johnson, 1985)). Where uncertainty or 

disagreement of the surface roughness existed, a sensitivity analysis to surface roughness 

was carried out. This effort was based on the bounds generated from the DEGADIS 2.1 

documentation (Havens et al 1990) and recommended and generally accepted good 

engineering practices, which in certain circumstances varied greatly from that specified in 

the MEP (Coldrick et al., 2010). Previous validation studies conducted for the 

experiments were also examined (Hanna et al., 1993) (Ermak et al., 1989) (Puttock et al., 

1984). 

Maplin Sands 

The MEP reports a surface roughness of 0.0003 meter (m) for Maplin Sands, 

which was conducted over waters protected by a bund (during periods of low tide) 

(Coldricket al., 2010). The Modeler’s Data Archive (MDA) reports a value of 0.0003 m 

(Hanna et al., 1993). Ermak et al. (1989) reports a surface roughness of 0.000058 m. The 

Maplin Sands Reports provides a surface roughness estimate of 0.00002 m based on a 

1:20 scale wind tunnel experiment to determine the effect on the surface roughness from 

the pontoons that were fitted with the sensor arrays (Puttock et al., 1984) (Colenbrander 

et al., 1984a), (Colenbrander et al., 1984b), (Colenbrander et al., 1984c). Based on 

photographic observations of the test site, most users could reasonably assume the 

surface roughness to correspond to open calm water or sea in coastal areas. The 

DEGADIS reports surface roughness of 0.0001 m for calm open seas and 0.001 m for sea 

in coastal areas (Spicer, Havens, 1982), (Havens, Spicer, 1990). Brutsaert reports 0.0001 

m to 0.0006 m for large water surfaces (Brutstaert, 1982). The base case used the value 

of 0.0003 m reported in the MEP; a sensitivity analysis was conducted using 0.0001 m 

and 0.001 m. A third simulation was ran specifying the Monin-Obukhov lengths 

provided in the MEP. It should also be noted that all the Maplin Sands tests were 

conducted at low tide, where the 300 m low-lying bund may have affected the surface 

roughness and dispersion. The pontoons equipped with the sensor arrays would also have 

an influence on the dispersion. 

Given the uncertainty in the surface roughness length that could be reasonably 

chosen, there was a moderate difference in downwind concentrations, as shown in 

Appendix A. As shown in Table 3.14-3, the distance to the LFL differs approximately 5-

15% from the base case, which is within the overall uncertainty of the experimental or 

modeling results. As expected, specifying a higher surface roughness generally results in 

lower concentrations and shorter distances to the LFL. 
28 

Table 3.14-3: 

Distance to LFL Uncertainty Due To Surface Roughness Length: Maplin 

Sands 

Test Base Case 

0.0003 m 

Lower Bound 

0.0001 m 

Upper Bound 

0.001 m 

Maplin Sands 27 204 m to LFL 214 m to LFL 175 m to LFL 

Maplin Sands 34 191 m to LFL 184 m to LFL 176 m to LFL 

Maplin Sands 35 223 m to LFL 246 m to LFL 200 m to LFL 

Burro and Coyote 

The MEP reports a surface roughness of 0.0002 m for Burro and Coyote, which 

were conducted over a spill pond surrounded by desert terrain. The spill pond was 58 m 

in diameter and 1.5 m below the surrounding terrain. The surrounding terrain had a slight 

upward slope rising 7 m above the water level at a downwind distance of about 80 m 

before leveling out thereafter (Coldrick et al., 2010). The MDA reports a value of 0.0002 

m (Hanna et al., 1993). Ermak et al (1989) also reports a surface roughness of 0.0002 m. 

The Burro and Coyote Series Reports reports a value of 0.000205 m (Koopman et al., 

1982a) (Koopman et al., 1982b) (Goldwire et al., 1983a) (Goldwire et al., 1983b) Based 

on photographic observations of the test site, users could reasonably assume the surface 

roughness to correspond to a desert or an area with sparse vegetation (Koopman et al., 

1982c). The DEGADIS documentation reports surface roughness of 0.0005 m for desert 

and 0.01 m for few trees, winter time (Spicer, Havens 1990). Pielke (2002) reports 

0.0003m for smooth deserts and 0.01m surface roughness value for the upper range of 

soils and short grass. Brutsaert (1982) reports 0.04 m for grass with some bushes and 

trees. The base case used the value of 0.0002 m reported in the MEP (Coldrick et al., 

2010); a sensitivity analysis was conducted using 0.01 m. Simulations were also run 

specifying the Monin-Obukhov lengths provided in the MEP. 

Given the great uncertainty in the surface roughness length that could be 

reasonably chosen, there was a noticeable difference in downwind concentrations, as 

shown in Appendix A. As shown in Table 3.14-4, the distance to the LFL differs by up 

to 40% from the base case, which is a source of significant uncertainty for the modeling 

results. With the exception of Burro 8, which was the only low-wind speed F stability 

test, the larger surface roughness resulted in lesser concentrations and a shorter distance 

to the LFL. 
29 

Table 3.14-4: 

Distance to LFL Uncertainty Due To Surface Roughness 

Length: Burro & Coyote

Test 

Base Case 

0.0002 m Upper Bound 0.01 m 

Burro 3 405 m to LFL 257 m to LFL 

Burro 7 388 m to LFL 242 m to LFL 

Burro 8 289 m to LFL 302 m to LFL 

Burro 9 492 m to LFL 307 m to LFL 

Coyote 3 392 m to LFL 254 m to LFL 

Coyote 5 396 to LFL 253 m to LFL 

Coyote 6 457 m to LFL 292 m to LFL 

Thorney Island 

The MEP reports a surface roughness of 0.01 m for Thorney Island, which was 

conducted at an abandoned airfield on an island with 3 kilometers (km) of sheltered water 

downwind and 1 km of runway and grass periodically cut to 20 centimeters (cm) upwind 

of the prevailing wind direction (Johnson, 1985). The MDA reports a value of 0.01 m 

(Hanna et al., 1993). Ermak et al. (1989) reports a surface roughness of 0.005 m. Based 

on photographic observations of the test site, users could reasonably assume the surface 

roughness to correspond to a tarmac or an area with sparse vegetation (Goldwire et al., 

1983b). The DEGADIS documentation reports surface roughness of 0.007 m for 3 cm 

cut grass, 0.01 m for few trees during winter time, and 0.03 m for the runway area of 

airports (Spicer, Havens 1990). Pielke (2002) reports a 0.01 m surface roughness value 

for the upper range of soils and short grass and 0.04 m to 0.1 m for long grass cut to 25 

cm to 1 m. Brutsaert (1982) reports 0.00002 m for a smooth tarmac and 0.0045 m for 

grass (airport). The base case used the value of 0.01 m reported in the MEP; a sensitivity 

analysis was conducted using 0.00002 m and 0.03 m. A third simulation was run 

specifying the Monin-Obukhov lengths provided in the MEP. 

Given the great uncertainty in the surface roughness length that could be 

reasonably chosen, there was a noticeable difference in downwind concentrations, as 

shown in Table 3.14-5. The concentration differs by up to a factor of almost 8 from the 

base case, which is a source of significant uncertainty for the modeling results. 
30 

Table 3.14-5: 

Concentration Uncertainty Due To Surface Roughness Length: 

Thorney Island 

Test Base Case 0.01 m Lower Bound 

0.00002 m 

Upper Bound 

0.03 m 

Thorney Island 45 

40 m 29.5% 12.8% 32.4% 

53 m 29.5% 12.8% 16.0% 

72 m 12.5% 12.8% 11.5% 

90 m 10.0% 12.8% 7.9% 

112 m 7.0% 12.8% 4.6% 

158 m 3.3% 12.8% 1.9% 

250 m 1.0% 3.3% 0.6% 

335 m 0.5% 1.7% 0.3% 

472 m 0.2% 0.8% 0.1% 

Thorney Island 47 

50 m 17.4% 11.0% 20.4% 

90 m 17.4% 9.2% 20.4% 

212 m 2.0% 7.7% 1.3% 

250 m 1.2% 6.9% 0.8% 

335 m 0.5% 0.6% 0.3% 

472 m 0.2% 0.5% 0.1% 

The ambient temperature values for the base case were taken from the MEP, 

which were verified to match the sensor data during the dispersion periods found in the 

original data series reports, where available (Goldwire et al 1983a), (Goldwire, et al 

1983b), (Koopman et al 1982a), (Koopman et al 1982b), (Colenbrander et al 1984a), 

(Colenbrander et al 1984b), (Colenbrander et al 1984c), (Johnson, 1985). If the MEP and 

original data series reports did not provide or record values, the values were assumed to 

take common values (e.g. 1 atmosphere). Given the little fluctuation and/or uncertainty 

(<10%) in all of the data, none warranted sensitivity cases. 

The ambient pressure values for the base case were taken from the MEP, which 

were verified to match the sensor data during the dispersion periods found in the original 

data series reports, where available (Goldwire et al 1983a), (Goldwire, et al 1983b), 

(Koopman et al 1982a), (Koopman et al 1982b), (Colenbrander et al 1984a), 

(Colenbrander et al 1984b), (Colenbrander et al 1984c), (Johnson, 1985). In some cases, 

the MEP and original data series reports did not provide or record values. For these 

cases, the values were assumed to take atmospheric pressure (i.e. 1 atmosphere). For 
31 

cases that did provide or record ambient pressure, the fluctuation was insignificant 

(<10%), and most cases would not warrant sensitivity cases. However, typically site 

specific values for ambient pressure are not available and atmospheric (i.e. 1 atmosphere) 

is assumed. To gauge this common assumption and determine the sensitivity of the 

model to this parameter, sensitivity cases were run where the ambient pressure differed 

from 1 atmosphere. 

The ambient relative humidity values for the base case were taken from the MEP, 

which were verified to match the sensor data during the dispersion periods found in the 

original data series reports, where available (Goldwire et al 1983a), (Goldwire, et al 

1983b), (Koopman et al 1982a), (Koopman et al 1982b), (Colenbrander et al 1984a), 

(Colenbrander et al 1984b), (Colenbrander et al 1984c), (Johnson, 1985). In some cases, 

the ambient relative humidity data listed in the MEP differed from the relative humidity 

sensor data provided in the original data series reports. In Maplin Sands 34, it is noted 

that the original data series report (Colenbrander et al 1984a) provides values of 72% at 

Maplin Sands test site and 74% at Foulness Met. Station (corrected to Maplin Sands site 

temp), which was located 5 km away in SW direction and about 1 km inland. The 

relative humidity sensor data showed a range from 70 to 77%. It is unclear where the 

90% value listed in the MEP originated. For that reason, the base case was taken as the 

72% average value provided in the original data series, and a sensitivity case to 90% 

relative humidity was provided. There was little fluctuation and/or uncertainty (<10%) in 

most of data, hence most cases did not warrant sensitivity cases, denoted N/A. However, 

typically site specific values for weather data are not available and nearby weather 

stations are relied upon. For this reason, sensitivity cases were also run where nearby 

weather station data was provided in the original data series report, such as the Maplin 

Sands trials. 

The surface/ground temperature values for the base case were taken from the 

MEP, which were verified to match the sensor data during the dispersion periods found in 

the original data series reports, where available (Goldwire et al 1983a), (Goldwire, et al 

1983b), (Koopman et al 1982a), (Koopman et al 1982b), (Colenbrander et al 1984a), 

(Colenbrander et al 1984b), (Colenbrander et al 1984c), (Johnson, 1985). If the MEP and 

original data series reports did not provide or record values, the values were assumed to 

take the temperature of the ambient temperature. Given the little fluctuation and/or 

uncertainty (<10%) in all of the data, none warranted sensitivity cases. In addition, the 

water transfer submodel within DEGADIS was used in the Maplin Sands trials. A 

sensitivity to the inclusion of this submodel was included for Maplin Sands. 

The molecular weight values for the base case were taken from the MEP, which 

were verified to match the sensor data during the dispersion periods found in the original 

data series reports, where available (Goldwire et al 1983a), (Goldwire, et al 1983b), 

(Koopman et al 1982a), (Koopman et al 1982b), (Colenbrander et al 1984a), 

(Colenbrander et al 1984b), (Colenbrander et al 1984c), (Johnson, 1985). For the LNG 
32 

field trials, the lower bound for the molecular weight was based on the molecular weight 

of methane assuming preferential boiloff; no upper bound was provided, as heavier 

molecular weights would not be expected than those listed in the MEP. Given the little 

fluctuation and/or uncertainty (<10%) in some of these values, some cases did not 

warrant sensitivity cases, denoted N/A. 

The inputs for each sensitivity case utilized are summarized in Table 3.14-6. The 

inputs and outputs for each trial are shown in Appendix A. 
33 

Table 3.14-6: Sensitivity Case Inputs 

 Maplin Sands 

27 

Maplin Sands 

34 

Maplin Sands 

35 

Burro 3 Burro 7 Burro 8 Burro 9 Coyote 3 Coyote 5 C

Source Term Base Case 0.167kg/m^2/sec 

ABS/FERC 

0.167kg/m^2/sec ABS/FERC 

0.167kg/m^2/sec ABS/FERC 

0.167kg/m^2/sec ABS/FERC 

0.167kg/m^2/sec ABS/FERC 

0.167kg/m^2/sec ABS/FERC 

0.167kg/m^2/sec ABS/FERC 

0.167kg/m^2/sec ABS/FERC 

0.167kg/m^2/sec ABS/FERC 

0.167ABS/

 Alternative 1 0.167kg/m^2/sec 

steady state 

0.167kg/m^2/sec steady state 

0.167kg/m^2/sec steady state 

0.167kg/m^2/sec steady state 

0.167kg/m^2/sec steady state 

0.167kg/m^2/sec steady state 

0.167kg/m^2/sec steady state 

0.167kg/m^2/sec steady state 

0.167kg/m^2/sec steady state 

0.167steady 

 Alternative 2 0.085kg/m^2/sec 

steady state 

0.085kg/m^2/sec steady state 

0.085kg/m^2/sec steady state 

0.085kg/m^2/sec steady state 

0.085kg/m^2/sec steady state 

0.085kg/m^2/sec steady state 

0.085kg/m^2/sec steady state 

0.085kg/m^2/sec steady state 

0.085kg/m^2/sec steady state 

0.085steady 

Wind Speed Base Case 5.6 (MEP) 8.5 (MEP) 9.6 (MEP) 5.4 (MEP) 8.4 (MEP) 1.8 (MEP) 5.7 (MEP) 6 (MEP) 9.7 (MEP) 4.6 (M Lower Bound 4.4 (25% quart.) 7.6 (25% quart.) 7.9 (25% quart.) 5.1 (25% quart.) N/A 1.5 (25% quart.) N/A N/A N/A N/A  Upper Bound 6.1 (75% quart.) 9.5 (75% quart.) 11 (75% quart.) 5.8 (75% quart.) N/A 2 (75% quart.) N/A N/A N/A N/A Atmospheric Stability Base Case C-D (MEP) D (MEP) D (MEP) C (MEP) D (MEP) E (MEP) D (MEP) C (MEP) C (MEP) D (M Lower Bound D (assumed) N/A N/A N/A N/A F (assumed) N/A N/A D (assumed) E (ass Upper Bound C (assumed) C (assumed) C (assumed) N/A C (assumed) N/A C (assumed) N/A N/A N/A Surface/Ground Roughness  Base Case 3e-4 (MEP) 3e-4 (MEP) 3e-4 (MEP) 2e-4 (MEP) 2e-4 (MEP) 2e-4 (MEP) 2e-4 (MEP) 2e-4 (MEP) 2e-4 (MEP) 2e-4 ( Lower Bound 1e-4 (assumed) 1e-4 (assumed) 1e-4 (assumed) N/A N/A N/A N/A N/A N/A N/A  Upper Bound 1e-3 (assumed) 1e-3 (assumed) 1e-3 (assumed) 1e-2 (assumed) 1e-2 (assumed) 1e-2 (assumed) 1e-2 (assumed) 1e-2 (assumed) 1e-2 (assumed) 1e-2 (Ambient Temperature  Base Case 288.1K (MEP) 288.4K (MEP) 289.3K (MEP) 307.75K (MEP) 306.96 (MEP) 306.02 (MEP) 308.52K (MEP) 311.45K (MEP) 301.49K (MEP) 297.2 Lower Bound N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A  Upper Bound N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A Ambient Pressure  Base Case 1 (assumed) 1 (assumed) 1 (assumed) 0.936 (MEP) 0.928 (MEP) 0.929 (MEP) 0.928 (MEP) 0.924 (MEP) 0.927 (MEP) 0.930  Lower Bound N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A  Upper Bound N/A N/A N/A N/A 1 (assumed) 1 (assumed) 1 (assumed) 1 (assumed) 1 (assumed) 1 (assAmbient Relative Humidity  Base Case 53 (MEP) 72 (avg. data) 63 (avg. data) 5.2 (MEP) 7.4 (MEP) 4.5 (MEP) 14.4 (MEP) 11.3 (MEP) 22.1 (MEP) 22.8 ( Lower Bound N/A N/A N/A N/A 5 N/A 6.5 3.5 7.2 4.5  Upper Bound 63 (avg. 

