Smoke

Smokeis a suspensionof airborneparticulatesandgasesemitted when a material undergoescombustionorpyrolysis, together with the quantity of air that isentrainedor otherwise mixed into the mass. It is commonly an unwantedby-productof fires (includingstoves,candles,internal combustion engines,oil lamps, andfireplaces), but may also be used forpest control(fumigation), communication (smoke signals), defensive and offensive capabilities in the military (smoke screen),cooking, orsmoking(tobacco,cannabis, etc.). It is used in rituals whereincense,sage, orresinis burned to produce a smell forspiritualormagicalpurposes. It can also be a flavoring agent and preservative.
Smoke inhalationis the primary cause of death in victims of indoorfires. The smoke kills by a combination of thermal damage,poisoningandpulmonaryirritation caused bycarbon monoxide,hydrogen cyanideand other combustion products.
Smoke is anaerosol(ormist) of solid particles and liquid droplets that are close to the ideal range of sizes forMie scatteringofvisible light.
The composition of smoke depends on the nature of the burning fuel and the conditions of combustion. Fires with high availability of oxygen burn at a high temperature and with a small amount of smoke produced; the particles are mostly composed ofash, or with large temperature differences, of condensed aerosol of water. High temperature also leads to production ofnitrogen oxides.Sulfur content yieldssulfur dioxide, or in case of incomplete combustion,hydrogen sulfide.Carbon and hydrogen are almost completely oxidized tocarbon dioxideand water.Fires burning with lack of oxygen produce a significantly wider palette of compounds, many of them toxic.Partial oxidationof carbon producescarbon monoxide, while nitrogen-containing materials can yieldhydrogen cyanide,ammonia, and nitrogen oxides.Hydrogengas can be produced instead of water.Contents ofhalogenssuch aschlorine(e.g. inpolyvinyl chlorideorbrominated flame retardants) may lead to the production ofhydrogen chloride,phosgene,dioxin, andchloromethane,bromomethaneand otherhalocarbons.Hydrogen fluoridecan be formed fromfluorocarbons, whetherfluoropolymerssubjected to fire or halocarbonfire suppression agents.Phosphorusandantimonyoxides and their reaction products can be formed from somefire retardantadditives, increasing smoke toxicity and corrosivity.Pyrolysisofpolychlorinated biphenyls(PCB), e.g. from burning oldertransformer oil, and to lower degree also of other chlorine-containing materials, can produce2,3,7,8-tetrachlorodibenzodioxin, a potentcarcinogen, and otherpolychlorinated dibenzodioxins.Pyrolysis of fluoropolymers, e.g.teflon, in presence of oxygen yieldscarbonyl fluoride(which hydrolyzes readily to HF and CO2); other compounds may be formed as well, e.g.carbon tetrafluoride,hexafluoropropylene, and highly toxicperfluoroisobutene(PFIB).
Pyrolysis of burning material, especiallyincomplete combustionorsmolderingwithout adequate oxygen supply, also results in production of a large amount ofhydrocarbons, bothaliphatic(methane,ethane,ethylene,acetylene) andaromatic(benzeneand its derivates,polycyclic aromatic hydrocarbons; e.g.benzo[a]pyrene, studied as a carcinogen, orretene),terpenes.It also results in the emission of a range of smaller oxygenatedvolatile organic compounds(methanol,acetic acid,hydroxy acetone,methyl acetateandethyl formate) which are formed as combustion by products as well as less volatile oxygenated organic species such as phenolics,furansandfuranones.Heterocyclic compoundsmay be also present.Heavier hydrocarbons may condense astar; smoke with significant tar content is yellow to brown.Combustion of solid fuels can result in the emission of many hundreds to thousands of lower volatility organic compounds in the aerosol phase.Presence of such smoke, soot, and/or brown oily deposits during a fire indicates a possible hazardous situation, as the atmosphere may be saturated with combustible pyrolysis products with concentration above the upperflammability limit, and sudden inrush of air can causeflashoverorbackdraft.
