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* 1Reprinted Horn the Archives of Environmental Health January 1971, Volume 22 Copyright 1971, American Medical Association Occupational Acroosteolysis II. An Industrial Hygiene Study Warren A. Cook; Paul M. Giever, MPH; Bertrrm D. Dinman, MD, ScD; and Harold J- Magnusor., MD, MPH Ann Arbor, Mich BOR 009756 -- 74 Occupational Acroosteolysis II. An Industrial Hygiene Study Warren A. Cook; Paul M. Clever. MPH; Bertram D. Dinman, MD, ScD; and Harold J. Mopmison, Ml), MPH, Ann Arbor, Mich An Industrial hygiene survey was conducted in respect to occupational acroosteolysis (AOL) in 32 plants engaged in production and compound ing of polyvinyl chloride. This survey was limited to inspection ol facilities, interrogation of tech nical personnel, and statistical analyses. All mar ulacturing processes and chemicals utilized were explored. A major objective was the iden tification ol variables in processes and chemicals that were peculiar to those plants affording known cases ot AOL No such processes or chemicals wore found. The survey brought to light b num ber of situations suspected ol relationship to the precise cause of AOL, some of which require additional exploration. Most positive of these was the finding that essentially all of the persons who developed AOL had served as reactor cleaners using manual methods. Polyvinyl chloride < PV('> has been in production and widespread use for more than 30 years. An extensive account of the chemistry, methods of production, materials utilized, properties, and uses of the PVC resins was recently published in a series of technical articles by Albright.1 Uses in clude such diverse products as floor tiles, films for food wrappings, sheeting for show er curtains, phonographic records, and coat ings for cables. As an indication of the magnitude of the PVC industry, the average operating capaci ty in this country for the year 1969 was about 3 billion lb.': Much 1'VC is produced in other countries. Kven with this extensive production involving thousands of operators, the occurrence of occupational acroosteolysis AOL) among these workers was not reeogniml until aUml lt)Gl.: t-`iilmiillrd for |ml>lii .11 m n I I Ii I', 1V70; i<<, cj,ti,l Apiil IS, I! 170. I'rniii llu- lii-li'tilf i,r l\n\ iiiuminiliil ami linin'. Iiial lli'illli, l I lii\ri M l v i,f Mhlit;',itiL Aim Ailmi lle.nl iK'fiite tlm Aniei 11 .111 I min-.It ml IKgiellc <`milCH'llrc, I Haixei. Max Is. l'*.!l He|nmt lei'iie-ir- In S linol I,f I'tililn llenllli. Utuxetsilv at Mi, lin-111, Atm Ail*. Mu ll ISUM 'l>i llmiii.uii. The clinical and epidemiological aspects of this condition are discussed in separate papers in this issue of the archives.*1' Industrial Hygiene Survey Surveys were made of 32 plants fay the authors of this paper, most of the plants being visited by a team of one physician and one industrial hygienist. Twenty-six of these were polymer production plants. Vinyl chloride mon omer production plants and plants engaged in compounding and fabricating of the polymer ized resin were a part of the manufacturing complex at a t of these locations. Five plants conduct! i|M>undmg and lubricating operations ontv one plant produced only flu1 vinyl chlorn.i mnomor. These plants were lucaled llirnngli'i: - lbe United Slates and one in Canada. This surxey was designed to nhlnin informa tion on equipment used, procedures followed, materials involved, extent of exposure to these, and names and descriptions of jolts in order to compare practices in the plants where eases of AOI. oivurred with those in plant- experienc ing no rases. The extent of exposures was estimated on the basis of general ohserxalion. a knowledge of the physical, chcnuc.il, anil phxsiologic.il prop BOR 009757 OCCUPATIONAL A CROOSTEOL YSIS--COOK ET A I, 75 Fig 1.--Flow diagram for production of PVC from vinyl chloride monomer. erties of the materials, and discussion with technically informed persons at the plants. By setting up three broad categories of duration and of relative severity of the exposure, semiquantitative estimates were made. Since mate rials responsible for causing AOL might be absorbed either through the respiratory tract or through the skin or both, such estimates were made for each of these avenues of ahsorption. Production Operations Vinyl Chloride Production.