Document ykRaeyzN5k1reeeOJp4YYZGeD

FILE NAME: Trade Publications (TR) DATE: 1975 Dec DOC#: TR062 DOCUMENT DESCRIPTION: Trade Journal Article - Handling Asbestos Chrysotile Asbestos in Plastics JOURNAL OF PAINT TECHNOLOGY - . ........ _ Asbestos .......... V-: W J p tg 3 . i * :^ Chrysotile Asbestos in . . .im*^ "-<*v C *!*.''s&SrA-'-'X :' 5cs5v> drtniJ-vn-. '** ;V 11 " : laS^av- j ^ .: J o h n L MYERS:; i ^ Plastics S1pij-TW "'"f WWPir><^r'.n I>n>rn>t~y> . ... afe wS--;! .., S * ' .........:!-, ` Asbestos has rRRftivflrt a great deal .of attention and publicity indecent years especially after it was designated a "target health hazard" by OSHA and a hazardous air pollutant" by the EPA. Many of the articles on asfrastos by the press have been emotionally oriented or distorted and, in some cases stories have been sensationalized, based on obvious misinterpretation of facts' The use of half-truths or unsubstantiated statements has led to general con fusion and the unfair castigation of asbestos and products containing asbestos The purpose of this paper is to put th e matter of asbestos use and asbestos hazards into a logical and practical perspective. In this paper, the different types of asbestos and their many uses are discussed, long with government regulations controlling the use of asbestos. The health hazards associated with asbestos, both occupational and environmental, and some industrial *ex- perience with air sampling and dust control^ measures are also covered/..,'-^ v- >i;**?4* " .V V,. i "' - KEY WORDS: Asbestos; Plastics; Air pollution; .Toxicology..^ .tTM,.. ,, i . ' T V , aw*: ___ .. floor tile and in phenolic molding compounds. It is also used in other plastics such as polypropylene, poly ester, nylon, melamine, epoxy, sili cone, and vinyl Asbestos provides valuable function in such products' as -brake linings, d utch fadngs, electrical i-components, automotive parts,-furni^ture, boats, sealants,' coatings, adhe"sives.and mastics. The most important -functions of asbestos in plastics are re inforcement, dimensional .-stability, h eat resistance, flow control, and gen- , eral-puipose filling. Most of die func tions are supplied: fry : short-fiber chrysotile - asbestos' fiber,' although What is Asbestos? u - - . ,, , ' * i - * Asbestos is a commercial or generic term used to describe six naturally occurring "asbestiform" minerals that are fibrous, hydrated metal silicates. The six varieties are divided into two classes--serpentine . and amphibole-- . based on their crystal -:structure. Chrysotile is the only member of the serpentine class, while the amphiboles include croridolite, amosite, antho- phyllite, tremolite, and actinolite. Chrysotile is by far the most-used variety and accounts for over 952 of U.S. consumption, as noted in Table 1. "ft ? Crocidolite, also known as blue as bestos, is imported from South Africa. Because of its high mechanical strength and good resistance to adds and alkalis, it is used to reinforce a limited variety of plastics w here its pronounced color is not objectionable. Amosite, also imported from South Africa, is used primarily in thermal P m m tc d ai the Golden Gate Society' Man* aarment Seminar held in San Fnneiaco, Calif., June 16. 1975. * Metal Div,, N iaaan Fall, N.V. 1450!. insulation. Although there are some deposits of anthophyllite in the U.S., most of it is imported from Finland. longer chrysotile fibers and other as bestos varieties are sometimes required for particular properties. ` I t is used prim arily as a filler fo r' polypropylene and in insulating ma- Why Use Chrysotile? ~terials.. A c_o_m^p_ar_i_so_n o__f__t_h_e__f_o_u_r Among the several advantages of -varieties of asbestos which are of o o m r.,d u y so tile , which set it apart from m erdal importance is presented. ;in ^ -die amphibole' minerals and account Table 2. I t should be noted th at there' for its widespread and increasing us are significant differences between age, are world-wide availabilityvm e chrysotile and amphiboles with regard chanical strength, flexibility, positive to chemical composition and certain surface charge, low iron content,'soft physical properties. . ness, and low refractive index. I t is conservatively estimated that chryso Where is Asbestos ... . tile asbestos is used in over 3,000 ap , Used and Why? . plications and, in most of these appli cations, if is an essentia] ingredient Asbestos has served mankind for more than 100 years in a broad vari