Document jydYny7XqQEOZ2Mv6zJX6gGxR

Brit.J. industr. Mtd., 1968,3$, 393. Mortality from Lung Cancer and Other Causes among Workers in an Asbestos Textile Factory J. F. KNOX, S. HOLMES, R. DOLL, and I. D. HILL From Tumor Mrotkon Athottot Co. Ltd., Kochdoh, artd tho Medical RotoartM ComciTt StatOtitol Kttoorch Unit, Umomity Coilcf Hotpitoi Modito! School, London, WjC.t. An account is given of walk in an asbcnoa textile factory and of die step* taken 10 reduce exposure to dust since the introduction of the Asbestos Industry Regulations in 1931. Measurements of the amount of dust to which men were exposed in the scheduled areas have been made by various methods since 1951, but the dam obtained by these methods are not directly comparable. Measurements made since 1960 show that the mean yearly dust level has been fairly constant from year to year and has varied from place to place between 1 and I particles (j to too microns lose and at least three times as lone as they were wide) per c.c. of air. Chrysotile was used predominantly in the factory, but small amounts of crocidolite were also processed at all relevant periods. Death rates have been recorded for all the 356 men who were employed for at least 10 yean in the scheduled areas since the first man completed so yean' exposure in 1916, and for the 338 men and 330 women who were employed for at least 10 yean in the scheduled areas but were never employed in these areas before 1933. The results show a substantially increased mortality foe men who were exposed for to or more yean before 1933 (48 deaths from all causes against ty-j expected). The increased mortality among these men can be accounted for by an increased mortality from cancer of the hing (13 deaths apinst 1-3 expected) and from diseases of the respiratory and circulatory systems associated with asbestosis. Men employed before 1933, but for less than to years, showed an increased mortality from lung cancer ($ deaths against 3-6 expected), but no significant increase from other causes. Men and women who were exposed only since January 1,1933, have had a mortality experience dose to the national avenge. Analysis of the trends in mortality shows (1) a decrease in mortality from lung cancer and other deaths associated with asbestosis with reduction in length of employment before 1933, and (3) an increase in mortality from lung cancer and ocher deaths without asbestosis with age. Twenty-three cases of lung cancer occurred in men who had been employed in the scheduled areas for at least 30 years. One etas regarded a* a pleural mesothelioma and the rest (approximately t8 in excess of expected) appear to have been ordinary bronchial carcinomas. Four other mesotheliomas have been <<igww~r since 1963, all in men and seamen with less than to years' exposure, one with only seven months' exposure, and one in a man who had been employed in the scheduled areas only since 1937. The results provide grounds for believing that the occupational hazard of bronchial carcinoma has been largely eliminated, but the dam are insufficient to estimate foe extent of the risk which may remain. Many studies of the mortality of asbestos workers have been reported in recent years and it has been Received for pnbbcstiea March u, Ifit. Request* for rcpfiws to Dr. JL DoO, Mcdkei Research Comcil'i Statistical Rrseerch Unit, University J~n Hint Hospital Medical School, iij Gower Street, London, W.C.I. shown that some groups of workers have suffered substantial risks of disability and death from cardio respiratory disease secondary to asbestosis end from bronchial carcinoma and pleural and peritoneal mesothelioma (New York Academy of Sciences, 1965; Gilson, 1966). In one such study Doll (19JJ) reported the mortality in a group of 113 men who had worked for at least 30 yean in the *93 GAF 19562 *94 J. F. Knox, S. Hohnts, F. Doll, and I. D. Hilt `scheduled areas' of a large asbestos textile factory. In that study the mortality experience was reported to the end of 1953. Subsequently the period of observation was extended to the end of 1961 and the scope was broadened to include men and women who had been employed since 1933 and had worked in the 'scheduled areas' for at least to yean (Knox, Doll, and Hill, 196$; Hill, Doll, and Knox, 1966). In the present study we have extended the period of observation to the end of June 1966, added further workers who have qualified for inclusion in the defined groups, and examined the trends in mortality attributed to different causes with aft and with the duration and period