Document JJBpk6VZ3z18G2rxZpo9zd0qB

r\ i * " MANUFACTURING CHEMISTS ASSOCIATION 1825 CONNECTICUT AVENUE, N. W. c WASHINGTON. D. C. 20009 < (202) 483-6126 To: November 19, 1971 Vinyl Chloride Producers Subject: Trace impurities in vinyl chloride monomer Gentlemen: Interested members of the vinyl chloride industry are now considering a proposal to conduct studies in which animals will be subjected to long-term exposures to vinyl chloride monomer. In order that the test materials be properly representative of current American practice, we are requesting that you provide the following data on (a) your current industrial product, and, (b) a "highest purity" product you would be willing to provide in tonnage quantities to a guaranteed analysis specification. Requested Data 1. Production process (identified by appropriate patent refer ence or commercial process description.) 2. Raw material source, i.e., acetylene from calcium carbide, from hydrocarbon cracking, etc. 3. Assay: Minimum % Typical % Maximum % 4. Identified impurities: Minimum Typical Maximum a. ppm ppm ppm b. ppm ppm ppm c. etc. For each item under question (4) please identify method of analysis and limits of detection. A copy of the list of the im purities reported as being in material used in an earlier Euro pean study is attached for your information. CCR 000082274 -1- Particularly for compounds that may be suspected of being highly toxic or carcinogenic (such as methyl `chloride* methyl bromide, or bischloromethyl ether), presence or absence at the fractional ppm level may be of interest. Sincerely, KDJ/cj Enclosures inneth D. Johns Staff Representative <7. CCr oooa2275 Impurities Present in Vinyl Chloride Monomer 1,2 dichloroethane 1,2 dichloropropane Tetrachloroethylene 1,1,2-trichloroethane Acetaldehyde 1,2 dichloroethylene-trans 1,2 dichloroethylene-cis Chloroprene Methylene chloride 1.1 dichloroethane Carbon tetrachloride 1.1.1 trichloroethane Chloroform Trichloroethylene Benzene Water Ethane Ethylene Propane Isobutane Carbon dioxide Propylene n-Butane Acetylene Cyclopropane 1- Butene Isobutene 2- Butene-trans 2-Butene-cis Allene 1,2 Butadiene Methylacetylene Methyl chloride Ethylacetylene 2-Chloropropene Ethyl chloride 1-Chloro-l-propene-trans 1-Chloro-l-propene-cis n-propyl chloride Vinylidene chloride Isopropyl chloride Vinyl bromide n-pentane Isopentane Methane Mercury CCR 000082276 Reprinted tram the Archives o l Environmental Health January J97J, Volume 22 C opyright 797f, A/nencan Medical Association II. An Industrial Hygiene Study Warren A . Cook; P aul M . Giever, M P H ; Bertram D . Dinman, M D .S c D ; Harold J. Magnuson, M D , M P H , Ann Arbor. Mich o O o C as N* e- > n *-oso co rtCD O^ <<T CO CO CCR 000082277 74 000082278 Occupational Acroosteolysis II. An Industrial Hygiene Study Warren A. Cook; Paul M. Giever. MPH; Bertram D. Dinman, MD, ScD; cuul Harold J. Magnuton, Ml), MPH, Ann Arbor, AficA 5 An industrial hygiene survey was conductad in that were peculiar lo those plants affording known reaped la occupational acroosteoijrsis (AOL) in cases el AOL. No such processat or chemicals 32 plants engaged in production and compound were lound. The survey brought to light a num ing ol polyvinyl chiorkJa. ibis survay was Untiled ber of ehuatiORe suspected ol relationship to the to inspection ol facilities, interrogation ol tech precise cause of AOL, aome ol which require nical personnel, and alalialieal analyses. AN additional exploration. Most positive ol these manulacluring processes and chemicals utilized wee the finding that essentially all of Ihe peraorta 1 were explored. A major objective woe the iden- who developed AOL had served aa reactor tltlcslion ol variables In processes and chemicals cleaners using manual methods. PoLYVINYL chloride (PVC) has been in The clinical and epidemiological aspects production and widespread use for more of this condition are discussed in separate than 30 years. An extensive account of the papers in this issue of the AKCHivEa.8 * chemistry, methods of production, materials utilized, properties, and uses of the PVC Industrial Hygiene Survey resins was recently published in a series of technical articles by Albright.15 Uses in Surveys were made of 32 plant* by the 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 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 