for which no replacement is readily available. ; ety of applications. The general areas in which asbestos is used in the U.S. are shown in Table 3. Based on infor mation from asbestos producers and The information in Table 1 shows that the use. of chrysotile asbestos and its share of die total market are stead ily increasing. This is due partiy to consumption surveys, it is estimated technical advances perm itting die th a t tire plastics industry uses about 33% of the 800,000 tons consumed an nually, which makes it die largest single user of asbestos fiber.. The largest uses of asbestos by die plastics industry are in vinyl-asbestos broader use of chrysotile in plastics and die general decline in die use of asbestos in certain fireproofing and in sulating materials. In addition, there is increasing evidence that crocidolite and amosite are more hazardous to Vol. 47, No. 611, December 1975 yf. y Year 1967 1968 1969 1970 1971 1972 Table 1--Apparent U.S. Consumption of Asbestos, T o n s ' Total 720,588 817,563 784321 TO8 H 1 Chrysotile Arrossite 686,044 (95) ` ' 12358(1.7) . 775,711(95) . 20,467 (23) _ : 749,708(96) "J ^.14,618(1.9) 695.770 (961 . '"T "14361 (2.0) Crocidol ite 14.917(2.1) 13,965(1.7) 10358(13) 8,936(13) (a) Information Bureau of Minet* * (b) Percent Table 3--Apparent U.S. Consumption of Asbestos By General Use Areas Area of Use Percent of Consumption Construction 1 . - v.v Floor tile .' ' \ . Felt paper = r ; T5^K' Friction and packing Insulation1 C*%V y4ir.,li3' Textiles - .* O th er-:-- --- .^x x * 11 i human h e a l* than chrysotile.1 wit Since.. T biT used Solely by fee inhaktion of Research on Cancer (a division of fee 1970, the use of croddolite in Britain _ ; asbestos fiber.'.Ancrfeer im portant con-~. W orld H ealth Organization): "There has been restricted after a panel o f. sidration .is the rektion "between is evidence of an association of meso- experts "concluded there was suffi * cigarette smoking and lung cancer, as thH1 tumors w ife air pollution in cient evidence to suggest other types reported by D r. E . C. Hammond and fee neighborhood of croddolite mines of fibre should be substituted for 'D r. I. J. Sehkoff.* In this study, they and of factories usingTM ixtures o fa s-- - croddolite wherever possible."*, T^V', . ''reported fe a t:."It seems clear, then,;. . ;- ' feat lung cancer is uncommon among . ` asbestos insulation workers w hohave bestos fiber types. The evidencej t -[w lates to conditions of nm yyears'-ago. - W hat i$ th e A s te s to s H ^ r d ? ./ , ,7 no history of dgarette smolong and T here is evidence of no excess risk - It is readily accepted that asbestos, ..feat if 3he risk J s Increased, such in -' of mesotheliomas from asbestos ;air -" ; like many other foreign bodies, -.can = cause disabling lung damage, (p u l-: .crease is not grea-at"?v-pCa/-1**'*'- pollution which has esasted a n jfe e . -neighborhood o f^ d u ^ tiW n ria am o ii; monary fibrosis), commonly referred .-.w _ A -feird.disease, m esofeehon^ more recently -been associated ,-wife r S a i t m reported differ-- ^ d e n c e '^ .mesofeeltoina to as asbestosis. This disease and .persons' exposed :to asbestos.. Meso-t'-s ^^``ban and rural areas,;fee ; bronchogenic carcinoma (lung can - thelioma is an extremely rare cancer J;:;';eJ,uses of which have not-been estab-, cer) are the two most common as ' of the lining of fee eheSt (pleura) o r1' . nciA T here is no evidence of a risk .; bestos-related diseases. It is important fee abdominal cavity (peritoneim )._... ^ general public atzpresentTyti? C to note that, based on epidemiological In contrast to fee lung diseases,-feere,?..'.;^,. *V -:.`*Vr"- data, these diseases. have -occurred is some evidence fe a t m esotheliom a- T h e san e body quoted above has primarily in workers with U gh, long UcaUnl Woc.cUu.r after b--r-i-e-f---e-x- posures to ' also concluded feat feere is, a t pres- term exposures to asbestos dust. It is rektively U gh fiber levels. ent, no evidence of lung damage by of further interest feat one noted .re asbestos lo "tiae general pubBc; and, : searcher has reported feat neither of - According to fee 33-member Ad such evidence as feere is does n o tin - ' these diseases is peculiarly related to visory Committee on Asbestos Can- dioate any risk of cancer resulting from asbestos fibers present in water, Formula Table 2--Comparative Data for Asbestos Minerals y, r - i - " ` Chrysotile Croeidolite Amoslte 3Mg02Si0s'2H>0 NosO F esO.