RICHLAND, Wash. (AP) — Workers in an area at the center of the Hanford nuclear reservation were ordered to take cover for several hours.

The order was issued from about 8:30 a.m. to noon Wednesday, The Tri-City Herald reported. Access to the site was restricted and the Rattlesnake Barricade secure entrance to the site was closed as a precaution.

The take cover order was issued after two work crews outside the REDOX facility in the 200 West Area noticed an unusual odor, according to Hanford officials. One crew was there with well drilling equipment, and the other was using equipment to scan for buried materials in preparation for excavation work, according to Hanford officials.

No radiation or chemical contamination above background levels was detected, officials said.

No injuries were reported and Hanford workers who smelled the odors were encouraged to visit Hanford’s onsite medical provider with concerns.

Some Hanford workers have reported serious respiratory and neurological illnesses they suspect are tied to exposure to chemical vapors where waste from Hanford’s defunct reprocessing plants is stored in underground tanks.

The 586-square-mile (1,518 square kilometer) Hanford site in Eastern Washington was used to produce two-thirds of the plutonium for the nation’s nuclear weapons program during World War II and the Cold War.

The REDOX, or Reduction-Oxidation, plant operated from 1952 through 1967 to chemically separate plutonium from irradiated uranium fuel rods.