of exposure. We also report, in relation to these findings, the extent to which it has been possible to limit exposure to asbestos dust in the factory. Places of Work In an asbestos textile'factory the sequence of operations proceeds from the receipt of the raw asbestos fibres to the finished textile product in woven or plaited (ottn. The states ate: (1) Fiberiziaf The raw asbestos, which has already been prepared at the mines by milling the rock, screening, and separating the fibres by air currents, arrives in bags. These are opened; the fibres are blended, and the fibre bundles art broken down further in enclosed drum-like fiberiring machines with rotary metal beaten. The fibres are then bagged again for transmission to the next process* (2) Carding The formless mass of fibrous material is converted into a gossamer-like web which is divided into tapes and rubbed into sliver consisting of strands of short fibres made parallel to each other (0-7 ts to cm. in length). Much dust is produced, and ventiiation at a rate of approximately 2,300 cu. ft. of air per minute (71 m.1 per minute} per carding machine is required to carry it away through ducts, a rate which pro duced the levels of fibre count at the from of the machine that are shown in the last two rwhuwm of Table I. Different grades of sliver are produced, some of which are used in other manufacturing processes without further preparation. (3) Spinning Mott sliver is spun into yam. (4) Weaving Preparations of warp (beaming) and of weft (pirn winding) are preliminary to weav ing on looms. A variety of woven materials ate produced from yams ranging from fine tapes (listing weaving) to wide cloths and including webbing and brake linings. (3) Plaiting Ropes are produced of different specification. which are sometimes impregnated with graphite or other lubricant for the manufacture of packings. `Scheduled areas' are the parts of the factory to which the regulations for the asbestos industry apply (Asbestos Industry Regulations, 1931). They comprise areas for the operation of crushing and opening, textile processes, insulation fabrication, mattress making or repairing, all sawing and grind ing, and the cleaning of chambers or appliances for asbestos dust collection. The repost by Merewether and Price (1930) suggested that `to prevent the full development of the disease (asbestosis) among workers within the space of an average working life-time, it is necessary to reduce the concentration of dust in the air of the workroom to a figure below that pertaining to spinning at the time over which the cases (i.e., those dealt with in the Asbestos Report) were exposed'. To implement the practical application of this principle the asbestos industry in 1931 collaborated with the Factories Department (then in the Home Office, now in the Department of Employment and Productivity) hi devising methods of dust control. As a result, it was agreed that the conditions arising from flyer spinning, carried on without exhaust, but under good conditions of room ventilation, should be taken as `dust datum' for practical purposes (Report on Conferences between Employers and Inspectors, 1931). This level of dust production was accepted as the basis on which to assess the dustiness of other processes, and it is of interest to note that in 1936 Meiklejohn considered that nothing had emerged to suggest the need to depart from this practical standard. The principal methods laid down to achieve dust control are: () application of exhaust draught at dustproducing points; () installation of enclosed mechanical methods for hand conveyance; (c) effective enclosure of dust-producing machines and plant; and (d) substitution of wet methods for dry. In situations where these methods cannot be applied, respirators must be worn. The regulations were made in 1931 to come into force by stages during 1932; we have, therefore, regarded January t, 1933, as the commencing date for workers whose mortality can be related to the GAF 19563 Mortality from Lung Cancer and Other Causa among Workers in an Asbestos Textile Factory 295 improved conditions. The technical developments necessary for effective dust control were not immed iately available, and much research and experiment were needed. Comprehensive accounts of the development of dust control have been given elsewhere by Bamblin (1959) and Hills (196}). Measurement of Exposure The type of asbestos that has been used pre dominantly is chrysotile, which has been imported mainly from Rhodesia and Swaziland. No workers in the