Default Values
This table details the many variables used by Phast and their default values. Almost all models are run without many of these parameter values being changed. These values can be modified with the Advanced Model. These values are only displayed for knowledgeable users of Phast. Most users do not need to change any of these values.
Dispersion parameters
Near field |
|
| Expansion zone length/source diameter ratio | 0.01 |
| Near field passive entrainment parameter | 1 |
| Modelling of instantaneous expansion | Standard method |
Momentum Jet |
|
| Jet model | Morton et. al. |
| Drag coefficient between plume and air | 0 |
| Jet entrainment coefficient alpha 1 | 0.17 |
| Jet entrainment coefficient alpha 2 | 0.35 |
Dense Cloud |
|
| Dense cloud parameter gamma – continuous | 0 |
| Dense could parameter gamma – instant | 0.3 |
| Dense cloud parameter K – continuous | 1.15 |
| Dense cloud parameter K – instantaneous | 1.15 |
Far Field |
|
Criteria for transition to passive dispersion |
|
| Maximum cloud/Ambient velocity difference | 0.1 |
| Maximum cloud/ambient density difference | 0.015 |
| Maximum non-passive dispersion | 0.1 |
| Maximum Richardson number | 15 |
Modelling the transition |
|
| Distance multiple for full passive entrainment | 2 |
Modelling passive dispersion |
|
| Ratio instantaneous/continuous sigma-y | 1 |
| Ratio instantaneous/continuous sigma-z | 1 |
Liquid |
|
Droplet modelling |
|
| Droplet evaporation thermodynamics model | Rainout, non-equilibrium |
| Ratio Droplet/expansion velocity for instantaneous release | 0.8 |
| Expansion energy cut-off for droplet angle | 0.69 kJ/kg |
Rainout modelling |
|
| Coefficient of initial rainout | 0 |
| Flag to rest rainout position | Do not reset rainout position |
Pool evaporation |
|
| Richardson Number for passive transition above Pool | 0.015 |
| Pool Vaporisation entrainment parameter | 1.5 |
Ground |
|
| Richardson number criterion for cloud lift-off | -20 |
Modelling of heat and water transfer |
|
| Flag for heat/water vapour transfer | Heat and Water |
| Surface over which the dispersion occurs | Land |
Modelling of impingement |
|
| Impingement option | 0 |
| Impinged Velocity limit | 500 m/s |
| Impinged velocity factor | 0.25 |
Limits |
|
| Treatment of top mixing layer | Constrained |
Minimum limits |
|
| Minimum temperature allowed | -262.1 degC |
| Minimum release velocity for cont. release | 0.1 m/s |
| Minimum cloud depth | 0.02 m |
| Minimum continuous release height | 0m |
Maximum limits |
|
| Maximum temperature allowed | 626.9 degC |
| Maximum distance for dispersion | 5E4 m |
| Maximum height for dispersion | 1000 m |
Building wake |
|
| Model in use | Best Estimate |
Calculation control |
|
| Lee Length Specified lee length |
Calculate |
| Lee Half-Width Specified lee half-width |
Calculate |
| Lee Height Specified Lee height |
Calculate |
| K-Factor Specified K-Factor |
Calculate |
| Switch Distance Specified Switch Distance |
Calculate |
Output Granularity |
|
| Maximum Initial Step Size | 10 m |
| Minimum Number of Steps per zone | 5 |
| Factor step increase | 1.2 |
| Maximum number of output steps | 1000 |
Other |
|
| Dispersion model to use | Version 2 Model |
Modelling of short duration releases |
|
| Flag for finite duration correction | QI without duration adjustment |
| Quasi-Instantaneous transition parameter | 0.8 |
Integration in calculations |
|
| Relative tolerance for dispersion calculations | 0.001 |
| Relative tolerance for droplet calculations | 0.001 |
Step sizes for cloud integration |
|
| Maximum integration step size – instantaneous | 100 s |
| Maximum integration step size – continuous | 100 m |
| Initial integration step size – instantaneous | 0.01 s |
| Initial integration step size – continuous | 0.01 m |
| Fixed step size – instantaneous | 0.01 s |
| Fixed step size – continuous | 0.1 m |
| Number of fixed size output steps | 20 |
| Multiplier for output step sizes | 1.2 |
Fire ball and BLEVE parameters
Fireball radiation |
|
Which radiation levels to calculate |
|
| Calculate dose | unselected |
| Calculate probit | unselected |
| Calculate lethality | selected |
Parameters |
|
| Mass modification factor | 3 |
| Fireball maximum exposure duration | 20 s |
Fireball parameters |
|
| Calculation method for fireball | DNV recommended |
