TULSA, Oklahoma - A white powdery substance was found in an envelope received at the Tulsa County jail Wednesday afternoon.

The Tulsa County Sheriff's Office said detention officers open all incoming mail, and shortly after noon, they found a powdery substance in one envelope. The envelope was addressed to an inmate.

TCSO Major Shannon Clark said the fire department's Hazmat Unit was called and the jail's mail room locked down. He said the detention officers have been isolated while tests on the substance were underway.

Wednesday night, the sheriff's office said the powder tested negative for biological agents. They say more tests are being run to determine just what the powder is. Those tests could take up to five days.

Clark said jail policy requires all mail to inmates be opened and inspected for contraband.

The sheriff's office said all staff members who came into contact with the substance were decontaminated and released by the Tulsa Fire Department.