Document omkBOeQ1vb2pYx5KJg1xRee2X

FILE NAME: Electrical Insulation (ELEC) DATE: 1967 DOC#: ELEC015 DOCUMENT DESCRIPTION: Article from Scientific Journal Brit. J . industr. M ed., 1967, 24, 232. Investigation of a Minor Asbestos Hazard M. C. S. KENNEDY and R. ROUTLEDGE 1 7 From the Department of Respiratory Physiology, City General Hospital, Stoke--on~ 'TGlt and the Medical Department, English Electric Company Limited, Stafford Twelve men who had been exposed to a minor asbestos hazard have been examined clinically, radiologically, and physiologically, and an assessment of the airborne asbestos concentration has also been made. Ten men had worked in a transformer department lagging transformer windings with asbestos paste for between 15 and 37 years. Tw o of these men showed minor radiological and minor physiological changes suggestive of early asbestosis. Two insulation workers had been engaged in milling and sawing asbestos sheets for five and 23 years respectively; both men showed minor radiological and abnormal physiological changes. These two men had been exposed to higher airborne concentrations of the asbestos dust than the transformer men. It is impossible to be dogmatic concerning the aetiology of these pulmonary changes, and further follow-up studies are planned. However, the findings are presented in view of the recommendation by Gilson (1966) that more evidence is required concerning possible pulmonary changes in men exposed to low concentrations of asbestos. After the classical work of Mereweather and examination alone, and increasing emphasis is being Price (1930), which first described the fully placed on the ancillary aids of radiology and developed condition of asbestosis, a considerable respiratory function tests. amount of work has been done on this occupational The following investigation on a group of hazard. This original work led to an improvement individuals who had been exposed to small amounts in dust control in some parts of the asbestos of asbestos was, therefore, undertaken to assess industry but, in spite of this, the Chief Inspector of whether such exposure had caused radiological, Factories reported in 1964 that the number of cases physiological, or clinical changes. of asbestosis had steadily increased. The association between asbestos and bronchial Present Investigation carcinoma was statistically proved by Doll in 1955. Wagner, Sleggs, and Marchand (i960) first drew In a large factory in the midlands manufacturing attention to the association of mesothelial tumour heavy electrical equipment, asbestos was used in and exposure to asbestos. Many of the cases two departments. The asbestos used consisted of reported by Wagner et al. had had little exposure to chrysotile, which was obtained from either Canadian asbestos, and the retrospective study of Newhouse or Rhodesian mines. It was decided to investigate and Thompson (1965) suggested that exposure to fully the environment and to monitor the personnel concentrations o f asbestos dust of a very low order in these departments. was sufficient to cause malignant changes. These developments, as Gilson (1966) has pointed Processes out, have underlined the necessity for further knowledge of the early changes which occur on Insulation Department In this department hard- exposure to low concentrations of asbestos and for board, consisting of 40% asbestos and 60% resin, attempting to detect very early changes with was used for insulation purposes (Fig. 1). Although existing methods of investigation. Over the years local and general exhaust ventilation was provided the many reports reflect the changes which have when this hardboard was being cut, milled, and taken place in diagnostic methods. The condition shaped, dust containing asbestos was produced. of asbestosis is no longer diagnosed on clinical Transformer Department Reclaimed mill board Received for publication December 13, 1966. with 71 to 72% asbestos, china clay, and starch was 232 FILE NAME: Electrical Insulation (ELEC) DATE: 1967 DOC#: ELEC015 DOCUMENT DESCRIPTION: Article from Scientific Journal of the NaSonal Utaiy of Medicine by a third party and may beprotecteS> U.S. CopyrigWla. Brit. J . industr. M ed., 1967, 24, 232. Investigation of a Minor Asbestos Hazard M. C. S. KENNEDY and R. ROUTLEDGE From the Department of Respiratory Physiology, City General