QUINCY (CBS) — Five workers were taken to the hospital following a small explosion and fire Monday afternoon at a Quincy sewage plant.

The incident happened shortly before 1 p.m. at the Massachusetts Water Resources Authority plant on Sea Street. On average, the plant processes 400 million gallons of raw sewage daily.

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Smoke rose from the sewage treatment plant at Nut Island Monday. (WBZ-TV)

Smoke rose from the sewage treatment plant at Nut Island Monday. (WBZ-TV)

The fire broke out several stories below the surface, fire officials say. Neighbor Carol Hallett told WBZ says she initially saw grey smoke before seeing black plumes.

Quincy Fire Chief Joe Barron told WBZ the fire in an air scrubber was difficult to get at, adding that there was mostly insulation in the contained area and firefighters didn’t have to worry about the blaze spreading.

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The five male employees who were injured will spend the night at Boston Medical Center.

“At some point, something went wrong and there was an explosion and subsequent fire,” MWRA Executive Director Fred Laskey told WBZ-TV’s Bill Shields. “Those employees had difficulty breathing and irritation to their eyes.”

Laskey says there are no environmental issues to be concerned about.

The cause of the fire is still under investigation, and the State Fire Marshal’s Office sent an investigator to the scene.

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Quincy Police say there was no danger to the public.