Spirometric abnormalities among welders

ENVIRONMENTALRESEARCH56, 15--24 (1991)

Spirometric Abnormalities among Welders SUBODH K . RASTOGI, 1 BRAHMA N . GUPTA, TANVEER H U S A I N , NEERAJ M A T H U R , AND SEEMA SRIVASTAVA

Epidemiology Division, Industrial Toxicology Research Centre, Mahatma Gandhi Marg, Post Box No. 80, Lucknow 226 001, India Received September 15, 1990 A group of manual welders (N = 57) engaged in gas welding joint faces of moulded brasswares, age group 13-60 years (mean: 29.2 -+ 1.37 years), having a mean exposure period of 12.4 --- 1.12 years (range: 1-35 years) were subjected to spirometry to evaluate the prevalence of spirometric abnormalities. The findings were compared with those obtained from a reference group (N = 131) (mean age: 31.2 +- 1.35 years) engaged in nonweldingjobs such as packing, labelling, and transportation of the finished brassware articles. The welders showed a significantly higher prevalence of respiratory impairment (28.0%) than that observed among the unexposed controls (6.1%) (P < 0.001), as a result of exposure to welding gases which comprised fine particles of lead, zinc, chromium, and manganese. This occurred despite the lower concentration of the pollutants at the work place. In the exposed group, the smoking welders showed a prevalence of respiratory impairment significantly higher than that observed in the nonsmoking welders (40.0 vs 18.7%) (P < 0.10). A similar trend was observed in the control group indicating that smoking had a deteriorating effect on spirometric tests. The results of the pulmonary function tests showed a predominantly restrictive type of pulmonary impairment (12.3%) followed by a mixed ventilatory defect (8.7%) among the welders. The effect of age on pulmonary impairment was not discernible either in the exposed or unexposed group. The analysis of data in relation to duration of exposure showed significant correlation between the prevalence of respiratory abnormalities and length of exposure. Welders exposed for over 10 years showed a prevalence of respiratory abnormalities significantly higher than those exposed for less than 10 years (44.4 vs 13.3%) (P < 0.01) thereby showing that occupational exposure to welding fumes resulted in increased prevalence of pulmonary impairment in the welders. Smoking also had a contributory role thereby suggesting an interaction between smoking and welding exposure on the prevalence of pulmonary impairment in the welders engaged in brassware industries. © 1991 Academic Press~ Inc.

INTRODUCTION Welding is a generic term encompassing various processes for joining metals, and the composition and quantity of the fumes and gases generated vary accordingly. They commonly contain aluminum, chromium, copper, fluorine, iron, lead, magnesium, manganese, nickel, silicon, titanium, vanadium, and zinc; and carbon dioxide, carbon monoxide, nitrogen oxides, and ozone are produced as byproducts. Cross-sectional epidemiologic studies have not consistently demonstrated an impairment of pulmonary function in occupationally exposed welders (Hunnicutt et al., 1964; Fogh et al., 1969; Kleinfeld et al., 1969; Peters et al., 1973; Barhad 1 To whom correspondence should be addressed. 15 0013-9351/91 $3.00 Copyright © 1991 by Academic Press, Inc. All rights of reproduction in any form reserved.

16

RASTOGI ET AL.

et al., 1975; Antti-Poika et al., 1977; Ross, 1978; Oxhoj et al., 1979; Akbarkhanzadeh, 1980). However, interpretation of the studies is complicated by the heterogenicity of welding exposures. Previous investigations have not been conducted on brassware welders. Therefore, an epidemiologic study was conducted to determine whether these welders of the brass industry have increased prevalence of impaired lung functions.

