Smoke - Revision history

Thomas: Improve Smoke: sourced explanations, calculations and internal links (Codex)

2026-11-02T17:58:42Z

Improve Smoke: sourced explanations, calculations and internal links (Codex)

← Older revision		Revision as of 18:58, 2 November 2026
Line 22:		Line 22:
	[[Soot yield]] expresses the mass of soot produced per mass of fuel burned. It depends on fuel and combustion conditions, with more complete combustion generally producing less soot. Plastics tend to produce more than wood in Van Rossum's examples, while ethanol produces so little that the smoke can be difficult to see.<ref name="VR-6.2" />		[[Soot yield]] expresses the mass of soot produced per mass of fuel burned. It depends on fuel and combustion conditions, with more complete combustion generally producing less soot. Plastics tend to produce more than wood in Van Rossum's examples, while ethanol produces so little that the smoke can be difficult to see.<ref name="VR-6.2" />

	~~Pre~~-flashover example ~~values include 1~~.5% for wood, 23% for polyurethane, 14% for PVC~~, 16% for polystyrene~~ and 19.5% for ~~expanded~~ polystyrene. ~~These~~ values ~~apply to oxygen excess in~~ the cited ~~source~~ and ~~should not be used as~~ universal material ~~constants. Ventilation-limited and suppressed fires can have different yields~~.<ref name="VR-6.2" />		Van Rossum summarises pre-flashover example soot yields of 0.015 kg/kg for wood, 0.23 kg/kg for polyurethane, 0.14 kg/kg for PVC and 0.16 kg/kg for polystyrene. The values describe the cited material and combustion conditions, including available oxygen. They are secondary data from the compilation he reports, rather than universal constants for those material names.<ref name="VR-yield-secondary">Van Rossum (2027), §6.2, summarising the compilation in Robbins and Wade (2008).</ref>

	Suppressed or smouldering combustion can have a higher yield per kilogram while burning less fuel overall. Total soot production therefore depends on both yield and mass consumed. Comparing materials only by percentage can misstate the actual smoke source strength.<ref name="VR-6.2" />		Suppressed or smouldering combustion can have a higher yield per kilogram while burning less fuel overall. Total soot production therefore depends on both yield and mass consumed. Comparing materials only by percentage can misstate the actual smoke source strength.<ref name="VR-6.2" />
Line 32:		Line 32:
	Particles reduce the luminous flux reaching the eye from an object and scatter background light into that line of sight. Both effects reduce contrast. Additional lighting can therefore fail to improve visibility when scattering overwhelms the contrast needed for recognition.<ref name="Jin-2-43" /><ref name="VR-6.5" />		Particles reduce the luminous flux reaching the eye from an object and scatter background light into that line of sight. Both effects reduce contrast. Additional lighting can therefore fail to improve visibility when scattering overwhelms the contrast needed for recognition.<ref name="Jin-2-43" /><ref name="VR-6.5" />

	[[Optical density]] expresses ~~light~~ attenuation ~~per metre and is related to particle concentration and~~ a ~~mass~~-extinction coefficient. ~~Van Rossum gives a generic average of 3,300 m²/kg for smoke from burning building~~ and ~~contents materials. It is a modelling average rather than a universal property of every smoke aerosol~~.<ref name="VR-~~6.4~~">~~Van Rossum~~ (~~2027~~), §6.4.</ref>		[[Optical density]] expresses attenuation using a base-10 logarithm. For attenuation per unit path length, it differs numerically from the extinction coefficient, which uses a natural logarithm. Both describe the same transmission when their respective exponential expressions and units are used consistently.<ref name="Mulholland-2-263">Mulholland (2002), p. 2-263.</ref>

	For approximately uniform smoke, Van Rossum gives practical visibility estimates of one divided by optical density for non-luminous objects and 2.5 divided by optical density for luminous objects. He cautions that these are rough rules. Different optical densities along the actual line of sight require integration and make visibility direction-dependent.<ref name="VR-6.5" />		For approximately uniform smoke, Van Rossum gives practical visibility estimates of one divided by optical density for non-luminous objects and 2.5 divided by optical density for luminous objects. He cautions that these are rough rules. Different optical densities along the actual line of sight require integration and make visibility direction-dependent.<ref name="VR-6.5" />