- 1.5M g05.5FeO 7MgO`8SiO. HjO beverages, food, or in fee fluids used * ' for fee administration W hile there seem s- be. general / 8SiOs HsO 8Sio.H ,o tw sn e y sx : . ' agreement feat fee public is .notjin -any present-danger from asbestos, it Composition,,% ; SiO. ' ., Mgo FeO " . . . __ F e,0 , . ` ai5o 4 h ,o ........... CaO ' .. NasO ' ` CaO+Na-O ' " Crystals . - . . Color . . - Texture . Flexibility Hardness, mohs Fiber diameter, A Tensile, mpsi . ..... Surface charge , Resistance to add Resistance to alkali 37-44 39-44 ` 0 -6 ' 0-5 ' 0 -2 . .12-15 "0 -5 Fine fibers . Cray green Soft silky Very good 33-4 180-300 800 Positive Poor . Good 4 9 - 5 3 '' ' 0-8 -r ' 13-20 : 17-20 2--5 '. 4--8 : . I--* ' Brittle fibers Blue , Harsh ; . Good, . ; 4 600-900 , , 600 . . Negative..Good Good .. ... 4 9 -5 3 -1' 5 6 -5 8 ;;ir; is also recognized fe a t excessive,'long term occupational exposure can cause - 34--44'- :'r': v " _ av:rrs-:. 3 --1y2 i"xv serious health problems. A lso/if . made emissions are not -controlled, 2-9 0 -2 i e if - ^ 'i- e 7\'r>`iL n n ; then"' environmental contamination could could approach harmful levels. D uring fee past two years, significant legislation bos been enacted b y 'fe e ; 0--3 . ; - Prismatic Gray/brown Harsh Good 55-6 - , 600-900 .200 . . , Negative . , Good -. :;_ Fair . . ,, Prismatic Gray Harsh. Poor . 53-6 <6040-90.0,,7r . Negative. Very good Good --- : Federal government to red u ce'an d control occupational exposure f as bestos fibers and to mmmrize fiber rwi-winns to fee environment.-Addi tional standards or reguktions have been proposed or enacted by many s ta te and local govern2men;^ts,' ^ -. ,. 5` - Summary of OSHA Regulations '- The W illiam-Striger Occupational Safety and Health Act of 1970 be- lil^ r * .: Mod Ptanio. Encyclopedia 1197. and Encwtopcdi. ot Chna. Tech, Vo1- * came effective on April 28,1971, wife To u r n a i , o f P a i n t T e c h n o l o g y the following Congressional purpose: Improper interpretation of die reg EPA Standards "To assure so far as possible every ulations has created many miscon W hereas OSHA is responsible for working man and woman in the na ceptions about equipment and pro the protection of the worker, the En tion safe and healthful working con cedures needed to properly use vironmental Protection Agency (EPA) ditions and to preserve our human asbestos. If exposure limits are not is charged with improving die en resources." The Act established the exceeded, -there are no further com vironment to which the general public Occupational Safety and Health Ad pliance requirements except fo r med- is exposed. On March 31, 1971, as- ministration (OSHA) within the D e ical examinations. Medical exam ina-' [ bestos, along with beryllium and ' r _ partm ent of Labor, which has re- tions re required for all employees - mercury, was identified as a'Thazard- "' ._ . sponsibiBty' for administration .and in any occupation exposed to airborne -v ' ous air pollutant" by the Admdnrstra- r ~ A enforcem ent Research a n d . related_ concentrations of asbestos fibers.,.The -" to r . of the .EPA. Natkjnal Emission . :s: functions are handled by the Depart- ' examinations re relatively simple*and 7;;' Standards for asbestos were then pub- * ; ment of Health, Education and Web ' ,[. should cost, no more tharn $ 5 0 p e r .y` lished by EPA in the Federal Regis-- , fare (HEW ) through th e National '[ 'yerTper ,tert Vol. 38, No. 66, April 6, 1973. " ' Institute of Occupational Safety and Respirators and sp ecial. clothing . -Although no numerical emission stan- - Health (N IO H ). Jiv e million em are required in die construction trade dards were established, -operating cri ployers and 60 million of th e nations for die spray application of insulation teria are prescribed^- to prevent' or - 80 million workers are covered by ..and fireproofing materials, and fo rth e limit asbestos emissions to -the out- ;=. OSHA. Specifically excluded -from 'removal of such materials. This spe- side air from asbestos m ills'roadw ays, y coverage are government employees d al protection is mot required for any- certain manufacturing operations, . and operations which are protected oth er use of asbestos unless exposure building demolition, -id die spray-on under other federal health and safety, lim its are exceeded. This is also true application of materials used -to in -'r' .'in laws. In a news release issued January for Jofher items such as