Mines and Bunkers Volume 10, Fire Safety Aspects of Polymeric Materials (1980) / Chapter Skim
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FIRE DYNAMICS AND SCENARIOS
FIRE DYNAMICS AND SCENARIOS
Pages 11-61
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From page 11... ...
As with other usefu l but potential l y dangerous an d destructive forces, it became i m perative that he learn to u se and control fire. Practica l solutions for many fi re situati ons were devel oped gradua l l y and empirica l l y, l argely on the basis of post-fire i nvestigation and without f u l l unde rstandi ng of the processes associated with ign ition, com bustion, fi re s pread, detection, and exti nguishment.
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From page 12... ...
I ncl uded may be i n formation on the general l ayout of the mine; the production rate ; the number of personnel em ployed per shift; the location of conveyors and vents; vent flow di rection and vol ume; the type and phys i ca l condition of the mining, transportation, and auxi l iary equ i pmen t em ployed ; mai ntenance records and housekeepi ng conditions (e.g., the accu m u l ation of coa l dust/oil mi xtu re on work ing mach inery ) ; and the location and condition of permanent and mova ble electric power distri bu tion l i nes, switch gear, and fai l u re protection equi pment.
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From page 13... ...
Thus, it is i m porta nt i n mine fire scenarios t o define the ty pe, concentrati on , a n d tem peratu re o f va rious fuels (or dust) and the ventilation air velocity ( ft./m i n .
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From page 14... ...
These combusti bles com prise electric insu l ation, hydra u l ic hoses, rubber veh i· cle tires, conveyor belts, venti l ation cloth or polyurethane foam used for tem porary or permanent seals, and structura l timber. The coal bed itself ( although not consid· ered as polymeric material )
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From page 15... ...
I n developing m ine fire scenarios i t is i mportant to note that the products o f smolder ing combustion are d ifferent from those of flaming com bustion and that a transi tion to flami ng combustion after a long smo l dering period m ay resu lt i n a rapidly spreading fi re because of the preheating of the fuels and the accum u l ation of com busti ble gases du ring smoldering. In addition, smol dering or deep-seated fi res are difficu l t to extinguish ( i .e., a gaseous extingu ish ing agent m ay exti ngu ish flam es but the residual charcoal may continue to bu rn by "glowing com bustion" and the flame mi ght rekindle after the extinguishant has dissi pated)
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From page 16... ...
Th is s ituation results i n i ncom plete com bustion and the production of highly tox ic gases and fu mes . Depen ding u pon the types of pol ymeric material present, the typica l products of i ncom plete combustion m ay i ncl ude carbon monoxide, hydrogen cyanide, n itrogen oxides, am monia, hydrogen sul fide, phosgene, and many other compounds .
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From page 17... ...
A consi deration of extingu ish ment tech n iques is beyond the scope of th is study, but it should be noted that the effectiveness of control and extin guishment efforts depen ds on the burn i ng characteristics of the polymeric materi als, the spread rate of the fi re , and the ti me l a pse between first ignition and detecti on . The accessi bi l ity of the fi re scene to firefighters and the time req u i red to reach the scene also a re factors to consider in mine fires.
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From page 18... ...
7. The possibi l i ty of smo l dering com bustion as a factor in the fire i ncident should be considered.
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From page 19... ...
2. Ign i tion Sou rce - What was the ignition source and for how l ong was it in contact with combusti ble material?
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From page 20... ...
Summary The fi re occu rred when a tra i l ing ca bl e short-circu ited on the reel of a cutt i ng machine at the face of the m ine. The nearest office of the U .
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From page 21... ...
It consisted of dry -chem ica l fire exti ngu ishers, water u nder pressu re with sufficient fire h ose to reach each working face, a nd roc k dust. Description When the fire occu rred, the cutting mach i ne had finished cu tting the face of an entry on the intake s i de of the working section , and the mach i ne operator's helper sumped the ba r of the mach i ne in the right ri b of the left crosscut.
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From page 22... ...
An i nvestigation was started immediately. The cause of the inci pient fire was determi ned to have been spontaneous com bustion ; there were no inju ries.
