Mines and Bunkers: Volume 10, Fire Safety Aspects of Polymeric Materials (1980)

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CHAPTE R 5 D ESIGN CRITE RIA IN MINE SAF E TY AND HAZARD CONTROL 5. 1 I ntroduction (Secretary of the I nterior, 1 974 ; Nagy and Hall 1 974; Chai ken and Burgess 1 977 ; and Mitchell and Verakis, 1 975. ) Resources extracted from the earth by mi ning have long been essential to man­ ki nd. M i n i ng, even in i ts cru dest form, provided materials for implements, weapons, jewe l ry, and coi ns. As societies grew m ore soph isticated and complex, the products of m i n i ng became even more i mportant and contri buted i m m easu rably to the devel­ opment of systems for transportation, communications, electric power generati on, heati ng, constructi on, industri al production, defense , and agricu ltu re. M i n i ng today is a l arge-scale i ndustrial activity i nvolv ing the u se of heavy elec­ tric- powered machi ne ry ( i.e., soph isticated h igh-productivity m i n i ng mach i nes, ex­ tensive rol l i ng and conveying transportation equi pment, hoists, and large venti l atio n systems ). Al l of th is factory- l i ke activ ity , however, occurs in a h igh ly hosti l e en­ v i ronment. Su rface mines are su bject to fal l s and other dangers, but u ndergrou nd mines are more hazardous. Access and egress routes m ust be excavated and main­ tai ned in a structu ra l l y safe condition ; electricity m ust be conducted i nto th e m ines to power lights and a l l production and transportation equi pment; artifi cial venti l a­ tion must be mai ntained to prov ide suffic ient oxygen for personnel and, often, to d i l ute tox ic gases and combusti ble dust and gas ; and structural integri ty must be mai ntained to prevent col l apse, to seal wa l ls aga inst abrasion, and to prevent water or gas seepage into the m i nes. The layou t of a mine, u n l i ke any other in dustri al fac i l ity . changes conti nuously as mine development (i.e., production) progresses. This requ i res th at power lines be extended, venti l ati on systems altered, and critical materials and suppl ies be rel ocat­ ed; it requ i res a conti nual lengthening of access, egress, and transportation routes. In additio n, exh austed mine areas, wh ich represent potential reservoirs for water or gas accumul ation as we l l as alternate escape or venti l ation routes, are su bject to structural fai l u res and must be maintained. Advanced design criteria are needed to el i m i n ate or reduce the hazards in m i nes, and the development of such criteria is the su bject of th is chapter. ( Efforts to control m i ne safety and hazards through legislation are descri bed in Appendix B . ) 5. 2 Approaches to Design Criteria Development The trad itional approach to mine safety and hazard control has been frag- 88 

D ES I G N CR ITER I A I N M I N E SAF ETY A N D HAZA R D CO NTR O L mented. A s h azards were discovered du ring post-fire o r ex plosion investigations, the proble ms were corrected, but little thought was given to the i nteracti on between the elements ( i.e., each material and each piece of production and transportation• equ i pment used in a mine was considered as a separate fi re or safety h azard ) . A m ore soph isticated method for dea l i ng with m i n e safety a n d hazard control i s the systems approach. When applying th is approach , the enti re min i ng operation i ncl u d i n g al l equi pment used is considered to be one system. The effect of each component on the whole syste m is exami ned and alte rnate pieces of equ i pment or materials are evaluated on the same basis. One way of uti l izing the systems approach is to devel op fire scenarios l i ke those descri bed in Chapter 3 to examine the effect of the incident on the whole system and to assess the probable impact of alternate materials or equi pment on the development and outcome of the incident. The decision tree descri bed by R ou x ( 1 97 7 ) i s a valuable t oo l for appl ying the systems approach a s i s com puter model­ i ng, wh ich permits rapid eva luation of a great number of alternates. To uti l i ze th e systems approach in developing new design criteria for m ines, the contents of the mine syste m must be considered in rel ation to fi re processes, and the mine system may be viewed as consisti ng of : 1 . Fuels - gases and dust ; structu ral l u m ber or other materi als ; com busti ble com ponents of production equ ipment, conveyor systems, transportation equi pment, condu its, electrical distr i bu tion systems, and venti l ation systems ( i ncluding insulation materials, hydrau l i c h oses and flu id, conveyor belts, venti l ation cloth, etc. ) ; sealants, stop pings, and barrier materials; wal l su rfaces and mine products ; materi als and equ i pment worn or carried by personne l ; a n d stored mate rials and su ppl i es. 2. I gnition sou rces - sou rces of spontaneous ign ition ; potential sou rces of arcs and sparks in ·an employed equ i pment; potential sou rces of electrical over­ heati ng in equipment; potential sou rces of mech anical (frictiona l ) overheating in equi pment; and appl ied sou rces of fl ame or arc (welding, brazing, smoking, etc. ) . 3 . F i re propagation poten tial - m i ne l ayout and natural drafts ; venti l ation effect; forced drafts and the i r routi ng and ava i l able alternates; air velocity and qua l ity, effect of potential fire on combusti ble gas devel opment; modification of draft effects and air qual ity considering ava i l able fuels and thei r locatio n ; ava i l able alternates for venti l ation rou ti ng and air velocity a n d its effect on fire p rop agation ; potential effect of fi re on structu ral integrity and col l apse potential ; and effect of structu ral modification on fire propagation (evolution of combusti ble gases alteration of draft effects, and accessi bil ity for vent modification ). 4. F i re detection and suppression systems - num ber, qual ity, and l ocation of portable and permanent (loca l and remote) fire detection sensors (tem pera­ ture probes, gas analyzers, particul ate detectors, etc. ) ; num ber, qua l i ty, and 89 

MI N E S A N D B U N K E R S l ocation of fi re su ppression devices, equi pment, and materials ( i nsta l led on face cutter, trans portation equipment, spri n kl ers, portable and stationery equ i pment, rock dust pi les, etc. ) ; n u m ber, avai labil ity, and quality of trained firefigh ti n g personnel, mai ntenance crew members, and miners ; extent and qual ity of commun icatio ns systems; extent and qual i ty of fi re disaster plans and models; and avail abi l ity and qual i ty of enforcing authority. The complete appl ication of the systems approach in developing design criteri a that provide for mine safety and hazard contro l requi res a greater understanding of fire dyna mics and rel ated processes than is possi ble today. For example, the sea· worthi ness of a damaged ship can be ascertai ned quickly, and the effect of correc· tive actions (e.g., flooding selected compartments) can be i nvestigated rapidly using a scale model. Si m i larly, alternative mine venti l ation patterns for use duri n g a fi re cou l d be i nvestigated using mathematical and com puteri zed models, but several of the input para meters h ave not yet been established. One- and two-d imensi on a l models o f venti l ation-th rottling developing in a m i n e fi re situation h ave been used and they provide a valuable starti ng poi nt. However, it appears that a fu l l thre e­ di mensional mode l is requi red and the deve lop ment of such a model wi l l be ex­ tremely compl icated, difficu lt, and ex pensive. Severa l aspects of fire propagatio n mechanisms also are poorly understood. The most reasonable way of investigating these areas appears to be th rough ex perimentation at various scales. Such programs now are under way, but scal i ng factors have not yet been establ ished to provi de even empi rical means of approx i mation . These research programs also are expensive and fu rther work is needed. Thus, although the objectives of m i ne design criteria h ave been brought into focus and the approach to criteria development is wel l de l i neated, the means to ach ieve the goa l s are not yet avai l a ble. The fol l owing d iscussion does not pretend to be all i ncl usive but rather attempts to present a broad overv iew of the state of the art and of recent developments in the most i mportant areas of mine safety h azard control. Considered are fuels; ign ition sources; and fi re detection, ignition quench­ i ng, and composite syste ms. Some topics are discussed i n greater detai l than others primari ly for pu rposes of i l l ustration. 5.3 Belt Conveyors (Diamond, 1 960; N utter, 1 977 ; Harstein and Forshey, 1 976; K uchla, 1 978) The belt conveyor was i ntroduced as a means of undergrou nd mine transport a­ tion in G reat Brita in at the tu rn of the centu ry and was adopted by the U.S. coa l m i n i ng industry in the early 1 920's. Initially considered to be a n ex perimental curiosity, the device ga i ned popu l a rity rapidly because of the cost savi ngs an d improved operational efficiency its use made possible. Bel ts, however, can cause ignition and contri bute to fire spread. They are made of com bu sti ble pol ymeric materi als and their drive system tends to overheat whe n mechan ica l com ponents malfu nction. Belt conveyors are insta l led along re lative l y 90 

D ES I G N CRITER I A I N M I N E SAF ETY A N D H AZARD CONTRO L l ong hori zontal distances and often on the air i nta ke s i de of ventilation syste ms. Belt conveyors are used extensively today in m i nes a l l over the world, and it is esti mated that 24 m i l l i on linear feet of belting was in service i n 1 977 i n U.S. u ndergrou nd coal m i nes al one. Statistics show th at between 1 952 and 1 969 at least 1 5 percent ( 1 34 out of 877 ) of reported coal m ine fi res i n the United States were attri bu table to conveyor belt igniti on , and 70 percent of these belt fires were caused by frictional heating (e.g., involving a stuck rol ler or snarled belt in the belt drive assembly). E xtensive efforts have been made to prov ide safer belt convey i n g system s : i n­ depth i nvestigations have been conducted to defi ne the problems; f i re-resistant belting has been developed ; sma l l - and large-scale com bustion experi ments have been performed ; and a l arge nu mber of safety regu l ations have bee n establ ished. These efforts have resulted i n a drastic reduction i n belt fi res ( i .e., to an average of l ess than two per year between 1 970 and 1 977), but the i ncreasing use of these systems and the potenti al fi re and tox ic hazard d ictate that add itional devel opment work be undertaken. Particul arly needed are i mproved flammabi l i ty and flame spread tests, an evaluation of the toxicity of belt com bustion products, and im­ proved fire detection and su ppression systems. 5. 3. 1 Description Conveyor belts genera l l y consist of three elements : a top or conveyi ng cover, a carcass, and a bottom or pul ley cover. The carcass is usu a l l y a texti le fa bri c woven of one or a combi nation of the fol l owing: cotton, glass, asbe�tos, nylon, polyester, rayon, other fi ber yams, and wire cords or cable (usually brass- or zinc-coated steel ) . The top and bottom covers usual l y a re made of thermosetti ng or thermo­ plastic el astomer, which also is used to bi nd together the vari ous com ponents of the belt carcass (e.g., the pl ies or layers of fabric and/or cords of natural or sy nthetic f i be rs and steel ) . A fi ber o r yarn i s selected for use i n a texti l e cord on the basis o f i ts physical properties ( i.e., strength, elongation, agi ng, dy namic fatigue resi stance, adh esion characteristics, mi l dew resistance, heat resistance, and other properties) . I n fabrica­ tion, very smal l fi bers are twisted together to form "singles," two or more "singles " are twisted together to form "plies ", and two or more "plies" form a "cable". Synthetic yarns are produced by extrusion or by s litting extruded or blown fi l m . Yarn s i zes are denoted by nu m bers ( Han k ) i n the American system depending o n the material ( i.e., cotton, asbestos, gl ass, etc . ) . Continuou s f i l ament synthetic fi bers a re measured by "den iers" (grams per 9000 meters of yarn ) or by the new, u n iver­ sal "tex num ber" (gra ms per 1 000 mete rs of yarn ) . Fabric is woven from warp yams, which ru n lengthwise, and fi l l ing yarns, which run crosswise. The properties of the fabri c depend upon its co nstruction, the m a­ terial from wh ich it was ma de, and the ty pe of weave. The most com mon weaving patterns are p l a i n, twist, basket, and leno. Modifications of these weave patterns are 91 

