Facebook released a statement on Tuesday morning saying test results on a suspicious package came back negative for sarin and other hazardous materials and no one was hurt.
FBI officials were at the scene after a chemical scare forced employees to be evacuated Monday morning.
Officials with the Menlo Park Fire Protection District responded to the Facebook complex on Hamilton Avenue following reports of two employees being possibly exposed to the nerve agent sarin.
During a routine check, one of the company's mail processing machines detected the presence of sarin on a package that had arrived around 11 a.m., although an open-air test later came back negative.
Four buildings were initially evacuated as a precaution, but just one remained closed into the evening hours as crews conducted their investigation.
New pictures from the Menlo Park Fire Department show the overnight work to remove the potentially hazardous package.
No one was hurt in the incident or exposed to hazardous chemicals, authorities say.
According to the Centers for Disease Control and Prevention, sarin is a chemical warfare agent that is clear, colorless, odorless, and tasteless. It can evaporate into the environment, prompting symptoms within seconds.
Exposure to large doses may result in paralysis and respiratory failure.
Sarin was used in two terror attacks in Japan in 1994 and 1995, the latter of which killed 13 people when the gas was released in the Tokyo subway system.
"The safety of our employees is our top priority and we will share additional information when it is available," said Facebook spokesperson Anthony Harrison.
#NOW: @menlofire crews are at the scene of a hazmat call at a Facebook warehouse facility on Hamilton Ave. in Menlo Park. FBI and National Guard have been called to assist. Two employees were tested for possible chemical exposure, but have shown no symptoms, per fire marshal. pic.twitter.com/iL8DkKZGfU— Chris Nguyen (@ChrisNguyenABC7) July 1, 2019
Fire officials say routine tests for chemicals detected the presence of sarin in a #Facebook mail facility. It’s possible that the detection is a false positive. We expect to get a briefing from @menlofire within the hour. Facebook officials have yet to comment. #ABC7Now pic.twitter.com/BcRnQePuYW— Chris Nguyen (@ChrisNguyenABC7) July 1, 2019