| TNO model flame temperature | 1727 degC |
Blast |
|
| Ground reflection | ground burst |
| Ideal gas modelling | model as real gas |
| Minimum distance | 0 m |
| Number of distance points | 100 |
Constants |
|
| Maximum surface emissive power | 400 kW/m2 |
| Radiation dose for fireball risk calculations | 5.78E+06 |
Flammable parameters
Flammables |
|
| Flammable mass calculation method | mass between LFL and FL |
| Flammable result grid step in x-direction | 10m |
| Flammable base averaging time | 18.75 s |
| Cut off time for short continuous releases | 20 s |
| LFL fraction to finish | 0.5 |
Heights for calculation and reporting |
|
| Height for calculation of flammable effects | 0 m |
| Heights for reports | centreline height |
Modelling of immediate flash fire |
|
| UFL multiple for immediate ignition | 1 |
| Cut off fraction for cloud volume | 0.001 fraction |
Short duration effects |
|
| For time-varying releases | don’t model short duration effects |
| Match fireball duration and mass released | no |
Fireball parameters |
|
Radiation |
|
| Number of radiation/distance points in linked radiation calculations Solar radiation | 50 |
| Solar radiation | exclude from calculations |
Observer properties |
|
| Observer type radiation modelling flag | planar |
| Observer direction | variable |
| Angle of inclination | 0 deg |
| Angle of orientation | 0 deg |
Radiation probit values (units in probit equation (1 term) are W.m-2 |
|
| Probit N value | 1.333 |
| Probit A value | -36.38 |
| Probit B value | 2.56 |
Tolerances in radiation calculations |
|
| Absolute tolerance for linked radiation calculations | 1.00E-10 |
| Relative tolerance for radiation calculations | 0.01 fraction |
Explosion parameters
TNT |
|
| Explosion efficiency | 10% |
| Air or ground burst | air burst |
Flammable mass |
|
Vapour liquid method |
|
| Use of mass modification factor | early and late explosions |
| Explosion mass modification factor | 3 |
Overpressures |
|
| Explosion location criterion | cloud front (LFL fraction) |
| Minimum explosive mass | 0 kg |
Explosion overpressure for reporting (gauge) |
|
| Over pressure level 1 | 0.02068 bar |
| Over pressure level 2 | 0.1379 bar |
| Over pressure level 3 | 0.2068 bar |
| Over pressure level 4 | bar |
| Over pressure level 5 | bar |
General parameters
General reference data |
|
| Height for concentration output | 0 m |
| Maximum release duration | 3600 s |
Geometry references |
|
| Rotation | 0 deg |
| Lower elevation | 0 m |
| Upper elevation | m |
Dispersion |
|
Handling of aerosols |
|
| Multicomponent aerosol behaviour | single aerosol modelling |
Discharge parameters
Velocity head losses |
|
| Excess flow valve velocity head loss | 0 |
| Non-return valve velocity head loss | 0 |
| Shut-off valve velocity head loss | 0 |
Frequencies |
|
| Frequency of bends in long pipes | 0/m |
| Frequency of couplings in long pipes | 0/m |
| Frequency of junctions in long pipes | 0/m |
Defaults |
|
| Line length | 10 m |
| Pipe roughness | 0.0457 mm |
| Air changes | 3 /hr |
| Elevation | 1 m |
| Atmospheric expansion method | Closest to initial conditions |
| Tank roof failure model effects | instantaneous effects |
Modelling of time-varying leaks and line ruptures |
|
| Vacuum relief valve | operating |
| Vacuum relief valve set point | 0 bar |
Modelling of liquid for in building releases |
|
| Handling of droplets | not trapped |
| Indoor mass modification factor | 3 |
Discharge constants |
|
| Critical pressure greater that flow phase | 0.3447 bar |
| Capping of pipe flow rates | use lead scenario cap, disallow flashing |
Capping options |
|
| Velocity capping method | fixed velocity |
| Maximum release velocity | 500 m/s |
Relief valves |
|
| Minimum RV diameter ratio | 1 |
| Relief valve safety factor | 1.2 |
Equation constants |
|
| Continuous critical Weber number | 12.5 |
| Instantaneous critical Weber number | 12.5 |
| Venting equation constant | 24.82 |
Reference |
|
| Use Bernoulli for forced-phase liq-liq discharge | use compressible flow eqn |
| Tolerance | 0.0001 |
Droplet handling |
|
| Continuous drop slip factor | 1 |
| Instantaneous drop slip factor | 1 |
| Droplet method – continuous only | modified CCPS |
Phase data |
|
| Minimum drop diameter allowed | 0.01 um |
| Maximum drop diameter allowed | 1E4 um |
| Default liquid fraction | 1 |
Radiation levels
