NewsOn6.com

TULSA, OK -- Fire officials have ruled an overnight grocery store fire was accidental.

The fire broke out shortly before midnight at the Super El Ranchero Grocery Store near 21st and Garnett.  

Fire investigators believe that store workers placed a piece of cardboard on the top of a commercial griddle in the restaurant area of the store. 

Fire Captain Michael Baker says the cardboard was used to absorb water on top of the griddle after the final cleaning.   

When firefighters arrived, they found heavy smoke pouring from the metal building.   

Baker says commercial griddle surfaces retain a large amount of heat and combustible materials should be kept away from them at all times.

Damage was estimated at $300,000. 

No one was hurt.