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' mm mm- 74 *4 MAY 1974 n(\ ILLEGIBLE DOCUMENT Occupational Acroosteolysis II. An Industrial Hygiene Study Warren A. Cook; Paul M. Civver, MPH; Bertram D. Dinman, MD, ScD: and Harold J. Magnuton. MD, MPH, Ann Arbor, Mich An Industrial hygisne 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 ot facilities, interrogation ol tech nical personnel, and statistical analyses. All manufacturing 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 case* ot AOL. No such processes or chemicals ware found. The survey brought to light a num ber ol situations suspected of relationship to the precise cause .of AOL, some at which require additional exploration. Most positive ol these was the finding (hat essentially all of the persons who developed AOL had served as reactor cleaners using manual methods. Polyvinyl chloride <PVO> has been in production and widespread use for.more than 30 years. An extensive account of the chemistry, methods of production, materials tltilized, properties, and uses of the PVC resins was recently published in a scries of technical articles by Albright.1 r* Uses in dude 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 oix'rntiug capaci ty in this country for the year 1969 was about 3 billion Jb." Much PVC is produced in other countries. Kven wilh this extensive production involving tlunisands of operators, I Ik* occurrence of ocvuixtlionnl acroosteolysis i AOl.) among these workers was not rmigninxi until alxuit l!Kil.T hfimillnl fur |HiiilHiiluni M !>, I!i70; mvcplist April lli, I!i70. Krnm tlie Ynslilntc ttf KnvitiMiineiilnl mvl Itslits liin) IIkiIiIi. llnivcrsilv of MAlin AiImii. Ilrenl |Ik, AiiH',m:iii littlti-.lit.tl I Iv^h-ih* * iHnwr. M.iv IS. I'.o*. tt)-|iruil p> Si-lsmt lit t'niilu' 1lr:illli. I limt'milv uf Mwliifiin. Amt Ailmr,, Mull IHIIU lllr. Uinniiini. The clinical and epidemiological aspects of this condition are discussed in separate papers in this issue of the archives.'111 Industrial Hygiene Survey Surveys were made of 32 plants by the authors of this |iaper, 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 ihu polymer ized resin were \i i>urt of the manufacturing complex at a I, ' `r of them* locations. Five pL-mls fondui-ti - t|Munding and lahricnling iifieniliunN only one plant produced only the vinyl clilorii.i .imtmcr. TIdsc plants were located thnuiglvn tlie United Stair's-anil one in Canada, Tliis survey was designed In olilaia informa tion on equipment used, procedure.) followed, materials involved, cxlcitl of exiwsure to these, and naan's and descriptions of johs in order to rnin|iurc prai'f h-es in I lie plants when- cases of AOl. occurred will! llmse in plants ex|**ricnc- iog n<> twis, Tin* exh'iif of i'X|s>siires Mas estimated on the liasis of general oltsi-rvalinn. a knowledge of the physical, I'lioiiiii'al. anil plpsiologicai pro|i 958 OCCUPATIONAL ACJWOSTKOT.YSIS--COOK ET AL 75 erties of the material)), 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 materials responsible for causing AOX- might be absorbed either through the respiratory tract or through the skin or both, such estimates were made for each of these avenues of absorption. 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 HO. In some plants, both methods were used, with the HC1 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 processes, each with many variations among different plants. The final polymer may have a molecular weight vary ing from SO.OOO to I50.(KM!, depending on conditions under which it is produced. The production processes are designated as sus pension. emulsion, bulk (or nonsolvontl. and solvent. A typical procedure is present ed in the (low-sheet Pig l . The essential steps of these alterations nre outlined in this ixiper. Kor more complete details, reference may he made to the pii|vrs by Albright.'" In.the widely used suspension process, deion ized water is first introduced into n large auto clave, usually glass-lined, followed by n wide variety of additives. These include suspending agents such as polyvinyl alcohol, methyl cellu lose. and gelatin, emulsifying agents such as sulfonatcd oils, surfactants such as sorbitan monolaurate. and hufTers such as sodium bicar bonate. Trichloroethylene may be added to pro duce the lower molecular weight polymers. Cat alysts nre added to initiate the polymerization These are nearly all organic peroxides, with lauroyl peroxide and diisopropyltteroxydicarbonatc (IPP) being 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 closed reactor following addition of the vinyl chloride. 