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From page 23... ...
Due to natu ral physica l conditions, the area was su bject to heavy bumps, heav ing, sloughage, and fractures in the bottom coal. F i refighti ng materi als consisting of portable fi refighti ng units, waterl ines, high· pressure rock-dusting mach i nes, and rock dust materials for construction of sea ls were ava i l able at the mine.
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From page 24... ...
The m i ne was opened by one slope and five shafts into the coal bed, wh ich averaged 84 i nches in thickness in the fi re a rea. The i mmediate roof consisted of wi l d coal, lami nated shale, and sandstone.
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From page 25... ...
He was able to reach and open a trol ley swi tch i n a crossover that was one of the power sou rces to the tro l ley wi re in the track leadi ng to the smoke-fi l led secti on. He then ran to a m i n e phone, noti fied mi ne officials and the crew in a nearby m i ne section and i nstructed a motorman to open the other trol ley switch that suppl ied power to the f i re area.
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From page 26... ...
Al most 26 months after the i n itial i nci dent, production was resumed in a l l but one of the active worki ngs of the m ine . Analysis The fi re most proba bly began when the end of the trol ley wire fe l l and came i n 26
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From page 27... ...
After removing the trol ley wire anchor bolt assembly, samples were col lected from the i nside of the hole and at the roof l i ne . The analyses of these samples i ndicated that the temperatu res had been h igher inside the hole th an at the roof l ine outside the hole.
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From page 28... ...
F i refighti ng equ i pment consisted of a 3Q-pou nd dry chem ical system on the m i n ing mach ine, dry-chemical fire exti ngu ishers on each mobi l e unit and at strate gic l ocations, and a hi gh-pressure rock-dusti ng mach i ne with ample quantities of rock dust. Description The fi re occurred when the min ing mach ine operator and a hel per completed u ndercutting the face of a working place and began tu rn ing the machine to start a crosscu t to the left.
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From page 29... ...
An hou r after the fire was detected compa ny officials ordered al l men except those attempti ng to control the fire out of the mi ne. The fi re was exti ngu ished com pletely with i n the next hour.
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From page 30... ...
They fou nd the wood door and the frame around the door on fire. This fi re was co n· trol led but not extingu ished using two 2Q-pou nd dry-chem ica l fire exti ngu ishers.
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From page 31... ...
Analysis of the scenario suggests that : 1 . Permanent stoppi ngs should be constructed of sol id, su bstantial, i ncom busti· ble material.
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From page 32... ...
Loadi ng of the bu rning material was started at three l ocations. The fire was considered total l y extingu ished when the fal len materi al was co mpletely removed 1 1 days after i nception of the fire.
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From page 33... ...
The fi re, wh ich was confined to the east approach, was exti ngu ished by flooding the bottom of the shaft with water. There were no i nju ries and no property damage.
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From page 34... ...
An explosi on of the d isti l l ate by- products from the burn i ng coal and other com busti bles i n the h igh-temperatu re, lean-a i r env ironment occu rred about an hour l ater, shortly after the main ventilating fan, wh ich had been stopped by a foreman for 1 5 to 20 m i n utes, was restarted. When the fire began two fo remen and five workmen were engaged in m isce l l ane ous work near the scene of the occu rrence and a foreman and two workmen were tram m i ng the continuous-min ing mach ine i nvolved in the fire.
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From page 35... ...
Ventilation was induced by an ax ial-flow ex haust fan insta l led on the su rface. Overcasts and permanent stopp ings were con structed of i ncom bustible material.
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From page 36... ...
One secti on foreman and two men were rock dusting in the west mains area ; another section foreman and th ree men were mov ing equ ipment in the north ma ins area. As the continuous mi ner approached the ju nction of west mains, after being moved some 4,000 feet towards its destination, the top of the traction pu m p drive of the mach i ne came i n contact with the energi zed trol ley and/or trolley feeder wi res.
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From page 37... ...
Duri ng the next seven days, the mov i ng out of the h ot material contin ued, and the roof and ri bs were supported by cross bars, posts, and n umerous roof bolts. Moving out of the hot m ateri al was completed 27 days afte r the fi re occu rred.
