Smoulder 4583585 220420805 2008-06-19T19:49:02Z Rhebus 890461 /* Some smouldering cases */ change 9/11 caption to: "The smouldering pile of debris after the [[September 11 Attacks]]" '''Smouldering''' (or '''smoldering''' in American spelling) is a [[flame]]less form of [[combustion]], deriving its heat from oxidations occurring on the surface of a [[Fuel#Solid fuels|solid fuel]]. Common examples are the initiation of fires on upholstered furniture by weak heat sources (e.g., a [[cigarette]], a [[Short-circuit|short-circuited wire]]), and the persistent combustion of [[biomass]] behind the flaming front of [[wildland fire]]s. ==Fundamentals== [[Image:Papierosa_1_ubt_0069.jpeg|thumb|''A lighted cigarette is the most common smouldering example'']] [[Image:Embers_01.JPG|thumb|''Smouldering combustion in glowing embers of BBQ coal briquettes'']] The fundamental difference between smouldering and [[flame|flaming]] combustion is that smouldering occurs on the surface of the solid rather than in the gas phase. The characteristic [[temperature]] and [[heat]] released during smouldering are low compared to those in the flaming combustion (i.e., ~600°C vs. ~1500°C). Smouldering propagates in a creeping fashion, around 0.1 mm/s, which is about ten times slower than flames spread over a solid. In spite of its weak combustion characteristics, smouldering is a significant fire hazard. Smouldering emits toxic gases (e.g., [[carbon monoxide]]) at a higher yield than flaming fires and leaves behind a significant amount of solid residue. The emitted gases are flammable and could later be ignited in the gas phase, triggering the transition to flaming combustion. <ref>[http://fire.nist.gov/bfrlpubs/fire02/art074.html http://fire.nist.gov/bfrlpubs/fire02/art074.html] "Smoldering Combustion" by T.J. Ohlemiller, SFPE Handbook of Fire Protection Engineering (3rd Edition),2002.</ref> ==Smouldering materials== [[Image:Smouldered.jpg|thumb|250px|right|Polyurethane foam sample from the NASA smouldering experiments.]] Many materials can sustain a smouldering reaction, including [[coal fire|coal]], [[tobacco]], decaying [[wood]] and sawdust, [[biomass]] fuels on the forest surface ([[wiktionary:Duff|duff]]) and subsurface ([[peat]]), [[cotton]] clothing and string, and polymeric foams (e.g., [[upholstery]] and [[bedding]] materials). Smouldering fuels are generally porous, permeable to flow and formed by aggregates (particulates, grains, fibres or of cellular structure). These aggregates facilitate the surface reaction with oxygen by allowing gas flow through the fuel and providing a large surface area per unit volume. They also act as thermal insulation, reducing heat losses. The most studied materials to date are [[cellulose]] and [[polyurethane]] foams. ==Some smouldering cases== The characteristics of smouldering fires make them a threat of new dimensions, taking the form of colossal underground fires or silent fire safety risks, as summarized below. * [[Fire safety]]: The main hazards posed by smouldering arise from the fact that it can be easily initiated (by heat sources too weak to ignite flames) and is difficult to detect. Fire statistics draw attention to the magnitude of smouldering combustion as the leading cause of fire deaths in residential areas (i.e., more than 25% of the fire deaths in the [[United States]] are attributed to smoulder-initiated fires, with similar figures in other developed countries). A particularly common fire scenario is a [[cigarette]] igniting a piece of [[upholstery|upholstered furniture]]. This ignition leads to a smouldering fire that lasts for a long period of time (in the order of hours), spreading slowly and silently until critical conditions are attained and flames suddenly erupt <ref> J. R. Hall, 2004, The Smoking-Material Fire Problem, Fire Analysis and Research Division of The National Fire Protection Association, Quincy, MA (USA). November 2004.</ref>. Smouldering combustion is also a fire-safety concern aboard space facilities (e.g., [[International Space Station]]), because the [[microgravity|absence of gravity]] is thought to promote smouldering ignition and propagation. * [[Wildfire|Wildland fires]]: Smouldering combustion has a great impact in [[forest]] fires, being responsible for a large amount of the fuel consumed and the [[pollutant]]s emitted. Smouldering combustion of the forest ground does not have the visually dramatic impact of flaming combustion; however, as the cause of the killing of [[root]]s, [[seed]]s, and [[plant stem]]s at the ground level, it is an important component of forest fires. Smouldering of forest [[biomass]] can linger for days or weeks after flaming has ceased, resulting in large quantities of fuels consumed and becoming a global source of [[emission]]s to the atmosphere <ref>A.A. Bertschi, R.J. Yokelson, D.E. Ward, R.E. Babbitt, R.A. Susott, J.G. Goode, W.M. Hao, 2003, Trace gas and particle emissions from fires in large diameter and belowground biomass fuels, Journal of Geophysical Research 108 (D13), pp. 8.1-8.12.