Document ZJD4ObYGLx66V02MyzjK97m1O

FILE NAME: Asbestos Cement Pipe and Sheet (ACPS) DATE: 1993 DOC#: ACPS036 DOCUMENT DESCRIPTION: Journal Article - Japan Journal of Industrial Health Originally published in Japanese in the Japan Journal of Industrial Health, 35 (1993), p. 178-87 ESTIMATION OF ASBESTOS EXPOSURE AMONG WORKERS REPAIRING ASBESTOS CEMENT PIPES USED FOR CONDUITS Sfatnji KUMAGAI,*1 Shigeharu Na KACHI,*2 Norio KURUMATANI,*2 Shingo NAKAGIR1*4 and Akihiko KATAOKA*5 A sbestos cem ent pipes (ACPs) containing 15 to 20% chrysotile or crocidolite have been used for underground conduits. Even today 16.2% of all conduits in Ja p a n are ACPs, though the production of ACPs w as suspended in 1985. W hen such a conduit is accidentally damaged the workers belonging to the W aterworks B ureau of a local governm ent cu t off the dam aged conduit using a high-speed disk cutter and replace it with a new conduit. This operation develops a cloud of d u st and the workers involved ru n the risk of asbestos exposure. It was the aim of the present study to estim ate asbestos exposure levels am ong these workers. First, in the experiment, we established the typical working conditions and requested an experienced w orker to cu t a n ACP u sin g a high-speed disc cu tter in a hole dug in the ground as he routinely does. The experiment was repeated three times. During a bout of each experiment, dust was sam pled at several points both inside and outside the hole. Second, a self-administered questionnaire survey was conducted to obtain inform ation from the workers regarding their working conditions in cutting ACPs. The subjects of the survey were 1,048 m en belonging to conduit repair sections of the Waterworks B ureau of 119 local governments. The results obtained can be sum m arized a s follows. 1) E ach b o u t of cutting ACPs required ab o u t five m inutes. The concentration of asbestos fibers longer th a n 5 /E m w ith 3: 1 aspect ratio ranged from 48 to 170 fibers/m l (92 fibers/m l on an average) inside an d 1.7 to 15 fibers/m l outside the hole. The concentration inside the hole exceeded the ceiling limit (10 fibers/m l) recom m ended for asbestos by the Japanese Association of Industrial Health. A concentration of 92 fibers/m l is equivalent to 0.96 fibers/m l as 8-h time-weighted average. 2) The n u m b er of subjects with experience of cutting ACPs w as 849 (81.0%). The average length of service in conduit repair section was 14.2 yr. Based on the information obtained from each subject regarding the average working days per yr for each decade from 1946, the cum ulative days to date expended in cutting ACPs was estim ated to average 235d, th at is, 17d per yr. Only 18.1% of the subjects used a protective respiratory device. 3) O n the assu m p tio n th a t these w orkers worked 17 d per yr in cutting ACPs for 14 yr and were exposed to 1 fiber/m l of asbestos per d, the life-time excess mortality rate of lung cancer would be 30 per 100,000 and th a t of m esotheliom a 30 per 100,000 by OSHA's model, and th a t of lung can cer would be 15 a n d th a t of m esotheliom a 28 by H ughes' model. These results suggested th at workers belonging to the Waterworks Bureau have a possibility of being exposed to relatively high levels of asbestos w hen cutting ACPs and have a risk of developing asbestos-related diseases. Key words: asbestos cem ent pipe; asbestos exposure; worker; W aterworks B ureau; life-time excess mortality; lung cancer; mesothelioma n Department of Occupational H ealth, Osaka Prefecturai Institute of Public Health. 42 N anrokai Matsuura Clinic 43 Department of Public Health, Nara M edical U niversity M Occupational Health and Safety Unit, A ll Japan Prefecturai and Municipal Workers' Union *5 Kansai Occupational H ealth and Safety Center Received for publication, July 8, 1992 Kumagai et al., Asbestos Exposure Accompanying Repair of Asbestos Cement Conduit I. Introduction The total volume of water supplied annually by Japanese waterworks is about 16.2 billion tons (1989). 1 W ater from lakes, dam s or rivers, or groundwater, is collected, purified, sterilized, and conveyed to end users by cast iron, asbestos cement, polyvinyl chloride (PVC) or pipes of other m aterial. The total length of the n a tio n 's water pipes is 438,000km , of which asbestos cem ent pipe ("ACP") or conduit accounts for 16.2% (1989). 1 AC pipe is m ade by (1) mixing asbestos (chrysotile or crocidolite) into cem ent and silica so as to am ount to 15-20% of the total volume, and combining same with water, (2) spreading the resulting m ixture into sheet form and wrapping it in layers around a m etal core so as to form a pipe, (3) removing the m etal core and curing the pipe in an autoclave (at about 180, 10 k g /c m 2), drying it, a n d (4) cutting the pipe into predeterm ined lengths.2 The reason for mixing asbestos into the cement is th at cement alone cannot withstand the pressure of the water or the force im parted by vehicles passing over the pipe. It is known th at breathing in asbestos causes lung cancer, chronic disease of the lining of the lungs (malignant m esotheliom a), and asbestosis.3'4 E b ihara5 h a s reported on malignant mesothelioma of a worker who had been employed in the production of ACP for 23 years. There are two problem s associated w ith the u se of ACP for w ater supply. One is the possibility th at after prolonged use particles of asbestos may separate from the pipe and be mixed in the water. Saito et al.6 have studied the concentration of asbestos in drinking water; whereas no asbestos was found in w ater conveyed in PVC w ater pipe, they reported th at crocidolite was found in the drinking w ater of regions w here ACP was in use. The second problem is th at w hen an ACP is broken, waterworks teams or others undertake repairs and are liable to breathe in asbestos fiber dust, as high-speed disc cutters are used to cut the pipe. ACP h a s been u se d for conveyance of water in Jap an since about 1932, but its use increased swiftly after about 1951, after which the combination of heavy vehicular traffic and aging of the pipe resulted in frequent ruptures, and su b seq u e n t replacem ent of ACP by pipe made of other, stronger