Foulness) 

90 (MEP) 77 (MEP) N/A N/A N/A N/A N/A N/A N/A 

Molecular Weight  Base Case 17.23 (MEP) 16.66 (MEP) 16.39 (MEP) 17.26 (MEP) 18.22 (MEP) 18.12 (MEP) 18.82 (MEP) 19.51 (MEP) 20.19 (MEP) 19.09  Lower Bound 16.04 (methane) 16.04 (methane) 16.04 (methane) 16.04 (methane) 16.04 (methane) 16.04 (methane) 16.04 (methane) 16.04 (methane) 16.04 (methane) 16.04  Upper Bound N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A 
34 

iv. Analysis of sub-models. 

The user is able to specify whether water transfer should be included in the 

analysis. If selected, a sub-model is utilized to calculate the effect of this 

phenomenon. Although all the LNG field trials were spilled over water, much of the 

dispersion was over land. Therefore, the water transfer sub-model was primarily 

applicable to the Maplin Sand trials, which were dispersed entirely over water. A 

sensitivity analysis of the water transfer sub-model was investigated. Negligible 

differences from the base case in the predicted concentrations and distance to LFL 

were found, as shown in Table 3.14-7. 

Table 3.14-7: 

Effect of Water Transfer Sub-Model 

Test With Water Transfer Without Water Transfer 

Maplin Sands 27 

58 m 30.9% 30.9% 

89 m 16.3% 16.3% 

131 m 10.1% 10.1% 

181 m 6.3% 6.4% 

248 m 3.3% 3.3% 

322 m 1.7% 1.7% 

399 m 1.0% 1.0% 

650 m 0.3% 0.3% 

Maplin Sands 34 

87 m 14.6% 12.6% 

179 m 5.6% 4.9% 

Maplin Sands 35 

58 m 28.4% 28.4% 

89 m 16.6% 16.6% 

129 m 10.4% 10.4% 

180 m 6.7% 6.7% 

250 m 4.3% 4.3% 

400 m 2.1% 2.1% 

No other sub-models (e.g., turbulence models) would be applicable or are able to 

be specified by the user. 
35 

v. Analysis of temporal discretization averaging. 

The DEGADIS model allows for specification of different time-averages. The 

time-averages specified in the validation study reflect the time-averaged data of the 

experimental measurements. For flammable gases, typically the short time averages are 

of most interest. Long time averages will reduce the maximum concentration as time 

progresses, which can result in concentrations predicted below that of interest (i.e., LFL) 

and potential under-prediction of the hazard. Longer time averages may provide insight 

into the duration of the hazard and/or the peak to mean ratio that may be a result of cloud 

meander or turbulence, which may be of importance in more detailed risk analyses. This 

is shown in Table 3.14-8. 

Table 3.14-8: 

Effect of Time-Average on the Maximum Arc-Wise Concentration

Test Short Long 

Burro 3 1 second 100 seconds 

57 m 66.7% 66.7% 

140 m 25.3% 25.3% 

400 m 5.1% 4.9% 

800 m 1.2% 0.8% 

Burro 7 1 second 140 seconds 

57 m 61.2% 61.2% 

140 m 22.7% 22.7% 

400 m 4.8% 4.8% 

Burro 8 1 second 80 seconds 

57 m 83.8% 83.8% 

140 m 22.0% 22.0% 

400 m 3.1% 3.1% 

800 m 1.0% 1.0% 

Burro 9 1 second 50 seconds 

140 m 30.6% 30.6% 

400 m 6.9% 6.6% 

800 m 2.1% 1.6% 
36 

Table 3.14-8 (cont’d): 

Effect of Time-Average on the Maximum Arc-Wise Concentration

Test Short Long 

Coyote 3 1 second 50 seconds 

140 m 23.9% 23.9% 

200 m 14.6% 14.6% 

300 m 7.9% 7.8% 

400 m 4.9% 4.3% 

500 m 3.0% 2.4% 

Coyote 5 1 second 90 seconds 

140 m 19.6% 19.5% 

200 m 13.4% 12.7% 

300 m 7.5% 5.3% 

400 m 4.9% 2.5% 

500 m 3.3% 1.5% 

Coyote 6 1 second 70 seconds 

140 m 21.6% 21.6% 

200 m 14.3% 14.3% 

300 m 9.2% 9.2% 

400 m 6.1% 6.1% 

The maximum arc-wise concentrations are not greatly affected by time averaging, 

but will generally reduce the concentration. Longer time averages with respect to spill 

duration, higher turbulence, and higher wind speeds exhibit a greater reduction in 

concentrations (especially in the far field). The lower concentration may be a result of a 

lesser hazard duration and/or higher peak to mean ratio from turbulence and/or cloud 

meander. This reduction in concentration between time averaging can be seen in Coyote 

5 where high wind speeds (>10 m/s) and neutral atmospheric stability were present. 

The time-averaging in DEGADIS is primarily to take into account cloud meander 

and will increase gas concentrations farther from the centerline (via the parameterization 

of horizontal turbulence), while the time-averaging in experimental data will primarily 

reduce gas concentrations. Therefore, time-averaging has a relatively larger impact on 

cloud widths than centerline concentration, as shown in Table 3.14-9. 
37 

Table 3.14-9: Effect of Time-Average on the Plume Width 

Test Short Long 

Burro 3 1 second 100 seconds 

57 m 16.4% 17.0% 

140 m 9.3% 12.4% 

800 m 17.3% 27.5% 

Burro 7 1 second 140 seconds 

57 m 11.2% 11.1% 

140 m 15.5% 16.7% 

400 m 14.7% 17.4% 

Burro 8 1 second 80 seconds 

57 m 29.0% 28.9% 

140 m 40.3% 39.2% 

400 m 44.1% 42.8% 

800 m 40.5% 39.4% 

Burro 9 1 second 50 seconds 

140 m 19.5% 27.7% 

400 m 35.1% 36.2% 

800 m 39.7% 47.6% 

Coyote 3 1 second 140 seconds 

140 m 19.7% 36.8% 

200 m 16.2% 32.7% 

400 m 25.7% 57.3% 

Coyote 5 1 second 80 seconds 

140 m 13.6% 13.7% 

200 m 20.1% 20.9% 

300 m 25.1% 27.7% 

400 m 28.9% 34.4% 

500 m 44.2% 57.5% 

Coyote 6 1 second 50 seconds 

140 m 22.7% 24.2% 

200 m 23.6% 24.8% 

300 m 23.6% 23.5% 

400 m 26.6% 26.8% 
38 

vi. Analysis of spatial discretization averaging and grid resolution. 

As use of a computational mesh is not related to DEGADIS, this section is not 

applicable. 

vii. Analysis of geometrical representation for sloped and obstructed cases. 

Sloped terrain and obstructions cannot be modeled with DEGADIS. Therefore, 

this analysis is not applicable. 

3.14.2 Uncertainty Analysis of Model Output 

This series of uncertainty analyses addresses model uncertainty due to uncertainty 

in the output used for evaluation. 

i. Analysis of spatial output. 

The DEGADIS model outputs concentrations at specific downwind distance 

intervals that do not always coincide with the experimental sensor locations. Therefore, 

interpolation of concentrations between downwind distances is often required to 

determine the concentration at the reflective experimental sensor location. The error 

associated with the interpolation is dependant on the model’s output with respect to the 

sensor location. Most often there are not large differences between the interpolation 

points from a model’s output with respect to the sensor locations and therefore this 

uncertainty is regarded as being inconsequential. 

The determination of the distance to the LFL (taken as 5% for methane) requires 

interpolation or extrapolation of the experimental data and the model output. The 

experimental uncertainty associated with the interpolation and extrapolation is dependant 

on the distance between sensor locations relative to the distance to the LFL concentration. 

Since there is the potential for large gaps when interpolating and extrapolating the 

distance to the LFL from the experiments, there is the potential for a greater amount of 

uncertainty when determining the distance to the LFL for the experiments. 

Linear, logarithmic-logarithmic (log-log) and power growth interpolation and 

extrapolation methodologies have been evaluated to determine the effect on the predicted 

results. Log-log interpolation of concentration and distance is generally more accepted 

for unobstructed dispersion compared to other methodologies, but it will generally 

provide less conservative results (i.e., shorter distances to LFL) and has the potential to 

under-predict the distances to the LFL. Linear interpolation will generally over-predict 

concentrations and was used in the Burro Series Report, but linear extrapolation will 

generally under-predict concentrations (Koopman et al., 1982a) (Koopman et al., 1982b). 

Linear interpolation and extrapolation also has the potential for higher uncertainties 

compared to the other methodologies. Power-growth interpolation tends to produce 

results in between linear and log-log interpolation. 
39 

In an attempt to “match” the uncertainty between the interpolation and 

extrapolation of the experimental data with the interpolation and extrapolation of the 

model output data, the distance to the LFL is interpolated and extrapolated using the 

sensor locations only. A more refined distance to the LFL from linear interpolation of the 

more detailed model spatial output is also evaluated to provide a better prediction of the 

distance to the LFL and an indication of the potential uncertainty from the interpolation 

and extrapolation methodologies using the experimental sensor locations. 

For comparative reasons, the results among the three interpolation and 

extrapolation methodologies is provided in Table 3.14-10. 

Table 3.14-10: 

Comparison of Interpolation / Extrapolation Methodologies: Experiment 

Results 

Test 

Linearly 

interpolated/ 

extrapolated 

distance to the 

LFL 

Power growth 

interpolated/ 

extrapolated 

distance to the 

LFL 

Log-log 

interpolated/ 

extrapolated 

distance to the 

LFL 

Maplin Sands 27 167m 165 m 158 m 

Maplin Sands 34 199 m 209 m 241 m 

Maplin Sands 35 190 m 188 m 187 m 

Burro 3 268 m 235 m 183 m 

Burro 7 309 m 276 m 256 m 

Burro 8 385 m 377 m 356 m 

Burro 9 361 m 341 m 315 m 

Coyote 3 212 m 210 m 207 m 

Coyote 5 277 m 274 m 267 m 

Coyote 6 281 m 278 m 271 m 

Falcon 1 293 m 312 m 371 m 

Falcon 3 280 m 292 m 315 m 

Falcon 4 6 m 31 m 34 m 

As expected for the unobstructed experiments, the linear interpolation provided 

the most conservative (i.e., farthest distances to the LFL) followed by the power growth 

interpolation and then the log-log interpolation. Note that the Falcon tests, which contain 

obstructions in the flow field and had to be extrapolated, follow the opposite trend, as 

shown in Table 3.14-10. 
40 

Table 3.14-11: 

Comparison of Interpolation / Extrapolation Methodologies: Model Results 

Test 

Linearly 

interpolated/ 

extrapolated 

distance to 

the LFL 

Power growth 

interpolated/ 

extrapolated 

distance to the 

LFL 

Log-log 

interpolated/ 

extrapolated 

distance to 

the LFL 

Refined 

linearly 

interpolated/ 

extrapolated 

distance to the 

LFL 

Maplin Sands 27 195 m 193 m 190 m 204 m 

Maplin Sands 34 186 m 189 m 194 m 191 m 

Maplin Sands 35 229 m 226 m 223 m 223 m 

Burro 3 411 m 408 m 404 m 405 m 

Burro 7 397 m 395 m 389 m 388 m 

Burro 8 374 m 360 m 310 m 289 m 

Burro 9 560 m 528 m 484 m 492 m 

Coyote 3 376 m 373 m 367 m 392 m 

Coyote 5 396 m 396 m 395 m 396 m 

Coyote 6 437 m 445 m 463 m 457 m 

The model results show a general convergence toward the refined linearly 

interpolated/ extrapolated results in the order of: linear, power growth, and then log-log 

interpolation/ extrapolation.1

 As expected, log-log interpolation appears to best predict 

the distance to the LFL (+7%, -7%) when evaluated against the more refined linear 

interpolated distances to the LFL from the model output. Also, as expected, linear 

interpolation generally resulted in more conservative distances to the LFL (up to +30%) 

when interpolating (Burro 8) and less conservative distances to the LFL (up to -5%) when 

extrapolating (Maplin Sands 34 and Coyote 6).2

 Power growth interpolation resulted in 

similar trends as linear (+25%, -3%), but less severe. 

 1

 The refined linearly interpolated/extrapolated results should have negligible 

uncertainty from interpolation/extrapolation given the model’s spatial and concentration 

output being within close proximity to the LFL concentration. 

2

 With the exception of Coyote 3, linear interpolation over-predicted the refined 

linear interpolated/extrapolated results. 
41 

The log-log interpolated experimental and model results using the sensor locations 

have been used (in lieu of more accurate model results) for evaluating the quantitative 

acceptance criteria for the concentration safety factor at the lower flammability limit 

(CSF_LFL) and the distance safety factor to the lower flammability limit (DSF_LFL) in 

order to “match” the uncertainty associated with the sensor location. However, as long as 

similar interpolation and extrapolation methodologies are compared, the values do not 

differ by much. Values are shown in Table 3.14-12. The log-log interpolation and 

extrapolation of the experimental and model results are compared in Table 3.14-13 with 

the more refined linear interpolated model results. 

Table 3.14-12: 

Experimental and Model Results for Lower Flammability Limits 

Factor Log-Log Linear Power Growth 

 CSF_LFL 1.80 1.81 1.75 

DSF_LFL 1.43 1.34 1.38 

Table 3.14-13: 

Interpolation and Extrapolation of the Experimental and Model Results 

Test 

Log-log 

interpolated/ 

extrapolated 

distance to the 

LFL (Experiment) 

Log-log 

interpolated/ 

extrapolated 

distance to the 

LFL ( model) 

Refined linearly 

interpolated/ 

extrapolated 

distance to the 

LFL ( model) 

Maplin Sands 27 158 m 190 m 204 m 

Maplin Sands 34 241 m 194 m 191 m 

Maplin Sands 35 187 m 223 m 223 m 

Burro 3 183 m 404 m 405 m 

Burro 7 256 m 389 m 388 m 

Burro 8 356 m 310 m 289 m 

Burro 9 315 m 484 m 492 m 

Coyote 3 207 m 367 m 392 m 

Coyote 5 267 m 395 m 396 m 

Coyote 6 271 m 463 m 457 m 
42 

In addition, the model assumes a top-hat and Gaussian concentration profile in the 

cross-wise direction. Maximum concentrations are based upon the maximum 

concentration predicted by the model, which corresponds to the centerline concentration 

predicted in the integral model. However, the maximum concentration may not always 

be captured by the experiment or occur along the centerline. This will cause the model to 

generally over-predict experimental data where the actual maximum concentration was 

not captured by the sensors in the experiment. Cloud meandering during the experiments 

may reduce this over-prediction, but for many experiments the wind direction was fairly 

steady and meandering may not be significant. 

The effect of this has been analyzed to some extent by evaluating the point-wise 

data that accounts for the offset between the vapor cloud centerline and the sensor that 

received the maximum concentration for the test. However, experimental data shows that 

maximum concentrations may not always exist along the centerline, which makes 

quantifying this effect more complex. 

ii. Analysis of temporal output. 

The DEGADIS model outputs concentrations at specific time intervals. The 

maximum concentration produced over the outputted time periods were utilized, and 

therefore no interpolation or extrapolations were utilized. This is not considered to be a 

large source of uncertainty. 

3.14.3 Uncertainty Analysis of Experimental Data 

This uncertainty analysis addresses experimental uncertainty due to uncertainty in 

the sensor measurement of gas concentration. The experimental uncertainty due to 

uncertainty in the sensor measurement was taken into account based upon the 90% 

confidence levels and uncertainties provided in the respective data series reports 

(Koopmanet al., 1982a) (Koopman et al., 1982b) (Goldwire et al., 1983a) (Goldwire et 

al., 1983b). This is shown in Table 3.14-14. 
43 

Table 3.14-14: 

Uncertainty in the Sensor Measurement of Gas Concentration

Test Measured (vol%) - (vol%) + (%vol) 

Maplin Sands 27 Short Time Avg. 

 58 m 16.9 5.3 5.2

 89 m 12.3 4.0 3.8

 129 m 9.5 3.2 3.1

 181 m 3.3 1.4 1.5

 248 m 3.0 1.3 1.4

 322 m 2.4 1.1 1.2

 399 m 2.9 1.3 1.4

 525 m - - -

 650 m 0.1 0.1 0.6

Maplin Sands 34 Short Time Avg.

89 m 18.1 5.6 5.6

180 m 7.3 2.6 2.5

Maplin Sands 35 Short Time Avg.

 58 m 13.3 4.3 4.1

 89 m 9.9 3.4 3.2

 129 m 7.9 2.8 2.7

 180 m 5.3 2.0 2.0

 250 m 3.4 1.4 1.5

 400 m 2.2 1.1 1.2
44 

Table 3.14-14 (cont’d): 

Uncertainty in the Sensor Measurement of Gas Concentration 

Test Measured 

(vol%) 

- 

(vol%)

+ 

(%vol) 

Measured 

(vol%) 

- 

(vol%) 

+ 

(%vol) 

Burro 3 Short Time Avg. Long Time Avg. 

 57 m 28.2 1.6 1.6 8.5 0.5 0.5 

 140 m 9.0 0.5 0.5 6.4 0.4 0.4 

 400 m 1.2 0.4 0.4 0.7 0.2 0.2 

 800 m 0.9 0.3 0.3 0.9 0.3 0.3 

Burro 7 Short Time Avg. Long Time Avg. 

 57 m 17.9 9.0 9.0 14.8 7.4 7.4

 140 m 7.3 3.7 3.7 4.5 2.3 2.3

 400 m 3.9 1.2 1.2 2.3 0.7 0.7

Burro 8 Short Time Avg. Long Time Avg. 

