PARKVILLE, Md. (WJZ)—We’ve just learned what sickened eight people at a group home in Baltimore County. The fire department says they suffered from carbon monoxide poisoning.

But as Kai Jackson reports, they don’t know from where the poisonous gas came.

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Investigators have determined what made residents and staff sick. Now they’re looking for the source.

Baltimore County firefighters responded to the 2800-block of Hillcrest Avenue just after midnight Monday morning.

“Came in, treated the patient, transported,” said Baltimore County Fire Department Lt. Jay Ringgold.

When firefighters responded to the Parkville house for the second time an hour later, they knew something was seriously wrong and so did employees, who alerted authorities.

“As soon as they recognized that there was a problem, they called police,” said Sherrie Jordan, Athelis Institute.

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The house is a group home for those with mental disabilities.

The residents and staff had become sick. It’s now been determined they had carbon monoxide poisoning and tests had already revealed the levels inside the house were high. A total of eight people- four residents and four staff members–were taken to area hospitals.

“Sometimes you can mix two household chemicals and create a dangerous environment. Sometimes a chemical can be knocked over or exposed with water. Those types of things could happen,” Ringgold said.

“Our concern mainly was, `Is the neighborhood safe?’ You know, if it was gonna happen, was this isolated to that house?” said neighbor D.J. Williams.

Administrators say while the investigation is underway, the residents will be assigned to other group homes.

“Ordinarily our emergency plan is to, no matter what has happened at one house, to transfer them to another place where there is available space,” Jordan said.

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The Maryland Department of the Environment is assisting in the investigation.