materials, such as cast iron or ductile iron. Consequently, production of ACP after peaking at 3,340,000 pipes in 1965 (these pipes were 3 to 5m long), declined and production ceased in 1985 (information as per a personal communication regarding th e inspection d a ta of ACP for use by Jap an W ater Works Association members, and total length). The Ministry of Health and Welfare created a system for subsidizing the replacem ent of ACP with ductile iron pipe and complete elim ination of ACP is expected by 10 years in the future.8 However, the appearance of symptoms of lung cancer and m alignant mesothelioma caused by asbestos exposure takes place after a laten t period of, commonly, 20-40 years,4 for which reason there is worry over the influence of exposure on the health of workers who installed or repaired ACP. It w as thought th a t this m ade it necessary to investigate the actual conditions of exposure to asbestos fibers w hen ACP is being cut, b u t a literature search failed to identify any prior studies. Because of this it was decided to m easure the concentration of asbestos fibers released during sim ulation of the cutting of ACP in order to ascertain the extent th at workers can be said to have been exposed to asbestos fibers as a result of cutting pipe. This report includes, in addition, the results of a questionnaire survey of waterworks employees, done in order to learn of the existing conditions at the time of cutting ACP. II. M ethodology 1. M easurement of Asbestos C oncentration When ACP is Cut To reproduce conditions of the cutting of ACP, a tren ch 1.2m deep w as dug in a 1.5m2 field within the grounds of a w aterw orks, a base (10 cm high) for the pipe was installed, and ACP 2 Japan Journal of Industrial Health, 35 (1993). (diameter, 100 and 150mm) was placed on th at base, after which a skilled waterworks employee, wearing a face mask, used a high-speed disc cutter (made by the Meiho Co., dry cutter MDC-300E) to cut the pipe. Normal repair work calls for cutting the existing pipe on both sides of a rupture, after w hich a new ACP would be cu t to the required length, inserted, and bonded to the existing pipe. In the present field experiment, since the only work done was to cut pipe, m easurem ent of asbestos fiber was done while the pipe was cut two times (total, about 5 m in u tes). A holder (Analytics) provided with a m em brane filter (diameter 25mm, pore size, 0.8pm) for sam pling the asbestos w as affixed to the w orker's collar (Fig. 1, No. 1), and a portable suction pum p (by S h ib ata Kagaku Kikai, MP-2N) was used to collect asbestos d u st a t 1.0 liters/m in. At the same time m easurem ents were made at one point within the trench (about lm from the worker, at a height of 0 . 8m; Fig. 1, No. 2) a n d outside the tre n c h (at a distance of ab o u t 0.5m; Fig. 1, Nos. 3 a n d 4). For th is latter sam pling work, m em brane filters (Toyo Filter Paper Co., diam eter 47m m, pore size 0.8pm) were placed in holders and the suction pum ps (No. 2: Y uasa Shokai AL-410); Nos. 3 and 4: Y uasa Shokai, D-50P), asbestos dust was collected at 1.0 lite rs/m in a t Nos. 2 an d a t 10 lite rs/m in u te a t Nos. 3 and 4. $ h <kMc>,o vict to*seciiotul vier He.! F ig.l. An illustration of the experimental setting for cutting an. asbestos cement pipe set in a hole in the ground; a bird's-eye view and a cross-sectional view. No. 1 to No. 4 represent the sampling sites for asbestos. No. 1 and No. 2 are inside and No. 3 and No. 4 are outside the hole. The sampling was done using both dry pipe (diameter 150mm) and moist pipe (diameter 100mm) that had been steeped in water for two weeks so as to fully absorb water. This was done in consideration of the probability that m oisture content of ACP to be repaired would vary according to the duration of time before repair or the degree of rupture. Further, although this was not being done at the time of actual work in the field, in order to stu d y the effect th a t spraying w ater by use of a hose on the broken surface of ACP would have in suppressing the release of asbestos dust, sampling was done at the position assum ed by the worker when doing the cutting. Additionally, in order to determ ine the background value of asbestos concentration, asbestos concentration was m easured at a point 100m from the worker. The sampling m ethod w as the sam e as for No. 3 and sample intake was done for a period of 2 hours. After the sampling, the filters were processed by use of a transparency solution (diethyl oxalate : diethyl phthalate = 1 : 1 ; phthalate dissolved at the rate of 0.05 g/ml) and using a phase-contrast microscope (Olympus BHB, 400x) the num bers of fibers with an aspect ratio of 3:1 or greater were counted. X-rays were used to confirm th a t the ACP contained chrysotile or crocidolite. 2. Questionnaire Results Concerning th e Work o f Cutting ACP The cooperation of waterworks departm ents or bureaus of 119 local governm ents in 16 prefectures (for 3 convenience, all referred to as "b u re a u s" below) w as obtained for im plem entation of a questionnaire adm inistered to male employees who are or were "w orkers belonging to the conduit repair section," the limitation to the repair section being made because those in other departm ents are believed to have had or presently have virtually no contact with ACP. Q uestionnaires were distributed to 1,408 male employees of w ater bureaus at 55 governments, and 1,138 completed forms were collected from them (rate of recovery, 80.8%), of which 423 responses conforming to the above criterion were selected for analysis. Because difficulties were encountered in distributing questionnaires to all bureau employees at the other 54 governments, distribution was limited to 776 men who were then working in pipe repair sections or had worked in such departm ents and completed forms were collected from 723 (rate of recovery, 93.2%) after which elimination of unusable responses yielded the forms completed by 525 men. Thus, two target groups were used b u t in both instances because the objective was the entire workforce it is considered th at the selected respondents belong to a single sam ple population. As a result, the total 1,048 subjects are analyzed below as a single body. Questionnaire items were age, timing when hired by the w ater bureau, tim ing w hen assigned to the present or past section, timing and frequency of perform ance of ACP cutting work, conditions regarding use of aids protective against inhalation of dust when doing cutting, smoking history, and so on. The survey was done two times, in February and July, 1991. 