Document DwNr4mZx8Mr2kVvZJkyJBZnn

CHEMICALS AND PLASTICS TO (NAME) Mr. R. W. Sealer, 515 company Mr. J. B. Leverton, 515 location Mr* D. E. Deese, 515 Mr. K. E. Ross, 515 Mr. R. L. Frantz, 515 Mr. G. F. Tacquard, 515 COPY TO Dr. D. R. Montgomery, 515 Mr. J. L. Carvajal, 514/ Mr. R. N. Wheeler, 514/ yet 7^^ UC 14 Mfinm M*IER. JR. , O. BOX 471, TEXAS CITY, TEXAS 77SRO April 30, 1975 subject VCM Standard - Bnalmd/Germany The attached, forwarded by Art Steele, you may find of interest. For those who have no desire to wade through the entire document, pages 4, 5, and the first paragraph of page 6 are an interesting discussion of monitoring. Page 13 reviews the German thinking on the matter. If I interpret this correctly, Germany will have a 10 ppm TWA and 30 ppm TLV. I believe England at this time has a 25 ppm TWA and 50 ppm TLV. Both of these are reasonable standards and should be fully protective of workers' health. As Mr. Lutz requests, please hold these documents in confidence. MEE/ebm M. E. Elsenhour -K> ucc 031422 N r;` ' i CORPORATION ' 5 & Plastics ______ 270 Park Avenue, New York, N. Y. April 18, 1975 TO: Dr. A. B. Steele 28th Floor f'C: Mr. T. W. Carmody SUBJECT: ICI's Position - VCM Art, As I told you on the phone, one of the people I ran across in Europe was A. W. (Barry) Barnes, who is in charge of ICl's vinyls activity. I was interested to find that their position and concerns are much the same as ours. They seem to feel that only a relative handful of European concerns are measuring thoroughly enough and with sufficient accuracy to understand what the problem really is. They are most concerned by the damaging comments being made by both U.S. and European com panies to the effect that the 1 and 5 limits are relatively easily attainable. They suggested that we exchange information including plant visits, so that actual, experimental techniques and analyzer probe placement, which drastically affect results, may be examined in detail. To this end, I have instructed them to contact Merle Eisenhour directly to arrange the details. X am also enclosing a number of documents which they gave me including the British Standard, which we may already have, and the German Standard, which was just issued. It is evident from these that the approach being taken in Europe by government agencies is much more rational and that the ef fect is a cooperative one rather than an adverse one. Also included are two "white papers" one of which is a basic document put together last Fall and the other a recent update. These data represent all manufacturing plants of all producers in the United Kingdom. These position papers have been cir culated to Government and Labor in the United Kingdom, but we have been asked to hold them confidential within our organiza tion, Please feel free to circulate them to anyone within _ rc: c 11 v t o uce 031423 A O c-n- H F. Dr. A. 8. Steele 2 *' April 18, 1975 rir organization to whom they might be useful, but with the .rricture that they hold them confidential. AWL:cr Attachments A. W. Lutz uce 031424 This retcr*. summarises the availaole information on the current vinyl chloride m nt'.o. phora levels in the reaction sections of tno UK PVC plants both for personal exposure data and for the results from area monitoring. Measurements carried out m tne downstream drying, packing rxc warehouae areas continue to confirm that ievele are generally significantly lower than in the respective reaction sections. 1 Personal Exposure fata - Reactor Operators. As outlines in the previous report (a !V 3ames l2/l2,/74. Vinyl Chloride Levels in UK Plants - Note to tne Tripartite Working Group) measurements are carried cut on all plants using a technique based on a portable continuous 'personal' air sampling cavice carried by individual operators for a 4 or 8 hour period during the r.orral working day or shift. The results are a direct measure of the average exposure over the sample period and hence relate directly to the 6 hour TWA referred to in the interim hygiene standard. The results for each of the UK plants car. be summarised as follows: Period 1 Plant 1975 ! r--1 A. March Number Results 33 ' Distribution of 6 0-5 6-10 11-15 46 22 18 hour TWA Results (>) 16-20 21-25 25.-50. 