number of these locations. Five about 3 billion lb.4 Much PVC is produced plants conducted compounding and fabricating in other countries. Even with this extensive production involving thousands of operators, the occurrence of occupational acroosteolysis (AOL) among these workers was not recog nized until about 1961.7 o|>erations only, and one plant produced only the vinyl chloride monomer. These plants were located throughout the United States and one in Canada. This survey wae designed to obtain informa tion on equipment used, procedures followed, f-'nbmitted for publication Feb 3, 1670; accepted materials involved, extent of exposure to these, Apiil IS, 19711. and names and descriptions of jobs in order to I From the Institute of Knvironmental and Indus compare practices in the plants where cases of trial Health, University ol Michigan, Ann Aibor. AOl. occurred with those in plants experienc Head before the American Industrial Hygiene Conference, Denver, May 16, 19(13. ing no cases. Heprim requests to School of Public Health, The extent of exposures was estimated on University of Michigan. Ann Arbor, Mich 4H104 the basis of general observation, a knowledge of <Dr. Hillman). the physical, chemical, and physiological prop- Arch Eiwiron Health--Vol Tl, Jan 1971 OCCUPATIONAL ACROOSTEOLYSIS--COOK F.T AL 75 76 OCCUPATIONAL ACROOSTEOLYSIS--COOK ET AL 000082^ Fig I.--Flow diagram (or production of PVC Irom 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 marie for each of these avenues of absorption. Production Operations Vinyl Chloride Production.--The two processes for production of vinyl chloride described by Albright12 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-dichloroethane is pyrolyzed in the presence of chlorine as a catalyst for the production of vinyl chloride and HCI. 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 processes, each with many variations among different plants. The final polymer may have a molecular weight vary ing from 50,000 to 150,000, depending on conditions under which it is produced. The production processes are designated as sus pension, emulsion, bulk (or non.solvent), and solvent. A typical procedure is present ed in the flow-sheet (Fig l). The essential steps of these operations are outlined in this paper. For more complete details, reference may be made to the papers by Albright.-1 5 In the widely used suspension process, deion ized water is first introduced into a large auto clave, usually gloss-lined, followed by a wide variety of additives. These include suspending agents such as polyvinyl alcohol, methyl cellu lose. and gelatin, emulsifying agents such as sulfonated oils, surfactants such as eorhitan monolaurate, and buffers such as sodium bicar bonate. Trichloroethylene may be added to pro duce the lower molecular weight polymers. Cat alysts are added to initiate the polymerization. These are nearly all organic peroxides, with lauroyl peroxide and diisopropylpcroxydicarbonate (1PP) being used at the greater number of plants The reactor is then dosed, evacuated to remove oxygen, and vinyl chlo ride, normally a gas, is piped in as a liquid under pressure from the lank 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 S5 C. Since the polymerization reaction is exothermic, cooling water must he run into the jacket after the reaction him begun to avoid excessive heating. After ten to 16 hours, the polymerization is essentially complete, and the reactor is brought down to atmospheric pres sure. In most plants, it is placed under vacuum for removal of unpolymerized vinyl chloride monomer and transfer to the monomer recov ery area. The suspension of PVC is then dis charger! into a blowdown tank below the reac tor. This tank is placed under vacuum for transfer of remaining vinyl chloride to the recovery area. In some plants, the blowdown lank is eliminated. The general appearance of the charging floor of a imlvmer plant is shown Arch fCniiirnn Heullh--Vol 22. Jan IH7I in Fig 2. The reactors extend for ten feet or so down to the floor below. The polymer slurry is pumped to blend tanka, then to centrifuges for removal of much of the water. The dewatered polymer is passed through a rotary dryer with healed 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 hulk. In some plants, the