Mines and Bunkers Volume 10, Fire Safety Aspects of Polymeric Materials (1980) / Chapter Skim
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MATERIALS
MATERIALS
Pages 62-87
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From page 62... ...
I n additi on, i n evaluating pol y meric materia l s with improved fire safety characteristics, competing fi re safe ty requ i rements must be assessed and trade·offs made (e .g., a decrease in ease of ignition or fl ame s pread that a lso leads to an i ncrease in the production of smoke or toxic com busti on products might not be tolerable i n situations where egress is l i mited )
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From page 63... ...
° ° Thermoplastic com positions gene ra l l y wi l l mel t between 1 00 C and 250 C The l oss of rigidity that occu rs at the softe n i n g poi nt of such materials and th e su bse q uent decrease in me lt viscos i ty as the temperature increases in many cases al low these l iquids to recede from the ignition sou rce at a sufficiently rapid rate to prevent thei r su bsequent pyrolysis and ignition.
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From page 64... ...
Therm a l l y stable polymers with superior fire safety ch aracteristics may be too ex pensive for routine u se. The appl ication of fi re-retardant coati ngs is sometimes a cost-effective approach ; how ever, it is l im i ted to a rel atively smal l number of uses.
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From page 65... ...
It can be formul ated into a wide variety of com positions with properties varying from soft elastomers to tough rigid poly mers. (The appl ications of PVC i n m i nes are discussed below i n Section 4.3)
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From page 66... ...
By far the largest usage for PVC in m ine appl icati ons is in p i pe ; pi pe fitti ngs ; condu i t, wi re, and cable coati ngs; and belt conveyors.
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From page 67... ...
As ex pected, the flammabil ity of the polyethylene is reduced as the ch lorosu l fonyl ch lo ride content is increased. Fl ammabi l ity has not been th orough ly stu died alth ough hydrogen chl oride and sulfu r d iox i de are major products of com bustion.
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From page 68... ...
Al though halogen and antimony compou n ds have been used to reduce the burn i ng rate and ease of ign ition of PMMA, less effort has been devoted to its fi re reta rdation than to that of other po lymers. Th is is due partly to the fact th at for most appl ications i t is difficu l t to affect the "u nzi pping" depolymeri zation mech a n ism so cha racteristic of this polymer.
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From page 69... ...
Thei r fi re resist ance h as been improved by the addition of hal ogenated materi als as additives or copol ymers. It is the tough ness, clarity, and im pact resistance of the pol ycarbonates th at make them attractive for use as hel mets, face shiel ds, an d glazing material in m ine appl icatio ns.
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From page 70... ...
These rei nforcements and fi l lers ofte n com prise m ore th an h a l f of t h e fi nal com position a n d can alter t h e fl ammabi l i ty o r fi re safety o f t h e total com posite signi ficantl y; therefore, it is i mportant to consider the tota l com position before deciding u pon the flammabi l ity characteristics or fire safety of th ese mate ri a ls. Because of thei r cross- l i n ked natu re, thermosets general ly do not soften or dri p when exposed to a flame.
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From page 71... ...
These compos itio ns are u sed for special a ppl ications. Molded phenol ics have been used extensively i n vari ous electrica l appl ications due to their com bination of desi ra ble electrical, mech an ical, and fi re-resista nce p roperties.
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From page 72... ...
The rel ative tox icity of halogenated polyester resi ns has been a su bject of con siderable discussion ever since thei r i ntroduction in 1 953. The chlorine contained in these com positions genera l l y has been shown to be converted largely, if not quanti· tativel y, i nto hydrogen chl oride, Reinforced pol yester formu lations fi nd appl ications i n panels, pipes, ducts, and tan ks.
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From page 73... ...
A variety of phos phorus and boron compounds have been used to reduce fl ammabil ity when re qui red. The various amino resins find l i mi ted appl ication as coati ngs on a variety of metal and reinforced plastic panel su bstrates.