3. Estim ation o f the Risk o f Lung Cancer or Malignant M esothelioma Induced by th e Work o f Cutting ACP The risk of mortality from lung cancer or m alignant m esotheliom a to waterworks bureau workers who had been assigned to do ACP repairs was estim ated using the exposure conditions obtained by the present study, models of the OSHA of the United S tates,9'10 and the model developed by H ughes.11 For the lung cancer mortality rate in the absence of asbestos exposure, use was made of Japanese national lung cancer mortality data for men by age bracket (1990, by esophageal cancer, bronchial cancer and lung cancer, stratification by 5-year b rackets)12 and for the survivors for each age, the simplified life tables for Ja p a n e se m ales (1990)12 weie used. Further, calculations of the incremental num ber of deaths for each age were made and the total from the age at which exposure began to age 75 was taken as the lifelong m ortality risk. Table 1, Asbestos concentrations measured while cutting asbestos cement pipes (ACPs) using a high-speed disk cutter. Sampling site Asbestos concentration (fibers/ml) 1st trial* 2nd trial* 3rd trial* No. 1 Breathing zone 60 48 63 No. 2 Inside the hole 91 170 No. 3 Outride the hole 1.7 8. No, 4 Outside the hole 6.6 15 No, 5 Background 0.00052 * ACPs used in the experiments were dry for the 1st trial and wet for the 2nd and 3rd trial. Water was sprinkled during the cutting in the 3rd trial. 4 III. R esults 1. Asbestos Concentration When Cutting ACP The results of m easurem ent of asbestos concentrations are shown in Table 1. W hen pipe cutting is was begun, the area where the worker was standing became white owing to the d u st from the cutting and the exhaust gas from the engine of the high-speed disc cutter, and the white area gradually expanded until it covered the entire bottom of the trench. Asbestos concentration at the inhalation position of the worker (No. 1) was 60 fibers/m l when cutting dry pipe and 48 fibers/m l when cutting moist pipe; although the latter figure is somewhat lower th an the first, the difference is not great but in both instances the values are high. Further, concentrations at the point about one m eter from the worker (No. 2) in th e tren ch were even higher, at 91 and 170 fibers/m l. It is thought th at this is because outdoor air currents caused dust from the place where the pipe was being cu t to drift to the No. 2 position, and that depending on the direction of the wind the concentration a t the place where the worker is could reach the sam e level as a t the No. 2 position. Comparison of values obtained when the dry pipe and the moist pipe was inconclusive; at the place where the worker was the value of the former was som ew hat higher, b u t a t No. 2 the value for the latter was twice as high as th at of the former. The average value for concentration of asbestos in the trench was 92 fibers/m l, and assum ing that during times when there was no pipe cutting there was no exposure to asbestos, the weighted 8-hour average concentration (8-h TWA) w as calculated at 0.96 fiber/ml. O utside the tren ch (Nos. 3, 4) the concentration of asbestos w as from 1.7 to 15 fibers/m l or from 1/3 to 1 /1 0 0 or so of the value in the trench. Even so, this value was 10,000 times the background value (0.00052 fibers/ml), indicating that the asbestos dust generated by cutting the ACP had spread to the peripheral area. When the cutting was done while water was sprayed from a hose the asbestos concentration was 63 fibers/ml, that indicates that wetting did not have the effect of reducing the dispersion of fiber particles. 2. Questionnaire Results The occupational history of the subjects was as shown in Table 2. The average age is 42.4 years and average duration of waterworks employment 20.1 years. Present assignm ents are: repair sections, 54.7%; water purification dep artm en ts, 13.9%; adm inistration and technical, 31.3%, and the average duration spent in the repair sections is 12.9 years. Among the subjects 849 or 81.0% of the total have had experience cutting ACP (they are called "ACP c u tte rs" below). Their average age is 43.4 years and average duration of employment 21.4 years; the average duration they spent in the repair section was 14.2 years. The num ber of persons studied who had been assigned to pipe or conduit repair, and the num ber who had been done pipe cutting while so assigned, are shown in Table 3. The ratios of subjects in repair sections to the total subjects in 1976-85 and 1986 onward were 74.2% an d 70.0% respectively, followed by 58.3% for 1966-75, w hen the ratio was above 50%, w hereas for 1946-55 and an56-65 the ratios were lower, at 2.6% and 27.6% respectively. The ratio of subjects who perform ed ACP cutting while in repair sections in each 10-year period was highest in 1966-75, at 79.4%, followed by 1976-85 and 1956-65 with nearly equal ratios of 71.9% and 70.9% respectively. After 1986, 56.4% had been ACP cutters, showing th a t even recently there has been ACP cutting work performed. Further, the num ber of days in a year w hen ACP cu tting was done, by decade, can be seen in Fig. 2. In every 10-year period, 1-10 days is the highest frequency, followed by 11-25 days, from which the overall frequency of such work was not high, and only a very small num ber of subjects had done such work more th a n 101 days in a year. Concerning frequencies of cuttm g work for each 10-year period, the ratio of subjects who did 26 days or more of 5 cutting work in a year is highest in 1956-65, and declines after that. Table &. Occupational history of Oie subjects. M l subjects Subjects w ith experience of cu ttin g ACPs* N um ber Age Length of service In years at Waterworks Bureau Conduit Repair Section Present assignment Conduit Repair Water PuriScation Office or Technical Work Asbestos cement pipes, 1,048 mean SD 42. 