Police seized an unknown quantity of PCP from a makeshift laboratory in a Southeast apartment this morning after firefighters discovered the volatile chemicals while fighting a mattress fire in the apartment, D.C. Police said.

Firefighters responded to a fire at 1700 29th St. SE shortly after 8 p.m., and in the process of getting the blaze under control, discovered a tub or drum that they suspected of containing PCP, police said.

The fire was brought under control within 20 minutes, fire officials said, and firefighters on the scene notified Seventh District police officers of the presence of chemicals.

It was unclear early this morning if anyone was injured in the fire, and it was unknown if any residents of the first floor apartment were present at the time of the fire.

But police said a suspect was arrested this morning after it was determined at about 1 a.m. that the chemical present was PCP. Charges against the suspect, as well as the suspect's identity, were not available.

Building residents had been evacuated by police about 10 p.m., and the area was cordoned off while police obtained a search warant from the U.S. Attorney's Office for the District of Columbia, police said. Drug Enforcement Adminstration technicians were called in to test the chemical, they said.

Alice Jones, a third floor resident, said she left the building about 15 minutes before the fire broke out and returned to find fire trucks on the street and smoke coming from the building.

"When I got back," Jones said, "there was white smoke . . . [and there was] a smell like gasoline or kerosene."

Jones said firefighters had broken through a deadbolt lock on her apartment door and "turned the bedroom upside down" because a neighbor had thought Jones was in the apartment at the time of the fire.