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Workplace
Original article
Short-term lung function decline in tunnel construction workers
  1. Bente Ulvestad1,
  2. May Brit Lund2,
  3. Berit Bakke1,
  4. Yngvar Thomassen1,
  5. Dag G Ellingsen1
  1. 1National Institute of Occupational Health, Oslo, Norway
  2. 2Department of Respiratory Medicine, Oslo University Hospital, Oslo, Norway
  1. Correspondence to Dr Bente Ulvestad, National Institute of Occupational Health, P.O. Box 8149 Dep, Oslo N-0033, Norway; bente.ulvestad{at}stami.no

Abstract

Objectives Tunnel construction workers are exposed to particulate and gaseous air contaminants. Previous studies carried out in the 1990s showed that tunnel construction workers were at increased risk of both short-term and long-term lung function decline. Since then, efforts have been made to reduce exposure. The objective of the present study was to investigate if current exposure may still cause short-term lung function impairment.

Methods Tunnel workers work 12 days consecutively, and then they are off for 9 days. Ninety tunnel workers and 51 referents were examined with spirometry and questionnaires before their work period started and again 11 days later. Personal exposure to particles and α-quartz in the thoracic aerosol subfraction, elemental carbon and organic carbon, oil mist, nitrogen dioxide and ammonia was assessed on two consecutive days between the two health examinations.

Results The geometric means air concentrations for particulate matter in the thoracic mass aerosol subfraction, α-quartz, oil mist, organic carbon and elemental carbon for all workers were 561, 63, 210, 146 and 35 μg/m3, respectively. After 11 days of work, the mean forced expiratory volume in 1 s (FEV1) in healthy participants had declined 73 mL (SD 173), p<0.001 in the tunnel workers, compared to 3 mL (SD 21), p=0.9 in the referents. Also, forced vital capacity (FVC) had declined significantly. Declines in FVC and FEV1 were significantly associated with exposure to organic carbon.

Conclusions In spite of reduced levels of exposure in modern tunnelling operations, a negative impact on lung function was still observed.

https://doi.org/10.1136/oemed-2014-102262

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    What this paper adds

    • Previous studies showed that tunnel construction workers were at increased risk of lung function decline and chronic obstructive pulmonary disease.

    • In recent years, efforts have been made to reduce occupational dust and gas exposure.

    • We aimed to find out whether current exposure in modern tunnel construction still remains a cause of decline in lung function.

    • We found that although overall exposure levels for many contaminants have been reduced, the air exposure in current tunnel work still appears to have a detrimental impact on lung function.

    • Better technical solutions to prevent exposure are called for.

    Respiratory diseases are frequent in tunnel construction workers.1 Work environment in tunnel construction was extensively studied in the 1990s, and it is well known that tunnel workers are exposed to both particulate and gaseous air contaminants. Previous studies revealed that tunnel workers were at increased risk of long-term and short-term lung function decline and chronic obstructive pulmonary disease (COPD).2–8 Cumulative exposure to nitrogen dioxide (NO2) showed the strongest association with a decrease in forced expiratory volume in 1 s (FEV1).8

    Since heavier wheel-going diesel machines were introduced in mines and tunnels, exposure to gases and particles from diesel emissions has been considered to be among the dominating burdens in these industries.9 ,10 Exposure to diesel exhaust has been reported to cause airways obstruction.11 ,12

    Since the 1990s, efforts have been made to reduce occupational dust and gas exposure in tunnel construction work. For example, ventilation during tunnel construction has been improved, the introduction of a new type of explosive has almost eliminated NO2 as an exposure factor,5 and diesel-powered machines are mostly equipped with particle filters. Exposure to diesel exhaust particles in tunnel construction, measured as elemental carbon (EC), appears to have decreased significantly during the past decade.13

    During drilling and blasting operations, workers in tunnel construction, like in mining, will be exposed to dust. The content of α-quartz in the dust from tunnels varies between <1% and more than 50% (Norwegian Tunnelling Society, Publication No.13). Epidemiological and pathological studies suggest that α-quartz exposure may lead to COPD, even in workers with normal chest radiographs.14–17

    Exposure to oil mist and oil vapour may occur during drilling. In tunnel construction, it has been speculated that more effective drilling equipment may produce more oil mist per time unit. Exposure to oil mist may cause occupational asthma and also pulmonary fibrosis.18 ,19

    Over the years, tunnel construction work has become increasingly more mechanised, and demands for reducing construction time have resulted in increased production intensity. The mechanised methods and higher production rates may introduce new hazards to the workers. The aim of this investigation was to study whether current exposure in modern tunnel construction still remains a cause of decline in lung function.