Hospital, Stoke-on-Trent and the Medical Department, English Electric Company Limited, Stafford Twelve men who had been exposed to a minor asbestos hazard have been examined clinically, radiologically, and physiologically, and an assessment of the airborne asbestos concentration has also been ! made. Ten men had worked in a transformer department lagging transformer windings with asbestos paste for between 15 and 37 years. Two of these men showed minor radiological and minor physiological changes suggestive of early asbestosis. Two insulation workers had been engaged in milling and sawing asbestos sheets for five and 23 years respectively; both men showed minor radiological and abnormal physiological changes. These two men had been exposed to higher airborne concentrations of the asbestos dust than the transformer men. It is impossible to be dogmatic concerning the aetiology o f these pulmonary changes, and further follow-up studies are planned. However, the findings are presented in view o f the recommendation by Gilson (1966) that more evidence is required concerning possible pulmonary changes in men exposed to low concentrations of asbestos. After the classical work of Mereweather and examination alone, and increasing emphasis is being Price (1930), which first described the fully placed on the ancillary aids of radiology and developed condition of asbestosis, a considerable respiratory function tests. amount of work has been done on this occupational The following investigation on a group of hazard. This original work led to an improvement individuals who had been exposed to small amounts in dust control in some parts of the asbestos of asbestos was, therefore, undertaken to assess industry but, in spite of this, the Chief Inspector of whether such exposure had caused radiological, Factories reported in 1964 that the number of cases physiological, or clinical changes. of asbestosis had steadily increased. The association between asbestos and bronchial Present Investigation carcinoma was statistically proved by Doll in 1955. Wagner, Sleggs, and Marchand (1960) first drew In a large factory in the midlands manufacturing attention to the association of mesothelial tumour heavy electrical equipment, asbestos was used in and exposure to asbestos. Many of the cases two departments. The asbestos used consisted of reported by Wagner et al. had had little exposure to chrysotile, which was obtained from either Canadian asbestos, and the retrospective study of Newhouse or Rhodesian mines. It was decided to investigate and Thompson (1965) suggested that exposure to fully the environment and to monitor the personnel concentrations of asbestos dust of a very low order in these departments. was sufficient to cause malignant changes. These developments, as Gilson (1966) has pointed Processes out, have underlined the necessity for further knowledge of the early changes which occur on Insulation Department In this department hard- exposure to low concentrations of asbestos and for board, consisting of 40% asbestos and 60% resin, attempting to detect very early changes with was used for insulation purposes (Fig. 1). Although existing methods of investigation. Over the years local and general exhaust ventilation was provided the many reports reflect the changes which have when this hardboard was being cut, milled, and taken place in diagnostic methods. The condition shaped, dust containing asbestos was produced. of asbestosis is no longer diagnosed on clinical Transformer Department Reclaimed mill board Received for publication. December 13, 1966. with 71 to 72% asbestos, china clay, and starch was 232 co oOJ xCD: 8:: -0O3 q . CCVOS sC0D3 CO Q03- 0 1To CT3 E03 t- FILE NAME: Electrical Insulation (ELEC) DATE: 1967 DOC#: ELEC015 DOCUMENT DESCRIPTION: Article from Scientific Journal copied from the collection of the NationaLfo-ary of Medicine by a third patty and may be protected by U.S. Copyright law B rit. J . industr. M ed ., 1967, 24, 232, Investigation of a Minor Asbestos Hazard M. C. S. KENNEDY and R. ROUTLEDGE From the Department of Respiratory Physiology, City General Hospital, Stoke-on-Trent and the Medical Department, English Electric Company Limited, Stafford Twelve men who had been exposed to a minor asbestos hazard have been examined clinically, radiologically, and physiologically, and an assessment of the