	Jin's experiments similarly find an approximately constant product of visibility and extinction coefficient for signs over selected ranges. The product depends on sign type, reflectance and illumination, and black smoke can give somewhat better visibility than white smoke at the same extinction coefficient. This reinforces that optical density alone does not define perception.<ref name="Jin-2-43" />		Jin's experiments similarly find an approximately constant product of visibility and extinction coefficient for signs over selected ranges. The product depends on sign type, reflectance and illumination, and black smoke can give somewhat better visibility than white smoke at the same extinction coefficient. This reinforces that optical density alone does not define perception.<ref name="Jin-2-43" />

			=== Keeping optical conventions consistent ===

			For a uniform smoke path, transmission can be written using either a natural exponential or a power of ten. Mulholland's definitions give the following conversion. The path length is part of the attenuation calculation; the coefficients themselves are expressed per metre.<ref name="Mulholland-2-263" />
			<math display="block">\frac{I}{I_0}=e^{-KL}=10^{-DL},\qquad K=\ln(10)D\approx2.303D</math>

			{\| class="wikitable"
			! Symbol !! Description !! Unit
			\|-
			\| <math>I/I_0</math> \|\| Transmitted intensity divided by incident intensity \|\| dimensionless
			\|-
			\| <math>L</math> \|\| Optical path length \|\| m
			\|-
			\| <math>K</math> \|\| Natural-logarithm extinction coefficient \|\| m⁻¹
			\|-
			\| <math>D</math> \|\| Decimal optical density per unit length \|\| m⁻¹
			\|}

			Van Rossum's simplified calculation uses D = 3,300C<sub>s</sub>, where C<sub>s</sub> is soot concentration in kg/m³ and the coefficient is in m²/kg. His approximate visibility rules are 1/D for non-luminous objects and 2.5/D for luminous objects. Substituting K for D in these rules would introduce a factor-of-2.303 error.<ref name="VR-6.4">Van Rossum (2027), §6.4.</ref><ref name="VR-6.5" /><ref name="Mulholland-2-263" />

			The shop example assumes 1 MW for 120 s, a heat of combustion of 20 MJ/kg and a soot yield of 0.1 kg/kg. This releases 120 MJ, consumes 6 kg of fuel and produces 0.6 kg of soot. Uniform distribution in the stated 450 m³ layer gives C<sub>s</sub> = 0.00133 kg/m³.<ref name="VR-6.5" />

			The resulting D is 4.4 m⁻¹, equivalent to K = 10.1 m⁻¹. The simple visibility estimates are approximately 0.23 m for non-luminous objects and 0.57 m for luminous objects. These very short distances follow the assumed homogeneous layer and coefficient; they are not measurements of the shop.<ref name="VR-6.5" /><ref name="Mulholland-2-263" />

			Real sightlines can cross regions of different concentration, and object illumination and contrast change detection. The example therefore explains the calculation chain from burning fuel to optical attenuation. It does not replace a visibility assessment that represents the actual smoke distribution, observer and target.<ref name="VR-6.5" /><ref name="Jin-2-42">Jin (2002), pp. 2-42–2-43.</ref>

	== Toxicity and inhalation ==		== Toxicity and inhalation ==
Line 88:		Line 113:
	Dilution does not eliminate the source. It reduces concentration while increasing total smoke volume, so the same or greater mass of toxic products can reach more people. The receiver's concentration and exposure time must be assessed.<ref name="VR-5.3" /><ref name="Purser-2-88" />		Dilution does not eliminate the source. It reduces concentration while increasing total smoke volume, so the same or greater mass of toxic products can reach more people. The receiver's concentration and exposure time must be assessed.<ref name="VR-5.3" /><ref name="Purser-2-88" />

	~~Finally,~~ smoke is not only a marker of fire. Unburnt components can ignite, and hot smoke can spread fire by radiation and convection. Its role includes fuel transport and heat transfer as well as toxicity and obscuration.<ref name="VR-6.1" /><ref name="VR-4.10" />		smoke is not only a marker of fire. Unburnt components can ignite, and hot smoke can spread fire by radiation and convection. Its role includes fuel transport and heat transfer as well as toxicity and obscuration.<ref name="VR-6.1" /><ref name="VR-4.10" />