4 9. 1 M. t 9-5 12,9 9 4 Number (??) 673 4-7) 14 {13.9) 329 (31.3) BSD mean SD 43. 4 8.7 M-4 3.8 14. i 9. 3 Number > 481 (55.7) 113 (13.3) 2SS 00-0) Table 3. Number of subjects belonging to the Conduit Repair Section and pumher of the persons cutting ACP**1 tat each decade from through 1901. Year Nunabr.r of th e subjects belOttgltig to the C onduit Repair Section N um ber a t the subject cutting ACP*1 1946-53 1956-65 1966-75 M i-85 1985-91 27 ( 6 * 6 289 (27.8**) 611 (58,3*6 778 74,3**) 734 {70.0**) ** Asbestos cement pipes. ** PtOpOtlion to alt subjects (.1,048). lag to tJ Conduit Repair Section, >*1 ..... .... . .......... ijSSH Ifij ' ..J....I. ,, M.'| ,| _ ii ic a m a u a> n k) O h @ui9 U5-w 3u-uigo:-.V; Fig.2. Distribution of the average 4/)rr when the subject were engaged in catting asbestos cement pipe* by IO-yr interval from 191C, tluough 1991. The cumulative num bers of days when pipes were cut, up to the time of the survey, are shown in Fig. 3. Calculation of these num bers was done by the following method. Frequency was tabulated on an annual basis for each 10- year period in steps of 1-10 days, 11- 25 days, 25-50 days, 51-100 days, and 101 or more days, and each of these is represented as being 6, 18, 38, 76, and 150 days respectively from which the cumulative num ber of days from the initial time when pipe cutting was done was calculated. Subjects having cumulative days of 1-100 are the most num erous, a t 46.8%, followed by 101-200, at 23.2%, and the average was 13 (44-4*6 205 (7 0 .9 * 6 485 (79,4 * 6 6S9 (7 1 .9 ) 414 (95.4**) Proportion to the subject* belong* 235 days. Because the average period spent in the repair section was 14.2 years, in average term s ACP cutting work was perform ed about 17 days per year per subject. If the above calculation is modified by using for the periods 1-10 days, 11-25 days, 25-50 days, 51-100 days, and 101 or more days the values of 1, 1, 26, 51 and 101 days, the a n n u al average for ACP cutting work was 9 days, a n d if the values of 10, 25, 50, 100 and 200 days are used, the average is 23 days. These are the minimum and m axim um a ssu m ed values for average work days. Fig. 3. Cumulative days to date when the sub jects were engaged in cutting asbestos cement pipes. 6 Table 4. Estimated life-time risk (death per 100,000 persons) among the workers cutting ACPs under the models proposed by OSHAW) and Hughes.' The values of lung cancer and mesothelioma represent excess death rate from asbestos exposure. Model Frequency of cutting ACP (d/yr) Lung cancer Mesothelioma Total OSHA Hughes 9 16 16 32 17 30 30 60 23 41 40 81 9 9 15 24 17 15 28 43 23 21 37 58 Lung cancer: fft,=ffEXALX i 'X/3i."*Eq. (1), where Rl : excess death rate of lung cancer caused by asbestos exposure, Re : expected death rate of lung cancer based on the Japanese male age-specific lung cancer death rates in 1990, Kl constant (0.01 in OSHA's model, 0.005 in Hughes' model), F : ex posure level in fibers/ml, Dl : exposure duration in years (at 10 years before observation point in OSHA's model and at observation point in Hughes' model). Mesothelioma: For (T--10))>D, Ru= Ku X F x {(T --10)TM--(T --10--iO"}, for D > ( T - 10) >0, Ru = K u x F x (T -1 0 ) , and for 0 > (T -1 0 ) , Ru = 0 --Eq.(2), where Ru ; excess death rate of mesothelioma caused by asbestos exposure, Ku : constant ( lx l0 ~ 8 in OSHA's model, 0 .2 X10~6 in Hughes' model), F : exposure level in fibers/ml, T : time after first exposure in years (used T instead of (T --10) in Eq.(2) in Hughes' model), D : exposure duration in years, : power (3,0 in OSHA's model, 3.2 in Hughes' model). Calculations were done for each age until the age of 75 yr by life table method, and then summed to obtain total life-time risk. At present 18.1% of subjects who do cutting work use dust m asks (national certification masks) and alm ost all of these subjects replied that they had begun wearing a m ask within 5 years. There are, in addition, subjects who utilize gauze m asks or towels but they are few in num ber, a t 5.1% and 17.1%. The rem aining 59.7% adopt no protective m easures. With regard to smoking, in the ACP cutting group the ratios of those who presently smoke and those who previously were smokers, and non-sm okers, was 66.7%, 20.5%, and 12.7%. 3. Lifetime Risk of Lung Cancer or Malignant M esotheliom a Attributable to C utting ACP The conditions of exposure, used as assum ptions for estim ating risk, are based on the field experim ent and questionnaire resu lts and are as follows. Because the average age of subjects is 43 years and average period of waterworks bureau employment 21 years, the start of waterworks employment was taken as 1970 at the age of 22 years. The concentration of asbestos subjects were exposed to w hen cutting ACP w as taken as 1 fiber/m l u n d e r 8-h TWA, and the annual average num ber of days worked while in the repair sections (average, 14 years) was 17 (minim um, 9; m axim um , 23). The period w hen subjects were assigned to repair sections was normalized as 1970-91. Inasm uch as future exposure to asbestos cannot be determined at this time asbestos exposure is taken as th at extending up the present time. On the basis of the above assum ptions, the life-time risk up to age 75 of contracting lung cancer or m alignant m esotheliom a as a result of cutting ACP w as estim ated with results as shown in Table 4. The estim ated value for the excess death rate from lung cancer, with annual average work days a t 17, is 30 persons u sin g the OSHA m odel (per 100,000 persons) and 15 persons using the Hughes model (per 100,000 persons). If the days of work is taken to be the low num ber, 9 days, the resu lts are 16 persons an d 9 persons, and if the high num ber of work days, 23, is used the values are 41 and 21. The estim ated value for the excess death rate from m alignant m esotheliom a, using 17 days as the an n u al average work days, is 30 persons (per 100,000) with the OSHA model and 28 persons (per 100,000) using the Hughes model; yielding similar values for the two. If the days of work is 7 taken to be the low num ber, 9 days, the resu lts are 16 persons an d 15 persons, and