polymer is stored in bins prior to being shipped. In the emulsion process, the equipment and process is essentially the same as in the suspen sion process up to the drying operations. In order to produce the finer polymer particles characteristic of the emulsion process, a wide variety uf emulsifying agents is used. These may be soaps such as ammonium or sodium laurate. surfactants such as salts of naphthalene sulfonic acid, or various synthetic detergents. Water-soluble initiators such as ammonium persulfate and hydrogen peroxide are used as 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 water is in troduced. Instead, the polymerization is con ducted jn such solvents as cyclohexane, acetone, or /-butane. Copolymer and Terpolymer Production. --In addition to the production of the homo- polymer PVC, many of the plants also produce copolymer and terpolymers, includ ing vinyl chloride. The greater percentage of the monomer tends to be the vinyl chloride in all of these. The copolymer vinyl chlor ide-vinyl acetate is in highest production Arch Environ Health--Vnl 22. .Inn IH71 OCCUPATIONAL ACROOSTEOLYSIS--COOK ET AL 77 among this group but is a TaM* 1.--Abaofufe Praasura-TIm* t'alvn minor product in cum|iarimd to thr homupolyiiM'r. Absolute Pressure Time Vslues Bela* 10 Absolute PressureTimo Values ol 10 or Above Other copolymers are vinyl chloride-vinylideM chloride and vinyl chloride-lauryl- Plant Coda No. of No. oi Rasctor Expected Cleaners AOL Cases Plant Code No. Of No. Ol Reactor Expected Cleaners AOL Cases vinyl ether. An example of a terpolymer ia vinyl chloride-n-butyl maleate-dibutyl maleste. Processes, additives, and catalysts essentially identi Plants With AOL Cases EE 31 O.S e E F R Plants With Possible AOL Cases CC 32 0.9 Totals 63 1.7 216 165 16 39 436 5.8 4.5 0.4 1.1 1 1.8 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 Q V W Totals DO Totals Plants With No AOL Cases 30 O.S 0 22 0.6 H 27 26 91 2.5 SO 1.4 L 29 s 17 T -9 193 5.3 Z 17 AA 8 132 Plants Started In Operation In 196S or 1966 2) 0.6 C 64 J 13 21 0.6 67 0.7 0.7 0.8 0.5 0.2 O.S 0.2 3.6 l.S 0.4 1.9 batch following completion of polymerization is conveyed to a vinyl chloride recovery area by the auction pump that places the reactor and the tripping 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 TaMa 2.--Classification oi Standard Job THIaa Job Title Coda Additive makeup (other i than catalyst) Rfigslns end thinning nnrglnr 2 Catalyst makeup man 3 Clerical, othsr office, staff 4 Compounding and fabricating 5 Dryer operator 6 Ganaral laborer, cuatodial Laboratory supervisor 7 a Laboratory technician 9 Maintenance, electrical 10 Maintenance, mechanical 11 Monomer maintenance operator 12 Monomer operator 13 Job Title Monomer recovery operatoi' Monomer supervisor Plant guard, security officer Reactor cleaner Reeclor cleaner, solvent Reactor operator Slurry blender Supervisor, polymer Tank farm operator Utilities area operator (water treatment, etc) Warehouse operator Transfer operator Other than PVC Code 14 15 16 17 18 19 20 21 22 23 24 25 30 to prevent spontaneous poly merization during its distillation, the method due on the agitator blades may require hammer used for its purification. The recovered vinyl and chisel for removal and sometimes even chloride, with the higher boiling phenol remain ing in the still, is then pumped to storage for reuse. Reactor Cleaning Operations.--After the axes. Pour plants use water jets with pressures of from 300 to 3,000 lb/sq in for the cleaning operation. One of these used water jets only in polymer has been discharged from the reactor one of two production buildings, as the etrucand the pressure brought to atmospheric, the tional features interfered with movement of the reactor is aerated. This ia accomplished by portable high-pressure water unit about the dropping a flexible duct connected to a portable building. Three other plants have been using blower to the bottom of the reactor, with dis solvents for reactor cleaning. One of these charge normally through the open manhole at started to use this method late in 1964, a the top of the reactor into the charging-floor area. The loose residue is washed out with water, after which one or two men enter the second in 1966. and the third from the begin ning of plant o|>eration in 1966. The reactor is tilled with the solvent which must be healed reactor to remove the skin of polymer remain ing on the reactor surfaces. The usual method is hy manual scraping with putty knives. Resi and agitated for a prolonged |>eriud, as the PVC is difficulty soluble. Polyvinyl Chloride Compounding.