M I NES A N D BU N K ER S produced by using a warp yarn that is stronger than the fil l i ng yarn. Fabrics made in this way often are used for the belt carcass and i nclude the woven cord, sol i d woven, a n d straight warp weave. Materials used for the top and bottom cover of mine conveyor belting are SB R ru bber, neoprene ru bber, and PVC. The manufacturi ng methods used for ru bber belting are more complex and expensive th an those used for PVC belting. Many types of ru bber are available and they can be blended and mixed with various chemicals to produce requ i red physical properties. They are com pou nded, pre­ formed i nto sheets, and cu red (chemica l l y cross-l i n ked ) on fl at or rotary presses. PVC belti ng is made essentia l l y of PVC homopolymer and a phthal ate ester or other plastici zer. Manufactu ri ng methods consist of re l atively simple co ntinuous coating operations. It is genera l l y conceded that ru bber belting is more abrasion resistant than the PVC type (especial l y to mixtures with a high rock content) ; however, total l ife cost and initial cost may be traded off between the two types. A recent investigation ( Hartstein and Forshey 1 976) reports that SB R ru bber belting exhi bits good fl ame resistance and is less hazardous than neoprene or PVC belting i n terms of tox ic co mbustion products. Manufactu rers of PVC belting ( N utter 1 977), on the other hand contend th at : ( 1 ) thermoplastic PVC belt wil l melt and separate when ex posed to excessive frictional heat (thus preventing it from acti ng as a sou rce of i gn ition), ( 2 ) PVC is i nh erently flame resistant, and (3} properly chosen formu l ations of PVC with flame-retardant additive wil l m i n i m ize the spread of an exte rnally produced fire and the formation of hydrogen ch l oride vapor. Most U. S. coa l companies use a combination of PVC and ru bber belting with ru bber be ing used more on the main l i nes and PVC, on panel and butt entries. According to Nutter ( 1 977), approx i mately 8 m i l l ion of the 24 m i l l ion l inear feet of belting in use in un dergrou nd coa l mines is the PVC type. 5.3. 2 History of Hazard Control Fol l owing Worl d War I I , rubber conveyor belts gained rapid acceptance in British coal mi nes because of their contri bution to i mproved operation efficiency . I n Sep­ tem ber 1 950, however, a disastrous fi re occurred in the Creswel l Col l iery i n E ng­ l and and 80 men l ost thei r lives. Th is disaster was caused by a sta l led ru bber be l t that ignited a n d helped t h e fire t o spread a t speeds esti mated a t 1 00 yards per hour. Fol l owing th is disaster, the Nationa l Coal Board di rected a l l belt manufacturers in G reat Britai n to proceed i mmediately with the development and production of a fi re-resistant belt. The National Coal Boa rd also establ ished specifications for the acceptance of fi re-res istant conveyor belting, and these included a mandatory drum friction test. Th is test, as currently used i n E ngland , is more severe than the Inte r­ national Stan da rds Organi zati�n ( I SO) or the Eu ropean standard drum friction test. The U. S. Bureau of Mi nes, in response to the Creswel l incident, also established a set of requ i rements, desi gnated Schedu le 28, under which conveyor belts h av e 92 

D E S I G N C R I T E R I A I N M I N E SAF ETY A N D H AZA R D CONTROL been qual ified for use since November 1 955. Two tests are requi red - one to measu re flame propagation an d the other, ignition. A drum friction test to qual ify belts for use in underground mines has not yet been adopted in the U n ited States in spite of the overseas ex perience and recom mendations of PVC belt manufactu rers. Early British work to devel op fi re-resistant belting involved treating the duck to render it fireproof or fi re resista nt and substituti ng a fi re-resista nt materi al (e.g., neoprene or PVC) for the rubber in the belt. Si nce the chemicals used to fi reproof the fabric adversely affected the properties of the carcass, efforts were concentrated on finding the proper fi re-resistant materi a l for the belti n g itself. Neoprene was not manufactured in England and was considerably more expensive than PVC; there­ fore, the latter material was preferred and was the fi rst to be approved for use in coal mi nes operated by the National Coal Board. The same type of PVC belting, wh ich was su pported by a nylon woven carcass, was introduced in U.S. m ines in the m i d- 1 950's. Early samples appeared to be fli msy and rapidly developed "edge wea r" , but they also ex hi bited good abrasion resistance and oth er advantages in actual use. The neoprene belting then avai l able exh i bi ted poor adhesion of cover to fabric, developed considerable gouging and stripping, and was significantl y more ex­ pensive. Si nce the 1 950's healthy competition has developed between manufacturers of rubber and PVC conveyor belts and has resu lted in great improvements in belt properties, price, and fire safety. Th is competiti on is sti mul ated both by the ever· expanding market and by the increasing stri ngency of govern ment regu l ations. The nu m ber of belt-related mine fires h as been reduced drastical l y in the Un ited States duri ng the past two decades. This is attri buted to the devel opment and use of fl ame-resistant belti ng, as specified by state and federal regu l ations, and other belt· rel ated di rectives. In Engl and, there has been no reported belt ign itions due to frictional heat bui l du p since PVC belts were introduced. 5.3.3 Current Research and Future Trends Current and projected efforts to i mprove conveyor belt syste m desi gn criteria a re focused on advancing understanding of the basic fire processes ( i nclud ing ge nera· tion of toxic gases ) ; developing i mproved tests of flammabi l ity, flame spread , and frictional heati ng behavior, and design ing sophisticated detection an d suppression systems. 5. 3.4 Fire Tests The Federal Schedule 28 test designated to determ i ne the fi re resistance of coal mine conveyor belts is considered of questionable rel iabi l ity. This test is performed on a sma l l sample ign ited in a ch amber with a B unsen burner and th e durati on of com bustion is noted at a single, fixed air vel ocity. Recent larger scale experi ments i nd i cate that the resu l ts of this test are not sufficientl y conservative since frictional h eating behavio r and tox icity of evo lved gases are not considered. The U.S. Bureau 93 

MI NES A N D B U N K E R S of Mi nes is conducti ng in-house and contracted experi mental programs to ascertai n the facts. I n one investigation ( Ha rstein and F orshey 1 976), the thermal ox idative decom­ position products of the basic belt materials and some of their pu re i ngredients were analysed in great deta i l . These data prov i de a valuable starti ng poi nt, but a greater number of samples an d pure ingredients must be assessed u nder a much greater variety of conditions (temperatu re , air ve locity , oxygen content, etc.). Such work is now in progress. Med i u m- and large-scale laboratory fi re test programs have been and are being conducted to study the behavior of conveyor belt systems. Belts made of SB R ru bber, neoprene, PVC, and natural ru bber compounds in com bination with nylon, rayon, and cotton carcass material have been tested for flammabi l ity using various intensities and sources of ignition and ai r velocity conditions. The abi l i ty to sustain fl ame propagation and the effects of preheati ng, belt width, and coal dust­ grease accu m u lations a lso h ave been evaluated. F u l l -scale fi re tests have confi rmed some of the l aboratory-scal e resu lts and trends, and the inadequacy of the existing fi re retardancy acceptance test h as been demonstrated fu rther. In these experiments, temperatu re profile versus duct length and time from ign i tion were studied to shed further light on fi re-related phenome­ na. In 1 978, experi me nts were un der way usi ng fu l l -scale "fire test ga l leries" having vari ous configu rations and slo pes, and belts were being tested under various mine fire conditions by varying belt width , air velocity, bu rning angle, preheati ng ti me, i gnition heat flux, and coa l dust-grease accu m u l ation . Belt fire resistance is deter­ mi ned from measure ments of flame spread rate , propagation distance, gal l ery tem­ peratu re, and the heat flux at various sections. The results of these tests wil l be used to develop a more re l i a bl e and mean i ngfu l l aboratory-scale fire-retardance test method that incl u des a quantitative rating system. The fu l l -scale tests also are uti l i zed to assess the tox ic gas formation characteristics of the various belt m ateri­ als. These resu lts wi l l be compared with the laboratory -scal e oxidative thermal decomposition stud ies mentioned above. I n itial results of the gal lery tests indicate that the most important vari ables are air venti lation rate, i gn ition heat flux, and distance between the belt and the roof of the simulated mine entry. This in formation is being used to design the prototype of a l a boratory-scale fire-resistance test for conveyor belts. 5.3.5 Fire Warning Systems Existi ng regu l ations require that a fi re se nsor system be insta l led at each coal mine belt conveyor to stop the belt drive and activate alarm s when a belt fi re occurs. The sensitivity, response, and durabi l ity of the various ty pes of sensor and opti mum sensor spacing have been of concern i n the past. In a recent comparison of the vari ous se nsors and thei r characteristics, it was 94 

D ES I G N C R I T E R I A I N M I N E SAF ETY A N D HAZA R D CO NTRO L fou nd that the thermal point and thermal conti nuous types are most suitable for mine conveyor belt appl ications. They ex h i bited adequate sensitivity for earl y de­ tection and sufficient durabi l ity for the environment and rel ativel y econom ical. Res ponse time, te mperature ran ge setting, and recommended spacing also were esta bl ished Com bustion detectors (photo-electric and ioni zation types) are high ly sensitive, but they are not rel i a bl e in dust-laden air. They also are suscepti ble to false activa­ tion by com bustion products origin ating in areas other than belt h au l ageways. The same l i mi tation appl ies to carbon monoxide detectors. Optical type detectors ( U V and I R ) a lso are sensitive, but the ir effective range i s l i mited and sensitivity to extraneous l i ght sources presents additi onal problems. F utu re developments in th is area, aside from technical refinement of th e instru­ ments, must be directed toward the systems approach to design. For exam ple, the conti nuous monitori ng of the enti re mine with a "tu be bundle" detection system wil l al l ow measure me nt of the differential of ai r qual i ty between belt haul ageways and su rrounding areas; therefore, the use of the more sensitive com bustion detec­ tors eventual ly may be preferred for this advanced design configu ration. 5.3.6 Suppression of Conveyor Belt Fires Ex isti n g regu l ations requ ire that automatic fi re exti nguish ing systems (spri n kler or deluge ty pe) be installed at coal mine belt conveyor drives in accordance with specified belt areas and water flow rates an d suppl ies. Provisions are made for use of alte rnative foam or dry powder chemical systems, including specifications for such systems. The gal l e ry experi ments descri bed above were u ti l i zed to eva l u ate the efficiency of the various suppression and detection systems in a simul ated belt hau l ageway with various belts and u nder a variety of fi re conditions. The adequacy of pertinent regul ations a lso was assessed, Automatic water spri nklers wi th self-contai ned actuaters were found to be re­ l iable and economical and to requ i re l ittle maintenance. The i m portance of spri n k­ ler spaci ng was determi ned a nd the effects of water pressu re, detecti on tem pera­ ture, and spray de nsity were eva luated. The pri mary disadvantage of such spri n kler systems is thei r fai lure when the contents freeze - a possi ble conti ngency near th e earth's su rface. H i gh expansion foam syste ms provide rapid fire su ppress ion with low water requirements but mai ntenance requi rements were h i gh, del ivery rates were slow, and gaps deve loped at the hau l ageway roof because of venti lation effects. The foam systems a lso are prone to fa i l u re at freezing te mperatu res. F i re su ppression syste ms employ i ng mu lti purpose dry powder chemicals worked rapidly, requ i red a rel atively sma l l amount of chemical, and operated at low tem­ peratu res. The disadvantages of such syste ms are that individual design is requ i red to provide proper powder dispersion , mai ntenance requ i rements are high , and cool­ ing capacity is smal l (creating the potential for re-ign iti on ) . 95 