airborne asbestos concentration has also been made. Ten men had worked in a transformer department lagging transformer windings with asbestos paste for between 15 and 37 years. Tw o of these men showed minor radiological and minor physiological changes suggestive of early asbestosis. Two insulation workers had been engaged in milling and sawing asbestos sheets for five and 23 years respectively; both men showed minor radiological and abnormal physiological changes. These two men had been exposed to higher airborne concentrations of the asbestos dust than the transformer men. It is impossible to be dogmatic concerning the aetiology of these pulmonary changes, and further follow-up studies are planned. However, the findings are presented in view o f the recommendation by Gilson (1966) that more evidence is required concerning possible pulmonary changes in men exposed to low concentrations of asbestos. After the classical work of Mereweather and examination alone, and increasing emphasis is being Price (1930), which first described the fully placed on the ancillary aids of radiology and developed condition of asbestosis, a considerable respiratory function tests. amount of work has been done on this occupational The following investigation on a group of hazard. This original work led to an improvement individuals who had been exposed to small amounts in dust control in some parts of the asbestos o f asbestos was, therefore, undertaken to assess industry but, in spite of this, the Chief Inspector of whether such exposure had caused radiological, Factories reported in 1964 that the number of cases physiological, or clinical changes. of asbestosis had steadily increased. The association between asbestos and bronchial Present Investigation carcinoma was statistically proved by Doll in 1955. Wagner, Sleggs, and Marchand (i960) first drew In a large factory in the midlands manufacturing attention to the association of mesothelial tumour heavy electrical equipment, asbestos was used in and exposure to asbestos. Many of the cases two departments. The asbestos used consisted of 5 arespbeosrttoesd, bayndWtahgenerretertoaspl.ehctaidvehsatdulditytloefeNxpeowshuoreustoe ochr rRyshootdilees,iwanhimchinweas.s oIbttawinaesddfercoimdeeditthoerinCvaenstaidgiaatne CCOD and Thompson (1965) suggested that exposure to concentrations of asbestos dust of a very low order fully the environment and to monitor the personnel in these departments. 0CC3DO CL was sufficient to cause malignant changes. CO These developments, as Gilson (1966) has pointed Processes 76 out, have underlined the necessity for further O knowledge of the early changes which occur on Insulation Department In this department hard- exposure to low concentrations of asbestos and for board, consisting of 40% asbestos and 60% resin, 02 ca attempting to detect very early changes with was used for insulation purposes (Fig. 1). Although E existing methods of investigation. Over the years local and general exhaust ventilation was provided 05 the many reports reflect the changes which have when this hardboard was being cut, milled, and taken place in diagnostic methods. The condition shaped, dust containing asbestos was produced. of asbestosis is no longer diagnosed on clinical Transformer Department Reclaimed mill board Received for publication December 13, 1966. with 71 to 72% asbestos, china clay, and starch was 232 Fig. i . An operative drilling hardboard (insulation department). 234 M . C . S . Kennedy and R . Routledge The tentative maximum allowable concentration of asbestos in air, using the hexhlet method of estimation, is 100 ftg./m3. (King 1966). Transformer Department Apart from the initial transfer of asbestos from the bag to the bucket by hand, the mixing was apparently dust-free and a thermal precipitator sample taken during the transfer showed less than 1 fibre per ml. of air. It is possible that the concentration of asbestos in the air is greater w h e n t h e d r i e d m i x i s removed by a wire brush from the welded copper bars, but this operation was not seen on the day of the visit. A second thermal precipitator sample was taken while the asbestos mix was used to protect the transformer components during welding, and this also showed less than 1 fibre per ml. of air. Both thermal precipitator samples were taken in the breathing zone of the workmen