A call for a person with breathing difficulties turned into a mass casualty incident in St. Mary's County early Saturday after numerous responders fell ill.
While inside the house treating the person who called 9-1-1, two EMTs and four firefighters started feeling ill.
Using a meter, firefighters detected carbon monoxide levels of 500 parts per million (ppm) inside the residence, Southern MD News Net reported.
Firefighters located a male victim unresponsive on the first floor and removed him from the residence. EMS personnel initiated CPR.
However, he was later declared dead at the sene.
Responders found a running vehicle inside a closed garage.
Three Maryland State Police helicopters responded along with the additional EMS and fire crews from St. Mary’s, Calvert, Charles, and Prince George’s Counties.
The helicopters transported four firefighters from the Bay District Volunteer Fire Department and both EMTs to area trauma centers for hyperbaric chamber treatment and additional evaluations.
A St. Mary’s County Sheriff’s Deputy, a Bay District firefighter, and a civilian were transported to a local hospital.
Eight firefighters, four children, and five adults declined transport or did not require treatment, reports indicated.
After more than 30 minutes of CPR, the patient was declared dead.
A multi-agency investigation is underway.

Susan Nicol | News Editor
Susan Nicol is the news editor for Firehouse.com. She is a life member and active with the Brunswick Volunteer Ambulance & Rescue Company, Oxford Fire Company and Brunswick Vol. Fire Co. Susie has been an EMT in Maryland since 1976. Susie is vice-president of the Frederick County Fire/Rescue Museum. She is on the executive committee of Frederick County Volunteer Fire and Rescue Association. She also is part of the Maryland Institute for Emergency Medical Services Systems (MIEMSS) Region II EMS Council. Susie is a board member of the American Trauma Society, Maryland Division. Prior to joining the Firehouse team, she was a staff writer for The Frederick News-Post, covering fire, law enforcement, court and legislative issues.