 57 m 55.9 3.1 3.1 31.0 1.7 1.7

 140 m 18.1 9.1 9.1 16.4 8.2 8.2

 400 m 6.1 1.8 1.8 5.4 1.6 1.6

 800 m 2.1 0.6 0.6 2.1 0.6 0.6

Burro 9 Short Time Avg. Long Time Avg. 

 140 m 10.6 0.6 0.6 6.6 0.4 0.4

 400 m 5.1 2.6 2.6 2.9 1.5 1.5

 800 m 2.2 0.7 0.7 1.4 0.4 0.4
45 

Table 3.14-14 (cont’d): 

Uncertainty in the Sensor Measurement of Gas Concentration 

Test Measured 

(vol%) 

- 

(vol%)

+ 

(%vol)

Measured 

(vol%) 

- 

(vol%) 

+ 

(%vol) 

Coyote 3 Short Time Avg. Long Time Avg. 

140m 10.7 0.6 0.6 5.4 0.3 0.3

200m 5.4 0.3 0.3 2.9 0.2 0.2

300m 1.9 0.2 0.2 0.9 0.1 0.1

400m 2.0 0.2 0.2 0.9 0.1 0.1

500m 0.4 0.1 0.1 0.1 0.0 0.0

Coyote 5 Short Time Avg. Long Time Avg. 

140m 11.5 0.6 0.6 4.2 0.2 0.2

200m 8.1 0.4 0.4 2.5 0.1 0.1

300m 4.1 0.4 0.4 1.1 0.1 0.1

400m 2.3 0.1 0.1 0.8 0.0 0.0

500m 1.8 0.5 0.5 0.5 0.2 0.2

Coyote 6 Short Time Avg. Long Time Avg. 

140m 12.7 0.7 0.7 8.4 0.5 0.5

200m 8.5 0.5 0.5 5.1 0.3 0.3

300m 4.2 0.4 0.4 2.2 0.2 0.2

400m 3.3 0.2 0.2 2.0 0.1 0.1

500m 2.6 0.8 0.8 1.9 0.6 0.6

Experimental uncertainty due to the sampling time, time averaging, 

spatial/volumetric averaging, cloud meander, and other errors or uncertainties associated 

with the experiment were not required to be quantified by the Advisory Bulletin; 

however, examination of all sensor data provided additional insight into uncertainty 

associated with the maximum concentrations recorded in the MEP. These uncertainties 

were noted in the validation database for each sensor and quantified, where possible. 

Where it was possible to estimate the uncertainty, it was included as part of the 

experimental uncertainty. Several qualitative examples are provided for the Burro series: 
46 

 In some tests the IST sensors became saturated with high concentrations 

(~18%) and became “pegged” out. Burro 3 data indicates that the 57 m arc 

may not be a good indication of the maximum concentration because there 

was no sensor that coincided with the “centerline” of cloud for this test and 

there was minimal fluctuation in wind direction. Therefore, the maximum 

concentration is based on sensors 14 m from the vapor cloud “centerline.” 

 Burro 7 data indicates that early in the test the wind direction may have 

prevented the vapor cloud from dispersing over the sensor array at the 57 m 

arc. This may have prevented the sensors from capturing the actual 

maximum concentration. 

 Burro 8 data indicates bifurcation of the vapor cloud. 

 Burro 9 data indicates that a large rapid phase transition occurred during the 

experiments that may have affected the accuracy of the sensor array at the 

57 m arc. In addition, the lowest positioned sensor at the 57 m arc was not 

operable and would have likely experienced the maximum concentration 

due to its low elevation. 

3.14.4 Uncertainty Analysis Results 

Graphical depictions of the predicted and measured gas concentration values for 

each experiment, with indication of the experimental and model uncertainty, are shown in 

the accompanying validation database. 

3.14.5 Additional Specific Performance Measures 

Calculation of the specific performance measures identified in the MEP and the 

Advisory Bulletin are shown in the accompanying validation database. 

3.14.6 Individual Specific Performance Measures 

Calculation of specific performance measures, as identified in the MEP and the 

Advisory Bulletin, for each experiment and data point, as well as the the average of all 

experiments, is shown in the accompanying validation database. 

3.14.7 Model Input/Output Results 

A tabulation of all simulations, including all specified input parameters and 

calculated outputs is provided in the accompanying validation database. 
47 

3.14.8 Specific Performance Measures Results 

A tabulation of all calculated specific performance measures is provided in the 

accompanying validation database. 

3.14.9 Input and Output Files 

All relevant input and output files used in preparation of this document are 

included in the accompanying validation database. 
48 

4.0 CONCLUSIONS 

4.1 SCIENTIFIC ASSESSMENT 

DEGADIS is an integral model developed by Spicer and Havens derived from the 

HEGADAS mathematical model published by Colenbrander et al at Shell (1980). 

DEGADIS solves for the concentration, advecting downwind, with parameterized 

turbulent diffusion coefficients and top entrainment velocity. DEGADIS also solves for 

the temperature of the vapor, and includes heat transfer from the air, including relative 

humidity, and from the ground. 

DEGADIS solves ordinary differential equations using the Runge-Kutta method 

using a variable step that is 4th order accurate. Although this methodology can be 

considered a source of uncertainty, it is not expected to be a large source of uncertainty 

for the results. 

DEGADIS does not include a source term model to simulate any characteristics 

associated with the release, such as flow rates associated with the release, flashing of 

superheated liquids upon a release, the formation, vaporization, or rainout of aerosol 

droplets upon a release, or the formation, vaporization, or spreading of a liquid pool upon 

a release. DEGADIS requires the specification of a gaseous source term from the user. 

DEGADIS is limited to handling a low-momentum source term where the 

diameter and vaporization rate are specified as a function of time, or a high momentum 

jet source term where the jet diameter, release rate, elevation, and duration are specified. 

DEGADIS is limited to a single source term. DEGADIS cannot be used to model 

multiple source terms (i.e., flashing and jetting sources that rainout to a pool, multiple 

release locations). 

 For an area source term, DEGADIS assumes the source is vertically oriented 

circular geometry with no momentum. Therefore, for area source terms, DEGADIS is 

limited to vertically oriented, low-momentum releases with regular geometries, such as 

vapors emanating from circular or rectangular sources (i.e., liquid pools or sumps). For 

area source terms for DEGADIS cannot be used for high-momentum releases (i.e. 

pressurized releases, flashing, jetting), or for releases that result in the emanation of 

vapors from irregular or high aspect ratio sources (i.e., trenches, or irregular liquid pools). 

For a jet source term, DEGADIS assumes the source is vertically oriented circular 

geometry that accounts for turbulence associated with the momentum of the release, but 

does not account for turbulence associated with a release reaching grade or impinging 

onto a surface. Therefore, for jet source terms, DEGADIS is limited to vertically 

oriented releases that do not reach grade (i.e., vent stack releases that do not reach grade, 

flashing from vertically oriented piping, and gaseous releases from vertically oriented 

piping that do not reach grade). The DEGADIS jet plume model cannot be used for 
49 

horizontally oriented source terms or releases that may reach grade level or impinge onto 

a surface (i.e., flashing from horizontally oriented piping, any release that reaches grade). 

DEGADIS is limited to simulating steady state wind profiles. DEGADIS cannot 

model transient wind speed or direction. Assuming a steady state wind speed and 

direction is often sufficient for hazard analyses, but can pose limitation in validation 

against experimental data where varying wind speed and direction may affect the 

experimental results. The selection of wind direction is not pertinent or possible in 

DEGADIS, since it assumes a circular source term where the dispersion will be axisymmetric. Assuming a steady wind direction will generally produce higher 

concentrations, because there would be less cloud meander and turbulent mixing caused 

from the change in wind direction. Assuming lower wind speeds will generally result in 

higher downwind concentrations and assuming a higher wind speed will generally result 

in lower downwind concentrations. DEGADIS generally produces the highest downwind 

concentrations at 2 m/s. DEGADIS should be specified with the lower wind speed that is 

reflective of the area or with wind speeds of 2 m/s to produce conservative results. For 

most applications pertinent to this study, DEGADIS will be used in accordance with 49 

C.F.R. § 193.2059, which specifies the lowest wind speed that occurs 90% of time for the 

area or 2 m/s. Steady state wind speed and direction is not expected to be a large 

limitation of the model. 

DEGADIS cannot account for sloped or varying terrain. Sloped or varying terrain 

will affect the gravity spreading of a dense gas release. For dense gas releases, such as 

LNG vapor, concentrations in the far field may be under-predicted along downward 

slopes and concentrations in the far field may be over-predicted along upward slopes. 

Correspondingly, cross-wise concentrations and cloud widths in the far field may be 

over-predicted for downward slopes and cross-wise concentrations and cloud widths in 

the far field may be under-predicted for upward slopes. On the contrary, gas may 

accumulate against an upward slope causing the model to under-predict gas 

concentrations and over-predict cross-wise concentrations and cloud widths in the near 

field or traverse along a downward slope causing the model to over-predict gas 

concentrations and under-predict cross-wise concentrations and cloud widths in the near 

field. DEGADIS was not validated against sloped terrain tests, since it is not designed to 

simulate those scenarios. Therefore, DEGADIS cannot be used to model dispersion 

along slopes or varying terrain. 

DEGADIS is limited to the specification of a single surface roughness. 

DEGADIS cannot account for terrain with varying surface roughness length. Assuming 

a uniform surface roughness is often sufficient. Assuming a higher surface roughness 

will generally result in lower downwind concentrations and assuming a lower surface 

roughness will generally result in higher downwind concentrations. DEGADIS should be 

specified with the lowest surface roughness that is reflective of the area to produce 

conservative results. For most applications pertinent to this study, DEGADIS will be 
50 

used in accordance with 49 C.F.R. § 193.2059, which specifies the surface roughness of 

0.03 m, so this is not expected to be a large limitation of the model. 

DEGADIS does not explicitly model turbulence generated in the flow field from 

obstructions and cannot take into account the change in flow field around obstructions 

that are relatively larger than the vapor cloud. For most instances, downwind 

concentrations assuming unobstructed terrain will be over-predictive since less 

turbulence, and subsequent mixing, would be generated in the flow field and no 

obstructions would restrict the movement of the dispersing vapor. However, there are 

instances where downwind concentrations could be under-predictive due to wind 

channeling effects (Melton & Cornwell, 2009, Gavelli 2011). Wind channeling may 

occur between adjacent LNG storage tanks, buildings, or large structures, which may 

result in the model being under-predictive for concentrations. Therefore, DEGADIS 

cannot be used to model releases that may disperse between large adjacent structures. 

DEGADIS accounts for atmospheric turbulent mixing and dilution through the use 

of empirically derived turbulent mixing coefficients and top entrainment. DEGADIS 

does not explicitly calculate stochastic fluctuations due to turbulence in the flow field. 

Stochastic fluctuations in concentration can result in concentrations higher or lower than 

predicted. Therefore, it is recommended that concentrations should be provided with a 

safety factor of 2 for the LFL to account for estimated peak to mean turbulent 

fluctuations (MER Section 2.3.5). In addition, for area source terms, DEGADIS 

assumes a no-momentum release and does not take into account possible turbulence 

generated by the release. Therefore, for area source terms, DEGADIS cannot be used for 

high-momentum releases (i.e. pressurized releases, flashing, jetting). Assuming no 

turbulence at a low-momentum source (i.e., turbulence generated at the surface of a 

boiling pool) will generally result in lower downwind concentrations because there is less 

turbulent mixing. For jet source terms, DEGADIS accounts for turbulent mixing from 

the jet release, but does not account for turbulence associated with impingement of a jet 

or with a dense vapor cloud reaching grade. Therefore, for jet source terms, DEGADIS 

cannot be used for releases that may reach grade level or impinge onto a surface (i.e., 

flashing from horizontally oriented piping, any release that reaches grade). 

4.2 VERIFICATION 

The verification of the model has been limited to accuracy of the conservation 

relations (e.g. conservation of mass), and has not been documented. The model predates 

the European Commission’s Model Evaluation Group publications and many other 

software quality assurance publications, certifications (International Organization for 

Standardization: Standard 9000 - Quality Management), or standards. The software is 

not proprietary and its executable and source code files are freely available to the public, 

which makes it possible for users to modify the source code and recompile the 

executable, making quality control unmanageable. To address the lack of quality 
51 

assurance / quality control possible with DEGADIS, it is encouraged that simulations be 

verified by an independent party or agency. 

4.3 VALIDATION 

As discussed in Section 4.1, “Scientific Assessment,” the DEGADIS model is 

limited to dispersion over unobstructed level terrain specified by the user. Therefore, the 

current validation study is limited to the following trials: 

 LNG Field Trials: Maplin Sands 27, 34, 35; Burro 3, 7, 8, 9; Coyote 3, 5, 6; 

 Other Field Trials: Thorney Island 45, 47; 

 Wind Tunnel Experiments: CHRC A; BA-Hamburg DA0120 

(Unobstructed), DAT223 (Unobstructed 2); and BA-TNO TUV01, FLS. 

DEGADIS met most of the MEP quantitative acceptance criteria for short time 

averages with the exception of mean relative bias, MRB, and mean relative square error, 

MRSE, as shown in Table 2.2-1. As shown in Figure 4.3-1 and supported by the 

statistical performance measure values, DEGADIS is generally over-predictive, but 

exhibits a large degree of scatter and only about half of its predictions are within a factor 

of 2. However, the MEP specific performance measures and quantitative acceptance 

criteria are based on an average of all the trials, which can be misleading. Therefore, it 

was recognized in the Advisory Bulletin that the approval or disapproval of a model 

should not be contingent only on the average of the experiments meeting the MEP 

quantitative acceptance criteria. Careful examination of all the sensor data and trends 

must be considered in concert with the MEP quantitative acceptance criteria. As shown 

in Table 2.2-2, these trends provide additional insight into the model performance against 

subsets of data. 
52 

Unobstructed Predicted and Measured Concentration

0.10

1.00

10.00

100.00

0.10 1.00 10.00 100.00

measured concentration (mol%)

predicted concentration (mol%)

Maplin Sands 27 short

Maplin Sands 34 short

Maplin Sands 35 short

Burro 3 short

Burro 7 short

Burro 8 short

Burro 9 short

Coyote 3 short

Coyote 5 short

Coyote 6 short

Burro 3 long

Burro 7 long

Burro 8 long

Burro 9 long

TI 45 long

TI 47 long

Coyote 3 long

Coyote 5 long

Coyote 6 long

CHRC A scaled

BA Hamburg DA0120 scaled

BA Hamburg DAT223 scaled

BA Hamburg DAT647 scaled

BA Hamburg DAT631 scaled

BA Hamburg DAT632 scaled

BA Hamburg DAT637 scaled

TNO FLS scaled

ideal

+FAC2

-FAC2

Figure 4.3-1 Predicted Concentration against Measured Concentration 

DEGADIS is generally over-predictive for maximum arc-wise concentrations for 

field trials often by a factor of 2 or more. A large percentage of the data is over-predicted 

with over a third of the data being over-predicted by more than a factor of 2 contributing 

to why the FAC2 did not meet the acceptance criteria. Field trials with short time 

averages may be the most pertinent data set for LNG flammable hazards, and agree the 

best with the data. The over-prediction is more severe for field trials with long time 

averages. The higher CSF for longer time averages can be attributed to the little 

sensitivity the model shows to longer time averages compared to the sensitivity the 

experimental data exhibits. DEGADIS becomes less conservative as the vapor cloud 

disperses downwind, and may be under-predictive in the far field (at typically less than 

LFL concentrations). DEGADIS is less conservative for dispersion over water and may 

be under-predictive for low wind speeds (<2 m/s) and high atmospheric stabilities (F 

stability), which is especially pertinent to the current federal regulations. DEGADIS is 
53 

generally under-predictive for wind tunnel experiments often by a factor of 2 or more. 

All wind tunnel data was under-predicted with the majority of the data being underpredicted by more than a factor of 2 contributing to the FAC2 not meeting the acceptance 

criteria. Similar to the field trials, DEGADIS becomes less conservative as the vapor 

disperses downwind, and may be under-predictive in the far field at lower concentrations. 

DEGADIS performs better for the CHRC test, which was designed to be used as a scale 

model for LNG dispersion. 

DEGADIS compares much better with maximum gas concentration distances, and 

meets nearly all the acceptance criteria. DEGADIS shows similar trends for field trials 

and wind-tunnel tests. DEGADIS generally over-predicts the distance to a given 

concentration for field trials by approximately a factor of 1.5, and under-predicts windtunnel tests by approximately a factor of 1.5. The relatively better agreement is because 

large concentration differences may manifest themselves as much smaller differences in 

distance. 

DEGADIS generally over-predicts point-wise gas concentrations that are located 

at an angle corresponding to the wind direction where the maximum arc-wise 

concentration often occurred, and under-predicts point-wise gas concentrations that are 

located farther from the “centerline”. The under-prediction of concentrations farther 

from the “centerline” is much more drastic than the over-prediction near the “centerline,” 

which results in an average under-prediction and a high degree of scatter. In addition, 

DEGADIS generally seems to under-predict short time averages and over-predict long 

time averages with a difference of a factor of 2 or more between them. 

Similarly to maximum gas concentration distances, DEGADIS compares much 

better with cloud widths. However, DEGADIS generally under-predicts the cloud width 

by a factor of 1.5. Cloud widths are also less influenced by large concentration 

differences, which may manifest themselves as much smaller differences in cloud widths. 

