Four Alaska Airlines flight attendants have filed a lawsuit against Boeing in which they claim that toxic cabin fumes caused them to vomit or pass out.

Flight attendants Vanessa Woods, Faye Oskardottir, Darlene Ramirez and Karen Neben allege that a defect in the Boeing jets' bleed-air ventilation system can cause clean air to become toxic. When valves leak, chemicals from heated jet oil can seep into the cabin’s air, they say.

The lawsuit also claims that Boeing has long been aware of the problem.

The suit stems from a 2013 cross-country flight where three of the four flight attendants lost consciousness, forcing the pilot to make an emergency landing in Chicago.

Paramedics took all four flight attendants to the hospital, and two never returned to work. The four women say that they’ve had long-term medical problems ever since.

British Airways pilot Richard Westgate died in 2012 after taking 15 months of medical leave, claiming that he had been poisoned by toxic cabin fumes. A coroner’s findings supported that.

“Cabin air is safe to breathe,” Boeing said in a statement. “Research has consistently shown that cabin air meets health and safety standards and that contaminant levels are generally low.”

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