	The smoke source should be characterised before its transport is calculated. Fuel, combustion mode, mass-loss rate, soot yield and toxic-species yield provide different parts of that description. Missing one can lead to a smoke volume estimate that cannot support optical or toxic assessment.<ref name="Mulholland-2-259" /><ref name="IFEG-2.4-11" />		The smoke source should be characterised before its transport is calculated. Fuel, combustion mode, mass-loss rate, soot yield and toxic-species yield provide different parts of that description. Missing one can lead to a smoke volume estimate that cannot support optical or toxic assessment.<ref name="Mulholland-2-259" /><ref name="IFEG-2.4-11" />
Line 95:		Line 120:

	A receiver-focused analysis follows the actual sightline and breathing location. Optical density can vary along the route, and particle deposition can change composition before the gas arrives. These local conditions are more useful for exposure assessment than an unqualified building-average smoke density.<ref name="VR-6.5" /><ref name="Mulholland-2-259" />		A receiver-focused analysis follows the actual sightline and breathing location. Optical density can vary along the route, and particle deposition can change composition before the gas arrives. These local conditions are more useful for exposure assessment than an unqualified building-average smoke density.<ref name="VR-6.5" /><ref name="Mulholland-2-259" />

	Test conditions should remain attached to yield and visibility data. Specimen orientation, oxygen concentration, external heat flux and smoke-collection method can all affect results. Comparing values without those conditions can create false agreement or disagreement between materials.<ref name="Mulholland-2-259" /><ref name="Jin-2-43" />

	For control-system review, nominal airflow should be converted into an actual smoke balance. Make-up air, leakage, plug holing and pressure differences can alter the effective path. The result should be checked at occupied locations and during the period when the system is expected to operate.<ref name="VR-6.8" /><ref name="IFEG-2.5-7" />		For control-system review, nominal airflow should be converted into an actual smoke balance. Make-up air, leakage, plug holing and pressure differences can alter the effective path. The result should be checked at occupied locations and during the period when the system is expected to operate.<ref name="VR-6.8" /><ref name="IFEG-2.5-7" />
Line 107:		Line 130:

	The smoke's thermal role should also remain in the energy balance. Hot gases and particles emit radiation, while convection transports energy to boundaries and adjacent rooms. These pathways can expose people and fuel even where the visible plume has become diluted.<ref name="Tien-1-73">Tien, Lee, and Stretton (2002), p. 1-73.</ref><ref name="VR-5.3" />		The smoke's thermal role should also remain in the energy balance. Hot gases and particles emit radiation, while convection transports energy to boundaries and adjacent rooms. These pathways can expose people and fuel even where the visible plume has become diluted.<ref name="Tien-1-73">Tien, Lee, and Stretton (2002), p. 1-73.</ref><ref name="VR-5.3" />

	Where source or transport data are weak, alternative scenarios should make the uncertainty visible. Changing yield, ventilation, layer volume and deposition can reverse the predicted visibility or dose. A range of outcomes is more informative than a precise but unsupported smoke condition.<ref name="Mulholland-2-259" /><ref name="VR-1.7">Van Rossum (2027), §1.7.</ref>

	The definition used in a report should also be stated. Aerosol-only and broader smoke definitions answer different questions about particles and the complete smoke volume. Declaring that scope prevents soot, gas composition and entrained air from being omitted by accident.<ref name="Mulholland-2-258" /><ref name="VR-6.1" />

	== See also ==		== See also ==

	* [[~~Optical density~~]]		* [[Smoke stratification]]
	* [[~~Soot yield~~]]		* [[Smoke detector]]
	* [[~~Visibility in smoke~~]]		* [[Tenability criteria]]
			* [[Smoke filling]]

	== Notes ==		== Notes ==
Line 131:		Line 151:
	* Ohlemiller, T. J. (2002). Smoldering combustion. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.		* Ohlemiller, T. J. (2002). Smoldering combustion. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
	* Purser, D. A. (2002). Toxicity assessment of combustion products. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.		* Purser, D. A. (2002). Toxicity assessment of combustion products. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
			* Tien, C. L., Lee, K. Y., & Stretton, A. J. (2002). Radiation heat transfer. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
	* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.		* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