Cloud widths are not a particular concern with 49 CFR Part 193, but may cause under 

prediction of the hazard footprint, which can affect risk analyses or performance based 

design of gas detectors. 

DEGADIS may be less conservative or under-predictive for maximum arc-wise 

concentrations for field trials with low wind speed and high atmospheric stabilities, a 

particular concern for 49 CFR Part 193. Although the field trials are most applicable to 

the scenarios considered under the Part 193 regulations and generally show overprediction, there are a number of uncertainties that indicate potential under-prediction by 

a factor of 2. Until these uncertainties are resolved, it is recommended that a safety factor 

of 2 be used when evaluating predicted maximum arc-wise concentrations from 

DEGADIS. Alternatively, a distance safety factor of 2 may be used. 
54 

4.4 SENSITIVITY ANALYSES 

The sensitivity analyses for DEGADIS indicates little sensitivity to the pool 

spread velocity, vaporization rate, and pool diameter for spills over water. However, all 

the LNG field trial releases were conducted over water and the associated source terms 

will be different than those used on land. For spills over water with significant depth, the 

heat transfer to the pool is generally considered constant due to convective motion of the 

water. For spills over land, the heat transfer to the pool is generally considered to be 

transient due to conductive cooling of the substrate. Pressurized releases may further 

deviate from the more idealized source term for spills over water. Therefore for spills 

over land and pressurized releases, it is recommended that the source term is evaluated 

before usage. 

Longer time averages result in slightly lower maximum arc-wise gas 

concentrations, and significantly higher maximum point-wise concentrations away from 

the centerline. The maximum point-wise gas concentrations are affected more 

significantly because DEGADIS parameterizes its horizontal turbulence coefficients 

based on time averaging to take into account cloud meander. In contrast, longer time 

averages of experimental data will only result in lesser concentrations. Therefore, 

comparison with longer experimental time averages may cause the model to appear more 

conservative than it actually is. Short time averages are more appropriate for the hazard 

and should be used when predicting flammable vapor centerline concentrations. 

Many of the trials did not have wind speeds that differed by more than 10%. For 

trials that did not have wind speeds that differed by more than 10%, lower wind speeds 

generally produced higher downwind concentrations and dispersion distances, and higher 

wind speeds produced lower downwind concentrations and dispersion distances. The 

exceptions were Burro 8 where very low wind speeds (< 2 m/s) occurred and Maplin 

Sands 34 where very high wind speeds (> 8 m/s) occurred. 

The surface roughness values have the largest uncertainties. The values specified 

in the MEP are generally low and result in higher concentrations and longer dispersion 

distances to the LFL, which may cause the model to appear more conservative than it 

actually is. However, even with less conservative parameters, the model still generally 

over-predicts concentrations. If the surface roughness is prescribed, such as the case in 

49 C.F.R. § 193.2059, it should be made sure that the surface roughness is appropriate 

based on photographic documentation, visual observations, or meteorological data 

representative of the site. For LNG releases that disperse over land, a surface roughness 

of 0.03 may be justified, however, for LNG facilities that release over water, such as for 

offshore facilities or marine loading/unloading platforms that are situated away from the 

shoreline, a lower surface roughness may be more appropriate. 
55 

Lower atmospheric stabilities generally produced lower downwind concentrations 

and dispersion distances, and higher atmospheric stabilities produced higher downwind 

concentrations and dispersion distances. Where the surface roughness uncertainty was 

low, the atmospheric stability often formed the upper or lower bound of the predictions. 

Ambient temperature and surface temperature had little fluctuation, and therefore 

no sensitivity cases were run. However, higher ambient temperatures and surface 

temperatures should generally produce lower gas concentrations and downwind 

dispersion distances. 

None of the trials had ambient pressures that differed by more than 10% from 

atmospheric pressure, but in order to test the sensitivity, Burro 7, which had the lowest 

ambient pressure was tested. Higher ambient pressure showed slightly lower 

concentrations and downwind dispersion distances. 

Many of the trials did not have ambient relative humidity that differed by more 

than 10%, but some of the values disagreed with those reported in the original data series 

reports. For trials that did not have ambient relative humidity that differed, lower ambient 

relative humidity generally produced higher gas concentrations in the near field, but 

lower gas concentrations in the far field, and vice-versa. 

The water transfer submodel showed negligible differences when included in the 

predicted concentrations and distance to LFL. 

The molecular weight specified in the MEP reflects the composition of the LNG 

and does not take into account preferential boiloff. The lower molecular weight of 

methane results in higher concentrations and longer dispersion distances to the LFL. 

However, even with less conservative parameters, the model still generally over-predicts 

concentrations. The molecular weight of methane is recommended to be used to account 

for potential preferential boiloff and conservatism. 

Overall, the sensitivity analysis showed concentrations may differ by more than a 

factor of four and downwind dispersion distances to the LFL may differ by up to a factor 

of two, dependant on the uncertainty in the user input and sensitivity to that input. 

4.5 MODEL SUITABILITY AND LIMITATIONS 

DEGADIS requires a source term to be inputted into the model. The specification 

of the source term is a key parameter in determining the gas concentrations and 

dispersion distances, but is not examined under the MEP or the Advisory Bulletin. The 

suitability of the source term model must be reviewed before being used in Part 193 

calculations. 
56 

DEGADIS may be used to model the maximum arc-wise concentration for: 

 Dispersion from circularly shaped LNG pools; 

 Dispersion from LNG pools with low-aspect ratios, including most 

impoundments; 

 Dispersion from vertically oriented releases that do not reach grade, 

including releases from flashing, venting, vent stacks, and pressure relief 

discharge; or 

 Dispersion over flat or upward sloped terrain. 

DEGADIS may not be appropriate to be used to model the maximum arc-wise 

concentration for: 

 Dispersion from irregularly shaped LNG pools 

 Dispersion from LNG pools with high-aspect ratios, including some 

impoundments and nearly all trenches; 

 Dispersion from vertically oriented releases that reach grade, including 

releases from flashing, venting, vent stacks, and pressure relief discharge; 

 Dispersion from horizontally oriented releases, including flashing, jetting, 

venting, and pressure relief discharge; 

 Dispersion from multiple coincident releases, including multiple release 

locations; 

 Dispersion over varying or downward sloped terrain; or 

 Dispersion between large obstructions that may cause wind-channeling. 

DEGADIS may not be appropriate to model point-wise concentrations, and may 

be under-predictive for cloud widths. 

The ambient conditions required under 49 CFR § 193.2059 should produce 

conservative results (i.e. higher downwind gas concentrations and dispersion distances). 

DEGADIS should be used with a safety factor of 2 (i.e. 1⁄2 LFL) to compensate for 

uncertainties related to potential turbulent fluctuations, wind tunnel experiment validation 

results, and low wind speed and high atmospheric stability validation results. 
APPENDIX A: SENSITIVITY CASE RESULTS 
Test a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_

Maplin Sands 27 

58m 30.9% 30.6% 30.4% N/A 30.6% 30.1% N/A 35.5% 25.4% 31.3% N/A 31.3% N/A N/A 29.789m 16.3% 16.3% 16.9% N/A 13.7% 16.3% N/A 19.0% 13.3% 16.3% N/A 15.5% N/A N/A 14.5

129m 10.1% 10.2% 10.0% N/A 9.2% 9.9% N/A 11.4% 8.5% 10.1% N/A 9.8% N/A N/A 8.2181m 6.3% 6.4% 6.4% N/A 6.8% 5.6% N/A 7.0% 4.7% 6.8% N/A 6.8% N/A N/A 4.8248m 3.3% 3.3% 4.1% N/A 4.7% 2.7% N/A 3.7% 2.2% 3.9% N/A 4.6% N/A N/A 2.6322m 1.7% 1.7% 2.6% N/A 3.0% 1.4% N/A 1.9% 1.2% 2.0% N/A 3.2% N/A N/A 1.4399m 1.0% 1.0% 1.5% N/A 1.7% 0.8% N/A 1.1% 0.7% 1.1% N/A 2.3% N/A N/A 0.9650m 0.3% 0.3% 0.4% N/A 0.4% 0.3% N/A 0.3% 0.2% 0.3% N/A 0.8% N/A N/A 0.3

Dist to 

LFL 204m 206m 216m N/A 236m 190m N/A 214m 175m 220m N/A 234m N/A N/A 177

Maplin Sands 34 

89m 14.6% N/A 14.1% 12.7% N/A 12.6% N/A 14.8% 12.2% 14.4% 14.2% N/A N/A N/A 12.2

180m 5.6% N/A 5.5% 5.4% N/A 5.0% N/A 5.5% 4.8% 5.5% 4.0% N/A N/A N/A 3.9

Dist to 

LFL 191m N/A 191m 191m N/A 180m N/A 184m 176m 188m 161m N/A N/A N/A 160

Maplin Sands 35 

58m 28.7% 28.1% 21.7% N/A 31.4% 25.7% N/A 32.7% 24.2% 28.0% 26.5% N/A N/A N/A 28.289m 16.6% 16.5% 13.6% N/A 16.6% 15.8% N/A 19.5% 14.2% 16.6% 16.2% N/A N/A N/A 16.2

129m 10.4% 10.4% 8.8% N/A 11.4% 9.9% N/A 12.3% 8.8% 10.5% 9.9% N/A N/A N/A 9.9180m 6.7% 6.7% 5.8% N/A 7.4% 6.4% N/A 7.6% 5.7% 6.7% 5.5% N/A N/A N/A 6.2250m 4.3% 4.2% 3.7% N/A 5.0% 4.0% N/A 4.9% 3.6% 4.3% 2.7% N/A N/A N/A 3.5400m 2.1% 2.1% 1.9% N/A 2.5% 2.0% N/A 2.4% 1.8% 2.1% 1.0% N/A N/A N/A 1.5

Dist to 

LFL 223m 222m 202m N/A 249m 213m N/A 246m 200m 223m 187m N/A N/A N/A 206
Test a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_1

Burro 3 

57m 66.7% 66.3% 64.4% 66.7% 68.3% 64.5% 67.0% N/A 41.2% N/A N/A 68.0% N/A N/A N/

140m 25.3% 25.2% 25.1% 25.3% 26.0% 24.8% 25.1% N/A 12.2% N/A N/A 26.6% N/A N/A N/400m 5.1% 5.0% 4.9% 4.9% 5.2% 5.0% 5.1% N/A 2.4% N/A N/A 5.3% N/A N/A N/800m 1.2% 1.2% 1.6% 0.8% 1.1% 1.3% 1.2% N/A 0.5% N/A N/A 1.8% N/A N/A N/

Dist to 

LFL 405m 402m 394m 395m 414m 397m 404m N/A 257m N/A N/A 414m N/A N/A N/

Burro 7 

57m 61.2% 60.7% 49.4% 61.2% N/A N/A 61.4% N/A 33.9% 60.9% 60.0% N/A N/A 60.0% 58.9

140m 22.7% 22.4% 2.2% 22.7% N/A N/A 23.2% N/A 11.0% 22.5% 21.4% N/A N/A 21.5% 22.7400m 4.8% 4.8% 4.4% 4.8% N/A N/A 4.8% N/A 2.4% 4.8% 4.6% N/A N/A 4.6% 4.8

Dist to 

LFL 388m 387m 368m 388m N/A N/A 390m N/A 242m 388m 381m N/A N/A 374m 386

Burro 8 

57m 83.8% 100% 100% 83.8% 88.3% 89.8% 83.9% N/A 67.2% 85.5% N/A 80.2% N/A N/A N/

140m 22.0% 22.5% 21.0% 22.0% 16.3% 25.1% 21.9% N/A 15.7% 23.1% N/A 21.8% N/A N/A N/400m 3.1% 2.9% 3.3% 3.1% 2.1% 3.6% 3.1% N/A 3.5% 3.5% N/A 2.9% N/A N/A N/800m 1.0% 1.0% 1.1% 1.0% 0.7% 1.2% 1.0% N/A 1.3% 1.1% N/A 1.0% N/A N/A N/

Dist to 

LFL 289m 291m 308m 289m 221m 329m 290m N/A 302m 328m N/A 284m N/A N/A N/

Burro 9 

57m 76.4% 76.1% 73.6% 76.4% N/A N/A 76.5% N/A 45.7% 76.5% N/A 74.9% N/A N/A 76.9

140m 30.6% 29.5% 29.7% 30.6% N/A N/A 31.2% N/A 15.9% 30.8% N/A 30.4% N/A N/A 32.5400m 6.9% 6.6% 6.3% 6.6% N/A N/A 6.9% N/A 3.4% 6.9% N/A 6.7% N/A N/A 6.6800m 2.1% 2.2% 2.2% 1.6% N/A N/A 2.1% N/A 0.9% 2.1% N/A 1.4% N/A N/A 2.0

Dist to 

LFL 492m 482m 465m 491m N/A N/A 492m N/A 307m 493m N/A 481m N/A N/A 462
Test a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_1

Coyote 3 

140m 23.9% 22.4% 21.4% 23.9% N/A N/A 23.6% N/A 11.9% 23.2% N/A 24.2% N/A N/A 24.0200m 14.6% 13.7% 13.3% 14.6% N/A N/A 14.6% N/A 7.4% 14.6% N/A 15.0% N/A N/A 14.6300m 7.9% 7.6% 7.3% 7.8% N/A N/A 7.8% N/A 4.0% 7.7% N/A 8.1% N/A N/A 7.6400m 4.9% 4.8% 4.7% 4.3% N/A N/A 4.9% N/A 2.2% 5.0% N/A 5.1% N/A N/A 4.6500m 3.0% 2.9% 2.9% 2.4% N/A N/A 3.2% N/A 1.3% 2.9% N/A 3.6% N/A N/A 2.8

Dist to 

LFL 392m 392m 385m 378m N/A N/A 396m N/A 254m 399m N/A 405m N/A N/A 383

Coyote 5 

140m 19.6% 19.7% 14.9% 19.5% N/A N/A 19.4% N/A 10.0% 19.9% N/A 20.8% N/A N/A 20.200m 13.4% 12.5% 10.3% 12.7% N/A N/A 12.8% N/A 6.8% 13.5% N/A 13.8% N/A N/A 13.300m 7.5% 7.3% 6.3% 5.3% N/A N/A 7.3% N/A 3.8% 7.6% N/A 7.7% N/A N/A 7.3400m 4.9% 4.7% 4.3% 2.5% N/A N/A 4.8% N/A 2.3% 5.0% N/A 5.1% N/A N/A 4.7500m 3.3% 3.0% 3.0% 1.5% N/A N/A 3.1% N/A 1.4% 3.3% N/A 3.8% N/A N/A 3.4

Dist to 

LFL 396m 387m 358m 310m N/A N/A 392m N/A 253m 400m N/A 408m N/A N/A 387

Coyote 6 

140m 21.6% 23.0% 24.8% 21.6% N/A N/A 22.6% N/A 14.1% 21.7% N/A 21.1% N/A N/A 29.4200m 14.3% 14.7% 15.2% 14.3% N/A N/A 14.7% N/A 8.9% 14.4% N/A 14.2% N/A N/A 16.7300m 9.2% 9.1% 9.1% 9.2% N/A N/A 9.3% N/A 4.9% 9.3% N/A 9.1% N/A N/A 8.1400m 6.1% 6.8% 6.0% 6.1% N/A N/A 6.3% N/A 3.3% 6.2% N/A 6.4% N/A N/A 4.8500m 4.3% 4.3% 4.2% 4.2% N/A N/A 4.4% N/A 2.3% 4.3% N/A 4.6% N/A N/A 3.3

Dist to 

LFL 457m 455m 451m 455m N/A N/A 459m N/A 292m 462m N/A 467m N/A N/A 393
Test a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_1

Thorney Island 45 

40m 29.5% 28.2% N/A N/A N/A N/A N/A 12.8% 32.4% 30.0% 26.7% N/A N/A N/A N/53m 29.5% 28.2% N/A N/A N/A N/A N/A 12.8% 16.0% 28.9% 20.4% N/A N/A N/A N/72m 12.5% 22.4% N/A N/A N/A N/A N/A 12.8% 11.5% 12.9% 12.4% N/A N/A N/A N/90m 10.0% 15.2% N/A N/A N/A N/A N/A 12.8% 7.9% 9.9% 7.8% N/A N/A N/A N/

112m 7.0% 8.8% N/A N/A N/A N/A N/A 12.8% 4.6% 6.7% 4.9% N/A N/A N/A N/158m 3.3% 3.3% N/A N/A N/A N/A N/A 12.8% 1.9% 3.1% 2.1% N/A N/A N/A N/250m 1.0% 0.9% N/A N/A N/A N/A N/A 3.3% 0.6% 1.0% 0.7% N/A N/A N/A N/335m 0.5% 0.5% N/A N/A N/A N/A N/A 1.7% 0.3% 0.5% 0.4% N/A N/A N/A N/472m 0.2% 0.2% N/A N/A N/A N/A N/A 0.8% 0.1% 0.2% 0.2% N/A N/A N/A N/

Thorney Island 47 

50m 17.4% 17.0% N/A N/A N/A N/A N/A 11.0% 20.4% 15.6% 25.1% N/A N/A N/A N/90m 17.4% 17.0% N/A N/A N/A N/A N/A 9.2% 20.4% 15.6% 9.0% N/A N/A N/A N/

