At least four buildings at Facebook’s campus in Menlo Park in the United States were evacuated on Monday after a package at the social media company’s mail facility tested positive for the nerve agent sarin, Reuters reported.

Menlo Park Fire Marshal Jon Johnston said on Monday that incoming mail that went through routine processing by machines tested positive for sarin, but that there were no reports of injuries at the site. “Right now we don’t have anybody that has any symptoms,” Johnston said, according to AP. “We’re just doing verification.”

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Sarin is a chemical warfare agent that is colourless, odourless, and tasteless. It evaporates into the environment and prompts symptoms within seconds. Exposure to large doses may result in paralysis and respiratory failure.

Johnston said the Facebook facility tests all incoming packages and initiated standard protocol after a package tested positive for sarin. “Now we’re just waiting to verify whether that’s true or not,” Reuters quoted Johnston as saying. Johnston added that everything was contained and quarantined within the building, reported ABC7News.

Officials at the Menlo Park Fire Protection District arrived at the Facebook headquarters after reports of two employees being possibly exposed to the nerve agent sarin.

Facebook spokesperson Anthony Harrison said the company evacuated four buildings following the positive test. “Authorities have not yet identified the substance found,” Harrison said. “As of now, three of the evacuated buildings have been cleared for repopulation.”