BOULDER, Colo. -- Federal regulators will inspect a Boulder lab where 22 workers were exposed to radioactive particles from a glass vial that cracked and spilled plutonium.

The U.S. Nuclear Regulatory Commission said Wednesday a health inspector will interview workers and investigate the response to the spill.

It happened Monday at the National Institute of Standards and Technology in Boulder.

NIST officials said 20 workers washed off the trace amounts of contamination on their shoes and clothes. Two other workers who handled the radioactive material with their hands also were able to clean off using soap and water.

The glass vial that cracked had about a 1/4 gram of a powder containing plutonium.

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

Some contamination in a nearby hallway was also cleaned.

NIST spokesman Ben Stein said the lab has been sealed off for further testing. Congressman Mark Udall (D-Eldorado Springs) called the accident a "matter of deep concern."

"As a Member of the Science and Technology Committee, I will continue to work closely with NIST to ensure that they are doing everything they can to protect their staff as well as the entire Boulder community," he said.