Potomac Heights Volunteers and surrounding departments including NDW Indian Head Haz Mat Unit, NDW Stump Neck, Department of Emergency Service HAZ MAT resources are currently operating in the area of 4090 Lower Wharf Road in Indian Head due to a hazmat emergency. Command (Special Ops Chief Gimmel) assisted by Chief 11A (Delozier) on scene reporting a Roberts Oxygen Truck with 6,000 Gallons of CO2 leaking after a line ripped from tank. A 300' perimeter was established, businesses and residences in the immediate area were evacuated as a precaution until the product in the tank ran off. Crews are unable to stop leak due to damage to the shut off valve. As it was determined a safe incident, command scaled back to units from 7, 11, all Haz Mat resources. Once product stopped free flowing, crews went to surrounding homes to take hazardous materials reading to be certain all oxygen levels were within normal. All units cleared in about 2.5 hours, no injuries were reported