Workers exposed to welding fumes are more likely to develop lung cancer than those not exposed to the fumes, and the new study published in the BMJ Occupational and Environmental Medicine suggests this holds true regardless of other risk factors like smoking or exposure to asbestos. This research will likely result in an increase of workers’ compensation claims for lung cancer by employees in this industry.

“Welding fumes have previously been classified as ‘possibly carcinogenic’ to people,” said Dr. Denitza Blagev, a researcher at the University of Utah and Intermountain Medical Center in Murray, Utah.

“Although welders have been observed to experience higher lung cancer rates, there are many other factors – including smoking, asbestos and other carcinogen exposures – that were likely contributing to that increased risk,’ Blagev, who wasn’t involved in the study, said by email according to the summary reported in Reuters Health.

For the current analysis, researchers examined data from 45 previously published studies with a total of roughly 17 million participants. Overall, people who worked as welders or had exposure to welding fumes were 43 percent more likely to develop lung cancer.

When researchers looked only at data from studies that accounted for both smoking and asbestos exposure, welding was still associated with a 17 percent higher risk of lung cancer.

“It is now clear that the increased lung cancer risk in welders is not fully explained by these other factors,” Blagev said by email. “And with this review, welding fumes can be classified as ‘carcinogenic’ to humans.”

Worldwide, an estimated 110 million workers are exposed to welding fumes either as welders or as bystanders, Dr. Neela Guha of the California Environmental Protection Agency and colleagues note in Occupational & Environmental Medicine.

Welding fumes are generated when metals are heated above their melting point and then vaporize and condense into very fine solid particles in the air. The exact blend of chemicals in these vapors can depend on the type of metals involved, the welding process, and the occupational setting where the work is performed.

For example, nickel compounds and chromium are both known to cause lung cancer and are typically present in fumes when workers weld stainless steel, the study team writes. These metals are in much lower concentrations in other types of steel, which tend to produce fumes with more fine particulate matter – tiny solid and liquid bits of soot, dust and chemicals that can damage the lungs.

“The process can take decades of exposure,” said Paul Cullinan, an occupational and environmental health researcher at Royal Brompton Hospital and Imperial College London in the UK.