212m 2.0% 6.8% N/A N/A N/A N/A N/A 7.7% 1.3% 1.9% 2.1% N/A N/A N/A N/250m 1.2% 4.0% N/A N/A N/A N/A N/A 6.9% 0.8% 1.2% 1.2% N/A N/A N/A N/335m 0.5% 1.4% N/A N/A N/A N/A N/A 0.6% 0.3% 0.5% 0.7% N/A N/A N/A N/472m 0.2% 0.5% N/A N/A N/A N/A N/A 0.5% 0.1% 0.2% 0.3% N/A N/A N/A N/
Maplin Sands 27 Measured vs Predicted 

Maximum Arcwise Concentration

Short Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 1000

Downwind distance (m)

Maximum arcwise concentration (%)
Averaging Time

Ambient 

Temperature

Ambient 

Pressure

Ambient 

Relative 

Humidity

Base Case Alternative 1 Alternative 2 Alternative Lower Upper MEP Wind Speed Lower Upper Alternative Lower Upper

Run Name a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_12 Source Term ABS/FERC 0.167kg/m^2/sec0.085kg/m^2/sec ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC 

Wind Speed 5.6 5.6 5.6 4.4 6.1 5.6 5.6 5.6 5.6 5.6 Reference Height 10 10 10 10 10 10 10 10 10 10 Surface Roughness 3.00E-04 3.00E-04 3.00E-04 3.00E-04 3.00E-04 1.00E-04 1.00E-03 3.00E-04 3.00E-04 3.00E-04 Wind Stability C C C C C C C C D C Averaging Time 3 3 3 3 3 3 3 3 3 3 Atmospheric Parameters

DELTA Y 0.10461 0.10461 0.10461 0.10461 0.10461 0.10461 0.10461 0.10461 0.06767 0.10461 BETA Y 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Monin-Obukhov Length -10.5 -10.5 -10.5 -10.5 -10.5 -7.5 -15.1 -22.3 infinite -10.5 

Sigma X Coefficient 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.04 0.02 Sigma X Power 1.22 1.22 1.22 1.22 1.22 1.22 1.22 1.22 1.14 1.22 Sigma X Minimum Dista 130.00 130.00 130.00 130.00 130.00 130.00 130.00 130.00 100.00 130.00 

Wind Power Constant 0.08611 0.086 0.086 0.086 0.086 0.073 0.105 0.094 0.114 0.086 Friction Velocity 0.20954 0.20954 0.20954 0.16464 0.22825 0.19064 0.23549 0.20222 0.1882 0.20954 Ambient Temperature 288.1 288.1 288.1 288.1 288.1 288.1 288.1 288.1 288.1 288.1 Ambient Pressure 1 1 1 1 1 1 1 1 1 1 

Ambient Relative Humidit 53 53 53 53 53 53 53 53 53 63 

Isothermal? N N N N N N N N N N Heat Transfer? Y Y Y Y Y Y Y Y Y Y 

Surface Temperature 288.8 288.8 288.8 288.8 288.8 288.8 288.8 288.8 288.8 288.8 Correlation 1 1 1 1 1 1 1 1 1 1 

Water Transfer? Y Y Y Y Y Y Y Y Y Y Molecular Weight 17.11 17.11 17.11 17.11 17.11 17.11 17.11 17.11 17.11 17.11 Release Temperature 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 Density 1.792 1.792 1.792 1.792 1.792 1.792 1.792 1.792 1.792 1.792 Mean heat capacity const 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 

Mean heat capacity powe 555 55 555 5 5 

Upper Concentration 15.00% 15.00% 15.00% 80.00% 15.00% 15.00% 15.00% 15.00% 15.00% 15.00% Lower Concentration 0.50% 5.00E-03 5.00E-03 0.50% 0.50% 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 Height for isopleths 1 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 Max Concentration at:58m centerline 30.9% 30.6% 30.4% 30.6% 30.1% 35.5% 25.4% 31.3% 31.3% 29.7% 89m centerline 16.3% 16.3% 16.9% 13.7% 16.3% 19.0% 13.3% 16.3% 15.5% 14.5% 129m centerline 10.1% 10.2% 10.0% 9.2% 9.9% 11.4% 8.5% 10.1% 9.8% 8.2% 181m centerline 6.3% 6.4% 6.4% 6.8% 5.6% 7.0% 4.7% 6.8% 6.8% 4.8% 248m centerline 3.3% 3.3% 4.1% 4.7% 2.7% 3.7% 2.2% 3.9% 4.6% 2.6% 322m centerline 1.7% 1.7% 2.6% 3.0% 1.4% 1.9% 1.2% 2.0% 3.2% 1.4% 399m centerline 1.0% 1.0% 1.5% 1.7% 0.8% 1.1% 0.7% 1.1% 2.3% 0.9% 525m centerline 0.5% 0.5% 0.7% 0.8% 0.4% 0.6% 0.4% 0.6% 1.3% 0.4% 650m centerline 0.3% 0.3% 0.4% 0.4% 0.3% 0.3% 0.2% 0.3% 0.8% 0.3% Distance to:

16.9% 87 87 89 78 87 96 75 87 84 81 12.3% 108 109 112 96 110 120 95 108 104 97 

9.5% 137 137 134 124 134 149 118 136 133 117 3.3% 247 247 283 307 228 261 210 264 314 222 3.0% 257 256 298 320 239 272 218 273 337 233 2.4% 280 281 331 350 261 296 240 299 390 257 2.9% 261 260 303 325 242 275 220 276 344 237 

-- - - - - - - - - - 

0.1% 1002 1017 1087 1118 973 1050 907 1023 1367 988 

LFL 204 206 216 236 190 214 175 220 234 177 

Source Term Wind Speed Surface Roughness Stability
Maplin Sands 34 Measured vs Predicted 

Maximum Arcwise Concentration

Short Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration 

(%)
Averaging Time

Monin Obukhov 

Length

Ambient 

Temperature

Ambient 

Pressure

Ambi

Relat

Humi

Base Case Alternative 1 Alternative 2 Alternative Lower Upper Alternative Lower Upper Specified Lower Upper

Run Name a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_1Source Term ABS/FERC 0.167kg/m**2*se0c.085kg/m**2*sec ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/F

Wind Speed 8.5 8.5 8.5 7.6 9.5 8.5 8.5 8.5 8.5 8.5 Reference Height 10 10 10 10 10 10 10 10 10 10 Surface Roughness 3.00E-04 3.00E-04 3.00E-04 3.00E-04 3.00E-04 1.00E-04 1.00E-03 3.00E-04 3.00E-04 3.00EWind Stability D D D D D DDDC D 

Averaging Time 3 3 3 3 3 3333 3 Atmospheric Parameters

DELTA Y 0.06767 0.06767 0.06767 0.06767 0.06767 0.06767 0.06767 0.06767 0.10461 0.067BETA Y 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Monin-Obukhov Length infinite infinite infinite infinite infinite infinite infinite -71.2 -10.5 infinSigma X Coefficient 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.02 0.0Sigma X Power 1.14 1.14 1.14 1.14 1.14 1.14 1.14 1.14 1.22 1.1Sigma X Minimum Distance 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 130.00 100.

Wind Power Constant 0.114 0.114 0.114 0.114 0.114 0.102 0.132 0.104 0.086 0.11Friction Velocity 0.28566 0.28566 0.28566 0.25542 0.31927 0.2584 0.323 0.2955 0.31805 0.285Ambient Temperature 288.4 288.4 288.4 288.4 288.4 288.4 288.4 288.4 288.4 288Ambient Pressure 1 1 1 1 1 1111 1 Ambient Relative Humidity 72 72 72 72 72 72 72 72 72 90 Isothermal? N N N N N NNNN N Heat Transfer to be Included in cal Y Y Y Y Y YYYY Y 

Surface Temperature 289.0 289.0 289.0 289.0 289.0 289.0 289.0 289.0 289.0 289Correlation 1 1 1 1 1 1111 1 

Water Transfer? Y Y Y Y Y YYYY Y Molecular Weight 16.66 16.66 16.66 16.66 16.66 16.66 16.66 16.66 16.66 16.6Release Temperature 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111Density at release temperature and 1.792 1.792 1.792 1.792 1.792 1.792 1.792 1.792 1.792 1.79

Mean heat capacity constant 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60EMean heat capacity power 5 5 5 5 5 5 94878733 5 5 5 Upper Concentration 15.00% 15.00% 15.00% 15.00% 15.00% 15.00% 15.00% 15.00% 15.00% 80.0Lower Concentration of Interest 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% 0.50Height for isopleths 1 1 1 1 1 1111 1 Max Concentration at:58m centerline concentration 26.5% 25.4% 20.4% 25.5% 24.3% 28.1% 22.4% 25.6% 24.7% 24.789m centerline concentration 14.6% 14.1% 12.7% 12.6% 14.2% 14.8% 12.2% 14.4% 14.2% 12.2129m centerline concentration 9.0% 8.9% 8.2% 7.9% 9.1% 9.2% 7.9% 9.1% 8.4% 7.2180m centerline concentration 5.6% 5.5% 5.4% 5.0% 5.6% 5.5% 4.8% 5.5% 4.0% 3.9250m centerline concentration 3.2% 3.1% 3.6% 2.8% 3.2% 3.2% 2.7% 3.1% 2.1% 2.2325m centerline concentration 2.0% 1.9% 2.5% 1.7% 1.8% 2.0% 1.7% 1.9% 1.2% 1.4400m centerline concentration 1.2% 1.2% 1.8% 1.1% 1.2% 1.2% 1.0% 1.2% 0.7% 1.0525m centerline concentration 0.7% 0.7% 1.2% 0.6% 0.7% 0.7% 0.6% 0.7% 0.4% 0.6650m centerline concentration 0.4% 0.4% 0.8% 0.4% 0.4% 0.4% 0.4% 0.4% 0.2% 0.4Distance to:

18.1% 76 74 65 70 74 78 68 76 75 71 

7.3% 151 150 141 137 155 153 137 152 137 12

LFL 191 191 191 180 192 184 176 188 161 16

Source Term Wind Speed Surface Roughness Stability
Maplin Sands 35 Measured vs Predicted 

Maximum Arcwise Concentration

Short Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration 

(%)
Averaging Time

MoninObukhov 

Length

Ambient 

Temperature

Ambient 

Pressure

Ambien

Relativ

Humidit

Base Case Alternative 1 Alternative 2 Alternative Lower Upper Alternative Lower Upper Alternative Lower Upper

Run Name a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_12 Source Term ABS/FERC 0.167kg/m**2-se0c.085kg/m**2*sec ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FER

Wind Speed 9.6 9.6 9.6 7.9 11 9.6 9.6 9.6 9.6 9.6 Reference Height 10 10 10 10 10 10 10 10 10 10 Surface Roughness 3.00E-04 3.00E-04 3.00E-04 3.00E-04 3.00E-04 1.00E-04 1.00E-03 3.00E-04 3.00E-04 3.00E-0Wind Stability D D D D D DDDC D Averaging Time 3 3 3 3 3 3333 3 Atmospheric Parameters

DELTA Y 0.06767 0.06767 0.06767 0.06767 0.06767 0.06767 0.06767 0.06767 0.10461 0.0676BETA Y 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Monin-Obukhov Length infinite infinite infinite infinite infinite infinite infinite -54 -10.5 infinite Sigma X Coefficient 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 2.00E-02 4.00E-0Sigma X Power 1.14 1.14 1.14 1.14 1.14 1.14 1.14 1.14 1.22 1.14 Sigma X Minimum Distance 100 100 100 100 100 100 100 100 130 100 

Wind Power Constant 0.11438 0.11438 0.11438 0.11438 0.11438 0.10172 0.13233 0.10182 0.08611 0.1143Friction Velocity 0.32263 0.32263 0.32263 0.2655 0.36968 0.29185 0.3648 0.33619 0.35921 0.3226Ambient Temperature 289.3 289.3 289.3 289.3 289.3 289.3 289.3 289.3 289.3 289.3 Ambient Pressure 1 1 1 1 1 1111 1 Ambient Relative Humidity 63 63 63 63 63 63 63 63 63 77 Isothermal? N N N N N NNNN N Heat Transfer? Y Y Y Y Y YYYY Y 

Surface Temperature 289.8 289.8 289.8 289.8 289.8 289.8 289.8 289.8 289.8 289.8 Correlation 1 1 1 1 1 1111 1 

Water Transfer? Y N N Y Y YYYY Y Molecular Weight 16.39 16.39 16.39 16.39 16.39 16.39 16.39 16.39 16.39 16.39 Release Temperature 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 Density 1.792 1.792 1.792 1.792 1.792 1.792 1.792 1.792 1.792 1.792 Mean heat capacity constant 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-0Mean heat capacity power 5 5.00E+00 5.00E+00 5 5 5555 5.00E+0

Upper Concentration 15.00% 15.00% 15.00% 15.00% 15.00% 15.00% 15.00% 15.00% 15.00% 15.00% Lower Concentration 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% 0.50% Height for isopleths 1 1 1 1 1 1111 1 Max Concentration at:58m centerline 28.4% 28.1% 21.7% 31.4% 25.7% 32.7% 24.2% 28.0% 26.5% 28.2% 89m centerline 16.6% 16.5% 13.6% 16.6% 15.8% 19.5% 14.2% 16.6% 16.2% 16.2% 129m centerline 10.4% 10.4% 8.8% 11.4% 9.9% 12.3% 8.8% 10.5% 9.9% 9.9% 180m centerline 6.7% 6.7% 5.8% 7.4% 6.4% 7.6% 5.7% 6.7% 5.5% 6.2% 250m centerline 4.3% 4.2% 3.7% 5.0% 4.0% 4.9% 3.6% 4.3% 2.7% 3.5% 324m centerline 2.9% 2.9% 2.5% 3.5% 2.7% 3.4% 2.5% 2.9% 1.6% 2.3% 400m centerline 2.1% 2.1% 1.9% 2.5% 2.0% 2.4% 1.8% 2.1% 1.0% 1.5% 525m centerline 1.3% 1.3% 1.2% 1.4% 1.1% 1.6% 1.0% 1.3% 0.5% 0.8% 650m centerline 0.8% 0.8% 0.9% 0.8% 0.7% 1.0% 0.6% 0.8% 0.3% 0.5% Distance to:

13.3% 107 106 91 106 102 121 94 106 101 104 

9.9% 135 134 117 143 129 151 118 135 129 129 7.7% 163 162 145 175 156 179 144 164 150 157 5.3% 213 214 193 236 204 235 192 215 183 200 3.1% 311 309 284 352 298 343 279 310 233 268 

-- - - - - - - - - - 

2.3% 378 378 348 416 363 416 342 377 271 321 

-- - - - - - - - - - -- - - - - - - - - - 

LFL 223 222 202 249 213 246 200 223 187 206 

Source Term Wind Speed Surface Roughness Stability
Burro 3 Measured vs Predicted 

Maximum Arcwise Concentration

Short Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 100

Downwind distance (m)

Maximum arcwise concentration (%) 
Burro 3 Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 100

0

Downwind distance (m)

Maximum arcwise concentration 

(%)
Averaging Time

MoninObukhov 

Length

Ambient 

Temperature

Ambient 

Pressure

Ambient 

Relative 

Humidity

Base Case Alternative 1 Alternative 2 Alternative Lower Upper Alternative Lower Upper Alternative Lower Upper

Run Name a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_12 Source Term ABS/FERC 0.167kg/m^2*sec0.085kg/m^2*sec ABS/FERC ABS/FERC ABS/FERC ABS/FERC case ABS/FERC 

Wind Speed 5.4 5.4 5.4 5.4 5.1 5.8 5.58 5.4 5.4 Reference Height 2 2 2 2 2 2 3 2 2 Surface Roughness 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 1.00E-02 2.00E-04 

Wind Stability C C C C C C C C D Averaging Time 1 1 1 100 1 1 1 1 1 Atmospheric Parameters

DELTA Y 0.10461 0.10461 0.10461 0.14675 0.10461 0.10461 0.10461 0.10461 0.06767 

BETA Y 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Monin-Obukhov L -9.26 -9.26 -9.26 -9.26 -9.26 -9.26 -9.26 -30.4 infinite 

Sigma X Coefficie 2.00E-02 2.00E-02 2.00E-02 2.00E-02 2.00E-02 2.00E-02 2.00E-02 2.00E-02 4.00E-02 

Sigma X Power 1.22 1.22 1.22 1.22 1.22 1.22 1.22 1.22 1.14 Sigma X Minimum 130 130 130 130 130 130 130 130 100 

Wind Power Consta 0.110 0.110 0.110 0.110 0.110 0.110 0.102 0.227 0.127 

Friction Velocity 0.21611 0.21611 0.21611 0.21611 0.2041 0.23212 0.21659 0.36994 0.2052 

Ambient Temperatu 307.75 307.75 307.75 307.75 307.75 307.75 307.75 307.75 307.75 

Ambient Pressure 0.936 0.936 0.936 0.936 0.936 0.936 0.936 0.936 0.936 

Ambient Relative H 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 5.2 

Isothermal? N N N N N N N N N Heat Transfer to be Y Y Y Y Y YY Y Y 

Surface Tempera 307.75 307.75 307.75 307.75 307.75 307.75 307.75 307.75 307.75 

Correlation 1 1 1 1 1 1 1 1 1 

Water Transfer? N N N N N N N N N Molecular Weight 17.26 17.26 17.26 17.26 17.26 17.26 17.26 17.26 17.26 Release Temperatu 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 

Density at release t 1.6773 1.6773 1.6773 1.6773 1.6773 1.6773 1.6773 1.6773 1.6773 

