Burning rate - Revision history

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2026-11-02T21:32:45Z

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← Older revision		Revision as of 22:32, 2 November 2026
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	* [[Heat release rate per unit area]]		* [[Heat release rate per unit area]]
	* [[Effective heat of combustion]]		* [[Effective heat of combustion]]
	* [[Boilover]]		* Boilover

	== Notes ==		== Notes ==

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2026-11-02T17:12:51Z

Add Intermediate SVG figures with Fire Safety Academy watermark at planned locations; preserve article text

← Older revision		Revision as of 18:12, 2 November 2026
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	The burning rate is therefore governed by how much heat reaches the fuel surface and how much energy the fuel needs to turn into gas. Tewarson describes the mass loss rate as the net [[heat flux]] into the surface divided by the heat of gasification.<ref name="Tewarson-3-98">Tewarson (2002), p. 3-98.</ref> The net heat flux is the sum of the radiative and convective heat flux from the flame and any external heat flux, minus the heat that the hot surface radiates away.<ref name="Tewarson-3-98" /> The heat of gasification is the energy needed to turn a unit mass of the fuel into vapour.<ref name="Babrauskas-3-25" />		The burning rate is therefore governed by how much heat reaches the fuel surface and how much energy the fuel needs to turn into gas. Tewarson describes the mass loss rate as the net [[heat flux]] into the surface divided by the heat of gasification.<ref name="Tewarson-3-98">Tewarson (2002), p. 3-98.</ref> The net heat flux is the sum of the radiative and convective heat flux from the flame and any external heat flux, minus the heat that the hot surface radiates away.<ref name="Tewarson-3-98" /> The heat of gasification is the energy needed to turn a unit mass of the fuel into vapour.<ref name="Babrauskas-3-25" />

			[[File:fse-burning-rate-v1.svg\|thumb\|upright=1.5\|alt=Cross-section of a burning fuel slab with arrows for flame and external heat flux in, re-radiation out and fuel vapour rising into the flame.\|Heat balance at a burning surface: the net heat flux divided by the heat of gasification gives the mass loss rate. Based on Tewarson (2002), p. 3-98.]]

	A worked example in the SFPE Handbook shows the size of the effect. A material with a heat of gasification of 1.8 kJ/g receives a combined flame and external heat flux of 70 kW/m² and loses 10 kW/m² by re-radiation.<ref name="Tewarson-3-100">Tewarson (2002), p. 3-100.</ref> Its mass loss rate is then (70 − 10)/1.8, or about 33 g/(m²·s). Over a burning area of 2 m², this gives about 67 g/s.<ref name="Tewarson-3-101">Tewarson (2002), p. 3-101.</ref> If the incoming heat flux rises, for example because hot smoke radiates down on the fuel, the burning rate rises with it.<ref name="IS-3-5">Iqbal and Salley (2004), p. 3-5.</ref>		A worked example in the SFPE Handbook shows the size of the effect. A material with a heat of gasification of 1.8 kJ/g receives a combined flame and external heat flux of 70 kW/m² and loses 10 kW/m² by re-radiation.<ref name="Tewarson-3-100">Tewarson (2002), p. 3-100.</ref> Its mass loss rate is then (70 − 10)/1.8, or about 33 g/(m²·s). Over a burning area of 2 m², this gives about 67 g/s.<ref name="Tewarson-3-101">Tewarson (2002), p. 3-101.</ref> If the incoming heat flux rises, for example because hot smoke radiates down on the fuel, the burning rate rises with it.<ref name="IS-3-5">Iqbal and Salley (2004), p. 3-5.</ref>
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	Babrauskas distinguishes four burning modes by diameter. Pools below 0.05 m burn in a convective laminar mode and pools of 0.05 to 0.2 m in a convective turbulent mode.<ref name="Babrauskas-3-25">Babrauskas (2002b), p. 3-25.</ref> Between 0.2 and 1.0 m, burning is radiative but the flames are optically thin. Above 1.0 m, the flames are optically thick, and the burning rate per unit area approaches a constant maximum.<ref name="Babrauskas-3-25" /><ref name="GW-2-309" /> Pools smaller than about 0.2 m rarely pose a significant hazard, so most fire hazard calculations concern the radiative regime.<ref name="Babrauskas-3-25" />		Babrauskas distinguishes four burning modes by diameter. Pools below 0.05 m burn in a convective laminar mode and pools of 0.05 to 0.2 m in a convective turbulent mode.<ref name="Babrauskas-3-25">Babrauskas (2002b), p. 3-25.</ref> Between 0.2 and 1.0 m, burning is radiative but the flames are optically thin. Above 1.0 m, the flames are optically thick, and the burning rate per unit area approaches a constant maximum.<ref name="Babrauskas-3-25" /><ref name="GW-2-309" /> Pools smaller than about 0.2 m rarely pose a significant hazard, so most fire hazard calculations concern the radiative regime.<ref name="Babrauskas-3-25" />