    Methods

    The tunnel workers recruited for the study work 12 days consecutively, and then they are off work for 9 days. A normal work shift lasts 10–12 h. The typical tunnel worker is multiskilled. The crews are organised as autonomous work groups, led by qualified shift leaders. Despite the ever-changing nature of tunnel construction work, similar tasks are performed successively by the workers, from one construction site to the next. However, the exposures of the workers may vary because of the location of the sites, type of project and environmental conditions.

    Study population and design

    All tunnel workers (N=92) and tunnel administrative personnel (N=52 referents) employed by three different construction companies and currently working at 11 consecutively available tunnel construction sites were invited to participate in the study. The reference group consisted mainly of shift leaders performing guidance and inspection work. Seventeen of the shift leaders were former tunnel workers.

    The investigation was designed as an 11-day follow-up study. The work period starts with six consecutive night shifts, from 18:00 to 4:00. All medical tests were performed shortly before the work shift, between 16:00 and 18:00, on the first day back on site after 9 days off work. After 11 days of work, the participants were re-examined at the end of a day shift, and at the same time of day. Ninety tunnel workers and 51 referents agreed to participate. The study was performed during wintery conditions.

    Informed written consent was obtained from all participants. Participation in the study was voluntary. The study was approved by the Norwegian Regional Medical Committee for Medical Research (REK2).

    Occupational exposure

    The air contaminants that were measured were particles in the thoracic aerosol fraction, α-quartz, EC and organic carbon (OC), oil mist, oil vapour, ammonia (NH3) and NO2. Job groups included in this study were drill and blast workers, drill and blast mechanics, loaders, support workers, injection workers, shotcreters and shaft drillers. Personal air measurements were carried out on two consecutive working days between the two health examinations. Sampling of oil mist and oil vapour was restricted to a 2 h sampling period with a flow rate of 1.4 L/min to prevent evaporation of oil mist from the filter. Also, the oil mist measurements were targeted to measure air concentrations of expected high-exposed work tasks (eg, rock drilling) to capture exposure from lubricating oil, and was not measured in all the tunnel workers. The air sampling methods and results of the exposure assessment are presented elsewhere.13

    Spirometry

    Spirometry was performed according to the American Thoracic Society (ATS)/European Respiratory Society (ERS) guidelines.20 All participants are experienced in performing spirometry from previous annual health examinations carried out by the occupational health services (OHS). All pulmonary function tests were performed by the same well-trained technician, regardless of the tunnel construction company or tunnel site. The same daily calibrated spirometer was used for all testing.

    The following parameters were recorded: forced vital capacity (FVC), FEV1, and forced expiratory flow rate at 50% (FEF50) of the FVC. The lung function parameters were expressed in absolute values and as the percentage of the predicted values according to the published reference values for Europeans.21 The medical examinations were carried out at the respective worksites.

    Questionnaire

    Background data were recorded using a questionnaire applied in an earlier study.22 Questions were included on respiratory symptoms, allergy, physician diagnosed asthma and self-reported symptoms of cold at one of the two examinations. Participants were classified as never smokers, former smokers and current smokers. Former smokers were defined as those who had stopped smoking more than 12 months earlier.

    Statistical analysis

    Distribution of all continuous variables was assessed, and when skewness exceeded 2.0, the variable was ln-transformed to achieve normal distribution. The geometric means (GM) are presented for these variables; otherwise, the arithmetic mean (AM) values are presented. Demographic data were summarised using AM and range for continuous data and prevalence of categorical data. The relationships between respiratory symptoms (yes/no), smoking status (ever/never) and years employed as a tunnel construction worker (<10, 10–20 and >20 years) were investigated using logistic regression. Independent samples t tests and one-way analysis of variance were used to compare groups. The differences in lung function (ΔFVC, ΔFEV1, ΔFEF50) between the start of the working period (after 9 days off work) and towards the end of the working period (after 11 days of work) were evaluated using paired t tests. Multiple linear regression analysis (backwards procedure) was used to assess statistical associations between outcome variables and several independent variables simultaneously. Statistical analyses were carried out with SPSS V.21.0 (SPSS Inc, Chicago, Illinois, USA).