--Cnm- Arrh Environ Health--Vol 22, Jan 1971 78 OCCUPATIONAL ACIIOOSTEOLYSIS--COOK ET AL TaMa 3.--Magnitude of Dosage fiprnml at Shtgl* Concept at a weekly, monthly, or Sevsnty/Dii (ahem Exposure Parameters! Magnitude* ol Dosage less Then 1 hr/Week IB hr/Week More Than 6 hr/Week Slight 1 2 3 4 5 6 Negligible Moderate Moderate Moderate None Negligible None Negligible Nona None Negligible None None Negligible Intermediate 7 8 9 10 11 12 Appreciable Aooreclable Appreciable None Negligible Moderate Moderate None None Negligible Norte Negligible Moderate Major 13 14 IS 16 17 18 Appreciable Appreciable Moderate Appreciable Appreciable Appreciable Nona Moderate None Negligible Moderate Appreciable Expressed in order ol Increasing dosage received trom exposure, which ts the summation ol the three columns to the right. t Severity of eaposure It estimated a a none, negligible, moderate, or appreciable for indicated durations. other period. A classification of 26 job 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 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 tails of the manner in which this was done are discussed in the accompanying paper on epidemiological aspects of AOL.8 Job 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 sheets, films, or pellets. These are used in fabricating operations. are many reactors, this work does not require the entire time of the employee. Part 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 tion of these at any one time. 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 plants surveyed and even in different units of the same plant in regard to nearly every phase of the operations. Investigation of unit jobs in the plants disclosed a wide assortment of job titles. In fact, 8 job title as used by the technical supervisors often dif fered from that for the same job in the same plant as listed by the personnel de partment. Furthermore, a job assignment in one plant might include a different group of unit operations than in another plant. Also, the either as full time for a period of months or dividing their time within a given week or even day. The latter occurs particularly among maintenance personnel. Where production of vinyl chloride is part of the operation, operators may rotate be tween jobs in the production of the mono mer and those associated with the produc tion of the polymer. The length of time spent at various jobs is a function of production needs, economic conditions, plant growth rates, and activity of other product lines. proportion of time devoted to the several unit operations often differed. To compound Occupational Exposures to Materials the difficulties of classification, workers Extent of Exposures.--Information was would frequently rotate through several jobs obtained not only on each of the materials Arch Environ Health--Vol 22. Jan J971 CCR 0 0 0 0 8 2 2 8 0 OCCUPATIONAL ACROOSTEOLYtilS--COOK ET AL 79 used or produced but also on the extent of Tsbt* 4.--Us* of inhibitor* With Vinyl Chloride exposure to each. Since this is a funelion of both duration and severity, emit of Hawfactors was estimale<l. Tlte duration of ex|*>sure was recorded as less than one hour a week, from one to eight hours a week, or more 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 Plants wilh AOL cases or possible cases Plants without AOL case* Use of Inhibitor * 111 Virgin Vinyl Chloride In Vinyl Chloride Recovery 22 34 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 de grees of duration and severity, the 18 possi ble combinations of duration and severity were listed in increasing order of dosage and cias&ified 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 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 tion provided and odor observed. The odor of vinyl chloride could be detected in the immediate vicinity of reactors as (hey 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 bv odor Is accept"ed AS"40U ppm. Except under the foregoing ttmditionfe, 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 