factory were exposed exclusively to croddolite for any considerable part of their working life. It cannot be affirmed that any were not exposed to it at all, but the amount of exposure must have been relatively small. It is not possible to obtain a single evaluation of the total hazard to which the workers have been exposed by relating time of exposure to dust level in the working area. One man began to be exposed at the end of the nineteenth century and dust records are not available until 1951. The changes made since 1951 have resulted in a steady improve ment in working conditions, and the dust con centration has not been constant in any area. In 1933, ventilation systems were introduced in carding and weaving. In 1939, damping techniques were established in addition in the weaving process; the improvement was considerable and the con ditions of this process have remained reasonably constant from that time to the present day. In 1942, the dust settling chambers in the ventilation system were replaced by cotton fabric sleeve Alters. This immediately removed the need for the hazardous operation of cleaning out the chambers. The years immediately following the war saw many other changes. Damping was extended to yarn doubling, and in the period >953-57 the design of the card extraction system was improved. During this period, oiling of the fibre was introduced at the mixing stage to suppress dust during its subsequent processing.1 Before 195S, fibre had been blended on an open floor under dust exhaust hoods, but at this time an entirely new and totally enclosed system, covering the whole fiberszing process before carding, came into operation, and it became possible to add the optimum amount of oil necessary for dust suppression, which had not been possible on the old mixing floor. 'The oil used ii wtuic mineral textile oil (Beteoaus, Shell), tolvcnt refined with low aromatic content; viscosity (Redwood) jo-to see. at 70'F , ipedfie gravity 0 ISj st *o'F. Various methods of dust sampling were used at irregular intervals until 1951 when routine dust sampling in the principal parts of the factory was introduced. The Casella Thermal Precipitator instrument was used and the samples were incinerated before being counted at a magnification of 1,000; ail visible particles were counted. This system was in use until i960, and was invaluable in assisting the engineers in the many improvements then being made. Unfortunately, while panicles were included down to the limit of visibility (01 micron), the instrument was not efficient in capturing the large fibres (above to microns long), and these fibres were not generally seen in the dust deposited on the counting slides. The Long Running Thermal Precipitator, which collected the sample by a combination of settlement and thermal precipitation, was therefore adopted. Counting was done without incineration at a magnification of - 500 and only those fibres were counted which were between 5 and too microns long and whose length wes at least three times the diameter. Correlation between the two sets of results proved difficult because the new fibre count was in a sector of the dust spectrum only partly included by the old sampling method. A subsequent change in 196$ from the Long Running Thermal Precipitator to cellulose membrane sampling did not introduce any further complication, as the results, when the new method was properly established, were directly comparable with those obtained previously. Table I shows average dust levels in parts of the factory where different processes were carried out at the beginning (1951) end the end (i960) of the Casella Thermal Precipitator period, at the begin ning of the Long Running Thermal Precipitator period, and with the cellulose membrane fibre counters at the end of the period under observation. There were considerable deviations from the mean figures from time to time, a typical figure for the coefficient of variation in the 1966 data being 40".,. The location of the process itself was in some cases changed during the period under review, and sampling points have also changed over the years. It should be noted that sampling, in the past, was geared to the engineering work in progress and not specifically directed towards an assessment of the biological hazard. The fibre count figures in the Table have been rounded off to the nearest fibre per c.c. These show that considerable improvements were made in the period 1952 to i960, during which time the factory was modernized. Since then conditions have remained