    Results

    Air measurements

    Results from the exposure assessment have been extensively described and discussed elsewhere.13 A total of 90 tunnel workers carried personal sampling equipment on two consecutive days between the two health examinations. Only the shotcreting operators used disposable half-masks with filters for particles (3M) during most of the sampling time.

    Exposure data assessed by personal sampling on two consecutive days are shown in table 1. The GM air concentration for oil mist was 210 μg/m3. Statistical differences of air concentrations between job groups were observed for all contaminants, except for OC, EC and NH3 (p>0.05). Air concentrations of OC were moderately correlated with air concentrations of oil mist (rSpearman=0.56 (p<0.0001)). Overall, the exposure to NO2 and NH3 was low (GM=120 and 251 μg/m3, respectively).

    View this table:
    Table 1

    Background and exposure data among 90 tunnel workers and 51 referents

    Characteristics of the study population

    The tunnel workers were slightly younger than the referents, had a lower BMI, and included more current smokers among them (table 1). The prevalence of ‘wheezing in the chest’ was higher in the tunnel workers than in the referents, but did not differ with respect to other reported subjective airways symptoms (ie, morning cough, cough during the day, shortness of breath on exercise). Table 2 summarises ORs describing the associations between the symptom ‘wheezing in the chest’ and years of exposure in tunnel work, and smoking habits. This airways symptom seems to be associated both with exposure in tunnel construction work and smoking habits.

    View this table:
    Table 2

    Determinants of the airways symptom ‘wheezing in the chest’

    Lung function

    Eighty-eight tunnel workers and 50 referents achieved the ATS/ERS criteria at both examinations. All lung function parameters were normally distributed, including the lung function changes. Skewness was near to zero. There were no statistically significant differences between the tunnel workers and the referents at baseline for any of the lung function parameters (table 3). There were no differences in the individual Tiffeneau index (FEV1/FVC) between the tunnel workers and the reference group (79.3 (range 47.9–91.1) vs 78.2 (range 62.0–91.1)). In never smokers, however, the individual Tiffeneau index (FEV1/FVC) in ‘ever tunnel workers’ was 79.0 (range (65.3–91.1) vs 81.7 (range 67.6–89.7) in never tunnel workers, and the Tiffeneau index was associated with years of tunnel work (p=0.008).

    View this table:
    Table 3

    Lung function (SD) in tunnel workers and referents before the start of the working period

    The reference group, however, included 16 former tunnel workers who had significantly lower lung function values than both the active tunnel workers (p<0.01) and the referents who had never worked in tunnels (p<0.01). There was a statistically significant difference in FEV1 per cent of predicted between ‘never tunnel construction workers’ (N=33) and ‘ever tunnel construction workers’ (99.9% (SD 11.5) vs 94.6% (SD 13.3); p=0.03). When including potential confounders (BMI, smoking habits, and self-reported infection or illness) in a multiple linear regression model, the analyses indicated that FEV1 per cent of predicted was negatively associated with BMI, physician diagnosed asthma and years of tunnel work (FEV1%=115–0.24 tunnel years (p=0.02) −0.6 BMI (p=0.047) −10 asthma (p=0.007)).

    Changes in lung function at follow-up

    The differences in lung function between baseline and 11 days of follow-up are shown in table 4. At the end of the work period, FEV1 was 51 mL (p=0.01) lower in the tunnel workers, in contrast to 6 mL (p=0.9) lower in the referents. Ten tunnel workers and seven referents reported having a cold at one of the examinations. In the tunnel workers (n=79) who did not report colds, FVC declined 69 mL (p=0.004) and FEV1 73 mL (p<0.001). The absolute changes in lung function parameters in the tunnel workers compared with the changes in the referents were found to be significant for FVC (p=0.03) and FEV1 (p=0.046).

    View this table:
    Table 4

    Lung function changes after 11 days of work in all participants, and in participants who did not report having a cold at any of the examinations

    Within the reference group, there were no statistically significant differences in FVC or FEV1 changes between former tunnel workers and never tunnel workers. There were no significant differences in FVC or FEV1 decline between current smoking and non-smoking tunnel workers. Participants reporting ‘wheezing in the chest during the past year’ had a significantly (p=0.02) larger decline in FEV1 than those who did not report this symptom (65 mL (SD 167) vs 24 mL (SD 206). No statistically significant differences in lung function changes were observed between different tunnel job groups (not shown).