Presence of sulfur can lead to formation of gases like hydrogen sulfide,carbonyl sulfide, sulfur dioxide,carbon disulfide, andthiols; especially thiols tend to get adsorbed on surfaces and produce a lingering odor even long after the fire. Partial oxidation of the released hydrocarbons yields in a wide palette of other compounds:aldehydes(e.g.formaldehyde,acrolein, andfurfural), ketones,alcohols(often aromatic, e.g.phenol,guaiacol,syringol,catechol, andcresols),carboxylic acids(formic acid,acetic acid, etc.).
The visibleparticulate matterin such smokes is most commonly composed ofcarbon(soot). Other particulates may be composed of drops of condensed tar, or solid particles of ash. The presence of metals in the fuel yields particles of metaloxides. Particles of inorganicsaltsmay also be formed, e.g.ammonium sulfate,ammonium nitrate, orsodium chloride. Inorganic salts present on the surface of the soot particles may make themhydrophilic. Many organic compounds, typically thearomatic hydrocarbons, may be alsoadsorbedon the surface of the solid particles. Metal oxides can be present when metal-containing fuels are burned, e.g.solid rocketfuels containingaluminium.Depleted uraniumprojectiles after impacting the target ignite, producing particles ofuranium oxides.Magneticparticles, spherules ofmagnetite-likeferrous ferric oxide, are present in coal smoke; their increase in deposits after 1860 marks the beginning of the Industrial Revolution.(Magnetic iron oxidenanoparticlescan be also produced in the smoke frommeteoritesburning in the atmosphere.)Magneticremanence,recordedin the iron oxide particles, indicates the strength of Earth's magnetic field when they were cooled beyond theirCurie temperature; this can be used to distinguish magnetic particles of terrestrial and meteoric origin.Fly ashis composed mainly ofsilicaandcalcium oxide.Cenospheresare present in smoke from liquid hydrocarbon fuels. Minute metal particles produced byabrasioncan be present in engine smokes.Amorphous silicaparticles are present in smokes from burningsilicones; small proportion ofsilicon nitrideparticles can be formed in fires with insufficient oxygen. The silica particles have about 10 nm size, clumped to 70–100 nm aggregates and further agglomerated to chains.Radioactive particles may be present due to traces ofuranium,thorium, or otherradionuclidesin the fuel;hot particlescan be present in case of fires duringnuclear accidents(e.g.Chernobyl disaster) ornuclear war.
Smoke particulates, like other aerosols, are categorized into three modes based on particle size:
Most of the smoke material is primarily in coarse particles. Those undergo rapiddry precipitation, and the smoke damage in more distant areas outside of the room where the fire occurs is therefore primarily mediated by the smaller particles.
Aerosol of particles beyond visible size is an early indicator of materials in a preignition stage of a fire.
Burning of hydrogen-rich fuel produceswater vapor; this results in smoke containing droplets of water. In absence of other color sources (nitrogen oxides, particulates...), such smoke is white andcloud-like.
Smoke emissions may contain characteristic trace elements.Vanadiumis present in emissions fromoilfired power plants andrefineries; oil plants also emit somenickel. Coal combustionproduces emissionscontainingaluminium,arsenic,chromium,cobalt,copper,iron,mercury,selenium, anduranium.
Traces of vanadium in high-temperature combustion products form droplets of moltenvanadates. These attack thepassivation layerson metals and causehigh temperature corrosion, which is a concern especially forinternal combustion engines. Moltensulfateandleadparticulates also have such effect.
Some components of smoke are characteristic of the combustion source.Guaiacoland its derivatives are products of pyrolysis ofligninand are characteristic ofwoodsmoke; other markers aresyringoland derivates, and othermethoxyphenols.Retene, a product of pyrolysis ofconifertrees, is an indicator offorest fires.Levoglucosanis a pyrolysis product ofcellulose.Hardwoodvssoftwoodsmokes differ in the ratio of guaiacols/syringols. Markers for vehicle exhaust includepolycyclic aromatic hydrocarbons,hopanes,steranes, and specific nitroarenes (e.g.1-nitropyrene). The ratio of hopanes and steranes to elemental carbon can be used to distinguish between emissions of gasoline and diesel engines.
