Authorities in Trumbull say construction may have freed a pocket of carbon monoxide, causing elevated levels of the poisonous gas in some residences Friday and Saturday.

Firefighters began responding to the Plumb Creek Road area Friday morning on a series of carbon monoxide alarm. Testing of houses continued until just before noon Saturday, according to Trumbull Volunteer Fire Company Public Information Officer David DeLibro.

At 12:30 Saturday afternoon, DeLibro issued a statement saying CO levels were within normal ranges, and expressing that construction is suspected of causing the gas to be released.

The Trumbull Center, Long Hill and Nichols fire departments were joined in the investigation by Trumbull Police, Trumbull EMS, the Trumbull Health Department, the Trumbull Office of Emergency Management, the Office of the First Selectman, the Trumbull Fire Marshals, the federal Environmental Protection Agency, the state Department of Energy and Environmental Protection, United Illuminating, Southern Connecticut Gas, Aquarion Water Company, Call Before You Dig, the state Department of Emergency Services and Public Protection, and the state Fire Marshals’ Office.

According to the Connecticut Department of Public Health website, "Carbon monoxide (CO) is a colorless, odorless and deadly gas produced by the incomplete burning of fossil fuels used in appliances such as furnaces and portable gas generators."

There is no word on anyone suffering symptoms of carbon monoxide poisoning. According to the state Department of Public Health, "Symptoms for carbon monoxide poisoning often are the same as for the cold or flu."

Symptoms for carbon monoxide poisoning are headache, fatigue, dizziness and nausea, according to the Department of Public Health.