MATERIALS AND METHODS

The study population consisted of 57 male manual welders (32 nonsmokers and 25 smokers) and 131 controls (78 nonsmokers and 53 smokers). The prevalence of smoking was found to be similar in the welders and controls (43.8 vs 40.4%). The welders were engaged in manual gas welding of the joint faces of the moulded brasswares with the help of the soldering material (50% lead and 50% tin) in open spaces. Prior to welding, the welders cleaned the joint faces by applying borax powder. The mean values of welding period were 10.2 __- 1.2 years for nonsmoking welders and 15.6 --+ 1.8 years for smoking welders. The controls were also employed in the brassware industries and were engaged in the packing, labeling, loading, and unloading of finished brasswares. The controls had no exposure to known respiratory toxicants at the workplace. The smoking welders had smoked a mean of 16,5 pack years, a minimum of 5.5 pack years, and a maximum of 20.4 pack years. All the exposed and the control workers were medically examined. The medical examination included full size chest X-ray and a routine physical examination. Respiratory effects were studied by spirometry. Everyone, exposed and unexposed, was studied by the same technician and the same equipment during a regular working day to avoid any personal and equipment variation. A forced expired vital capacity maneuver was recorded in the standing position with a low-resistance bellows spirometer (Vitalograph). The subject was carefully instructed about the spirometric procedure before the test. The spirometry conducted in the present study followed the criteria laid down by the ATS Snowbird workshop (American Thoracic Society Statement, 1979). Each individual performed three tests. The best result for each variable was chosen, even if the results were to be selected from different recordings, and were expressed at body temperature and ambient pressure saturated with water vapor (BTPS) (Cotes, 1979). The following parameters were studied: 1. 2. 3. 4. 5. 6. 7.

Forced vital capacity (FVC) Forced expiratory volume in one second (FEV0 FEVJFVC ratio Maximum breathing capacity (MBC) Peak expiratory flow rate (PEFR) FEF25_75%

FEF2o0_12oo

The peak expiratory flow rate was measured with the help of a Wright peak flow meter. FEV1/FVC percentage values between 70 and 80 were normal and values less than 70% indicated bronchial obstruction. Standard reference values for

SPIROMETRIC ABNORMALITIES

17

spirometry were taken from Rastogi et al. (1983). They predicted ventilatory norms in healthy and asymptomatic north Indian population which best suited the exposed and control groups as they matched ethnically. The ventilatory disturbances were classified as per Miller (1956) and the severity of respiratory impairment graded as per Conrad (1983). Miller et al.'s prediction quadrant (1956) was used to classify the ventilatory disturbance as follows: (i) Restrictive pulmonary impairment: Observed VC value less than 80% of the predicted value. (ii) Obstructive pulmonary impairment: Observed VC value more than 80% of the predicted value and FEV1/FVC percentage ratio less than 70%. (iii) Mixed pulmonary impairment: Observed VC value less than 80% of the predicted value and FEV1/FVC percentage ratio less than 70%. The severity of pulmonary impairment was graded as per Conrad (1983) as follows: (i) Mild respiratory impairment: Observed spirometric values (Viz., VC, FEV0 ranging between 61 and 79% of the predicted values. (ii) Moderate respiratory impairment: Observed values of VC and FEV 1ranging between 40 and 60% of the predicted values. (iii) Severe respiratory impairment: Observed VC and FEV 1 values less than 40% of the predicted values. INDUSTRIAL HYGIENE STUDIES The suspended particles present in the breathing zone of workers on the shop floor were measured using personal dust samplers and high-volume air samplers. The airborne dust collected from the work environment where welding was performed was analyzed for various metals. For the estimation of metals, the airborne dust was collected on accurately weighed filters which were then treated with concentrated nitric acid, digested to dissolve the mass, and finally made to volume using N/IO nitric acid. These samples were analyzed by atomic absorption spectrophotometer (Model Norwalk, 5000). STATISTICAL ANALYSIS Students t test was used to analyze the significant differences of means of lung function values between the exposed and the control groups. The homogeneity of variance was tested before applying t test. The direct method of standardization (Armitage, 1971) was used for adjusting smoking habits. The significance of difference in the prevalence rates was analyzed by Chi square test (Mantel and Haenszel, 1959). RESULTS The mean values of age, height, and weight of the welders and the controls are shown in Table 1. The exposed and the controls showed similar values of physical characteristics. Similarly the smokers and the nonsmokers in the exposed and the control groups when compared in their respective groups showed insignificant

