The method
A vapour cloud explosion (VCE) occurs when a flammable cloud, mixed with air within its flammability limits, ignites in a congested or confined area: the flame speed accelerates and generates an overpressure wave. Two common approaches estimate it: the Baker-Strehlow-Tang method, which accounts for fuel reactivity and congestion, and TNT equivalence, simpler but whose explosion yield remains the main uncertainty.
A BLEVE (boiling liquid expanding vapour explosion) occurs when a tank containing a pressurised liquid, heated for example by an external fire, ruptures suddenly: the instant flash of the superheated liquid produces both an overpressure wave and, if the contents are flammable, a fireball radiating intense heat flux over a large radius.
Fires (pool, jet, torch) radiate a heat flux that decreases with distance and the viewing angle of the flame; their models combine released thermal power, flame geometry and a radiated fraction. In all three cases, the final result is a distance for each chosen effect threshold (overpressure in mbar, heat flux in kW/m² or thermal dose), used in safety reports.
When to use it
- Safety report for facilities storing pressurised flammable liquids or flammable gases (major-hazard, chemical sites).
- Determining effect distances for land-use planning around a site.
- Comparing scenarios to prioritise prevention measures (reducing inventory, separation distance, thermal protection).
Watch out for
- A VCE’s explosion yield (often 1 to 10% of theoretical energy) dominates the uncertainty of a TNT-equivalent calculation: never adjust it to reach an expected result.
- A BLEVE can occur even without a flammable cloud if the liquid is simply superheated; do not confuse BLEVE with a fireball, which is only one possible consequence.
- Thermal effect distances depend strongly on orientation relative to the flame, not only on distance.
- As with dispersion, a calculation tool not validated against a reference code remains a teaching aid, not a real decision tool.
Steps
- Characterise the scenario: mass and nature of the fuel involved, confinement or congestion conditions for a VCE, tank geometry for a BLEVE.
- Choose the suitable method (Baker-Strehlow-Tang, TNT equivalence, heat flux model) based on available data.
- Compute overpressure or heat flux as a function of distance.
- Compare with the chosen effect thresholds (for example 20/50/140/200 mbar for overpressure, or regulatory heat flux thresholds).
- Draw the corresponding distances or footprints.
Explosion, fire and BLEVE software
List from the Aurorisk catalogue, links checked on 2026-09-26. Confirmed free access is listed first; unknown information is labelled.
| Tool | Source · licence · access | Scope | Description |
|---|---|---|---|
| ALOHA (EPA/NOAA) ↗ | Public bodyFree | United States | Dispersion, BLEVE, fires and explosions for emergency response; a long-standing reference in the field, used with CAMEO/MARPLOT. |
| Aurorisk — explosions (VCE, BLEVE, TNT) | Free for teaching | France | Teaching tool: vapour cloud (Baker-Strehlow-Tang), BLEVE and TNT equivalence. Compared with ALOHA on reference cases, but not validated for real studies. |
| FLUMilog (INERIS) ↗ | Public bodyFree | France | Heat flux from a warehouse or storage cell fire. |
| PRIMARISK (INERIS) ↗ | Public bodyFree with registration | France | BLEVE, pool fire, boilover, multi-energy; registration required. |
| Phast (DNV) ↗ | Commercial publisher | International | Fire and explosion models. |
Standards and references
- TNO — Yellow Book (CPR 14E) et Purple Book (CPR 18E)
- Baker Q. et al. — Baker-Strehlow-Tang (CCPS)
- INERIS — Ω (études de dangers)