			[[File:fse-burning-rate-v2.svg\|thumb\|upright=1.5\|alt=Line chart: burning rate per unit area of four liquid fuels rises with pool diameter and levels off above about 2 m.\|Burning rate per unit area of four liquid fuels as a function of pool diameter, with the burning regimes. Based on Babrauskas (2002b), pp. 3-25 to 3-26.]]

	The following relation is the usual way to turn a tabulated burning rate into a heat release rate. It assumes that the heat of combustion stays roughly constant while the fuel burns.<ref name="Babrauskas-3-1" /> For large pools, the heat release rate follows from the burning rate per unit area, the effective heat of combustion and the area of the pool:<ref name="IS-3-3" /><ref name="Babrauskas-3-25" />		The following relation is the usual way to turn a tabulated burning rate into a heat release rate. It assumes that the heat of combustion stays roughly constant while the fuel burns.<ref name="Babrauskas-3-1" /> For large pools, the heat release rate follows from the burning rate per unit area, the effective heat of combustion and the area of the pool:<ref name="IS-3-3" /><ref name="Babrauskas-3-25" />
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	Tabulated burning rates vary considerably between fuels. Heptane burns at 0.101 kg/(m²·s), kerosene at 0.039 kg/(m²·s) and PMMA at 0.020 kg/(m²·s).<ref name="Babrauskas-3-26" /> Alcohols show little flame radiation and burn slowly. For methanol and ethanol, Babrauskas recommends 0.015 kg/(m²·s) for pools below 0.6 m and 0.029 kg/(m²·s) for pools above 3.0 m.<ref name="Babrauskas-3-25" />		Tabulated burning rates vary considerably between fuels. Heptane burns at 0.101 kg/(m²·s), kerosene at 0.039 kg/(m²·s) and PMMA at 0.020 kg/(m²·s).<ref name="Babrauskas-3-26" /> Alcohols show little flame radiation and burn slowly. For methanol and ethanol, Babrauskas recommends 0.015 kg/(m²·s) for pools below 0.6 m and 0.029 kg/(m²·s) for pools above 3.0 m.<ref name="Babrauskas-3-25" />

			[[File:fse-burning-rate-v3.svg\|thumb\|upright=1.5\|alt=Horizontal bar chart of large-pool burning rates from 0.020 kg/(m²·s) for PMMA to 0.101 kg/(m²·s) for heptane.\|Large-pool burning rates per unit area of common fuels. Based on Babrauskas (2002b), p. 3-26.]]