--The two processes for production of vinyl chloride described by Albright1 - were found to be in current use. One of these involves the reac tion of hydrogen chloride with acetylene in the presence of a mercuric chloride catalyst. In the other process, 1. 2-dichIoroethane is pyrolyzed in the presence of chlorine as a catalyst for the production of vinyl chloride and HC1. In some plants, both methods were used, with the HCI produced in the latter of these processes being used in the former. Polyvinyl Chloride Production.--Poly vinyl chloride can be produced in accord ance with four protvsses, each with many variations among different plants. The final polymer truly have a molecular weight vary ing from 50,000 to IfiO.OOd, depending or. conditions under which it is produced. The production processes are designated as sus pension. emulsion, bull; i or nonsoivenl), and solvent. A typical procedure is present ed in the flow-shed t Fig 1 . The essential steps of these operations are outlined m this fiaper. For more complete details, relerence muy he made lo the pujiors by Albright. In the widely used suspension process, deion ized water is first introduced into a large auto clave, usually glass-lined, followed by ^ wide variety of additives. These include su.pending agents such as polyvinyl alcohol, methyl cellu lose, and gelatin, emulsifying agents such as sulfonated oils, surfactants such as >. irbitan monnlaurate. and buffers such ns sodium bicar bonate. Trichloroethylene may be added tu pro duce the lower molecular weight polytr.e' i. Cat alysts are added to initiate the polymer! -ation These are nearly all organic peroxides, with lauroyl peroxide and diisopropylperovvdicarbonate (IPP) heing used at the greater number of plants. The reactor is then closed, evacuated to remove oxygen, and vinyl chlo ride, normally a gas, is piped in as a liquid under pressure from the tank farm or the vinyl chloride plant! In some plants, the catalyst is added to a charge tank from which it is intro duced into the closetl reactor following addition of the vinyl ehloride. The mixture is agitated with rotating propel ler blades, and steam initially is directed into the reactor jacket to raise the temperature to 50 or 55 C. Since the polymerization reaction is exothermic, cooling water must he run into the jacket after the reaction has hegun to avoid excessive heating. After ten lo l(i hours, the polymerization is essentially complete, and the reactor is brought flown lo ntniiKplierio pres sure In must plants, it is placed under vacuum lur removal ot uupolvmerized vinyl clilorid'1 monomer and transfer to the monomer recuvery area. The suspension of PVC is then nischarged into a blowdown tank neiow the reac tor. This tank is placed under vacuum fur transfer of remaining vinyl chloride to the recovery are-i. In some plant- the hiowdowr tank is eliminate;: The genera! appearance cf Ine charging floor ol a polymer plant is shown A i'll. Enrunn //cri/p,--Vnl 'J`J, -Inn HIT! BOR 009758 OCCUPATIONAL ACROOSTKOLYStS--COOK KT AL Fig 2.--Charging floor of PVC production plant showing top portion of reactors. in Fig 2. The rout-tors extend for ten feet or so down to the floor below. The polymer slurry is pumped to blend tanks, then to centrifuges for removal of much of the water. The dewstered polymer is passed through a rotary dryer with heated air, the temperature of the polymer being kept below 140 F to avoid degradation. The dried granular polymer is pneumatically conveyed into a cy clone separator, with finer particles being re moved from the air stream by means of a filter-type collector. The polymer particles are sized by vibrating screens, then bagged for transfer to compounding and fabricating plants or shipped in bulk, fn some plants, the polymer is stored in bins prior to lieing shipped. In the emulsion process, the equipment and process is essentially the same as in the sus|>cnsion process up to the drying operations, in order to produce the finer polymer particles characteristic of the emulsion process, a wide variety of emulsifying agents is used. These may Ih* soaps hui-Ii as ammonium