Technical Notes


Table of Contents back - top

  1. Basic information
  2. Intended field of application
  3. Model type and dimension
  4. Model description summary
  5. Model limitations
  6. Resolution
  7. Schemes
  8. Solution technique
  9. Input requirements
  10. Output quantities
  11. User interface availability
  12. User community
  13. Previous applications
  14. Documentation status
  15. Validation and evaluation
  16. Frequently Asked Question
  17. Portability and computer requirements
  18. Availability
  19. References

1. Basic Informations back - top

Full Model Name
Model version and status
Contact person
Contact address

Web Site
SEVEX – SEVeso EXpert system
Last update version 2.4
ATM-PRO s.p.r.l.
consulting in Environment & Software Development
Rue Saint-André, 5
B-1400 Nivelles (Belgium)
+ 32 (0)67 84 33 04
+ 32 (0)67 84 33 09

2. Intended field of application back - top

The fields of applications of SEVEX are :

  • Simulation of accidental release from chemical activities
  • Risk Area mapping taking into account toxicity, over-pressure and radiation
  • Emergency response planning preparedness and training

SEVEX is suitable for accidental release from single or multiple pipe, vessel or pool sources. The release can be continuous, transient or catastrophic. At this stage, 34 chemical substances are considered in the data base. Its extension to the most common substances is in progress.

SEVEX is not a real time software but intends to produce IN ADVANCE the most realistic mapping of risk areas around chemical industries in order to build up effective and manageable Emergency Response Plans.

3. Model type and dimension back - top

Following the Model Evaluation Group (MEG) protocol [1] SEVEX can be considered at once as an intermediate model and a fundamental one. The dense gas module is a box model and it can be coupled to two different passive dispersion models : a 2-D Gaussian and a 3-D lagrangian particle ones. The lagrangian particle model is coupled to a 3-D meteorological model which solves the time dependent Navier-Stokes equations to compute the wind field over complex terrain.

4. Model description summary back - top

The SEVeso EXpert system or SEVEX is a software designed to estimate risks zones around hazardous materials handling and storage facilities like chemical activities, in particular the " Seveso-type " industries (cfr. the European SEVESO Directives), railway marshalling yards, ports area or pipe-line terminals (cfr. announced European Directives). It has been developed by the Walloon Region of Belgium in collaboration with the " Faculté Polytechnique de Mons ", the " Université Catholique de Louvain ", the " Université de Liège " and the SOLVAY s.a. company.

SEVEX computes all the aspects and consequences of accidental releases of hazardous materials (toxic or flammable) through a set of coherent scientific models :

  1. The source term module (SEVEX-SOURCE) that includes calculations of : gaseous, liquid and two-phase flow rates, jet dispersion, aerosol vaporisation, pool formation and evaporation, dense gas dispersion, unconfined vapour cloud explosion (UVCE) and fireball thermal radiation (BLEVE). For quick assessment purposes allowing to design most relevant scenarii and situations the SEVEX-SOURCE module can be coupled to simple Gaussian dispersion model.
  2. The 3-D meso-meteorological module (SEVEX-MESO) that is a 3-D numerical model solving the simplified Navier-Stokes equations for the wind flow in a vorticity mode. This model takes into account the topography and the main surface characteristics such as roughness length, heat and radiation transfer between the surface and the atmosphere which extend up to 2000 m. Computations are made for different synoptic wind speeds and directions during cloudy days and clear nights. Those situations have been chosen because they lead to worst dispersion conditions.
  3. The 3-D dispersion module (SEVEX-TOXIC) that is a Lagrangian dispersion model. It simulates passive transportation and dispersion of particles of toxic or irritating substances at a rate and in a state given by the SEVEX-SOURCE module. The wind fields and turbulence characteristics are taken from the SEVEX-MESO module.
These different modules are linked together and implemented into a user-friendly interface. Starting from a source description (or accidental release scenario) deduced from a safety analysis, SEVEX enables to produce maps directly usable by emergency planning teams. These maps show various danger zones considering toxicity, overpressure and heat effects. Three levels of danger are taken into account : temporary diseases, permanent injuries out door and danger indoor. SEVEX maps show also where no danger is expected. These information enables to define clearly the behaviour to adopt facing the danger : no change in behaviour, avoiding exposure advised, self-confinement or evacuation.

The outputs of SEVEX are compiled into a Data Base of potential accident maps showing accidental scenario information (substance, effects, danger to public, meteorological conditions, ...), realistic mapping of risk zones corresponding to defined thresholds and behaviour to adopt. In case of an emergency, this so-called "SEVEX Atlas" provides an immediate answer or anticipated decision about the behaviour to adopt and the instructions to enforce in each danger zone.

