21 injured after Heathrow airport terminal evacuation but ‘no trace’ of adverse substance found

Several people reported injuries after a terminal at Heathrow airport was closed and evacuated for three hours following a “possible hazardous materials incident”.

Dozens of flights were delayed and thousands of travellers were affected by the incident at Terminal 4 of Europe’s busiest airport on Monday evening, which sparked a multi-agency response from the Metropolitan Police, London Fire Brigade (LFB) and London Ambulance Service.

Some 21 people reported injuries at the airport in west London but “no trace of any adverse substance was found”, police later said.

Crowds gathered outside the terminal and staff handed out foil blankets to passengers as temperatures began to fall. Witnesses said they were confused as “no one really knew what was going on”.

At 8.27pm, the airport said on X (Twitter) 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 Met Police said in a statement: “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. Enquiries are ongoing.”

The LFB said it was in the process of standing down its response, and that the cause of the incident remained under investigation.

Earlier on Monday evening, the airport had advised passengers not to travel to Terminal 4, while National Rail said trains were unable to call at the terminal because of the incident. Transport links to the airport were already affected by London Underground strikes.

The LFB said it was first called about the incident at 5.01pm and that crews from Feltham, Heathrow, Wembley and surrounding fire stations had attended.

Transport secretary Heidi Alexander said she was monitoring updates from those at the scene and the airport.

“Emergency services are responding to an incident at Heathrow’s Terminal 4 which has prompted its evacuation,” she wrote on X. “I’m monitoring updates from those on the scene, as well as Heathrow Airport itself. Passengers should not travel to Terminal 4 until advised otherwise.”

FlightRadar24 data analysed by The Independent showed that a number of flights were delayed by the emergency evacuation. Qatar Airways appeared to have three flights running behind schedule, as were two Etihad flights to Abu Dhabi, with the delays set to jeopardise hundreds of connections.

The incident comes months after Heathrow airport closed following an “unprecedented” electrical substation fire that halted 1,300 flights.

London Heathrow is the UK’s busiest airport, and just last month it recorded its busiest day ever. The airport saw more than a quarter of a million passengers pass through its four terminals – a total of 270,869 passengers – on 1 August.

It came after a month in which it saw almost no growth in passenger numbers, which executives said was due to capacity constraints.

Heathrow said that 7,981,137 passengers flew in and out of the terminals in July, compared with 7,980,455 during the same month in 2024.