Free Engineering Tool · CCPS method
Fireball Calculator
Estimate the fireball from a BLEVE of propane, butane or another liquefied gas. Enter the fuel mass and the vessel pressure or emissive power, and get the fireball size and duration, the heat flux and thermal dose at a target, and the distances at which bare skin would suffer pain and burns.
- Based on CCPS method
- Free, runs in your browser; your inputs stay on your device
- Screening tool, not reviewed or sealed by a licensed engineer
- Last updated October 2026
Screening tool, not engineering advice. This calculator estimates results with simplified published methods. It has not been reviewed or sealed by a licensed engineer for your project, and DGA does not warrant that its results are accurate, complete or suitable for any use. Check every result independently and have the licensed professional responsible for your project review it before you rely on it. Use is subject to the Terms of Use.
Advanced method. The correlations behind this tool come from research and test data with narrow ranges of validity. Outside those ranges results can be wrong by a wide margin, and they are no substitute for a fire model or an analysis by a qualified fire protection engineer.
Fuel and Fireball
Target and Air
Result
Heat Flux Against Distance
About This Tool
When a vessel of liquefied flammable gas fails in a fire, the released fuel can burn as a rising ball of flame that lasts only seconds but radiates intensely. The calculator follows the correlations collected by the Center for Chemical Process Safety (CCPS). The maximum diameter is D = 5.8 m1/3 (meters, with m in kilograms), the form Roberts derived from test data. The burning time is t = 0.45 m1/3 seconds for releases below 30,000 kg (66,000 lb), where the momentum of the flashing release controls burning, and t = 2.6 m1/6 above it, where buoyancy controls. The center of the fireball is taken at 0.75 D above the ground; it actually rises from about D/2 to well above D during the event, so the height ratio is an input.
The surface emissive power comes from the fraction of the heat of combustion that is radiated: E = fr m ΔHc / (π D2 t), with Roberts’ radiative fraction fr = 0.27 P0.32 (P, the vessel pressure at failure, in MPa). Measured emissive powers for large propane and butane fireballs are about 320 to 370 kW/m2, and 350 kW/m2 is a common fixed value. The heat flux at the target is q = τ E F. The view factor F is the exact value for a sphere seen from a small surface: (r / L)2 cos θ when the whole sphere is in view, with the full partial-view expression when part of it is below the surface’s horizon. The atmospheric transmissivity is τ = 2.02 (Pw X)−0.09 (Pietersen and Huerta), where Pw is the partial pressure of water vapor in pascals and X the path from the fireball surface to the target in meters.
Because the exposure is short, harm to people is judged by thermal dose, q4/3 t, in thermal dose units, (kW/m2)4/3 s. For bare skin, about 80 units causes pain, second-degree burns occur from about 240 to 730 units, and third-degree burns from about 1,000 units, following the human response data reviewed by Hockey and Rew. The calculator turns these doses into the flux that reaches them within the fireball duration and finds the ground distance at which a person facing the fireball would receive each one.
Worked example
A tank releases 20,000 lb (9,072 kg) of propane at a failure pressure of 200 psia (1.38 MPa) on a 77 °F day at 50% relative humidity. The fireball is 5.8 × 9,0721/3 = 121 m (397 ft) across and lasts 0.45 × 9,0721/3 = 9.4 s, centered 91 m (298 ft) up. The radiative fraction is 0.27 × 1.380.32 = 0.30, so the emissive power is 292 kW/m2. A person 600 ft (183 m) away is 204 m from the center, the view factor is (60.5 / 204)2 = 0.088 and the transmissivity 0.67, giving 17.0 kW/m2. Over 9.4 s that is a dose of 411 units, in the second-degree burn range. Second-degree burns extend to about 753 ft (230 m) and pain to about 1,160 ft (353 m).
Assumptions and limits
The fireball is treated as a sphere of full size, at a fixed height and with a constant emissive power for its whole duration, which overstates the dose close in. Using the whole vessel contents as the fireball mass is the conservative choice; part of the liquid may instead rain out and burn as a pool fire. The radiative fraction correlation was fitted to vapor pressures of 0.2 to 1.4 MPa. The dose thresholds apply to bare skin of people who do not move away or find shelter. The tool does not address the blast wave or fragments from the vessel failure, which govern the hazard close to the tank.
When to bring in an engineer
Separation distances and exposure protection for liquefied gas storage depend on the code requirements, the credible release, and how the fireball interacts with buildings and people nearby. DGA runs fire hazard and radiation modeling and provides code consulting for storage and process facilities.
References
- Center for Chemical Process Safety, Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVEs, American Institute of Chemical Engineers, New York, 1994: fireball diameter, duration and height.
- A.F. Roberts, “Thermal Radiation Hazards from Releases of LPG from Pressurised Storage,” Fire Safety Journal, Vol. 4, 1981/82, pp. 197 to 212.
- K. Hasegawa and K. Sato, “Study on the Fireball Following Steam Explosion of n-Pentane,” Second International Symposium on Loss Prevention and Safety Promotion in the Process Industries, Heidelberg, 1977.
- C.M. Pietersen and S.C. Huerta, Analysis of the LPG Incident in San Juan Ixhuatepec, Mexico City, 19 November 1984, TNO Report 84-0222, TNO, Apeldoorn, 1985: atmospheric transmissivity.
- J.R. Howell, A Catalog of Radiation Heat Transfer Configuration Factors, University of Texas at Austin (online catalog): differential planar element to a sphere.
- S.M. Hockey and P.J. Rew, Review of Human Response to Thermal Radiation, HSE Contract Research Report 97/1996, Health and Safety Executive, 1996.
Frequently Asked Questions
How big is a BLEVE fireball?
The maximum diameter is about 5.8 times the cube root of the fuel mass in kilograms, in meters. A release of 1,000 kg (2,200 lb) of propane gives a fireball about 58 m (190 ft) across, and 10,000 kg (22,000 lb) gives about 125 m (410 ft). Fireballs from releases of 1,000 to 30,000 kg last roughly 4.5 to 14 seconds.
What heat flux from a fireball causes burns?
Because a fireball lasts only seconds, the harm depends on the thermal dose, the flux to the four-thirds power times the duration. About 80 thermal dose units causes pain on bare skin, second-degree burns begin near 240 units, and third-degree burns near 1,000. For a 10-second fireball these correspond to roughly 5, 11 and 32 kW/m2.
Does all of the fuel in the tank burn in the fireball?
Not always. Part of the liquid flashes to vapor at once, more is torn into droplets that vaporize in the fire, and some may fall out and burn as a pool fire. A common rule takes the fireball mass as three times the flash fraction, up to the whole contents; assuming the whole contents is the conservative choice.
Why is the heat flux on a roof lower than on a person facing the fireball?
The flux depends on the view factor, which falls with the cosine of the angle between the surface normal and the line to the fireball center. A surface facing the fireball directly receives the most, a vertical wall a little less, and a horizontal roof much less when the fireball is far away and low in the sky.
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Engineering aid only, provided as is and without warranty. Results depend on the inputs and on the simplifying assumptions of the method summarized on each tool page, and DGA has not verified them for your application. They do not replace code-required design, testing or review by the licensed engineer responsible for the project. Use of the tools is subject to the Terms of Use.