Shortly after 9 a.m. Monday, the family members started waking up and complaining of headaches and nausea. The parents called 911 and reported that there might be a carbon monoxide leak in their home.

Firefighters detected carbon monoxide at 170 parts per million at the house in the 8600 block of Reicher Street in Glenarden. A normal atmosphere contains zero to 30 ppm of the gas, and exposure to higher levels than that for a prolonged period of time is considered unhealthy, Prince George's County Fire/EMS officials said.

Paramedics evaluated the family members and detected low levels of carbon monoxide in their bloodstreams. The mother, father and children, ages 6, 11, and 16, were treated at the scene and then taken to a hospital for possible treatment in a hyperbaric chamber. The family members were in good condition, officials said.

Firefighters shut down the house's natural gas furnace and water heater, and ventilated the house. Fire/EMS spokesman Mark Brady said officials believe that the carbon monoxide leak was caused by one of the two appliances, most likely the water heater.