or sodium lauralc. surfactants such as salts of naphthalene sulfonic acid, or various synthetic detergents, Water-soluble initiators such as ammonium persulfate and hydrogen peroxide are used us catalysts. Since the fine polymer particles can not be readily separated from the emulsion by centrifuging or filtering, a spray dryer is em ployed in this process. The bulk process is similar to suspension polymerization but is characterized by the pre cipitation of the polymer from the liquid phase, as about 10% of the vinyl chloride becomes polymerized. Solution |olyrnerization is much the same as suspension polymerization, but no water is in troduced. Instead, the polymerirattcn is con ducted in such solvents as cyrlohevane. acetone, or n-butane. Copolymer and Terpolymer Production. --In additiun to the production e: :re homopolymer PVC, iitiny of the y.-ints also product' cofmlynier and terjxily tr.i includ ing vinyl chloride. The greater pt*.\r.tage of the monomer tends to be the vinyl chloride in nil of these. The copolymer v'*-.yl chlor ide-vinyl acetate is in highest : vduction Arrh Knt'inu) /Ivtiltli -- Vnl J'J, .hut /.'/"/ BOR 009759 OCCUPATIONAL ACItOOSTEOLi'SIS--COOK ET AL 77 among thw group but is n Tablt 1.--Absolute Prassuro-TImo Valuas minor product in compari son to the homojmlynv'r. Other copolymers arc vinyl chloride-vinylidcrie chloride and vinyl chloride-lauryl- Absolute Pirtsiur T hoc Vftltic* Below 10 _____ .._____ - -- No. of No. of Plant Reactor Expected Code Cleaners AOL Cases Absolute Pressure Tllllf Value* o< 10 or Above . e- -- -- --- - -- * - -x No. of No. of Plant Code Reactor Expected Cleaners AOl Cases vinyl ether. An example of a terpolymer is vinyl chloride-n-butyl maleate-dibutyl maleate. Processes, additives, and catalysts essentially identi Plants With AOL Cases EE 31 0.8 8 E f R Plants With Possible AOL Cases cc 32 0.9 Totals 63 1.7 246 165 16 39 436 5.8 4.5 0.4 1.1 11.8 cal to those used for the homopolymer are employed in the production of the co polymers and terpolymers with the addition to the re action mixture of the addi tional monomers. Vinyl Chloride Recovery.-- The unpolymerized vinyl chloride removed from the P 0 V w Totals DD Totals Plants With No AOL Cases 30 0.8 D 22 0.6 H 91 2.5 L 50 1.4 S T Z AA 193 5 3 27 26 28 17 9 17 8 132 Plants Started in Operation in 1965 or 1966 21 0.6 c 54 J 13 21 0.6 67 0.7 0.7 0.8 0.5 0.2 0.5 0.2 3.6 1.5 0.4 1.9 hatch following completion of polymerization is conveyed to a vinyl chloride recovery area Table 2.--Classification of Standard Job Titlas by the suction pump that places the reactor and the stripping tank under reduced pressure. Here the vinyl chlo ride gas that is removed is placed under pressure to con dense it together with water vapor to a liquid. The water and the vinyl chloride are im miscible, permitting their sep aration. In some plants, an inhibitor, usually phenol, is added to the vinyl chloride Job Title Code Additive makeup (other than catalyst) Bagging and snipping operator Catalyst makeup man Clerical, other cf'ice, staff Compounding and fabricating Dryer operator 2 3 4 5 6 General laborer, custodial Laboratory supervisor 7 8 Laboratory technician 9 Maintenance, electrical 10 Maintenance, mechanical 11 Monomer maintenance operator 12 Monomer operator ___ 13 Job Title Monomer recovery operator Monomer supervisor Plant guard, security officer Reactor cleaner Reactor cleaner, solvent Reactor operator Slurry blender Supervisor, polymer Tank farm operator Utilities area operator (water treatment, etc) Warehouse operator Transfer operator Other then PVC Code la 15 16 17 18 19 20 21 22 23 24 25 30 to prevent s|ntaneous poly merization during its distillation, the method used for its purification. The recovered vinyl chloride, with the higher boiling phenol remain ing in the still, is then pumped to storage for due on the agitator blades may require hammer and chisel for removal and sometimes even axes. Four plants use water jets with pressures of reuse. Reactor Cleaning Operations,--After flic Itolvmer has hi-en discharged from the rc.ieto- and the pressure brought to atmospheric, the from 300 to 3,000 Ib/sq in for the cleaning operation. One of these u.sisl wiper jets only in one of two