Mean heat capacity 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 

Mean heat capacity 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 

Upper Concentratio 80.00% 80.00% 15.00% 80.00% 80.00% 80.00% 80.00% 80.00% 80.00% 

Lower Concentratio 0.50% 1.00% 0.50% 0.50% 0.50% 0.50% 0.50% 1.00% 0.50% 

Height for isopleths 1 1 1 1 1 11 1 1 

Max Concentration at:57m centerline 66.7% 66.3% 64.4% 66.7% 68.3% 64.5% 67.0% 41.2% 68.0% 140m centerline 25.3% 25.2% 25.1% 25.3% 26.0% 24.8% 25.1% 12.2% 26.6% 400m centerline 5.1% 5.0% 4.9% 4.9% 5.2% 5.0% 5.1% 2.4% 5.3% 800m centerline 1.2% 1.2% 1.6% 0.8% 1.1% 1.3% 1.2% 0.5% 1.8% x=40, y=-40.6, z=1 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% x=49, y=-28.7, z=1 0.8% 1.0% 1.1% 1.2% 1.0% 0.5% 0.8% 1.3% 0.4% x=55.6, y=-14.9, z= 13.2% 12.8% 11.2% 12.4% 13.8% 12.4% 13.0% 19.8% 14.2% 

x=55.6, y=14.9, z= 14.1% 13.4% 11.4% 13.5% 14.4% 13.5% 13.9% 21.1% 14.2% x=49, y=28.7, z=1 1.5% 1.8% 2.0% 2.0% 1.8% 1.1% 1.4% 2.4% 1.0% x=37, y=38, z=1 0.0% 0.2% 0.0% 0.1% 0.1% 0.0% 0.0% 0.1% 0.0% x=127, y=58, z=1 0.4% 0.4% 0.7% 0.7% 0.4% 0.3% 0.4% 0.2% 0.1% x=140, y=0, z=1 13.5% 13.3% 12.1% 13.5% 14.0% 13.1% 13.4% 9.4% 14.0% x=395.5, y=-59.8, z 1.0% 1.0% 1.4% 1.1% 1.0% 0.9% 1.0% 0.3% 0.8% 

x=796, y=79.9, z=1 0.5% 0.6% 0.7% 0.5% 0.5% 0.6% 0.5% 0.2% 0.5% x=184, y=159, z=1 0.0% 0.0% 0.1% 0.1% 0.0% 0.0% 0.0% 0.0% 0.0% Distance to:

28.2% 127 127 128 127 131 126 127 77 134 

9.0% 279 276 275 279 281 274 278 173 285 0.9% 892 904 990 750 879 895 887 622 1104 0.5% 1129 1142 1237 944 1114 997 1123 812 1418 

LFL 405 402 394 395 414 397 404 257 414 

Source Term Wind Speed Surface Roughness Stability
Burro 7 Measured vs Predicted 

Maximum Arcwise Concentration

Short Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration 

(%)
Burro 7 Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 100

Downwind distance (m)

Maximum arcwise concentration 

(%)
Averaging Time

Monin-Obukhov 

Length Ambient Pressure

Am

Base Case Alternative 1 Alternative 2 Alternative Lower Upper Alternative Lower Upper Alternative Lower Upper

Run Name a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_11 Source Term ABS/FERC 0.167kg/m^2*sec 0.085kg/m^2*sec ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC Wind Speed 8.4 8.4 8.4 8.4 8.75 8.4 8.4 8.4 8.4 Reference Height 2222 3 222 2Surface Roughnes 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 1.00E-02 2.00E-04 2.00E-04 2.00E-04 

Wind Stability DDDD D DDC DAveraging Time 1 1 1 140 1 1 1 1 1 Atmospheric Parameters

DELTA Y 0.06767 0.06767 0.06767 0.10166 0.06767 0.06767 0.06767 0.10461 0.06767 BETA Y 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Monin-Obukhov infinite infinite infinite infinite infinite infinite -114 -9.26 power Sigma X Coeffici 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 2.00E-02 4.00E-02 

Sigma X Power 1.14 1.14 1.14 1.14 1.14 1.14 1.14 1.22 1.14 Sigma X Minimu 100 100 100 100 100 100 100 130 100 

Wind Power Const 0.127 0.127 0.127 0.127 0.122 0.110 0.125 0.110 0.127 

Friction Velocity 0.3192 0.3192 0.3192 0.3192 0.31848 0.55437 0.32134 0.33617 0.3192 

Ambient Temperat 306.96 306.96 306.96 306.96 306.96 306.96 306.96 306.96 306.96 

Ambient Pressure 0.928 0.928 0.928 0.928 0.928 0.928 0.928 0.928 1 

Ambient Relative H 7.4 7.4 7.4 7.4 7.4 7.4 7.4 7.4 7.4 

Isothermal? NNNN N NNN NHeat Transfer to be YYYY Y YYY Y

Surface Tempera 306.96 306.96 306.96 306.96 306.96 306.96 306.96 306.96 306.96 

Correlation 1111 1 111 1

Water Transfer? NNNN N NNN NMolecular Weight 18.22 18.22 18.22 18.22 18.22 18.22 18.22 18.22 18.22 Release Temperat 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 

Density at release 1.663 1.663 1.663 1.663 1.663 1.663 1.663 1.663 1.792 Mean heat capacit 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 

Mean heat capacit 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 

Upper Concentrati 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 Lower Concentrati 5.00E-03 1.00E-02 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 Height for isopleths 1111 1 111 1

Max Concentration at:57m centerline 61.2% 60.7% 49.4% 61.2% 61.4% 33.9% 60.9% 60.0% 60.0% 140m centerline 22.7% 22.4% 20.2% 22.7% 23.2% 11.0% 22.5% 21.4% 21.5% 400m centerline 4.8% 4.8% 4.4% 4.8% 4.8% 2.4% 4.8% 4.6% 4.6% 

800m centerline 1.7% 1.7% 1.5% 1.1% 1.7% 0.9% 1.7% 0.9% 1.6% 

x=57, y=0, z=1 10.2% 9.6% 13.2% 9.5% 10.0% 12.0% 10.1% 9.0% 9.2% 

x=55.6, y=14.9, z=1 15.5% 15.3% 15.0% 15.5% 15.5% 19.6% 15.8% 16.1% 15.2% 

x=49, y=-28.7, z=1 14.1% 13.7% 15.0% 12.9% 13.8% 17.7% 13.9% 12.5% 13.1% 

x=37, y=38, z=1 0.2% 0.1% 0.7% 0.5% 0.2% 0.2% 0.2% 0.4% 0.1% x=140, y=0, z=1 0.6% 0.6% 1.2% 1.1% 0.6% 0.4% 0.6% 0.9% 0.5% 

x=137, y=30, z=1 12.8% 12.7% 11.2% 12.7% 13.2% 8.6% 12.9% 12.3% 12.4% x=127, y=58, z=1 10.6% 10.5% 10.6% 9.7% 10.8% 7.3% 10.5% 9.1% 9.7% x=112, y=84, z=1 0.1% 0.1% 0.2% 0.2% 0.1% 0.0% 0.1% 0.2% 0.0% 

x=382, y=118, z=1 4.0% 4.0% 3.6% 4.0% 4.1% 2.2% 4.0% 3.9% 3.8% x=360, y=174, z=1 0.3% 0.3% 0.6% 0.5% 0.3% 0.2% 0.3% 0.4% 0.2% 

Distance to:

17.9% 167 166 155 167 167 94 167 160 161 

7.1% 310 307 292 310 310 192 310 306 300 3.9% 468 462 435 461 468 287 468 440 452 

LFL 388 387 368 388 390 242 388 381 374 

Source Term Wind Speed Surface Roughness Stability
Burro 8 Measured vs Predicted 

Maximum Arcwise Concentration

Short Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration 

(%)
Burro 8 Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 9

Downwind distance (m)

Maximum arcwise concentration 

(%)
Averaging Time

MoninObukhov 

Length

Ambient 

Temperature

Ambient 

Pressure

Ambie

Relativ

Humid

Base Case Alternative 1 Alternative 2 Alternative Lower Upper Alternative Lower Upper Alternative Lower Upper

Run Name a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_12 Source Term ABS/FERC 0.167kg/m^2*sec0.085kg/m^2*se ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC 

Wind Speed 1.8 1.8 1.8 1.8 1.5 2 1.94 1.8 1.8 1.8 Reference Height 2222223 22 2 

Surface Roughness 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 1.00E-02 1.33E-03 2.00E-04 Wind Stability EEEEEEE EE F 

Averaging Time 1 1 1 100 1 1 1 1 1 1 Atmospheric Parameters

DELTA Y 0.04617 0.04617 0.04617 0.07128 0.04617 0.04617 0.04617 0.04617 0.04617 0.02544 BETA Y 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Monin-Obukhov Length 9.26 9.26 9.26 9.26 9.26 9.26 9.26 30.4 16.5 6.06 Sigma X Coefficient 1.70E-01 1.70E-01 1.70E-01 1.70E-01 1.70E-01 1.70E-01 1.70E-01 1.70E-01 1.70E-01 1.70E-01 Sigma X Power 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 0.97 Sigma X Minimum Distance 50 50 50 50 50 50 50 50 50 50 

Wind Power Constant 0.168 0.168 0.168 0.168 0.168 0.168 0.178 0.262 0.195 0.188 Friction Velocity 0.06161 0.06161 0.06161 0.06161 0.05134 0.06846 0.06096 0.11226 0.07988 0.05853 Ambient Temperature 306.02 306.02 306.02 306.02 306.02 306.02 306.02 306.02 306.02 306.02 Ambient Pressure 0.929 0.929 0.929 0.929 0.929 0.929 0.929 0.929 0.929 0.929 Ambient Relative Humidity 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 4.5 Isothermal? NNNNNNN NN N 

Heat Transfer? YYYYYYY YY Y 

Surface Temperature 306.02 306.02 306.02 306.02 306.02 306.02 306.02 306.02 306.02 306.02 Correlation 1111111 11 1 

Water Transfer? NNNNNNN NN N 

Molecular Weight 18.12 18.12 18.12 18.12 18.12 18.12 18.12 18.12 18.12 18.12 Release Temperature 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 Density 1.6648 1.6648 1.6648 1.6648 1.6648 1.6648 1.6648 1.6648 1.6648 1.6648 Mean heat capacity constant 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 Mean heat capacity power 5 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5 5.00E+00 5.00E+00 5.00E+00 Upper Concentration 0.8 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 0.8 8.00E-01 8.00E-01 8.00E-01 Lower Concentration 0.005 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 Height for isopleths 1111111 11 1 

Max Concentration at:57m centerline 83.8% 100.0% 100.0% 83.8% 88.3% 89.8% 83.9% 67.2% 85.5% 80.2% 140m centerline 22.0% 22.5% 21.0% 22.0% 16.3% 25.1% 21.9% 15.7% 23.1% 21.8% 400m centerline 3.1% 2.9% 3.3% 3.1% 2.1% 3.6% 3.1% 3.5% 3.5% 2.9% 800m centerline 1.0% 1.0% 1.1% 1.0% 0.7% 1.2% 1.0% 1.3% 1.1% 1.0% x=40, y=-40.6, z=1 32.2% 22.7% 30.6% 32.2% 16.3% 24.3% 11.9% 34.4% 25.0% 29.4% x=49, y=-28.7, z=1 30.1% 24.8% 30.2% 30.1% 15.2% 24.7% 14.4% 43.6% 26.4% 28.3% x=57, y=0, z=1 29.5% 25.3% 30.2% 29.5% 14.9% 25.3% 14.3% 42.4% 26.9% 27.9% x=55.6, y=14.9, z=1 30.3% 24.7% 30.2% 30.3% 15.3% 24.6% 14.3% 43.9% 26.2% 28.4% x=49, y=-28.7, z=1 33.0% 21.3% 31.0% 33.0% 16.8% 24.2% 5.4% 10.6% 20.3% 30.6% x=37, y=38, z=1 34.5% 13.5% 35.3% 34.5% 18.5% 1.0% 0.0% 0.0% 0.2% 35.1% x=112, y=-84, z=1 12.4% 16.2% 10.5% 11.5% 13.0% 12.0% 12.3% 0.4% 13.6% 13.9% x=127, y=-58, z=1 17.2% 16.2% 17.6% 17.2% 13.1% 18.1% 17.1% 12.6% 17.9% 15.2% x=137, y=-30, z=1 16.5% 15.1% 16.9% 16.5% 12.3% 17.1% 16.4% 14.0% 17.4% 14.8% x=140, y=0, z=1 16.8% 15.6% 17.2% 16.8% 12.6% 17.5% 16.7% 14.3% 17.5% 15.0% x=137, y=30, z=1 17.7% 17.2% 16.7% 17.3% 13.8% 19.1% 17.6% 3.2% 18.9% 15.5% x=127, y=58, z=1 0.9% 3.5% 0.8% 1.7% 2.2% 0.7% 1.0% 0.0% 0.7% 0.4% x=112, y=84, z=1 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 

x=360, y=174, z=1 0.1% 0.1% 0.0% 0.1% 0.0% 0.1% 0.1% 0.0% 0.2% 0.0% x=382, y=118, z=1 2.5% 2.4% 2.6% 2.3% 1.8% 3.0% 2.5% 0.9% 3.2% 2.5% x=395.5, y=-59.8, z=1 3.0% 2.8% 3.2% 3.0% 2.0% 3.5% 3.0% 3.4% 3.4% 2.8% x=400, y=0, z=1 1.3% 1.6% 1.3% 1.4% 1.1% 1.7% 1.3% 0.3% 2.2% 1.5% x=395.5, y=59.8, z=1 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% x=784, y=-159, z=1 1.0% 1.0% 1.0% 1.0% 0.7% 1.2% 1.0% 1.0% 1.1% 1.0% x=796, y=-79.9, z=1 0.7% 0.7% 0.6% 0.6% 0.5% 0.8% 0.7% 0.3% 0.8% 0.7% x=800, y=0, z=1 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% Distance to:

55.9% 83 89 84 83 81 83 84 65 77 82 16.5% 156 160 160 164 138 182 164 135 183 156 

4.3% 324 313 338 324 255 370 322 342 368 304 2.1% 501 503 535 501 397 558 503 566 540 498 

LFL 289 291 308 289 221 329 290 302 328 284 

Source Term Wind Speed Surface Roughness Stability
Burro 9 Measured vs Predicted 

Maximum Arcwise Concentration

Short Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 100

Downwind distance (m)

Maximum arcwise concentration (%) 
Burro 9 Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration 

(%)
Averaging Time

MoninObukhov 

Length

Ambient 

Temperature

Ambient 

Pressure

Ambie

Relativ

Humid

Base Case Alternative 1 Alternative 2 Alternative Lower Upper Alternative Lower Upper Alternative Lower Upper

Run Name a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_12 Source Term ABS/FERC 0.167kg/m^2*sec0.085kg/m^2*sec ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FE

Wind Speed 5.7 5.7 5.7 5.7 5.94 5.7 5.7 5.7 5.7 Reference Height 2222 3 22 2 2 Surface Roughness 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 1.00E-02 2.00E-04 2.00E-04 2.00E-Wind Stability DDDD D DD C D Averaging Time 1 1 1 100 1 1 1 1 1 Atmospheric Parameters

DELTA Y 0.06767 0.06767 0.06767 0.09504 0.06767 0.06767 0.06767 0.10461 0.0676BETA Y 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Monin-Obukhov Length infinite infinite infinite infinite infinite infinite -141 -9.26 infinite Sigma X Coefficient 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 2.00E-02 4.00E-Sigma X Power 1.14E+00 1.14E+00 1.14E+00 1.14E+00 1.14E+00 1.14E+00 1.14E+00 1.22E+00 1.14E+Sigma X Minimum Distance 1.00E+02 1.00E+02 1.00E+02 1.00E+02 1.00E+02 1.00E+02 1.00E+02 1.30E+02 1.00E+

Wind Power Constant 0.127 0.127 0.127 0.127 0.122 0.240 0.125 0.110 0.127 Friction Velocity 0.2166 0.2166 0.2166 0.2166 0.21621 0.37618 0.21779 0.22811 0.216Ambient Temperature 308.52 308.52 308.52 308.52 308.52 308.52 308.52 308.52 308.5Ambient Pressure 0.928 0.928 0.928 0.928 0.928 0.928 0.928 0.928 0.928 Ambient Relative Humidity 14.4 14.4 14.4 14.4 14.4 14.4 14.4 14.4 6.5 Isothermal? NNNN N NN N N Heat Transfer? YYYY Y YY Y Y 

Surface Temperature 308.52 308.52 308.52 308.52 308.52 308.52 308.52 308.52 308.5Correlation 1111 1 11 1 1 

