A man has been arrested after 21 people had to be assessed by paramedics following a possible hazardous materials incident that led to a partial evacuation of Heathrow Airport.
Terminal 4 check-in was evacuated as a precaution on Monday evening and the London Fire Brigade (LFB) later confirmed that “no elevated levels of hazardous materials were discovered”.
On Tuesday a 57-year-old man is in custody after being arrested on suspicion of possession of a firearm (CS spray) and causing a public nuisance, the Metropolitan Police said.
A force spokesman said: “Met officers located a cannister of what is believed to be CS spray.
“It is thought that this substance caused a reaction to those within the airport.”
Around 20 people were assessed at the scene by paramedics after suffering “irritation” in the incident, which is not being treated as a terrorist-related, the police said.
One person was taken to hospital as a precaution.
Emergency services have confirmed Terminal 4 is safe to reopen and we are doing everything we can to ensure all flights depart as planned today. We are very sorry for the disruption caused, the safety and security of our passengers and colleagues is our number one priority. We… pic.twitter.com/AykEmpgnKh
— Heathrow Airport (@HeathrowAirport) September 8, 2025
The LFB said Terminal 4 check-in was evacuated “as a precaution” as firefighters assessed the scene.
Specialist police officers alongside the LFB and London Ambulance Service rushed to the scene after the force was called at 4.56pm on Monday.
An LFB spokesman said: “The Brigade was informed that several people were reporting a variety of minor symptoms, which could indicate exposure to a chemical or another type of substance.
“As is routine for these types of incidents, specialist crews were deployed to carry out an assessment of the scene.
“We can confirm no elevated levels of hazardous materials were discovered by the Brigade and the area was declared safe.”
It is understood when the LFB assessed the area, the spray had already dissipated, leading to the scene being declared safe.
London’s Heathrow is the UK’s busiest airport.
Earlier on Monday evening, the airport had advised passengers not to travel to Terminal 4, while National Rail Enquiries said trains were unable to call at the terminal because of the incident.
According to the airport’s website, flights from Terminal 4 were largely unaffected – with only a few delays expected.
Footage posted on social media showed passengers with their luggage waiting outside the airport, with some wrapped in foil blankets.
