By Mark Abrams

COLLEGEVILLE, Pa. (CBS) — Authorities are continuing to investigate the source of a noxious odor which caused the evacuation of more than 100 people Sunday night in Skippack Township, Montgomery County.

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Emergency response teams were called to the 4200 block of Gorski Lane in the Fairlawn Court townhouses shortly before 7 p.m. after residents in an end unit complained of a mysterious odor.

In all, some 150 people who live in the area were asked to leave their homes and some went to a shelter at the nearby Skippack Elementary School set up by the American Red Cross.

As of Monday morning, the source of the odor was unknown. Residents were allowed back into their homes if the readings were clear.

Hazardous materials crews and fire personnel say they detected readings of hydrogen cyanide in dozens of homes in the development, located just off Route 113.

However, one fire investigator says they suspect that chemical is likely masking another chemical.

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Officials say hydrogen cyanide is generally a byproduct of fires and can be deadly if inhaled in large quantities. It can cause headaches and nausea to those exposed to it.

No one has suffered any injuries.

Area utility companies and a pipeline operator responded with personnel to investigate their connections and are reporting to authorities that they found nothing unusual and no signs of any leaks.

Montgomery County officials have asked the state Department of Environmental Resources and the federal Environmental Protection Agency to assist in tracking the source.

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