- Firefighters and paramedics are responding to an incident involving potentially hazardous materials contained in an envelope that was opened at the base.
- At least 11 people were reportedly being treated for symptoms, including nose bleeds and burning sensations.
- Victims included two US Marines who opened the letter.
An emergency task force was sent to Joint Base Myer-Henderson Hall after an "envelope containing an unknown substance" was opened, according to a statement from a Marine Corps spokesperson that was cited by a Washington Post reporter.
At least 11 people were fell ill and were being treated for symptoms that included nosebleeds and burning sensations. Three patients were taken to hospitals and were said to be in stable condition, according to the Arlington Fire Department.
A second statement from the Marine Corps on Tuesday evening confirmed the number of victims, but made no mention of what caused the symptoms.
Engine 161#emo#s crew evacuated... @ IAFF LOCAL F253
The building was evacuated and a decontamination station was deployed. The FBI and the Naval Criminal Investigative Service will be conducting a joint investigation, according to the Marine Corps.
Henderson Hall is located near the US Army's Ft. Myer, and is the headquarters of the US Marine Corps. It is also located next to the Arlington National Cemetery and nearby the Pentagon.