M I NES A N D B U N K ER S The i n i ti a l resu l ts of these tests confirmed the adequacy of ex isti ng regul ations and provided additional knowledge conce rn i ng the operation and applications of the various systems. A more comprehensive conclusion concern ing what methods to use in particu l a r situations and h ow to integrate these in an overa l l system design remains to be developed. 5.4 Wire and Cable I nsulation (Taylor 1 977) In mine fires, wi re and ca ble insul ation frequently h as been the fi rst materi al i gn ited by such sources as an overheated conductor or electric spark . The bu rn i n g i nsulation often ignited secondary fuels, smoke a n d tox ic fum es were generated as it decomposed, and the conductor was ex posed in an un insulated form . Exam ina­ tion of wire and ca ble insu l ation as a potential fi re, fu me, and toxic h azard is therefore an important design conside ration. Although wi re i nsu lation fi res have l ong been of concern to the mining industry, un iform criteri a and test methods have been lacki ng. A progra m recently initiated by the Department of Transportati on (Taylor 1 977) is aimed at establish i ng criteria for test methods ; developing standard tests for flamm abi l ity, smoke emiss ion, toxicity, and integrity ; and applying these tests to wire and cable insulating materials presently in use and to the newer polymeric materi als being proposed. Althou gh this study is be i ng conducted pri mari l y for th e rapid transit i ndustry, i ts resu lts should prov i de val uable data to the mining indus­ try, as wel l as all others, si n ce ra pid transit tu nnel and mine requ i rements for electrical power and large equ ipment in confined spaces are very si m i l ar. The re­ sults, however, wi l l h ave a low probabi l ity of appl ication to trail i ng ca bles, which are reported to ran k h i gh among causes of mine fi res. The i ntermediate resu lts and conclusions of th is progra m are presented below. 5.4. 1 Test Program I n July 1 976, the Department of Transportation ( DOT) awarded a contract for the study of electrical insul ation. The stated o bjective of th is contract is : to determine whether any of the cu rrently used electrical insu lations can provide a fire safe environ ment i n terms of very low flame propaga­ tion, s mo ke and toxic gas evol ution . . . and determ ine whether any of these can meet criteri a wh ich wi l l be establ ished by taking into account the fi re hazards i nherent in transit systems. This study is di rectly appli­ cabl e to wire insulation used i n mines. Although the portion of the ( DOT) study dealing with test method development is outside the scope of this chapter, it shou l d be mentioned that criteria were developed for the desired test methods and that all existi ng test procedures were eva l uated Some test procedures were m od ified or new ones developed as needed to provide meaningfu l standard tests for flam mabil ity , smoke emission, ci rcu it i ntegri­ ty, and toxicity of wi re and cable insul ation materials. 96 

D E S I G N CR I T E R I A I N M I N E SAF ETY A N D HAZAR D CONTRO L Sam ples of the various insul ation materi als and wire and cable constructions then were obtai ned from suppliers and su bjected to the newly devel oped standard tests. When the committee received a report on the program (Taylor 1 977), it was not complete, but i nteri m resu l ts ����e re avai l a ble and prel i m inary concl usi ons were offered by the program manager (exce pt for smal l an i mal tox icity which was n ot com plete ) . 5.4.2 Test Results The fol lowi n g materials and constructions were su bjected to the test program : Single Wires (74 to tal samples) Poly (ethylene-chlorotrifluoroethylene) ( Ha lar®) ( E-CT F E ) Pol y i m i de ( K apton®) Mica Sil icone R u bber Pol y (fluorinated Ethylene-propylene ) (Tefl on®) ( F EP) Pol y-tetrafluoroethylene ( Tefl on®) ( PT F E ) Poly (ethylene-tetraflu oroethylne) (Tefzel®) ( ETF E ) X L Polyethy lene ( P E) X L Polyolefi n X L Pol yv i nylch l oride (PVC) Braids G l ass Nomex® Multiconductor Cables Kapton® (twisted, no jacket) Polyol efi n /pol yolefin jacket Si l i cone ru bber/s i l i cone ru bber jacket Teflon®/Tefl on® jacket Tefzei®/Tefzel® jacket Tefzei®/Shield/Tefzel® jacket The flammabil ity tests i n dicated that : 1 . The selected test method is capable of providi ng repeatable test resu lts. 2. The selected test method is capable of prov iding sufficient i nformation to categorize the behav ior of vari ous insu l ation m aterials and constructions when exposed to fire. 3. The selected test method is capable of providing sufficient informatio n to determ ine which materi als and constructi ons provi de a fi re safe environ ment i n terms of flamm abi l ity and to ran k these materials and constructions ac­ cordi ngly, 4. Overa l l , s i l icone ru bber and pol y i m i de ( Kapton®) insul ati ons perform best, and the performance of the basic insulation can be i mproved by constructi on features such as braids and jackets. 97 

M I N ES A N D B U N K E R S The smoke emission tests revealed that: 1 . The National Bureau of Standards ( N BS) cham ber method is a viable approach to testing electrical wire and cable i nsu lation materi als. 2. I t wil l be possi ble to use the test resu lts to categori ze the smoke em ission characteristics of the candidate insulation. 3. I t wil l be possi ble to use the test resu lts to ran k the materials and constru e· tions in terms of thei r abi l ity to provide a fi re safe environment in terms of smo ke emission. 4. I t wi l l be possi ble to use the test resu lts to develop standard length versus AWG s ize for wi re and cable testing and to esta bl ish rea l istic acceptance criteria with respect to what is ava i l able. 5. The Teflon®, Kapton®, and m ica insul ati ons have the l owest smoke em ission. As can be ex pected, any constructions that add other materials to the basic materi al decrease smo ke emiss i on perfo rmance (e.g,, Kapton® alone performs better than Kapton® with Nomex® braid). The ci rcu it integrity tests indicated that : 1 . The B I W test ( B I W test = Boston I nsulated Wire test. Detai ls are ava i l able from Boston I nsul ated Wi re and Ca ble Co., 65 Bay St., Boston, Mass. 021 25 or in the cited article), is a practical test for measu ring the integrity of single-wi re insul ation during and after exposure to fl ame. 2. I t wil l be possi ble to use the test resu lts to categori ze and ran k insu l ation materials and constructions with respect to thei r abil i ty to provide a fire safe env i ron ment in terms of circu it integrity. 3. For single wi res, sil icone ru bber provi des the best circuit integrity when ex­ posed to a fi re. Due to the interi m nature of the test data, it was not poss i bl e to ran k the i nsu lations with respect to their abi l ity to present a fire safe envi ronment. I t is i ntended, however, that this ran king wi l l be done fo r each of the fou r tests of i nterest ( i .e., fl a mmabi l i ty, smoke emission , tox ic gas eva luation, and circu it integri­ ty). It also is intended that some method wil l be derived to develop a combined hazard index for the insul ati ons an d constructions that wi l l incorporate al l fou r characteristics. The study contractor appea rs to recogn i ze th at, alth ough flammabil­ ity, smoke emission, and tox ic gas evol ution are very i mportant factors i n the selecti on of the insul tion material for electric wire and cable for use i n rapid transit veh icles, they must be put i n perspective with other i mportant characte ristics such as abrasion resistance, resistance to con tamin ants and fluids, instal l ation flex i bi l ity , abi l ity to strip for termi nation, abil ity to su rvive mechan ical stress and elongati o n , smal l be n d radi us, l ong l ife, a n d good el ectrical properties (e.g,, h igh insu l atio n resistance and h i gh dielectric withstand voltage) . The insul ation materials a n d constru ctions therefore also wi l l be ran ked i n terms of these cha racteristics. By establish ing th is fu rther ran king, it is postu lated that th e i nformati on made available to the rapi d transit system desi gner will be i n the most 98 

D ES I G N CR ITER I A I N M I N E SAF ETY A N D HAZARD CONTRO L usable form. The mine operator also can use this information. Based on the interi m data, the fol l owi ng pre l i minary concl usions were drawn : 1 . Standard test methods and gu i de l i nes for electrical wire and cable insu lations are needed. 2. The resu l ts of this program wil l be a significant step towards fu lfi l l i ng the above need. 3. It has been poss ible to develop simple, inexpensive, repeata ble tests to meas­ u re the flammabi l ity and critical circu it integrity characteristics of wire and cable. 4, The stu dy wi l l not be complete until the toxicity tests are completed. 5, It appears that there are insulations and constructions presently avai lable that can provi de a fire safe envi ron ment in terms of flammabil ity, sm oke em ission, and circuit integrity. 6. The resu l ts of this study wi l l provide val uable data to all industries and are n ot l i m ited to rapid trans it system design. 7. The results of this stu dy must be consi dered with other wire and ca ble i nsu la­ tion and construction sel ection cri teria. 5.5 Hydraulic Systems ( Ladov and Law 1 978 ) Hydra u l ic syste ms have been present in underground m ines ever since power equ ipment was i ntroduced. With the advance of mining tech nology, the m ach inery has become more powerfu l and larger and the hydrau l i c systems have become more com plex. Hydrocarbon- based hydrau l i c flu id systems have l ong been recognized as a seri­ ous fi re hazard. In many mine fi res, a malfu ncti on ing el ectrica l ignition sou rce ignited the hydraulic hose and hydrau lic fl uid di rectl y or through the bu rning electri c insu l ation. The hydra u l ic system then ignited a secondary or te rtiary fuel, often with the aid of ex ternal l y accu mulated coal dust and grease, and a large-scale fire resulted. Cou nter measures to e l i m inate or m i n i mi ze th is hazard involve : 1 . I mproved design to physical l y separate the el ectrica l and hydrau lic com­ ponents of power machinery. 2. I mp roved design of hydraulic hoses and connections to ren der them fire resistant and lea kproof. 3, Development of fire-resistan t h ydrau l ic fl u i ds, 4. Design of sel f-contained fire detecti on and su ppression systems to com bat a developing hydrau l i c fire, Items 1 and 2 are outside the scope of this stu dy and I tem 4, which is not u n i que to hydrau lic syste ms, is discussed l ater in th is chapter. Thus, on l y cu rrent research efforts dealing wi th the development of fi re-resistant hydraulic fl u ids are discussed below. The use of fire- resistant hydraulic fl uids in u ndergrou nd mining equ i pm ent has 99 

MI N E S A N D B U N K E R S i ncreased du ring the past 20 years. Differe nt cou ntries have adopted different legis· l ative phi l osophies concern ing these fl u ids ( i.e., the use of fi re-resistant flu ids is requ i red i n essenti ally al l hydrau l i c systems used u ndergrou nd in the Un ited Ki ng­ dom and is advised [ as an altern ate to fire-suppressant devices on u nattended h y­ draulic systems] in the United States ). In 1 975, a research program concerned with improved fire safety of coal mine hydrau l ic systems was initiated ( Ladov and Law 1 978). Its objectives are to develop design and performance criteria for fire-resistant hydrau l ic fl uid systems for use in u ndergrou nd equipment i n U. S. coal m ines and to devel op fi re-resistant hydrau l ic fluids for use in systems meeti ng these criteria. Prior to in iti ati on of the ex peri· mental portion of th is program, pu bl ished U.S. and foreign experience with fi re· resistant hydrau lic fl u ids was reviewed together with the cost-perform an ce features of the various cl asses of avai l a ble fi re-resistant hydraul i c fl uids. Work under this progra m was n ot yet complete in early 1 978 ; however, pre l i m inary resu lts are ava i l able and are summarized below. A review of the state of the art indicated that ava il able fi re-resistant h yd rau l ic fluids are classified by the I nternational Standards Organi zation ( I SO ) as fol l ows: Class Descrip tion HS.A O i l -i n-water emulsions contai n i ng a max imum of 20 percent com· bustible materia l (usu a l l y containing 95 percent water) HS.B Water-in-oil emu lsions contai n i ng a maximum of 60 percent com· busti ble material (usually conta i n i ng 40-45 percent water) HS.C Water-glycol so lutions ( usual l y containing at least 35 perce nt water) H S. D Water-free fl u i ds (usu a l l y phosphate-ester-contai n i ng fl uids) I t was concl u ded that the HS.B f l u i ds were the most promising for possi ble u se in u nderground hydrau l ic systems, specifical ly i n conti n uous mi ners, shuttle cars, and roof bolters ; therefore, devel opment of advanced water·in-o i l emulsions was i n iti ated Since the contract u nder wh ich this program is being conducted s pecifies that fi re-resistance levels not be com promised, the interrel ations between physical properties of the oils, the emu lsions, and the i r water content and the fi re·resistance of the emulsions were careful l y i nvesti gated. Fi re-retardancy was measu red by the procedures publ ished in Federal Schedu le 30 and in Factory Mutual Stan dard 6 930. The ensu i ng investigation esta bl ished the target rel ationsh i ps and guided the development of an ex peri mental fi re-resistant hydra u l ic fl u id, designated XR L 1 1 1 0. Concu rrent with fluid se lection, the establ ishment of performance criteria also was pursued, and the fol lowi ng interi m necessary feas i ble parameter developmen t h as been visua l i zed : 1 . Defi nition of emulsion stabi l ity 2. R ust and corrosion perfo rmance 3. Performance eval u ation in preva i l i n g ty pes of pumps (vane, ax ial piston and gear pu mps) ; and 1 00 