Many compounds can be associated with particulates; whether by beingadsorbedon their surfaces, or by being dissolved in liquid droplets. Hydrogen chloride is well absorbed in the soot particles.
Inert particulate matter can be disturbed and entrained into the smoke. Of particular concern are particles ofasbestos.
Depositedhot particlesofradioactive falloutand bioaccumulated radioisotopes can be reintroduced into the atmosphere bywildfiresandforest fires; this is a concern in e.g. theZone of alienationcontaining contaminants from theChernobyl disaster.
Polymers are a significant source of smoke. Aromaticside groups, e.g. inpolystyrene, enhance generation of smoke. Aromatic groups integrated in the polymer backbone produce less smoke, likely due to significantcharring. Aliphatic polymers tend to generate the least smoke, and are non-self-extinguishing. However presence of additives can significantly increase smoke formation. Phosphorus-based and halogen-basedflame retardantsdecrease production of smoke. Higher degree ofcross-linkingbetween the polymer chains has such effect too.
Thenaked eyedetects particle sizes greater than 7 μm (micrometres).Visibleparticles emitted from a fire are referred to as smoke.Invisibleparticles are generally referred to as gas or fumes. This is best illustrated whentoastingbread in a toaster. As the bread heats up, the products of combustion increase in size. The fumes initially produced are invisible but become visible if the toast is burnt.
Anionization chambertypesmoke detectoris technically a product of combustion detector, not a smoke detector. Ionization chamber type smoke detectors detect particles of combustion that are invisible to the naked eye. This explains why they may frequentlyfalse alarmfrom the fumes emitted from the red-hot heating elements of a toaster, before the presence of visible smoke, yet they may fail to activate in the early, low-heatsmolderingstage of a fire.
Smoke from a typical house fire contains hundreds of different chemicals and fumes. As a result, the damage caused by the smoke can often exceed that caused by the actual heat of the fire. In addition to the physical damage caused by the smoke of afire– which manifests itself in the form of stains – is the often even harder to eliminate problem of a smoky odor. Just as there are contractors that specialize in rebuilding/repairing homes that have been damaged by fire and smoke,fabric restorationcompanies specialize in restoring fabrics that have been damaged in a fire.
Smoke from oxygen-deprived fires contains a significant concentration of compounds that are flammable. A cloud of smoke, in contact with atmospheric oxygen, therefore has the potential of being ignited – either by another open flame in the area, or by its own temperature. This leads to effects likebackdraftandflashover.Smoke inhalationis also a danger of smoke that can cause serious injury and death.
Many compounds of smoke from fires are highly toxic and/or irritating. The most dangerous iscarbon monoxideleading tocarbon monoxide poisoning, sometimes with the additive effects ofhydrogen cyanideandphosgene. Smoke inhalation can therefore quickly lead to incapacitation and loss of consciousness. Sulfur oxides, hydrogen chloride and hydrogen fluoride in contact with moisture formsulfuric,hydrochloricandhydrofluoric acid, which are corrosive to both lungs and materials.
Cigarette smokeis a major modifiable risk factor forlung disease,heart disease, and manycancers.  Smoke can also be a component of ambient air pollution due to the burning of coal in power plants, forest fires or other sources, although the concentration of pollutants in ambient air is typically much less than that in cigarette smoke.  One day of exposure to PM2.5 at a concentration of 880 μg/m, such as occurs in Beijing, China, is the equivalent of smoking one or two cigarettes in terms of particulate inhalation by weight.The analysis is complicated, however, by the fact that the organic compounds present in various ambient particulates may have a higher carcinogenicity than the compounds in cigarette smoke particulates.Secondhand tobacco smoke is the combination of both sidestream and mainstream smoke emissions from a burning tobacco product. These emissions contain more than 50 carcinogenic chemicals. According to the United StatesSurgeon General's 2006 report on the subject, exposures to secondhand tobacco smoke can activate platelets causing increased clotting and increased risk of thrombus and potentially damage the lining of blood vessels, decrease coronary flow velocity reserves, and reduce heart rate variability, potentially increasing the risk of a heart attack. The chances of these effects occurring increase with increased exposure and time of exposure.The American Cancer Society lists "heart disease, lung infections, increased asthma attacks, middle ear infections, and low birth weight" as ramifications of smoker's emission.
