A 57-year-old man was arrested Tuesday on suspicion of possessing tear gas after a device thought to contain a synthetic irritant prompted the partial evacuation of the departures area at Heathrow Airport's Terminal 4, the Metropolitan Police said.
The incident late Monday led to the temporary closure of the departures area for about three hours while police, firefighters and ambulance crews responded to what was treated as a potential hazardous-material incident. About 20 people were treated by paramedics for effects from the irritant; none were seriously injured, authorities said.
Officers discovered a canister believed to contain CS gas, a synthetic irritant commonly used by police as a form of tear gas. The man was taken into custody on suspicion of possessing CS spray, an item that is classified as a firearm under U.K. law, and on suspicion of causing a public nuisance. Police said the incident was not believed to be terror-related but that the investigation remained ongoing.
Metropolitan Police advised that suspects in England are not named unless they are charged with a crime. Authorities have been working to establish the precise circumstances that led to the release of the irritant, how the canister came to be in the terminal and whether others may face charges as the probe continues.
Heathrow, one of the United Kingdom's busiest airports, has contingency plans for hazardous-material events and regularly coordinates responses with local emergency services. Airport operations were restored after the scene was declared safe and the closures lifted, though flights and passenger processing were disrupted during the response.
London firefighters and ambulance crews were among the emergency teams that attended, treating passengers and staff affected by the irritant. Police said further forensic and investigative work was under way, and urged anyone with information or who may have been affected to contact investigators.
The arrest and investigation follow a growing international sensitivity around the possession and use of irritant sprays in public spaces. U.K. authorities continue to review evidence gathered at the scene to determine the full course of events and any potential charges that may follow.