D ES I G N C R I T E R I A I N M I N E SAF ETY A N D H AZAR D CONTRO L 4. Defi nition of l i miting operati ng temperatu res, pressu res, and mainten ance (fil trati on ) recommendation s. The X R L 1 1 1 0 fl u i d was manu factu red in fac i l ities approx imating those of com­ mercial producers, its re producibil ity in commercial production was eva l uated, and a n i ne- month mine demonstration test i n two con ti nuous miners (one using both constant variable vol u me axial piston pu mps with hydraulic p ressu res up to 3200 pou nds per squ are inch and the other usi ng th ree tandem gear pum ps operati ng at hydrau l ic pressu res u p to 1 700 pou n ds per square i nch ) was initiated. The resu l ts of the fi rst five months of the testi ng period were ava ilable to the com m ittee, and it appears that the ex peri mental fl u i d has performed sati sfactori l y both as a l u bricant and as a fire-resistant hydrau l i c fl u id. I nitial inspections of both pu m ps and flu id indicated that: 1 . Four production batches of X R L 1 1 1 0 have met the performance criteria sti pul ated in the research contract, demonstrati ng that the fl uid can be m anu­ factured i n n ormal producti on facil ities i n a reproduci ble man ner. 2. Essenti ally al l problems possi bl y rel ated to hydrau lic system m alfu nction were not rel ated to lu bricant performance. 3. The apparent viscosity and water content of the emulsion rem ained essential­ l y u nchanged. 4. Contamination levels were in the range of 3 to 8 mil l igrams per 1 00 in one miner and h ighe r in the other u nit, which requ i red a l u bricant change. 5. The fi re resi stance of the X R L 1 1 1 0 used i n both mi ners remai ned good ( as measu red by the Schedu le 30 test procedu re). These intermedi ate resul ts seem to indicate that successfu l performance can be expected for the enti re test period. The final resu lts also may shed l i ght on areas that need fu rther develo pment (e.g., improved mechanical performance, corrosion protection, and improved hydrau l i c fl u i d filtration ) . 5.6 Polyurethane Foam (Wilde, 1 972; Walter Kidde and Co., 1 974, Mitchel l et al. 1 964 and 1 966 ; Nagy, 1 973; Stephenson, 1 968 ; Vines, 1 973; Troley, n .d., Franklin et al., 1 9n) Pol yurethane foam is a tough cel l u l ar materi al usually produced on site from a two-com pon ent mixture, dispersed through a nozzle, and sprayed onto a su rface. Duri ng the resulting exothermic che mical reaction, chemica l l y or ph ysical l y gener­ ated gas bu bbles expand the mixtu re up to 30 ti mes in vol u me. Urethane foam has been u sed in m i nes si nce the early 1 960's. I t serves as an excel lent sealant and insul ator for venti l ation controls and strata. It is tough, flex­ ible, and eas i l y appl ied, and it ex pands during curi ng and h as good adhesion qual­ ities. The foam, however, is fl ammable and su bject to spontaneous combustion, and its decom posi ti on products represent a signifi cant tox ic hazard. Past developments in foam tech nology were concerned with appl ication tech­ nique, testi ng, flammabi l i ty, flame propagation research, and the use of flame- 1 01 

M I N E S A N D B U N K ERS reta rdant additives. More recent research has concentrated on fi re dynam ics, tox­ i city of foam combustion products, and devel opment of fi re-resistant coati ngs. 5. 6. 1 Description Pol yurethane foam is for med by the reaction of a pol y isocyanate with a h y­ droxyl compound. A typica l formu l ation used in m i nes wi l l contain approx i m atel y 5 0 percent diphenyl methane di·isocyanate, 30 percent polyether polyol, 6 percent tri·chloroethyl phosphate, 1 5 percent trichlorofluoro·methane, and smal l amounts of cata lysts and an emulsifying agent. The foa m is made by mixing the com ponents and spray ing the mixture on the desi red surface . The heat of reacti on between the polyol and the isocyanate vapori zes the trichlorofluoromethane whose expansion produces the foam. The trichl oroethyl phosphate is included as a fi re retardant. U rethane foam application usual l y requ i res no preparation of dry, wet, or dusty surfaces of coal, rock, metal , wood, concrete, or fabric. It is used in m i nes to : 1 . Provide stoppi ngs in recovery operations fol l owing fi res and explosions. 2. Provide stoppi ngs, overcasts, bu lkheads, and door frames that are resistan t t o air lea kage, low-level grou nd movement, and bl asti ng vi brations. 3. Control the weathering of ex posed strata. 4. Reduce heat and moisture transfer from rock to the venti l ating air and fac i l itate ai rfl ow. 5. Seal strata against efflux of gases ( i .e., methane, radioactive gases) . 6. Provi de non-load- beari n g wal ls (e.g., those requ i red for au x i l i ary venti l ati o n ducts a n d undergrou nd ex plosive maga zi nes ) . 7 . Control ground water seepage a t l o w hydrau l ic heads. a Reduce con densation and freezing i n machi nes, pi pes, and air shafts. 9. Hold shaped charges against vertical wal ls. 1 0. I n case of a rescu e o peration (and on l y i n such an emergency ), consol idate and seal bu rni ng gob and fi l l voi ds. Th is is a hazardous usage. The use of u rethane foam in m ines was accepted rapi dly because of its obvio u s contri bution t o productivity a n d cost sav ings. However, fi re a n d tox ic effect i n ­ cidents soon curtai led wi despread use . The disadvantages of usi n g urethane foa m in m ines are that : 1 . It is easy to ignite. 2. It has a h i gh fl ame spread rate. 3. The poss i bi l ity of spontaneous ign ition exists ( bu t only with in four h ou rs afte r appl ication and only i f i m prope rly appl ied ) . 4 . The smoke a n d gases produ ced on combustion are tox ic. 5. It tends to deve lop fi res that vi rtua l l y deplete the ai r or ox ygen (in contrast to wood and coal fi res that go out at between 1 0 and 1 5 pe rcent ox ygen content). 6. F lammable solvents may be used to clean equ i pment. 7. Speci a l i zed equ i pment may be used for foam appl icati on (e.g., mix i ng nozz l e, 1 02 

D E S I G N CR ITER IA I N M I N E SAF ETY A N D HAZA R D CONTR O L pumps, a n d mixing chamber). 8. Extensive operator training is requ i red to ensu re proper proporti oning and mixing of ingredients, choice of i n gredients, appl ication tech nique, protectio n and against the person al hazards i nvo lved in appl i cation. The advantages of urethane foam derive from its outstanding prope rties in mine applications and include its : 1 . Low porosity and permeabi l i ty, wh ich m akes it an effective seal ant against air, moisture, methane, and radi oactive gases. 2. Strong adherence to strata and mine constructi ons, i ncl u d i ng damp and dusty su rfaces. 3. Low thermal conductiv ity, wh ich makes it a good thermal i nsu l ator. 4. Abil ity to expan d on cu ring, which faci l itates application over i rregu lar su rfaces and i n fi l l ing voids. 5.. Flex i bi l i ty, wh ich minimizes detri mental effects of ground movement and devel opment of cracks. 6. Relative l y high shear-strength in comparison to other sealants. 7. Rapid cu ri ng ti me. 8. Appl icabil ity in very hu mi d environ ments because cu ri ng is accompl ished by chemica l reaction (rather than by wate r evaporation). 9. Ease of appl ication ( i.e., the avai lability of self-contai ned, portable packs for appl ication in remote areas). 1 0. Low cost ( both material and appl ication l a bor) due to eas.a of application and speed of constru ction. 5.6.2 Hazard Control The appl icati on of u rethane foam in m i nes started in the early 1 960's. In 1 964, Mitchel l et al. reported that it had been used successfu l l y in experi ments to con­ struct stoppi ngs, seal mi ne surfaces, control watter effl ux, and serve as i nsulation. They descri bed the foam formu lations, appl ication techn i ques, and physical proper· ties of the foam as wel l as the fire and potentia l toxicity hazards ; presented resu lts of l arge-scale s i m u l ated coa l mine fi re tests and vari ous l aboratory flame spread and therma l deformation tests; and proposed a fl ame penetration test as an acceptance requi re ment. A l ater report by these same researchers ( M itche l l et al. 1 966) is devoted entirely to the fire haza rd of urethane foam i n mi nes. It descri bes a large number of mine and ga l lery fire tests and presents an analysis of the resu lts. Appl i cati on recom­ mendations, i ncluding l i mitations, are m ade and fou r certification tests ( i .e., excess or residual tolylene diisocyanate [ because of tox icity] , water-vapor permeabi l ity [ to esti mate foam qual ity] , flame spread, and flame endura nce) are proposed. The report also covers spontaneous ignition of u reth ane foam ( its causes and prevention methods). I n September 1 967, a serious coal mine fi re ki l l ed nine men at the Michael 1 03 

MI NES AND BUNKERS Col l iery in E ngl and ( Stephenson 1 968) . It was concluded th at the fi re was initiated by spontaneous heati ng of coal and reached disastrous proportions when the poly­ u rethane l i n i ng started bu rning. Su bsequentl y, five l arge-scale experi ments were conducted to study the behavior of polyurethane foam when su bjected to ign iti ng agents of di ffe rent intensity. It was concluded "that polyureth ane foam as at present constituted is an unacceptable risk and that its use in an d near the entrances to a l l mines shou l d be disconti nued." Apparently th is was not to be, h owever. I n 1 972, a B ritish researcher (Wi l de ) described seven large-scale experi ments designed to study several aspects of polyu rethane foam fi res, i ncluding ign ition, flame s pread, fu me composition, te mperatu re profile, effects of fi re reta rdant su rface coati ngs, and burn ing of treated ti mber down wi nd of pol yureth ane fi re. This report exami n es the appl i ca bi l i ty of usi ng the foa m to seal m ine fi res ( rather l i m ited ) and offers conclusions on ex peri mental results but n o recommendations concerning the use or rejection of urethane foam in m ines. More recent U. S. investigations revea led th at at least 1 0 m ine fires reported duri ng 1 964 and 1 974 involved u rethane foa m (8 in coa l m i nes and 2 in meta l and non metal mines). Although th is i ncident rate is rel ativel y low, it is serious enough to warrant conside ration of significant modifications or alte rnate approaches. Th is com m i ttee possessed no information that wou l d explain the discrepancy between the British and American ex perience with urethane foa m although it is read i l y admitted that there may be subtle differences i n compos ition a n d appl icati on . I t i s not very l i kely that chemical com position shou l d b e a factor, but the differences i n appl ication tech nol ogy or prevai l ing strata may offer a n expl anation. Today, pursuant to government order less than a mile re mains in certa i n m etal m i nes of the many m i les of passageways in coa l , metal, and non-metal mines th at were coated wi th urethane foam. Recogn izing the considerable fi re and tox icity hazard th at these instal l ati ons represented, the U. S. Bureau of M i nes sponsored a series of ex peri ments to eva lu ate vari ous surface coati ng materials su itable to pro­ tect the existing i nsta l l ations from excessive flammabil ity and flame spread (Walter K idde and Co. 1 974 ) . The results of th is p rogram ind icate that fibrous concrete appears to be th e most effective coati ng ; it exh i bits excel lent strength and adhesion, and mini mal spa l l i ng, and an appl ication of only 1 /2 to 1 i nch (preferably 1 i nch ) p rovi des the desi red protection. I n order of decreasing efficiency, the other coati ng materials evalu ated were : Shotcrete (same as fi brous concrete with ou t the steel fi bers), F i regua rd (a magnesiu m oxysu lfate cement contain ing pe rl i te ) , Mandosea l ( a vermiculite cement ), mineral wool, a n d sodiu m-s i l icate·based coatings. It is d is­ cou ragi ng to note that the appl ication of even the two best materi als is difficu l t, that material is l ost because of rebou nding, and that it is difficu lt to ach ieve a uniform coating thickness. These problems, however, are not considered to sign i f i­ cantly alter the test resu lts and it may be that experience wi l l i mprove the appl ica­ tion tech nol ogy, Assuming that such improvements wi l l be m ade, the report in­ di cates th at at l east two (and possibly fou r) acceptable and econ om ical protective 1 04 

