An ammonia leak in a Sterling plant Wednesday night sent 33 people to the hospital.
Declaring it a mass casualty incident, crews from Fairfax County, Washington Metropolitan Airport Authority and Prince William County responded to assist Loudoun County, WUSA9 reported.
Four of the victims having critical or significant respiratory-related issues.
Authorities say five people are in serious condition, 17 are in serious but non-life-threatening condition and 11 are in minor non-life-threatening condition. A majority of the people affected by the leak were employees inside the impacted building.
The leak was discovered by building maintenance staff, who were able to get it under control. Assistant Fire Chief Travis Preau said crews ventilated the building overnight.
HAZMAT crews were called to the area to evaluate the air around the building. There does not appear to be any concern for people who live or work near the building where the leak happened.