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From page 38... ...
It appears that th is fire occu rred when a continuous m i ner being trammed in the mine came in con tact with the energ i zed trol ley and/or trol ley feeder wires ; the resu lting short circu it caused i ntense arcing and fl ame that ignited the coal roof and ribs and hydrau l ic rubber belti ng used as insul ation. When the main fan was stopped, explosive gases accumul ated i n and arou nd the fi re zone; when the fan was restarted, some of the oxygen-en riched gases were moved i n to the fire area where they were ign ited.
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From page 39... ...
Summary The fire was discovered at a metal overcast along a bel t conveyor a bout 1 80 feet from the be lt conveyor drive. The fire was i nitiated when electrical arcing ign ited com bu st i ble materials.
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From page 40... ...
The fi re was exti ngu ished with the contents from two fire extingu ishers and fou r bags of rock dust, which we re obtai ned from the nearby bel t conveyor drive. Although the flame was completely extingu ished, additional wate r was applied for several hours to coo l the fire area.
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From page 41... ...
. Because com bustion occurs on ly i n the i mmed i ate vicini ty of the com bust i bl e materia l , considerable quantities of ox ygen can pass through the fire with out be ing consumed.
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From page 42... ...
I n the excess fue l section of the py rol ysis zone, the fumes are su fficiently hot to cause pyrolysis of the com busti ble material . The a bsence of oxygen w i l l , however, pre vent com bustion and the pyrolys i s products remain as excess fuel in the fumes.
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From page 43... ...
F I R E DYNAMICS A N D SC ENAR IOS Cooling Zone Preheating Zone Figure 2 Zones delltlloped by oxygen-rich fires (Greuer, 1973)
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From page 44... ...
Si nce for fuel rich fires the pyrol ysis zone has to have a certa i n length and considerable cool ing of the fu mes due to heat transfer to the walls occurs and since a consi derable temperatu re difference between combusti ble material and air m ust exist to faci l i tate heat transfer, the heat quantities needed to ign ite a fuel rich fi re are most probabl y much h igher than predicted . A burn ing rate of 40 l b/m in of m i neral oil ove r 1 0 m i n utes i n a venti l ation current of 22,000 ft 3 /m i n was about the m i n i m u m to start a fu.e l rich t i m ber fire.
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From page 45... ...
"How ever, the fire control l i ng mechani sms and the rel ati onsh i p of the dom inating para meters do not depend on the ty pe of com busti ble material so that the insights ga i ned from ti m be r fi res can be used for other fi res, too." The great number of fire ex peri ments conducted routinely by experimental m i nes a l l over the wo rl d usually aim at testi ng the inflammabi l ity or fire resistance of materials and equi pment used underground or at measu ring the efficiency of fire e x t i nguish ing devices . Si nce the fi res have usua l l y no opportu nity to deve lop fu l l y to an equ i l i bri u m state, the results obtai ned from these tests have l ittl e general val idity.
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From page 46... ...
For incomplete com bustion it m ust be corrected by su btracti n g the heat o f com bustion o f a n y u n burnt f u e l d u e t o l ack o f oxyge n or d issociatio n .
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From page 47... ...
Beh ind fuel-rich fi res the tem peratu res are much lower than the ad iabatic flame tem pe ratu res. The reasons for th is are the large heat transfer from the fl a mes to the wal l s of the airway .
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From page 48... ...
3.3.2.1 Steady State Heat Exchange with A irway Walls The assumption of an infinite heat capacity of the rock surrou nding an ai rway l eads to constant rock temperatu res and to a steady heat exchange process between air and rock. If the rock, before exposu re to the fu mes with the temperatu re t, h ad assu med t h e average tem peratu re t o f the venti l ating air, the heat transfer d from the fu mes to the rock can be descri bed by : whe re a = heat transfer coefficient p = peri meter of ai rway L = length of a i rway Th is w i l l cause a change of tem peratu re in the fumes by : 48
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From page 49... ...
