Fireball and BLEVE thermal radiation calculator
A BLEVE produces a short, extremely intense fireball rather than a sustained fire. Because the event lasts only seconds, the harm criterion is a thermal dose rather than a steady radiation level, and the calculation must give diameter, duration and height together with the radiation field.
Open the Fireball / BLEVE moduleWhat this calculator returns
- Fireball diameter and burn duration
- Centre height at lift-off
- Peak radiation intensity versus distance
- Thermal dose and distance to dose-based harm criteria
Required inputs
- Mass of flammable material in the fireball
- Component heat of combustion
- Ambient temperature and relative humidity
- Target height and orientation
Calculation method
Fireball diameter and duration are correlated with the mass of fuel involved using the standard power-law relations.
The fireball is treated as a sphere at its lift-off height, radiating at a surface emissive power derived from the radiative fraction of the combustion energy.
Received radiation uses the spherical view factor and atmospheric transmissivity; the thermal dose integrates intensity over the burn duration.
Governing equations
D = 5.8 M ^ (1/3)Fireball diameter in metres for a fuel mass M in kg.
t = 0.45 M ^ (1/3) (M < 30000 kg)Fireball duration in seconds.
Dose = q ^ (4/3) tThermal dose unit used for short-duration exposure criteria.
Nomenclature
- M
- mass of fuel in the fireball, kg
- D
- fireball diameter, m
- t
- fireball duration, s
- q
- received radiation, kW/m2
- H
- fireball centre height, m, typically 0.75 D
Assumptions and limitations
- The whole flash-atomised inventory participates in the fireball.
- The fireball is spherical, isothermal and at constant emissive power over its duration.
- Blast and fragment effects of the vessel failure are assessed separately.
Reference practice
- Correlations follow the CCPS Guidelines for Consequence Analysis and TNO Yellow Book practice.
Worked example
A 20 tonne propane vessel failing under fire attack, producing a BLEVE fireball.
| Step | Value | Basis |
|---|---|---|
| Fuel mass | 20000 kg | Full inventory assumed to participate |
| Fireball diameter | about 157 m | D = 5.8 M^(1/3) with M^(1/3) = 27.1 |
| Duration | about 12 s | t = 0.45 M^(1/3) |
| Centre height | about 118 m | H = 0.75 D at lift-off |
A 12 second exposure at high intensity is dose-driven: fatality contours are set by q^(4/3) t rather than by a steady kW/m2 threshold, which is why BLEVE contours reach much further than a pool fire of comparable inventory.
Illustrative numbers only — rerun the module with the project basis of design before using any result.
Common questions
What is the difference between a fireball and a BLEVE?
A BLEVE is the vessel failure mechanism — a boiling liquid expanding vapour explosion. The fireball is the combustion event that follows when the released flammable inventory ignites.
Why is a thermal dose used instead of kW/m2?
Because the exposure lasts only seconds. Harm depends on the accumulated dose q^(4/3) t, so a very high intensity for a short time can be less harmful than a moderate intensity sustained for minutes.
Does the whole inventory form the fireball?
Conservative practice assumes it does. If a portion rains out as a pool, that fraction is modelled as a pool fire instead.
Related calculators
- Pool Fire — Pool fire radiation calculator for liquid spill fires
- Jet Fire — Jet fire flame length and radiation calculator
- Vapour Cloud Explosion — Vapour cloud explosion overpressure calculator