aliphatic and aromatic, ketones, esters, and small number of plants with more sereitive 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 waa 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 instruments, such as the gas chromatograph, it has been found that the vinyl chloride concentration inside the reactor during scraping operation tends to he 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 terials and also to certain details of procedure. tions close to the hand during scraping in Vinyl Chloride Kyponurm In evaluating the range of 600 to 1,000 ppm. the role of vinyl chloride as a possible in Although this study provided no evidence fluence in the causation of AOL, the esti to suggest that vinyl chloride per se is the mates of the extent of the exposure of re etiological agent, the measurement of vinyl actor cleaners and reactor operators were chloride concentrations may serve as a use reviewed. Since the authors conducted no air ful index to the adequacy of reactor ventila analyses, they had to judge the presence of vinyl chloride in the charging floor area principally on the basis of general ventila tion. Inhibitors in Vinyl Chloride.--An inhibi tor, usually phenol, may be added to the Arch Environ Health--Val 22, Jan 1971 80 OCCUPATIONAL ACIIOOSTEOLYSIS--COOK ET AL Table 5.--fleecier Cleaning Procedure! as a passible factor in the Hrf'ttf S(Yrfptfrrg Plant Alter Every Code Batch Lass * ban Every Cycle Plants with AOL cases BX EX FX KX (through 1964) RX U Every 5-12 cycles (building A) EE X Plants with possible AOL cases be Every ''severs!'* cycles Plants with no AOL cases AX (to September 1964) CX 0 HX i Every 2'ft cycles l Every 4-B dsys NX P Weekly through 1964, every 2 weeVs 1965 1966 0X sX T X Every 1 3 cycles (emulsion) (suspension) V Every 10 cycles zX AA Every 4 or more cycles DO X GG (.Jr'rtfitru' Irv Wdtei let from 1965 From 1962 (building B) From 1962 from 1965 by Solvent On glasS'lmed, intermittently In 1966. entirely by December 1966 From September 1964 From start of operations causation of AOL. Contact with Ihnse inorganic and or ganic peroxides occurs as they are handled prior to their introduction into the reactor and also during re actor cleaning if any unre acted catalyst remains in the residue. Twenty-two of the 26 plants used lauroyl perox ide. Eight of these were plants with AOL cases or possible AOL cases, and 14 were plants without AOL casts. The next most com mon organic peroxide was the IPP, and it, too, was in the negative plants, in four of the former and in eight of the latter. No catalyst or group of catalysts was used in all positive plants and in no negative plants. Constituents of Scrapings, --Other suspect materials arc constituents of scrapings removed from the reactors during manual cleaning. These are believed to include some partially polymerized resins, along with some un reacted catalysts and addi tives, and unpolymerized vinyl chloride. Little specif ic information is currently vinyl chloride to prevent spontaneous poly available concerning these constituents. It has 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 PVC particles, from the reactor. The phenol is removed by treatment with caustic soda prior to its transfer to the reactor. The practice over the years covered by the study is presented in Table 3. The use of the inhibitor in the virgin vinyl chloride at two of the positive plants and three of the negative plants, with inhibitor being added in the vinyl chloride recovery operation in Iwo positive plants and four negative plants, leads to the con whereas little of the IPP remains unreacted in the polymer.1 Further investigation of the scrapings from the reactor may be expected to furnish information that may lead to a better under standing of the factors involved in causation of AOL. A difficulty in such investigation is that the composition of the scrapings is continually changing from the time they are removed from the surfaces of the reactor, ft clusion that inhibitors probably are not a is obvious that comparatively small mole factor in AOL causation. Catalyst Exposures.--Since the catalysts are all active compounds, they were suspect cules of partially polymerized vinyl chloride are increasing in size with passage of time, and active constituents such as residua! tl- trih puritan Health--Vitl 22. JiW 1971 CCR 0000Q 22Q 1 OCCUPATIONAL ACKOOSTEOLYSIS--COOK ET AL 81 Table .