production buildings, oh`the structional features inlcrlereri with movement of the reactor is aerated. This is neromphshi-d hv imrtnhlc high-pressure wider unit about the dropping a flexible duet connected to a portable building. Three oilier plaids have lieen tiring blower to tin* bottom of the reactor, with dis charge wirmalh through (he open manhole at the top of I he re,-a lor inlo the charging-floor area, The loose residue is wasfu-d out with water, after which one or two men enter the nvh'tnr to remove the skin of imlymor remain iilg on tin re.ii ior Milfoil-* The itMini mellioil 1" hv manual serapne: with pufiy knhes I,Vri solvents for reactor cleaning. One of these slarted to use this method late in lOlil, i. second in !!)(i(h anil the third from (he In-gin ning of plant operation in IfMiti. The reactor is filled with tin- solvent which must he heated and agilaled for a prolonged fK-riud. as the rVC-is diliii nil' soluble I'ol.w hiyl Chloride Compounding.-- ''iiin- Afrh A'uriut/i fhiiifli -V ttl :*: *ftih /?##*/ 00976 bor 78 OCCUPATIONAL ACPOOSTFOLYSIS--COOK ET AL Tabl* 3.--Magnitude of Dosage Expressed as Single Concept at a weekly, monthly, or Sevcnty/Oiiration Exposure Parameters! other period. A classification of 26 job Magnitude* ol Dosage Slight 1 2 3 4 5 6 Less Than 1 hr/Week Negligible Moderate Moderate Moderate 1-6 hr/Week None Negligible None Negligible More Than 8 hr/Week None None Negligible None None Negligible titles for the statistical pur poses of this study was pre pared (Table 1). These job titles corresponded to com parable operations in all the plants and to a common group of types of ex]>osures Intermediate 7 a 9 10 11 12 Appreciable Appreciable Appreciable None Negligible Moderate Moderate None None Negligible None Negligible Moderate to production materials. Ev ery job in each of the plants was given its fraction of time related to the job title as defined for the study. De Mr,/or tails of the manner in which 13 Appreciable Moderate None 14 Appreciable Moderate IS Appreciable None 16 Appreciable Negligible 17 Appreciable Moderate 18 Appreciable Expressed in order of increasing dosage received from exposure, which t the summation of the three columns to the right. f Severity of exposure is estimated as none, negligible, moderate, or appreciable for indicated durations. this was done are discussed in the accompanying paper on epidemiological aspects of AOL. Job Progression.--Often the first job assignment of the new employee is that of reactor cleaner. Unless there jounding consists of mixing PVC with a multi, are many reactors, this work docs not require plicity of plasticizers, antioxidants, pigments, the entire time of the employee. Part of his emulsifiers, stabilizers, and other special com pounds in ribbon blenders and mills. The mix tures are then passed through roll mills or mixers, such as are used in the rubber industry, where the temperature may rise sufficiently to vaporize some of the plasticizer and other vola tile constituents. The compounded polymer is then extruded through rolls or dies to form time may be spent in bagging or shipping finished polymer or in the handling of enta iysts and other additives. As job openings arise and with accretion of seniority, this employee may progress to higher skilled jobs such as reactor, monomer recovery or dryer operator, or any combina sheets, films, or pellets. These are used in tion of these at any one time. fabricating operations. In plants producing other products in ad Job Classification dition to vinyl chloride polymers, employees may transfer between these product areas Many variables were introduced in the either as full time for a period of months or plants surveyed and even in different units dividing their time within a given week or of the some plant in regard to nearly every even day. The latter occurs particularly phase of the operations. Investigation of among maintenance personnel. unit jobs in the plants disclosed a wide Where production of vinyl chloride is part assortment of job titles. In fact, a job title as of the operation, operators may rotate be used by lhe technical suiH-rvisors often dif tween jobs in the production of the mono fered from that for the same job in the mer and those associated with lhe produc same planL as listed by the personnel ele- tion of the* iKjlymer. jwirt merit. The length of lime s|>ent at various jobs is Furthermore, a job assignment in one a function of production m*ods, economic plant might inc lude a different group of unit conditions, plant growth rate's, ami activity O|x-r;itions (ban in another plant. Also, the of other product lines. proportion of lime devoted to tin* several unit op-Malion;. tiflcii di/lered To compound Occupational Kx|w>sures to Materials the dillirultie-. of elassilical ion, workers Extent of Exposure's.