fairly steady, although work on dust control has continued. In particular, engineering GAF 296 J. F. Knox, S. Holmes, R. 1X0, and 1. D. Hill TABLE I Doit Ljviu taeotanmsn Dmnni Turns Ptoaun, 1953-1964 Drpmtmmt Fibcnxint............................................... Coding .. ......................... Spinning............................................... Warns Platting............................................... Mixing floor Opining Bog timing Midmnicol hogging Fiat cord* Medina ardo Coanc cards EIocbmoI oBitr ovdo Fine tynnnmg ILmof fnmt latnntdkt* front* Baaing Fin winding Qod waring lifting waring Ploumg Yttriy Afan Dtat Ltoth CtuUm Tktrmmi Fttdpiwa CpmtieU* ptr tx.) Lomg Rmmtg Tktimtl Prtdpittim <r CdUtJ** Mtmketm (Jikrtt per tx.) if}* JOO 440 ion Ito M40 490 170 510 J10 190 990 xflo *90 19*0 `t*i s*e* now 1 Kofiy ndo td no 5 tin 4 too 4 400 4>0 7 Ido 3 ISO 4 150 5 too 5 no S 190 9 *40 9 no l 4 4 9 9 3 9 $ 9 4 9 1 1 X40 to 4 4 ^"1" u die Electrical Sliver Cards and at RMtmtg have bed an appreciable effect in reducing fibre counts. Consistently low figures bave bees obtained at Weaving, and the levels at Listing Weaving bave been the lowest in the scheduled areas of the factory. number of person-years observed are shown in Table II, grouped according to tbe total duraboo of exposure, and durance of expoaurc before January t, 1933. Men in group 4 (10-19 years' exposure, none before 1933) were transferred to group 3 (20 or mot* years' exposure, none before 1933) when they Mortality repei Is tire The study has been confined to observelions on men and women who were employed in tbe scheduled areas. All men are included who were employed in these areas for more than 20 years at any time since the factory opened, and men and women who were employed foe more than so years are also included if they were first employed on or after January t, 1933. Altogether 17$ workers have been studied, and the observations extend over a 30-year period from 1916' to the end of June 1966. The numbers of men and women studied and the la DoU'i (1955) wady the period aI observation started ham teas. Fttnbcr ionttipiiaa has ata shown that ana bbsb oaatihul as years' employment in what warn tahaaquaatiy KhrdnUd trass io 191* TABLE U Noon oe Woaxsxs w Nmom o* Pmsen-mu r Kmt H Dimatm Exposes* Catsooam Dirosa nr Group Sa gtgonri m StkMtd Arm*(jrt) ftr*rim f fpiwr *9SS (yn) N*. tf Workm* 1 M to at man soaraor* 57 % M Man km than to *3 1 M lovnoR AOOC IS* 4 M IO-If now JJl 3 F xoormorr BOW 110 No. f yam* m Auk *IS 9X4 in *,jaa aj*l lndading tbe Ij4 naa la grasp 3 before they had washed for >0 ytan m tbs icbtdoled srsas. GAF 19565 Monahry from Lung Cancer and Othtr Count among Worktn m art Asbtsun Ttxnlt Factory 297 had completed 10 yean in the scheduled areas. The person-year** that they contributed while in group 4 remain with group 4, but at from the date oftransfer they stan contributing to group 3 instead. The person-years in Table II are. therefore additive! but the number of workers is not additive since all the 136 men of group 3 have passed through group 4, and are included in its total of 338 men. The personnel records of the company were used 10 decide who fulfilled the criteria for inclusion, and the Personnel Department carried out the subsequent follow-up. This was relatively simple for the men who had been reposed for so yean since they either continued working for the company, or were in receipt of a pension until their death. Follow-up of wotten who had been employed in the scheduled areas for less than so yean was more difficult as some had ceased being employed by the company and had not received a pension. All but one man and one woman, however, were successfully traced. Death entries could not be found for the untraccd employees at Somerset House, and for the purpose of the present analysis they have been assumed to be alive. For each of foe five groups a three-dimensional table of person-years at risk waa constructed, the dimensions being age of the subject, calendar year, and duration of rime since the subject entered the surrey, using a five-year grouping for ends scale. The numbers of person-years were then multiplied by the corresponding national death rates for various causes and the products summed to give the numbers of deaths expected for comparison with the numbers observed. The computer program for this purpose was written in Hill's (1968) `Man Years Computer Language' end the calculations were made on the London University Atlas, National death rates for selected causes