A machine Facebook uses to detect poisonous substances in the company’s mail facility in Menlo Park, California, alerted employees Monday that a package contained possible traces of sarin.

Facebook filters its mail and packages through a system designed to detect dangerous substances, according to the Menlo Park Fire District. A Facebook representative said several buildings in the area were evacuated.

Only one building remains evacuated. (RELATED: Conservatives Say Facebook Is Suppressing Much Of Their Content. Here’s What Experts Say)

Fire officials initially reported two people may have been exposed. It is possible the machine made a false positive, a fire official said, meaning it incorrectly identified a toxic substance. Sarin is a nerve agent that can cause loss of consciousness, convulsions, paralysis and death, according to the Centers for Disease Control and Prevention.

Facebook has not yet responded to the Daily Caller News Foundation’s request for comment.

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