	[[Category:Smoke, Toxicity & Tenability]]		[[Category:Smoke, Toxicity & Tenability]]

Sanne: Add diagrams fse-smoke-v1.svg, fse-smoke-v2.svg, fse-smoke-v3.svg (level-1 visual plan)

2026-11-02T07:02:05Z

Add diagrams fse-smoke-v1.svg, fse-smoke-v2.svg, fse-smoke-v3.svg (level-1 visual plan)

← Older revision		Revision as of 08:02, 2 November 2026
Line 14:		Line 14:

	White smoke commonly contains fine droplets and light aerosols, including condensed water or pyrolysis products, while water vapour itself is invisible. Black smoke usually contains more soot. These are tendencies in the cited descriptions, not a reliable classification of every fire.<ref name="VR-6.1" /><ref name="Mulholland-2-258" />		White smoke commonly contains fine droplets and light aerosols, including condensed water or pyrolysis products, while water vapour itself is invisible. Black smoke usually contains more soot. These are tendencies in the cited descriptions, not a reliable classification of every fire.<ref name="VR-6.1" /><ref name="Mulholland-2-258" />
			[[File:fse-smoke-v1.svg\|thumb\|upright=1.5\|alt=Smoke cloud containing soot, droplets, gases and entrained air with invisible water vapour noted.\|Smoke is a mixture of particles, droplets, gases and entrained air. Based on Van Rossum (2027), §6.1 and Mulholland (2002), p. 2-258.]]

	== Soot and smoke yield ==		== Soot and smoke yield ==
Line 52:		Line 53:

	Entrainment increases the total mass and volume of smoke while reducing concentration and temperature. This dilution does not necessarily make the smoke harmless, because a greater volume can spread toxic products and energy to more locations. Source strength and receiver exposure both matter.<ref name="VR-5.3" /><ref name="IFEG-2.5-2">Australian Building Codes Board et al. (2005), p. 2.5-2.</ref>		Entrainment increases the total mass and volume of smoke while reducing concentration and temperature. This dilution does not necessarily make the smoke harmless, because a greater volume can spread toxic products and energy to more locations. Source strength and receiver exposure both matter.<ref name="VR-5.3" /><ref name="IFEG-2.5-2">Australian Building Codes Board et al. (2005), p. 2.5-2.</ref>
			[[File:fse-smoke-v2.svg\|thumb\|upright=1.5\|alt=Air entrained into a plume increases volume while smoke travels to another room.\|Entrainment dilutes smoke while increasing its volume and spread. Based on Van Rossum (2027), §5.3 and Australian Building Codes Board et al. (2005), p. 2.5-2.]]

	Particle and gas transport can differ. Soot can coagulate, evaporate or deposit on surfaces, and additional droplets can form through condensation. Gases may then remain hazardous farther from the fire even when visibility improves.<ref name="Mulholland-2-259">Mulholland (2002), p. 2-259.</ref><ref name="VR-6.1" />		Particle and gas transport can differ. Soot can coagulate, evaporate or deposit on surfaces, and additional droplets can form through condensation. Gases may then remain hazardous farther from the fire even when visibility improves.<ref name="Mulholland-2-259">Mulholland (2002), p. 2-259.</ref><ref name="VR-6.1" />
Line 76:		Line 78:

	Zone and field models estimate smoke production and movement from fire, plume and ventilation inputs. Their layer and mixing assumptions are simplifications, and local optical and toxic conditions can differ from model averages. Results should be checked against the intended receiver and time.<ref name="VR-9.2">Van Rossum (2027), §9.2.</ref><ref name="IFEG-2.5-2" />		Zone and field models estimate smoke production and movement from fire, plume and ventilation inputs. Their layer and mixing assumptions are simplifications, and local optical and toxic conditions can differ from model averages. Results should be checked against the intended receiver and time.<ref name="VR-9.2">Van Rossum (2027), §9.2.</ref><ref name="IFEG-2.5-2" />
			[[File:fse-smoke-v3.svg\|thumb\|upright=1.5\|alt=Generic yield gives OD 4.4 and visibility 0.23/0.57 m; wood gives OD 0.66 and visibility 1.5 m.\|Worked smoke example with two soot-yield assumptions. Based on Van Rossum (2027), §6.5.]]

