ROANOKE COUNTY, Va. -

Roanoke County fire investigators determined that a fire at Adams Construction Thursday night was started near a hot oil heater.

It’s not clear what component of the hot oil heater failed. The heater is fed by natural gas and diesel fuel.

The fire caused an estimated $70,000 in damage.

No injuries were reported.

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Firefighters immediately called for back-up after encountering flames 20-30 feet tall when they arrived at Adams Construction around 11:50 p.m. Thursday.

Crews were able to knock down the flames quickly at that plant on Peaceful Drive in Roanoke County.

As of 6:30 a.m. Friday investigators were still on the scene.