Water Transfer? NNNN N NN N N Molecular Weight 18.82 18.82 18.82 18.82 18.82 18.82 18.82 18.82 18.82 Release Temperature 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 Density 1.663 1.663 1.663 1.663 1.663 1.663 1.663 1.663 1.663 Mean heat capacity constant 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-Mean heat capacity power 5555 5 55 5 5 Upper Concentration 80.0% 80.0% 80.0% 80.0% 80.0% 80.0% 80.0% 80.0% 80.0% Lower Concentration 0.5% 0.5% 0.5% 0.5% 0.5% 0.5% 0.5% 0.5% 0.5% Height for isopleths 1111 1 11 1 1 Max Concentration at:57m centerline 76.4% 76.1% 73.6% 76.4% 76.5% 45.7% 76.5% 74.9% 76.9% 140m centerline 30.6% 29.5% 29.7% 30.6% 31.2% 15.9% 30.8% 30.4% 32.5% 400m centerline 6.9% 6.6% 6.3% 6.6% 6.9% 3.4% 6.9% 6.7% 6.6% 800m centerline 2.1% 2.2% 2.2% 1.6% 2.1% 0.9% 2.1% 1.4% 2.0% x=127, y=-58, z=1 4.4% 4.53% 6.35% 5.03% 4.63% 1.86% 4.48% 5.23% 5.77% x=137, y=-30, z=1 18.2% 17.11% 15.88% 18.23% 18.51% 12.74% 18.21% 18.02% 17.72% x=140, y=0, z=1 18.3% 17.18% 15.93% 18.27% 18.50% 12.80% 18.19% 18.03% 17.71% x=127, y=58, z=1 0.0% 0.00% 0.01% 0.01% 0.00% 0.00% 0.00% 0.02% 0.00% x=382, y=-118, z=1 0.9% 0.92% 1.43% 1.10% 0.86% 0.08% 0.87% 1.14% 0.90% x=395.5, y=-59.8, z=1 5.9% 5.60% 5.25% 5.91% 5.94% 3.04% 5.93% 5.77% 5.70% x=400, y=0, z=1 3.0% 3.06% 3.66% 2.98% 3.02% 0.61% 3.03% 2.90% 2.99% x=784, y=-159, z=1 0.6% 0.73% 1.04% 0.73% 0.63% 0.21% 0.64% 0.69% 0.60% x=796, y=-79.9, z=1 1.8% 1.92% 1.99% 1.46% 1.82% 0.79% 1.83% 1.27% 1.70% x=800, y=0, z=1 0.1% 0.15% 0.31% 0.24% 0.12% 0.03% 0.12% 0.26% 0.11% Distance to:

-- - - - - - - - - 

10.6% 298 291 285 298 300 185 299 296 292 

4.0% 552 556 539 546 553 359 553 528 532 1.4% 960 993 1022 841 959 658 959 800 929 

LFL 492 482 465 491 492 307 493 481 462 

Source Term Wind Speed Surface Roughness Stability
Coyote 3 Measured vs Predicted 

Maximum Arcwise Concentration

Short Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 100

Downwind distance (m)

Maximum arcwise concentration (%) 
Coyote 3 Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration (%) 
Averaging Time

MoninObukhov 

Length

Ambient 

Temperature

Ambient 

Pressure

Ambient 

Relative 

Humidity

Ambient 

Surface 

Temperature

Water Transfer 

Submodel

Molecular 

Weight

Base Case Alternative 1 Alternative 2 Alternative Lower Upper Alternative Lower Upper Alternative Lower Upper

Run Name a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_12 a_13 a_14 a_15

Source Term ABS/FERC 0.167kg/m^2*se0.085kg/m^2*secABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC

Wind Speed 6666 6.77 6 6 6 6 6

Reference Height 2222 3 22 2 2 2

Surface Roughness 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 1.00E-02 2.00E-04 2.00E-04 2.00E-04 2.00E-04

Wind Stability CCCC C CC D C C

Averaging Time 1 1 1 50 1 1 1 1 1 1

Atmospheric Parameters

DELTA Y 0.10461 0.10461 0.10461 0.12776 0.10461 0.10461 0.10461 0.06767 0.10461 0.10461

BETA Y 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9

Monin-Obukhov Length -9.26 -9.26 -9.26 -9.26 -9.26 -30.4 -6.32 infinite -9.26 -9.26

Sigma X Coefficient 2.00E-02 2.00E-02 2.00E-02 2.00E-02 2.00E-02 2.00E-02 2.00E-02 4.00E-02 2.00E-02 2.00E-02

Sigma X Power 1.22E+00 1.22E+00 1.22E+00 1.22E+00 1.22E+00 1.22E+00 1.22E+00 1.14E+00 1.22E+00 1.22E+00

Sigma X Minimum Distance 1.30E+02 1.30E+02 1.30E+02 1.30E+02 1.30E+02 1.30E+02 1.30E+02 1.00E+02 1.30E+02 1.30E+02

Wind Power Constant 0.110 0.110 0.110 0.110 0.102 0.227 0.106 0.127 0.110 0.110

Friction Velocity 0.24012 0.24012 0.24012 0.24012 0.26278 0.41104 0.24362 0.228 0.24012 0.24012

Ambient Temperature 311.45 311.45 311.45 311.45 311.45 311.45 311.45 311.45 311.45 311.45

Ambient Pressure 0.924 0.924 0.924 0.924 0.924 0.924 0.924 0.924 0.924 0.924

Ambient Relative Humidity 11.3 11.3 11.3 11.3 11.3 11.3 11.3 11.3 3.5 11.3

Isothermal? NNNN N NN N N N

Heat Transfer? YYYY Y YY Y Y Y

Surface Temperature 311.45 311.45 311.45 311.45 311.45 311.45 311.45 311.45 311.45 311.45

Correlation 1111 1 11 1 1 1

Water Transfer? NNNN N NN N N N

Molecular Weight 19.51 19.51 19.51 19.51 19.51 19.51 19.51 19.51 19.51 16.04

Release Temperature 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7

Density 1.6558 1.6558 1.6558 1.6558 1.6558 1.6558 1.6558 1.6558 1.6558 1.6558

Mean heat capacity constant 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08

Mean heat capacity power 5 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5 5.00E+00

Upper Concentration 80.0% 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 80.0% 8.00E-01

Lower Concentration 0.5% 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 0.5% 5.00E-03

Height for isopleths 1111 1 11 1 1 1

Max Concentration at:

140m centerline 23.9% 22.4% 21.4% 23.9% 23.6% 11.9% 23.2% 24.2% 24.0% 29.0%

200m centerline 14.6% 13.7% 13.3% 14.6% 14.6% 7.4% 14.6% 15.0% 14.6% 18.6%

300m centerline 7.9% 7.6% 7.3% 7.8% 7.8% 4.0% 7.7% 8.1% 7.6% 9.7%

400m centerline 4.9% 4.8% 4.7% 4.3% 4.9% 2.2% 5.0% 5.1% 4.6% 6.2%

500m centerline 3.0% 2.9% 2.9% 2.4% 3.2% 1.3% 2.9% 3.6% 2.8% 4.3%

x=140, y=0, z=1 0.5% 0.4% 0.5% 0.7% 0.4% 0.3% 0.5% 0.2% 0.6% 1.0%

x=112, y=84, z=1 4.6% 4.0% 4.4% 4.8% 4.1% 2.8% 4.5% 4.2% 5.2% 6.9%

x=127, y=58, z=1 14.2% 13.2% 12.5% 14.2% 13.7% 9.4% 13.8% 14.3% 13.4% 15.0%

x=137, y=30, z=1 11.0% 10.0% 10.0% 10.6% 10.3% 7.0% 10.8% 12.3% 11.2% 13.4%

x=186.5, y=72, z=1 10.3% 9.6% 9.3% 10.3% 10.1% 6.3% 10.3% 10.5% 10.1% 11.8%

x=196.6, y=36.9, z=1 4.0% 3.5% 3.7% 4.0% 3.7% 2.0% 3.9% 3.9% 4.3% 6.6%

x=200, y=0, z=1 0.1% 0.0% 0.1% 0.1% 0.0% 0.0% 0.1% 0.0% 0.1% 0.2%

x=296, y=48.3, z=1 0.5% 0.5% 0.6% 0.7% 0.5% 0.2% 0.5% 0.3% 0.6% 1.5%

x=395.5, y=59.8, z=1 0.1% 0.1% 0.1% 0.1% 0.1% 0.0% 0.1% 0.0% 0.1% 0.4%

x=382, y=118, z=1 2.6% 2.5% 2.5% 2.5% 2.6% 1.1% 2.6% 2.8% 2.4% 4.3%

x=330, y=226, z=1 0.1% 0.1% 0.1% 0.2% 0.1% 0.0% 0.1% 0.1% 0.1% 0.6%

x=495, y=71.2, z=1 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.1%

Distance to:

10.7% 257 238 232 241 241 151 246 246 239 285

5.4% 379 373 366 367 380 243 374 386 369 435

1.9% 593 589 589 542 608 424 584 697 580 807

2.0% 582 577 578 534 599 416 575 683 567 788

0.8% 832 824 833 764 850 634 820 998 772 1076

LFL 392 392 385 378 396 254 399 405 383 453

Source Term Wind Speed Surface Roughness Stability
Coyote 5 Measured vs Predicted 

Maximum Arcwise Concentration

Short Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 1000

Downwind distance (m)

Maximum arcwise concentration (%) 
Coyote 5 Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration 

(%)
Averaging Time

MoninObukhov 

Length

Ambient 

Temperature

Ambient 

Pressure

Ambie

Relativ

Humid

Base Case Alternative 1 Alternative 2 Alternative Lower Upper Alternative Lower Upper Alternative Lower Upper

Run Name a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_12 Source Term ABS/FERC 0.167kg/m^2*se 0.085kg/m^2*se ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC Wind Speed 9.7 9.7 9.7 9.7 10.47 9.7 9.7 9.7 9.7 Reference Height 2 2 2 2 3 2 2 2 2 Surface Roughness 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 1.00E-02 2.00E-04 2.00E-04 2.00E-Wind Stability CCCC C CC D C Averaging Time 1 1 1 90 1 1 1 1 1 Atmospheric Parameters

DELTA Y 0.10461 0.10461 0.10461 0.14369 0.10461 0.10461 0.10461 0.06767 0.1046BETA Y 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Monin-Obukhov Length -9.26 -9.26 -9.26 -9.26 -9.26 -30.4 -26.5 infinite -9.26 Sigma X Coefficient 2.00E-02 2.00E-02 2.00E-02 2.00E-02 2.00E-02 2.00E-02 2.00E-02 4.00E-02 2.00E-Sigma X Power 1.22E+00 1.22E+00 1.22E+00 1.22E+00 1.22E+00 1.22E+00 1.22E+00 1.14E+00 1.22E+Sigma X Minimum Distance 1.30E+02 1.30E+02 1.30E+02 1.30E+02 1.30E+02 1.30E+02 1.30E+02 1.00E+02 1.30E+

Wind Power Constant 0.110 0.110 0.110 0.110 0.102 0.227 0.118 0.127 0.110 Friction Velocity 0.3882 0.3882 0.3882 0.3882 0.40639 0.66452 0.3775 0.3686 0.388Ambient Temperature 301.49 301.49 301.49 301.49 301.49 301.49 301.49 301.49 301.4Ambient Pressure 0.927 0.927 0.927 0.927 0.927 0.927 0.927 0.927 0.927 Ambient Relative Humidity 22.1 22.1 22.1 22.1 22.1 22.1 22.1 22.1 7.2 Isothermal? NNNN N NN N N Heat Transfer? YYYY Y YY Y Y 

Surface Temperature 301.49 301.49 301.49 310.49 301.49 301.49 301.49 301.49 301.4Correlation 1 1 1 1 1 1 1 1 1 

Water Transfer? NNNN N NN N N Molecular Weight 20.19 20.19 20.19 20.19 20.19 20.19 20.19 20.19 20.19 Release Temperature 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 Density 1.6612 1.6612 1.6612 1.6612 1.6612 1.6612 1.6612 1.6612 1.661Mean heat capacity constant 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 1.78E+Mean heat capacity power 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 Upper Concentration 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-Lower Concentration 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-Height for isopleths 1 1 1 1 1 1 1 1 1 Max Concentration at:140m centerline 19.6% 19.7% 14.9% 19.5% 19.4% 10.0% 19.9% 20.8% 20.8% 200m centerline 13.4% 12.5% 10.3% 12.7% 12.8% 6.8% 13.5% 13.8% 13.8% 300m centerline 7.5% 7.3% 6.3% 5.3% 7.3% 3.8% 7.6% 7.7% 7.3% 400m centerline 4.9% 4.7% 4.3% 2.5% 4.8% 2.3% 5.0% 5.1% 4.7% 500m centerline 3.3% 3.0% 3.0% 1.5% 3.1% 1.4% 3.3% 3.8% 3.4% x=140, y=0, z=1 12.45% 12.5% 10.2% 12.4% 12.5% 8.2% 12.5% 13.0% 11.9% x=127, y=-58, z=1 0.00% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% x=137, y=-30, z=1 5.08% 4.9% 4.9% 5.0% 4.8% 2.8% 5.2% 5.5% 6.3% x=200, y=0, z=1 9.55% 8.9% 7.6% 8.9% 9.2% 5.7% 9.6% 9.8% 9.3% x=196.6, y=36.9, z=1 1.01% 0.8% 1.0% 1.2% 0.9% 0.4% 1.1% 0.7% 1.6% x=196.6, y=-36.9, z=1 3.81% 3.3% 3.5% 3.6% 3.5% 1.9% 3.9% 3.9% 4.8% x=296, y=-48.3, z=1 0.43% 0.4% 0.4% 0.6% 0.4% 0.1% 0.5% 0.2% 0.7% x=296, y=48.3, z=1 2.15% 1.9% 2.0% 1.9% 1.9% 0.9% 2.2% 2.1% 2.6% x=300, y=0, z=1 5.68% 5.5% 4.9% 4.2% 5.5% 3.1% 5.8% 6.1% 5.6% x=395.5, y=59.8, z=1 0.18% 0.2% 0.2% 0.3% 0.2% 0.1% 0.2% 0.1% 0.3% x=395.5, y=-59.8, z=1 1.23% 1.2% 1.2% 1.0% 1.2% 0.6% 1.3% 1.2% 1.5% x=400, y=0, z=1 3.71% 3.6% 3.4% 2.1% 3.6% 1.9% 3.8% 4.2% 3.7% x=495, y=71.2, z=1 0.10% 0.1% 0.1% 0.2% 0.1% 0.0% 0.1% 0.0% 0.2% x=495, y=-71.2, z=1 0.85% 0.8% 0.8% 0.6% 0.8% 0.3% 0.9% 0.7% 1.0% Distance to:

11.5% 222 213 181 212 218 124 224 225 223 

8.1% 283 277 245 252 280 172 287 290 279 4.1% 451 431 413 338 430 289 456 475 468 2.3% 572 562 568 415 563 398 577 700 615 1.9% 634 611 624 444 606 433 641 789 668 

LFL 396 387 358 310 392 253 400 408 387 

Source Term Wind Speed Surface Roughness Stability
Coyote 6 Measured vs Predicted 

Maximum Arcwise Concentration

Short Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 100

Downwind distance (m)

Maximum arcwise concentration (%) 
Coyote 6 Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration (%) 
Averaging Time

MoninObukhov 

Length

Ambient 

Temperature

Ambient 

Pressure

Ambien

Relativ

Humidit

Base Case Alternative 1 Alternative 2 Alternative Lower Upper Alternative Lower Upper Alternative Lower Upper

Run Name a b c a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_12 Source Term ABS/FERC 0.167kg/m^2*sec0.085kg/m^2*sec ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FERC ABS/FER

Wind Speed 4.6 4.6 4.6 4.6 5.04 4.6 4.6 4.6 4.6 Reference Height 2 2 2 2 3 2 2 2 2 Surface Roughness 2.00E-04 2.00E-04 2.00E-04 2.00E-04 2.00E-04 1.00E-02 2.00E-04 2.00E-04 2.00E-0Wind Stability DDDD D DD E D Averaging Time 1 1 1 70 1 1 1 1 1 Atmospheric Parameters

DELTA Y 0.06767 0.06767 0.06767 0.0885 0.06767 0.06767 0.06767 0.04617 0.0676BETA Y 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Monin-Obukhov Length infinite infinite infinite infinite infinite infinite 73.5 9.26 infinite Sigma X Coefficient 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 4.00E-02 1.70E-01 4.00E-0Sigma X Power 1.14E+00 1.14E+00 1.14E+00 1.14E+00 1.14E+00 1.14E+00 1.14E+00 9.70E-01 1.14E+0Sigma X Minimum Distance 1.00E+02 1.00E+02 1.00E+02 1.00E+02 1.00E+02 1.00E+02 1.00E+02 5.00E+01 1.00E+0

Wind Power Constant 0.127 0.127 0.127 0.127 0.122 0.240 0.132 0.168 0.127 Friction Velocity 0.1748 0.1748 0.1748 0.1748 0.18345 0.30358 0.17241 0.15746 0.1748 Ambient Temperature 297.26 297.26 297.26 297.26 297.26 297.26 297.26 297.26 297.26 Ambient Pressure 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 0.93 Ambient Relative Humidity 22.8 22.8 22.8 22.8 22.8 22.8 22.8 22.8 4.5 Isothermal? NNNN N NN N N Heat Transfer? YYYY Y YY Y Y 

Surface Temperature 297.26 297.26 297.26 297.26 297.26 297.26 297.26 297.26 297.26 Correlation 1 1 1 1 1 1 1 1 1 