    In the final multiple regression model, current smoking, current asthma medication, having a cold at any of the examinations, exposure to thoracic dust, α-quartz, EC and OC were included. Only OC had a significant impact on the model. The declines in FVC and FEV1 in currently exposed tunnel workers were associated with the air concentrations of OC; ΔFVC: lnOC=−0.150 (95% CI −0.233 to −0.062), p=0.001 and ΔFEV1: lnOC=−0.085 (95% CI −0.164 to—0.007), p=0.034. No association was shown with any of the other exposure variables (p>0.15).

    Discussion

    This investigation was designed as a follow-up study of 90 tunnel workers and 51 referents before and at the end of a 12-day work period. Lung function declined significantly in the tunnel workers, but not in the referents during this time period. When excluding participants who reported having a cold at any of the examinations, the decline was even more pronounced. Reporting the symptom ‘wheezing in the chest’ was identified as a risk factor for lung function decline. The decline in FVC and FEV1 was significantly associated with exposure to OC. The decline in FEF50 was not associated with any of the exposure variables. FEV1 per cent of the predicted registered at the first examination was negatively associated with physician diagnosed asthma and years of tunnel work.

    Seventeen of the 51 referents were former tunnel workers who now worked as supervisors and were rarely or no longer exposed to underground pollution. Their lung function changes during follow-up did not differ from the changes in the other referents. Since the current investigation was a study of short-term effects, these supervisors were considered suitable as referents, although their lung function was lower at baseline.

    The two health examinations were carried out at the same time of the day in order to avoid diurnal variations in lung function. Reversibility after a new period off work was not examined. We can therefore only speculate that lung function returns to baseline levels, as shown in a previous study of tunnel workers.5 It is not known whether the temporary lung function changes observed in the tunnel workers will lead to chronic changes. It is, however, well documented that exposure causing temporary lung function decline may be associated with airway inflammation, which in turn may induce accelerated lung function decline and chronic changes.23–25 The finding of lower lung function in the former tunnel workers (shift leaders) may be indicative of such a development over time.

    Overall, the air concentrations of most of the compounds determined in this study have decreased when compared to measurements 10–15 years ago.3 It is, however, interesting that the current oil mist exposure is almost two times higher than in the previous study (210 vs 120 μg/m3). The data indicate that the decline in lung function is associated with oil mist exposure. To what extent the remaining types of exposure may have contributed to the lung function decline remains to be elucidated. It could be that exposure to other air contaminants have been too low to induce effects.

    Oil mist at the tunnel face is generated when lubricating oil is emitted from the drilling equipment into the working atmosphere. The oil mist measurements were targeted to measure air concentrations of expected high-exposed work tasks (eg, rock or shaft drilling) to capture exposure from lubricating oil, and was not measured in all the tunnel workers. The GM air concentration of oil mist in this study varied between <0.05 and 9.1 mg/m3.13

    The highest air concentrations were measured during shaft drilling (GM=9.1 mg/m3), but significant concentrations were also measured among drill and blast workers and drill and blast mechanics. There was a positive correlation between air concentrations of OC and oil mist, and OC may therefore partly be an expression of exposure to oil mist in tunnelling. Sampling of oil mist was restricted to a 2 h sampling period to prevent evaporation of oil mist from the filter, whereas measurements of OC were conducted throughout the work shift. The air concentration of OC may therefore be an indicator of oil mist concentrations when these types of oils of low volatility are used.

    There are few reports18 ,26–28 on lung function in workers exposed to oil mist. Machine workers exposed to an average of 0.33 mg/m3 of oil mist in car production had no restrictive or obstructive lung function impairments, but they reported more respiratory symptoms than the referents.26 In another study from car production, an increased prevalence of self-reported respiratory symptoms was reported, which was connected to the use of mineral oil-based products.27 The research group reported no untoward pulmonary effects caused by ongoing exposure, but an association between past exposures to mineral oil-based mist and reduced FVC was reported.28 Cable plant workers exposed to time-weighted average levels of 0.15–0.30 mg/m3 oil mist had a moderately decreased vital capacity and FEV1.18 These studies suggest that exposure to oil mist in humans may cause both restrictive and obstructive patterns in lung function.