D ES I G N CRITER I A I N M I N E SAF ETY A N D HAZARD CONTR O L coatings are available t o prov ide sufficient fire protection for existi ng u rethane foam i nsta l lations. The same report also descri bes successfu l fire testi ng of a new fi re-resistant foam , designated X- 1 0 3 S. I n t h e experi ment, fla me did not spread o n t h e su rface of the foam upon appl ication of an i ntense ign ition sou rce, and it was concl uded that the material does not present a fi re hazard even without a protective coati ng. Other efforts to mod ify or replace traditional polyurethane foam a lso have been undertaken, Cal l ery Chemica l , under a contract to the U.S. Bureau of Mi nes, h as formul ated a nu m ber of modified ureth ane and isocyanu rate foams th at offer vastl y improved fi re-retardant properties com pared to standard u rethane foam (Vines 1 973), Coati ngs formu l ated with portland cement, m i neral wool, and vermicu l i te have been developed and can be sprayed on with day-process equ i pment. Th is is a process that involves no mixing of dry material and no clean up of equ ipment. I n addi tion, the equi pment does not ge t plugged with cement after a mine power loss. F rankl i n et al. ( 1 977 ) have reported that two spray coat appl ications of a water­ based epoxy sealant have su bstantially reduced sh ale degradation in a coal m ine. Materi a l and appl ication costs seem reasonable, and endurance ( after 1 8 months) appears to be noteworthy, but no deta i l s concerning the fire and toxicity hazard or com parison with u rethane foam were presented. 5.7 Mine Fire Detection ( Nagy and Hall 1 974, Hertzberg 1 978, Hertzberg and Litton 1 976) The se riousness of the fire hazard in m i nes was recognized by Congress when it enacted the Federal Coa l M i ne Health and Safety Act of 1 969. Section 3 1 1 of the Act establ ishes nu merous requirements for fire protection including the use of fire detection devices. The requ irements fo r these devices are ampl ified in the standards publ ish ed in the Federal Register to implement the Act. There is little dou bt that rapi d and re l i a ble fi re detection is the essenti al fi rst step in an y fi re-suppress i on or alarm system and escape plan. I niti a l ly, em ph asis was pl aced on detecti ng methane-air face ign i ti ons and d ust ex plosions an d the early activation of quenchi ng devices. More recently, efforts have concentrated on the detecti on of fi res du ring their early or incipient stages. Current research programs i nclude the contin u i ng devel opment of a tu be bundle sampl ing tech n i que, develop­ ment and evaluation of new ty pes of fire sensors, and general stu dies of the pro b­ lem o f spontaneous combustion. 5,7. 1 Sensors and Systems The traditional methods of detecti ng the presence of fi res may be classified by the type of detector used as fo l l ows : 1 . Thermal con tact sensors th at respond to the temperatu re or th e rate of tem ­ peratu re i ncrease a t a point o r a l on g a continuous l i ne. Examples are therm � cou ples, bi meta l l ic ele ments, the fus i ble plug of a spri n kler head, and twisted 1 05 

MINES AND BUNKERS wi re with insulation that melts at a given temperatu re. These sensors genera l l y must be l ocated cl ose t o the fire if they are t o operate successfu l ly. 2. Optica l sensors that respond to the l i ght emitted by a fire or flame. These sensors are l i mited by field of view constraints and are su bject to blockage by dust. 3. Com busti on product detectors that can be i nsta l led l ocal l y or at remote areas to sense carbon mon oxide, carbon diox i de , visible smoke, su bm icrometer particles ( invisible smoke), or a variety of other pyrolysis products carried by ventil ation or fi re convection currents. 4. Aerodynamic sensors that res pond to the fl ow distu rbances caused by the fire, These sensors are usefu l for ex plosion detection but are rarel y used for fires. 5. H u man observers, the most ve rsati le and sensitive "sensors". These observers, however, are present on ly part of the ti me in l i m ited areas and cannot be present in sealed areas, gobs, and other inaccessible pl aces. Cu rrent practice genera l l y assumes the presence of and depends heav i l y on human observers. The only cu rrent coal m ine requ i rements for automatic fire sen­ s ors rel ate to their use with underground conveyor belt haulageway protection. The regu l ations are written in terms of thermal poi nt type sensors (or com bustion product sensors if they offer equivalent protecti on). Metal and non-metal m i n e regu l ati ons require fi re a l a r m systems; however, automated sensors t o activate the a l arms are not requ i red. F ire detection systems currently used and under devel opment in m ines can be categorized as : 1 . Attended equ i pment systems, 2. Unattended equi pment systems, 3. I gn i tion su ppression systems, 4. Spontaneous combustion detection system, and 5. Whole-mine mon itoring systems. When fire su ppressi on syste ms are i nsta l led on attended equ i pment, the operator usually must detect the hazardous condition and must activate the suppression equ ipment. Use of fi re-resistant h ydrau lic flu i d wou l d make su ppressi on equ ipment superfl uous on this ty pe of system. Properly instal led devices (e.g., water sprin klers and temperature sensors ) are used to detect fires on unattended equi pmen t, such as belt conveyor drive u nits and automatic loadi ng stations, and to activate su ppression systems. Additional manu al activators also are required on some syste ms. I f equi pment uses a hydrau l ic fl u i d, fire-resistant hydraulic fl u i d must be used in conju nction with the suppression systems. 5.7. 2 R ecent Developments 5.7. 2.1 Tube Bundle Sampl ing 1 06 

D E S I G N CRITER I A I N M I N E SAF ETY A N D HAZA R D CONTRO L Bui l di ng o n British work conducted between 1 968 and 1 972, the devel opment of a continuous monitoring technique is being pu rsued ( Hertzberg and Litton 1 976). The method i nvolves the pneu matic, sequential sampl i ng of many poi nts in a system th rough branching tu be bun dles th at lead to a si mple ana l ytical station of h igh sensitivity, good re l iabi l i ty, and conven ient location. The samples can be ana· lyzed for a l arge number of components such as carbon monoxide, oxygen, meth­ ane, or products of combustion (for the detection of rapidly developing fires). An obvious advantage of this system is th e potenti al for monitori ng many sam­ pling stati ons, i ncluding inaccess i ble sealed areas, at frequent intervals on a conti n­ uous basis. I ts limitations are relatively slow response ti me, due to long lengths of narrow sa mpling tu bes, and wal l -diffusion l osses for su bm icrometer smoke particles. These l i mitations were qu antitatively eval uated by measu ring tu be transit ti mes and smoke particul ate transmissions as a fu ncti on of tu be length, diameter, and pressu re drop ( Hertzberg and Litton 1 976) . 5.7. 2.2 Detection of Spontaneous Heating The gob regi ons of mines can now be routinely monitored for spontaneous heating by sampl ing tu be bundles. This system was developed at the Somerset m i ne in Col orado ( Hertzberg 1 978), and the initial system mon itored 38 points in various inta kes, retu rns, working sections, and sea led areas for carbon monoxide and oxy­ gen. Regions as far as a mile away from the sensi ng station were routinely moni­ tored, and it was possi bl e to fol l ow the actua l growth of a spontaneous com bustion situation i n a conventional room and pillar section . Although the system is adapt­ able to gobs, abandoned regions and sealed areas of a m ine where the human observer is not present, it also can be used in attended areas to detect problems sooner than the human observer. System instru mentati on, tu bing arrangements, and power supply now are being refined. 5.7. 2.3 Spontaneous Combustion Research The main factors that contribute to spontaneou s com bustion in coal mines are : ( 1 ) the intrinsic reactivity of the coal, (2) the geometry and configu ration of the seam, (3) the geol ogical conditions and structure of the seam and its su rrou ndings, and (4) the mining method and venti l ation conditions. The intri nsic reactivity of the coal is the concern of a cu rrent progra m initiated by the U.S. Bureau of M i nes ( Hertz berg 1 978). The sel f-heati ng characteristics of the coal are being determ ined with an adia batic ca l ori meter, and the calori mete r data show th at various other methods of eva l uating re l ative reactivities correl ate we l l with one another. The rate of tem peratu re rise corre lates we l l with the rate of production of carbon monox ide ( CO ) and carbon diox ide. Coals with h igh rates of CO production per u nit volume of oxygen absorbed also have h igh sel f-heating rates in the adiabatic calori mete r. The CO index corre l ates we l l with the initial oxygen content of the coa l . The devel opment of these correl ati ons and analysis of various coa l deposits are expected 1 07 

MINES AND BUNKERS t o enhance t h e meani ngfu l uti l i zation o f t h e tube bundle system. 5.7. 2.4 Development of Sensors In the hope of achieving greater mine safety, advanced sensor deve l opment is being pursued. Laboratory stu dies i ndicate that su bm icromete r particles are m ore universal indicators of spontaneous sel f-heating th an CO generati on . Other mine com busti bles such as wood, cel l u lose, and pl astics generate these particles at tem­ peratu res much lo����e r than those at wh ich they generate CO. A highly sensitive and i nexpensive sensor for these particles h as been developed ( Hertzberg 1 978) and is being eva l uated for i n-mine performance. The sensor is compati ble with a properly designed tu be bundle sampl ing system. The development of ultra-v iolet and infra-red sensors for use in ignition suppres­ sion syste ms also is being pu rsued. When devel oped, such sensors shou ld hel p to prevent methane ignition in the face areas of coa l m i nes. Other cu rrent projects are concentrating on the evalu ation and testing of new sensors (e.g., ionization detec­ tors and sem i conductor sensors ) and their perfo rmance u nder normal an d pyrol itic conditions. 5.8 Ignition Quenching and Fire Suppression ( Fu rno 1 978, L iebman et al . 1 976, Liebman and Richmond 1 978, K ing, 1 978) 5.8. 1 Mine Face I gnition Quenching ( Fu rno 1 978 ) The incidence of fricti onal spark ign ition at the mine face has i ncreased signifi· cantly wi th the advent of the continuous mining machine. The m ajor h azard of a face i gnition lies in the possi bi l ity that it may i n i tiate an extensive coal dust ex­ plosion. The research that resu lted from the 1 969 Act focu sed on the fol lowing app roaches to the face ignition problem : ( 1 ) the reduction of methane concentra­ tion th rough i mproved face venti l ation, water infusion, and methane drainage ; ( 2) the reduction of the i ncendiary tenden cy of tool bits th rough i m proved meta l l u rg y o f the bi t o r reduced bit speed; a n d (3) the development o f an ign ition·quench i n g devi ce that might b e i ncorporated into the design o f a conti n uous m i n er. The G raviner system, wh ich may be cal l ed an ign i ti on·quenching device, was developed in the 1 940's. Its early appl ication was for fixed i nsta l l ations and adapt­ i ng it to mach i ne- mounted appl ications was recognized as a form idable problem . D ifficu lties i ncluded the vi brati on and shocks on a conti nuous mi ner, roof fal ls, the dusty and h u m i d atmosphere, and the awkward geometry with in wh ich th e flame detecti on and exti nguishant dispersal are requ i red to operate. Resea rch in th is area was started in th e Un ited States i n the early 1 960's. I t was di rected toward devel oping a syste m th at would prov ide rapid detection of a n i nci pient methane·ai r igniti on, an exti ngu ishing agent th at wou l d be effective 1 08 

