SALINA, Kan. (AP) -- A chemical odor that caused headaches in a north Salina neighborhood has been traced to a 55-gallon drum inside a shed.

But the substance inside the drum remained a mystery Wednesday.

The Salina Journal reports (http://bit.ly/QsQmAG ) firefighters went to the area Tuesday evening but were unable to pinpoint the odor. Several residents were evacuated as a precaution, and Kansas Gas Service crews worked through the night but also couldn't find the source.

Residents complained of the odor and headaches again Wednesday. The Fire Department's hazardous materials team went house-to-house and came across the drum.

But authorities were unable to identify the substance inside. Haz-mat crews were packing the drum Wednesday into a safe container. The contents will be analyzed by the Kansas Department of Health and Environment.

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Information from: The Salina Journal, http://www.salina.com