--Inleiriii.'ilioii wu.- would ficciuenllv rotate through several jobs obtained not onlv em each of the* materials Arth h'.mimt I linllh \`itl I*:*, ./fin /?!','/ BOR 009761 OCCUPATIONAL ACROOSTF.OIS SIS--COOK KT AL 79 used or produced but also on the extent of exposure to each. Since this is a function of both duration and severity, each of 11 test* factors was estimated. Tlu* duration of cx|msure was recorded as less than oik; hour a week, from one to eight hours a week, or mv>re than eight hours a week; the severity as negligible, moderate, or appreciable. Since, it was not known whether the materi als might be absorbed through the re spiratory tract, through the skin, or both, the extent of exposure as related to each of these avenues of absorption was recorded. For statistical purposes, it was desirable to combine these two factors of exposure into a single dose value. Although admitted ly the effect of exposure to materials with differing physiological responses would vary somewhat with different combinations of aegrees of duration and severity, the 18 possiole combinations of duration and severity were listed in increasing order of dosage and classified in three groups of dose values desgnated as slight, intermediate, or major. These combinations are presented in Table 2. Materials Involved.--A total of 227 different materials were used or produced in the forma tion of PVC, the copolymer vinyl chloride-vinyl acetate, and other copolymers and terpolymers incorporating vinyl chloride. These materials included monomers, polymers, catalysts, disper sants, inorganic compounds for coalescence reg ulation, emulsifying agents, surfactants, and or ganic solvents (including hydrocarbons, both aliphatic and aromatic, ketones, esters, and chlorinated hydrocarbons). This total of 227 materials does not include the many more used in the compounding and fabricating plants. A computer analysis of exposures to these materials was undertaken, but up to the pres ent time, this has disclosed no constellation of materials introduced into the batch at the plants exhibiting cases of AOL that was not used in plants without cases. However, special consideration was given to certain suspect ma terials and also to certain details of procedure. Vinyl Chloride Exposures.--In evaluating the role of vinyl chloride as a possible in fluence in the causation of AOL, the esti mates of the extent of the exposure of re actor clamors and reactor operators were reviewed. Since the authors conducted no air analyses, they hail to judge the presence of vinyl chloride in the charging floor area principally on the basis of general vontila- Tabla 4.--Us* of Inhibitors With Vinyl Chlorld* Plants with AOL cases or possible cases Plants without AOL cases Uic ol Inhibitors In Virgin Vinyl Chloride j In Vinyl j Chloride Recovery ______ 22 34 tion provided and odor observed. 'The odor of vinyl chloride could be detected in the immediate vicinity of reactors as they were first opened and also when they were first being vented into the charging room area. Air analyses conducted by others have shown vinyl chloride concentrations in the reactor prior to ventilating to lie in the order of 3,000 ppm. The lower limit of detection of vinyl chloride by odor is accept ed as 400 ppm. Except under the foregoing conditions, the odor of vinyl chloride was not observed in the general room air. The reactor cleaner enters the reactor af ter the aeration has reduced the vinyl chlor ide exposure to what is considered satisfac tory limits, normally 15 or 20 minutes. The test is either by sniffing at the manhole opening or by use of a fiammaoie vapor