	Spills differ from deep pools. A thin layer of liquid on a smooth floor, less than 1 mm deep, burns with a much lower heat release rate per unit area. On smooth surfaces, measured values were only about one-fifth of those for deep pools.<ref name="Babrauskas-3-25" /> Tests with unconfined jet fuel spills on concrete confirmed this. For diameters above about 1 m, their burning rates were about one-fifth of the maximum rates of confined pools, because the thin fuel layer loses much heat to the concrete.<ref name="GW-2-311" />		Spills differ from deep pools. A thin layer of liquid on a smooth floor, less than 1 mm deep, burns with a much lower heat release rate per unit area. On smooth surfaces, measured values were only about one-fifth of those for deep pools.<ref name="Babrauskas-3-25" /> Tests with unconfined jet fuel spills on concrete confirmed this. For diameters above about 1 m, their burning rates were about one-fifth of the maximum rates of confined pools, because the thin fuel layer loses much heat to the concrete.<ref name="GW-2-311" />
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	In a fuel-controlled fire, enough oxygen is available, and the fire is governed by the rate at which the fuel releases pyrolysis gases.<ref name="VR-4.8">Van Rossum (2027), §4.8.</ref> In a [[ventilation-controlled fire]], the supply of oxygen through the openings limits the burning. A fully developed fire in a room is usually ventilation-controlled.<ref name="VR-4.8" /> The heat release rate in the room is then limited by the available air. For most fuels, about 3000 kJ of heat is released for each kilogram of air consumed.<ref name="WT-3-174">Walton and Thomas (2002), p. 3-174.</ref>		In a fuel-controlled fire, enough oxygen is available, and the fire is governed by the rate at which the fuel releases pyrolysis gases.<ref name="VR-4.8">Van Rossum (2027), §4.8.</ref> In a [[ventilation-controlled fire]], the supply of oxygen through the openings limits the burning. A fully developed fire in a room is usually ventilation-controlled.<ref name="VR-4.8" /> The heat release rate in the room is then limited by the available air. For most fuels, about 3000 kJ of heat is released for each kilogram of air consumed.<ref name="WT-3-174">Walton and Thomas (2002), p. 3-174.</ref>

			[[File:fse-burning-rate-v4.svg\|thumb\|upright=1.5\|alt=Two room cross-sections: left, a small fire with ample air; right, a room full of fire with air entering low in the door and flames leaving at the top.\|Fuel-controlled fire (left) and ventilation-controlled fire (right): in the second case the air flow through the opening limits the burning. Based on Van Rossum (2027), §4.8, and Walton and Thomas (2002), pp. 3-173 to 3-174.]]

	For ventilation-controlled room fires, the SFPE Handbook gives an empirical rule from early wood fire tests by Kawagoe. Wood in rooms with small windows burned at about 0.09 kg/s for each unit of the ventilation factor, the opening area times the square root of the opening height.<ref name="WT-3-174" /> For a door of 0.8 m by 2.0 m, the ventilation factor is 1.6 × √2.0, or about 2.26 m<sup>5/2</sup>. The rule then gives a burning rate of about 0.20 kg/s. With an effective heat of combustion of 10.75 MJ/kg for wood in fully developed fires, this corresponds to about 2.2 MW.<ref name="WT-3-174" />		For ventilation-controlled room fires, the SFPE Handbook gives an empirical rule from early wood fire tests by Kawagoe. Wood in rooms with small windows burned at about 0.09 kg/s for each unit of the ventilation factor, the opening area times the square root of the opening height.<ref name="WT-3-174" /> For a door of 0.8 m by 2.0 m, the ventilation factor is 1.6 × √2.0, or about 2.26 m<sup>5/2</sup>. The rule then gives a burning rate of about 0.20 kg/s. With an effective heat of combustion of 10.75 MJ/kg for wood in fully developed fires, this corresponds to about 2.2 MW.<ref name="WT-3-174" />

Daan: New FSE wiki article: Burning rate (written by Claude Opus 5.5)

2026-11-01T22:47:48Z

New FSE wiki article: Burning rate (written by Claude Opus 5.5)

New page

The '''burning rate''' of a fire is the rate at which its fuel is consumed. It is usually expressed as the mass of fuel lost per second (kg/s), or per second and square metre of burning surface (kg/(m²·s)).<ref name="IS-3-3">Iqbal and Salley (2004), p. 3-3.</ref> It is also known as the mass loss rate and is measured by weighing the fuel as it burns.<ref name="IS-3-3" /> Multiplied by the heat of combustion, the burning rate gives the [[heat release rate]], the quantity that describes how large a fire is.<ref name="Babrauskas-3-1">Babrauskas (2002b), p. 3-1.</ref>