    Particles are generated by drilling, blasting, crushing, grinding, shotcreting and transport operations. In this study, we found that the GM air concentration of particles in the thoracic aerosol fraction was 0.56 mg/m3. The thoracic aerosol fraction was measured because it is considered the most relevant fraction with regard to studying respiratory effects.13 In our previous studies of tunnel construction workers, the GM concentrations of particles were 2.3 mg/m3 in the ‘total’ aerosol fraction and 0.91 mg/m3 in the respirable fraction.2 This suggests that exposure to dust is lower today than what it was 10–15 years ago.

    α-Quartz was measured in the thoracic aerosol subfraction and cannot be directly compared to previous measurements in the respirable aerosol subfraction. The main exposure to α-quartz in tunnelling occurs during rock drilling and blasting. α-Quartz is one important occupational respiratory toxin, and exposure to α-quartz may cause lung function decline and COPD.14–17

    The particulate fraction of diesel exhaust is dominated by solid carbon particles (EC), and EC has been proposed to be the most relevant measure of the particle phase of diesel exhaust.29 The overall GM air concentration of EC varied from 31 to 54 μg/m3 for all job groups.13 Exposure to diesel exhaust has been shown to cause respiratory symptoms in experimental studies.30–33 The exposure to diesel exhaust monitored by EC was considerably lower when compared to the EC exposure described previously in studies of tunnel construction workers in Norway2 and other studies from mines and underground construction work (range 27–658 μg/m3).34 Substantial epidemiological studies have demonstrated that daily exposure to particulate matter may cause acute respiratory effects.35 The small size of diesel exhaust particles favours their penetration into the lung.36 Chronic exposure to diesel exhaust may induce decrements in pulmonary function.12

    The main sources of NO2 in tunnel work are blasting fumes and exhaust from diesel powered machines. The amount of gases released after blasting depends on the type of explosive used.5 In this study, size-sensitised emulsion (SSE; Dyno Nobel Europe, Norway) was the explosive of choice in all 11 tunnels. The use of SSE is known to produce less amounts of NO2, and this may explain the reduced air concentrations compared to previous findings, where ammonium nitrate fuel oil (ANFO; Dyno Nobel Europe, Norway) was the explosive of choice.5

    In an earlier study, we investigated short-term lung function changes in tunnel workers exposed to two different explosives—ANFO and SSE.5 ANFO was back then the regular explosive of choice. The tunnel workers using ANFO had a mean temporary decline in FEV1 of 270 mL after 11 days of work, whereas those using SSE had no significant changes. Repeated peak exposures to NO2 appeared to be the most likely explanation. Therefore, in this study, it was surprising to find lung function decline (the mean decline in FEV1 was 73 mL) since SSE was the only explosive in use. We have no explanation why no lung function decline was found in the SSE group studied in the 1990s. Altogether, one may consider a decline in FEV1 of 73 vs 270 mL after 11 days of work as an improvement.

    Several factors may bias the validity of the observed relationship between exposure in tunnel work and decline in lung function. The exposure itself often leads to health-selective turnover in the sense that the most affected individuals tend to quit the job while those more resistant to exposure will remain (healthy worker effect). This will inevitably lead to an underestimation of work-related symptoms and disease. In this study, some subjects with pronounced airways symptoms and decline in lung function had left the blue collar workforce and become administrative personnel. This may explain the differences in lung health within the reference group, and, if anything, our data underestimate the risk among the active tunnel workers. Only two subjects (one tunnel worker and one shift leader) declined to participate in the study, so volunteer bias has hardly occurred.

    We can conclude from this study that although the overall exposure levels for many of the contaminants have been reduced, the air exposure in current tunnel work still appears to have a detrimental impact on lung function. We can only speculate that repeated, short-term loss of lung function, probably due to inflammation caused by exposure, may be linked to the risk of developing chronic lung function decline.

    Acknowledgments

    The tunnel workers and their administrative personnel are acknowledged for participating in the study. The authors highly appreciate the co-operation within the occupational health services of the participating companies.

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    Footnotes

    • Contributors All authors contributed to the preparation of the protocol. BU has examined the tunnel workers and collected the air samples. She also analysed the data and has been the principal author of the article. BB and YT have been responsible for the analysis of the air samples. They have also contributed to the writing of the article. DGE and MBL have both served as mentors and have contributed in the writing process.

    • Funding The project received financial support from the Statoil Working Environment Fund and from The Fund for Regional Delegate for the Construction Industry in Norway.

    • Competing interests None.

    • Patient consent Obtained.

    • Ethics approval The Norwegian Regional Medical Committee for Medical Research (REK2).

    • Provenance and peer review Not commissioned; externally peer reviewed.