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 be run into the jacket after the reaction has hegun to avoid excessive heating. After ten to 1G hours-, the polymerization is essentially complete, and the rwtur is brought down la iilmiKphoric pres sure. in most plants, it is placed under vacuum (or remove', ot unpolymerized vinyl rhlorid" monomer nnd transfer to the monomer recov ery area. The *us|H*nxuin of I'Vt! is then aUchnrgetl into a Mmrdnwn tank below the reac tor. This tank is placed under vacuum fur transfer of remaining vinyl chloride to the n-covcry area. In some plant)-, the hiowdowrlank is eliminate::. The' general ap|M>arance ef tne charging Goor nl a ixilvmer point is shown Arrh Knnrun ItmUh--VtJ fl>. Jan III?I 7G OCCUPATIONAL ACROOSTF.OLYSIS--COOK KT Ah in Fig 2. The reactors extend tor ten feet or so down to the floor below. The polymer slurry is pumped to blend tanks, then to centrifuges for removal'of much o! -the water. The dewatered 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. In some plants, the polymer >s stored in bins prior to being shipired. In the emulsion process, the equipment and process is essentially the same ns in the sus|tcnsion process up to tin* drying ojienitions. In order to produce the finer polymer inrtiiiis characteristic of the emulsion process, u wide variety of emulsifying agents is used. These may Ik* wm| such ns ammonium or sodium laumtc, surfactants such su* salts of naphthalene silfmik 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 polymerization is much the same as suspension polymerization, but no r.tr is in troduced. Instead, the polymfriran-.n is -con ducted in such solvents as cyclohex.'.r.e. acetone, or n-butane. Copolymer and Tcrpolymer Production. --In addition to the production c? :he homo- polymer PVC, utmy of the yl.utts also product* co|*>lynicr and tenx'lytv.t v. includ ing vinyl chloride. The greater ptr.-.ntage of the monomer tends to be the \ itv. 1 chloride in ail of l hose. The copolymer n :-*1 chlor- itle-vinyl ucelale is in highest : -eduction Arrh Environ llrtillli -- Vnt TJ, -Inn 11171 - OCCUPATIONAL ACItOOSTEOLYSIS--COOK ET AL T7 among this grou|i but is ft . Tablg l.--Abto/ate Pressure-Time Valuta minor prodiK-t in ounpnrion to the homojxilvntrr. Absolute Pressure I line Values Below 10 Absolute Pressure Time Values ol 10 or Above Other copolymers arc vinyl chloride-vinylidene chloride and vinyl chloride-lauryl- Plant Code No. of No* of Reactor Expected Cleaners AOL Cases Plant Code No. of No. of 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 B E f R Plants With Possible AOL Cases cc 32 0.9 Totals S3 1.7 216 165 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 to-, 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 t` Q V w Totals DD Totals Plants With No AOL Casas 30 0.6 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 08 as 0-2 as 02 3.6 1.5 04 1.9 hatch following completion of polymerization is conveyed to a vinyl chloride recovery area Table 2.--Classification of Standard Job THIas by the suction pump that Job Title Code Job Title Coda places the reactor and the tripping tank under reduced pressure. Hem 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 (lie vinyl chloride am im miscible. permitting their sep aration. In some plants, an inhibitor, usually phenol, is added to the vinyl chloride Additive makeup (other 1 than catalyst) Bagging and shipping operator 2 Catalyst makeup man 3 Clerical, other otfice. staff 4 Compounding and fabricating 5 Dryer operator 6 General laborer, custodial 7 Laboratory supervisor 18 Laboratory technician 9 Maintenance, electrical 10 Maintenance, mechanical 11 Monomer maintenance operator 12 Monomer operator 13 Monomer recovery operator Monomer supervisor Ptsnt gusrd. security officer Reactor cleaner Reactor cleaner, solvent Reactor operator Slurry blender Supervisor, polymer Tank farm operator Utitties area operator (water treatment, etc) Warehouse operator Transfer operator Other than PVC 14 IS 16 17 18 19 20 21 22 23 24 25 30 to prevent spontaneous 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 pumix'd to storage for reuse. Reactor Cleaning Operations.--After the irolymcr has been disrliarged from the re.iefnand the pressure brought to atmospheric, the reactor is aerated. This is accomplished hy dropping a flexible duct connected to a |Kirlahlc* blower to the lioliutn of the reactor, with dis charge normally through the o|>cn manhole at due on the agitator blades may require hammer and chisel for removal and sometimes even axes. Pour plunfs use water jets with pressures cf from 300 to 3.000 lli/sq in for the cleaning o|M*ration. One of these* list'd water jets only in one nf two production buildings, as the strucI ional' features interfered with movement of the tmrlahle high-pressure water unit alxiul the building. Three other plants'haw been u-ing solvents for reactor cleaning. One of them started to use this method late in IfliVl. a the top of the reactor into the clmrging-floor area. The loose residue is washed out with water, after which one or two men enter the reactor to remove the skin of tsilynu-r remain ing on tin reactor surfaces The usuai lo-lhod is by inanoai scrapin:; with put:v knives. |{esl second in IIKifi. and the third from the In-gin ning of plant o|M*mlion in 19G(i. The reactor is filled wifh the solvent which must lie heated nni! agitated for n prolonged periixl, as the I'VC is difiicullv soluhle Polyvinyl Chloride Compound i --"'nrn- Arrf; 'lilin.i, 1li-nltli ~\nl o;'. Jnli iU7t w 78 OCCUPATIONAL ACEOOSTF.OLYSIS--COOK ET AL Table 3.