662 i3 March 30 40 25 22 6 5 iI 2 'I c Jan 12 90 10 - - - m D 1 Jan 18 63 21 11 5 - 1 S Jan 14 92 8 - - - P 1* ?ab 14 100 - - - - - C March 63 77 12 5 5 - 1 H Feb 18 44 28 17 6 - 5 I Feb 12 92 8 - - - - Tne overall industry situation can be obtained by adding together the resulta from the individual plants as follows; i Inuustry ; Situation 1 ----------- No. of Kssuits Period 1st garter 1975 222 Distribution of individua1 8 hour Ti.'A Results zm0-5 6-10 11-15 16-20 21-25] 25-50 PPO 146 37 22 9 In appraising tr.ese results it is important to reoemoer that the UK Code of Practice allows no personnel to be exposed above the interim hygiene standard ana hence all the 6 hour T.VA results should be belo* 25 ppm. 1 ucc 031425 2 Area Monitoring Results - Reaction Sections. The reaction sections on all plants except Plant I are no* equipped with fixed culti-point analyser systeos based on either gaa chromatography or infra red analysis. Theae ayatema which are baaed on 'instantaneous* sampling *ith an analysis time for each sample of appioximately one minute, produce approximately 10,000 resulta per week and hence on line computer facilities are neceBaary to proceaa the data, Pler.t I ie currently being equipped with a multi-point analyser system which will be operational by the end of April. Although all plants are installing in line computer facilities, to date only Plant A, B, C and P have such equipment operational. The area monitoring results for the reaction sections can be summarised as follows: Period Plant 1975 VCM in Atmosphere Levels from lAilti-Point Analysers Average (ppm) i Results >25 ppm i Results >50 ppm sil A March 1-- B March C Jan D 2 * >- 7 'Cf) '* c* H Jan Jar. March March March I Jan (Based on 1 spot1 camples) 7 4 - 4 6 4 12 3.5 2.1 1.7 6.2 2.7 2.3 3.8 1.8 10.0 1.2 0,8 0.4 1.7 0.4 1.4 1.5 0.7 3.3 It is important to streoa that this data is generally based on.either one week or one month average and hence is not directly related to the interim hygiene standard which is based on 8 hour/day averages. The data for Plant A has bean extracted for a one week period in Pebruary to demonstrate the sort of differences which can occurt Plant A Distribution of the 21 Individual 8 hour Shift Averages H) Weekly Average 0 - 5 ppm 6 - 10 ppm 11-15 ppo 9pp 5 71 24 Routine full analysis of the individual results from the multi-point analyser on a shift basis is not practicable until in line computer facilities art installed. ucc 031420 / / /' -3- 3 funeral Progre-iS. Durii.j the Last three months further procedural changes have been instituted or. the plants while the riant modification programmes aimed at cininisirg VCK exposure levels have continued as a matter of 'ii>cf.cy. The major effect has been a further reduction in the average Vcv in atuoephere levels in the plants and hence in the average 8 hour TWA results. In addition the proportion of individual area monitoring results over ^0 rpo has shown a marked decrease over me period. However, the mam problem continues to be the 3mall proportion of high area .monitoring and personal monitoring results arising as a direct consequence of periodic vinyl chloride leakages. All plants are currently installing local zoned alarm systems based on the multi point analyser results and this will enable immediate action to be taken in the event of an excursion in VCM levels. The current major engineering programmes on the various plants are directed at eliminating known sources of vinyl chloride leakage and it is still expected that when the work is completed at the end of 1975 the maximum 8 hour TWA exposure will be substantially below the 25 ppm level, 1 WFI0JCT/8 April 1975 -3 * uec 031427 CONFIDENTIAL y chemical industries association ) I VINYL CHLORIDE : EXPOSURE LEVELS ON UK PLANTS At the last meeting of the Tripartite Wording Group, I was asked if the industry could present a report indicating the current level of achievement in controlling vinyl chloride levels in plant atmospheres. The following paragraphs summarise the position: they deal successively with the following items: (a) the methods of measurement and the significance of results obtained (b) the detailed position on one UK plant (c) the summarised position on each of the UK plants. ) Methods of Measurement > Two basically different methods of measurement and control exist. (i) The first of these involves the repeated and frequent measurement of vinyl chloride concentrations in the plant atmosphere at a number of positions on the plant, selected to be representative of areas where personnel normally work. This method tells us what the actual vinyl chloride concentrations are at a number of places on the plant, and provided enough places are monitored and the frequency of measurement is high, it gives us an accurate and continuous picture of the state of the atmosphere throughout the plant. What we are primarily concerned to control, however, is the total exposure of any individual person and since all plant personnel move from one area to another during their normal activities, we could only find this out, from fixed pointm>nitoring alone by noting how long and when each individual was in each monitored area, and