About 21 people were exposed during a hazmat incident on Monday afternoon involving a "chemical release in a clean room" unrelated to biohazard materials, the city of Redwood City said in a statement on social media.
The incident occurred at the 1100 block of Island Drive in Redwood Shores.
In an update, fire officials confirmed the gas was determined to be Freon and that crews determined that a faulty air conditioner was the source.
About 16 people were without symptoms, and another five were receiving treatment. As of 4 p.m., emergency personnel were on site, and fire officials were inspecting the building.
According to a case study by the National Institutes of Health (NIH), exposure to Freon caused "transient loss of consciousness, bradycardia, hypotension and anaesthesia" in at least three people. In all three cases, patients made a full recovery.
On Monday, officials said that they did not issue a shelter-in-place or evacuation notice.