Such anticipated decisions are the only way to avoid the chaos of misleading orders. Indeed SEVEX prevention policy is to be prepared to the worst "realistic" situations. This will lead to conservative decisions for better conditions. SEVEX integrates in each level of the analysis the inherent uncertainties of emergency situations and builds up the most suitable emergency plan on the basis of the very few certainties available.

SEVEX limits the problem to realistic danger extent and leads to an effective emergency response.

5. Model limitations back - top

  • SEVEX is not a "real-time" emergency response tool.
  • SEVEX do not consider chemical reactions and multicomponent material.
  • SEVEX handles topography with slopes up to ~ 10 %.
  • SEVEX atmosphere goes up to 2000 m.
  • Indoor concentration are not predicted. They are supposed equal to outdoor ones.
  • No model for fire smoke
  • In the dense gas module the topography is not taken into account
  • Pool evaporation model only used if continuous flow.

6. Resolution back - top

Domain extent : 37 km x 37 km
Grid resolution :
  • 1 km x 1 km for the wind field calculations by SEVEX-MESO
  • 0.1 km x 0.1 km for the concentration calculations by SEVEX-TOXIC

7. Schemes back - top

As far as the SEVEX software integrates a series of interlinked modules, the reader is referred to the SEVEX Evaluation document [3], where more information concerning the various schemes used in the software are given.

8. Technical Solution back - top

The SEVEX software is designed as an integrated modular code. Each part or module has been tested, verified and validated.

9. Input requirements back - top

Two levels of inputs are necessary. A first set is needed to produce the SEVEX Atlas. The second one enables to use the SEVEX Atlas in practical situations of emergency once the SEVEX Atlas exists.

Production of the SEVEX Atlas :

  • Site description : topography, land use (as a standard a 5 land types data base provides : emissivity, roughness length, albedo and heat capacity) and corresponding scanned road map (or equivalent)
  • Accidental scenario : substance involved, description and type of storage, vessels and pipe sizes, description of potential leak (those data are coming from a peer review of the studied facilities.)
Use of SEVEX Atlas
  • Synoptic wind speed and direction,
  • Substance involved,
  • Accident type,
  • Time of the day (day or night)

10. Output quantities back - top

The SEVEX software is build in such a way that a sequence of steps is to be performed in order to produce the risk zones maps (taking into account concentration/radiation/pressure effects). Each step offer the possibility to produce some outputs, either at screen (tables, summaries, graphs or maps) or on paper. These different steps are :

  • "CASE" - potential release data base definition : flow rates (liquid, vapour and total), released quantities, ...
  • "METEO" - wind field data base definition : wind field at 5 m height overplotted on the topography and/or the land use digitised maps,
  • "SCENARIO" - combination of CASE and METEO items : iso-contour plot of individual event risk areas corresponding to the pre-defined levels of danger (three), overplotted on scanned road-map,
  • "ACCIDENT" - combination of SCENARIO items : map providing :
    • Information about the danger
    • Description of the accident scenario
    • Description of meteorological conditions
    • Danger thresholds (cfr. toxicity, overpressure and/or heat) with respect to health effects
    • Behaviour to adopt in each risk zone
    • Road map and overplotted risk areas necessary to prepare the emergency response
This is the main output of SEVEX. It takes into account the uncertainties of any accidental situation (e.g. fluctuation of wind direction, released quantity, …) through a combination of various "SCENARIO" items. From each of these items, SEVEX will only keep and map the maximising effects. This is necessary with respect to the required enforcement of conservative decisions in the crisis situation.

11. User interface availability back - top

Windows 95 - 98 - 2000 - NT

12. User community back - top

  • Ministry of Environment of the Walloon Region of Belgium
  • Solvay S.A.
  • SEVEX is made for Agencies in charge of civil protection, industrials and consultants

13. Previous applications back - top

SEVEX is used by the Ministry of Environment of the Walloon Region of Belgium in order to produce risk areas necessary to review emergency plan of SEVESO type industries present on its territory.

SEVEX is used in an international training exercise for emergency response called COMPROTEX 99 and organised by NATO, Hungary, Austria, Slovakia. This exercise will consider a catastrophic rupture of a 43T chlorine vessel in the region of Bratislava (Petrzalka) in Slovakia.

14. Documentation status back - top

Level (2) : "Rather good scientific documentation and less complete users manual" (to be improved in the new version in preparation)

15. Validation and evaluation back - top

Level (2) : "Extensive and good model evaluation has been performed, but still uncertainties because major limitations in the measured data".