	== Limits and common misunderstandings ==		== Limits and common misunderstandings ==

Jan: New FSE wiki article: Smoke (written by Kimi Code CLI)

2026-11-01T23:54:55Z

New FSE wiki article: Smoke (written by Kimi Code CLI)

New page

'''Smoke''' is a mixture of solid particles, liquid droplets and gases produced during combustion and thermal decomposition. In fire safety, the smoke volume also includes entrained ambient air, because its temperature and total volume determine smoke movement and exposure. This broader usage differs from definitions that reserve smoke for only the condensed-phase aerosol.<ref name="VR-6.1">Van Rossum (2027), §6.1.</ref><ref name="Mulholland-2-258">Mulholland (2002), p. 2-258.</ref>

Smoke can reduce visibility, deliver toxic and irritant products, carry unburnt fuel and transfer heat. Its appearance and behaviour vary with fuel, combustion mode, oxygen supply, mixing and time. White, black, hot or weakly visible smoke therefore cannot be interpreted by colour alone.<ref name="Mulholland-2-258" /><ref name="VR-6.1" />

The mixture is produced by flaming combustion, pyrolysis and smouldering, then transported by plume and building airflows. Entrainment dilutes concentration and temperature while increasing total mass flow. A small combustion source can consequently create a large smoke volume.<ref name="Mulholland-2-258" /><ref name="VR-5.3">Van Rossum (2027), §5.3.</ref>

== Components and formation ==

Solid particles include carbonaceous soot and other condensed material, while droplets can form when low-vapour-pressure products condense. Gases include carbon monoxide, carbon dioxide, water vapour, unburnt fuel and many other decomposition products. Their proportions depend on material and combustion conditions.<ref name="Mulholland-2-258" /><ref name="Drysdale-1-95">Drysdale (2002), p. 1-95.</ref>

Flaming combustion produces smoke through a balance between growth processes in the fuel-rich flame and burnout with oxygen. Aromatic polymers such as polystyrene tend to produce more smoke than hydrocarbons with single carbon-carbon bonds in the cited comparison. Flaming smoke often contains substantial elemental graphitic carbon.<ref name="Mulholland-2-258" />

Pyrolysis occurs when an external heat source decomposes a fuel surface. Vapour can then condense into light-coloured droplets as it rises and cools. Smouldering is self-sustaining surface oxidation rather than forced pyrolysis, and also produces droplet-rich smoke with different particle properties.<ref name="Mulholland-2-258" /><ref name="Ohlemiller-2-200">Ohlemiller (2002), p. 2-200.</ref>

White smoke commonly contains fine droplets and light aerosols, including condensed water or pyrolysis products, while water vapour itself is invisible. Black smoke usually contains more soot. These are tendencies in the cited descriptions, not a reliable classification of every fire.<ref name="VR-6.1" /><ref name="Mulholland-2-258" />

== Soot and smoke yield ==

[[Soot]] is the carbonaceous particulate component associated with incomplete combustion. It contributes to dark colour, optical extinction and flame radiation. Soot is therefore one component of smoke rather than a synonym for the entire smoke mixture.<ref name="VR-6.2">Van Rossum (2027), §6.2.</ref><ref name="Mulholland-2-258" />

[[Soot yield]] expresses the mass of soot produced per mass of fuel burned. It depends on fuel and combustion conditions, with more complete combustion generally producing less soot. Plastics tend to produce more than wood in Van Rossum's examples, while ethanol produces so little that the smoke can be difficult to see.<ref name="VR-6.2" />

Pre-flashover example values include 1.5% for wood, 23% for polyurethane, 14% for PVC, 16% for polystyrene and 19.5% for expanded polystyrene. These values apply to oxygen excess in the cited source and should not be used as universal material constants. Ventilation-limited and suppressed fires can have different yields.<ref name="VR-6.2" />

Suppressed or smouldering combustion can have a higher yield per kilogram while burning less fuel overall. Total soot production therefore depends on both yield and mass consumed. Comparing materials only by percentage can misstate the actual smoke source strength.<ref name="VR-6.2" />

