[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2009/US/08/17/bleed.air.tests/art.williams.jpg caption="Terry Williams hugs her two boys - Jake, left, and Zack - in 2006, before she says toxic cabin air made her sick."]
(CNN) - Inside a freezer in a research laboratory at the University of Washington are blood and blood plasma samples from 92 people who suffer from mysterious illnesses, including tremors, memory loss and severe migraine headaches.
They are mostly pilots and flight attendants who suspect they've been poisoned in their workplace - on board the aircraft they fly.
Clement Furlong, University of Washington professor of medicine and genome sciences, leads a team of scientists who have been collecting the samples for 2 ½ years.
Furlong said his team is a few months away from finalizing a blood analysis test that will be able to definitely confirm whether the study participants were indeed poisoned by toxic fumes.
Results of Furlong's research could expand recognition of what a select group of researchers believes is a largely unrecognized risk of flying: the chance that poisonous fumes enter the cabin.
"There's a danger of inhaling compounds that are coming out of the engine," said Furlong in his laboratory.
The air we breathe on board a plane is a 50-50 mix of filtered, recirculated air and so-called "bleed air" - which bleeds off the engines, and then is pressurized and cooled before being sent into the cabin through vents. If an engine oil seal leaks, aviation engineers and scientists say, the bleed air can become contaminated with toxins.