and both were below any currently accepted maximum concentration. F ig . p3r.o teActneodpweriathtivaesbwesetlodsinpga.stTe h(teratrnasnfosfromrmeredrewpainrtdminegnst)a.re mixed with water to form a thick paste which was used to protect transformer windings when welding operations were carried out on the terminals (Figs. 2 and 3). The heat dried the paste and some asbestos dust was produced locally which could be inhaled by the operative. Exposure to the dust also occurred when the dry asbestos was transferred from the bag to the bucket by hand for mixing and when the dried mix was removed from the welded copper bars with a wire brush. Dust Sampling Since the dust hazards in the insulation and transformer departments were obviously very different, the dust sampling procedures were modified accordingly and are given below. Insulation Department Two hexhlet samples were taken in the department. They were not breathing zone samples but were representative of the conditions in the immediate working area of the men. The first sample, taken over a period of two and a half hours, when the operatives were mainly engaged in sawing and fifing `ebony', gave less than 47 /rg./m3. asbestos. The second sample was taken over a period of three hours and during this time the operatives were sawing and drilling bakelized asbestos (one and a half hours) and also working epoxy glass on the router (one and a half hours). This three-hour sample yielded 57 /xg./m.3 asbestos. Investigation of Men Exposed to Asbestos Methods T h e 10 transformer fitters and the two insulation workers were examined in detail, and the following points were covered: occupational history; symptomatology; clinical examination; radiology and sputum examination; and physio logical investigations. T h e physiological investigations included simple spirometry. The total lung capacity and its subdivisions and the helium dilution time were measured by closed spirometry, and the assessment of the transfer factor at rest and on exercise by using the steady-state carbon monoxide uptake method. The ventilatory cost of exercise was assessed using the Hugh-Jones and Lambert (1952) technique at a work level o f 300 kg.m./minute. The chest radiographs were read independently and finally jointly. Relevant Findings The relevant clinical, radiological, and physiological findings are listed in Tables I and II. Transformer Fitters The 10 transformer fitters had worked with the process described above for periods ranging from 15 to 37 years; their ages ranged from 36 to 54 years. None of them had a history of untoward chest symptoms but two men had minor symptoms o f exertional dyspnoea. There was no evidence of clubbing of the fingers. Radiologically four of the 10 men were classified as having normal chest radiographs and five of them had minor basal changes which for the most part consisted of a few scattered pinhead opacities, usually at the right base. One man (no. 6) had three Investigation o f a M inor Asbestos H azard 235 TABLE I C linical and X -ray F indings Subject Age Height Weight Years in (yn) (in.) (ib.) Work1 Smoking (cigs/day) Chest Symptoms Diaphragm Movement (mm.) X-ray Results Remarks Transformer Work *rs I 54 70 260 2 3 3369 66 161 67 193 4 42 71 194 5 38 72 233 6 45 68 193 7 38 66 137 8 46 68 158 9 44 73 232 10 43 68 174 Insulation Workers 11 21 68 140 12 47 69 170 R. L. 37 <20 Cough a.m. 60 70 Abnormal mediastinal and heart shadow ; hilar shadows -f- 15 16 Occasional pipe Nil 0 M ild exertional 40 32 40 45 Normal ? old basal left pleurisy dyspnoea (grade 2/3) 28 40 up to 5 yrs N il 20 17 A few pinhead opacities ago now 0 right base 16 > 20 Cough a.m. 52 55 Slight cardiac enlargement; basal changes 28 < 20 up to i yr M ild exertional 40 38 Left ventricle enlarged; 3 ago now 0 dyspnoea small opacities left upper (grade 2/3) zone and left mid-zone; some small bilateral basal pinhead opacities 24 0 Nil 36 35 A few scattered basal pin- head opacities 30 0 Nil 29 20 Nil 36 52 60 62 Normal Normal 20 0 Nil 37 39 Normal 5 <20 M ild exertional 16 34 Normal dyspnoea (grade 2/3) 23 6 M ild exertional 5 5 Pinhead opacities left base; dyspnoea distorted lung pattern right (grade 2/3) base; bilateral tilling costo- phrenic angles ^None of the 12 men had worked in other dusty processes likely to cause lung changes. small opacities in the left upper zone