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June 2010 Dear Phast User,
About Phast v6.6 We are pleased to announce the release of Phast
v6.6 containing updates in a number of areas of the program and a
new extension containing more advanced methods for calculating the
risks from vapour cloud explosions. Many of the new features and
enhancements are described briefly below. For a full detailed
description, please refer to the release notes.
Major New Features and Enhancements - For Consequence and
Risk
Droplet Modelling enhancements As well publicised over the last
few years, DNV Software has initiated a number of Joint Industry
Projects (JIP) to improve the modelling of rainout. The most recent
of these, JIP Phase 3, on flashing and sub-cooled liquid releases,
has provided improved correlations to characterise droplet size and
size distribution. This new correlation is included in Phast v6.6
as a non-default option. Although validated against droplet size
measurements, it may require further refinement before it can be
successfully validated against rainout measurements. In the
meantime the default remains the CCPS correlation included in
previous releases.
Improved Unified Dispersion Model There are two versions of the
Unified Dispersion Model (UDM) available in Phast v6.6. The UDM
Version 1 (default) model is the one currently available in v6.54
and earlier versions, whilst the UDM Version 2 model is an enhanced
model introduced in v6.6. UDM 2 has improved modelling of droplets
inside the cloud, and of evaporation and dispersion following
rainout. It also gives greater control over the time-steps at which
dispersion results are reported. In addition, UDM 2 includes
improved CO2 modelling as described below.
CO2 Modelling
Solid Effects This new feature has been described in detail in
recent Status Notes and there is a Technical Datasheet available
should you require more information. To use the improved CO2
modelling you must select UDM Version 2 as described above. In
v6.54 solid CO2 phase was never allowed for a released component,
only liquid or vapour. Liquid properties would be applied resulting
in post-expansion temperature being too low, liquid fraction being
too high or a failure of the UDM to converge. In v6.6 using UDM
Version 2, upstream of the orifice the release phase is still
presumed to be either liquid or vapour but post-atmospheric
expansion and during UDM dispersion, solid properties can be
applied rather than liquid properties.
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Non-Ideal Gas Effects For discharge of supercritical CO2 from
long pipelines v6.54 assumed the gas to be ideal while v6.6
includes non-ideal (compressibility) effects. At very large
pressures, non-ideal effects are important and may therefore
significantly increase the expelled mass.
Toxic Effects In order to asses the possible toxic effects of
CO2 it is necessary to define it as a toxic material and specify
the appropriate probit function. Furthermore, we recommended you
set the core averaging time equal to the toxic averaging time of
600 seconds. This will only affect the results following transition
to passive dispersion, and for most scenarios the cloud is no
longer hazardous at this distance.
In v6.6 several warnings have been added to indicate when less
accurate results might be expected due to solid effects not being
handled. We therefore recommend that you switch on warnings using
the menu Options->Preferences->General and check Display
Warning Messages on the Miscellaneous tab. A detailed description
of CO2 modelling can be found in the HSE C02 paper available on
HSE's web site at:
www.hse.gov.uk/seveso/co2-hazardous-substance.pdf
Major New Features and Enhancements - For Risk Extended Risk
Reporting
The Extended Risk Reporting, which is available in Phast Risk
only, is built around a SQL Server database and uses Risk Framework
technology to provide powerful graphing and data drill-down
capabilities for detailed analysis of risk results. The Extended
Risk Reporting provides many different charts and reports which are
described in more detail in the Release Notes. When you first run
the Extended Reporting, the first report displayed is the Risk
Dashboard. This includes a default selection of risk metrics
intended to give you an immediate overview of the key risk
contributors in your study. In addition, the Extended Reporting
allows you to explore risk results more transparently. All results
can be filtered and grouped by event, outcome, weather and
direction, population category and area.