Smoke can obscure visibility, impeding occupant exiting from fire areas. In fact, the poor visibility due to the smoke that was in theWorcester Cold Storage Warehouse fireinWorcester, Massachusettswas the reason why the trapped rescue firefighters could not evacuate the building in time. Because of the striking similarity that each floor shared, the dense smoke caused the firefighters to become disoriented.
Smoke can contain a wide variety of chemicals, many of them aggressive in nature. Examples arehydrochloric acidandhydrobromic acid, produced fromhalogen-containingplasticsandfire retardants,hydrofluoric acidreleased bypyrolysisoffluorocarbonfire suppression agents,sulfuric acidfrom burning ofsulfur-containing materials,nitric acidfrom high-temperature fires wherenitrous oxidegets formed,phosphoric acidandantimonycompounds from P and Sb based fire retardants, and many others. Suchcorrosionis not significant for structural materials, but delicate structures, especiallymicroelectronics, are strongly affected. Corrosion ofcircuit boardtraces, penetration of aggressive chemicals through the casings of parts, and other effects can cause an immediate or gradual deterioration of parameters or even premature (and often delayed, as the corrosion can progress over long time) failure of equipment subjected to smoke. Many smoke components are alsoelectrically conductive; deposition of a conductive layer on the circuits can causecrosstalksand other deteriorations of the operating parameters or even cause short circuits and total failures.Electrical contactscan be affected by corrosion of surfaces, and by deposition ofsootand other conductive particles or nonconductive layers on or across the contacts. Deposited particles may adversely affect the performance ofoptoelectronicsby absorbing or scattering the light beams.
Corrosivity of smoke produced by materials is characterized by the corrosion index (CI), defined as material loss rate (angstrom/minute) per amount of material gasified products (grams) per volume of air (m). It is measured by exposing strips of metal to flow of combustion products in a test tunnel. Polymers containing halogen andhydrogen(polyvinyl chloride,polyolefinswith halogenated additives, etc.) have the highest CI as the corrosive acids are formed directly with water produced by the combustion, polymers containing halogen only (e.g.polytetrafluoroethylene) have lower CI as the formation of acid is limited to reactions with airborne humidity, and halogen-free materials (polyolefins,wood) have the lowest CI.However, some halogen-free materials can also release significant amount of corrosive products.
Smoke damage to electronic equipment can be significantly more extensive than the fire itself.Cablefires are of special concern;low smoke zero halogenmaterials are preferable for cable insulation.
When smoke comes into contact with the surface of any substance or structure, the chemicals contained in it are transferred to it. The corrosive properties of the chemicals cause the substance or structure to decompose at a rapid rate. Certain materials or structures absorb these chemicals, which is why clothing, unsealed surfaces, potable water, piping, wood, etc., are replaced in most cases of structural fires.
Wood smoke is a major source ofair pollution,especiallyparticulate pollution,pollution bypolycyclic aromatic hydrocarbons(PAHs)andvolatile organic compounds(VOCs)such asformaldehyde.
In theUnited Kingdomdomestic combustion, especially for industrial uses, is the largest single source ofPM2.5annually.In some towns and cities inNew South Wales, wood smoke may be responsible for 60% of fine particle air pollution in the winter.A year-long sampling campaign in Athens, Greece found a third (31%) of PAH urban air pollution to be caused by wood-burning, roughly as much as that ofdieselandoil(33%) andgasoline(29%). It also found that wood-burning is responsible for nearly half (43%) of annual PAH lung cancer-risk compared to the other sources and that wintertime PAH levels were 7 times higher than in other seasons, presumably due to an increased use offireplacesand heaters. The largest exposure events are periods during the winter with reduced atmospheric dispersion to dilute the accumulated pollution, in particular due to the lowwindspeeds.Research conducted about biomass burning in 2015, estimated that 38% of European total particulate pollution emissions are composed of domestic wood burning.
