Heathrow Airport, one of the world’s busiest travel hubs, was thrown into chaos on Monday, September 8, 2025, after a suspected tear gas incident forced the partial evacuation of Terminal 4. According to multiple news outlets, including CTV News, Devdiscourse, and The Associated Press, the disruption began around 16:56 local time when emergency services were called to respond to a hazardous materials alert.
The incident centered on a 57-year-old man who, as police later confirmed, was found with a canister believed to contain CS gas—a synthetic irritant commonly known as tear gas and typically used by law enforcement for crowd control. In the United Kingdom, CS spray is strictly regulated and classified as a firearm under national law, making its possession a serious offense.
As the situation unfolded, the departures area of Terminal 4 was closed for approximately three hours, leaving travelers stranded and airport staff scrambling to manage the fallout. Paramedics treated about 20 people for irritation caused by exposure to the gas, but, as reported by The Evening Standard, none of the affected individuals suffered life-changing or life-threatening injuries. The Metropolitan Police were quick to reassure the public that, despite the alarming circumstances, the incident was not being treated as terror-related—a crucial detail in an era of heightened airport security and public anxiety.
"On Monday, 8 September at 16:56hrs police were called to a potential hazardous materials incident at Heathrow Airport, Terminal Four," a Metropolitan Police spokesperson told reporters, as cited by The Evening Standard. "Following the search, Met officers located a canister 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 reported to paramedics after the (believed) CS spray caused irritation. It has been confirmed that the spray did not cause any life-changing/threatening injuries."
Emergency response was swift and comprehensive. Police, firefighters, and ambulance crews converged on the terminal, initiating standard protocols for hazardous material incidents. Their coordinated efforts ensured that the affected area was evacuated quickly and that those exposed to the gas received prompt medical attention. The closure of Terminal 4, though disruptive, was necessary to secure the scene, ventilate the area, and allow for a thorough investigation.
By Tuesday, September 9, the Metropolitan Police had arrested the 57-year-old man on suspicion of possession of a firearm (CS spray) and causing a public nuisance. As is customary in England, the suspect’s name has not been released, as individuals are generally not identified unless formally charged with a crime. The man remains in police custody as the investigation continues. Authorities have not yet disclosed any possible motive for the man’s actions or how he came to possess the canister.
According to AP News and Devdiscourse, officers found the canister believed to contain CS gas as they searched the area following the initial alert. The incident caused significant disruption, with the departures area of Terminal 4 closed late into the evening. Flights were delayed, and passengers were forced to wait outside or in other parts of the airport until the situation was declared safe. For some, it was an unexpected and frustrating interruption to their travel plans; for others, a stark reminder of the ever-present challenges facing airport security in the modern era.
CS gas, or 2-chlorobenzalmalononitrile, is a chemical compound that irritates the eyes, skin, and respiratory system. While it is not typically lethal, exposure can be extremely uncomfortable and, in rare cases, dangerous for individuals with underlying health conditions. In the United Kingdom, the possession of CS spray by civilians is prohibited, and its use is largely restricted to police and military personnel. The law is clear: carrying such a substance without proper authorization can result in severe legal consequences.
The Metropolitan Police emphasized that their investigation remains ongoing. While the incident is not believed to be terror-related, authorities are taking the matter seriously, examining how the canister entered the airport and whether any security protocols were breached. The presence of a hazardous chemical in a crowded public space has naturally raised questions about screening procedures and the effectiveness of existing safeguards.
For travelers and staff caught up in the incident, the experience was unsettling. "It was chaos for a while—alarms going off, people coughing, and then we were told to leave everything and get out," one passenger told Devdiscourse reporters. While most people remained calm, the confusion and uncertainty were palpable as emergency crews worked to assess and contain the situation.
Heathrow Airport, located west of central London, is no stranger to security incidents, given its status as a major international gateway. However, events involving hazardous substances are rare, and the airport has a robust emergency response system in place. Monday’s incident tested those protocols and provided a real-world stress test for the teams on the ground.
In the aftermath, airport authorities and police have been keen to reassure the public that safety remains their top priority. "The safety and security of our passengers and colleagues is always our main concern," a Heathrow spokesperson said. "We are cooperating fully with the police and emergency services as they continue their investigation."
As of Wednesday, the suspect remains in custody, and no further arrests have been reported. The authorities have not indicated when they expect to conclude their investigation or whether charges will be filed. For now, the incident stands as a cautionary tale about the risks posed by hazardous materials in public spaces and the importance of vigilance—not just by security professionals, but by the traveling public as well.
While the disruption at Terminal 4 was significant, the quick response by emergency services and the absence of serious injuries have been widely praised. For Heathrow and its millions of annual passengers, the hope is that lessons learned from this scare will help prevent similar incidents in the future—and ensure that London’s busiest airport remains a safe gateway to the world.