The term is used loosely. In the SFPE Handbook, Babrauskas notes that "burning rate" may mean either the heat release rate or the mass loss rate. He recommends reserving it for qualitative descriptions and using the more precise terms in calculations.<ref name="Babrauskas-3-1" /> Some fire models even specify a "burning rate" in kW/m².<ref name="McGrattan-2005-36">McGrattan et al. (2005), p. 36.</ref>

The burning rate depends on the fuel and its form, on the heat flux that reaches the fuel surface and on the supply of air.<ref name="IS-3-7">Iqbal and Salley (2004), p. 3-7.</ref><ref name="WT-3-173">Walton and Thomas (2002), p. 3-173.</ref> Typical values for large pools of hydrocarbon liquids are about 0.02 to 0.1 kg/(m²·s).<ref name="Babrauskas-3-26">Babrauskas (2002b), p. 3-26.</ref> Engineers use the burning rate to estimate the heat release rate of a fire and how long a given amount of fuel can burn.<ref name="IS-3-3" /><ref name="IS-3-8">Iqbal and Salley (2004), p. 3-8.</ref>

== Definitions and related quantities ==
NUREG-1805 is a set of fire dynamics tools for nuclear power plants in the United States. Its glossary defines the mass loss rate as the mass of fuel turned into vapour, but not necessarily burned, per unit time.<ref name="IS-F-41">Iqbal and Salley (2004), p. F-41.</ref> The burning rate per unit area of fuel surface is called the mass burning flux.<ref name="IS-F-41" /> The difference between evaporated and burned fuel matters in a fire with too little air. In such a fire, part of the fuel vapour leaves the room unburned.<ref name="WT-3-173" />

For liquid pools, the burning rate is also expressed as a regression rate. This is the speed at which the liquid surface descends as the fuel burns, often given in mm/min.<ref name="GW-2-308">Gottuk and White (2002), p. 2-308.</ref> The regression rate equals the mass burning rate per unit area divided by the density of the liquid.<ref name="IS-3-8" /> For confined pools larger than 1 m in diameter, experiments by Blinov and Khudiakov found a regression rate of roughly 4 mm/min for all the fuels they tested.<ref name="GW-2-309">Gottuk and White (2002), p. 2-309.</ref>

The burning rate links three quantities that are used throughout fire safety engineering. The heat release rate is the energy released per second. ''Introduction to Fire Safety Engineering'' gives about 2.5 MW for an average sofa and a peak of about 8.5 MW for a car.<ref name="VR-4.5">Van Rossum (2027), §4.5.</ref> The [[heat of combustion]] is the energy per kilogram of fuel, for example 42 MJ/kg for diesel oil and 18 MJ/kg for beech wood.<ref name="VR-4.4">Van Rossum (2027), §4.4.</ref> The burning rate connects the two: it tells how many kilograms of fuel are consumed each second.

== Why fuels burn at a certain rate ==
A solid or liquid does not burn directly. It must first be turned into gas, by evaporation for most liquids or by [[pyrolysis]] for solids such as wood and plastics.<ref name="VR-3.1">Van Rossum (2027), §3.1.</ref> Pyrolysis is the decomposition of a material by heating into smaller molecules, which form flammable pyrolysis gases.<ref name="VR-3.1" /> The fire heats the fuel, and the gases released by the fuel in turn feed the fire. When this exchange stays in balance, the fire sustains itself.<ref name="VR-3.1" />

The burning rate is therefore governed by how much heat reaches the fuel surface and how much energy the fuel needs to turn into gas. Tewarson describes the mass loss rate as the net [[heat flux]] into the surface divided by the heat of gasification.<ref name="Tewarson-3-98">Tewarson (2002), p. 3-98.</ref> The net heat flux is the sum of the radiative and convective heat flux from the flame and any external heat flux, minus the heat that the hot surface radiates away.<ref name="Tewarson-3-98" /> The heat of gasification is the energy needed to turn a unit mass of the fuel into vapour.<ref name="Babrauskas-3-25" />