for quinquennia up to 1936-60 were taken from Case and Pearson's (1937,1963) tables. Outside the range of these tablet, quin quennial death rates were compiled from the reports of the Registrar-General; 1961-63 rates were used to estimate the numbers of deaths expected in the first half of 1966. In previous studies the causes of death arete mostly obtained from post-mortem reports and the records of the medical department of the company. Death certificates were obtained only when the cause was in doubt or not known. In the present study death certificates have been obtained relating to all deaths but one (which occurred abroad), and the causes of death have been classified in two vrays: first, according to the cause given os the death certificate *g the method of ifirariim in use by the Registrar-General at the relevant period, and, secondly, according to the best information obtainable from all-sources. Table III shows the observed numbers of deaths classified according to the certified cause in com parison with those expected from national rates. As previously reported, the men who were exposed for 10 or more yean before 1933 (group 1) are shown to have had highly significant excess of deaths from lung cancer and also from disrates of the circulatory and respiratory systems. In three jnatanrrs cancer of the lung ana discovered pest morttm but was not mentioned on the death certificate; these deaths have not been attributed to lung cancer at it is not now possible to discover whether the information was reported to the Registrar General.1 The small excess of deaths due to other neoplasms is not statistically significant. It may be noted, however 'in view of the finding of an excess mortality from gastro-intestinal cancer in insulation workers who were regularly exposed to asbestos in the United States of America (Sdikoff, Chnrg, and Hammond, 1964)--that the five deaths were attributed respectively to cancer of the stomach (i), colon (), gall-bladder (1), and prottate (1). A ifn,6rit excess of deaths from lung cancer is recorded also among men who worked in the scheduled areas before 1933 but for less than to years (group 2). The ratio of observed to expected deaths (3-2:1) is, however, much smaller than for men who were exposed for 10 or more yean (to-2:i). In addition to the five men whose deaths were attributed to lung cancer, one other man, whose death eras certified as due to myo cardial degeneration, was found to have cancer of the lung port morttm} The number of deaths from diseases of the circulatory and respiratory systems (tl) is only slightly greater than the expected number (7-94); asbestosis was, however, mentioned on nearly half of the death certificates (3 out of ). Among men and women who have worked in the scheduled areas only since 1933 (groups 3,4, end 3) the observed mortality from all causes is dote to the expected (79 against St 03). The total observed experience is substantial, and the result provides grounds for believing that the occupational hazard has been largely eliminated. Four facts, however, `Thaw Oraihs wm attribute is hat ---- is prmoua rrpero (Dell, 1933; Km a ai., 1963; Hill 0 ml., 19M). *Dtath iniibutcd to hag esaear ta pHtiwa reports GAF 19566 98 J. F. Knox, S. Holmes, R. Doll, and 1. D. Hill TABLE HI N'omssxs or Dunn Oassavso and Extsctsd, ar Exrostmt Cimon and Causi Obi*TV*d No. *i Dtotks Ate. tf Cmm 0/ D*sir* 'J.C.D. cod* numbert) Cresp Atbettom m Deoik Cernftcote 4Canctr of hng or pteon (t a, xfj) Xt a3 41 l 0 30 Other neoplasms (140-139, except its and itj) I a ) 45 0 0 0 0 0 Disease of drculasory system (eoo-ett) 17 aa 4$ 0 1 34 47 5 7Discstt of mpimorr tjutm < ^ * ) AH other ouMi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AD cmuci ........................................................................ 1 a 3 4 5 1 a 43 3 1 a 43 j 11 ) 0 3 4 a 1 0 1 1 IS 41 3 X Atbettom not mentiomd 4 a 4 a *3 1 4 l 44 9 13 a 1 0 1 3 t 77e/ ta 3 4a a 3 3 1 41 *3 t 9 *4 a 314 t a i Deaths from Natiaml Rota ill 1-57 40*44m41 4a* i s>-533* 9*`7>13 3 33 4*03 xa-Se It* **37 sal `43 055 4a '4 3 aa 4aSs*394* 15 3511 ta 43 ala ao >4 4t 1147-4I7t >314 so-dt 49 34 4s-at 9 10 in Frobubiitty Observed No. or More <4-001 e-oaa 0-341 oit 0-0*5 904-M*54 9 907SS * tl 0934 0-003 oau o-oaa 0413 0*343 <o40o---40730s94419c 0-4*3 00-4S0317 44o- o 0*49 0-3*3 <0-001 00&4 o0-*i4s1o 0joa suggest that it is necessary to suspend judgement about the extent of the risk that may still remain. First, asbestosis was mentioned on the death certificate in seven instances. Secondly, the