== Visibility and optical properties ==

[[Visibility in smoke]] is the distance over which a person can perceive an object or sign. It depends on optical density, object contrast, illumination, smoke scattering and the observer. Irritants can further reduce effective visibility by causing eye pain and impaired vision.<ref name="VR-6.5">Van Rossum (2027), §6.5.</ref><ref name="Jin-2-43">Jin (2002), p. 2-43.</ref>

Particles reduce the luminous flux reaching the eye from an object and scatter background light into that line of sight. Both effects reduce contrast. Additional lighting can therefore fail to improve visibility when scattering overwhelms the contrast needed for recognition.<ref name="Jin-2-43" /><ref name="VR-6.5" />

[[Optical density]] expresses light attenuation per metre and is related to particle concentration and a mass-extinction coefficient. Van Rossum gives a generic average of 3,300 m²/kg for smoke from burning building and contents materials. It is a modelling average rather than a universal property of every smoke aerosol.<ref name="VR-6.4">Van Rossum (2027), §6.4.</ref>

For approximately uniform smoke, Van Rossum gives practical visibility estimates of one divided by optical density for non-luminous objects and 2.5 divided by optical density for luminous objects. He cautions that these are rough rules. Different optical densities along the actual line of sight require integration and make visibility direction-dependent.<ref name="VR-6.5" />

Jin's experiments similarly find an approximately constant product of visibility and extinction coefficient for signs over selected ranges. The product depends on sign type, reflectance and illumination, and black smoke can give somewhat better visibility than white smoke at the same extinction coefficient. This reinforces that optical density alone does not define perception.<ref name="Jin-2-43" />

== Toxicity and inhalation ==

[[Fire toxicity]] includes asphyxiation, irritation and other physiological effects caused by combustion products. Carbon monoxide, hydrogen cyanide, low oxygen, carbon dioxide and irritant compounds can all contribute. Their yields depend on the same combustion conditions that shape the aerosol.<ref name="Purser-2-85">Purser (2002), pp. 2-85–2-86.</ref><ref name="Gottuk-Lattimer-2-54">Gottuk and Lattimer (2002), p. 2-54.</ref>

[[Smoke inhalation]] exposes the respiratory system to this mixture. Effects can include breathing difficulty, respiratory tract pain, confusion and loss of consciousness. Heat and eye irritation can further impair escape, so toxicity influences both survival and the ability to reach safety.<ref name="Purser-2-85" /><ref name="Purser-2-86">Purser (2002), p. 2-86.</ref>

[[Carbon monoxide]] is often the principal asphyxiant, but atypical materials require other species to be assessed. Smouldering polyurethane foam, for example, can yield significant hydrogen cyanide in the 2005 guidance. A smoke assessment based only on one gas can therefore miss the dominant hazard.<ref name="IFEG-2.4-11">Australian Building Codes Board et al. (2005), p. 2.4-11.</ref>

Dose depends on concentration, exposure time and breathing response. Visibility can be poor while toxic dose is small during a short escape, or good while carbon monoxide remains high after particles deposit. Visibility and inhalation hazard must therefore be evaluated separately.<ref name="VR-6.1" /><ref name="Purser-2-88">Purser (2002), p. 2-88.</ref>

== Smoke movement and dilution ==

[[Smoke movement]] results from buoyancy, expansion, wind, mechanical systems and pressure differences across openings. Hot smoke rises in a plume, entrains air and can accumulate as an upper layer. Later flow through vents and shafts can expose remote spaces.<ref name="VR-6.6">Van Rossum (2027), §6.6.</ref><ref name="IFEG-2.5-6">Australian Building Codes Board et al. (2005), p. 2.5-6.</ref>

Entrainment increases the total mass and volume of smoke while reducing concentration and temperature. This dilution does not necessarily make the smoke harmless, because a greater volume can spread toxic products and energy to more locations. Source strength and receiver exposure both matter.<ref name="VR-5.3" /><ref name="IFEG-2.5-2">Australian Building Codes Board et al. (2005), p. 2.5-2.</ref>

Particle and gas transport can differ. Soot can coagulate, evaporate or deposit on surfaces, and additional droplets can form through condensation. Gases may then remain hazardous farther from the fire even when visibility improves.<ref name="Mulholland-2-259">Mulholland (2002), p. 2-259.</ref><ref name="VR-6.1" />

