The Charlotte Fire Department responded to a structure fire at the Charlotte Douglas International Airport Thursday morning.

Heavy smoke was observed coming from the old control tower shortly after 8 a.m.

Firefighters said four construction workers were initially trapped by the smoke.

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While the fire did make it to two alarms, it was controlled within 10 minutes, according to firefighters.

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All four construction workers were then able to self-evacuate and did not suffer any injuries.

Firefighters said the cause of the fire is under investigation; however, operations at the airport were not affected by this event.

This is a developing story; check wsoctv.com for updates.

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