A machine in one of Facebook's mailing facilities in Menlo Park, Calif., detected what it thought was sarin in a package on July 1, causing the social media giant to evacuate the facility, according to CNBC.
The CDC defines sarin as a "human-made chemical warfare agent classified as a nerve agent."
The fire department said no employees had been exposed to the chemical. Facebook has all of its mail and packages tested in a machine that detects dangerous substances.
After a 14-hour evacuation, Facebook announced on July 2 that the package later tested negative for sarin and other hazardous materials, ABC News reports.