18

RASTOGI ET A L . TABLE 1 COMPARISON OF MEAN VALUES OF DEMOGRAPHIC VARIABLES IN WELDERS AND CONTROLS BY SMOKING STATUS

Demographic variables Number Age (years) Height (cm) Weight (kg) Exposure (years)

Total

Smokers

Welders

Controls

Welders

57 29.28 1.37 1 6 2 . 4 6 0.78 48.53 1.11

131 31.21 1.35 162.8 0.71 4 8 . 4 1 0.86

25 34.36 1.96 163.36 0.96 50.56 1.54

12.49

1.12

--

--

15.68

•.85

Nonsmokers

Controls

Welders

53 32 36.64 1.73 25.31 1.57 164.64 0.68 161.75 1 . 1 6 49.75 1 . 3 8 46.94 1.5 --

--

10

1.2

Controls 78 25.47 1.64 159.63 1.97 47.82 0.95 --

--

differences in their physical characteristics. The welders were exposed to metallic fumes for a mean period of 12.4 + 1.1 years in the brassware industries. The smoking welders showed slightly higher value of mean exposure (15.6 _ 1.8 years) in comparison to their nonsmoking counterparts (10.0 -+ 1.2 years). The chest X-ray findings obtained in the welders and the unexposed controls are presented in Table 2. Fourteen percent of the welders in our study had reticular shadows and micronodular opacities (p and q types) while in the control group only 3 percent cases suffered from reticular shadows. We tried to correlate the radiological findings with the pulmonary abnormalities observed in the welders and failed to observe any correlation between the two. The mean percentage of the predicted values of lung function in the welders and the controls in relation to a smoking habit are shown in Table 3. The mean values of all respiratory parameters showed significant impairment in the exposed group in comparison to the normal values obtained in the unexposed controls. However, the FEVt/FVC percentage ratio was found to be normal (84.7 -+ 2.70%) in the exposed population thereby indicating absence of bronchial obstruction in central larger airways. The welders primarily showed the mild category of respiratory impairment in all the respiratory parameters. The impairment in FEFzs_75~, FEF25~, and FEFso% parameters suggested obstructive changes in small peripheral airways. Comparison of the lung function data in the smokers and nonsmokers in the exposed and the control groups showed that smokers in the exposed group particularly showed significantly greater impairment in all respiratory variables than those in the nonsmoking group. However, such marked differences were not TABLE 2 CHEST X-RAY ABNORMALITIES IN WELDERS AND UNEXPOSED CONTROLS A b n o r m a l chest X-rays

Welders (N = 57)

Controls (N = 131)

R e t i c u l a r s h a d o w s (%) Small r o u n d e d opacities " p " T y pe (%) " q " Type (%)

10.5

3.05

1.75 1.75

---

Total (%)

14.0

3.05

SPIROMETRIC

19

ABNORMALITIES

TABLE

3

MEAN VALUES OF PULMONARY FUNCTION VARIABLES (PERCENTAGE OF THE PREDICTED) FOR WELDERS AND CONTROLS BY SMOKING HABITS

Smokers

Pulmonary variables

Welders

Number FVC FEV1.0 FEV1.0/FVC% IMBC PER FEF25-75% FEF200-1200

60.1 64.4 78.6 62.6 68.3 58.7 63.4

25 -+ 1.44 --- 1.80 --- 1.77 - 1.32 -+ 2.02 -+ 1.93 - 2.21

Nonsmokers

Controls 87.63 82.22 80.93 83.03 92.71 80.03 80.23

Welders

53 --- 1.23 "4" 1.06 --- 2.13 --- 2.13 -+ 3.01 -+ 3.21 -+ 2.86

66.8 70.6 90.8 76.2 78.2 64.4 75.9

32 --- 1.35 --- 1 . 6 1 -+ 1.25 -+ 1.09 -+ 1.80 - 1.76 --- 2.08

Total

Controls 88.43 84.51 83.70 86.70 94.82 81.32 82.24

78 - 1.10 -+ 1.20 -+ 2.00 -+ 2.00 -+ 2.31 -+- 3.33 -+ 3.60

Welders 63.45 67.50 84.70 69.40 73.25 61.55 69.65

Controls

57 + 1.65 -+ 2.85 + 2.70 --- 4.00 - 2.60 +- 4.31 -+ 3.91

131 88.31 +-- 2.31 83.43 - 1.70 82.39 +-- 1.10 84.30 --- 2.21 93.00 +-. 2.32 80.41 +- 3.49 81.69 - 3.14

