Story highlights Sweeps of the building found no elevated readings, fire officials say

Traveler: "We all just ran. Nobody knew what was going on"

(CNN) London City Airport was declared safe Friday after reports of a "chemical incident" spurred an evacuation, fire officials said.

"Two complete sweeps of the airport building were carried out jointly by firefighters and police officers both wearing protective equipment," the London Fire Brigade said in a statement. "No elevated readings were found and the building was ventilated, searched and declared safe."

Authorities believe the incident might have been caused by a CS gas spray -- a type of tear gas -- but are still investigating. "Whilst the cause of the incident has not yet been confirmed, officers are investigating if it was the result of an accidental discharge of this canister," a statement says.

Passengers wear emergency blankets to keep warm outside the terminal.

"At this early stage officers are investigating whether it may have been discarded by a passenger prior to check-in. There have been no arrests and enquiries continue."

The airport was evacuated after a number of passengers reported feeling unwell, police said.

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