In John Shea and John Greco’s day, the cavernous Pratt & Whitney Aircraft plant was filled with an oily mist that sprayed from the grinding machines, coated the ceiling and covered the workers, who came home drenched in pungent machine oil. Degreasing pits, filled with solvent for cleaning the engine parts, dotted the factory floor; workers used squirt cans of solvent to clean their hands and clothes. Shea spent 34 years grinding engine blades and vanes at the million-square-foot facility in North Haven, Conn. In 1999, at age 56, he was diagnosed with brain cancer. Six months later Shea’s friend and co-worker Greco learned he had the same disease: glioblastoma multiforme, the most aggressive type of brain tumor. A year after Shea’s diagnosis, both men were dead, but their widows had already begun asking questions about the seemingly unusual number of cases of this deadly form of cancer at one of the world’s top jet-engine manufacturers.