London Heathrow Airport’s Terminal 4 was thrown into chaos on Monday evening after a suspected hazardous materials incident forced an emergency evacuation.
As a result, thousands of passengers were grounded and dozens of international flights were delayed.
The alert was first raised at 5:01 pm on 8 September, when the London Fire Brigade (LFB) received reports of a possible chemical threat inside the check-in area of Terminal 4.
Within minutes, the Metropolitan Police and London Ambulance Service joined the operation, deploying officers in hazmat suits to assess the situation.
Crews from Feltham, Heathrow, Wembley and surrounding fire stations rushed to the scene.
Evacuation and Confusion
As passengers queued to check in for flights to destinations across Europe, Asia, the Middle East and Africa, the terminal’s check-in area was abruptly cleared. Those on the “landside” before passing through security were directed outside to wait in the evening chill. With temperatures falling, airport staff distributed foil blankets to travellers, while confused crowds gathered along the roadside.
Witnesses described the situation as unsettling and disorganised. “No one really knew what was going on,” one passenger told the BBC. Inside the airport, travellers who had already cleared security were allowed to remain “airside,” and a small number of flights were permitted to depart close to schedule.
Adding to the disruption, National Rail suspended trains to Terminal 4, while the Tube station serving the terminal was already closed due to a London Underground strike. Heathrow Airport urged passengers on social media not to travel to Terminal 4 until further notice.
During the evacuation, 21 passengers reported minor injuries, with some complaining of breathing difficulties or dizziness. Paramedics treated most on site, while one individual was taken to hospital. Police later confirmed that none of the cases were life-threatening or life-changing.
By 8:27 pm, Heathrow Airport announced that emergency services had declared the area safe, and at 9:00 pm, the terminal reopened.
The Metropolitan Police released a statement later in the evening:
“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 twenty people reported an injury. None were deemed to be life-threatening or life-changing. Enquiries are ongoing.”
The London Fire Brigade confirmed that it had stood down its response, with investigations into the cause still underway.
Possible Mass Hysteria
Although the exact cause of the scare remains uncertain, reports suggest the incident may have been the result of mass hysteria rather than the presence of hazardous substances. Experts have noted that busy public spaces like airports, where travellers are often under stress and heightened alert, can create conditions for collective panic.
Dr. Kit Yates, a mathematical biologist at the University of Bath, wrote: “An airport is a setting in which heightened awareness and anxiety amongst the people filling the departure halls can provide the ideal conditions for mass psychogenic spread.”
The impact on flights was significant. Although no cancellations were reported, dozens of departures were delayed by three to four hours, with knock-on effects across global airline networks.
Qatar Airways, the largest carrier at Terminal 4, saw three flights to Doha delayed, while Etihad Airways, Malaysia Airlines, Korean Air, and several Chinese carriers also faced major setbacks. Many travellers missed onward connections at Gulf and Asian hubs, leaving airlines to rebook passengers and arrange overnight accommodation where necessary.
The final departure of the night; China Southern’s flight to Guangzhou did not leave until 12:30 am, long after Heathrow’s usual final departure slot.
A Heathrow spokesperson apologised for the disruption, saying:
“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.”
The UK’s Transport Secretary, Heidi Alexander, also confirmed she was monitoring developments. “Emergency services are responding to an incident at Heathrow’s Terminal 4 which has prompted its evacuation. 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.”
Heathrow Terminal 4’s Reputation
The scare comes at a time when Heathrow is experiencing record traffic. Just last month, on 1 August, the airport recorded its busiest day ever, handling 270,869 passengers across its four terminals.
Terminal 4, however, has long been seen as the airport’s most inconvenient facility. Built in the 1980s as a temporary measure, it sits south of both runways, making aircraft movements cumbersome. Despite refurbishments, it remains less popular with airlines and travellers compared to the modern Terminals 2 and 5.
Today, Terminal 4 is primarily used by Middle Eastern and Asian carriers, with Qatar Airways, Etihad, Korean Air, Malaysia Airlines, and multiple Chinese airlines forming the bulk of its operations.
As of Tuesday, 9 September, Terminal 4 is operating normally, though airlines continue to deal with rebookings for passengers who missed onward flights. Investigations into the cause of the incident are ongoing, but authorities have confirmed there was no chemical threat and that safety has been restored.
