Document daRrGpdkYLEJeErLY2Znpp57q

'Fi iijj /PPG INDUSTRIES, INC. DID NOT COME FROM IT'S FILES AND CANNOT BE AUTHENTICATED BY PPG INDUSTRIES, IN'C. NOTE: THIS DOCUMENT D'D NOT'COME FROM ppQ FILES upon an embarrassingly obvious structural characteristic of asbestos, it is supported by uncentastad docu mented experimental findings as wall as by data from soma promising pre liminary experimenta. The Uttar, however, require confirmation. Theory and Supportive Data . The now theory is simply this; tha locus of pathogenicity of asbastos dust resides in tha polyfiiamsntaua struc ture of its fibrous particle*. Various data support this theory. Man*made mineral fibers, is con trast to poiyfiUaentoua asbestos ' fibers, era monofilamantoua. The dust of those moDofilamantous fibers (fibrous glass,1 ceramic aluminum sil icate/ and silicon carbide whiskers*) that have been studied have proved to be senfibrogenic when inhaled or in jected mtrstracheally. Synthetic chryeotile is-noafibrogenie when it ia injected intrstracheslly. It ia monofilamentous, It dif fers from natural chryeotile in that ita tubular crystals are discrete and not in cioee parallel apposition to cadi ocher, as is the case with the natural product. When a grinding fora is applied to asbestos fibers, they tend to split lon gitudinally rather than to fracture transversely. Consequently, asbestos that has been ground to a fiber length of less than 5m will consist largely of fibers that axe monofilamentous. Those bundlee of fibers still remain ing will be greatly reduced in thick ness and will approach the monofila mentsus state. It ia the fact that most of the fibers in such finely ground asbestos are either monofilamentous or nearly so, that offers a logical ex planation of ita nonfibrogsnidty. When asbestos is heated to 1,000 C, its pathogenicity is either lost or se verely reduced (P. Cross, MD and 2LA. Harley, Jrn MD, unpublished dais). At this temperature, the fibrils composing the bundles tend to be come fused into unitary structures, ie, the fibers tend to become monofilementous (Fig U. Although chemical changes do occur as a result of the heat, such changes have no bearing on the resulting loss of pat hogenicity since it has been shown (with syn* Fig l.-iaowtw. tasted far lee hours in n Metric muffle furnace at 900 la 1,000 C- rum, Chrrtetiie taeted la 900 C. Mttaugft fibrous structure >s fetsmed. fidnti ire oOlitereted by founded tanwieneifiee of efferent Canvty. seovsted from ana mother by leu dense cam. (Toe rignu, Oecweata iwateo to LOQO C. Oouc-sse densities snd ram feoons ebUlerste fibr*. lar structure af fibers. (Bottom ngnti, AmoUi, heated te 950 C. Oboows fusion af cansbtwens in fiber bwwtes hat formed |toM af electrersdense matanat, thereby leering other portion* gt fibers reit**y efectrarMrenseerent (enginel msgnifwstan as1,0001. thatic chrysotile) that the chemical coapoeition of aabeetce ia not nsponable for its pathogenicity. By cementing the fibrils of asbestos fiber bundlee together chemically, it Is poaiiblt to convert the polyfilamaotows structures into monofilamentous ones. This has been successfully ac complished with various eKi-et* such is those of lead, iron, and mag nesium. The use of other water-insol uble cementing substances, such ss those of magnesium and calcium py rophosphate, calcium hypophosphat*. and calcium metaphosphata, is con templated. The method haa been to suspend finely ground asbestos in a diluta *olution (1% to 5%) of an appropriata soluble metal salt (lead nitrate, iron chloride or magnesium chloride). Af ter washing the asbestos free of all excess salt, it ia suspended is 1% solution of sodium silicate. The latter Fig Z-Ovyeetile fibers sememe* witn tmd sSicste. Pretence ef leed uiicste mucetsd by efictron oems tip>mg --fnm lunwn at me fibrils end eueetaie (engine* iwsgnificsuon x 2X3,003. Aren Cnvimn HaartfWbf 27, Oct 1973 Loctia of Ptftogenicity/Gm*s A Harter 3*1 ilroojjajr] 5753