Unburnt pyrolysis gases add a combustion hazard to the mixture. If they mix with oxygen under suitable thermal or ignition conditions, they can ignite as a smoke explosion or backdraft. Smoke is therefore not only a passive consequence of fire; it can become fuel for a later event.<ref name="VR-6.1" /><ref name="VR-4.10">Van Rossum (2027), §4.10.</ref>

== Smoke control ==

[[Smoke control]] uses natural ventilation, zone pressurisation, extraction, dilution and containment to limit where smoke travels and accumulates. The 2005 guidelines identify these as the principal smoke-management approaches. Each changes concentration, pressure or the available flow path.<ref name="IFEG-2.5-7">Australian Building Codes Board et al. (2005), p. 2.5-7.</ref>

Extraction removes smoke and transported energy but requires a compatible make-up-air path. Excessive extraction at one outlet can cause plug holing, drawing clean air from below and wasting capacity. Outlet arrangement and layer depth therefore affect actual performance.<ref name="VR-6.8">Van Rossum (2027), §6.8.</ref>

Pressurisation aims to keep selected spaces clear by maintaining a pressure difference, while containment limits the region available to smoke. Dilution reduces concentration but increases the total air-smoke mixture. These approaches should be evaluated against the fire and building conditions rather than treated as interchangeable.<ref name="IFEG-2.5-7" />

Smoke control can also change combustion. Additional oxygen can support more complete burning and lower carbon monoxide yield, but it can also increase heat release and spread. The effect on the whole fire must be considered, not only the concentration at one receiver.<ref name="Gottuk-Lattimer-2-55">Gottuk and Lattimer (2002), p. 2-55.</ref><ref name="VR-6.6" />

== Measurement and modelling ==

Smoke production can be described by mass produced per mass of fuel burned, but this conversion factor depends on combustion mode and test scale. Mulholland reports values from 0.001 to 0.17 for flaming combustion and from 0.01 to 0.17 for pyrolysis and smouldering in the reviewed experiments. Reduced ventilation can strongly change these results.<ref name="Mulholland-2-259" />

Particle size distribution is another basic property. It influences light extinction, deposition and detectability, and often spans several orders of magnitude. A logarithmic size axis is therefore useful when comparing distributions.<ref name="Mulholland-2-259" /><ref name="Mulholland-2-260">Mulholland (2002), p. 2-260.</ref>

Concentration, particle size, optical density and toxic-gas content answer different questions. A measurement of one cannot be substituted for another without a model. Full exposure assessment needs the mixture composition and its time history at the receiver.<ref name="Mulholland-2-258" /><ref name="Purser-2-88" />

Zone and field models estimate smoke production and movement from fire, plume and ventilation inputs. Their layer and mixing assumptions are simplifications, and local optical and toxic conditions can differ from model averages. Results should be checked against the intended receiver and time.<ref name="VR-9.2">Van Rossum (2027), §9.2.</ref><ref name="IFEG-2.5-2" />

== Limits and common misunderstandings ==

Smoke is not only soot. Droplets and gases can dominate visibility, toxicity and movement, and water vapour itself is invisible. Treating every visible cloud as only carbon particles excludes much of the actual mixture.<ref name="VR-6.1" /><ref name="Mulholland-2-258" />

Colour does not establish composition or hazard. White smoke can contain irritants and toxic gases, while weakly visible smoke can still contain carbon monoxide. A clear line of sight does not prove that inhalation is safe.<ref name="VR-6.1" /><ref name="Gottuk-Lattimer-2-54" />

Dilution does not eliminate the source. It reduces concentration while increasing total smoke volume, so the same or greater mass of toxic products can reach more people. The receiver's concentration and exposure time must be assessed.<ref name="VR-5.3" /><ref name="Purser-2-88" />

Finally, smoke is not only a marker of fire. Unburnt components can ignite, and hot smoke can spread fire by radiation and convection. Its role includes fuel transport and heat transfer as well as toxicity and obscuration.<ref name="VR-6.1" /><ref name="VR-4.10" />

The smoke source should be characterised before its transport is calculated. Fuel, combustion mode, mass-loss rate, soot yield and toxic-species yield provide different parts of that description. Missing one can lead to a smoke volume estimate that cannot support optical or toxic assessment.<ref name="Mulholland-2-259" /><ref name="IFEG-2.4-11" />