observations oo men who have worked in the scheduled areas for more than ao yean (group 3) arc few, and previous experience has shown that the risk of lung ranter is relatively small until after ao yean' exposure. Thirdly, the ratio of all observed to expected deaths in men in group 3 (1-4:1) is the same as in men who were exposed before 1933, but for less than to yean (group a). Fourthly, two deaths from lung cancer occurred in women an unexpected observation in view of the rarity of the disease in women in the country as a whole (P - 0-033). One explanation of this last fimtiwy may be that women who work in factories smoke more than other women of the same ages, so that the national mortality rates provide an unsuitable standard for assessing the existence of a specific occupational haxard. One of the two women who died of lung cancer, hosvever, was a non-smoker. The only other notable finding is the excess of deaths from disrates of the circulatory system in men who had worked for ao years in the scheduled areas, but only since 1933 (9 deaths against 4 03 expected). None of the men were known to have had asbestosis and the group showed no correspond ing excess of deaths from respiratory disease. It seems probable, therefore, that this it a finding of no medical importance (P - 0 0x1, GAF 19567 Mortality from Lung Cancer and Other Comes among Workers m an Asbestos Textile Factory 299 one-oil test), but the possibility of a continuing hazard must be borne in mind. One of the difficulties in interpreting these results is that duration of employment before 1933 is closely correlated with the duration of observation and the individual worker's age, both of which may be related to the risk of developing disease. An analysis has, therefore, been made of the trends in mortality in rdarioc to each of these factors after standardizing for the other two. The analysis has been limited to men who were employed for ao or more years (groups 1, a, and 3) and the expected numbers of deaths have been calculated for each cell of the three-dimensional table formed by three exposure groups (more than 10 years before 1933, some exposure before 1933 but less than to years, and no exposure before 1933); six duration of observation groups (0-4 years to 05-09 years after completing ao years' exposure); and 10 five-year age groups (30-34 years to 75-79 years). The analysis has been made separately for three categories of death (hug cancer, ocher causes with asbestosis, and ocher causes without asbestosis), and for this purpose--since the comparisons are entirely within the series and not with national mortality data--we have classified death as being due to lung cancer whenever the rtiirsir was diagnosed at necropsy, irrespective of the diagnosis on the certificate. The total number of lung cancer deaths available for analysis is, therefore, 33. In these Tables, it will be noted, the 'expected' numbers are derived from the experience of the workers studied as a whole and bear no relation to the 'expected' numbers in Table III which are derived from national death rates. The results show: (I) a statistically significant reduction in mortality from lung cancer, and other diseases with asbestosis, with reduction in length of exposure before 3933 (Table IV); (3) a highly significant increase in mortality from lung cancer and other diseases without asbestosis with increase in age at exposure (Table V); and (3) no evidence of a change in mortality for any causes of death with the passage of time after completion of 20 years' work in the scheduled areas (Table VI). These results are, in large pan, those that would be expected if exposure to asbestos dust was responsible for a substantial proportico of Ac deaths from lung cancer and from othrt diseases with asbestosis but was unrelated to other diseases with out asbestosis. They confirm that there has been a significant rlerrysie in the occupational hazards since 1933. Two ocher findings call for comment. First, the trend in the mortality from lung cancer with age at exposure accords with some other data, but is contrary to the conchisioos that have been drawn from animal experiments (Doll, 1964). In pan it may be due to the inclusion of four or five cases due to other and noo-occuparional causes. Secondly, it is surprising to find that, after standard ization for age, neither the mortality from hmg cancer nor the mortality from other diseases with asbestosis increases with the passage of time after the completion of 30 years' work in the scheduled