Absence of conflict of interest.
Citation
Highlights
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The study examined the impact of a ban on spray-on asbestos materials, implemented under the National Emission Standards for Hazardous Air Pollutants (NESHAP), on health and safety outcomes for sheet metal workers, a construction trade with recognized historical exposure to asbestos.
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Using data collected by the Sheet Metal Occupational Health Institute Trust (SMOHIT), the authors used a nonexperimental design to compare respiratory health outcomes across cohorts of sheet metal workers who entered the trade before and after 1973, when the NESHAP ban on asbestos materials in spray-on products went into effect.
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The study suggested that sheet metal workers who entered the trade before the NESHAP ban went into effect were more likely to display chest radiograph abnormalities indicative of parenchymal disease or pleural disease, compared to sheet metal workers who entered the trade after the NESHAP ban went into effect.
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The quality of causal evidence presented in this study is low, because the authors did not include sufficient controls in their statistical analysis to adjust for possible differences in the composition of the treatment and comparison groups. This means we are not confident that the estimated effects are attributable to NESHAP’s ban on asbestos materials in spray-on products; other factors are likely to have contributed.
Intervention Examined
National Emission Standards for Hazardous Air Pollutants (NESHAP)
Features of the Intervention
In 1973, the U.S. Environmental Protection Agency (EPA) established the National Emission Standards for Hazardous Air Pollutants (NESHAP). NESHAP regulations included a ban on the use of asbestos material in spray-on products.
Features of the Study
The study used a nonexperimental design to evaluate the impact of the NESHAP ban on asbestos materials in spray on products on health outcomes for sheet metal workers, a construction trade with recognized exposure to asbestos. The study relied on data from SMOHIT, a medical program that since 1981 has offered chest screening exams to sheet metal workers in the United States and Canada. Chest screenings are conducted every 3 to 5 years at local unions. To be eligible for a chest screening, a sheet metal worker must have been employed in the trade for at least twenty years. This study used SMOHIT screening data from the period 1986 to 2016, with a study sample of 26,397 male sheet metal workers. Within the sample, 3,920 workers began work after 1973, when the NESHAP ban went into effect.
To conduct their analysis, the study authors divided sheet metal workers into three cohorts, based on the year that they entered the trade. The authors use a statistical analysis to compare the incidence of respiratory illness (parenchymal disease and pleural disease) among sheet metal workers who entered the trade after 1973 (when the NESHAP ban went into effect) to the incidence of respiratory illness among sheet metal workers who entered the trade prior to 1950, and those who entered the trade between 1950 and 1973. The analysis includes additional controls for worker age, years worked in the sheet metal trade, and smoking history.
Findings
Health and Safety
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The study suggested that the prevalence of respiratory disease was higher among sheet metal workers who entered the trade prior to the implementation of the NESHAP ban, compared to sheet metal workers who entered the trade after the NESHAP ban went into effect.
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The prevalence of parenchymal disease was 17.4 percent for sheet metal workers who started work prior to 1950, compared to 0.8 percent for those who started work after 1973.
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The prevalence of pleural disease was 35.4 percent for sheet metal workers who started work prior to 1950, compared to 1.7percent after 1973.
Considerations for Interpreting the Findings
This study used a nonexperimental design to estimate the impact of the NESHAP ban on asbestos materials on respiratory health outcomes for sheet metal works. The analysis included controls for three additional risk factors: worker age, years worked in sheet metal, and smoking history. Given the limited number risk factors included in the study’s models, estimates of the impact of the NESHAP ban may not be accurate. The authors also note several other workplace health and safety measures implemented during the same period, such as a 1978 ban on asbestos in pipe coverings as well as progressive reductions in permissible asbestos exposure limits set by the Occupational Safety and Health Administration (OSHA). These other policy measures may also have contributed to the study’s findings.
Causal Evidence Rating
The quality of causal evidence presented in this study is low because the authors did not include sufficient controls in their statistical analysis to adjust for possible differences in the composition of the treatment and comparison groups. This means we are not confident that the estimated effects are attributable to NESHAP’s ban on asbestos materials in spray-on products; other factors are likely to have contributed.