BOULDER, Colo. (AP) - Federal regulators will inspect a Boulder laboratory where 22 workers were exposed to radioactive particles from a glass vial that cracked and spilled a tiny amount of plutonium.

The U.S. Nuclear Regulatory Commission said Wednesday a health inspector will interview workers and investigate the response to the spill Monday at the National Institutes of Standards and Technology.

NIST officials said 20 workers washed off trace amounts of contamination on their shoes and clothes. Two other workers who handled the radioactive material with their hands cleaned up using soap and water. Some contamination in a hallway was also cleaned.

The glass vial that cracked had about a 1/4 gram of a powder containing plutonium. Workers were using the powder for a project to improve radiation detectors.

Federal officials said the workers are undergoing medical tests. Radiation from plutonium is weak but hazardous if ingested or inhaled.

NIST is an agency within the U.S. Department of Commerce best known for running the atomic clock that is used to maintain the official U.S. time.