People who use Lambert-St. Louis Airport a lot do not see many friendly faces at the security checkpoints. It’s not that people who work there are not friendly, it’s just that they don’t stick around very long. A federal study shows Lambert has the nation’s highest employee turnover rate among airport security employees–416 percent in one year. A federal agency says high stress and low pay contribute. The study says some workers at airport fast-food places earn more each hour than those who make sure nobody takes a gun or bomb through the gates.