and left mid-zone, which could possibly have been pleural plaques (Fig. 4). Three men (nos. 1, 5, and 6) had a slight abnormality of either the mediastinum or heart shadow. No asbestos bodies were found on examination of the sputa. The physiological findings are listed in Table II together with the predicted normal value for each physiological index based on the age and height of the individual. With the wide scatter which occurs in normal individuals about the predicted normal values, we have arbitrarily decided that the various parameters are normal if they fall within 20% of the predicted normal1. The ventilatory cost of exercise has been judged to be abnormal if either 1T h e predicted normal values were estimated using the T a b les published by Cotes (1965). the exercise ventilation ventilation (S.V.) was (E.V.) more 1 or the standardized than 35 ./minute. The transfer factor was considered to be abnormal if at rest the uptake of carbon monoxide was less than 15 ml./min./mm.Hg. The transfer factor on exercise was considered to be abnormal if the values were less than 25 ml./min./mm.Hg. In all the 10 transformer workers, the lung volume studies were within 20% of normal with the exception of the inspiratory capacity, which was abnormally small in four men (nos. 2, 3, 4, and 5). The bellows function was abnormal in only two of the 10 men (nos. 3 and 5). The transfer factor, both at rest and on exercise, was subnormal in two men (nos. 3 and 8). Two further men, whose transfer factor at rest had been normal, had a subnormal transfer factor on exercise (nos. 1 and 5). 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M tO VO O0J0 "t4o to to to N) OJ OV VO CA -- --- 4 KJ IP , _____ i-------------- g -- ^ jonal Library of Medicine by a Tiri part, a n i ma, be p r o The materiel on M s page was copied from the collection of the National by U S Copyright Investigation o f a Minor Asbestos Hazard msfer Facto 'm in ./m m .h Exerc\ C30D5 CD O=3 C/i "O ' 355 C0CO5D $ 05c/> o o CqDg. o3 28 ECDr o 25 o=3 29 CD Z -- g . : 36 o' . 5> i * cr 22-5 05 ^; o CD. ! 27 Q. ; O* ! 05 38 .3.1-7 T3 ^ i- 305Z3 - ' 05; - Q - ----- - 22 : OCD* T3 O?D : CL . er *<! F ig. 4. Postero-anterior film o f a man aged 45 (No. 6, Tables I and II) showing three small shadows in the left upper zone which are probably pleural plaques. 3 5 in excess of normal in live of the 10 men (nos. 1, , 4, , and 9). Insulation Workers In general, the two insulation workers showed far more abnormality than the transformer fitters. One of the insulation workers aged 21 years (no. i i )j who had worked for only five years in the insulation process, had a normal radiograph but showed the greatest physiological change of any of the men investigated. He had abnormal lung volume, viz., a raised residual volume, an increased R .V./T.L.C. ratio, and a greatly decreased inspir atory capacity (51% less than normal). His ventilatory capacity or bellows function, as measured both indirectly and directly, was between 25% and 40% below the predicted normal. His transfer factor, as measured at rest, was within normal limits but did not increase normally on exercise. His ventilatory cost of exercise was within normal limits. The other insulation worker aged 47 years (no. 12), who had worked for 23 years in the process, had radiological evidence of pinhead opacities at the left base and a distorted lung pattern suggestive of destructive emphysema at the right base. He also had bilateral filling of the costophrenic angle. As regards the physiological tests, the residual volume and the R .V./T.L.C. ratio were over 20% more than the predicted normal values. The bellows function or ventilatory capacity, as measured either indirectly or directly, was reduced but was within 20% o f the predicted normal value. The transfer factor at rest and on exercise was low and the ventilatory cost of exercise was slightly raised. Discussion Williams and Hugh-Jones (1960b) have investi gated, in detail, advanced cases of asbestosis and in their study they found that the following parameters o f lung function were frequently disordered: 1. standardized ventilation (S.V.) was increased when performing the standardized Hugh-Jones exercise tolerance test; 2. the maximum breathing capacity was usually reduced; 3. the most striking change in the lung volume studies was the reduction in