found in the control group. Even the nonsmoking welders showed mean values of spirometric functions significantly more reduced than the ones observed in the nonsmoking controls. Thus the findings suggested that smoking had a deleterious effect on the pulmonary functions of the welders exposed to welding fumes and gases. A comparison of pulmonary abnormalities in smokers and the nonsmokers among the welders showed a prevalence of ventilatory impairment in the welders (28.0%) significantly higher than that observed in the controls (6.1%) (P < 0.001) (Table 4). The smoking welders showed significantly increased frequency of respiratory impairment in comparison to that noted in the nonsmoking welders (40.0% vs 18.7%) (P < 0.10). In fact, smoking and welding doubled the percentage of those having abnormal pulmonary function tests while there was less difference in the two groups who were nonsmokers. However, this difference could not be seen in the controls (9.4% vs 3.8%). The effect of age on the prevalence of respiratory impairment in the exposed and the control groups is shown in Table 5. In both the age groups (less than 35 and more than 35 years) the welders showed significantly higher prevalence of ventilatory impairment as compared with those observed in the respective age TABLE 4 PREVALENCE OF RESPIRATORY IMPAIRMENT IN WELDERS AND CONTROLS IN RELATION TO SMOKING HABITS

Smokers

Respiratory impairment

Nonsmokers

Total

Welders

Controls

Welders

Controls

Welders

Controls

n = 25

n = 53

n = 32

n = 78

n = 57

n = 131

N

%

N

%

N

%

N

%

N

%

N

%

Restrictive Obstructive

4

16.0

2

3.7

3

9.3

1

1.2

7

12.3

3

2.3

3

12.0

3

5.6

1

3.1

2

2.5

4

7.0

5

3.8

Mixed

3

12.0

--

--

2

6.2

--

--

5

8.7

--

--

Total

10

40.0*

5

9.4

6

18.7

3

3.8

16

28.0**

8

6.1

* P < 0.100. ** P < 0.001.

20

RASTOGI ET AL. TABLE 5 EFFECT OF AGE ON RESPIRATORY IMPAIRMENT IN CONTROLS AND WELDERS 35 years

435 years

Respiratory impairment Restrictive Obstructive Mixed Unadjusted rates Smoking adjusted standardized rates

Controls

Welders

Controls

Welders

n = 87

n = 29

n = 44

n = 28

N

%

N

%

N

%

N

2 3 --

2.2 3.4 --

2 2 2

6.89 6.89 6.89

1 2 --

2.2 4.5 --

5 2 3

5

5.7

6

3

6.8

10

20.7

5.80

Relative r i s k

20.5

% 17.8 7.14 10.7 35.7

6.6

36.0

3.53

5.45

groups in the controls (Smoking adjusted standardized rates: 5.80 and 20.5; 6.6 and 36.0). In the control group, the effect of age on the prevalence of respiratory impairment could not be found in the controls under 35 years and those more than 35 years of age showed similar values of respiratory impairment (5.7% and 6.8%). Although the welders over 35 years of age showed prevalence of respiratory impairment higher than that found in the younger welders (35.7% vs 20.7%), the difference was not statistically significant. The effect of exposure on the prevalence of respiratory abnormalities is shown in Table 6. The welders with more than 10 years of exposure to welding fumes showed risk of respiratory impairment more than three times greater than those exposed for less than I0 years (relative risk: 3.18) as indicated by the smoking adjusted standardized rates (13.5 and 43.0, respectively) in the two exposure groups, thereby suggesting significant contribution of period of exposure on respiratory impairment (P < 0.01). TABLE 6 EFFECT OF EXPOSURE ON RESPIRATORY IMPAIRMENT IN WELDERS

Respiratory impairment Restrictive Obstructive

N

< 1 0 years

> 10 years

Welders n = 30

Welders n = 27 %

N

%

2

6.6

5

Mixed

1 1

3.3 3.3

3 4

18.5 11.1 14.8

Unadjusted rates

4

13.3

12

44.4*

Smoking adjusted standardized rates Relative r i s k * P < 0.01.