</ref>. [[Image:TOMS indonesia smog lrg.jpg|thumb|200px|Smoke and pollution from fires in Borneo, 1997.]] * Subsurface fires: Fires occurring many meters below the surface are a type of smouldering event of colossal magnitude. Subsurface fires in [[Coal mine fire|coal mines]], [[Peat#Peat fires|peat lands]] and landfills are rare events, but when active they can smoulder for very long periods of time (months or years), emitting enormous quantities of combustion gases into the atmosphere, causing deterioration of [[air quality]] and subsequent health problems. The oldest and largest fires in the world, burning for centuries, are smouldering fires. These fires are fed by the oxygen in the small but continuous flow of air through natural pipe networks, fractured [[stratum|strata]], cracks, openings or abandoned [[mining|mine]] shafts which permit the air to circulate into the subsurface. The reduced heat losses and high thermal inertia of the underground together with high fuel availability promote long-term smouldering combustion and allow for creeping but extensive propagation. These fires prove difficult to detect, and frustrate most efforts to extinguish them. The dramatic 1997 [[Peat#Peat fires|peatland fires in Borneo]] caused the recognition of subsurface smouldering fires as a global threat with significant economic, social and ecological impacts <ref>S.E. Page, F. Siegert, J.O. Rieley, H.-D.V. Boehm, A. Jaya, S. Limin, 2002, The amount of carbon released from peat and forest fires in Indonesia during 1997, Nature 420, pp. 61-61.</ref> <ref>Fire Group at the University of Edinburgh. http://s0237382.googlepages.com</ref>. The summer of 2006 saw the resurgence of the Borneo peat fires <ref>Forest fire haze brings misery to Indonesia and beyond, The Guardian, October 6, 2006. http://environment.guardian.co.uk/waste/story/0,,1889323,00.html</ref>. [[Image:WTCgroundzero.jpg|thumb|280px|''The smouldering pile of debris after the [[September 11 Attacks]]'', Manhattan, NY (USA).]] * [[World Trade Center site|World Trade Center Debris]]: After the attack, fire and subsequent [[Collapse of the World Trade Center|collapse of the Twin Towers]] on [[September 11, 2001 attacks|September 11 2001]], the colossal pile of debris left on the site smouldered for more than five months. It resisted attempts by fire fighters to extinguish it until most of the rubble was removed. The effects of the gaseous and aerosolized products of smouldering on the health of the emergency workers were significant but the details are still a matter of debate. ==Beneficial applications== Smouldering combustion also has a few beneficial applications. * In [[controlled burn|wildland fire management]], controlled smouldering fires aiming at reducing the load of ground fuels are useful because they are easy to control and propagate, and because of their reduced effect on the ecosystem. * Smouldering of tires produces tar and energy at the same time, fostering the [[Tire#Other use and recycling|recycling of tires]]. * [[Petroleum#Extraction|In-situ combustion]] of [[petroleum]] sites is increasingly used for oil recovery when traditional extraction methods prove inefficient or too costly. * In-situ smouldering combustion is being explored as a novel remediation technology for [[NAPL|land contaminants]]<ref>In Situ Smouldering Combustion: A Novel Remediation Concept for NAPL Source Zones, J.I. Gerhard, J.L. Torero, C. Switzer, P. Pironi, and G. Rein, 2006 Fall Meeting of the American Geophysical Union, Invited talk, December 12, 2006. http://www.see.ed.ac.uk/IIE/research/environ/isc.html</ref>. ==References and external links== <div class="references-small"> <references/> </div> * [http://www.me.berkeley.edu/mcl/ Microgravity smouldering (NASA-funded) research facility at the University of California at Berkeley.] [[Category:Fire]] [[Category:Firefighting]] [[Category:Fire prevention]] [[Category:Fire protection]] [[de:Schwelbrand]] [[lt:Rusenimas]] [[sv:Glöd]]