IRSN, Institut de radioprotection et de sûreté nucléaire

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Computer codes

ISIS code

3D fire simulation in industrial enclosures
ISIS is a computer tool dedicated to the study and the numerical simulation of fires in industrial facilities.

Physical models


ISIS is a computer tool developed by the IRSN for simulating fires. It comprises a coherent set of models capable of describing flow turbulence, combustion, soot production and heat transfers, in order to predict the development of a fire in large compartments that are either naturally ventilated or confined and mechanically ventilated.


The various physical models implemented in the code can simulate three-dimensional, instationary, poorly compressible, turbulent, reactive or chemically inert flows. The ISIS software is validated on a series of tests involving flows with and without chemical combustion reactions (visit for further details)


 Fire simulation in compartments mechanically ventilated


Numerical Schemes


The system of mass, momentum and energy balance equations is discretized in time using fractional step methods. Spatial discretization is based on the finite element method for hydrodynamic equations and the finite volume method for transport equations. It makes it possible to simulate enclosures with complex geometries using unstructured meshes.


For the particular case of structured meshes, a finite volume type discretisation for the hydrodynamic equations is also possible. 



Implementation and portability


ISIS implementation is based on the PELICANS software component platform developed at IRSN and distributed under an open-source license ( The parallel solver libraries enables running numerical simulations with several million mesh cells. Portability is assured across Linux, Solaris and Mac OSX.


ISIS uses meshes generated by PELICANS – it should be noted that other meshers can be used, such as GAMBIT®, Gmsh®. As for post-processing, this is performed using freeware such as GMV® or PARAVIEW®.





The Isis code will in the short term be coupled to the Sylvia software system, developed by IRSN Using a zone-based approach, SYLVIA simulates fire development in facilities with multiple rooms and complex ventilation systems. . The coupling of the Isis and Sylvia software systems will mean it will be possible to benefit, in a same tool, from both the precision of Isis, which provides a 3-D simulation of the development of a fire in the premises, and the ability of Sylvia to describe a complete ventilation network linked with these premises.


Furthermore, the code evolves permanently. Constant efforts are devoted firstly to software validations and secondly to the improvement of the physical models and the performance of digital methods. The aim is a better understanding and describing of the complex physical phenomena involved in fires. The major developments envisaged in the medium term are, firstly, the implementation and the validation of an LES approach for turbulence, which will complete the RANS approach used until now and, secondly, taking the sprinkling of water into account during a fire scenario. On the numerical front, many research studies have been conducted for several years in close collaboration with the Topology Probabilities Analysis Laboratory (LATP) of the University of Marseille.


ISIS is provided under an open-source license with the aim of favouring collaborations with French universities and facilitating application of the software to industrial problems.

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Collaborative space

ISIS is distributed under the open-source license CECILL. A collaborative space is dedicated to the code at the adress
The 3.0 version is available since the end of 2011.

Involved IRSN laboratory

Description video

Presentation sheet



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