43.0

13.5 3.18

21

SPIROMETRIC ABNORMALITIES

The severity of pulmonary impairment observed in the welders and the controls is shown in Table 7. The majority of the welders (17.5%) showed respiratory impairment of the mild category as a result of exposure to welding fumes and gases. The moderate degree of respiratory impairment was found in 8.7% of the welders while only 1.7% of the cases suffered from severe pulmonary impairment. In the case of the controls mild and moderate categories of respiratory impairment was observed (3.8 and 2.2%, respectively). The welders showed prevalence of mild respiratory impairment significantly higher than that found in the controls (17.5% vs 3.8%) (P < 0.005). The concentrations of various metals in the air samples in the welding process are shown in Table 8. The level of zinc ranged from 0.292 to 1.249 ~g/m3 air (mean value: 0.703 t~g/m3 air). The concentration of copper ranged from 0.027 to 0.894 ~g/m3 air (mean value: 0.355 tLg/m3 air). The concentration of other metals such as chromium (0.0086 i~g/m3 air) and manganese (0.0062 tLg/m3 air) were found to be quite low in the welding industries. DISCUSSION

The effect of welding fumes and gases on pulmonary function was examined through comparisons of the prevalence of respiratory abnormalities observed in the welders and unexposed controls. In accordance with most of the previous studies (Hunnicutt et al., 1964; Barhad et al., 1975; Antti-Poika et al., 1977; Oxhoj et al., 1979; Akbarkhanzadeh, 1980) we found prevalence of respiratory impairment in the welders significantly higher than that observed in the reference group. The welders showed predominantly restrictive pattern of pulmonary impairment followed by a mixed ventilatory defect while Akbarkhanzadeh (1980) observed that the inhaled fine particles of welding gases and fumes on gaining access to alveoli may cause inflammatory changes in the respiratory system and lead to functional disturbances particularly of the mixed ventilatory variety. Mur et al. (1985) reported that the pattern of respiratory function impairment suggested a predominant dysfunction of central airways, while peripheral airways remained unaffected on exposure to welding fumes. However, our findings disagree with some of the previous studies which reported similarity in the status of respiratory functions in the welders and the unexposed controls (Fogh et al., 1969; Kleinfeld et al., 1969; Schneider and Rebohle, 1981; Keimig et al., 1983; Flechsig, 1988). TABLE 7 SEVERITY OF RESPIRATORY IMPAIRMENT IN WELDERS AND CONTROLS Controls (n = 131)

Respiratory impairment

Mild

Moderate

Severe

Welders (n = 57) Total

Mild

Moderate

Severe

Total 7 4 5

Restrictive Obstructive Mixed

2 3

1.5 2.2

1 2

0.76 1.5

3 5

2.3 --

5 2 3

8.7 3.5 5.2

2 2 1

3.5 3.5 1.7

1

1.7

Total

5

3.8

3

2.2

8

6.1

10

17.5"

5

8.7

1

1.7

* P < 0.005.

12.3 7.0 8.7

16 28.0

22

RASTOGI ET AL. TABLE 8 METAL CONCENTRATION (b~g/m3) IN AIR SAMPLES IN THE WELDING PROCESS

Sample No.