if the high num ber of work days, 23, is u se d the values are 40 a n d 37. As the result, the total excess death rates from lung cancer and m alig n an t m esotheliom a in the sequence of 9, 17, and 23 days of annual work, are 32, 60 a n d 81 persons using th e OSHA model and 24, 43 and 58 using the Hughes model. IV. O bservations 1. Exposure to A sbestos When Cutting ACP ACP h a s been m ade w ith diam eters from 50 to 1,500m m,2 and pipe which has had frequent need of repair is 50-200m m in diam eter.13-15 For this study, 100mm and 150mm pipe was used. The depth at which pipe is laid varies according to the relevant situation, but pipe of 350mm or less is buried at about one m eter from the su rface.16 For cutting to be done it is necessary to completely expose the pipe, requiring earth to be removed from under the pipe, slightly deepening the immediate area. Since in the present experiment the tren ch was excavated to a depth of 1.2 meters and a base of about 10cm height was installed, it is believed th at conditions approximated actuality. In the experiment both dry pipe and moist pipe were cut, and in both cases the asbestos concentration in the trench was high, from 48 to 170 fibers/m l, and no difference based on the pipe being diy or moist was observed. Further, no effect was observed of sprinkling water on the surface being cut. The high-speed disc cutter is a tool th at u ses a disc blade of ab o u t 5m m thickness, to cut ACP. This causes scattering of fine d u st particles at a high velocity during the cutting of pipe, a n d it is th o u g h t th a t su ch dispersion is not influenced by the pipe being moist or sprinkling with water. It is also thought th at although the cutting is performed out of doors it is performed in a narrow trench, slowing the decline of concentration through dispersion and creating a high concentration at the work site. OSHA10 h a s u n d e rta k e n a n um ber of studies on m easures to control dust particles resulting from asbestos-related work, and has indicated that there was a possibility of a high concentration when cutting ACP. No p apers have been published in J a p a n on cutting of ACP but there has been a report dealing with use of an electric drill on calcium silicate asbestos-cement board used as outdoors building m aterial. Calcium silicate asbestos cem ent board is made by combining coal or cement, calcium silicate etc. with about 20% asbestos (chrysotile, or amosite) with water, formed into sheets, cured and dried; the content of asbestos as well as m ethod of m anufacture is close to the content and m ethod for ACP.17 As electric saws use rotary blades to cut, it is thought th at the particles released are coarser than those from a high-speed disc cutter, that cuts by grinding b u t the work itself is about the sam e in both cases. According to K im ura,18 the concentration of asbestos to which a worker is exposed when no suction device is used during work is 147-393 fibers/m l, and H isanaga et a l19 have reported 103-787 fibers/m l for the same work. Values obtained for this study were somewhat lower than these but Kimura and Hisanaga et al collected data indoors whereas in the present instance work was done outside. According to the results of the questionnaire, only 18.1% of the workers were users of face m asks. There were some others who used gauze m asks or towels b u t they were not many. Therefore, m ost workers cu t ACP w ithout use of protective m asks and in the absence of protective devices are exposed to asbestos particles. A Jap an Association of Industrial H ealth advisory gives 10 fibers/m l as the standard for 15-m inute average exposure to asbestos d u st (ceiling value). If values obtained by m easurem ents in the trench are adjusted to a 15-minute base the result is 16-57 fibers/m l; the entire range exceeds the advisoiy's limit. Further, as stated in the conclusions above, conversion to 8-h TWA yields the average 0.96 fiber/m l. This assum es th at there is no exposure to asbestos other th a n w hen cutting pipe, b u t if 8 exposure to asbestos subsequent to the cutting is taken into consideration, it is thought th at the actual exposure is higher th a n the m easured value. To be sure, the present study included a sim ulation of actual work and it is possible th at a different dispersion of fibers would resu lt w hen ACP th a t h a s been in use for m any years is cut. Also, although it cannot be denied that because of the limited num ber of data points collected the average for asbestos exposure concentration on the day the pipe was cut may have a wide m argin of error, but nevertheless is considered to represent the degree of exposure. The value of 0.96 fiber/m l in the case of 8-h TWA is 4.8 tim es greater th a n the allowable concentration of crocidolite as recommended by the Jap an Association of Industrial Health. In addition, it is about half in com parison to the allowable level of chrysotile (0.25 fiber/ml), b ut exceeds the acceptable levels in the United States and Europe: for the U nited States (0.2 fiber/m l), Germany (0.5 fiber/m l) and Britain and Sweden (0.5 fiber/ml). As stated a t the outset, ACP h a s been in use in Jap an as w ater conduits since 1951. That year 110,000 pipes were produced; output increased to 1,460,000 in 1955 and further to 3,340,000 in 1965 (personal com m unication from the Ja p an W ater Works Association). Production then declined, but continued through 1985. Therefore, it can be concluded th a t the total length of ACP continued to increase after 1965. Estimating on the basis of the production volumes and the length of ACP th a t w as removed, it is believed th a t the total length reached a peak in or about 1975 an d fell thereafter. In this connection, information about the total length of ACP in J a p a n is available only from 1979 onward; in 1980 it was 86,806km, of 25.8% of the total conduit length, and in 1989 was 70,759km or 16.2% of the total.1 The first subject responding to the questionnaire to start at a waterworks bureau began in 1946 b u t the average is 1970. Therefore it is thought th at if we examine the work experience of the questionnaire subjects, in cutting ACP, by each 10-year