--fleecier Cleaning Procedural Method Manual scraping after vary raaclor eycla Manual scraping aftar 2 3 cycles Manual scraping alter 4-12 cycles Water-jet cleaning Organic solvent cleaning Positive Plant* 7 0 2 2 1 Negative Plants 9 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 md the one exception had cleaned laboratory reactors,* 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 clean the reactors depended not only on the number of reactors but also on the frequency of cleaning. Jn 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 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 residua remaining on the reactor surfaces following discharge of (he batch might be factors in AOL causation, infor mation was obtained concerning the degree of vacuum applied to the reactor prior to o|>ening it and the length of time that the reactor wua under this reduced pressure. The amount of volatile materials remaining in the residue on the reactor surfaces was considered to be roughly proportional to the absolute pressure and inversely proportional to some function of Uie time. Since the rate of removal of volatile material would tend to decrease with time, the logarithm of this factor was used in calculating an absolute pressure-time (AP-T) value. It was hypothesized that the relative amount of vola tile materials remaining in the residue follow ing application of vacuum would approximate a nondimensional value obtained by dividing the absolute pressure in inches of mercury hy the logarithm of the time in minutes during which the vacuum was applied. Thus, the lower the AP-T value, the leu is the amount of volatile materials remaining in the 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 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. The AP-T values ranged from 0.5 to 21. The AP-T values were 10 or above (an 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 bb compared with those in the negative plants. The total number of reactor cleaners at risk in the positive 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 more is 436. The relotion of these two totals is to be compared will) 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-T above that value. The number of expected cases of AOL for each plant is also listed in Table 6. These values were obtained by dividing the num ber of reactor cleaners at risk by 37 This An-h Environ Health--Vot 22. Jim 1971 82 OCCUPATIONAL ACROOSTEOLYSIS--COOK ET AL figure derives from the paper on epidemio logical aspects of AOL8 which reports the prevalence of AOL or possible AOL as one case per 37 reactor cleaners at risk. Of tire negativt 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. Hiis 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 an AP-T value of less than 10 to the total number in such plants was 193 to 325. Hus propor tion for the positive plants was 63 to 499. A X* test demonstrated that the probability of this difference between the negative and the positive plants occurring by chance 1b 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 are 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 constituen cy 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. Albiight t.F: Vinyl chloride procereea. Cheat Eng 74:123-130, 1967. 2. Albright LF: Manufacture of vinyl chloride. Chem Eng 74:219-226. 1967. 3. Albright LF: Polymerization of vinyl chloride. Chem Eng 74:151 168. 1967. 4. Albright LF: Vinyl chloride polymerization by suspenskn prnreeneg yields polyvinyl chloride res in* CArm Eng 74:145-162. 1967. 5. Albright U: Vinyl chloride polymerization by emulsion, bulk and solution processes. Chem Eng 74:85-92. 1967. 6. PVC producers Chem Eng New* 47:18-19, 1969 7. Wilson RH. McCormick WE, Tatum CF, at al: Occupational acroonteolysis: Report of 31 cases. JAMA 201:577-581. 1967. 8. Dinman HD. Cook WA. Whiletwuae WM. et al: Occupational acroosteofysis: I. An epidemiologi cal study. Arch Environ Health 22:61-73, 1971. 9. Dodson VN, Dunnan UD, Whilehouse WM, et al: Occupational acroosleolysis: III. A clinical study. Arch Envirrm Health 22:83-91. t871. Arrh Environ Health--Vot 22, Jan 1971 Printed and Pubtished m the United States of Ame/tce CCR 0 0 0 0 8 2 2 8 2