In addition you can: Drill-down on the FN Curve to find the
outcomes contributing to the risk at any point, view
FAR, N, RI values by area and population category
Contour risk to any effect level (eg overpressure) or
combination of effects If you have licensed the Extended Explosion
Modelling you can also:
Filter and group all results by building type Produce Exceedence
Curves for Overpressures or impulse at ranking points
The Extended Reporting uses Filter Sets to help you organise and
analyse results. These are managed using the Filter Set Manager
which is described in more detail in the Release Notes. Three
Filter Set types are available; societal, risk contour and risk
ranking point. The program allows you to edit existing or create
new Filter Sets and then select any of these from the Filter Set
list. The options available then change depending on the type of
Filter Set selected. Once a Filter set is created, you can generate
the relevant reports or charts using the appropriate Results
Processor buttons. A typical screen image highlighting the Filter
Set Manager and Results Processor panes is shown below. More
information is provided in the Release Notes.
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Extended Explosion Modelling (chargeable extension)
Extended Explosion Modelling is available only for Phast Risk
users who purchase a separate license for the extension. It relies
on the Extended Risk Reporting functionality for presentation of
results. If you have licensed the extended explosion modelling,
then you have the option to use a different method for modelling
explosions in the risk calculations. The standard explosion
modelling does not consider the nature of the confinement or
obstructions in the area affected by the dispersing cloud, and it
does not calculate overpressure or impulse. The new method allows
you to define regions of congestion and confinement within your
model. The calculations will then consider the interaction between
the dispersing cloud and these regions and calculate the
overpressure and impulse generated if the cloud is ignited within
an obstructed region or regions.
You can also define any number of sets of explosion
vulnerability parameters, defining the relationship between
overpressure and impulse to fatality-probability for different
groups of people (e.g. for people in different types of building),
and for different types of risk-presentation (e.g. for societal
risk or individual risk). Phast Risk v6.6 with the Extended
Explosion modelling is able to provide much more accurate
predictions of the probable explosion damage and resulting
lethality.
The Multi-Energy Method and Baker-Strehlow-Tang Model have been
implemented within the extension, both of which are widely accepted
for calculating effects from gas explosions. The risk calculations
also take into account buildings and occupant vulnerability. Using
this extension provides increased accuracy and transparency when
calculating risks from vapour cloud explosions.
Results Processor
Filter Set Manager
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The workflow for creating a model using the new functionality is
as follows:
Define appropriate Obstructed Regions on your map - these are
used to define levels of congestion and confinement and thus assess
maximum expected overpressure and overpressure decay if an
explosion occurs
Define Building Types an empty Building Set is provided for you
where you can define all the different buildings you require.. An
example Building set is available for download from the support
website.
Provide data for vulnerability characteristics for Toxic,
Explosion Overpressure, Radiation and Flash Fires effects for each
Building Type you have defined
Define Buildings on your map - each building belongs to a
specific Building Type and you can insert population from a range
of Categories within each building
Associate buildings with areas if desired This is useful when
performing risk assessment and mitigation (e.g. reporting
separately on risks to those onsite and offsite or personnel in
storage, production and admin areas)
A more detailed and comprehensive description of the new
modelling is available in the V6.6 Release Notes and Theory
Documents provided with the release.
For more information about licensing this extension, please
contact your local DNV Software Sales Manager.
Other New Features and Enhancements
Below we provide brief descriptions of a number of the other
enhancements provided in v6.6 which we believe may be of general
interest to you.
For Consequence and Risk
Time Varying Discharge The robustness of the thermodynamic
calculations has been improved and the calculations now include the
ability to model systems containing vacuum relief valves. The
documentation has been consolidated and updated to reflect these
enhancements.
Long Pipeline Model The model has been enhanced to handle
non-ideal gas and two new valve types have been added; an excess
flow valve and a non-return valve.
New Report Export to Excel This new feature allows you to export
a wide range of consequence results to Excel. This can be useful
for exporting results for multiple concentrations of interest to a
spreadsheet for graphing and results comparison, for example.