indicator. With the lower explosive limit of vinyl chloride at 4%, it requires 400 ppm for the usual type of flammable vapor indi cator to give a positive reading. Where air analyses have been made in a small number of plants with more sensitive instruments, such as the gas chromatograph, it has been found that the vinyl chloride concentration inside the reactor during scraping operations tends to be below 100 ppm and usually about 50 ppm. With the residue containing some unpolymerized vi nyl chloride, small amounts of this gas are released as scraping is carried on. Air anal yses have shown vinyl chloride concentra tions close to the hand during scraping in the range of 600 to 1 .(>00 ppm. Although this study provided no evidence to suggest that vinyl chloride per so is tin* etiological agent, the measurement of vinyl chloride concentrations may serve as it use ful index to the adequacy of reactor ventila tion. Inhibitors in Vinyl Chloride.--An inliihi tor, usually phenol, may lx* added to the t Arch Kuril mi llrtillh--V'o/ Jan 1971 BOR 009762 80 OCCUPATIONAL A CROOKTF-0L YHIS--COOK ET AL Table 5.--Reactor Cleaning Procedures as a possible, factor in the Hand Scraping Plant Alter Every lei* than Cleaning hy Water Jet Cleaning by Solvent causa I ion of AOl-. Contact with thr*c inorganic and or ganic peroxides occurs as Code Batch they are handled prior to Plant* with AOL ca*ei BX EX FX KX (through 1964) From 1965 their introduction into the reactor and also during re actor cleaning if any unre acted catalyst remains in the residue. Twenty-two of the RX U Every 5-12 cycles From 1962 (building A) (building B) EE X 26 plants used lauroyl perox ide. Eight of these were plants with AOL cases or Plant* with possible AOL cases BB Every "several" cycles On glass-lined. Intermittently In 1966, entirely possible AOL cases, and 14 were plants without AOL cast's. The next most com Plan's with no AOl esses AX ,to September 1964) CX D From 1962 by December 1966 From September 1964 mon organic peroxide was the IPP, and it, too, was in use in both the positive and the negative plants, in four of the former and in eight of the latter. No catalyst or HX J Every 2'h cycles L Every 4-8 days NX group of catalysts was used in all positive plants and in no negative plants. P Weekly From 1965 through 1964, every 2 weeXs Constituents of Scrapings. --Other suspect materials 1966-1966 are constituents of scrapings Q* Sx T X Every 1-3 cycles removed from the reactors during manual cleaning. (emulsion) (suspension) V Every 10 cycles Z AA Every 4 or more These are believed to. include some partially polymerized resins, along with some un- cycle* DO QG from itart of operations reacteri catalysts anti addi tives, and unpolynicrized vinyl chloride. Little specif ic information is currently vinyl chloride to prevent .sfxmtaiieous poly available concerning those constituents. It hus merization in storage. An inhibitor may also been reported that lauroyl peroxide is definite be added to the vinyl chloride recovered ly associated with residual PVO particles, from the reactor. The phenol is removed by whereas little of the 1TP remains unreacted treatment with caustic soda prior to its in the polymer.1 transfer to the reactor. The practice over the Further investigation of the scrapings years covered ttv the study is presented in from the reactor may be ex|)ectetl to furnish, Table C. The use of the inhibitor in the information that may lead to a belter under virein vinyl chloride at two of the ixisitivc standing of the factors involved m causation plants and three of tVie negative plants, with of AOL. A difficulty m such investigation is inhibito- being added in the vinyl chlorine that the composition of the scrapings i.- recovery operation in Iwo positive plants contiiHially changing from (lie time they art. and four neitative plants, leads te the con removed I rum the surfaces of the reactor. It clusion that inhibitors proilnhiv are not a is obvious that comparatively small mole factor in AOL causation cules of imrtiallv polymerized vinyl chlorine Catalyst Exposures.--Snieo im catalyst.-. are increasing it: si/e with passage oI turn are all .leltve mini.... ml-, lliev were siis|h-<.-; anri active coiislilui'ot;. such as residu.