Facebook’s Menlo Park campus in Silicon Valley has been given the all clear after fears of a sarin exposure yesterday led to the evacuation of several buildings. A spokesperson for the company confirmed the news to The Verge after it was first reported by Reuters.

Facebook’s spokesperson said the scare started after mail delivered to one of the company’s mail rooms was “deemed suspicious.” According to a report from Business Insider, the social media company uses automatic detectors to spot dangerous chemicals and substances, and these flagged a mailbag as containing traces of the nerve agent sarin.

“Out of an abundance of caution, we evacuated four nearby buildings and began a thorough investigation in coordination with local authorities,” said Facebook’s spokesperson. “Authorities have confirmed test results were negative for any potentially dangerous substance and the buildings have been cleared for repopulation. Our rigorous security and safety procedures worked as intended to limit exposure and keep our people safe.”

Menlo Park’s city fire marshal Jon Johnston told Reuters that exhaustive tests of the site had found no traces of toxic material. “There is no sarin,” Johnston told the news agency.

Facebook has previously been the target of at least one bomb scare, last December, which also led to the evacuation of several buildings.

Update, Tuesday July 2nd, 8:04AM ET: Story has been updated with comment from Facebook.