interval, we will be able to trace the change in actual work conditions. However, because of the small num ber of persons who were working in a conduit repair departm ent in 1946-55, it is possible th a t resu lts for this period will not accurately reflect reality. The ratio of workers who did ACP cutting in the conduit repair departm ents in 1946-55 was the lowest, 44.4%, and subsequently the ratio increased so that in each of the 1956-65, 1966-75 and 1976-85 periods it was above 70%, corresponding to the increase over tim e of ACP production a n d total ACP installed length as can be surm ise from production data. The highest ratio was 79.4% for 1966-75; this was the period during which use of ACP peaked, an d also w as the time w hen road traffic increased rapidly, causing breakage of m any ACP. Until th a t time, cutting was done using hand saws, but about in 1965 high-speed disc cutters became available. Although the ratio of workers engaged in cutting operations dim inished after 1986, this is thought to represent a n effect of the ending of ACP production and he consequent decline in the total length of such pipe in place. Nevertheless, since 1986, 56.4% of persons in conduit repair departments have cut ACP, and given the low rate of use of protective m asks it is presum ed that their exposure to asbestos has continue to take place. A variety of tasks are undertaken by repair workers. In addition to ACP, conduits are made of cast iron, ductile iron, steel, PVC and lead and workers m ust deal with repairs of all such pipe. They replace hydrants and home water m eters, and patrol for prevention of m ishaps. Local governments contract for some of the conduit repair work to be done by outside parties. According to findings of the present study, the highest frequency of u n d ertak in g AP cutting, in every 10-year period, was in the 1-10 days a year category (Fig. 2), and it is estimated that the average annual days per subject is 17. Therefore, this is not to imply th a t cutting ACP is the m ajor task of the repair departm ents. However, m any epidemiological studies reported to date recognize a cau sal relationship between asbestos and lung cancer, malignant mesothelioma and other 9 d iseases.23-4*' 22 There is the thought th a t carcinogens have no threshold values,; in actuality five cases have been reported of the occurrence of m alignant mesothelioma among residents who have not been exposed on the job in the vicinity of crocidolite mines or asbestos plants.3 If these points are kept in mind and consideration is given to the short time b u t high exposure to asbestos, need does exist to adopt m easures to reduce asbestos exposure. The fundam ental m easure adopted is to replace ACP w ith ductile iron or other pipe. One m ethod is to leave th e old ACP in the ground, and lay new conduit; this is being implem ented by local governments as a m easure for replacem ent of superannuated conduit, but it would be desirable to provide additional incentive for this by increasing Ministry of Health subsidies for such work, or expanding the scope of qualified subsidy recipients. It is further necessary, since total avoidance of cutting ACP is not possible, to develop new m ethods of cutting ACP so as not to scatter asbestos fibers, and to prepare safety m anuals to prevent asbestos exposure through the use of protective m asks. The latent period of lung cancer and m alig n an t mesothelioma caused by asbestos exposure is long and symptoms often ap p ear w hen the diseased p erso n 's memory concerning asbestos exposure is not sharp. It is therefore thought to be im portant to keep records of the dates, worker nam es, nature of work performed, conditions of exposure, and so on in relation to ACP cutting tasks. 2. Estim ation of Lifetime Death Risk from Lung Cancer and Malignant M esotheliom a Induced by ACP Cutting Work Here, a linear model as indicated by equation (1) (in Table 4) w as u sed to estim ate the excess death rate from lung cancer. This model is supported by epidemiological studies of asbestos m an u factu rin g p la n ts,23 spinning m ills,24 asbestos m ines and other situations and has been used to estim ate excess death rates by OSHA, 9-10 the E nvironm ental Protection Agency (EPA, US),26 WHO,27 C onsum er Product Safety Com m ission (CPSC, US),28 the Health and Safety Executive (HSE, England),29'30 National Research Council (NRC, US)30 an d others. However, the coefficient iff in equation (1) varies greatly according to the work process and type of asbestos; the eight epidemiological studies cited by OSHA shows a two-place difference, from 0.0006 to 0 .0 4 8 .10 OSHA, judging from the results of chrysotile studies and eight studies regarding amphibolic asbestos (crocidolite and amosite) uses Kl=0 .0 1 .10 In view of th e u se of chrysotile a n d crocidolite for m anufacture of ACP, it was judged appropriate to use the OSHA model for estim ation of the risk of ACP cutting. Further, as the Hughes method utilizes as the Kl value 0.005, the average gained from several asbestos p lan t stu d ie s,23'32 this too w as selected for u s e .11 It is thought th a t there is a m ultiplier effect of asbestos exposure a n d sm oking as causes of lung cancer,33 m aking it necessary to consider the smoker ratio among the population whose excess death rate from lung cancer is to be estim ated. According to the questionnaire results, the smoker ratio among the subjects who have cut ACP is 66.7%, w hich is not greatly different from the national average (60.5%, 1990).34 Therefore it is thought th at there is no impedim ent to using the Japanese m ortality rate due to smoking for estim ation of excess deaths. Estimation of the excess death rate attributable to m alignant mesothelioma was by use of an exponential model as indicated by equation (2) (in Table 4). This model assum es that risk increases linearly according to the extent of asbestos exposure. While adequate proof of this is not available, in epidemiological studies a t gasm ask factory in England35 and at a crocidolite mine in West A ustralia36 there are indications th at risk increases in accordance with prolongation of the exposure period or increase in the extent