specially sulate -or fireproof equipment -and 4 4, 1972, OSHA announced a Target- - equipped tools, change rooms, clothes machinery. The law further Tequires .. ' " Health Hazards Program -aimed a t laundering,'and waste disposal. R es that spray-on materials 'used to to y - . improving health factors .associated " pirators are not a substitute for en su k te or .fireproof buddings, struc- . with working conditions. The follow- -i-' ^gineering controls, but the law,,allows tu re s,.pipesyond -conduits, shall -con ing five substances were designated their use while controls ^are ^bemg - tain less tb a n -li .asbestos trn a dry- to be die focus of initial and con-' implemented, in ' :spedal. situations . weight basis. This should significantly oerted efforts by OSHA and NIOSH: -where controls a re not "feasible or '. "reduce emissions^to *which die gen-, - asbestos, cotton dost, silica, lead, an d - adequate, in emergencies, and forJn- - eralpublic may b e exposed, especially . carbon monoxide.'v-":: * S*. . frequent short-term. job. assignments. 'in large uiban areas. At the present time, new standards Caution, labels are required on prod- : ; i , - ; . ; the Administrator (of EPA) "1C have been established only for asbes ucts containing asbestos except where has determined that, in order to p ro -' tos, although, of die 8,000 toxic sub ..die fibers bave been modified by-a vide an ample margin of safety to stances on die NIOSH list, only 500 bonding agent or other material to protect the public health from as are covered by standards and many prevent dusting during any normal bestos, it is necessary to control emis- of those need updating. The new subsequent use or handling. Besides sions from major man-made sources . Standard for Exposure to Asbestos raw asbestos fiber, products which of asbestos emissions into d ie atmos- 5 ' D ust was published in the Federal require package labeling could in phere, -but d iat it is.n o t necessary to Register, V oi 37, No. 110, on June 7, clude: dry acoustical spray products prohibit all emissions. y ,-,tyry ~- 1972. The basic exposure standard is and joint cements, unsaturated roof- - . "In this determination, th e Admin an 8-hr tim e weighted average ing fe lt;and textiles, and some -in ' istrator has relied "on the National - (TWA) of five fibers, longer than 5 sulating products made w ithout ade- Academy .--of Sciences' -report on -as ; micrometers, per cubic centimeter of quate binders. T he labeling of ap ro d - -' " bestos, which concludes:'""Asbestos is y- - air. The TWA limit is t be reduced net does no t prohibit .its-u se . It * too important in our technology "and - to two fibers per cubic centimeter on " should be noted here that in a t least economy for its essential use to be . July 1, 1976. A peak concentration 902 of the products containing as stepped. But, 'because of the known - of 10 fibers p er cubic centimeter is bestos, the fibers are solidly locked serious effects of uncontrolled inha not to be exceeded a t any time. All into ,the product thereby presenting lation of asbestos minerals in indus of the fiber concentrations are those little danger of dust generation dur try, and uncertainty as to the shape to which an employee may he ex ing normal use and handling of the and character of the dose-response posed w ithout protective clothing and product* -Lx'.;.-..- ....- .'.'T q 'j. curve in man, it would be highly im- equipment. The first basic require ment of the new standard is monitor ing to determine whether or not fiber concentrations are in excess of the exposure limits. Some asbestos sup pliers provide a monitoring service to customers, and a similar service may be obtained fpom state health depart ment officials, insurance carriers, or private consultants. The law requires JOHN L. MYERS, Marketing Manager for the Calidria Asbestos Group in Union Carbide's Metals Div., received his B.S. Degree in Chemical Engineering from Purdue University in 1951. Joining Union Carbide th a t same year, h e se rv e d in th e N u c le a r D ivision until 1966, w h en h e b e c a m e a R e se a rc h E n g in e e r in the a s b e s to s group. H e w as promoted to his present position in 1970. : that monitoring be repeated as nec essary to ensure that employees are not exposed to levels in excess of tire exposure limits. . . . . . . . . . . . ; Vol. 47, N o. 611, December 1975 prudent to permit additional con tamination of the public environment with asbestos. Continued use a t min imal risk to the public requires that the major sources of man-made as bestos emission into die atmosphere be defined and controDed.'