areas. It must be remembered, however, that exposure to asbestos dust has changed at irregular intervals throughout the whole period of observa tion and the crude classification of exposures into three groups according to the length of employment before 1933 cannot adequately allow for these changes. How this has biased the results TABLE IV DmuaimoN or Dunn sin Exrosuas won 19)3 Studasdisb roa Tims ssncs Comtutimo ao Yuas' EMnovauxt *mo Am Expouot Stfmt ttsilyni Ow 10 (group t) Up to 10 (group a) Non* (group j) AQ group* ...................... Tew of lifniftcaar* of tread .. ftuwiuui* ef Lm$Cmu* Dmtkt OtMfW Eiptatd <5 pti * *'4 a 47* *) 1) 00 i* * * 70 B X f OOI Diuribmnom Otktr Dmtkr muk A+utwnt OOwrvdd IT n je 5 07 0 * 55 a1 uo r* m j a 1 f - 0 003 Dumtuftoe of Otktr Dtstks mtkemt A+tttoat O+urMd Expttttd i 16 91 ia ia oi i) 11 ia 41 41 Ol r* 0 ja a 1. t - 0*47 GAF 19568 300 J. F. Knox, S. Hobntt, R.DoU, and I. D. Ha TABLE V DutxnenoM or Diaim with Asa Stahpaopotb sob Pnuoc or Exrocou amo Tub sdscs Comtutimo AO Yuas' EurLonanr Ar'tyn) AH afes 39-J4 JJ- 4*44 45-49 50-54 55-59 *o-* `J-* 70-54 75-59 ......................... Test of u^uficsace of tread .. Diantarimtf LmgCmntr Dtukt OAiwW Expend O 0*09 0 03d 0 4J a 4^0 5 5 79 4 ea 9 33 9 *'45 5 1-09 0 04 >9 2|-O0 1* - ts-ia a mi p <0-001 OMaM tf OOmDmUa with Adatoms Ohterved CxfcuO O 0-03 t or a 1*52 1 939 1 4 53 7 445 * id a a-70 a 0 oao aa 22-00 .- id a I P - O-SJ Dismkvam tf Other Deatht tettheta Adtestemt Ohutved Expected 0 0*01 0 0*26 0 1 *9o a 4 54 5 10 9-5* 9 ** 10 5*57 3 l 59 a 027 41 40*9 K* m JO 4S O | P <0*001 TABLE VI DsnmnoN or Diatw witm Tims ass CoMftsmro so Yus' Emtlotmiwt yin tfler CampUtiap jo Pars* Em$leymim 0-4 5-9 10-14 5-9 2CK24 25-29 AH periods ........................ Test of Mgnifcancs of tread .. Dumhmarncf LmgCmeer Death* Otmwed s*ntcuO 4 ISJ t j-oa 7 54J 1 j* 1 jsa a IU 23 23-00 s* - 0-97 a 1 P - 03a Oiftniwim Other Deetkt with Adettamt Observed Expected 4 47* 4 420 4 5<d 4 4* 3 jr a o-7J 22 22-00 0*20 a" 1 P - 044 Ditmkwdmef Other Deaths mtheta Athcttea* Observed Expected tj 12*01 *37 5 7-sa 4 444 % 44* l t 3* 4X 0-99 H - 0*77 0 1 P - 0 j# is doc dear, but it rmphasitrs tbe oecd for caution in interpreting the trends with age and duration of observation. Tjrpca of Long Tumour Details of the occupational histories of tbe 23 men who had been employed for 20 or more yean in tbe scheduled areas and who developed lung tumours arc given in Table VII, along with the pathological diagnoses. Twenty-oneof the cases were confirmed at necropsy and 22 by histological exami nation. All but one of the tumours were regarded as bronchial carcinomas, inditringuithahle bom the type of tumour that bat occurred commonly in the goteral population during the last 30 years. Tbe exception was diagnosed as `endothelioma of the pleura' in 1936. The expected number of lung GAF 19569 Mortality from Lung Cancer and Other Comet among Workers a an Asbestos Textile Factory 301 TABLE VII Occupational. and Pathological Data Rxlatdic to Mm Dttno wmr Lung Canoi: Mm Empioyid roa to Yiam cm Man Mocorporatinf data bon Table in Dofi'i (195s) paper. *Coapleted yean, as a rceah the ram of the total eapowua tad the dumann Iron laat eapoeure to death may be kaa than the duration bon fine eipoaure to death, even if the period of irpmiirt wm oabroken. GAF 19570 303 J. F. Knox, S. Hobtm, R. Doll, and I. D. HOI tumours is estimated to have been about four (Tabk III) or perhaps somewhat more as a high proportion of man who died with respiratory symptoms came to necropsy (see `mortality experi ence' page 396 and Doll, 1953)- The excess number of deaths from this cause is, therefore, about I9> of which one can be attributed to a pleural mesothe lioma and about It to bronchial carcinoma. Awareness of pleura] mesothelioma as a separate oncological entity has increased greatly in recent years, particularly since Vagner, Sleggs, and Matchand (1960) drew attention to its character istic association with exposure to crocidolite asbestos. The possibility must, therefore, be con sidered that some pleural mesotheliomas hare been nrisdassified as bronchial carrinomas. In our view this is unlikely to have occurred. In nearly every case the tumours classified as bronchial carcinomas were found to have their origin in the substance of the lung at necropsy and were readily identified by their microscopic appearances.1 Moreover, it may be noted that the distribution of cases of bronchial carcinoma and pleural meso thelioma is not dissimilar from that repotted by