--Magnitude el Dosage Expressed as Single Concept at a weekly, monthly, or Magnitude* * of Dosage Slight 1 2 3 4 5 6 tntarmadiata 7 8 9 10 11 13 Seventy/Ouration Exposure Parameterst Lass Than 1 hr/Week 1-8 hr/Week More Than 8 hr/Week Negligible Moderate Moderate Moderate None Negligible None Negligible None None Negligible None None Negligible Appreciable Apprecieble Appreciable * None Negligible Moderete Moderete None Non* Negligible None Negligible Moderate other period. / A classification of 26 job titles for the statistical pur poses of this study was pre pared (Tabic 1). These job titles corresponded to com parable operations in ail the plants and to a common group of types of exposures 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 Ma|or 13 14 15 16 17 ' IS Apprecieble Appreciable Moderete Apprecieble Appreciable Appreciable None Moderete None Negligible Moderete Appreciable Expressed in order of increasing dosage received from exposure, which Is the summation of the three columns to the right. t Severity of exposure is estimated as none, negligible, moderate, or appreciable tor indicated durations. tails of the manner in which this was done are discussed in the accompanying paper on epidemiological aspects of AOL Jab Progression.--Often the first job assignment of the new employee is that of reactor cleaner. Unless there pounding consists of mixing PVC with a multi plicity of plasticizers, antioxidants, pigments, 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 are many reactors, this work docs not require the entire time of the employee. Fart of his time may be spent in bagging or shipping finished polymer or in the handling of cata lysts 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 same 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 joh titles. In fact, a job title as of the oixration, operators may* rotate be u*d by the technical su|iervisors often dif tween jobs in the production of the mono fered from licit for the same joh in Ihe mer find those associated with the produc same plant as listed by the jiersonnel de tion of the iHjlyiner. partment. The length of time s|ient at various jolis is Furthermore, a job assignment in one a function of production needs, t'cunomic plant might inelude a different group of unit condilions, plant growth rates, and activity operations than m another plant. Also, the of other pnxluct lines. |iro|x>rtinn of linn* devoted to the several tiuit o|i'T.iliiin;, often dillered. To cnm|M>imd Occupational Kx|xtsurcs to Materials life diflieultie*'. of elassificalinti, workers Extent of Kx|M*sures.---Iiilorni.'iliiin vvs. would fieriuenlly rotate through several jolts ohlauiisl not only on each of the material* Arch I'ncimi llcnllh \'nl Jtm HI'/1 962 "^atSME SgF."j .. OCCUPATIONAL ACnoOSTF.nhVSIS-CnOh' FT At 70 used or produced but nlso on the extent of exposure to each. Since Ibis is a function of belli duration and severity, each of these factors was estimated. The duration of exi>n- sare was recordfed as less than out; hour a week, from one to eight hours a week, or more than eight hours a week; the severity aa 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 whs 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 de grees of duration and severity, the 18 possi ble combinations of duration and severity were listed in increasing order of dosage and classified in three groups of dose values des ignated 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 FVC, the copolymer vinyl chloride-vinyl acetate, and other copolymers and terpolymers incorporating vinyl chloride. These materials included monomers, polymers, catalysts, disper sant*. 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 material* 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 plante exhibiting cases of AOL that was not used in plants without cases. However, special consideration was given to certain suspect ma terial* 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 cleaners nnd- reactor operators were reviewed. Since the authors conducted no air analyses, they had to judge the presence of vinyl chloride in the charging floor area principally on the basis of general ventila- Table 4.