then calculating from the results what his total 8 hour exposure had been. A second parallel method of monitoring is therefore needed, to measure directly the exposure of an individual, and to ensure that calculations of this sort are and continue to be reliable. (ii) The second basic method therefore is "personal" monitoring. With this, the individual is supplied with a portable apparatus which samples continuously the air he is breathing over a 4 or 8 hour period. The total sample is collected- at the end of the period and its vinyl chloride content measured in a laboratory. The result should be a direct measure ment of the exposure of the person concerned over the period and should therefore tell us unambiguously that the wearer has or has not operated within the hygiene standard. The method does have its deficiencies though in terms of accuracy it depends, for example, on the wearer remembering to switch off the sampling device -hen he puts on a respirator and to note how long the period is before it is switched on again. If he doesn't do the first of these, the apparatus will continue to absorb possibly high concentrations of vinyl chloride, to which the worker is not in fact exposed, and the overall result will be too high: if he does the first, but forgets to switch the apparatus on again the result could be * uec 031428 lower than the true exposure. So the method does depend for its accuracy on continuous vigilance and concentration on the part of the wearer; and this would be difficult for anyone to achieve con sistently over many 8-hour periods. A more serious deficiency of the method, if used alone however is that the result is not available till after the end of the period of sampling; and if the result then proves to be too high, the time for action is long past. This is not a deficiency of the fixed point monitor referred to in (i) above since, with thi6, instantaneous measurements of plant atmospheres are made with a time lag between sampling and measurement of only a few seconds; and action can be taken immediately if adverse movements in vinyl chloride levels are recorded. To ensure complete protection of workers on PVC plants both methods are required. The fixed point sequential monitor will tell us the actual atmospheric con centration at any one place on the plant every 23 minutes; and points close to one another will be measured every 1-2 minutes. It is the results from this equipment which will enable action to be taken immediately, through procedures already agreed, whenever a significant change in the levels is observed. Complementary to this, periodic checks with personal monitors should show directly that individual exposures are indeed at the level suggested by the fixed point results, and are within the prescribed hygiene limits. Because of the variation in VCM levels between different points on the plant and because operators do move from place to place, the personal monitor results should always be below the average levels recorded at the worst point, so that plant action to keep atmospheric levels below a particular figure should result in each operator having a personal exposure level which is reduced below this figure. This summarises the methods and philosophy of measurement and control which we are aiming at. The present position in the UK is that five plants already have continuous 6, 12 or 24 point monitors installed and by January 1 eight of the nine major operating plants will be equipped with 12, 24 or 30 point analysers. The ninth plant, and the other smaller plants presently shut down through lack of orders, will be equipped in the first quarter of 1975* In the meanwhile, the plants which still await equipment are being monitored through the usa of grab sampling and a variety of off-line measuring devices. The results from these plants are necessarily fewer in number since a fully equipped 24 point monitor produces at least 10,000 measurements per week whereas off-line measurements are limited to tens per day. Where measurements are few the results usually tend to suggest an average VCM level which is lower than it really is. This is because PVC plants are characterised by a generally low continuous level of VCM interspersed with peak concentrations which are of short duration, but which nevertheless contribute significantly to the time-weighted average. When few measurements are taken, the chances of recording these higher levels are very low. r ucc 031429 Hy ourpose in describing measuring methods at some length is partly to indicate where the industry now stands but primarily to emphasise that the results 50 far available come from a variety of different techniques (varying marnedly in frequency and in type