Due to the i mportance of accu rate tem perature precalcu l ations in deeper m ines with cl imatic difficul ties, many attempts at the calcu l ation of the non-steady state heat exch ange between ai r and rock have been made. Within the scope of th is report it is imposs i ble to quote every single paper wh ich ex ists on th is topic.
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From page 50... ...
2 aT ar r ar Under the add itional assumptions : the origi nal rock tem perature remains p re· served at a sufficient distance fro m the airway ; the wal l temperature equals th e a i r tem peratu re ( heat transfer coeff.
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From page 51... ...
Heat transfe r radi ation is, therefore , neglected u nder ord i nary venti l ation conditions with few exceptions by venti lation engi neers. Polar, un· sym metric molecu l es, such as C0 2 , H 2 0, CO, S0 2 and many hyd rocarbons can enter i n to th ermal rad iation exch ange appreciably at the tem pe ratu res encountered in m i n e fires.
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From page 52... ...
With i n a venti lation system a can u ndergo considera bl e ch anges. This has the consequence that equal e nergy qu antities must someti mes be expressed by consider a bl y d i fferent pressu res, a fact wh ich comp l i cates the appl ication of energy bal ances.
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From page 53... ...
The natu ral draft expressed as energy per unit weight of air is cal led the natural venti l ation head h N and its magn i tude is consequently : N atu ral draft is always tied to a cycl ic process, to a l oop . State ments on natural draft without specifying the loop where it is devel oped are not too meani ngfu l .
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From page 54... ...
If enough com bustible material is present, the i ncreased oxygen supply wi l l then i ntensify the fire so that considera ble natural d rafts are fina l l y deve l oped. The in crease in a i rflow in the a i rway at fire is accompan ied by a decrease i n parallel airways.
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From page 55... ...
Except for the case of l i mi ted natural drafts due to smal l elevation ch anges beh ind the fi re and a lack of com busti ble material or for the case of very h igh origi nal venti lating pressu res, one can ex pect a violent fl uctuati on of the airflow i n desce n sional l y venti l ated ai rways on fire . Whether a perma nent airflow reversal takes pl ace depends on seve ral factors .
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From page 56... ...
They shou l d conta i n the main features of the venti l ation system , without confus i ng deta i l s and the sign i ficant venti l ation data. The former shou l d com prise the ai rways, location of fans, venti l ation doors, regul ators, seals and dams, ventila tion cu rtains and ducts, crossings, explosion barriers, produ ction wo rki ngs, trol ley and D iesel haul age roads.
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From page 57... ...
They are, however, gai n ing i ncreas i ng popu larity in other cou ntries as the basis of emergency plans, too, si nce they are especially suited to detect possi ble i nstabi l i ties in venti lation systems. To judge the influence of several pressu re sou rces i n a venti l ation network on the stabi l ity of the a i rfl ow i n se lected ai rways qual itatively and, as fa r as possi ble, quantitati ve l y the Po l ish engi neer B udryk su ggested the use of a so-ca l l ed "closed 57
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From page 58... ...
Si nce they indicate the stabil ity and economy of ex isti ng a i rflow as wel l as the di rection of potenti al airflow, thei r use h as become very popu lar with venti lation engi neers. According to the above def i n i tion of heads and pressu res, m i ne venti l ating heads h M v are energy d i ffe rences per u n i t weight and mine venti l ation pressu res P M V per u n i t vol ume of air.
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From page 59... ...
Network calcul ations for the vicin ity of the fire are usua l l y based on p ressu res, si nce the specific wei ght of the air in a l i m i ted area, except for the changes caused by the fi re itself, rema i ns fai rl y constant. As pointed out above, it m a kes no d i fference in principle if venti lation calcul ations are based on energies per unit weight (heads )
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From page 60... ...
l aye rs and fire spread u nde r a wide range of venti l aton conditions and duct i ncl i nation angles. Conclusion: Coal dust fi res, although mo re frequent and h av i ng l ower ign ition temperatu res than ti mber fires, have not been stu died, proba bly because of the i r l ow propagation rate.
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From page 61... ...
Woropajew, A F., Discussion of a Self-Produced Airflow Reversal When a Mine Fire Starts.
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