By Cecilio Padilla

CALISTOGA (CBS13) — The destructive Glass Fire that has burned in Napa and Sonoma counties is now 50 percent contained, Cal Fire says.

New numbers released by the fire agency on Tuesday are showing encouraging numbers as the firefight continues. As of Tuesday, the fire has grown to 66,840 acres.

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Despite the encouraging numbers, Cal Fire says crews are still dealing with above-average temperatures at higher elevations – prompting some moderate fire behavior through the night.

On Tuesday morning, 16 firefighters were evaluated for possible exposure to carbon monoxide outside of the fire zone, according to Cal Fire. One of the firefighters was taken to the hospital for further evaluation and the remaining 15 were released back to the firelines.

Chances are also improving of a change in weather that could bring the season’s first precipitation at the end of the week.

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Mop-up operations are now going on in areas where forward progress of the flames has been stopped.

Firefighters are still concerned about heavy dead and down fuels that could still threaten fire lines.

Some evacuations still remain in place. A total of 1,411 structures have been destroyed in the wildfire.

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Exactly what started the wildfire is still under investigation, Cal Fire says.