Authorities took eight D.C. firefighters to a clinic for observation Wednesday night after they complained of feeling light-headed or dizzy, several hours after extinguishing an apartment fire in Northeast, officials said.

The firefighters work at Engine 10 in the 1300 block of Florida Avenue NE and complained of the symptoms when they were at the station about 8:30 p.m., said Battalion Chief Brian K. Lee, a spokesman.

The firefighters told officials they had worked at a fire in the 3700 block of Hayes Street NE about 11 a.m. Six families were displaced in the fire, officials said. The cause of the fire is under investigation.

It was not clear what may have caused the firefighters’ dizziness. But three sources with knowledge of the probe said authorities are investigating the possibility that drug-making chemicals were inside the apartment building during the fire.