A National Institute of Standards and Technology facility in Gaithersburg, Md., is undergoing a special inspection following an incident in August that led to an employee potentially receiving an unsafe dose of radiation.

Initial testing showed the employee had absorbed a higher level of radiation than the Nuclear Regulatory Commission, the federal body that oversees the handling of radioactive material and is heading the inspection, recommends an individual experience over the course of a year.

Three employees who had been in the room around the time the leak was discovered were tested. The tests revealed only one had elevated levels of radiation present in his or her body, officials said.

Guidelines state the amount of radiation an employee can safely be exposed to as measured in rem or roentgen equivalent man, as 5 REM per year. Tests showed the worker was initially estimated to have received 9.1 REM in this incident

The level of exposure the employee is believed to have received will not cause any immediate health effects, but it may marginally increase the worker’s likelihood of cancer, said Neil Sheehan, a spokesman for the NRC.

The level of increased risk at this point is still unclear, he said.

The employee is doing well and has returned to work under a new assignment that should not expose them to radiation, said Jennifer Huergo, a NIST spokeswoman.

The NRC conservatively sets its recommended exposure limits in collaboration with international scientific bodies to safeguard worker health, Sheehan said.

On Aug. 18, routine lab surveillance discovered radioactive contamination from Americium-241 in two NIST labs, officials said. The affected employee worked in one of the labs studying radioactive components, to set scientific measurements to be used by nuclear power plants and hospitals, Huergo said.

Part of the Commerce Department, NIST works to build standards scientists, manufacturers, government agencies and others need to ensure the measurement systems they use are uniformly practiced throughout their fields. Americium-241 is commonly used in smoke detectors, and it is also used in some medical devices.

The source of the radiation was traced to a shattered glass capsule containing americium that sat in a lead-lined case alongside other samples inside a larger protective box.

The capsule holding the radioactive material was shattered so totally one couldn’t tell there had even been one, Huergo said. It is still unclear when and how the capsule was broken, and the other samples were intact, she said.

This story has been updated.