the inspiratory capacity; 238 M . C . S . Kennedy and R . Routledge 4. the diffusing capacity was reduced in all their cases except two. In their investigation these authors found that the changes in the ventilatory capacity often bore no relation to the changes in the diffusing capacity. Furthermore, they found considerable observer variability in grading asbestosis radiologically, and often the radiological findings bore no relation to the physiological changes. Thus, since both the radiological and physiological findings can vary so much in men exposed to a severe asbestos hazard, it is very difficult to be dogmatic about the findings in our investigation where the men were exposed to only a minor asbestos hazard. Bearing this in mind, we would make the following observations about the xo transformer workers and the two insulation workers. The io Transformer Workers In general, one can say that five of the 10 transformer workers show very minor basal changes radiologically which would often be recorded as normal changes at routine screening sessions. The transfer factor findings are a little difficult to assess in view of the low level of exercise the employees were asked to do. However, most of the transfer factor results at rest are within normal limits though below normal on exercise in four men (nos. i, 3, 5, and 8). When the diffusing capacity or transfer factor is defective on exercise, one expects this abnormality to be associated with an increased ventilatory cost for standardized exercise. This occurred in three of these men (nos. 1, 3, and 5). Two of the four men (nos. 3 and 5) with a reduced transfer factor on exercise and an increased ventilatory cost of exercise also had a reduced inspiratory capacity and an appreciable reduction in the indirect maximum breathing capacity. It is interesting that these two employees show minor basal radiological changes and are among those with the shortest exposure to asbestos dust. In short, we consider that two of the 10 trans former workers show minor radiological and som physiological changes suggestive of early asbestosis One man was a non-smoker, the other a heav cigarette smoker (> 20 cigarettes/day). The Two Insulation Workers Both th insulation workers show a great increase in thR .V./T.L.C. ratio and a considerable reduction : their ventilatory capacity. One of these two men (no. xi) has the lowest transfer factor o f the whole group, the highest R .Y ./T .L .C . ratio, the greatest impairment of inspiratory capacity and maximum breathing capacity, and has been `at risk' for the shortest time. Although this man had a normal chest radiograph, the physiological findings showed definite evidence of impaired pulmonary function. It is probable that the inhalation of asbestos dust has been the cause o f some at least o f the abnormal findings in these two insulation workers. Those patients showing abnormal pulmonary function studies are listed in Table III. From this Table it can be seen that there is abnormality of four or more parameters o f lung function in four patients only, viz., nos. 3, 5, 11, and 12. A ll these patients showed the following features: an abnorm ally low carbon monoxide uptake on exercise, a decrease in the inspiratory capacity, and a decrease in the Indirect M .B.C. Three of these four patients showed an increase in the ventilatory cost of exercise, and three of them showed an increase in both the residual volume and in the R.V./T.L.C. ratio. In general, the index of pulmonary function most deranged in these men was the inspiratory capacity (Table II). Leathart (i960), in his study of 10 cases of asbestosis and 11 radiologically normal asbestos workers, found that a low vital capacity accompanies fibrosis o f the lungs in asbestos workers and TABLE III Asbestos W orkers with Abnormal P ulmonary F unction Test D l at rest 15 ml./min./mm.Hg or less D l on exercise 25 ml./min./mm.Hg or less Inspiratory capacity reduced Maximum breathing capacity reduced E.V. and S.V. raised (35 I./min. or over) R.V. raised and increased R .V ./T .L .C . ratio I 33 5 6 (I) 2 33 4 55 I 3 4 (55) in dividual showing the greatest abnormality. Values between xo and 20% abnormal were obtained for subjects given in parentheses. 