Since 1990, welding fumes have been classified as “possibly carcinogenic,” or cancer-causing. However, although it’s true that people exposed to welding fumes have higher rates of lung cancer, they’re often exposed to other carcinogens and asbestos, and it hasn’t been clear how much smoking contributes to the risk.

Recently, however, an international group of researchers performed a meta-analysis of 45 existing studies involving approximately 17 million participants. They found that welding fumes increase a person’s lung cancer risk by 43%. And, when they considered only those studies involving welding fumes, asbestos and smoking, the fumes were still associated with an increased lung cancer risk of 17%

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

Indeed, in 2017, welding fumes were reclassified as “carcinogenic to humans” as a result of the studies included in this meta-analysis.

What are welding fumes and who can be exposed?

During welding, metal is heated above its melting point. This vaporization results in microparticles of metal and soot being formed in the air. What, exactly, is in those fumes depends on what metals are involved, what welding process is used, and the occupational setting.

For example, chromium and nickel compounds are both known causes of lung cancer. They’re also known to be present in the fumes when someone is welding stainless steel. Other types of steel aren’t much safer, even though they don’t produce chromium or nickel compounds. Instead, the fumes from other types of steel contain more fine particles of soot, dust and chemicals that can become embedded in the lungs.

According to the researchers, some 110 million welders and bystanders are exposed to welding fumes.

Still unknown from the study: techniques and timing

Are some welding processes more dangerous than others? To limit the risk of lung cancer, does it matter if you’re a gas metal arc welder or a gas tungsten arc welder, for example? The meta-analysis does not come to any conclusions. It’s also not clear how much exposure to welding fumes would be required to increase your cancer risk, or for how long. However, it is likely the process takes decades.

Reducing the risk to workers

A British occupational and environmental health researcher interviewed by Reuters said the risk of lung cancer should encourage workplaces to reduce exposure to welding fumes, especially in high quantities.

“The best way to do this is through the use of local ‘exhaust’ ventilation which carries the fume away from the worker’s breathing zone,” he explained. “Second best is the use of protective masks.”

If you are exposed to welding fumes and develop lung cancer, you should be eligible for a workers’ compensation claim. However, because cancer is caused by many factors, your employer may dispute that it was caused by exposure to welding fumes. Working with an experienced workers’ compensation attorney can help by ensuring all relevant medical records and other evidence are considered.