1、英文原文 MINE FIRE 1. Introduction The most feared of hazards in underground mines or other subsurface facilities are those of firseand explosions. Like airplane crashes ,these do not occur often but, when they do ,have the potential of causing diaastrous loss of life and property as well as a temporary
2、 or permanent sterilization of mineral reserves. Fuithermore,” near-misses” occur all to frequently .the incidence of min fires appears not to be declining despite greatly improved methods of mine environmental design and hazard control .this is a consequence of two matters .first the growing varity
3、 of material that are imported into modern mine workings, varying from resins and plastics to liquid fuels and hydraulic fluids. a second factor is the contions increase in the employment of mechanized procedurds, mang of the maching involving flammable liquids and materials that can produce toxic f
4、umes when over-heated .the enormous loss of life due to mine fires and explosions during the eighteenth and nineteenth centuries preoccupied the minds of mining engineers and scientists of the time .through the 1980s ,mine fires reemerged as a topoc of prissing research need . The majority of deaths
5、 arising from mine fires and explosions are caused ,not by burning or blast effects ,but by the inhalation of toxic gases ,in particular ,carbon monoxide. There are two major differences between underground fires and those that occur in suifacestrucrures. thefirsr concerns the long distances, often
6、seversl kilometers, that personnel might be required to travel in passageways that may be smoke-filed. Secondly, the ventilation routes are bounded by the confines of the airways and workings, causing closely coupled interactions between the airflows and behaviour of the fire. It is difficult for an
7、yone who has not had the experience, to comprehend the sensations of compete isolstionand disorientation involved in feeling ones way through a long smoke-files mine airway and to walk just a few steps ,even without the trauma of a highly polluted atmosphere . It is, therefore, a matter of ongoing i
8、mportance that all personnel involved in the design and detection of subsurface fires ,as well as procedies of personnel warning systems ,escapeways , firefighing, toxic gases, training, fire drills and the vital need for prompt resporise to a fire emergency. these are some of the topic s that are d
9、iscussed in this chapter. 1.1 The fire triangle and the comcuetion process Peihaps the most basic precept in firefighter training is the fire triangle shown on figure 12.1. this illustrates that the combustion process which we term “fire” requires three comptnents: furs, heat and oxygen. Remove any
10、one of thest and the fire will be extinguished. the fuel may be solids, liquids or gases .the liquids and gases might be introduced into the mine environment at ambient temperature by natural or mining processes, or may be produced by heating solid materisls. Whenever a solid or liquid is heated to
11、a sufficiently high temperature ,it will produce a vapour that is capable of being ignited by a flame, spark or hot surface which has the required concentration and duiation of thermal energy. Gasoline has a flashpoint of -45 degrees C while most commonly available solids require the application of
12、a flame for them to reach flashpoint theignition temperature of any given substance is the lowest temperature at which sustsined combustion is initisted. Flaming is the process of the vapoursaccompanied ,usually ,by the emission of heat and light .in the case of self-sustained burning ,that heat is
13、sufficient to raise the temperarure of the newly exposed or surrounding areas of suiface to flashpoint. however, combustion cancontinue at a slower tate without flaming through the process we knows as smouldering. in this case ,the oxidation process continues on the suiface of the material and produ
14、ces sufficient heat to be selfsustaining, but not enough to cause the emission of vapours in the quantity required for flaming combustion. The oxygen which forms the third side of the fire triangle is normally provided by the air. Flammable liquids such as the oil of a flame safety lamp will cease t
15、o burn when the oxygen content of the air is reduced to some 16 percent .flaming combustion of all kinds is extinguished at oxygen concentrations below 2 percent .however ,some materials may contain sufficient inherent oxygen for slow combustion to continue at wvenfurthen reduces levels of atmospher
16、ic oxygen .coupled tith the low values of thermal conductivity of crushed material ,this can result in “hot spots ”lying dormant in abandoned ateas for long perods of time ,but capable of re-ignition if a renwwed air supple is admitted suesequently . 1.2 Classification of mine fires Fires undergroun
17、d can be classified into two broad groups ,open and concealed fires.open fires occur in airways ,faces and other openings that form part of the active ventilation system of the mine and , hence, affedt the quality of the mine airflows quickly and directly .as the term might imply ,open fires are oft
18、en accompanied by flaming combustion because of the concealed firesoccur in areas that are difficult or impossible to access such as caved or abandoned zones. These are usually, but not necessarily ,initiated as a result of spontaneous combustion and can occur in both coal and sulphide ore minerals
19、as well as within any imported organic matter such as paper diacarded fabrics or timbering in abandoned areas. the degree to which concealed fires propagate and pollute the mine atmosphere depends upon the rate at which air lesks through the areas affected. the matter of spontaneous combustion is di
20、ancussed in further fetail in section 12.4 2. Causes od ignitions The variety of proceduies, processed and materials used in modern mining provides mang opportunities for the ignition of flammable materials .however ,the most commonly reported causes of fires and ecplosions in mines are lisred in th
21、e following subsectiongs. 2.1 Mechanized equipment Manchines intended for use underground should be designed to operstetith a high degree of safety in a harsh physical environment, and are subject to legal requirementsandconditiongs in most mining countries. it is no suiprise, therefore,thst the maj
22、ority of fires attributable to machines arise out of : Misuse Lack of proper maintenance Removal or bywpassing of safety features such as diagnostic devices, environment monitors or thermal trip switches and Running unattended for long periods of time Exhaust systems on diesel equipment should be fi
23、tted with scrubbers that nor only reduce airborne pollution ,but also provent the emission of incandescent particles. furthermore, hoses, transmission or brake fluids and a variety of components made from synthetic materials on modern diesels may be capable of producing toxic gased when ignited. all
24、vehicles or other diesel equipment should be fitted with on-board fire extinguishers . It is particularly importsnt that equipment which contains significant quantities of oil, such as large transformers or air compressors, shoule be safeguarded by thermal trips, pressure relief valves, and other de
25、vices necessary for automatic cut-off in the even of any abnormal codition. such devices should be subjected to routine testing and maintenance. wherever possible non-mobile equipment soule be located within enclosures with fire-resistant roof,floor and walls, and which are ventilated to a retuin ai
26、rway. Again ,fireextinguishers and ,preferably,an automatic fire suppression system should be bvailable within the chanber. In coal mines, the surroundings in adjacent airways should routinely be coated with stonedust. 2.2 Electrical apparatus In assttion to the general comments on mechanized equipm
27、ent made in the preceding suvsection,electrical gear can give rise to incendive hazards from aparking and overheating. awitchgear should be sited such that it is not affected by convergence or falls of roof .this is mosr liable to ovvur close to mneral winning arwas. fuithermore, start switches shou
28、le be protected against accidental operation glancing blows from falling debris or passing traffic. Electrical sub-stations and battery charging chambers should be equipped with non-aqueous fire extinguishers . Cables in airways should be hung in catenary fashion on cradles suspended from the roof.
29、they should be located such that they will not be convergence or the yielding of roof supports nor be impccted by vehicles.the insulation and type of sheathing must be suitable for the edectrical load and rigours of the under groungenvironmeng .all such cables shoule be inspected routinely for evide
30、nce of physical damage . Electrical failures should result in immediate isolation of the power by means of overload and earth leakage protective devices.in gassy mines ,all electrical motors and heavy urrent devices shoule be enclosed within flameproof casings so that any ignition of methane is contained within the equipment ,signaling or other light current apparatus should be certified as intrinsically safe,ie Incapable of producing sparks of sufficient energy to ignite a methane: air mixture.