8 9 8 9 II II 11 12 II II 11 ((1122)) II1 (12) 12 Fthe 10 transical and some arly asbestosis, 1er a heavy zfr y 2 Both the w3, iase in the eduction in ~ e two men = Fthe whole |T he greatest -o maximum (S sk' for the g l a normal g> igs showed "05. y function. iestos dust S . ? abnormal 33 !, j!i) j pulmonary 2. From this g rmality of o an in four o All these ~ 1 abnormixercise, a gF a decrease o ' ir patients if exercise, Co-. i both the 3 !atio. 2 function ispiratory $ ~C3D ; cases of asbestos ry pmpames and Investigation o f a Minor Asbestos Hazard 239 suggested that the vital capacity of all exposed workers should be measured at regular intervals and that a progressive decline should be taken as a warning of impending disease. In our series the vital capacity was, in all cases, within 20% of the predicted normal whereas there were five men who had a marked reduction in the inspiratory capacity. Thus, if the changes we have observed are the result of the inhalation of asbestos dust, it is probable that a reduction in the inspiratory capacity may be a more sensitive and earlier index of change than the vital capacity. T he findings of Williams and Hugh-Jones (1960a and b) and those of Thomson, Pelzer, and Smither (1965) support this view. Our observation that the total lung capacity was not decreased in any o f the men examined indicates that lung fibrosis, if present, was not extensive. I f lung fibrosis was present one would assume that there would be some degree of associated emphy sematous change, in view of the finding that the R.V. as well as the R .V ./T.L.C. ratio was sub stantially increased in three of the four men showing the greatest derangement of pulmonary function. We feel that probably there is no point in dis cussing these results further at this stage until follow-up investigations have been carried out on this group of men. However, the results so far agree with the observations o f Williams and Hugh-Jones that the finding of lung changes specific for an interstitial fibrosis in patients with an exposure to asbestos is suggestive evidence of asbestosis, whatever the radiological appearances. Clearly, the minor asbestos hazard to which the men were exposed was only intermittent and occasional in the case of the transformer workers. In the case of the two insulation workers, the exposure was greater and more frequent. However, we think it has been useful to assess this minor hazard fully before it has had time to produce severe biological changes. The hazard has now been reduced in both depart ments. In the transformer department mica paper scrap has been substituted for asbestos, and in the insulation department the ventilation has been redesigned and greatly improved. This investigation was initiated by Dr. George Ritchie, H. M. Medical Inspector of Factories, and we wish to record our gratitude for his continued help and collaboration. We also wish to thank Dr. T. A. Lloyd Davies, Senior Medical Inspector of Factories, for his encouragement and advice in this investigation, Mr. E. King and Mr. M. K. Molyneux for their assessment of the dust hazard, Dr. B. Herzenshorn for his help in the radio logical assessment, Dr. E. Peters for the industrial and clinical histories of the men examined, Mr. P. G. Wilkes and Mrs. J. Arnold for their skilled physiological assessments, and Mrs. J. Beardmore for her help in compiling this joint communication. R eferences Cotes, J. E. (1965). Lung Function: Assessment and Applica tion in Medicine. Blackwells Scientific Publications, Oxford. Doll, R. (1955). Brit. J. industr. Med., 12, Sx. Gilson, J. C. (1966). Trans. Soc. occup. Med., 16, 62. 65 Hugh-Jones, P., and Lambert, A . V. (1952). Brit. med. J ., I, - King, E. (1966). Personal communication. Leathart, G . L . (i960). Brit. J. industr. Med., 17, 213. Mereweather, E. R. A ., and Price, C. W. (1930). Report on the Effects of Asbestos Dust on the Lungs, and Dust Suppression in the Asbestos Industry. H .M .S.O ., London. Newhouse, M . L ., and Thomson, H. (1965). B rit.J. industr. Med., 22, 261. Thomson, M . L . Pelzer, A. M ., and Smither, W . J. (1965). Biological Effects of Asbestos. Ann. N .Y. Acad. Sci., 132, 421. Williams, R., and Hugh-Jones, P. (1960a). Thorax, 15, 103. ------, ------(1960b). Ibid., 15, 109. Wagner, J. C. Sleggs, C. A ., and Marchand, P. (i960). Brit. J. industr. Med., 17, 260. Annual Report ofH .M . Chief Inspector of Factories on Industrial Health, 1964. [Cmnd 2723]. H .M .S.O ., London.