.T!-..:i\-.t-:,; is*f ^l* l'*-'*' V>*~ W hat I s In d u s try D oing?'f;cJv Table 4--Typical Air Sampling Results* . Celling . Type-Plant - Concentration, Or Operation Asbestos Fibers/cc Dust-Control Measures Asbestos producen and users are spending a considerable amount of time and money on various dust-con trol measures. Conventional .means to achieve minimum dust levels include: ventilation system son process 'local ventilation'-for saws The Asbestos Information Assooia- tion/N orth America reports that, dur ing the past 30 yean, the asbestos in dustry has spent millions of dollars to improve mining, milling, and manufac turing methods.* The establishment of safer working conditions has been a prime target and this work continues unabated and in close association with government agencies and independent m edical researohers.*-''v.;m-E~ / T h e ultim ate goals of the asbestos industry are: Reduction of work-area dust to minimum, levels; Protection of workers from asbestos-related dis eases; Maintenance of environmental emissions a t levels low enough to pre dude public endangerment.' ' A ir Sampling y 7 ,^ V .. In order to comply with OSHA standards and to determine die need for dust control measures, air monitor ing should he conducted in areas where asbestos is regularly handled or used. OSHA standards require that "all determinations of airborne con centrations of adjestos fibers shall be made by the membrane filter method at 400-450X (magnification) (4 milli m eter objective) with phase contrast illumination."1* The equipm ent. for collecting, air samples .costs less than $400 and is readily available. A phase contrast microscope can be obtained for as little as $600, or an existing microscope can be modified for "counting" the asbestos fibers in com pliance w ith NIOSH criteria.11 . Air samples have been collected and analyzed on a regular basis by the asbestos industry for years. Ex cept for a few applications where dust control is an engineering problem, in dustry is finding that dust levels are already within acceptable standards or- that minimum changes are nec essary to achieve compliance. Al though data on many asbestos/plastic applications are not available, the summary in Table 4 is typical of our measurements of dust levels during asbestos handling in various types of plants and operations. The dust levels reported are ceiling concentrations, and it should be noted that file allow- - " - -- *5 "7r- ---f -V'-* () Source: Union Carbide Carp monitoring report, rr**. - i,v*> handling, and automatic bag*openers/ "Unusual innovations Include: ' pel-; letized asbestos, special packaging, vu* t : able OSHA level is 10 fibers/cc. 'In and treated p ro d u cts/i^i-ru - Only short-fiber chrysotile is avail able as pellets, but this product serves' most cases, the TWA exposure level ,,a rfair portion ioftuhiec.-asubcessktos manrkteest,. would h e well below OSHA stan-.T ^pellets m ot -only reduce-dust during dards. Most of the data w erecollebted -J/conventional handling h u t they -are totally . before-the instalktion of ahy;'Sp ^ l - r - : al ^ i v^ ay eiQ ^ hooper cars a n d ' ^-co n tro l measures! Monitoring c f* ;;? W b e transferred mid used in -enclosed systems, fianing leaks m .fire' ditions -are caused by materials other-'-. Tsystem.dust in -work:areas is virtually fhan asbestos.This does not preclude - "".eliminatea. TJsedlan; huIk,.asbestos' . th e need for controls,'T w t-It ro o u ia ' /i "pellets^ a W aeducer ship p in g -W ts," - -change their scope and facilitate com-"-,' .eliminate r warehouse'-. storage R and pliance with government r e g u la tio n s .; handling, facilitate automation, reduce: Because of Trad press, asbestos is '. 