AUSTIN (KXAN) — Several agencies are investigating after potentially hazardous materials were found at a state office building in downtown Austin.

The Austin Fire Department said on social media at 9:20 a.m. that special operations crews and Austin-Travis County EMS were investigating the William P. Clements building on West 15th Street in downtown Austin.

The Department of Public Safety told KXAN there was an “envelope with substance” being investigated.

DPS said Thursday afternoon that “all tests came back negative.” It’s not clear what tests DPS ran. DPS also confirmed that the FBI has joined the investigation to determine what material was inside the envelope.

ATCEMS said three ambulances and two district commanders are on the scene, and three patients have been decontaminated. Medics evaluated them for potential symptoms, with ATCEMS posting all three were asymptomatic but would be transported to Dell Seton Medical Center for additional evaluation “out of an abundance of caution.”

The William P. Clements building houses the Texas Office of the Attorney General. According to DPS, all three of the patients were employees of the OAG.

Officials cautioned extensive road closures near the scene are expected, adding that ATCEMS would have no additional information on the incident.

Todd Pomroy, battalion chief with AFD Special Operations, said there is a chain of events that begins once a call like this comes in.

“We do our best to make sure that anybody that’s around it is out of harm’s way. Then we basically have a line or process. If there’s some substance available, take that substance, test it, then with our partners discover how harmful or not harmful it’ll be according to our monitors,” Pomroy said.