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From page 74... ...
pol yurethanes are fi nding increasing use on automobi le exteriors in such appl ications as front and rea r fender exten sions, fro nt fender s k i rts and panels, and front or rear fen der fi l lers ; appl icati ons in uti l i ty veh i cles can be expected to fol low. 4.2.4.5 Polysulfide Rubbers The polysul fide ru bbers, also known as th i okols, are pol ymers composed of al i phatic hyd rocarbon chains con nected by di·, tri·, and tetra-sulfi de l i n ks.
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From page 75... ...
They a r e rel atively expensive (less s o than fl uorocarbons, b u t more so than hydrocarbon ru bbers) and thei r mechanical properties are m arginal for many appl ications.
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From page 76... ...
Because of the l o w thermal conductivity , the h igh surface heat flu x generated from an i gn iti on sou rce, can cause a l most i nstantaneous conversion of a polyurethane to fl amm able gases. Th is often results in very rapi d surface flame spread a n d h i gh fla m i n g tem peratu res once the surface i s ign ited.
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From page 77... ...
4.2.5.2 Polystyrene Foams Low-density po lystyrene foam is used as thermal insu l ation, and h igh density foam is used for structu ral appl ications. The major fi re hazards from ce l l u l ar poly styrene are the potential for h igh bu rn ing rate, high smoke production, and rapid flame spread.
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From page 78... ...
The ou tstanding properti es of these foams are the i r rel atively good fi re safety ( l ow smoke production, low flame spread rate, and l o w fuel va lue) , good insu l ation efficiency ( K factor = 0.
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From page 79... ...
The flammabil ity hazard of glass fibers i n actu a l use, therefore, is sign ifi· cantly modi fied by the presence of these organic materials. 4.2.7 F i re- Retardant Coatings The use of fi re-retardant coati ngs is one of the ol dest methods for protecti ng f l ammable and nonfl ammable su bstrates from reach ing ign ition or softening tem· peratu res.
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From page 80... ...
. " I ntumescent coati ngs are used to protect flammable su bstrates such as wood and pl astics from reach ing i gn ition tem peratu res.
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From page 81... ...
M u rphy ( 1 972) has com piled data i l lustrati ng that perform ance in a large-sca le trial in an experimental mine correl ates wel l with the fl ame spread i ndex determ ined using ASTM Method E- 1 62 and th at a fl ame spread index of 25 or less is reasonably safe for venti lation cloth.
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From page 82... ...
No t o il re• i a tan t . BR Po l ybu tad i ene Pol ybu tad iene A synthet ic rubber in tha &aneral purpoaa f ie l d .
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From page 83... ...
EPM Ethyl ene E t h y l ene A seneral pur po s e synthe t ic which haa P r o p y l ene Propylene sood a g ing , abr a s ion a nd heat res i s Ru b b e r t a nc e . EPDH Ethyl ene Ethyl ene Same a s EPH .
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From page 84... ...
4.3.3 E lectrical Conductor I nsulation The probl em of fi re safety of electrical con ductor insu lation in m ines is essen tial l y the same one faced by electric uti l ities and i n naval vessel s, industrial instal l a ti ons, and a l l ty pes of bu ildings. Polyvin y l ch lori de has been the pri nci pa l resin used for almost a l l appl ications since about 1 938.
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From page 85... ...
Coati ngs to protect ex isti ng polyureth ane sea l ant insta l l ations also are being s ought. Warner ( 1 97 5)
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From page 86... ...
Conclusion: The venti l ation cloth used to direct a i r currents during normal working and emergency conditi ons can contri bute to the fi re safety hazard by igniting easi l y and spreading flame rapidly. Recommendation: The tentative gu ide l i ne specifyi n g that venti lation cloth ex hi bit a flame spread rati ng of less than 25 in ASTM Method E- 1 62 shou ld be conti nued unti l evi dence ind icates that it is not sufficient.
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From page 87... ...
M M urphy, Flame Spread Eval uation of Venti lation Cloth , Report of /nlltl$tigations 7625, U.S.
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