Excel Import and Export Improvements All new objects and several
previously unhandled objects can be exported to and imported from
Excel. For Phast this includes Jet Fire, Pool Vaporisation, TNT
Explosion, ME Explosion, BST Explosion, BLEVE Blast, External
Connection, Feature Class and Raster Image. As with 6.54, Caselist,
Effect Model & Parameters are not included.
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Pool Vapourisation When using the Version 2 UDM, the standalone
pool source model now gives results which are consistent with those
from rained out pools in the linked modelling. When using the pool
source model in v6.54, creating a user-defined source from a
standalone pool could give very different results to an equivalent
case with 100% rainout of liquid spill. This inconsistency has been
largely removed. The 'trailing pool' model used in v6.54 when
initiating dispersion from a pool which has been left behind by a
dispersing vapour cloud is now also used for the standalone pool
source model. The link between the cloud and the pool has also been
improved.
Convert Case List to Model You can convert multiple or single
case lists, or individual cases within lists, to equivalent models
using this new feature. This can prove extremely useful when you
are re-structuring studies or using spreadsheet import/export.
For Risk only Excel import and Export improvements All new
objects and several previously unhandled objects can be exported to
and imported from Excel. For Phast Risk, this includes: Jet Fire,
Pool Vaporisation, TNT Explosion, ME Explosion, BST Explosion,
BLEVE Blast, External Connection, Feature Class, Raster Image,
Building Type, Building, Defined Strength Obstruction Group,
Defined Strength Obstruction, Calculated Strength Obstruction
Group, Calculated Strength Obstruction, Defined Flame Speed Group,
Defined Flame Speed, Calculated Flame Speed Group, Calculated Flame
Speed, Population Set, Risk Ranking Point and Risk Transect. As
with 6.54, Run Row Set, Run Row, Caselist, Effect Model, Parameters
& Vulnerabilities are not included.
Risk Transect improvements Risk Transects are now defined by
adding them to a Risk Transect Set on the Risk Tab. Only one Risk
Transect Set is allowed but this may contain any number of
transects. In addition, you can now define a Risk Transect as a
Polyline as well as a Line.
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Changes to results With each new version of the product, you are
likely to see some changes to results in existing studies. This
version is no exception and the release notes go into the details,
with more technical description in the theory documents. A brief
summary of areas where you are likely to see changes is given
below. full description can be downloaded from the support
website.
UDM Version 1 (Default) Using this dispersion model, most
results will be the same. However, there have been some bug fixes
in the atmospheric property calculations which could result in some
differences.
New UDM Version 2 and Droplet Correlations The new UDM and
Droplet Correlations described above will have a significant effect
on results. However, the existing v6.54 options have been retained
as the default in v6.6, so you will not see any impact on results
from these enhancements unless you select the new options.
Time Varying Discharge and Long Pipelines Significant
improvements have been made to the time varying discharge model and
these will have an unavoidable effect on the results. The Long
Pipeline model for gases now considers compressibility by default.
This will typically lead to more mass being released than for an
equivalent release treated as an incompressible gas. The 6.54
method is retained as a non-default parameter (Ideal gas
modelling). Additionally, improved models for choked flow and time
interpolation have been implemented for the long pipeline model for
gases which will generally lead to larger flow rates.
Jet Fire Duration Adjustment In 6.54 and earlier versions, jet
fires were assumed to have a duration corresponding to the jet fire
maximum exposure time parameter which defaulted to 20s. The
lethality calculations will now use the actual duration if shorter
than this parameter. Therefore, for release durations less than
20s, Jet fire lethality ellipses will get smaller.
There are other smaller changes, including bug fixes, which will
also affect results and these are described in more detail in the
release notes.
Thank you for your continued support of DNV Software products
and we look forward to serving your software needs now and in the
years to come.
Kind regards,
Dr Nic Cavanagh Head of Safeti Business Development DNV
Software