LINCOLN, Neb. (AP) — Investigators say a small fire in a Nebraska prison was set deliberately.

The State Fire Marshal’s Office said Tuesday that the blaze was an act of arson, but declined to comment further because the investigation is ongoing.

Two inmates and a staff member at the Lincoln Correctional Center were treated for smoke inhalation as a precaution after the fire around 10 p.m. Monday.

Lincoln Fire Department Battalion Chief Jeremy Gegg says the fire was extinguished by the time emergency crews arrived.

The fire comes after a disturbance with inmates last month sent nine employees to the hospital.

Corrections spokeswoman Dawn-Renee Smith says the fire was contained to one cell. She says fires in cells aren’t a common occurrence, but they have happened in the past.