Wood smoke (for example fromwildfiresor wood ovens) can cause lung damage,artery damage and DNA damageleading to cancer,other respiratory and lung disease and cardiovascular disease.Air pollution, particulate matter and wood smoke may also cause brain damage because of particulates breaching the cardiovascular system and into the brain,which can increase the risk of developmental disorders,neurodegenerative disordersmental disorders,and suicidal behavior,although studies on the link betweendepressionand some air pollutants are not consistent.At least one study has identified "the abundant presence in the human brain of magnetite nanoparticles that match precisely the high-temperature magnetite nanospheres, formed by combustion and/or friction-derived heating, which are prolific in urban, airborne particulate matter (PM)."Air pollution has also been linked to a range of other psychosocial problems.
As early as the 15th centuryLeonardo da Vincicommented at length on the difficulty of assessing smoke, and distinguished betweenblack smoke(carbonized particles) and white 'smoke' which is not a smoke at all but merely a suspension of harmless water particulates.
Smoke from heating appliances is commonly measured in one of the following ways:
In-line capture.A smoke sample is simply sucked through a filter which is weighed before and after the test and the mass of smoke found. This is the simplest and probably the most accurate method, but can only be used where the smoke concentration is slight, as the filter can quickly become blocked.
TheASTM smoke pumpis a simple and widely used method of in-line capture where a measured volume of smoke is pulled through a filter paper and the dark spot so formed is compared with a standard.
Filter/dilution tunnel.A smoke sample is drawn through a tube where it is diluted with air, the resulting smoke/air mixture is then pulled through a filter and weighed. This is the internationally recognized method of measuring smoke fromcombustion.
Electrostatic precipitation.The smoke is passed through an array of metal tubes which contain suspended wires. A (huge) electrical potential is applied across the tubes and wires so that the smoke particles become charged and are attracted to the sides of the tubes. This method can over-read by capturing harmless condensates, or under-read due to the insulating effect of the smoke. However, it is the necessary method for assessing volumes of smoke too great to be forced through a filter, i.e., frombituminous coal.
Ringelmann scale.A measure of smoke color. Invented by ProfessorMaximilian Ringelmannin Paris in 1888, it is essentially a card with squares of black, white and shades of gray which is held up and the comparative grayness of the smoke judged. Highly dependent on light conditions and the skill of the observer it allocates a grayness number from 0 (white) to 5 (black) which has only a passing relationship to the actual quantity of smoke. Nonetheless, the simplicity of the Ringelmann scale means that it has been adopted as a standard in many countries.
Optical scattering.A light beam is passed through the smoke. A light detector is situated at an angle to the light source, typically at 90°, so that it receives only light reflected from passing particles. A measurement is made of the light received which will be higher as the concentration of smoke particles becomes higher.
Optical obscuration.A light beam is passed through the smoke and a detector opposite measures the light. The more smoke particles are present between the two, the less light will be measured.
Combined optical methods.There are various proprietary optical smoke measurement devices such as the 'nephelometer' or the 'aethalometer' which use several different optical methods, including more than one wavelength of light, inside a single instrument and apply an algorithm to give a good estimate of smoke. It has been claimed that these devices can differentiate types of smoke and so their probable source can be inferred, though this is disputed.
Inference fromcarbon monoxide.Smoke is incompletely burnedfuel, carbon monoxide is incompletely burned carbon, therefore it has long been assumed that measurement of CO influe gas(a cheap, simple and very accurate procedure) will provide a good indication of the levels of smoke. Indeed, several jurisdictions use CO measurement as the basis ofsmoke control. However it is far from clear how accurate the correspondence is.
Throughout recorded history, humans have used the smoke ofmedicinal plantsto cure illness. A sculpture fromPersepolisshowsDarius the Great(522–486 BC), the king ofPersia, with twocensersin front of him for burningPeganum harmalaand/orsandalwoodSantalum album, which was believed to protect the king from evil and disease. More than 300 plant species in 5 continents are used in smoke form for different diseases. As a method ofdrug administration, smoking is important as it is a simple, inexpensive, but very effective method of extracting particles containing active agents. More importantly, generating smoke reduces the particle size to a microscopic scale thereby increasing the absorption of its active chemical principles.