A neighborhood in Pennsylvania was forced to evacuate Sunday after a mysterious chemical was detected in several different homes.

Firefighters discovered a strong odor from what has been described as an unidentified gas Sunday evening and a voluntary evacuation was issued for 150 homes in Skippack Township, a suburban community about 25 miles northwest of Philadelphia, CNN reported.

The odor was first reported by a resident who called authorities to make a complaint around 5:45 p.m.  Firefighters used meters to investigate the smell and found that a gaseous volatile organic compound was coming from the basement sump pumps in several homes, the department said.

They could not immediately identify the gas, but the county Department of Public Safety released a statement saying that the Montgomery County hazardous response team, state Department of Environmental Protection and federal Environmental Protection Agency are working to identify the "volatile organic compound," The Associated Press reported.

Fire Chief Haydn Marriott told CNN affiliate WPVI-TV that fire crew testing the homes had gotten high readings of a poisonous gas called hydrogen cyanide. However, by Monday morning, rescuers ruled out hydrogen cyanide, calling it a "false positive."

Evacuated residents in need of a place to stay overnight stayed at a local elementary school that the American Red Cross of southeastern Pennsylvania uses as an emergency shelter. According to the Red Cross, 10 people from four families slept there. Some other residents checked into a hospital and were released.

Volatile organic compounds are found in thousands of products, including paints and lacquers, paint strippers, cleaning supplies, pesticides and permanent markers, according to the Environmental Protection Agency. They can can seep into ground water from spills or leaking storage tanks or in storm water runoff from roads and parking lots.