of sampling and analysis) and from two quite different philosophies of approach (personal and fixed point) which, by their nature, will give different numerical results, even when describing the same situation. In any discussion of vinyl chloride levels, we have to ha absolutely precise in our definition of what we are talking about, for a Single number (x ppm) can describe several quite different actual situations depending on the method used to obtain it. (b) Detailed Results for one Plant (A) I have chosen one plant for detailed analysis in order to illustrate some of the points made above. The particular choice was made because, in mid 1974, this was the plant with the highest average VCM concentration of all UK plants and because it now has had the most sophisticated measurement system for the longest period and as a result is most fully characterised. The polymerisation section of the plant has continuous sequential measurement at 24 points. The weekly average of all 24 points, over the period February to November, is shown in the attached graph and summarised below. Weekly average all points (ppm) Feb June 60 35-40 Sept 30 Nov 7-13 13 The decrease, from February to September, came from alteration of procedures and many detailed engineering modifications. The large change between Sept ember and November resulted from major increases in ventilation. Still further detailed modifications have yet to be done but these do not include any further single major change and it is expected that future progress will be only gradual and its extent is not yet predictable. Note especially though that the figure of 13 ppm represents the average, for the week of Nov 7-l3 of results from 24 points. This is not how the interim hygiene standard is defined and so the result is not a measure of how easily we are meeting that standard. The standard is concerned with each individual and no one man can be in 24 places at oncet If, as a first approximation to possible individual exposures, we take the weekly averages for each of the 24 points separately (ie. we assume a man might remain in one position throughout a week) then we find the range of results spreading from a low of 3 to a high of 22 ppm, with no particular plant logic explaining the differences between points ie. these are random, very small leaks which may occur in a different place next time we measure. The hygiene standard however requires a 25 ppm limit measured over 8 hours not over a week: our computer does not yet automatically give us the results for each measurement point and for any 8-hour period but, with one point showing a weekly average of 22 ppm, this point must, for some 8 hour periods, have exceeded 25 ppm* Indeed a back-check of the results shows that the maximum 8 hour figure for any single point varied, through the week, from 1? to 47 ppm. ucc 031430 1- - Tur.iing now to the hygiene standard's maximum of 50 ppm, a different computer analysis (the lower curve on the graph) shows the percentage of results which exceeded 50 ppm over the complete period. Again 1 summarise the graph below H of results above 50 ppm Feb 45 June 15-20 Sept 15 Nov 7-13 4 A marked improvement can once again be seen, particularly after September as a result of improved ventilation. And if we recall that the hygiene standard is concerned, not with instantaneous, transient readings, but with peaks over a 15-30 minute period then the percentage results outside the standard will decrease below the figures shown above. This is about all we can extract from the fixed point monitoring results. They show that a lot of progress has been made but that if the hygiene standard were concerned with positions rather than people we should be exceeding it for a significant time, even though the plant might be charact erised in general terms as operating at 15 ppm. The table shows how different numbers, all correct, can give different impressions of our achievements so far. Weekly average all 24 points Ppm Comments 13 Suggests we are well inside standard Weekly average individual points range 3-22 5054 of results are between 13 and 22 ppm so, contrary to impression above, we are working close to standard for high proportion of time 8 hour average individual points range 3-4? Borderline to standard for part of time, over standard on significant number of occasiona. The first conclusion is that if we were to regard the standard as a positional and not a personal one, then, read in conjuction with the detailed monitoring requirements, we are just going to meet it by the year-end; the position would, of course, be different if monitoring was a more infrequent affair. The second conclusion is that the problem of meeting it lies in the