'lean-up, and eliminate bag handling' frequently ordered out o f use without and disposal The pellets-contain ,no; . regard to 'w hether -or n o ta Thazard hinder and are Jnable_nough to b e . . actually exists d u e -to air contamina dispersed in dry form .or.in aqueous : tion. ' If -acceptable dust "'levels "are o r resinous.systems with conventional feasible, there is n o need to replace high-shear grinding equipment." - asbestos at the expense of product . Several types of special packaging quality or economic penalty. Gordon are currently available, and suppliers Everett of EPA points out that in consider customer requests for -unus- - formation on the biological effects of ual requirements. The floor tile Indus- ' asbestos is very limited and that the try can obtain asbestos in plastic bags effects of many substitutes have not which can be added directly to th e . been investigated a t all. Before as compounding operation. Asbestos -in . bestos is replaced, it should be cer bleached paper bags assembled w ith taTMin that 7a s"afer --alter;native is avail- , wwaacter--saowluubwle ggnluieea,annad pprriimnteead wwiimth .nmtetawr liliisVpnenrasnifHlilne jnk1:- h i a.d1d1e_dJ - Obviously there re moro p e o p le ,.. exposed to products containing asbes tos than there -are to raw asbestos fibers. As noted previously,' more than 90 of file asbestos used in this coun try is in products in which the asbes tos -is "locked in" -or bound w ith cement, plastics, or other binders, so ,, that there is no release, or at least no significant release, of fibers in woik areas or to the environment Materials or products with locked-in fibers would include: floor tile, polyester directly -to paper-m aking.finishes'hr acoustical tile formidations. /'.r^V r^i- - ; Although "wetted" asbestos^is not generally available, .most . suppliers are working w ith customers to pro vide "dustless" products. W hen justi-. fled by market demand, asbestos can be treated with water, mineral spirits,, glycol, or other materials compatible with the application or system. CT'V5.Vf? . Conclusion resins, phenolics, sealants, coatings, Asbestos is one of industry's many brake linings, friction materials, rub ber, roofing compounds, and rein forced plastics. Since an abrading ac tion on some of these products could release asbestos fibers, appropriate monitoring and/or control measures should be instituted if it is thought that such action would release fibers. raw materials w hich, involves a po tential hazard when not used w ith reasonable respect and care. Although all forms of asbestos are recognized as hazardous to health when inhaled excessively, there is growing evidence that crocidolite and amosite are more hazardous than chrysotile. Fortunate- J ournal o r Paint T echnology ]y, die plastics industry uses primarily chrysotile asbestos and, in most prod* ucts, the fibers are k>cked-in to pre vent airborne contamination. Al though asbestos dust levels are gen* . erally lower than expected, industry continues to expend large amounts of time and money to further the quality, o f the. -workplace, though die general public is n o t rendy in danger,' occupational ' are required " vironm ental Chrysotile and necessary the nation1 w ith proper control, it can be used safely and in compliance w ith govern* / < . 4 V ` , -'fi - ment regulations. Medical, scientific,' government, and industrial personnel m ust continue to work closely s-i*j*-*V**'%, ' " ./**'*Ve<' Wr'.'.i gether to establish reasonable expo- ~- sure limits, ` ' " and eUhnarate endangennent jj] - 's^ ,y"* , - (5) (6) (7) (8) (9) (10) (11) (12) (13) posed occupational asbestos stan dard, " ` " ` Hammond "Relation Risk ated Disease among Insulation Workers in the U J A .," presented at meeting of the Working Group to Assess Biological Effects of As bestos, International Agency for Re search on Cancer. Lyon, France (Oct. 4, 1972). `Report of the Advisory Committee on Asbestos Cancers," Brit. J . In- dustr. "Asbestos, (Oct, . . "National Emission Standards for Hazardous Air Pollutants," federal Register, 38, No. 66, 8820 (April 6, 1978). ~ ' "Protecting the Asbestos Worker," Booklet No. 101D37. T h e Asbestos Information Association/North America, p S. Selikoff. I. J.. Industr. Medicine, 39, No. 4, 21 (April 1970). "Standard for Exposure to Asbestos Dust," federal Register, 37, No. 110, 11320 1972). Bayer, S. G,, et al, "Equipment and Procedures for Mounting MHliporc Filters and Counting Asbestos Fibres by Phase-Contrast Microscopy," Bureau of Occup. Safety and Health. UA. Dept, of Health. Edu cation, It Welfare (Feb. 1969). "Asbestos Health Question Per plexes Experts," Chem. Eng. News, 18 (Dec. 10, 1973). - Myers. J. L., "Calidria Asbestos Pel lets." ASBESTOS (Oct. 1971). . Vol. 47, N o. 611, December 1975 * , / J i "'I \ ' r-*> '' *",,r ' -V 1* <'u vs V -- - - " - - ~ Z~-` 'V r' r-V' tv, *' **. a. 7v*.1 r "~ ^*iv.%*4?*.' .-'y-i -V;t* r. y> . Asbestos Information Association -* North America ' .. ' 1660 L Street, N .w .- ;i I Washington, D. C, 20036,,. y