D E S I G N C R I T E R I A I N M I N E SAF ETY A N D H AZ A R D CONT R O L aga i nst such ign iti ons, and an agent dispersa l method that wou l d en su re adequate temporal and spatial distri bution of the exti n gu ishant. The resulting dev ice uti l i zed u l tra-v i olet flame detectors, dry powder exti n gu ishant ( potassi u m bicarbonate ) , and a n explosive dispersal syste m ( primacord). A worka ble model eventu a l l y was devel­ oped and successfu l l y tested. It consisted of a 2 inch diameter, 2 foot l on g scored aluminum tube fitted with the dry powder and pri macord and mounted on a base pl ate. The model had several shortcomings in that it generated un acceptable noise and a dust and grease accu mulation cou l d cause a malfunction. These and oth er problems su bsequentl y were i nvesti gated in l ate 1 972 ( F u rno 1 978). Th is effort led to the development of a cannon type dispersal system that uti l i zed mono­ ammon i u m phosphate pro pe l l ed by high-pressure ni trogen th rough a diaph ragm ru ptu red by an electric detonator u pon signal from an u ltra-vi olet detector. I t was dete rmi ned i n trials that five cann ons were requ i red to provi de adequate protection for a ri pper-type miner and six can nons, for a contin uous-type m iner. Th is equ i p­ ment was a techn ical success ; however, space l i m itations make use of the required number of quench i ng devices i mp ractical . A q uench ing device uti l izing a commerci a l l y ava i l a ble extinguisher fi l l ed with Halon 1 301 or a hy bri d syste m of th is chemical also has been developed ( F u rno 1 978). The exti nguisher is a spherical bottle equ i pped wi th a dispersion nozzle and an explosive release device that is actuated by the signal from a flame detector. Halon 1 30 1 was found to be a ve ry efficient extingu ishing agent by itself; however, its effectiveness im proved when it was used in com bi n ation with water or with dry powder ( potassium bicarbonate ), and these hybrid systems are preferred for futu re i nvestigation because of their synergistic action. The fi re exti nguishment ch aracter­ istics of this device were investigated, and the generation of toxic fu mes ( H Br and HF) was determin ed at va rious quenching delay ti mes and corresponding fireba l l diameters. I n addition, the syste m was tested for uti l i zation o n a tunnel-bori ng machine that now is being used experi menta l l y as a new meth od of entry develop­ ment and that can deve l op into a frictional ign ition h azard like other coal m i ning machi n es. 5.8.2 Coal Dust Explosion Barriers ( Liebman et al. 1 976; Liebman and R ichmond 1 978) Coa l dust ex plosions are a constant h azard in u nderground coal min ing opera­ tions. Such disaste rs usual l y fo l l ow accidental ign ition of a methane poc ket or roof l ayer, wh ich may develo p sufficient violence to pick up, disperse, and ignite coal dust lying on nea rby mine surfaces. A sel f-generati ng dust explosion then can develop and propagate for great distances in the m ine. l nerting the coal dust by spreadi ng rock dust on the mine surfaces has been the traditional means of contro l­ ling dust ex pl osions in U. S. coal mi nes; however, rock dusting is not complete l y adequate for conveyor bel tways, transfer points, wet roadways, parked mine ca rs, return ai rways, longwalls, and isol ated sections. 1 09 

MI NES AND BUNKERS The passive water barrier system that has been tested and used abroad appears to be an attractive means of defense against coal dust ex plosions and h as become the principal means of protection in a number of countries. Such barrier systems n ormally are made u p of a n u m ber of water·fil led containers or tu bs m ou nted in the vicin ity of the mine roof. D u ring a dust explosion, the dynamic pressure of the a i r resu lti ng from the air motion ahead o f the propagating flame ti l ts or shatters the water containers to release and disperse the water, which acts to suppress the oncom ing ex plosi on. However, E u ropean research indicates that the effectiveness of these barriers is li mited to a moderate ly strong dust explosion ; the water barriers fai l wh en the explosion is wea k s ince the dynamic pressu re is not strong enough to fractu re or ti p the water conta iners. These studies also show th at the passive water barrier is not effective when less than a bout 200 feet from the explosion i n itiator. Three experimenta l water barri ers designed especial l y for the suppress ion of sl ow moving coal dust explosions have been developed an d tested ( Liebm an , et al . 1 976). One of these barriers, a modified version of a West German type, responds to dyn amic pressu res generated ahead of an ex plosion to ti lt the tu b and re lease its water for the suppression of the oncoming explosi on. The other two ba rriers oper­ ate in response to i ncreased static pressure devel oped ahead of the explosion. Tests i ndi cate that the first barrier begi ns to re lease its water at air speeds as low as 50 feet per second and that the other barriers wi l l operate at a rise in static pressu re of as l ittl e as 0. 5 psi. The ba rriers were fou nd to be effective i n stoppi ng coal dust explosions propaga· ti ng at speeds as slow as 1 00 feet per second. One ch arge of 1 80 pounds of water was sufficient to suppress explosions i n a single entry with an ave rage cross section of 55 ft2 • Resu lts of the tests indicated that the minimum distance between th e barrier and expl os i on in itiator shou l d be about 75 feet. The barrier system's effec· tiveness in su ppressing explosions re mains h igh when as l i ttle as half of the water of a si ngle barrier (90 pou n ds ) is spil led prior to the flame arrival . I ts effectiveness is di minished, however, when the barrier is located a great distance (more than 300 feet) from the expl osion ini tiator. A plan has been deve loped to test these water barriers i n a working m ine on a trial basis. The plan cal l s for insta l l ation of al l th ree ty pes, of close ly specified si zes, d istances, and spati al arrangement for the protection of a beltway. Actual p e r· formance behavior wi l l be uti l i zed as the basis for refinem ents and the devel opment of specifications and to sti mu l ate wi despread appl ication of the new type of coa l dust explosion barriers. 5.8.3 Remote Sealing System for Exti nguishing Coal Mine F ires ( King 1 978) Uncontro l led coal mine fires are of great concern to the m i n i ng i ndustry becau se they can not be d i rectl y exti ngu ished and may requ i re th at the enti re mine be sealed. The conventional practice of constructing ai rti ght stoppi ngs from with i n the 1 10 

D ES I G N C R I T E R I A I N M I N E SAF ETY A N D HAZA R D CONTR O L mine is difficu l t a n d can involve a h igh fi re or ex pl osion risk ; therefore, th is approach cannot always be used. In sea rch of a more desira ble approach, the U.S. Bu reau of Mi nes ex plored the concept of re mote sea l i ng from the su rface and fou nd fly ash to be a suitable sea lant for this pu rpose. Th is tech n i que m i n i m i zes th e risk to the fi refi ghter, l i m its the seal i ng to the establ ished fi re area, and ex pedites the m i ne recovery operati on, thus reducing potential costs and production l osses. The syste m was deve l oped to contro l the Federal No. 1 mine fi re and explosion i n 1 963 ( private commun ication M. Jacobson ). The com plete system i ncludes : ( 1 ) a son ar pro be and cl osed circu it televis ion ca mera for initial p robing of the mine entry to be sea led, ( 2) a fl y ash or fly ash-cement syste m for constructi ng the seals, (3) a froth foam topping syste m for com pleting each seal, (4) a com bustion ty pe inert gas generator for convey ing the fly ash and inerti ng the sea led area, and ( 5) acousti ca l equi pment for assessing the com pletion and i ntegrity of a sea l . T h e re mote sea ling o f an u ndergrou nd coal mine fi re requires considera ble plan­ ning to resolve logistic and site pre paration problems and to en sure th at a l l the operational phases are properl y coo rdi nated. I n iti a l l y , a probe is lowered th rough a borehole to determine the geometry or nature of the passageway to be sealed ; the borehole must be cased and grouted to prevent water seepage and it su bsequently serves as a sealant borehole. In the second ph ase , two adjacent boreholes are dri l led to deploy the acoustical equi pment th at is used to mon itor the formation of the gross fly ash sea l and then the passageway is fi l led with the fly ash bu l k seal ant th at is pneumatica l l y transported from a su pply truck on the su rface. I n the final ph ase, a froth foam toppi ng is added to fi l l the crater formed by the fly ash and to com plete the seal ; the foam is for med in pl ace at the bottom of the borehole. An i nert gas generator is used to m i n i m i ze the ex plosion hazard during the fly ash fi l l i ng phase and to inert the sealed area of the passageway . In add ition, a mod ified fly ash mixture must be used if a waterti ght seal is required. Al l com ponents of the system are mou nted on skids or trai lers. The probe asse mbly used in the fi rst phase incl udes a low-light-l eve l closed circuit te levision camera (CCTV ) for visual o bservation of the downh ole conditi ons and a sonar ranging devi ce for accu rately determining di mensions of the passageway or distances to large objects. I t also is equ i pped with a rotator to faci l itate scanning and a remote reading com pass to establ ish pro be orientation. The pro bi ng i nform a­ tion is usefu l to determine the suitabi l ity of borehole locations, sealing material requirements, potential obstructions to sea l i ng, and rel i abi l ity of m ine maps and e ngi neeri ng surveys. Another i nstru mentati on syste m that is vital to the su ccesss of the remote seal­ i ng operation is one that monitors the fi l l ing of the m ine passageway and deter­ mines the integrity of the sea l. The syste m developed in this work uses acoustic devi ces, n amely a high-i ntensity speaker and a sensitive micro phone. The speaker and m i crophone probes are lowered i nto boreholes that are on opposite sides of the sea l ant borehole. These probes are usual ly at least 50 feet fro m the seal being constructed 111 

MI NES AND BUNKERS The theory of operation is based on the proven pre m ise that a decrease i n the level of signal received by the microphone is proportional to a decrease in the open area of the passageway being sea led. In this system, the speaker probe transm its an ampl ified sonic pulse from a random n oise generator. The sou nd is picked up by a cera mic m icrophone and transmitted to a sou nd level meter i n the control consol e . A s ignal processing modu l e subtracts background noise, a n d t h e signal then i s d ispl ayed o n the control console a n d correl ated with prior information t o define the completeness of the seal. Sensitivity of the sea l checking syste m is greatest as the seal nears com pletion ( greater than 99 pe rcent). Both m icrophone and speaker u nits a re i ntri ns ica l l y fi re and explosion safe. Over the past 1 5 years, several attem pts have been made to app l y the remote seal ing concept in underground fi res in active coal mines, but most of these efforts have achi eved on l y l i mi ted or no success becau se of inadequate seal ant m ateria l s, seri ous equipment l i m itations, or i nsurmountabl e mine wate r problems. A parti a l l y successful effort occu rred a few yea rs a go when a prototype o f the present re mote seal ing system was used to iso l ate and extingu ish an underground fire at the Eastern Associated Coal Corporation 's Jaonne mine i n R achel , West V i rgin ia. Th is fire resulted from a dera i l m ent and subsequent short circu it that caused a fan stop­ page and made it necessary to evacuate the m i ne. An attempt was th en made t o seal re motely. The remote sea l ing was made from two su rface sites that were over 2500 feet apart and located on opposite sides of a h i l l a bove the m i ne . Six sea ls were constructed and each requ i red d ri l l ing two adjacent boreholes t o accom m o­ date acoustic seal checkers. The boreholes were 600 feet deep or l ess. Three of the seals were 95 percent ash topped with urethane foam, and the othe r three were 1 00 percent f l y ash. M os t o f these requ i red approxi mately 1 50 tons ( 9 5 percent sea l ) o r 250 tons ( 1 00 percent sea l ) o f f l y ash. Those that were com pleted with a foa m toppi ng required at least 2200 pou nds of foam. The sea l ing operati on was carried out using liquid nitrogen tankers to prov i de the inert gas for deploy i n g the fly ash and i nerting the completed seals. A gas monitori ng system was usefu l in indicating the effectiveness of the com­ pleted seals, the adequacy of the inert gas supply system, and the potenti a l gas explosion hazard before and during the remote seal ing operati on. The carbon mon­ oxide and oxygen levels decreased to a pprox i mate l y 0.01 percent with in a bo ut 60 days after the fire began ; thereafter, they were essenti a l l y constant until the re mote seal ing was started. In comparison, the methane and carbon dioxide concen trati ons i ncreased and reached max i mu m levels of approximately 30 and 4 percent respec­ tively withi n about 80 days. Because of su pply and del ivery problems with the l i qu i d n itrogen system, i t was not possible to maintain an inert atmosphere in the sealed area for extended pe ri ods during the recovery phase. Neverthe less, the seal emplacements by the m ine rescue teams were thought to be sufficientl y successfu l so that the mine was reventi l ated 1 12 