-u ea. li./i l.iiriiini Ihiilln * *. .Inn Uhl BOR 009763 4 OCCUPATIONAL ACItOOSTKOLYSIS--COOK KT At, HI Tbt 6.--Reactor Cleaning Procedures Method Manual scraping after every reactor cycle Manual scraping attar 2-3 cycles Manual scraping after 4-12 cycles Water-jet cleaning Organic-solvent cleaning Positive Plants 7 0 2 2 1 Negative Plants 9 2 4 2 2 alyst and vinyl chloride monomer are de creasing or may no longer be present. Procedures Affecting Exposures of Reactor Cleaners Since all but one of the 25 operators diagnosed as positive for AOL had worked as reactor cleaners and the one exception had cleaned laboratory reactors,8 additional inquiry was made of procedures that might affect the exposures of this group of workers. Reactor Cleaning Procedure.--The numher of man hours required to clean the reactors depended not only on the number of reactors but also on the frequency of cleaning. In 16 of the 26 production plants, reactors were manual ly cleaned after every batch. This was true of six of the seven positive plants and one of two plants with possible AOL cases. In only nine of the 17 plants with no AOL cases were reactors manually scraped after every batch. The procedures followed in each of these plants anpears in Table 4 and an analysis of the types of procedure by positive and nega tive plants in Table 5. Procedures Following Completion of Poly merization.--Since vinyl chloride and other vol atile components of the residue remaining on the reactor surfaces following discharge of the batch might he factors in AOL causation, infor mation wns obtained concerning the degree of vacuum applied to the reactor prior to aliening it and the length of lime that the reactor was under this reduced pressure The amount of volatile materials remaining in the residue on the reactor surfaces was considered to ) roughly proportional to the. absolute pressure' and inversely pro|Ktr(ioual to some function of the time. Since the rate of-removal of volatile material would lend to decrease with time, the logarithm of this tai lor was used in calculating an atisolule pressure-time (AP-T) value. H was hy|Hithesi/eil that the relative amount of vnl.i. tile materials remaining iti the residue follow ing application of vacuum would approximate a nondimcnsinnal value obtained by dividing the absolute pressure in inches of mercury hv the logarithm of the time in minutes during which th vacuum was applied. Thus, the lower the AP*T value, the less is the amount of volatile materials remaining in tho residue. Another factor affecting removal of vola tile materials is the temperature range over the period that the reactor is under vacuum. The variables in temperature control were so diverse that this factor defied classi fication and could not be incorporated in the parameter under consideration. Actually, variations in degree of vacuum and timing of its application were such that meaningful calculation of an AP-T value could be ac complished only for five of the seven posi tive plants, one of the two with possible cases, and 14 of the 17 negative pli.nts. In the subsequent discussion ot these val ues, the three plants that started :r. opera tion as recently as I9G5 and 1966, all with no AOL cases, are not included as it is not known whether sufficient time had elapsed for cases to have developed by the terminal date of the study period. These I lants are listed separately in Table 6. The AP-T values ranged from 0.5 to 21. The AP-T values were 10 or above fan entirely arbitrary division line) for four of the five positive plants and for one of the two plants with possible AOL cases. Four of the negative plants gave AP-T values below 10, and seven gave values of 10 or above. Consideration is directed to the number of reactor cleaners and the corresponding num ber of expected AOL cases in the two groups of positive plants as compared with those in the negative plants: The total number of reactor cleaners at risk in the imsilive or possibly positive plants with an AP-T value of less than 10 is 63; that in such plants with an AP-T value of 10 or mure is 436. The relation of these two totals is to be compared with that of the negative plants in which 193 reactor clean ers at risk are