Plume entrainment then links the source with layer formation. It determines how much air joins the combustion products and therefore affects both concentration and volume. Treating smoke production as fuel mass alone would omit the process that creates most of the moving mixture.<ref name="IFEG-2.5-2" /><ref name="VR-5.3" />

A receiver-focused analysis follows the actual sightline and breathing location. Optical density can vary along the route, and particle deposition can change composition before the gas arrives. These local conditions are more useful for exposure assessment than an unqualified building-average smoke density.<ref name="VR-6.5" /><ref name="Mulholland-2-259" />

Test conditions should remain attached to yield and visibility data. Specimen orientation, oxygen concentration, external heat flux and smoke-collection method can all affect results. Comparing values without those conditions can create false agreement or disagreement between materials.<ref name="Mulholland-2-259" /><ref name="Jin-2-43" />

For control-system review, nominal airflow should be converted into an actual smoke balance. Make-up air, leakage, plug holing and pressure differences can alter the effective path. The result should be checked at occupied locations and during the period when the system is expected to operate.<ref name="VR-6.8" /><ref name="IFEG-2.5-7" />

The possibility of delayed combustion should also remain in the scenario. Unburnt gases can accumulate under oxygen restriction and ignite after mixing later, producing a smoke explosion or backdraft. A model that treats smoke only as an inert transport tracer would miss this hazard.<ref name="VR-4.10" /><ref name="VR-4.9">Van Rossum (2027), §4.9.</ref>

A complete report therefore separates production, entrainment, transport, deposition and reception. It identifies which components are evaluated for visibility, toxicity and heat transfer, and which can burn later. This allows the same smoke mixture to be assessed for several different outcomes without losing its physical meaning.<ref name="VR-6.1" /><ref name="Purser-2-85" />

Different smoke metrics should not be collapsed into one index. Mass production describes source strength, optical density describes attenuation, toxic yield describes species production and visibility describes perception. A defensible assessment selects the metrics required for the decision rather than treating smoke as universally heavy or light.<ref name="Mulholland-2-258" /><ref name="VR-6.4" /><ref name="Purser-2-88" />

The smoke's thermal role should also remain in the energy balance. Hot gases and particles emit radiation, while convection transports energy to boundaries and adjacent rooms. These pathways can expose people and fuel even where the visible plume has become diluted.<ref name="Tien-1-73">Tien, Lee, and Stretton (2002), p. 1-73.</ref><ref name="VR-5.3" />

Where source or transport data are weak, alternative scenarios should make the uncertainty visible. Changing yield, ventilation, layer volume and deposition can reverse the predicted visibility or dose. A range of outcomes is more informative than a precise but unsupported smoke condition.<ref name="Mulholland-2-259" /><ref name="VR-1.7">Van Rossum (2027), §1.7.</ref>

The definition used in a report should also be stated. Aerosol-only and broader smoke definitions answer different questions about particles and the complete smoke volume. Declaring that scope prevents soot, gas composition and entrained air from being omitted by accident.<ref name="Mulholland-2-258" /><ref name="VR-6.1" />

== See also ==

* [[Optical density]]
* [[Soot yield]]
* [[Visibility in smoke]]

== Notes ==

<references />

== References ==

* Australian Building Codes Board, National Research Council of Canada, International Code Council, & Department of Building and Housing New Zealand. (2005). ''International fire engineering guidelines'' (2005 ed.). Australian Building Codes Board.
* Drysdale, D. D. (2002). Thermochemistry. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Gottuk, D. T., & Lattimer, B. Y. (2002). Effect of combustion conditions on species production. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Jin, T. (2002). Visibility and human behavior in fire smoke. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Mulholland, G. W. (2002). Smoke production and properties. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Ohlemiller, T. J. (2002). Smoldering combustion. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Purser, D. A. (2002). Toxicity assessment of combustion products. In P. J. DiNenno (Ed.), ''SFPE handbook of fire protection engineering'' (3rd ed.). National Fire Protection Association.
* Van Rossum, E. (2027). ''Introduction to Fire Safety Engineering''. Fire Safety Academy.

[[Category:Smoke, Toxicity & Tenability]]