FLACS 25.1, the latest version, introduces significant upgrades in simulation performance times for Linux, improved combustion modelling, and better grid and results handling. Most excitingly, this version includes Multiscenario, a new feature for generating multiple scenarios at once. These new improvements are summarised below.

Multiscenario: Scenario Generation at Scale

Modelling multiple cases has always been core to effective consequence and explosion analysis. But building and managing dozens — or hundreds — of variations was slow, repetitive, and error-prone.

Multiscenario in CASD changes that:

• Create and manage many scenarios from one base case.

• Quickly vary wind, cloud size, geometry, ignition, or any scenario input.

• Use a drag-and-drop graph to visualise, edit, and link variations.

• Automatically export all combinations, ready to simulate, without the need for scripting .

Why this matters:

• Analysts save hours of manual setup time.

• Reduces input errors and ensures consistent case structure.

• Simplifies sensitivity studies, worst-case selection, and QRA input generation.

• Directly integrates with Flowvis features like jump tables and aggregation for faster review.

Whether you're comparing ignition points in a congested module or assessing how release size affects consequences, Multiscenario helps you get there faster, with more confidence.

Other Improvements

Faster Simulations (Linux Only)

• FLACS now compiled with AVX and FMA instructions.

• Up to 30% performance improvement on modern CPUs (Haswell and newer).

• No changes to model setup—just faster results.

Improved combustion modelling

• New interpolation for burning velocity: replaced 3rd-order polynomial with piecewise cubic Hermite—smoother and more accurate transitions.

• Added detonation quenching (DDT reverse) logic based on fuel concentration.

• Species flammability limits now aligned with DIPPR database values for consistency.

Better Grid and Result Handling

• Auto-grid settings now apply per scenario in multiscenario projects.

• Simulator output grid indices now match CASD's numbering—easier post-processing and verification.

• Fixed heat flux and wall temperature calculations at thin walls.

Stability and Usability Fixes

• More robust handling of dump/load operations (panels, DTM rays).

• CASD now handles multi-material models more efficiently.

• Improvements to transparency and geometry display in complex scenes.

What else is new in this release?

FLACS 25.1

• Upgrade from Python 3.9 to 3.11 and newer versions of most bundled Python packages

• Upgraded FLACS installation program and it now supports installation from command-line / unattended install.

Simulators

• FLACS runs up to 30% faster, at the cost of requiring the CPU to support the FMA instruction set (Haswell architecture and newer). This is available in most CPUs produced since 2013. Linux only.

• Aligned species flammability limits with DIPPR database values.

• Updated interpolation scheme for burning velocity data: change from 3-order polynomial to piecewise cubic hermite interpolating polynomial.

• Introduced detonation quenching (DDT reverse) criterion based on fuel concentration.

• Aligned grid indices written to the logfile to the numbering used in CASD.

• Fixed heat flux and wall temperature values at thin walls.

• Fixed dump/load with opening panels.

• Fixed dump/load with adaptive number of DTM rays.

• Other minor fixes.

FGC

• New data structure used for complex mesh objects. This fixes problems with some mesh objects which resulted in incorrect porosities, as well as improving performance and memory usage in some cases.

• Fixed a bug causing incorrect porosities when left difference was used in instanced objects.

• Fixed a bug causing incorrect porosities when left difference was used in zero-thickness primitives (such as plates).

CASD

• New multi-scenario functionality. See the multiscenario page.

• Auto-grid regions are now shown in 3D view.

• Various improvements for Auto-grid.

• Improved MDI performance when geometry has many materials.

• Fixed transparency not working correctly when MDI is enabled.

• Fixed the ”Convert to box” function not working in some cases.

Flowvis

• Make offset interpolation for surface plot in 3D view work also when interpolation is disabled.

• Fixed 3D exceedance not working as expected.