Pool fire radiation calculator for liquid spill fires
A pool fire is the burning of a liquid spill with a nearly stationary flame anchored over the pool. The consequence question is almost always the same: how far does the thermal radiation reach at the criteria that matter for people, escape routes and adjacent equipment. The calculation chain runs from the spill and pool geometry, through the burning rate and flame shape, to a solid-flame radiation field.
Open the Pool Fire moduleWhat this calculator returns
- Equilibrium pool diameter for a bunded or unbunded spill
- Mass burning rate per unit pool area and total burn rate
- Flame height and tilt under wind
- Radiation intensity versus distance and distance to each radiation criterion
Required inputs
- Liquid component and release rate or spill inventory
- Bund or pool area, or unconfined spreading
- Wind speed, ambient temperature and relative humidity
- Target height and orientation
Calculation method
The burning rate per unit area is obtained from the heat of combustion and the heat of vaporisation of the liquid, corrected for pool diameter so that small pools burn less efficiently than large ones.
Flame height follows the Thomas correlation from the dimensionless burning rate, with wind tilt applied when the wind speed is significant.
The flame is treated as a solid grey emitter; the received radiation is the surface emissive power multiplied by the view factor between flame and target and by the atmospheric transmissivity.
Governing equations
m'' = 0.001 dHc / ( dHv + Cp ( Tb - Ta ) ) [ 1 - exp( -k b D ) ]Mass burning rate per unit pool area, including the small-pool correction.
H / D = 42 [ m'' / ( rho_a sqrt( g D ) ) ] ^ 0.61Thomas flame height correlation for a still-air pool fire.
q = SEP F tauReceived radiation from the solid-flame model.
Nomenclature
- m''
- mass burning rate per unit area, kg/(m2 s)
- dHc, dHv
- heat of combustion and heat of vaporisation, J/kg
- D, H
- pool diameter and flame height, m
- SEP
- surface emissive power of the flame, kW/m2
- F
- view factor between flame and target, dimensionless
- tau
- atmospheric transmissivity, dimensionless
Assumptions and limitations
- The pool is circular and burns at a steady rate once the equilibrium diameter is reached.
- The flame is an optically thick grey emitter at a uniform surface emissive power.
- Smoke shielding is not credited unless a reduced emissive power is entered.
Reference practice
- Consistent with the pool fire treatment in the CCPS Guidelines for Consequence Analysis and the radiation criteria of API 521.
Worked example
A 10 m diameter bunded condensate pool fire, still air, target at ground level.
| Step | Value | Basis |
|---|---|---|
| Burning rate | about 0.055 kg/(m2 s) | Typical for a light hydrocarbon at a 10 m diameter, where the small-pool correction is nearly saturated |
| Total burn rate | about 4.3 kg/s | m'' multiplied by the pool area of 78.5 m2 |
| Flame height | about 18 m | Thomas correlation, so the flame is roughly 1.8 pool diameters tall |
| Distance to 12.5 kW/m2 | about 20 m from the pool edge | Solid flame model with SEP near 60 kW/m2 and transmissivity near 0.8 |
For a 10 m pool the escalation criterion of 37.5 kW/m2 stays close to the bund, while the 4 kW/m2 personnel criterion reaches several pool diameters — this is what sets escape route and manned building spacing.
Illustrative numbers only — rerun the module with the project basis of design before using any result.
Common questions
What are the pool fire radiation criteria?
37.5 kW/m2 is normally used for equipment damage and escalation, 12.5 kW/m2 for unprotected steel and short exposure, 4 to 5 kW/m2 for personnel escape and 1.6 kW/m2 for extended exposure.
How is the pool diameter found for an unbunded spill?
The pool spreads until the burning rate equals the spill rate; the equilibrium diameter is where the spill rate divided by the burning rate per unit area equals the pool area.
Does wind increase the hazard?
Wind tilts and drags the flame downwind, which increases the received radiation on downwind targets even though the flame height is reduced.
Related calculators
- Jet Fire — Jet fire flame length and radiation calculator
- Flare Radiation — Flare thermal radiation calculator
- Fireball / BLEVE — Fireball and BLEVE thermal radiation calculator