CFD crews were responding to the 18th Police District station near Larrabee and Division streets just before 10:30 a.m., officials said.
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There were no reports of any injuries later Tuesday morning.
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Chicago police said a resident walked into the police station just before 9:20 a.m. after finding a piece of mail with an unknown substance on it.
Hazmat responded, and tested the envelope, which was found to be negative for any suspicious substance, and cleared, CPD said.
The incident is classified as non-criminal.
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