random spread of results about the mean. To improve the situation we must narrow the range of results by eliminating the higher figures; but this will only be achieved by a sustained effort from engineers, plant management and plant operating groups working together as a team. However, the hygiene standard is a personal one and we must, therefore, con sider what we know of the plant's progress against the standard proper. In October, after the weekly average results had fallen to 15 ppm, a number of personal monitoring measurements were taken. The results gave an average of 23 ppm, with 2654 of them greater than 25 ppm and a tail of figures up to 60 ppm. 7 UCC 031431 -fi- There Jere disturbing figures, since personal results should be below the plant average, certainly not above it: and 4 hour figures as high aa 60 ppm are difficult to explain when only 756 of all fixed point results are above 50 ppm. A repeat operation was, therefore, carried out in November with all participants operating in pairs (to remind one another of the need for control and recording), and with a third operator checking atmospheric con centrations with a portable meter. Good agreement was this time reached within groups;and -ith a plant average of ppm, the personal exposure levels (52 results) averaged 10 ppm and ranged up to 20 ppm. These are early results and need confirmation, but they do suggest that this particular plant may now be just inside the interim hygiene standard. Proof of this, however, requires extreme care in the use of personal monitoring equipment and even when this is achieved there are strong indications of a quite wide range of results. As with fixed point results, the conclusion must be that a sustained investigative effort is required over several months to eliminate results at the high end of the range and thus to bring down both the average and peak exposures. This effort is already deployed and will be maintained by the whole team. (c) Situation on all UK Plants Having discussed one plant in detail, we can now examine the position throughout the industry. The fold-out table attached summarises this, starting with Plant A which has been discussed above. Plants A to E These are all sequentially monitored and so are best characterised and should therefore be best controlled. Points to note in the table are (1) Atmospheric concentrations (a) The figures for Plant B may be overoptioistic 6ince a six-point analyser is inadequate for complete characterisation. (b) At this point, analysis of performance on all except Plant A is incomplete since installation of monitors is very recent on the other plants. (e) The average figure quoted is very sensitive to a relatively few short-duration peaks: and in calculating the average figure it is assumed that a peak figure at any point persists until that position is monitored again 24 minutes later. To illustrate the influence of peaks, a plant which has 95)6 of its results at 10 ppm but 556 at 100 ppm will have a calculated average figure of 14.5 ppm: and the real average may be between 10 and 14.5 PP> if the peaks in fact are very transient. ucc 031432 9- (d) la view of this sensitivity, and the incidence of peaks - up to 5# - it seems clear that the problem now ia not one of controlling the general background level but of decreasing the number of peaks* (ii) Personal Monitoring Results Tne results suggest that on these plants we are close to achieving a 25 ppm TwA since the average TWA's are in the 10-12 ppm range: but we still, on the majority of the plants get 6-15# of all TWA's above 25 ppm* The example of Plant A might suggest however, that some improvement of the figures would result from more accurate personal monitoring. (iii) In Summary, there is a need fcr more work on all these plants to achieve closer correlation between sequential and personal monitoring so that accurate control can be established. The indications, though, are that, with close attention to detail, all these plants can be brought within the personal TWA of 25 ppm and that with continuing team effort and further engineering changes an 8 hour TWA for every operator significantly below 25 ppm should be achievable. Plants G to 1 Information on atmospheric levels in these plants is so far derived solely from grab-sampling. It is much more limited; and action to deal with specific causes of VCM emissions has therefore been more difficult. For the reasons given earlier when discussing grab sampling, the average results for atmos pheric concentrations in the table may be giving an optimistic picture of the true situation. However the (limited) personal monitor results suggest a similar position to that of the sequentially monitored plants (A to