of exposure. This model assum es th at risk increases in parallel to the exponent of elapsed years since initial exposure. This has been observed11'28 am ong Am erican and Canadian workers handling insulation m aterials,22 production workers a t an O ntario asbestos p la n t,37 and a British spinning m achine operator.38 The 10 observation period of these studies, moreover, was about 40 years long and although it is not known th at risk continued to increase beyond those periods, these studies have been utilized by the WHO and the above-mentioned institutions for estim ation of excess death rates due to m alignant m esothelioma by use of a model. Epidemiological study has found that differences in the type of asbestos, specifically, a group of subjects th at had been exposed to amphibolic asbestos had a higher mortality rate from malignant m esothelioma than a group of subjects who had been exposed to chrysotile,3 and OSHA derived the coefficient E m= 0 .2 x 1 0 -8 on the basis of risk estimation using results of studies on both chrysotile and amphibolic a sb esto s.9'10 Hughes et al have proposed k M = 0 .0 4 x l0 -8 in case of exposure solely to chrysotile and E m= 0 . 2 x 1 0 -8 in the case of combined exposure; for the present study, the K m for combined exposure was used. Further, in both the Hughes model and the OSHA model the indexes were different, at 3 .0 and 3.2. Reflecting the differences between the two models, the estim ate of lifetime excess deaths from lung cancer and m alignant mesothelioma combined, in the case of 17 work days a year, is 60 persons with the OSHA model and somewhat less, 43, with the Hughes model. These values are only approximations, on which basis they can be said to be equivalent. It is necessary, further, to clearly state that, as has been m entioned by the WHO3, estim ated risk values, such as obtained by the present study, are very rough num bers, that represent a wide range of actual values. For the present study it was assum e that there was no asbestos exposure other th a n at the time of cutting pipe, b u t it is thought th at there is additional exposure to asbestos particles that rem ain in the trench after the pipe has been cut and w hen new pipe is attached to the existing one. F u rth er, the a n n u a l n u m b er of 17 days of work represents cutting done by the subject b ut not that done by coworkers at the same work site; indirect exposure at such times has not been taken into consideration. From these points it can be said that our values are underestim ations. Furthermore, some use of hand saws continued after the high-speed disc cutter became available (about 1965) and it is thought th at there was less exposure to asbestos particles in the case of the hand saw as compared to the cutter. This would tend to raise the value obtained by the study. Iwai et al22 have estim ated the lifetime excess m ortality in Ja p an from lung cancer and m alignant mesothelioma, caused by asbestos in the atm osphere (0.0004 to 0.002 fibers/ml), combined, at 1.6 to 8.2 persons (per 100,000), using a model similar to th at of th e OSHA (Al= 0 .0 1 , Am= 1 .9 x 10-8 a n d T instead of T-10 in equation (2), and with risk a t 4.2 tim es after adjusting for exposure at day and night times and on vacation days. Compared to this value range, the level of risk of conduit repair workers th at were subjects of this study of pipe cutting is 3 to 50 times greater, indicating that this special group faced higher risk than the general population. Yokoyama et al40 have reported on the occurrence of m alignant mesothelioma in waterworks employees who have installed ACP over a period of years, and this possibility too is well within the range of probability judging from the risk estimation of the present study. V. C onclusion In order to clarify the actual conditions of the work of cutting ACP, a Field experim ent was m ade in order to m easure the asbestos exposure concentration when pipe was cut, and a questionnaire survey of waterworks employees who have repair work experience was carried out. The information thereby gathered was used for iterations of the OSHA model and the Hughes model to estimate risk associated with lung cancer and m alignant m esotheliom a attributed to exposure to asbestos. As a result we have learned the following. 1) W hen ACP is c u t the asbestos exposure concentration is extremely high, at 48 to 170 fibers/m l. Moreover, only 18.1% of workers used protective m asks when performing this work. 2) The ratio of employees who undertook pipe cutting work in the conduit repair sections was highest in 11 1966-75, a t 79.4%, followed by 1976-85 when the ratio was 71.9% and 1956-65 w hen it was 70.9%. Further, during all the 10-year periods the greatest frequency rating was 1-10 days a year, and the average was 17 days. 3) The resu lt of estim ation of the lifetime risk, up to 75 years of age, attributable to asbestos exposure at the tim e from w hen the pipe w as first cut to the present, in the case of 17 days a year of cutting work, was that the estimated excess m ortality from exposure to asbestos was found to be 60 persons (per 100,000, OSHA model) and 43 persons (per 100,000, Hughes model). References (Translator's note: Family names of Japanese: capitals; asterisks indicate documents in Japanese Minimal changes to the references have been made. Japanese academics are less disciplined in citations than are Americans. The spelling of given names in particular is often moot and may need clarification by the individual concerned. Most proper nouns given in Japanese have been translated without attempting verification, in most cases, but there is enough information to track down the Japanese originals if necessary.) 1) M inistry of H ealth an d Welfare, E nvironm ental H ealth B ureau, W aterw orks E nvironm ent D epartm ent, W aterworks Improvement Section (supervision). Annual Waterworks Statistics for 1979 to 1989, Facilities and Administration sections. Tokyo: Ja p a n W aterworks Assoc., 1981-1991.* 2) USHIMARU Kenji. A sb esto s Cement Pipe. J a p a n W aterworks Assoc., 1977: 46 (5), p. 156-163.* 3) World H ealth O rganization. A sb estos an d other natural mineral fibers. 1986. 