NEW HAVEN, Conn. (CBSNewYork/AP) — Authorities in Connecticut say several people have been exposed to an unidentified radioactive substance after a hospital’s nuclear medicine lab was broken into.

New Haven Fire Chief John Alston says employees discovered the lab in the cancer center at St. Raphael’s Hospital had been vandalized when they arrived at around 8 a.m. Saturday.

As WCBS 880’s John Metaxas reports, the workers soon realized the black powder on the bottom of their shoes might present a problem.

Officials say at least three lab technicians were exposed to radioactive material and underwent decontamination. Overall, a total of twelve employees were exposed to the unidentified radioactive substance, but none have exhibited symptoms.

The hospital says the exposure was contained.

Alston says the victims are expected to be OK. It’s unclear why the lab was broken into.

The Connecticut Department of Energy and Environmental Protection is leading the investigation.

(© Copyright 2017 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)