in the four plants with an AP-T of less than 10 and 132 are in the seven plants with an AP-'I' above that value. The number of ex|H*cted cast's of AOL for each plant is also lisletl in Table 6. These values were obtained by dividing the numlior of realtor cleaners at risk by 37 Tbi" Arrh Hiifinoi Ihollli \'ol .too lull BOR 009764 .4 82 OCCUPATIONAL ACROOSTEOLYSIS--COOK ET AL figure derives from the paper on epidemio logical aspects of AOL* which reports the prevalence of AOL or possible AOL as one case per 37 rcactot cleaners at risk. Of the negative plants with an AP-T val ue of 10 or more, none of those in operation earlier than 1965 had enough reactor clean ers at risk to expect an AOL case, whereas two of the four plants with an AP-T value under 10 have enough workers to expect cases. Cases would be expected from the total population of reactor cleaners in the entire group of the seven negative plants with AP-T values of 10 or more, but the total number would be 3,6, as compared with 5.3 expected cases from the entire group of four negative plants with an AP-T value of less than 10. This contrasts with expected cases in the group of positive plants with an AP-T value of less than 10 as 1.7, compared with 11.8 in such plants with an AP-T value of 10 or more. The proportion of the number of reactor cleaners in the negative plants with on AP-T value of less than 10 to the total number in such plants was 193 to 325. This propor tion for the positive plants was 63 to 499. A X2 test demonstrated that the probability of this difference between the negative and the positive plants occurring by chance is less than 0.001. In order to make this comparison between the positive and negative plants with AP-T values below and above 10, it was necessary to oversimplify a multiplicity of varying de tails of operational procedures from the time the polymerization is completed to the time the cleaner enters the reactor. Accordingly, any interpretation of the findings that re duction of the AP-T value below 10 by reducing the absolute pressure or keeping the reactor at reduced pressure for a longer time or both may results in reduction in development of AOL cases should be ap proached with great caution. Preventive Measures '' The present knowledge as to AOL is such that categoric statements as to preventive measures arc not justified. However, on a somewhat speculative basis, some measures are indicated that may be conducive to AOL prevention: 1. Although some manual removal of resi due from reactor surfaces may be required when solvents or high-pressure water jets are used for cleaning, the more extensive employment of these methods would greatly reduce the number of man hours required for conducting this operation by manual methods, 2. The adequacy of ventilation of reactors prior to entry should be checked with flammable vapor indicator equipped with a scale of greater sensitivity than 1% of the lower explosive limit of vinyl chloride or with other instruments of such sensitivity. 3. Further investigation of the cons'ituency of the scrapings from the reactor surfaces should be considered, as such information might disclose the factor responsible for the causation of the disease. References 1. Albright LF: Vinyl chloride processes. Chem Eng 74:123-130. 1967. 2. Albright I.F: Manufacture of vinyl chloride. Chem Eng 74:219-220, 1967. 3. Albright I.F: Polymerization of vinyl chloride. Chem Eng 74:151-158. 1967. 4. Albright LF: Vinyl chloride polymerization by suspension processes yields polyvinyl chloride res ins. Chem Eng 74:145-152. 1967, 5. Albright LF: Vinyl chloride polymerization by emulsion, bulk and solution processes. Chem Eng 74:85-92, I9C7. 6. PVC producers. Chem Eng New* 47:18-19, 1969. 7. Wilson HH, McCormick WE, Tatum CF, et at: Occupational ncroosteolysis: Report of 31 cases. JAMA 201:577-581, 1907. 8- Dinman HD, Cook WA, Wliltehoiaa? WM, et at: Occupational ncroosloolysis: I. An epidemiologi cal study. Areh Enrimn Health 22:01-73, 1971. 9. Dodson VN, Dinman Mil, Whilehouse WM, el al: Oinipntionnl acmosteolvsis: III. A clinical alu-ly. Arch Enrimn Health 22:83 91 I97|. 0 / Arch Enrinm llmlth--Vol i'2. Jon HITl Pnntr.l ,iad PiiMnned in toe United S/.ifrs nt Amvnc-r BOR 009765