--Use ol Inhibitors With Vinyl Chloride Use ol Inhibitors Plants with AOL cases Or possible cases Plants without AOL cases In Virgin Vinyt Chloride - ! 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 be 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 flammable 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 l.tXiO ppm. Although this study provided no evidence to suggest that vinyl chloride |X-r so is the etiological agent, the measurement of vinyl chloride concentrations may serve as a use ful index to the adequacy of reactor ventila tion. Inhibitors in Vinyl Chloride.--An inhibi tor, usually phenol, may lx* added to IIh- Arrh Knviron Urnlih--Vol :*?, -Inn J0TI 0 OCCUPATIONAL ACHOOSTFOLYSIS--COOK ET AL Table 5.--Reactor Cleaning Procedures as a possible factor in the ------- Hand Scrrfpmc Plant After Every Cod* Catch Lett than Every Cycle Cleaning tiy Water Jet Cleaning by Solvent causation of AOL Contact with these inorganic anil or ganic peroxides occurs as they are handled prior to Plants with AOL cates 6X EX rX 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 512 cycles From 1962 (building A) (building B) EE X 26 plants used lauroyl perox ide. Sight of these were plants with AOL cases or Ptents with possible AOL esses SB Every "severer' cycles On gless-hned. intermittently in 1966, entirely possible AOL cases, and 14 were plants without AOL cases. The next most com Punt* with no AOL case* AX (to September ' 1964) CX 0 by December 1966 From September 1964 From 1962 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 i Every 2<fy cycles i Every 4-8 days NX P Weekly From 1965 through 1964, every 2 wee'IS group of catalysts was used in all positive plants and m no negative rlants. Constituents of Scrapings. --Other suspect materials 1 0 s T V Z AA X X X (emulsion) X 1965-1966 Every 1-3 cyciet (suspension) Every 10 cycles Every 4 or more are constituents of scrapings removed from the reactors during manual cleaning. These are believed to include some partially polymerized resins, along with some un CD X 00 cycles From eUrt ol _ - . operetione reacted catalysts and addi tives, and unpolyintrizrd vinyl chloride. Little specif ic information Is currently vinyl chloride to prevent K|>ontaneou.s poly available concerning those constituents. It has merization in storage. An inhibitor niay also been reported that lauroyl peroxide is definite be added to the vinyl chloride recovered ly associated with residual TVC perUclts, from the reactor. The phenol is removed by whereas little of the IT'.'-remains unrcactcd treatment with caustic soda prior to its in the polymer.* _. transfer to the reactor. The practice over the Further investigation of the scrapings years covered bv tin; study is presented in from the reactor may be exfiectcd to furnish Table 3. The use of the inhibitor in the information that may lead to a better under virgin vinyl chloride at two of the |x>sitivc standing of the factors involved in causation plants sod three nr the negative plants, with of AOL A difficulty in such investigation is inhibitor being added in (lie vinyl chlorine Ihat the eoni[Misition of the scrapinp-- L-. ri'covery alteration .in two ixtsilive plants continually changing from the time they arc and four negative plants, leads ter the con removed from the surfaces of flu* reactor. It clusion that inhibitors prottahly are not a is obvious that comisirativeiy small mole laclor in AOL causation cules of iiartinlly |>olvmcrizod vinyl cfilorirlc Catalyst 1'ixposures.--Since lh< catalysts are increasing it; si/e with |>assuge of Inm . an* all active (oniiHiuuds. Ihev were siis|ht; ami active eiuisliliients sticli as residua* ii. ti*/ r.tnittm Il'-itllli - \r<<! *>. Jim Ill'll OCCUPATIONAL ACItOOSTEOLYSIS--COOK ET AL * Ml Table 6,--Reactor Charting Procedures Method Manual scraping after very reactor cycle? Manual scraping after 2-3 cycles Menual scraping atter 4-12 cycle* Water-jet cleaning Organic-solvent cleaning Pojltive Plant* 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 Affcctirig 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 number of man hours required to dean 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. 