E), which is what we would hope for, since the same types of process and engin eering modifications have or are being incorporated on.all plants. Plants E and F These are important results since both these plants are of the open-air type; and Plant F is the newest in the UK with the largest autoclaves, and already incorporates most of the modifications planned for the other plants. The plant therefore represents the best that has been chieved in modern practice and technology, and it ought to give us some guidance on the ultimate we can strive towards with all our plants. In using it as a guide however we must note that the other plants, with all modifications completed, will probably always run at somewhat higher levels than Plant F since they do not have the intrinsic advantage of large reactors and open structures. Unfortunately, in view of its importance, this plant has been operating at low output for the last few months. As a result the average atmospheric concentration of 5 ppm may be optimistically low. Certainly, an all-out approach at full output, to minimising concentrations has not been possible: and the measurement of meaningful personal exposures has equally been impossible so that we do not know what these are. By analogy with Plant E however it seems possible that personal TWA's ought to be at the 10 ppm average level: and the distribution of results may be quite narrow. * ucc 03M33 -/- (d) Conclusions from Total Data (i) More work needs to be done and data obtained on atmospheric levels and personal exposures in all plants. (ii) Adequate sequential monitoring methods for atmospheric measurement are known and are being installed. (iii) Development of improved, more reliable personal monitors is required and is under way - but will take time. (iv) In the meanwhile, more precise correlation between the two methods is required in order that the main control mechanism may be through sequential monitoring. (v) Despite their present limitations, however, it appears that all plants ' are approaching conditions where all personal exposures will be below ?5 ppm in any 8-hour period. The total achievement of this depends however on engineering work still in progress and then on sustained effort by the whole plant team to reduce the number of short term, higher concentration emissions. (vi) The industry is already committed to the expenditure of 6m on engineering and process modifications for the reduction of VCM concentrations in the plant atmosphere. (In addition further expenditure will go on reducing environmental emissions and reducing monomer contents of PVC). (vii) With all this work done, levels will be lower than those recorded in the table. The CIA, in June, mentioned a 10 ppm average concentration in the atmosphere as a possible ultimate target for existing plants. The results so far from all plants suggest that this is achievable but we are now more aware of the spread of results about the mean, and there fore of the increased difficulty of achieving this level for every 8-hour period at every point on the plant. The very limited results from Plant F confirm too that about 10 ppm may be an ultimate level for other plants which do not have its intrinsic advantages: but we shall be able to speak more positively when we have operated this plant normally under controlled conditions. (viii) One point can be stated categorically. The industry does not regard the achievement of a 25 ppm TWA/30 ppm maximum atmospheric concentration as a stopping point in its efforts. Actions already under way are aimed at getting the lowest possible atmospheric concentrations and, as a result, the lowest possible personal exposures for all plant personnel all of the time. It is expected therefore that the achieved personal TVA levels will, in fact, decrease below 25 ppm as this engineering work is completed and as the work of the plant operating teams becomes increasingly effective It is not expected that the maximum atmospheric levels will decrease so markedly Bince present indications are that biggest improvements will come from progressive reduction in the number of "leaks" rather than from a reduction in the size of each of them. A W Barnes /O ucc 031434 ucc totkir Mn figurt pea 100, 90 eo purr * - Aurocm- srcuut - mu* w:aar averages t * recjIboso ppw j AmCEftitRIC CCnCOTTiATlCIG raeoui nanToiiiitc reslits further dorcvlxoit opened tvrcug* 24 point sequential wekly mrt( (oil points) 1i pps 8 tour average (all points) J-e? pps 8 r.Air av. (single point) 3-47 ppn results over 50 pjs * 6 point sequential wetiy t vrrge (all points) 10 ppn results over 50 ppn 5* Average Range up to 10 p|B 20 pps Results oeer 25 pfP til Teas approach and datailad engineering