D E S I G N CRITER I A I N M I N E SAF ETY A N D HAZAR D CONTRO L with in a few days after com pletion of the seals. A prompt carbon monoxide bu i l d· up emergency was qu ickly responded to by the fi re-control managers who "saved the day". The fact that the mine was reventi l ated pri or to its recovery was a sign i ficant accompl ishment despite the i ncomplete sea l i ng. This fie l d experience has been very usefu l i n cu rrent efforts to devel op a more rel ia ble and accepta ble remote seal ing system for use by the min ing industry in fighting m ine fi res . As noted above, this effort was not tota l l y successfu l ; it hel ped even though tech nical l y it was a fai l u re . It was the fai l u re that led to the subsequent develop­ ment of the CCTV and the inert gas generator. The costs to u se the system are so h igh (from $500,000 for a rel atively small job such as the Joan ne mine to many mi l l ions of dol lars for other scenarios ) that it is the "l ast resort" choice ( private communication M. Jacobson ) . 5.8.4 Mine Shaft Fire and Smoke Protection System ( Nagy and Hall 1 974) As metal and non- metal mi nes become deeper, larger and more mech an i zed, the fire danger increases because of increased fuel l oading in the mines and restricted access. This hazard was emphasi zed by the Sunshine mine fi re at Wal l ace, I dah o, in May 1 972. N i nety-one m i ne rs lost their lives in this disaster. To hel p solve this health and safety problem and to better protect the produ c­ tion ca pabi l i ty of the nation's mines, deve lop ment of a mine shaft fi re and smoke protection system for metal and non-meta l mines was in itiated by the U.S. B u reau of M i n es. The methodol ogy for hardware devel opment and in-mine testing fol lowed that used in the Bureau 's success fu l program to develop automatic fi re protecti on systems for l arge mobi l e min ing equi pment. A contract to eval u ate the non-coal mine shaft fi re and smoke hazard problem and to develop an d demonstrate a rel i a bl e mine shaft fire and smoke control system was awarded in 1 974. This system was to be flexi ble in design so that with modifications it wou l d be appl icable to the majori ty of metal and non-metal mine shafts and adjoi ning sh aft stations. As a result of the fire and smoke problem anal ysis portion of the contract, design criteria for a mine shaft fire and smoke protection system were developed and the fi rst system design was generated. It uti l i zes thermal, carbon mon ox ide, and i on i zed-particle smoke detectors and remote l y contro l led smoke doors and spri n k· lers. The system protects both the shaft and shaft stati on areas. The su rface control unit receives the fi re warn in g signal via mu lti plex wi ring th rough two separate routi ngs, and undergrou nd control un its and odor a l arm are activated from the surface to warn the mi ne rs at each shaft station and elsewhere. The spri n klers and doors can be opened or closed from either thei r local control unit or the maste r control unit on the su rface. Fire warning horns and l i ghts and mine evacuation signals at the underground un its also can be controlled from the surface control unit. Automatic spri nkler actuati on cu rrently is not a feature of the system bu t cou l d be added easi ly. 113 

M I N ES A N D B U N K E R S A shaft a n d shaft stati on mock-up su bsequently was bui l t a n d system com­ pon ent tests were conducted. These included smoke tests of possi ble sensors to be used in the shaft system and test fires in the fi re box. Th is box was used to contai n the fi re in the mock-up and the i n-mine testi ng. The progra m concl uded with the completion of actu al fi re tests. After the mock-up testi ng, the final design was developed fo r the mine shaft fi re and smoke protection system prototy pe to be insta l l ed at the 3000 foot level of Consolidation Silver Corporation 's Si lver Summit shaft near Wal l ace, I daho. The system then was insta l led in the shaft and in-mine fire tests were conducted. The contract was extended for an additional 1 5 months to perm it i nsta l l ation of the prototype system i n at least two operating m i ne shafts, l on g-te rm re l i abil ity testi ng, and conduct of cost-effectiveness eva l u ations of optional system designs and uses. I t appears that the fi rst-generation mine shaft fi re and smoke protection system has a fast response to fi re situ ations and that the presence of spri n klers i n the shaft a nd shaft station area is much more effective in extingu ish i ng fi res than the com­ mon ly used shaft-col l ar water ri ngs. The cost of the syste m is esti mated to be fro m $1 0,000 t o $40,000 per shaft station leve l , depending o n the desi red sophisticatio n o f the system. Thi s is a considerable i nvestment, but given the cost of a sh aft a n d the increased protection provi ded to the miner, the syste m represents a sign ificant contri bution to unde rground mine safety. However, it has been suggested that th e fol l owing simpl e-t�achieve th ings wou l d be a major contri bution to l i fe safety i n mines : properly teaching use of se l f-rescuers, mainta i n i n g positive venti l ation i n hoist rooms, having a trained mi ne rescue team ava i l a ble, maintaining an effective escapeway, and ma i ntain ing co-activated fire doors. 5.9 Su rface Mining Equipment Protection Systems (Johnson 1 976) In surface mines, protection from equ i pment-generated fi res is best provided by protection devices for subsystems (e.g., veh icles and stati onery mach inery ) . As surface mining trucks, shovels, bu l l dozers, etc., become larger, the danger to drivers duri ng a fire emerge ncy increases. The cabs usu a l l y are located h i gh above the grou nd, and the access l adder usu a l l y is next to the en gine com partment where most veh icle fi res occur. I n addition, some operating com partments are cramped a nd egress is diffi cu lt. This increas i ng fire hazard is i l l u strated by the records of mine equ i pment operator inju ries resu lti ng from fires or because a driver j u m pe d from h is vehicle to escape a fire. To hel p solve this problem and bette r protect expensive pieces of equi pment, the U.S. B u reau of Mi nes has developed reasonably priced, re l ia ble automatic fire pro­ tection systems. The prototype systems sense the flame and/or heat of a fi re and suppress the fi re with a B-C cl ass, dry chemical (eith er autom atica l l y or u po n man u a l activati on ) . The first system was developed i n a n d was successfu lly demon- 1 14 

D E S I G N C R I T E R I A I N M I N E SAF ETY A N D H AZAR D CONTR O L strated during i n- m i n e fire tests o n a 100-ton-capacity truck. Other systems have been developed and i n-mine tested on coal augers and large bul l dozers. Future plans cal l for modi fication and long-term endurance testing of alternate systems on large dri l l s, shovel s, and dragl i nes. 5.9. 1 Automatic F i re Protection Systems for Large Haulage Vehicles (Johnson 1 976; Johnson and Forshley 1 977) As mine hau l age vehicles beco me larger, the fire hazard i ncreases because of the i ncreased height of the ca b above ground, the l ocation of the l adder, and the driver's inabi l ity to see the fi re in time to escape because of the position of the ca b on the vehicle, To a l l evi ate this pro ble m and better protect expensive equ i pm ent, the U. S. B u reau of M i nes sponsored two efforts to develop automatic fire sensing and su ppressi on systems for l arge haul age vehicles (Joh nson and Forshey 1 977) . One of these efforts was ai med at defi n i n g the l arge mobi le veh icle fi re problem and developing improved fi re system design criteria to solve i t. Another objective of the fi rst work was to find the most fireprone class of equi pment and to solve its fi re problem using a system flexi ble enough to be appl ied to other l arge m obi le mine equ i pment. This hazard analysis stu dy resu lted in deve l opment of "dual sen si ng, automatic with manu al overri de, fi re detection and su ppression system" for rear­ dump haulage trucks with a capacity of over 1 00 tons. Prototypes of the system were bu i l t and demonstrated in actu�l truck fi re tests and l ong-term in-mine endu rance tests. The system protects the engine com­ partment and fuel tan k area with i mproved com ponents and featu res optical and therma l sensors ; automatic controls with manual ove rri de ; and fixed fire ex· tinguishers with pressurized B·C class dry chemical. Control panels are located in the ca b and can be activated manual l y via switches at ground leve l . Automatic engi ne shutdown was not a feature of the prototype system, but such a design alternative cou l d be added easi l y. The system is flexi ble en ou gh for use, with modifi cations, on most large mobi l e m i n i ng equi pment. As part of the second effort, the auto matic fi re protection syste m prototype was to be i nsta l led on the 1 �ton mine truck and long-term rel i abil ity testi ng was to be performed. This testi ng resulted in devel op ment of a second-generation system that then was su bjected to long-term on-veh icle testing in 1 974. During the testing, an acci denta l fi re occurred on the test truck and the prototype system automatica l l y sensed and exti ngu ished the fire. Fortu itously, the Bureau's program demonstrated success in a real verification. 5.9.2 Fire Protection System for Coal Augers (Johnson 1 976, Technology News 1 976) F ol l owing the open pit truck fire work , the U.S. Bureau of Mi nes expanded its mine equi pment fi re protection efforts to surface coal mini ng. This invo lved letti ng a contract to the Lease A F E K Corporation of Raleigh, North Carol i na, to modify 115 

MI N E S A N D B U N K E R S and test i n- m i ne a l ow-cost automatic fi re protection syste m for su rface coa l augers. This system was fa bricated and then tested on a Com pton auger at the Cedar Coal Company, Chel yan, West Virginia. The A F E K system features point-sou rce heat sensors and two inde pen dent dry chemica l extin gu ish ing su bsystems, one for each engine and operator area on the auger. The system was su bjected to six months of i n-mine testi ng and test fi red in 1 975. The val idation tests indicated that an effective, rel i a ble, and econom ica l fi re su ppression system can be deve loped and that : 1 . Such a system can be instal led for approxi mately $2,200. 2. The system requ ires l i ttle mai ntenance and is simple in design . 3. The use o f a non pressuri zed exti ngu isher ensures rel iable discharge even after prol onged non-use by usin g the charging gas to violently distu rb the d ry chemical before discharge. 4. This ty pe of extinguisher can be readily recharged in the fiel d without special equi pment and by rel ativel y untrai ned people. 5. The poi nt-type thermal sensors are not damaged by vi bration, sh ock and envi ron mental conditions. 6. The system's havi ng its own battery power provi des for 24-hour protection independent of the auger electrica l syste m either attended or unattended. 5.9.3 Fire Protection of Surface Mining Machinery (Johnson 1 976 and 1 978, Nagy 1 978) I n 1 975 the U. S. B u reau of M i nes entered into a cooperative agreement with the Ansul Company, Marinette, Wisconsin, to hel p in the eva l u ation of a new, pneu­ matica l l y operated, low-cost, automatic fire protection system. On-veh icle testing on front-end loaders and hau lage trucks was the main activity of this project, and Ansul's syste m currently is being further tested and refi ned. The B u reau 's most recent work concern i ng im proved fi re protection systems involves testing A F E X-type syste m on large bu l l dozers. The Bureau 's Twi n Citi es M i n i ng Research Center, M i nneapol is, M i nnesota, is conducting th is i n -house proj· ect with the help of Lemmons and Company, Boonvi l le, I ndiana. By the spri ng of 1 976, the A F E X system had been insta l l ed on a Giat/AI I is HD 4 1 tractor at the com pa ny's Boonv i l l e and Sholes m i ne for approxi mately six months. The system was test fi red during March 1 976 and the dry chem ical appeared to cover the fi re hazard areas of th is l a rge bull dozer wel l. No exti ngu ishant entered the cab and the system ex pelled the 40 pounds of dry chem ical i n approx i mately 1 5 seconds, which wou l d give the operator enough ti me to shut down his mach i ne and ex it. Concu rrent with the bu l l dozer fi re syste m work, the Bureau is work ing with various m i nes, fi re protection equi pment compan ies, and mine equ i pmen t manu· factu rers to ma ke ava i lable rugged, cost-effective, automatic fi re protection systems for other classes of large, mobi le mining equi pment (e.g., shovels an d l a rge down­ hole dri l ls). Also under way is a major metal and non -metal health an d safety 1 16 