A worked example in the SFPE Handbook shows the size of the effect. A material with a heat of gasification of 1.8 kJ/g receives a combined flame and external heat flux of 70 kW/m² and loses 10 kW/m² by re-radiation.<ref name="Tewarson-3-100">Tewarson (2002), p. 3-100.</ref> Its mass loss rate is then (70 − 10)/1.8, or about 33 g/(m²·s). Over a burning area of 2 m², this gives about 67 g/s.<ref name="Tewarson-3-101">Tewarson (2002), p. 3-101.</ref> If the incoming heat flux rises, for example because hot smoke radiates down on the fuel, the burning rate rises with it.<ref name="IS-3-5">Iqbal and Salley (2004), p. 3-5.</ref>

The form of the fuel matters as well. The burning rate depends both on the chemistry of the fuel, such as cellulosic or petroleum-based, and on its form.<ref name="IS-3-7" /> An important form factor is the ratio of the surface area available to burn to the total mass of the material.<ref name="IS-3-7" /> For wood cribs, which are regular stacks of sticks, the burning rate is governed by one of three limits. These are the free burning of the stick surfaces when the sticks are widely spaced, the flow of air through a tightly packed crib, or the oxygen supply of the room.<ref name="Babrauskas-3-14">Babrauskas (2002b), p. 3-14.</ref>

== Pool fires ==
A liquid pool is possibly the simplest arrangement of fuel, and [[pool fire]]s have been studied extensively for decades.<ref name="Babrauskas-3-24">Babrauskas (2002b), p. 3-24.</ref> NUREG-1805 defines a pool fire as a fire on a horizontal, upward-facing fuel surface. This is usually a liquid, but flat slabs of plastics such as PMMA that decompose like liquids also qualify.<ref name="IS-3-5" /> The burning rate per unit area depends on the pool diameter. Small pools are heated mainly by convection and by conduction from the walls of the pan, large pools mainly by radiation from their own flames.<ref name="GW-2-309" />

Babrauskas distinguishes four burning modes by diameter. Pools below 0.05 m burn in a convective laminar mode and pools of 0.05 to 0.2 m in a convective turbulent mode.<ref name="Babrauskas-3-25">Babrauskas (2002b), p. 3-25.</ref> Between 0.2 and 1.0 m, burning is radiative but the flames are optically thin. Above 1.0 m, the flames are optically thick, and the burning rate per unit area approaches a constant maximum.<ref name="Babrauskas-3-25" /><ref name="GW-2-309" /> Pools smaller than about 0.2 m rarely pose a significant hazard, so most fire hazard calculations concern the radiative regime.<ref name="Babrauskas-3-25" />

The following relation is the usual way to turn a tabulated burning rate into a heat release rate. It assumes that the heat of combustion stays roughly constant while the fuel burns.<ref name="Babrauskas-3-1" /> For large pools, the heat release rate follows from the burning rate per unit area, the effective heat of combustion and the area of the pool:<ref name="IS-3-3" /><ref name="Babrauskas-3-25" />
<math display="block">\dot{Q} = \dot{m}'' \cdot \Delta H_{c,\mathrm{eff}} \cdot A_f</math>

{| class="wikitable"
! Symbol !! Description !! Unit
|-
| <math>\dot{Q}</math> || heat release rate of the fire || kW
|-
| <math>\dot{m}''</math> || burning rate (mass loss rate) per unit area of a large pool || kg/(m²·s)
|-
| <math>\Delta H_{c,\mathrm{eff}}</math> || effective heat of combustion of the fuel || kJ/kg
|-
| <math>A_f</math> || horizontal burning area of the fuel || m²
|}

The relation holds for free-burning pools in the open, in still air, in a pan or tank without a high lip.<ref name="GW-2-311">Gottuk and White (2002), p. 2-311.</ref> It assumes that the pool is at least several millimetres deep.<ref name="Babrauskas-3-25" /> For pools of a few metres or less, the burning rate per unit area is lower than the large-pool value. NUREG-1805 and the SFPE Handbook therefore multiply by a correction factor that depends on the diameter and on an empirical constant for each fuel.<ref name="IS-3-3" /><ref name="Babrauskas-3-25" /> The effective heat of combustion is slightly lower than the value from an oxygen bomb calorimeter, but for most liquids the difference is small.<ref name="Babrauskas-3-25" />