| Intensity levels | 0 |
| Non-return valve velocity head loss | 4 12.5 37.5 kW/m2 |
| Probit levels | 2.73 3.72 7.5 |
| Dose levels | 1.27E6 5.8E6 2.51E7 |
Jet fire parameters
Jet fire radiation |
|
Which radiation levels to calculate |
|
| Calculate dose | unselected |
| Calculate probit | unselected |
| Calculate lethality | selected |
Parameters |
|
| Rate modification factor | 3 |
| Jet fire maximum exposure duration | 20 s |
Jet fire parameters |
|
Cone model options |
|
| Cross wind angle | 0 deg |
| Correlation | DNV recommended |
| Horizontal options | Use standard method |
Emissivity calculation |
|
| Emissivity methods | E and F calculated |
| Flame emissive Power | kW/m2 |
| Emissivity fraction | fraction |
Jet fire reference data |
|
| Maximum SEP for a jet fire | 400 kW/m2 |
| Jet fire averaging time | 20 s |
Pool fire parameters
Pool fire radiation |
|
Which radiation levels to calculatee |
|
| Calculate dose | not selected |
| Calculate probit | not selected |
| Calculate lethality | selected |
Parameters |
|
| Radiative fraction for general fires | 0.4 fraction |
| Maximum exposure duration | 20 s |
Pool vaporisation parameters
Pool vaporisation |
|
| Concentration power to use in pool rate load calculation | 1 |
| Maximum number of pool evaporation rates | 10 |
Cut-offs for pool evaporation rates |
|
| Toxics cut-off rate for pool evaporation | 0.001 kg/s |
| Flammable cut-off rate for pool evaporation | 0.1 kg/s |
Bund |
|
Bund description |
|
| Type of bund surface | concrete |
| Bund height | 0 m |
| Bund failure mode | bund cannot fail |
User defined bund properties |
|
| Pool minimum thickness | 5 mm |
| Surface thermal diffusivity | 9.48E-7 m2/ |
| Surface roughness factor | 2.634 |
| Surface thermal conductivity | 0.00221 kJ/m.s.degK |
Toxic parameters
Toxic parameters |
|
Indoor calculations |
|
| Indoor calculations | unselected |
| Wind dependant exchange rate | case specified |
| Building exchange rate | 0.001 kg/s |
| Flammable cut-off rate for pool evaporation | 4 /hr |
| Tail time | 1800 s |
Exposure time data |
|
| Set averaging time equal to exposure time | use a fixed averaging time |
| Cut-off fraction of toxic load for exposure time calculation | 0.05 fraction |
| Cut-off concentration for exposure time calculations | 0 fraction |
Toxics |
|
| Toxics: height for calculation of effects | 0 m |
| Toxics: minimum probability of death | 0.001 |
| Toxic averaging time – New parameter | 600 s |
Calculation methods |
|
| Multi-comp. toxic calc. method | mixture probit |
| Probit calculation method | use probit |
Results grid steps |
|
| Toxics: results grid step in X-direction | 25 m |
| Toxics: results grid step in Y-direction | 2.5 m |
Weather parameters
Atmospheric parameters |
|
General atmospheric parameters |
|
| Atmospheric temperature | 9.85 deg C |
| Relative humidity | 0.7 fraction |
| Solar radiation flux | 0.5 kW/m2 |
Mixing layer height vs Pasquil Stability |
|
| Mixing layer height for Pasquil Stability A | 1300 m |
| Mixing layer height for Pasquil Stability A/B | 1080 m |
| Mixing layer height for Pasquil Stability B | 920 m |
| Mixing layer height for Pasquil Stability B/C | 880 m |
| Mixing layer height for Pasquil Stability C | 840 m |
| Mixing layer height for Pasquil Stability C/D | 820 m |
| Mixing layer height for Pasquil Stability D | 800 m |
| Mixing layer height for Pasquil Stability E | 400 m |
| Mixing layer height for Pasquil Stability F | 100 m |
| Mixing layer height for Pasquil Stability G | 100 m |
Building data |
|
| Building exchange rate | 4 /hr |
| Tail time | 1800 s |
Substrate data |
|
| Surface roughness | use parameter |
| Surface type | User-defined |
| Parameter | 0.1 |
| Length | 183.2 mm |
Surface temperature |
|
| Surface temperature for dispersion calculations | 9.85 degC |
| Surface temperature for pool calculations | 9.85 degC |
Atmospheric constants |
|
Constants |
|
| Atmospheric pressure | 9.85 degC |
| Atmospheric molecular weight | 28.97 |
| Atmospheric specific heat at constant pressure | 1.004 kJ/kg.degK |
Temperature and pressure data |
|
| Atmospheric T and P profile | Temp. Logarithmic; Pres. Linear |
| Temperature reference height | 0 m |
Wind speed data |
|
| Wind speed profile | Power Law |
| Wind speed reference height | 10 m |
| Cut-off height for wind speed profile | 1 m |