Denver, CO- Two people were taken to a local hospital Friday morning to be treated for exposure to high levels of carbon monoxide.

The Denver Fire Department responded at 5:21 a.m. to a single-family home in the 300 block of High Street, said Mark Watson, a fire department spokesman.

The pair were hospitalized for “observation,” Watson said.

High, dangerous levels of carbon monoxide were detected in the home, which was vented by the firefighters.

Investigators are looking into what caused the elevated levels.