As a worked example, consider a petrol (gasoline) spill that forms a pool of 3 m diameter in a diked area. The SFPE Handbook gives a large-pool burning rate of 0.055 kg/(m²·s), a heat of combustion of 43.7 MJ/kg and a density of 740 kg/m³ for gasoline.<ref name="Babrauskas-3-26" /> The pool area is 7.07 m², so the heat release rate is 0.055 × 43,700 × 7.07, or about 17 MW. With the empirical constant of 2.1 m<sup>−1</sup> for gasoline, the diameter correction changes this result by less than 1% for a pool of this size.<ref name="Babrauskas-3-26" /> The fire is about twice as large as the peak of a burning car.<ref name="VR-4.5" />

The same data give the duration of the fire. The regression rate is 0.055/740 m/s, or about 4.5 mm/min.<ref name="IS-3-8" /> If 100 litres of petrol spread over the 3 m pool, the layer is about 14 mm deep, and the pool burns out in roughly 3 minutes. NUREG-1805 notes the general rule behind this result. For a given amount of fuel, a spill with a large surface burns with a high heat release rate for a short time, while a small spill burns longer at a lower rate.<ref name="IS-3-5" />

Tabulated burning rates vary considerably between fuels. Heptane burns at 0.101 kg/(m²·s), kerosene at 0.039 kg/(m²·s) and PMMA at 0.020 kg/(m²·s).<ref name="Babrauskas-3-26" /> Alcohols show little flame radiation and burn slowly. For methanol and ethanol, Babrauskas recommends 0.015 kg/(m²·s) for pools below 0.6 m and 0.029 kg/(m²·s) for pools above 3.0 m.<ref name="Babrauskas-3-25" />

Spills differ from deep pools. A thin layer of liquid on a smooth floor, less than 1 mm deep, burns with a much lower heat release rate per unit area. On smooth surfaces, measured values were only about one-fifth of those for deep pools.<ref name="Babrauskas-3-25" /> Tests with unconfined jet fuel spills on concrete confirmed this. For diameters above about 1 m, their burning rates were about one-fifth of the maximum rates of confined pools, because the thin fuel layer loses much heat to the concrete.<ref name="GW-2-311" />

== Burning rate in a compartment ==
Free-burning data apply to fires that are not influenced by the room around them, like a fire outdoors on a calm day.<ref name="WT-3-173" /> Inside a room, two effects change the burning rate. Hot smoke and heated walls and ceiling radiate back to the fuel surface and increase the burning rate. At the same time, small openings may limit the oxygen supply and reduce the heat release rate.<ref name="IS-3-5" /> Babrauskas suggests that free-burning pool data become unreliable once the fire would raise the room temperature by more than about 100 °C. Above that, radiative feedback becomes important and no simple formula is available.<ref name="Babrauskas-3-26" />

In a fuel-controlled fire, enough oxygen is available, and the fire is governed by the rate at which the fuel releases pyrolysis gases.<ref name="VR-4.8">Van Rossum (2027), §4.8.</ref> In a [[ventilation-controlled fire]], the supply of oxygen through the openings limits the burning. A fully developed fire in a room is usually ventilation-controlled.<ref name="VR-4.8" /> The heat release rate in the room is then limited by the available air. For most fuels, about 3000 kJ of heat is released for each kilogram of air consumed.<ref name="WT-3-174">Walton and Thomas (2002), p. 3-174.</ref>

For ventilation-controlled room fires, the SFPE Handbook gives an empirical rule from early wood fire tests by Kawagoe. Wood in rooms with small windows burned at about 0.09 kg/s for each unit of the ventilation factor, the opening area times the square root of the opening height.<ref name="WT-3-174" /> For a door of 0.8 m by 2.0 m, the ventilation factor is 1.6 × √2.0, or about 2.26 m<sup>5/2</sup>. The rule then gives a burning rate of about 0.20 kg/s. With an effective heat of combustion of 10.75 MJ/kg for wood in fully developed fires, this corresponds to about 2.2 MW.<ref name="WT-3-174" />

