About 20 people reported an injury but “no trace of any adverse substance was found” after officers were called to Heathrow, the Metropolitan police has said.
Terminal 4 check-in was evacuated as a precaution on Monday evening while emergency services responded to a “potential hazardous material incident” at the airport, the London Fire Brigade said.
According to police, about 20 people had reported an injury but no trace of any hazardous substance was found after officers conducted a thorough search of the area.
A London ambulance service spokesperson said a total of 21 patients had been treated and one had been taken to hospital while all the others had been discharged at the scene.
In a statement, a spokesperson for the force said: “On Monday, 8 September at 16:56hrs police were called to a potential hazardous materials incident at Heathrow Airport, Terminal 4.
“Specialist officers attended the scene alongside the London fire brigade and London ambulance service and conducted a thorough search of the area.
“No trace of any adverse substance was found. Around 20 people reported an injury. None were deemed to be life-threatening or life-changing. Inquiries are ongoing.”
At 8.27pm, the airport said on X that emergency services had confirmed the terminal was “safe to reopen” and it was doing “everything we can to ensure flights depart as planned today”.
The LFB said it was in the process of standing down its response, and that the cause of the incident remained under investigation.
Passengers leave Terminal 4 after an evacuation was called. Photograph: Suzanne Plunkett/Reuters
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.
The LFB said it was first called about the incident at 5.01pm and crews from Feltham, Heathrow, Wembley and surrounding fire stations had attended.
The transport secretary, Heidi Alexander, said she was monitoring updates from those at the scene and the airport.
According to the airport’s website, flights from the 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.
London’s Heathrow is the UK’s busiest airport.