D E S I G N CR ITER I A I N M I N E SAF ETY A N D H AZAR D CONTRO L progra m to i mprove fire protection for shafts and shaft stations. 5, 1 0 Conclusions and Recommendations Conclusion: The fragme nted approach to design criteria development for m ine hazard control is no longer accepta ble. Recommendation: Al l basic information and techni ques needed to apply the overa l l systems approach in mine safety and h azard control shou l d be developed, Conclusion: Bel t conveyor systems sti l l represent a major fire hazard in m ines ; acceptance test methods seem inadequate a n d large-scale fire testing is i ncom plete. Recommendation: Test methods that provide a mean i ngfu l and quantitative rati ng of the fl a mmabi l i ty, fl ame spread, and toxicity of com bustion products of belti ng materi als shoul d be developed. A d ru m friction test ( being cl ose to real-life condi­ tions) for use as an acceptance standard shou l d be devel oped and adopted. Large­ scale fire gal lery tests on belt conveyor systems shoul d be completed or, if nec­ essary, conti nued to col l ect a l l the important data. These data shou l d be correl ated with s ma l l-scale test data and uti l i zed for acceptance test and desi gn criteri a de· vel opment. Development of more sensi tive, rel i a ble, and economical fi re detection, alarm, and su ppression syste ms fo r belt conveyors shou ld be contin ued using overal l system design pri nci ples. Conclusion: The fi re safety of wi re and cable insu lation materials has i m proved in recent yea rs, but no un iversal test methods are ava i l able for behav ior c lassification. Recommendation: Si mple, rel i able test methods shou l d be deve loped or adopted to evaluate flamma bi l ity, smoke emissions, tox ic fu me evol ution, and ci rcu it integrity of wi re and cable i nsu l ations appl icable to mine i nsta l l ations. A com bined ''h azard index" rati ng system incl uding these and other criteria important in m ine h azard evaluation shou l d be developed, Conclusion: As the size and nu mber of conti nuous m i ners and other u nder­ grou nd power equi p ment em pl oyed increases, the size of the hydra u l ic systems employed also increases. The petroleu m- based hydrau lic flu i ds represent a defi n i te fi re hazard, and the currently avai l able fi re-resistant hydrau l i c fl uids (water-i n-o i l emu lsions) are i nsufficient i n terms of mech anical and chemical performance (cor­ rosion ) . Recommendation: The development of the H S- B type hydraulic fl u i ds shou l d be continued as an interi m measure, but emphasis shou ld be placed on deve lopment of a water-free fi re-reta rdant hydraulic flu i d that has qual ities equal or superi or to petroleum- based fl u i d. Conclusion: Development and refine ment of fire sensing dev ices has progressed, but the i r fu l l potential h as not yet been explored. Recommendation: Deve l opment and refinement of all types of fire sensor shou l d be conti nued and their uti l i zati on in the most promising appl ications shou l d be supported, but this sh ou l d not be a reason to avoid using state-of-the-art technology cu rrently. Conclusion: The tu be bundle information relay system recently employed i n U.S. mines a n d used i n more than 40 mines i n United Kingdom a n d G ermany for 117 

MI NES AND BUNKERS sampl ing gases i s be i n g consi dered a breakthrough although 9 years o l d . I t h as already resulted i n great advances i n mine safety i m provements. Th is system also h as been employed in the chemical industry for m any decades for sampl i ng gases and l i quids and for pneu matical l y transmitti ng i nformation and com m and signals. Recommendation: The tube bundle as an information rel ay system shou l d be fu r­ ther expl oited for mine safety applicati ons. Existing knowledge and ongoi ng re­ search conce rn i ng the use of tu be bundles as a gas sampl ing dev ice sh ou l d be expl oited an d expanded. The absorption of submicrometer particles by various tubing materials (or coati ngs) shou l d be i nvesti gated. The use of tube bundles for l iqu i d sampl ing, pressure differenti a l sensi ng, liquid level indication, and tempera­ ture sensing ( l iquid fi l led tube) shoul d be explored. The use of tu be bundles for transmitting command signals (open ing or closing doors) and acti vati ng alarms and fi re or explosion su ppression devices shou l d be deve l oped. Tu be bundles also shou ld be uti l i zed as back-u p systems for electrical l y operated equ ipment. Conclusion: The problem of spontaneous combusti on in U.S. coal m ines is gain­ i ng increased attenti on for two reasons : the development of deeper seams and the exploitation of western mines, wh ich are more suscepti ble to this hazard. Recom­ mendation: Recent studies deal i ng with the characteristics of spon taneous com­ bustion and the i r detecti on (e.g., by tu be bundle sampl ing) shou l d be accelerated to m i n i m i ze this hazard in the new coal mi nes. Conclusion: Appl ied technology development in underground mine fi re and ex­ plosion preventi on and su ppression has m ade significant advances in re cent years. Recommendation: Deve l opment of methane drainage tech nol ogy shou l d be con­ tinued Face ignition quenching systems for conti nuous mi ners and tun nel bori ng m achines shou l d be refi ned, and these quench ing devices shoul d be integral parts of new machines. The demonstration and refinement of coal dust explosion barriers shou l d be continued, and their opti mum l ocation in relati on to face areas sh ou l d be identified The remote seal i n g technology recentl y developed for the control of coal mine fi res shou l d be perfected. The ongoi ng mine shaft fire and smoke protection system development progra m shou ld be ampl i fied ; this system shou l d be i nsta l l ed in metal and non-metal mines. Conclusion: F i re protection of surface mining veh icles and machinery can be greatly i m proved by the insta l l ation of automatic fi re detection and suppression systems. Recommendation: Existing devel opment efforts sh ou l d be conti n ued and new ones initiated as needed to provi de fi re protecti on e qu i pment for trucks, l arge haulage vehicles, augers, large down h i l l dri l ls, shovels, and draglines. F i re detection and su ppressi on systems shou l d be integra l pa rts of new su rface mining veh icles and m achinery. 5. 1 1 References R . E. Barrett, "Buildi ng Health and Safety into the Mines," Professi onal Safety , Jan . 1 977, pp. 8, 9. R . F . Chai ken and D. Burgess, " Selected Topi cs i n Mine Fire Research" paper presented at 1 18 

D E S I G N C R I T E R I A I N M I N E SAF ETY A N D H AZA R D CONTR O L American Chemica l Society , Division o f I ndustrial and Engineeri ng Chemistry National Symposium on F i re Safety Aspects of Poly meric Materials, Washi ngto n , D.C., June 6-8, 1 977. W. F, Diamond, Island Creek Coal Company's Exptlr/ence with Plastic Coated Conveyor Belt· ing, Washington , D .C., 1 960. J. C. F ran kl i n , K. B. Weverstad, and R . F. Marguard , Polymeric Sealan t Ust1d to Stop Shale Degradation in Coal Mines, U. S. B u Mi nes TI R-1 03, Washington, D.C., 1 977. A. L. F urn o, Mine Face Ignition Quenching, U. S. BuMines Tech nology Transfer Seminars IC 8768, Washi ngton , D.C., 1 978. A. M. Harstein and D. R. Fo rshey , Coal Mine Combustion Products: Conveyor Belts, U .S. BuMines Report of I n vestiga tion 8 1 07, Washington , D.C., 1 976. M. Hertzberg, Mine Fire Detection, U.S. BuM ines Technology Transfer Seminars IC 8768, Wash i ngton , D.C., 1 9 78. M. Hertzberg, and C. D. Litton , Multipoint Detection of Products of Combustion with Tube Bundles, U. S. BuMi nes Report of I nvestigation 8 1 7 1 , Washi ngton , D.C., 1 976. G. A. Johnson , " I mproved Fire Protection Systems for Surface Coal Mining Equi pment," paper presented before the NCA/NCR Coal Conference , 1 976. G. A. Johnson , Improved Fire Pro tection Systems for Surface Coal Mining Equipment, U . S. BuMines Tech nology Transfer Semi nars, I C 8768 , Washi ngton , D.C., 1 978. G . A. Joh nson and D. R. Forshey , Automatic Fire Protection Systems for Large Haulage Vehicles, U.S. BuMi nes I nfo rmation Circular 8683, Washington , D.C., 1 977. R . L. King, Remote Seeling System for Extinguishing Coal Mine Fires, U.S. BuMines Tech­ nol ogy Transfer Semi nars IC 8768, Washington , D.C., 1 978 . J. M. K uchta , Fire Pro tection for Mine Conveyor Belt Systems, U.S. BuMines Technology Transfer Seminars IC 8768, Washingto n , D.C. E. N . Ladov and D. A. Law, Improved Fire Safety of Coal Mine Hydraulic Systems, U .S. BuMines Technology Transfer Semi nars IC 8768, Washingto n , D.C . . 1 978. I. Liebman, Water Barriers for Suppressing Coal Dust Explosions, U.S. BuMines Report of I n vestigation 8 1 70, Wash ington , D.C., 1 976. I. Liebman and J. K. Rich mond , Coal Dust Explosion Barriers, U.S. BuMines Tech nology Transfer Semin ars I C 8768, Washi ngton, D.C., 1 978. D. W. Mitchel l , E. M, Murphy, and J. Nagy , Fire Hazard of Urethane Foams in Mines, U .S. B u M i nes Report of I nvesti gation 6837, Washington , D.C., 1 966. D. W. Mitche l l , J. Nagy , and E. M, Murph y , Rigid Foam for Mines, U .S. BuMines Repo rt of I n vestigations 6366, Washington , D .C., 1 964. D. W. Mitchel l and H. C. Vera kis, "An Overview of the Fire and Explosion Hazards in U nder­ ground Coal Mines," 1 st Symposium on U nderground Coal Mining, Vol . 1 , Oct. 21 -23, 1 975. J. Nagy , M ESA's Views on Mine Explosions and Fire Research, U.S. BuMines Technol ogy Transfer Se minars , IC 8768, Washingto n , D.C., 1 978. J. Nagy , Review of Use of Urethane Foam in Underground Minas, Memorandum to Acting Assistant Di rector, Tech, Support, 1 973. J. Nagy and P. M , Ha l l , " F i re Detection i n Coal Mi nes ," paper presented at 2nd West Vi rgi nia University Conference on Coal Mine Tech no l ogy , June 1 3 , 1 974, Morgantown, West Vi rgi n­ ia. J. I . Nutter, Fire Resistent Conveyor Belting for Underground Mines, PV C Belting Manufactur· ers Association , Washington , D.C., June 1 7, 1 977 . R. Pariser, J. J. Mc Evoy and P. R. Johnso n , Elasto mers and Flammabi l ity , tutorial lecture for the Committee on F i re SafetY Aspects of Polymeric Materials, Nati onal Research Counci l , 1 974. H . J. Roux, " Accommodation of Polymeric Materials in Systems Approach to Building F i re 1 19 

M I N ES A N D B U N K ERS Safety.'' paper presented at the American Chemical Society , Division of I ndustrial and Engineeri ng Chemistry Nati ona l Sy mposi u m on Fire Safety Aspects of Poly meric Materia ls, June 7, 1 977, H. s. Stephenson, Firt� at MichHI Colliery Fife, H. M, Stationery Office, London , 1 968. A. M. Tay lor, "Wire and Cable I nsu lation for Rapid Transit Systems," paper presented to American Chemical Society , Division of I n dustrial and Engineeri ng Chemistry National Symposium on Fire Safety Aspects of Polymeri c Materials, June 1 977 . Technology News . "Automatic Fire Protectio n for Coal Augers," 1 976. The Secretary of the Interior, Moving Ahead in Metal and Nonmetal Mine Health end Safety, (Annual Report to CongriiS$}, Admi nistration of Public Law 89-577 in 1 974 . Walter Kidde and Co mpan y , I nc., Evaluation of Materials for Protecting Existing Urt�thane Foam In Mintll, Prepared for U.S. BuMines, 1 974 . D. G, Wi lde, Combustion of Polyul'tlthane Foam in an Experimental Mine Roadway, Research Report 282, H,M, Stationery Office , London , 1 972. 1 20