Police investigating the suspected chemical incident which led to the evacuation of London City Airport have discovered what is "believed to be a CS gas spray", a spokesman said.
The airport was evacuated for several hours after the suspected chemical incident that left at least 26 people sick.
Hundreds of passengers were ordered to leave the terminal building and flights grounded after passengers suffered difficulties breathing.
The discovery of the suspected CS gas spray, which is more commonly known as tear gas, came after police and firefighters scoured the airport following the alert.
The airport spokesman said it was unclear what had caused the incident,but officers were "investigating whether it was the result of an accidental discharge of the spray".
Two patients were taken to hospital while specialist teams trained in hazardous situations swept the building.
The airport was later declared safe by the London Fire Brigade, which said it found no signs of harmful chemicals in the building.
Passenger David Morris, aged 28, was among those who become ill.
He had been queuing to check in for a flight to Edinburgh when he suddenly became unwell.
I was talking and started to cough to the point I was not able to keep talking.
Mr Morris said that BA staff had jumped over check-in desks to escape as panic set in.
He added that whatever was causing people to cough did not smell or have any colour to it.
A spokesman for the London Fire Brigade said that around 500 people were evacuated as they investigated together with police.
Two complete sweeps of the airport building were carried out jointly by firefighters and police officers both wearing protective equipment.
London Ambulance Service medics specially trained to treat people in hazardous situations also attended the scene.
The closure of the airport led to travel chaos as all flights were suspended.Several incoming planes from destinations such as Frankfurt, Amsterdam, Belfast City and Paris were diverted to other airports.
London City Airport said in a message posted on Twitter that the airport had fully reopened but disruptions would continue into the evening.