Zn

Cu

Cr

Ni

Pb

Mn

1 2 3 4 5

1.249 0.292 0.466 0.756 0.752

O.172 0.058 0.027 0.894 0.624

0.008 0.009 0.015 0.009 0.002

0.032 0.002 0.002 0.018 0.005

0.091 0.008 0.024 0.014 0.024

0.018 0.002 0.005 0.003 0.003

Mean Range

0.703 (0.292-1.249)

0.355 (0.027-0.894)

0.008 (0.002-0.015)

0.011

(0.002-0.018)

0.032 (0.008-0.014)

0.006 (0.002-0.018)

It has been reported that the effect of welding fumes and gases on respiratory functions depends upon the welding conditions such as the parent metal added, type of welding, adding metal, welding process, open or closed space welding, and on the length of exposure, smoking habits (interaction between welding and smoking), and genetic factors in the welders population (Hunnicutt et al., 1964; Cotes and Hall, 1970; Keskinen et al., 1980). The welders in the present study welded joint faces of the moulded brass materials with the help of gas welding. The welding operation was performed by welders manually in poorly ventilated and congested sheds in the forward bending position with their faces near welding operation. Thus it is observed that the respiratory system in the welders is very commonly affected possibly because of their posture and nearness to the vapors and fumes and gases, which chronically inhaled give rise to respiratory symptoms and functional abnormalities especially if no mask or respirator is used, as is the case in the brassware industries. Manual welding is still practiced in most of the household industries in India unlike other foreign countries where it is replaced by semiautomatic or automatic procedures. It has been reported that the manual welders compared to semiautomatic welders had more frequent recurrent respiratory infections, chronic bronchitis, and respiratory impairment due to great exposure to the welding fumes (Mur et al., 1985). Smoking is known to influence the lung function; in welders, smoking was either considered to mask the influence of occupational exposure (Keimig et al., 1983) or to strengthen it (Hunnicutt et al., 1964; Akbarkhanzadeh, 1980; and Zober, 1982). Our findings support the views of Hunnicutt et al. (1964), Akbarkhanzadeh (1980), and Zober 0982) as the smoking welders showed prevalence of respiratory impairment significantly higher than that observed in the nonsmoking welders. A similar trend was also observed in the control group thereby indicating that smoking had a deteriorating effect on spirometric abnormalities. A possible synergistic effect of smoking and welding exposure was considered by Hunnicutt et al. 0964), Fogh et al. (1969), and Zober (1982). Our study also showed a dose response relationship between the length of exposure and the prevalence of respiratory impairment as the welders with more than 10 years of exposure to welding fumes showed prevalence of respiratory impairment significantly higher than for those exposed for less than 10 years, thereby confirming the earlier reports (Kleinfeld et al., 1969 and Zober, 1982). However, McMillan and Heath (1979) failed to demonstrate any relation between

SPIROMETRIC ABNORMALITIES

23

length of exposure and respiratory disturbance. The study also indicated that most of the welders exposed to welding fumes and gases exhibited only the mild category of functional disturbances which may be attributed to low concentrations of metals such as zinc, copper, chromium, nickel, lead, and manganese in the air samples collected from the work environment where the welding was performed. CONCLUSION