An extensive evaluation has been performed by ATM-PRO s.p.r.l. in 1997 [3]. It is based on the guidelines of the Model Evaluation Group of the European Commission [4, 5]. It considers the model description, the database description, the scientific assessment, the user oriented assessment, the verification and the validation of SEVEX. Indeed it takes into account the integrated and multi-module structure of SEVEX.

The databases used for the validation of SEVEX are listed in chapter 2 of this evaluation report. These validations concern : leakage flow rate, dense gas, 2-D passive dispersion, UVCE, BLEVE, 3-D meso-meteorological fields and 3-D passive dispersion models.

Many references enable the reader to assess the scientific basis of SEVEX.

16. Frequently Asked Question back - top

Q : is SEVEX able to run in Real Time mode ?
A : No, SEVEX is made to simulate accidents in advance to provide the right answer/order in case of an emergency. To tackle this objective SEVEX takes into account the many uncertainties (source location and intensity, wind direction and speed, …) that can appear from real situation in order to build up realistic accidental scenarios. From these, the emergency teams can organise their work avoiding chaos coming out contradictory or undefined orders.

Q : Is SEVEX difficult to use ?
A : SEVEX has to be used by well-skilled person in order to build up scenarios and implement their calculations into the software. Then, once the SEVEX ATLAS, considering all potential accident and meteorological situations, is produced, anybody will be able to manage an emergency situation. Indeed, from very simple information (substance, night/day time, wind direction and wind speed) one map can be easily selected from the SEVEX Atlas. This map provides information about the substance and the potential risk it induces, about the accident scenario, about the danger levels and the map showing road map and risk zones overplotted. This is transmitted to rescue teams which have prepared the emergency response plan in order to improve time reaction and decision making process.

17. Portability and computer requirements back - top

Memory requirements
Storage device requirements

Operating System
Pentium or higher
64 MB RAM (minimum)
1 GB (minimum)
Screen (resolution : 1280 x 1024 / Colour depth : 256 min)
Printer (colour printer HP Paintjet XL/A3)
Connection Centronix //

18. Availability back - top

A commercial version of SEVEX is available. For commercial information please contact ATM-PRO

19. References back - top

  1. Cartage Th., Major Industrial Hazards : The SEVEX Project Determination of Risk Areas for Emergency Planning, Computational Methods in Applied Sciences ’96, p. 176-183, 1996.
  2. Delvosalle, C.,J. M. Levert, F. Benjelloun, GH. Schayes, B. Moyaux, F. Ronday, E. Everbecq, T. Bourouag, and J. P. Dzisiak, Major industrial hazards : The SEVEX Project - source term and dispersion calculation in complex terrain, 20th International Technical Meeting on Air Pollution Modelling and its Application (Valencia, Nov. 29 - Dec. 3), ed. Gryning and Millan, Plenum, p. 357-365, 1993 .
  3. Dutrieux A. and E. Dubois. "SEVeso EXpert system software evaluation (final report)". Evaluation report produced by ATM-PRO s.p.r.l. under contract with the Walloon Ministry of Environment, 77 pp., 1997.
  4. EC Model Evaluation Group. Model Evaluation Protocol - Version 5, may 1994, EC DGXII, 1994.
  5. Model Evaluation Group : Heavy Gas Dispersion Evaluation Protocol. In : "Model Evaluation Group Seminar : The evaluation of models of heavy gas dispersion", Rauwse Meren (Mol), Belgium, 25 November 1994.
  6. Ronday F., E. Everbecq, T. Bourouag, J.F. Deliège, J.P Dzisiak, C. Delvosalle, J-M Levert, F. Benjelloun, G. Schayes and J. Castel-Branco, Assessment and validation of the SEVEX PROJECT, Int. J. Environment and Pollution, 5, n° 4-6, pp 645-654, 1995.
  7. RW/UCL/ULG/FPMs/SOLVAY, Ils anticipent les accidents majeurs, l’Ecomanager, n° 27, October 1996.
  8. Schayes, G. and J. Smitz, P. Thunis, and L. Lesage, The SEVEX project, an integrated dispersion and contamination calculation for complex terrain and accidental releases. Air Pollution Modelling and its applications, Vol. VIII, Plenum Press, 643-648, 1990.
  9. Van Malder G., Determining Risk areas for emergency planning. Methodology and Tools Developed in the Walloon Region., Loss Prevention and Safety Promotion in the Process Industries, Volume II. Edited by J.J. Mewis, H.J. Pasman and EE. De Rademaeker (Eds) Elsevier Science B.V., 1995.


Produit développé par ATM-PRO sprl & Lakes Environmental Software Inc.