CHICAGO (CBS) — Two firefighters and five other people were taken to hospitals after a large ammonia leak at a food processing plant in Streamwood, and officials said it will take several hours to clear out the fumes.

Five workers and two firefighters were overcome by ammonia after a leak in the refrigeration system at the Fresh Express plant at 1109 E. Lake St. late Monday night. All seven were treated and released at hospitals

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Streamwood Fire Chief Chris Clark said the leak was likely caused when a forklift or other piece of equipment hit an anhydrous ammonia refrigeration pipe.

“They had some piping that was damaged, and did cause a leak, which they shut down very quickly,” he said.

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Ammonia fumes remained in the air, and some was still on the ground.

Clark said a large puddle of ammonia – about 5 feet by 50 feet – was being flushed into a recovery tank. Industrial fans from several fire departments were being used to vent the fumes.

Clark said an air boat from the Fox Lake area also was brought in to help vent fumes.

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“As an alternative, these air boats are fairly similar to that [industrial fan]. You know, leave the boat on a trailer, start up the fan,” he said.