SeUkoff, Hammond, and Churg (1967) among members of the Intatnational Association of Heat and Frost Insulators and Asbestos Workers who had first been exposed to asbestos dust more than 30 years previously. In the study by SeUkoff and hit 'ladadiat tbs asa shewn in Tabk VII as dying rf raaooa 01 the hang aad piaws in 1957. colleagues, which covered the period 1963-67, 34 deaths were attributed to bronchial carcinoma against 1] expected and 3 were attributed to pleural mesothelioma out of a total at 94 deaths from all causes. Since 193;, when the first death from lung cancer in our series was reported, records have also been kept of all coroners' necropsies on men and women known to have been employed at the factory.' Review of these records revealed four other esses which have been accepted as mesothelioma of the pleura by Dr. J. C Vagner. Occupational histories and ocher data relating to the five men and women who developed mesothelioma arc summarized in Tsble VIII. Only one man among these had been employed in the scheduled ares for more than to years. Three died more than 40 yean after first exposure to asbestos and one of these had been employed in the factory less chan one year. From previous experience (DoU, 1935), it appean that the specific risk of bronchial carcinoma is relatively small with leu than 30 yean' exposure to that the contrast with pleural mesothelioma in these data is marked. Follow-up informstian has not bean obtained for all men and women who have ever been employed in the scheduled areas, so that it is not now possible to make any accurate estimates of mortality. It it known, however, that over 12,000* *Nmppuu an ssbsstes wattes an ordered by tbt tuiaoaJoraswMisnviiaAw|i `t`efw"v1sor rthoawnn.it, ia bis opinioa, t guisfkwi at so TABU VIII J 'Alio iadudtd ia Table VII. Aim employed fee 15 ymn ifi tbt rubber tkpeniarnr (19*9-44) tad ao ran ia the werebome (1944-44). 'Alao imjiioyid ia tbt wrebome, :9*^)0- GAF 19571 Mortality from Lung Conor and Other Causes among Workers m an Asbestos Textile Factory 303 workers were employed in the scheduled trees * some period between 1930 tad 195** RmtsMCB Asbestos Industry Rcfuletioos (tfjs). Atbesta luduirry Regulancms: Statutory Rules omd Orders, /pj/, .Vtf It40. H.M.S.O , Loodoo. - Baabfca, V- P <i9J9)* Dust control in the sibestoi textile industry. Amt. eceup. Hyf., t, 54*74- Cw, tL A. M., end Pearson, J. T. (1957)* Tobias for com parative composite cohort analysis. Cancer, la: Camter statistics jot Sufiomd omd Walts, rpor-tf: VP' 57-99* Ocacral Betistcr Oftce. Stadia m modi re/ omd popuiehem subfeas, No. ij. NM.S.O., Lmim --, and -- (1965). Petwnion to cables far rtunporeiivu eobort analyses. (Personal communication.) Doll, It 0955). Mortality from fen* cancer in asbestos workers. Brit. J. imdiutr. Mod., U, 1(44 ---- (1964). Fpwfrmiolofkal obicrviiioni on suscspirtiflity to cancer to man with special reference co age. Atm Uu. tm. Comer., an, ?4?-75* Gtaa, ). C (1996). Health haaards of sibartns: recent studies on its bsotafifal effects. Tromt. Soc. uceup. Mod., Ii 61-74 HiA, L D. (1966). Draft Myd Manual. To be published --, DoS, R-, and Xaox, J. F. (1966). Mortally among aihswm workers. Aoc. toy. Sot. Mod., 99 59-60. Hills, D. V. (1965). Economics of dust control Atm. N. YAcad. So., ip, 511-554* Kaos, J. F., Doll, It S., and HiO, I. D. (1965). Cohort analysis of changes in inodtacc of bronchial carcinoma in a textile asbestos fecrory. Ibid., ip, Meiktejolm, A. (1956). la: Industrial Modiam omd Hypiene. Edited by. Mercwctbtr, E. It A., rot 5, p. 117. Bunerworth, London. Mctcwcther, E. It A., sad Frier, C W. (1950). Report 00 Effects tf Asbestos Oust om the Lmet, omd Dust Supprtttiom m the Atbatot Industry. H.M.S.O., Loodoo. Hew York Academy of Sciences (1965). Biototifii effects of ibmoa. Aim. N.Y. Atad. So., tp 1-766. Report on Conferences hirwirn rnifihijois sod Inspectors (S931). Bsparv an Cetjeremett kttmeem Employers omd Imptcten cmrmMr Methods of Suppresses Duet in Asbestos Textile Factories. ILM.S.O., London SetihofT, I. J., Chun, j., oad Hammond, E. C (1964)* Asbestos rapoaurt and neoplasia. J. Amor. mod. Ass., Stt, 03-16. --Hammond, tL C, and Quirt, I* (1967)* Asbestos exposure, imokinf and neoplasia Paper read to the section on rtisresrt of the chest and preventive medians, America* Medical Association, Adamic Cky, June, 1967* Wafncr, J. C, Sk&p C A., and Mardund, P. (>960). Diffuse pleural mtsothriinms and nbrscos iipntms in the North Western Cape Province. Brit. J. tmdttstr. Mod., rr 160-171. i j GAF 19572