The cause of an odor that sickened 11 airport security workers Thursday and forced the temporary closure of Lihue Airport remains a mystery, a state Department of Transportation spokesman said Friday.

A hazardous materials crew from the Kauai County Fire Department investigated, but couldn’t find the odor’s cause, said Transportation Department spokesman Dan Meisenzahl.

He said the odor was noticed near the central security checkpoint at Lihue Airport about 6 p.m. Eleven workers with the Transportation Security Administration felt sickened by the noxious odor, but they were all cleared by paramedics at the scene, he said.

As a precaution, 10 of them were also checked out at a hospital and released.

Roads leading to the airport were closed briefly while emergency crews investigated. Two flights were slightly delayed.