TULSA, Oklahoma - Investigators are working to find out what caused a fire at a Tulsa duplex.

Firefighters said no one was home when the fire started near 41st and Riverside.

They found smoke coming from both sides of the duplex when they arrived.

Captain Jacob Younger with the Tulsa Fire Department said the extreme cold forced crews to alter their strategy.

“Anytime it’s this cold, you have to deal with water in the tank that can freeze,” he said. It can work a little bit slower, and then you also have the effect on the crews.”

Younger said when it's that cold, it's really important to get firefighters out of their wet gear as soon as possible.