57-year-old detained on firearms charges as 21 passengers treated following ‘mass hysteria’ incident at Britain’s busiest airport
A 57-year-old man has been arrested on suspicion of possession of a firearm and causing a public nuisance after a canister of CS spray triggered a major evacuation at Heathrow Terminal 4, affecting hundreds of passengers and causing widespread panic yesterday evening.
The incident, which unfolded at 4.56pm on Monday, led to what specialist officers described as “mass hysteria” as 21 people required medical treatment following exposure to the tear gas substance. The Metropolitan Police confirmed they recovered a canister believed to contain CS spray during their search of the terminal.
Emergency services, including specialist hazmat teams wearing protective equipment, descended on Britain’s busiest airport after reports of a “potential hazardous materials incident” sparked fears of a chemical attack or terror-related event.
“It is thought that this substance caused a reaction to those within the airport,” a Metropolitan Police spokesperson said in a statement. The force confirmed the suspect remains in police custody and emphasised the incident is not being treated as terrorism-related.
The dramatic scenes saw Terminal 4’s check-in area completely evacuated as a precaution whilst firefighters conducted operations. Passengers were left standing outside in the evening air for approximately three hours, with airport staff distributing water and foil blankets to those waiting in the cold September weather.
London Ambulance Service confirmed it treated 21 patients at the scene, with one individual requiring hospital treatment whilst the others were discharged after receiving medical attention. The rapid spread of symptoms amongst those in the terminal appears to have contributed to what authorities termed “mass hysteria” – a psychological phenomenon where physical symptoms spread through a group without an identifiable physical cause.
CS spray, technically known as 2-chlorobenzylidene malononitrile, causes immediate and severe irritation to the eyes, nose, throat and respiratory system. Exposure typically results in intense tear production, eye pain, chest tightness, coughing and sneezing. The substance is classified as a tear gas and is commonly used by law enforcement for crowd control, though possession by civilians is illegal in the UK.
“The chemical reacts with moisture on the skin and in the eyes, causing a burning sensation and the immediate forceful and uncontrollable shutting of the eyes,” according to medical experts. Effects usually include tears streaming from the eyes, profuse coughing, exceptional nasal discharge, burning sensations, disorientation, and dizziness.
The psychological impact of the incident appears to have amplified the physical effects. Mass psychogenic illness, as documented by medical professionals, occurs when groups of people develop similar symptoms in response to a perceived threat, even when exposure levels may be minimal. In enclosed spaces like airport terminals, such reactions can spread rapidly through proximity and sight lines.
Specialist crews from Feltham, Heathrow, Wembley and surrounding fire stations were deployed to carry out a thorough assessment of the scene. London Fire Brigade said in a statement: “No elevated levels of hazardous materials were discovered by the brigade.”
The incident caused significant disruption to operations at Terminal 4, which houses check-in counters for major international carriers including Air France, Qatar Airways, Etihad Airways, Korean Air, and China Southern. Train services to the terminal were temporarily suspended, with National Rail Enquiries confirming trains were unable to call at Heathrow Terminal 4 during the emergency response.
Videos posted on social media showed emergency responders in masks and hazmat suits systematically checking the terminal, whilst crowds of passengers with luggage waited anxiously outside. The arrivals area of the terminal remained operational throughout the incident, and other terminals at Heathrow continued to function normally.
Transport Secretary Heidi Alexander confirmed she was monitoring updates from those at the scene. The government’s response highlighted the seriousness with which authorities initially treated the incident, given recent heightened security concerns at UK airports.
By 8pm, emergency services had confirmed Terminal 4 was safe to reopen. A Heathrow Airport spokeswoman said: “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.”
The spokesperson added: “We are very sorry for the disruption caused, the safety and security of our passengers and colleagues is our number one priority. We encourage passengers to check with their airline for the latest information about their flight this evening and our colleagues will be on hand into the night to assist.”
According to the airport’s website, most flights from the affected terminal departed on time, with only one delay reported – a Saudia Airlines flight to Jeddah in Saudi Arabia. The swift resolution prevented more widespread disruption to the airport’s operations.
The incident raises serious questions about airport security and how a prohibited substance like CS spray could be brought into a terminal. Under UK law, CS spray is classified as a prohibited weapon under Section 5(1)(b) of the Firearms Act 1968, making possession illegal and punishable by up to 10 years’ imprisonment.
Medical experts note that whilst CS spray effects are typically temporary, lasting 15 to 30 minutes after exposure ends, the psychological impact of such incidents can be more lasting. The phenomenon of mass hysteria, documented in similar incidents worldwide, shows how initial exposure to an irritant can trigger cascading symptoms throughout a crowd, particularly in confined spaces.
The suspect’s arrest on dual charges – possession of a firearm and causing a public nuisance – reflects both the serious nature of carrying a prohibited weapon and the substantial disruption caused to airport operations and passenger welfare.
This marks the latest in a series of security incidents at Heathrow in recent months. In July, two Just Stop Oil protesters were arrested after spraying orange paint in Terminal 5 as part of environmental protests. The airport has also faced disruption from Border Force strikes and various protest activities throughout 2024.
For the hundreds of passengers caught up in Monday’s evacuation, the experience highlighted the delicate balance between maintaining airport security and managing public safety incidents. Many wrapped themselves in the space blankets provided to keep warm as the sun went down, creating an unusual scene outside one of the world’s busiest international terminals.
The Metropolitan Police confirmed their specialist officers conducted “a thorough search of the area” before declaring it safe. The force emphasised that whilst around 20 people reported injuries, “none were deemed to be life-threatening or life-changing.”
As investigations continue, questions remain about how the CS spray came to be discharged in the terminal and whether additional security measures may be needed to prevent similar incidents. The Civil Aviation Authority and airport security services are likely to review protocols following this disruption.
The incident serves as a reminder of the vulnerability of crowded public spaces to both intentional and accidental releases of irritant substances, and the cascading effects such events can have on public health and transportation infrastructure.
Terminal 4, which was closed for two years during the coronavirus pandemic before reopening in June 2022 following refurbishment, has now returned to normal operations. However, for those caught up in yesterday’s frightening evacuation, the memory of the chaos and confusion is likely to linger far longer than the physical effects of the CS spray exposure.
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Image Credit:
View of Heathrow Airport (August 2023) from a Virgin Atlantic Airbus A330-900 — photo by DiscoA340, CC BY-SA 4.0