4) E nvironm ental Protection Agency, A tm osphere Protection B ureau, Planning Section (supervision). Everything about asbestos cem ent. Kawasaki: Ja p a n Environm ental Hygiene Center, 1987.* 5) EBIHARA Isam u, A clinical case of m alignant m esotheliom a am ong asbestos workers. J. Japanese Soc. o f Internal Med. 1986: 75, p. 400-405.* 6) SAITO K atsum i, TAKIZAWA Yukio, HIRANO Koichiro, C oncentration of asb esto s fibers an d their form, in w ater conveyed by asbestos cement conduit. Jpn. J. Hyg. 1992: 47, p. 851-860.* 7) J a p a n W aterw orks Assoc. History o f W aterworks in Japan, Overview section. 1967: p. 665-667, 724-725.* 8) All J a p a n Local G overnm ent W orkers Union. Fifteenth Union W aterworks Conference, Report and Agenda. 1992.* 9) O ccupational Safety an d H ealth A dm inistration (US). Quantitative risk a ssessm en t fo r asbestos related cancers. 1983 10) O ccupational Safety an d H ealth A dm inistration (US). Q uantitative exposure to asbestos, tremolite, anthophylite and actinolite. Federal Register 1986; 51: 22612-2790. 11) H ughes, JM , Weill H. A sbestos exposure quantitative a ssessm en t of risk. A m R ev Respir Dis 1986; 133: 5-13. 12) Hygiene S tatistics Assoc. H ygiene indicators a nd trends o f national hygiene. 1991: 38 (9), p . 425; 1992:39 (9), p. 427.* 13) ISHIDA Saburo. M aintenance m anagem ent of conduits. J. Jpn W aterworks Assoc. 1977: 46 (5), p. 52-59.* 14) HOSOI, Yuhiko, MURAKAMI Jinji, KOZAI M asao, MARUTAKA Shigemiki. O bservations on R upture C haracteristics of W ater Conduit. J. Jpn W aterworks Assoc. 1989: 58 (5), p. 10-16.* 15) HOSO Yuhiko, MURAKAMI Jinji, KOZAI M asao et al. Study on ru p tu re characteristics of w ater conduit in th e T okushim a City w ater supply system . J. Jpn W aterworks Assoc. 1988: 57 (8), p. 2- 11.* 16) OHASHI Fum io, KUBO Takeo, MATSUMOTO Ju n ich iro , et al (ed.). H ygiene Engineenng Handbook. Tokyo: A sakura Shoten, 1967, p. 177.* 17) J a p a n S ta n d a rd s Association. JIS A5418 (1983) Calcium silicate asbestos cem ent sheets. JIS Handbook, Construction: 1989, p. 1081-1085.* 18) KIMURA Kikuji. A sbestos an d Environm ental Issues. Science o f Labor, 1987, 42 (12), p. 4-13.* 19) HISANAGA Naomi an d SAKAI Kiyoshi. Three-way m anagem ent dealing w ith asbestos, particularly concerning environmental m anagem ent and work m anagement, in the construction industry. Science of Labor, 1988 (29 (8), p. 26-30.* 20) Ja p a n Association of Industrial Health. Report on allowable concentrations. Industrial Health 1991: 33, p. 277-298.* 12 21) Ja p a n Asbestos Association. Asbestos regulations in other countries. Sekimeti 1991: 542, p. 1-9.* 22) Selikoff IJ, H am m ond EC, Seidm an H. Mortality experience of in sulation w orkers in the United States and C anada, 1943-1976. Ann NY Acad Sci 1979; 330: 91-116. 23) H enderson VL, E nterline PE. Asbestos exposure: factors associated w ith excess cancer and respiratory disease mortality. Ann NY Acad Sci 1979; 330: 117-126. 24) D em ent JM , H arris RL, Sym ons MJ. E stim ates of dose-response for respiratory cancer am ong chiysotile asbestos textile workers. Ann Occup Hyg 1982; 26: p. 869-887. 25) Liddel FD, McDonald JC , Thom as DC. M ethods of cohort analysis: ap p raisal by application to asbestos mining. JR oyal Stat Soc Assoc 1977; 140: 4, p. 69-491. 26) E nvironm ental Protection Agency (US). A sbestos health a ssessm en t updata. Prepared by Nicholson W. W ashington DC: US E nvironm ental Protection Agency, 1984. 27) World H ealth O rganization. Limits o f occupational exposure to asbestos - Report fo r the WHO conference. Tokyo: Ja p a n Asbestos Association, 1990.* 28) C onsum er Product Safety Com m ission (US). Report o f the chronic hazard advisory panel on asbestos. W ashington DC, 1983. 29) H ealth a n d Safety Executive (UK). A sbestos: the control limit fo r asbestos. Prepared by Acheson AD, G ardner MJ. London: H ealth and Safety Com m ission, HMSO, 1979. 30) H ealth a n d Safety Executive (UK). A sbestos: the control limit fo r asbestos. A n updata o f the ralevant sections o f the ill effects o f asbestos upon health. Prepared by A cheson AD, G ardner MJ. London: Health and Safety Commission, HMSO, 1983. 31) National R esearch Council (US), Committee on N onoccupational H ealth Risks. Asbestiform fibers-nonoccupational health risks. W ashington DC: National Academy Press, 1984. 32) Weill H, H ughes J , W aggenspack C. Influence of dose an d fiber type on respiratory m alignancy risk in asbestos cem ent m anufacturing. A m Rev Respir Dis 1979; 120: 345-354. 33) H am m ond EC, Selikoff IJ, Seidm an H. Asbestos exposure, cigarette sm oking and death rates. Ann NY Acad Sci 1979; 330: p. 473-490. 34) Hygiene S tatistics Association. H ygiene Indicators. Trend o f National Hygiene. 1991: 38 (9), p. 97, 396.* 35) Jones JSP, Sm ith PG, Pooley FD, et al. The consequences of exposure to asbestos d u st in a war-time gas m ask factory. IARCSciPubl 1980; 30: p. 637-653. 36) H obbs MST, W oodward SD, M urphy B, et al. The incidence of pneum oconiosis, m esotheliom a and other respiratory cancer in men engaged in mining and milling crocidolite in W estern Australia. IARCSciPubl 1980; 30: p. 615-625. 37) Finkelstein MM. M ortality am ong long-term employees of a n O ntario asbestos cem ent factory. B rJIn d M ed 1983; 40: p. 138-144. 38) Peto J . The incidence of pleural m esotheliom a in chrysotile asbestos textile workers. In: Biological effects of m ineral fibres. Lyon: IARC, 1980: p. 703 (IARC Scientific Publications No. 30). 39) IWAI Kazuro, HOSODA Y utaka, YOKOYAMA Kunihiko et al. E xtent of asb esto s exposure and its relation to the rate of occurrence of m alignant mesothelioma and the extent-reaction relationship. Analysis of causes of data dispersion and calculation of risk posed by asbestos fibers in the general atm osphere. J. Atmospheric Pollution Soc. 1990: 25, p. 181-191.* 40) YOKOYAMA Kunihioko, SAKATANI M itsunori, YAMAMOTO Akira. Clinical diagnosis of asbestos related disease. Byorito Rinsho, 1989: 7, p. 695-701.* Reprint requests to Department of Occupational Health, Osaka Prefecturai Institute of Public Health 1-3-69. Nakamichi. Hitrashinari-ku. Osaka. 537 Jaoan CS. Kutnaeail 13