changes Average 12 pfa tango up to 44 pi* Results over 25 ppn 15* Ventilation iaprovtaeet (fab *75) Hydrodynamic cleaning tatailed engineering ohangas 12 point sequential (since 9/74) welly average (all points) 10 ppn results over 2b pps 3$ results over 50 ppn O.VV 12 point sequantial (sine* 11/74) wekly average (all points) 15 ppn results oeer 50 pps 2.3* 12 point sequantial (since 10/74) Weakly average (all points) 5 ppn resalts new 50 ppn 1% Average 6 pps taagn up to 15 Pta Rasults ever 25 pps U Teas approach and details anginearing changes Autanatia elaaning Average 13 pps tango up to 29 PPS taoults over 25 pps % Ventilaticn iaprovaswt (3rd Qtr *' Autowtis elaaning Average 10.5 ppa Taas app-oach and datailad tangs up to 24 pps nginaaring changas tasults ever 25 ppe til Grab saaplas (40-50 per day) average 5 pp occasional ewursiois >100 ppn Ho personal figures tveilable yet Teas approach and further anginearing chnngnn Crab sanplas weekly average results oeer 50 pps 15 m to Average 1* PPS tangs up to 42 ppn tasults over 25 pps 10* Vsntileti inprevanaat (Jan *75) Oatailed Mgineering changes Autonetic elaaning Grab saaplas average neons inanl eacureiws 14 P(S >100 pps Average 13 PR tango up to 40 p|P tasults oeer 25 pp 10* Datailad anginearing changas Autoantic cleaning Grea sanplrs 5 sonthly svnrngt results over 50 p(a 14 p|P i.to Avarsga tang* up to 20 ppn1 Engineering and process changes? 100 pps OAWQiaQUS HATDHAU5 TTOCTAL ggPQHLIC ordecisi(H3 na pakoeroos materials committee 3MA Notification of 19 March 197? - ITIb 4-3899.7 - 1^7/75 Kaference: Artbeltsachuta, 4 April 1975 Recommended industrial concentration (TRK) for ilnyl chloride The recommended industrial concentration for vinyl chloride &a fro:a 1.7.75 will be 5 ppm. The TKK value la to be interpreted aa the annual noan. The mean concentration over a period of 1 hour Bust not exceed } times the TRX value. The TRK value applies in particular to fields of activity involving: a) the production, recovery, storage, drawing-off, conveying and use of vinyl chloride monomer b) the conversion of vinyl chloride into unshaped vinyl chloride polymers (eg. the production of PVC) c) dealing with unshaped vinyl ehlorlde polymers and their soulding compositions. A TKK value of iQ ppm -ill be imposed for existing plants for the conversion of vinyl chloride Into unahaped vinyl chloride polymers (eg. the producti n or PVC), Under a transitional arrangement a value of 20 ppm will be allowed in these plants up to 1.7*76. The TRK valuta for vinyl chloride will be reviewed at 1.1.77 and adapted to suit the state of industrial development at that tine, taking account of th latest findings in tha field of industrial aedieine. Grounds The dsslslve factor in establishing the TBK value^ as an annual Man was that vinyl chloride la currently regarded from the toxicological and industrial medical standpoints as being a hamful substance with a primarily chronic soda of action. It is therefore admissible to use as s basis a long tern mean covering a period of on# year, assualag aa average working week of up to 4$ hours. (1) for broad definition see: Techniache Bichtkonzentration ftlr gefMhrliehe Arbeitsstoffe (Recommended industrial concentration for dangerous materials) Arbeitssohutt (1974) Mo* 5 pp. 169-170 ucc n^i437 ./ Tho establishment of thro* times th* TV value *s th* seen concentration ot*t 1 hour seta lisit oa p**k load#. Zt also sake* allowance,for th* natural fluctuation* in th* concentration of harmful substances^ Tho folio-ins were th* deelsivs factors in establishing th* magnitude of TRX value: a) The results of th* steps already taken with regard to process and ventilation technology, giving du* consideration to what is likely to be achieved industrially In th* near future; b) Th* facilities for th* analytical determination of the vinyl chloride oone*ntratioa,in th; vicinity of the TV value and for Monitoring and recording it. o) The fact that in th* light of experiences to date in the Industrial hygiene field, the proposed TSK value reduces th* risk of endangering health cospared with th* working conditions used hitherto. (2) For industrial regulation on "Measurement planning, statistical assessment" (In preparation) in association.with "Reooanendationa for th* measurement and assessment of toxic dusts" see Staub-Reiohalt Luft (1973), ho* 1, pp* 1-3 end Coenea Wt "Measurement and assessment of the concentration of toxie dusts, particularly those containing silica, in working areas in surface industries", Staub-Ueinhalt Luft ii, 1971. Ho. 12, pp. 484-490. (3) Brochure entitled "VC/PVCi Procedures for Safeguarding Health" published by the Verhaad Xuastatoffeneugender Industrie eV, Frankfurt 0974). iu ucc 031433