This comparative study of spirometric measurements in welders and nonwelders showed that the welders presented a significantly higher incidence of ventilatory impairment. Welders who smoked had an increased prevalence of abnormal pulmonary function tests, two to one greater than their nonsmoking counterparts. In fact, smoking and welding doubled the percentage of those having pulmonary abnormalities. This shows that the cigarette smoking and welding fumes had a cumulative effect on the pulmonary function. In view of the apparent cumulative effects of cigarette smoking and welding fumes, it appears that a strong effort should be made to persuade welders to stop smoking. The welders primarily suffered from restrictive type of ventilatory disorder. A dose-response relationship between the length of exposure and the prevalence of ventilatory abnormalities was observed in the present study. REFERENCES Akbarkhanzadeh, F. (1980). Long term effects of welding fumes upon respiratory symptoms and pulmonary function. J. Occup. Med. 22, 337-341. American Thoracic Society Statement (1979). Snowbird workshop on standardization of spirometry. Am. Rev. Respir. Dis. 119, 831-838. Antti-Poika, M., Hassi, J., and Pyyl, L. (1977). Respiratory diseases in arc welders. Arch. Occup. Environ. Health 40, 225-230. Armitage, P. (1971). "Statistical Methods in Medical Research." Blackwell, Oxford. Barhad, B., Teculescu, D., and Gracium, O. (1975). Respiratory symptoms, chronic bronchitis and ventilatory function in shipyard welders. Int. Arch. Occup. Environ. Hlth. 36, 137-150. Conrad, S. A., et al., Eds. (1983). "Pulmonary Function Testing: Principles and Practice," llth Ed. Churchill, 1984. Cotes, J. E., and Hall, A. M. (1970). The transfer factor for the lung: Normal values in adults. In "Introduction to the Definition as Normal Values for Respiratory Function in Men" (P. Arcangeli, J. E. Cotes, A. Cournand, H. Denolin, G. Dimaria, P. Sadoul, M. Scherrer, and G. L. Scarpe, Eds.). Panminerva Medica, pp. 327-343. Cotes, J. E. (1979). "Lung Function: Assessment and Application in Medicine," 4th ed. Blackwell, Oxford. Flechsig, R. (1988). What do we know today about welding fume effects on the respiratory system? Ind. Health 26, 93-100. Fogh, A., Frost, J., and Georg, J. (1969). Respiratory symptoms and pulmonary function in welders. Ann. Occup. Hyg. 12, 213-218. Hunnicutt, T. N., Cracovaner, D. J., and Myles, J. T. (1964). Spirometric measurement in welders. Arch. Environ. Health 8, 661-669. Keimig, D. G., Pomrehn, P. R., and Burmeister, L. F. (1983). Respiratory symptoms and pulmonary function in welders of mild steel: A cross sectional study. Am. J. Ind. Med. 4, 489-499. Keskinen, H., Kalliomaki, P. L., and Alanico, K. (1980). Occupational asthma due to stainless steel welding fumes. Clin. Allergy. 10, 151-159. Kleinfeld, M., Messite, J., Kooyman, O., and Shapiro, J. (1969). Welders siderosis. Arch. Environ. Health 19, 70-73.

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RASTOGI ET AL.

Mantel, N., and Haenszel, W. (1959). Statistical aspects of the analysis of the data from retrospective studies of disease. J. Nat. Cancer. Inst. 22, 719-748. McMillan, G. H., and Heath, Y. (1979). The health of welders in naval dockyard: Acute changes in respiratory function during standardized welding. Ann. Occup. Med. 31, 43-60. Miller, W. F., Wu, N., and Johnson, P. L. (1956). Miller's prediction quadrant. Anesthesiology 17, 480-493. Mur, J. M., Teculescu, D., Pham, Q. T., Gaertner, M., Massin, N., Meyerbisch, C., Moulin, N., Diebold, F., Pierre, F., Meurouponcelet, B., Muller, J., Henquel, J. C., Boudin, V., Betz, M., and Toamain, J. P. (1985). Lung function and clinical findings in a cross sectional study of arc welders. Int. Arch. Occup. Environ. Health 57, 1-17. Oxhoj, H., Baked, B., Wedel, H., and Wilhelmsen, L. (1979). Effects of electric arc welding on ventilatory lung function. Arch. Environ. Health 34, 211-217. Peters, H., Murphy, R. L. H., Ferris, B. G., Burgess, W. A., Ranadive, M. V., and Pedergrass, H. P. (1973). Pulmonary function in shipyard welders. Arch. Environ. Health 26, 28-31. Rastogi, S. K., Mathur, N., and Clerk, S. H. (1983). Ventilatory norms in healthy industrial male workers. Ind. J. Chest. Dis. Allied Sci. 25, 186-195. Ross, D. S. (1978). Welders health. The respiratory system and welding. Met. Constr. 119-121. Schneider, W. D., and Rebohle, E. (1981). Zur fruhdiagnostik mittles FluB-Volumen-kurve bei inhalativ exponierten Werktatigen. Z. Erkr. Atmorg. 157, 291-296~ Zober, A. (1982). "Arbeitsmedizinische untersuchungen zur inhalativen Belastung von LichtbogenSchmelzschweissern. Forschungsbericht Nr. 317." Bundesanstalt fur Arbeitsschutz and Unfalltorschung, Verlag fur neue Wissenschaft, Bremerhaven.