A practical consequence is that more fuel does not always mean a faster fire. In an example in the SFPE Handbook, doubling the fire load of a room does not double the burning rate, because the window area restricts the ventilation.<ref name="WT-3-175">Walton and Thomas (2002), p. 3-175.</ref> The extra fuel then mainly lengthens the fire, since the total heat released still grows with the fire load.<ref name="WT-3-175" /> Some of the unburned pyrolysis gases may also leave the room and burn outside it.<ref name="WT-3-173" />

== Uses and limits ==
The burning rate is mainly used to turn measured or tabulated fuel data into a heat release rate for design and hazard analysis. NUREG-1805 uses it to estimate the heat release rate of pool fires from oil leaks, transformer spills and transient liquids in nuclear power plants.<ref name="IS-3-6">Iqbal and Salley (2004), p. 3-6.</ref> It also uses it to estimate how long a given amount of fuel can burn.<ref name="IS-3-8" /> In fire models, the burning rate can either be prescribed or be calculated from the heat flux that reaches the fuel. In the computer simulations of the World Trade Center fires, NIST prescribed a burning rate of 450 kW/m² for the furnishings in the workstations.<ref name="McGrattan-2005-36" /> For damaged furnishings, the value was lowered to 300 kW/m².<ref name="McGrattan-2005-36" />

The simple relation between burning rate and heat release rate has limits. It assumes a constant heat of combustion, which is not always true. For a 17 mm thick sample of western red cedar, the effective heat of combustion rose from about 12 MJ/kg early in the test to about 30 MJ/kg during the charring stage.<ref name="Babrauskas-3-1" /><ref name="Babrauskas-3-2">Babrauskas (2002b), p. 3-2.</ref> The same mass loss rate can therefore correspond to very different heat release rates. When the effective heat of combustion is not constant, experimenters therefore normally measure the heat release rate directly instead of converting a mass loss rate.<ref name="Babrauskas-3-1" />

The ventilation rule also has limits. It was derived mainly from experiments in rooms the size of single offices or rooms in houses.<ref name="McGrattan-2005-110">McGrattan et al. (2005), p. 110.</ref> In experiments with long and wide compartments, the fires moved towards the openings, stayed there while local fuel lasted and then travelled through the floor.<ref name="TB-2000">Thomas and Bennetts (2000), as cited in McGrattan et al. (2005), p. 110.</ref> In such spaces the simple dependence on the ventilation factor does not predict the burning rate well.<ref name="McGrattan-2005-110" /> Most data are also for wood, often in the form of cribs, and other fuels may pyrolyse at different rates.<ref name="WT-3-174" />

== See also ==
* [[Heat release rate per unit area]]
* [[Effective heat of combustion]]
* [[Boilover]]

== Notes ==
<references />

== References ==
* Babrauskas, V. (2002b). Heat release rates. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-1–3-37). National Fire Protection Association; Society of Fire Protection Engineers.
* Gottuk, D. T., & White, D. A. (2002). Liquid fuel fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 2-297–2-316). National Fire Protection Association; Society of Fire Protection Engineers.
* Iqbal, N., & Salley, M. H. (2004). ''Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program'' (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
* McGrattan, K. B., Bouldin, C., & Forney, G. P. (2005). ''Computer simulation of the fires in the World Trade Center towers'' (NIST NCSTAR 1-5F). National Institute of Standards and Technology.
* Tewarson, A. (2002). Generation of heat and chemical compounds in fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-82–3-161). National Fire Protection Association; Society of Fire Protection Engineers.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.
* Walton, W. D., & Thomas, P. H. (2002). Estimating temperatures in compartment fires. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), ''SFPE handbook of fire protection engineering'' (3rd ed., pp. 3-171–3-188). National Fire Protection Association; Society of Fire Protection Engineers.

[[Category:Fire Dynamics]]