MANNSVILLE, Okla. -- Cindy Simpson will probably never know why her husband died. She says Oklahoma officials promised her they'd find out after David Simpson died last year. Fellow oil workers found the 57-year-old truck driver slumped over a tank hatch at an oil well here. But officials didn't do an autopsy or test for petroleum exposure. "I just feel like he was totally ignored by Oklahoma," Cindy Simpson said. "Isn't that what they're supposed to do in an investigation -- find out what happened? And they didn't." The investigation into Simpson's death, or the absence of it, highlights a common lack of understanding of the lethal dangers in the air at oil and gas sites.