11113 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 appears 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 hatch might lie factors in AOL causation, infor mation was obtained concerning ihe degree of vacuum applied to the reactor prior to ut>ening it and Ihe length of time that the reactor was under this reduced pressure. The nmounl of volatile materials remaining in the residue on tho renrior surface* was considered to lie roughly pro|s>rlional to the absolute pressure and inversely pro|mrtional to some funetion of the time, iiinco the rate of removal of volatile material would lend to decrease with time, the logarithm or this factor w:is user) in calculating n absolute pressure-time (AP-T) value. U was hypothesized that the relative amount of vola tile materials remaining in Ihe residue follow ing application of vacuum would approximate a nondimonsional value obtained hy dividing the absolute pressure in ini ics of mercury by the logarithm of the time in minutes during which the vacuum was applied. Thus, the lower Ihe 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 passible cases, and 14 of the 17 negative plants. In the subsequent discussion of these val ues, the three plants that started in opera tion as recently as 1965 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 plants are listed separately in Table 6. Hie AP-T values ranged fro n 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 positive or possibly jxjsitive plants with an AP-T value of less than 10 is 63; that in such plants with an AP-T value of 10 or more 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 Ihe four plants with an AP-T of loss titan 10 and 132 are in the seven plants with an AP-T above tliat value. The number of ex|x>cted eases of AOL for each plant is also listed in Table 6. *lhese values were obtaimyl by dividing the miniIter of n>netor cleaners at risk bv 37 This Arrh Environ Ih-nllli--Vnl jnn lull ^0^ 62 OCCUPATIONAL ACROOSTEOLYSIS--COOK ET AL figure derives from the paper on epidemio Preventive Measures logical aspects of AOT,s which reports the The present knowledge as to AOL is such prevalence of AOL or possible AOL as one that categoric statements as to preventive case per 37 roactoi cleaners at risk. measures arc not justified. However, on a Of the negative plants with an AP-T val somewhat speculative basis, some measures ue of IQ or more, none of those in operation are indicated that may be conducive to AOL earlier than 1965 hrd enough reactor clean prevention: ers at risk to expect an AOL case, whereas* 1. Although some manual removal of resi two of the four plants with an AP-T value due from reactor surfaces may be required wider 10 have enough. workers to expect when solvents or high-pressure water jets cases. Cases would be expected from the are used for cleaning, the more extensive total population of reactor cleaners in the employment of these methods would greatly entire group of the seven negative plants reduce the number of man hours required with AP-T values of 10 or more, but the for. conducting this operation by manual total number would be 3.6, as compared methods. with 5.3 expected cases from the entire 2. The adequacy of ventilation of reactors group of four negative plants with an AP-T prior to entry should be checked with value of less than 10. This contrasts with flammable vapor indicator equipped with a expected cases in the group of positive scale of greater sensitivity than 1% of the plants with an AP-T value of less than 10 as lower explosive limit of vinyl chloride or 1.7, compared with 11.8 in such plants with with other instruments of such sensitivity. an AP-T value of 10 or more. 3. Further investigation of the constituen The proportion of the number of reactor cy of the scrapings from the reactor surfaces cleaners in the negative plants with an AP-T should be considered, as such information value of less than 10 to the total number might disclose the factor responsible for the in such plants was 193 to 325. This propor causation of the disease. tion for the positive plants was 63 to 499. A X* test demonstrated that the probability of References 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 1. Albright LF: Vinyl chloride processes. Chtm Eng 74:133-130,1967. % Albright IF: Manufacture of vinyl chloride. Chtm Eng 74:219-220,1967. 3. Albright LF; Polymerization of vinyl chloride; Chtm Eng 74:161-158,1967. 4. Albright LF: Vinyl chloride polymerization by suapension procaasea yields polyvinyl chloride res ins. Chtm Eng 74:145-152. 1967. 5. Albright LF: Vinyl chloride polymerization by emulsion, bulk and aolution processes. Chtm Eng 74:85-92. 1967. the cleaner enters the reactor. Accordingly, sny 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. 6. I'VC producers. Chtm Eng Ntutt 47:18-19, 1969. 7. Wilson UK, McCormick WE. Tatum CF, et el: Occupational nrroosieolysis: Report Of 31 anas JAMA 201:577-581, 1967. 8. Dinman HD. Cook WA. Wbitefaouse WM. et el: Occupational ncrnosloolyxis: I. An epidemiologi cal study. Arch Eneimn llrallh 22:61-73, 1971. 9. Dodson VN, Dinman HIJ. Wliilehmiae WM. el nl: Occupational acroaaleolvxiii: fIT. A clinical atu-ly. Arch Envimn llrallh 2290 91, 1971. - / / Arch Envinm Health--Vnl 22, Jan 07/ jnd Published in Ihe United States nl Amrric.l