Water Transfer? NNNN N NN N N Molecular Weight 19.09 19.09 19.09 19.09 19.09 19.09 19.09 19.09 19.09 Release Temperature 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 111.7 Density 1.6666 1.6666 1.6666 1.6666 1.6666 1.6666 1.6666 1.6666 1.6666 Mean heat capacity constant 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-08 5.60E-0Mean heat capacity power 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+00 5.00E+0Upper Concentration 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-01 8.00E-0Lower Concentration 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-03 5.00E-0Height for isopleths 1 1 1 1 1 1 1 1 1 Max Concentration at:140m centerline 21.6% 23.0% 24.8% 21.6% 22.6% 14.1% 21.7% 21.1% 29.4% 200m centerline 14.3% 14.7% 15.2% 14.3% 14.7% 8.9% 14.4% 14.2% 16.7% 300m centerline 9.2% 9.1% 9.1% 9.2% 9.3% 4.9% 9.3% 9.1% 8.1% 400m centerline 6.1% 6.8% 6.0% 6.1% 6.3% 3.3% 6.2% 6.4% 4.8% 500m centerline 4.3% 4.3% 4.2% 4.2% 4.4% 2.3% 4.3% 4.6% 3.3% 600m centerline 3.1% 3.2% 3.1% 2.8% 3.2% 1.6% 3.2% 3.4% 2.5% x=140, y=0, z=1 15.7% 15.8% 15.9% 15.5% 16.0% 11.6% 15.8% 15.5% 17.2% x=127, y=-58, z=1 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% 0.0% x=137, y=-30, z=1 2.9% 4.6% 5.8% 3.4% 2.7% 1.4% 2.9% 2.5% 5.9% x=200, y=0, z=1 1.4% 2.6% 3.4% 1.9% 1.3% 0.6% 1.5% 1.0% 3.4% x=196.6, y=36.9, z=1 1.8% 2.7% 3.3% 2.2% 1.7% 0.7% 1.9% 1.5% 3.4% x=196.6, y=-36.9, z=1 11.2% 11.2% 11.2% 11.2% 11.4% 7.9% 11.3% 11.1% 12.2% x=296, y=-48.3, z=1 0.3% 0.6% 0.8% 0.6% 0.3% 0.1% 0.4% 0.2% 0.9% x=296, y=48.3, z=1 10.2% 10.8% 11.1% 9.7% 10.2% 6.1% 10.3% 11.0% 12.0% x=300, y=0, z=1 5.1% 5.5% 5.9% 4.9% 5.1% 1.7% 5.2% 5.4% 4.5% x=395.5, y=59.8, z=1 7.8% 7.5% 7.4% 7.8% 7.8% 4.4% 7.8% 7.6% 7.0% x=395.5, y=-59.8, z=1 5.5% 5.4% 5.2% 5.4% 5.5% 2.9% 5.5% 5.6% 4.4% x=400, y=0, z=1 2.0% 2.5% 2.8% 2.1% 2.1% 0.5% 2.1% 2.2% 1.5% x=495, y=71.2, z=1 3.9% 3.9% 3.8% 3.7% 3.9% 2.0% 3.9% 4.1% 3.1% Distance to:

12.7% 229 227 232 229 234 154 231 228 237 

8.5% 319 315 314 319 323 206 321 323 291 4.2% 504 506 502 498 510 337 509 527 432 3.3% 583 587 578 562 590 401 589 612 504 1.4% 883 911 924 799 881 631 891 1014 803 

LFL 457 455 451 455 459 292 462 467 393 

Source Term Wind Speed Surface Roughness Stability
Thorney Island 45 Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration 

(%)
Source Term Averaging Time Wind Speed Surface Roughness

Monin-Obukhov

Length Stability

Ambient 

Temperature

Ambient 

Pressure

Ambient 

Relative 

Humidity

Base Case Alternative 1 Alternative Lower Upper Alternative Lower Upper Alternative Lower Upper

Run Name a b a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_12 Source Term m diamter, 10.67k steady state 2m diamter, 10.67mk diamter, 10.67mk diamter, 10.67mk diamter, 10.67kg/s

Wind Speed 2.3 2.3 2.3 2.3 2.3 2.3Reference Height 10 10 10 10 10 10Surface Roughness 1.00E-02 1.00E-02 2.00E-05 3.00E-02 1.00E-02 1.00E-02Wind Stability F F FFFEAveraging Time 30 30 30 30 30 30Atmospheric Parameters

DELTA Y 0.03702 0.03702 0.03702 0.03702 0.03702 0.05603

BETA Y 0.9 0.9 0.9 0.9 0.9 0.9Monin-Obukhov Length 11.8 11.8 4.08 14.3 13.3 30.4Sigma X Coefficient 1.70E-01 1.70E-01 1.70E-01 1.70E-01 1.70E-01Sigma X Power 9.70E-01 9.70E-01 9.70E-01 9.70E-01 9.70E-01Sigma X Minimum Distance 5.00E+01 5.00E+01 5.00E+01 5.00E+01 5.00E+01

Wind Power Constant 0.349 0.349 0.318 0.386 0.334 0.257Friction Velocity 0.07396 0.07396 0.03268 0.08839 0.07709 0.09523Ambient Temperature 286.25 286.25 286.25 286.25 286.25 286.25Ambient Pressure 1 1 1111Ambient Relative Humidity 100 100 100 100 100 100Isothermal? N N NNNNHeat Transfer? Y Y YYYY

Surface Temperature 286.25 285.95 285.95 285.95 285.95 285.95Correlation 1 1 1111

Water Transfer? N N NNNNMolecular Weight 57.8 58.7 57.8 57.8 57.8 57.8Release Temperature 286.25 286.25 286.25 286.25 286.25 286.25Density 2.477 2.477 2.477 2.477 2.477 2.477Mean heat capacity constant 586.68 577.28 586.27 586.27 586.27 586.27Mean heat capacity powerUpper Concentration 2.50E-01 2.50E-01 2.50E-01 2.50E-01 2.50E-01 2.50E-01Lower Concentration 1.00E-04 1.00E-04 1.00E-04 1.00E-04 1.00E-04 1.00E-04Height for isopleths 0.5 0.5 0.5 0.5 0.5 0.5Max Concentration at:40m centerline 29.5% 28.2% 12.8% 32.4% 30.0% 26.7%53m centerline 29.5% 28.2% 12.8% 16.0% 28.9% 20.4%72m centerline 12.5% 22.4% 12.8% 11.5% 12.9% 12.4%90m centerline 10.0% 15.2% 12.8% 7.9% 9.9% 7.8%112m centerline 7.0% 8.8% 12.8% 4.6% 6.7% 4.9%158m centerline 3.3% 3.3% 12.8% 1.9% 3.1% 2.1%250m centerline 1.0% 0.9% 3.3% 0.6% 1.0% 0.7%335m centerline 0.5% 0.5% 1.7% 0.3% 0.5% 0.4%472m centerline 0.2% 0.2% 0.8% 0.1% 0.2% 0.2%Distance to:

20.0% 21 78 11 37 33 54

12.9% 69 96 33 66 72 71

8.9% 97 112 199 86 97 856.2% 119 128 199 99 117 1013.8% 150 153 120 145 1242.6% 173 173 283 141 169 1440.8% 282 272 484 224 275 2390.5% 331 321 579 264 327 2880.4% 384 371 663 304 375 335
Thorney Island 47 Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration (%) 
Source Term Averaging Time

Monin-Obukhov

Length

Ambient 

Temperature

Ambient 

Pressure

Ambient 

Relative 

Base Case Alternative 1 Alternative Lower Upper Alternative Lower Upper Alternative Lower Upper

Run Name a b a_1 a_2 a_3 a_4 a_5 a_6 a_7 a_8 a_9 a_10 a_11 a_12 Source Term 2m diamter, 10.2steady state, 2m diamter, 10.22kg/s 2m diamter, 10.22m diamter, 10.22m diamter, 10.22m diamter, 10.22kg/s

Wind Speed 1.50 1.50 1.50 1.50 1.50 1.50Reference Height 10.00 10.00 10.00 10.00 10.00 10.00Surface Roughness 1.00E-02 1.00E-02 2.00E-05 3.00E-02 1.00E-02 1.00E-02Wind Stability F F FFFEAveraging Time 30.00 30.00 30.00 30.00 30.00 30.00Atmospheric Parameters

DELTA Y 0.04 0.04 0.04 0.04 0.04 0.06BETA Y 0.90 0.90 0.90 0.90 0.90 0.90Monin-Obukhov Length 11.80 11.80 4.08 14.30 10.00 30.40Sigma X Coefficient 1.70E-01 1.70E-01 1.70E-01 1.70E-01 1.70E-01Sigma X Power 9.70E-01 9.70E-01 9.70E-01 9.70E-01 9.70E-01Sigma X Minimum Distance 5.00E+01 5.00E+01 5.00E+01 5.00E+01 5.00E+01

Wind Power Constant 0.349 0.349 0.318 0.386 0.372 0.257Friction Velocity 0.05 0.05 0.02 0.06 0.05 0.06Ambient Temperature 287.45 287.45 287.45 287.45 287.45 287.45Ambient Pressure 1.00 1.00 1.00 1.00 1.00 1.00Ambient Relative Humidity 97.40 97.40 97.40 97.40 97.40 97.40Isothermal? N N NNNNHeat Transfer? Y Y YYYY

Surface Temperature 287.65 287.65 287.65 287.65 287.65 287.65Correlation 1.00 1.00 1.00 1.00 1.00 1.00

Water Transfer? N N NNNNMolecular Weight 57.80 57.80 57.80 57.80 57.80 57.80Release Temperature 287.45 286.45 287.45 287.45 287.45 287.45Density 2.48 2.51 2.51 2.51 2.51 2.51Mean heat capacity constant 586.68 586.68 586.27 586.27 586.27 586.27Mean heat capacity powerUpper Concentration 20.00% 20.00% 20.00% 20.00% 20.00% 20.00%Lower Concentration 0.20% 0.10% 0.10% 0.10% 0.10% 0.10%Height for isopleths 0.50 0.50 0.50 0.50 0.50 0.50Max Concentration at:50m centerline 17.4% 17.0% 11.0% 20.4% 15.6% 25.1%90m centerline 17.4% 17.0% 9.2% 20.4% 15.6% 9.0%212m centerline 2.0% 6.8% 7.7% 1.3% 1.9% 2.1%250m centerline 1.2% 4.0% 6.9% 0.8% 1.2% 1.2%335m centerline 0.5% 1.4% 0.6% 0.3% 0.5% 0.7%472m centerline 0.2% 0.5% 0.5% 0.1% 0.2% 0.3%Distance to:

15.9% 136 145 19 21 20 82

7.4% 139 236 236 113 158 1141.5% 237 333 271 196 217 2490.7% 312 441 441 258 294 3350.5% 349 500 500 301 344 3790.2% 456 679 679 384 439 499

Wind Speed Surface Roughness Stability
CHRC A Scaled Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration 

(%)
BA Hamburg DA0120 Scaled Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 1

Downwind distance (m)

Maximum arcwise concentration 

(%)
BA Hamburg DAT223 Scaled Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 1

Downwind distance (m)

Maximum arcwise concentration 

(%)
BA TNO FLS Scaled Measured vs Predicted 

Maximum Arcwise Concentration

Long Time Average

0.0

10.020.030.040.050.060.070.080.090.0

100.0

0 100 200 300 400 500 600 700 800 900 10

Downwind distance (m)

Maximum arcwise concentration 

(%)
APPENDIX B: REFERENCES 
REFERENCES 

AcuTech Consulting Group (2009). Final Report: Review of the LNG Vapor Dispersion 

Model Evaluation Protocol. The National Association of State Fire Marshals. 

Blackmore, D.R., Eyre, J.A., Summers, G.G. (1982), Dispersion and Combustion 

Behaviour of Gas Clouds Resulting from Large Spillages of LNG and LPG on the 

Sea. Transactions of the Institute of Marine Engineers, Volume 94, Paper 92, 

1982. Institute of Marine Engineers. 

Blackmore, D.R., Colenbrander, G.W., Puttock, J.S., (1984). Maplin Sands Experiments 

1980: Dispersion of Refrigerated Liquid Propane and LNG, NATO Challendges 

of Modern Society—Air Pollution Modelling and Its Application 3, Volume 5, 

Pages 353-373, Plenum, New York, USA. 

Brutstaert, W. (1982). Evaporation into the Atmosphere: Theory, History, and 

Applications. Kluwer Academic Publishers, Netherlands. 

Coldrick, S., Lea, C.J., Ivings, M.J. (2010). Validation Database for Evaluating Vapor 

Dispersion Models for Safety Analysis of LNG Facilities, Version 11.0. The Fire 

Protection Research Foundation, Quincy, Massachusetts. 

Colenbrander, G.W., (1980). A Mathematical Model for the Transient Behavior of Dense 

Vapor Clouds, 3rd International Symposium on Loss Prevention and Safety 

Promotion in the Process Industries, Basel, Switzerland, 1980. 

Colenbrander, G.W., Evans, A., Puttock, J.S. ( 1983). Dense Gas Dispersion Behavior: 

Experimental Observations and Model Developments. International Symposium 

on Loss Prevention and Safety Promotion in the Process Industries, Harrogate, 

England, September 1983. 

Colenbrander, G.W., Evans, A., Puttock, J.S. (1984a). Spill Tests of LNG and 

Refrigerated Liquid Propane on the Sea, Maplin Sands, 1980: Dispersion Data 

Digest; Trial 27. Shell Research Limited, TNER.84.028. 

Colenbrander, G.W., Evans, A., Puttock, J.S. (1984b). Spill Tests of LNG and 

Refrigerated Liquid Propane on the Sea, Maplin Sands, 1980: Dispersion Data 

Digest; Trial 34. Shell Research Limited, TNER.84.030. 

Colenbrander, G.W., Evans, A., Puttock, J.S. (1984c). Spill Tests of LNG and 

Refrigerated Liquid Propane on the Sea, Maplin Sands, 1980: Dispersion Data 

Digest; Trial 35. Shell Research Limited, TNER.84.031. 

Eyre, J.A., Hirst, W.J.S. (1983), Maplin Sands Experiments 1980: Combustion of Large 

LNG and Refrigerated Liquid Propane Spills on the Sea. Proceedings, 2nd

Symposium on Heavy Gas and Risk Assessment II, West Germany, May 25-26, 

1983, D Reidel Publishing Company, Netherlands. 
REFERENCES (cont’d) 

Ermak, D.L, Chapman, R., Goldwire, H.C., Gouveia, F.J., Rodean, H.C. (1989). Heavy 

Gas Dispersion Test Summary Report. Lawrence Livermore National Laboratory. 

Federal Energy Regulatory Commission (FERC) (2004a). Consequence Assessment 

Methods for Incidents Involving Releases from Liquefied Natural Gas Carriers. 

Docket No. AD04-6-000. 

Federal Energy Regulatory Commission (FERC) (2004b). Staff’s Responses to 

Comments on the Consequence Assessment Methods for Incidents Involving 

Releases from Liquefied Natural Gas Carriers. Docket No. AD04-6-000. 

Havens, J., (1982),Dispersion of Dense Vapors, Volume 2, MIT-GRI LNG Safety and 

Research Workshop. GRI 82/0019.2, Gas Research Institute (GRI). 

Havens, J., Spicer, T.O., (1985), Development of an Atmospheric Dispersion Model for 

Heavier-Than-Air Gas Mixtures, Volume 1, Final Report Contract DT-CG-23-80-

C-20029, United States Coast Guard, Washington, D.C. 

Havens, J., (1988), A Dispersion Model for Elevated Dense Gas Jet Chemical Releases, 

Volume 1, EPA 450/4-88-006a, Environmental Protection Agency. 

Havens, J., Spicer, T. ( 1990). LNG Vapor Dispersion Prediction with the DEGADIS 

Dense Gas Dispersion Model. Report GRI 89/0242, Gas Research Institute (GRI), 

1990. 

Gavelli, F., Davis, S.G., Hansen, O.H., (2011), User Beware: When Simple Consequence 

Models Can Give the Wrong Answers, Proceedings of AIChE Spring Meeting, 7th Global 

Congress on Process Safety, Chicago, IL, March 16, 2011.

Goldwire, H.C., Rodean, H.C., Cederwall, R.T., Kansa, E.J., Koopman, R.P., McClure, 

J.W., McRae, T.G., Morris, L.K., Kamppinen, L., Kiefer, R.D., Urtiew, P.A., 

Lind, C.D. (1983a). Coyote Series Data Report LLNL/NWC 1981 LNG Spill 

Tests, Dispersion, Vapor Burn, and Rapid Phase Transition. Lawrence Livermore 

National Laboratory, UCID-19953, Volume 1. 

Goldwire, H.C., Rodean, H.C., Cederwall, R.T., Kansa, E.J., Koopman, R.P., McClure, 

J.W., McRae, T.G., Morris, L.K., Kamppinen, L., Kiefer, R.D., Urtiew, P.A., 

Lind, C.D. (1983b). Coyote Series Data Report LLNL/NWC 1981 LNG Spill 

Tests, Dispersion, Vapor Burn, and Rapid Phase Transition. Lawrence Livermore 

National Laboratory, UCID-19953, Volume 2. 

Hanna, S.R., Strimaitis, D.G., Chang, J.C. (1993). Final Report: Hazard Response 

Modeling Uncertainty (A Quantitative Method), Vol II - Evaluation of Commonly 

Used Hazardous Gas Dispersion Models. Air Force Engineering & Services 

Center, Environics Division, AD-A270-095, ESL-TR-91-28. 
REFERENCES (cont’d) 

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APPENDIX C: LIST OF PREPARERS 
LIST OF PREPARERS 

Kohout, Andrew - Federal Energy Regulatory Commission 

 B.S., Mechanical Engineering, 2006, University of Maryland 

 B.S., Fire Protection Engineering, 2006, University of Maryland