MENLO PARK (KRON) – Menlo Park fire crews responded to Facebook’s Menlo Park mailing facility Monday after reports of a suspicious package were made.

Menlo Park Fire Marshal Jon Johnston said Monday that incoming mail going through routine processing tested positive for sarin.

Sarin is a highly toxic chemical that disrupts the functioning of the nervous system.

FBI San Francisco also responded to the scene at the request of the San Mateo Hazmat team.

Johnston said authorities were checking to see if the test was a false positive or something else. At this time, hazmat crews have not identified the substance.

Four buildings were evacuated, according to the fire department. They say the building where the package was only had five people inside.

Johnston said no one showed signs of illness and that the building is under quarantine.

People evacuated from the other three buildings have since been able to go back inside, officials say.

A Facebook spokesperson, Anthony Harrison, released this statement on the situation:

“At 11:00 AM PDT this morning, a package delivered to one of our mail rooms was deemed suspicious. We evacuated four buildings and are conducting a thorough investigation in coordination with local authorities. Authorities have not yet identified the substance found. As of now, three of the evacuated buildings have been cleared for repopulation. The safety of our employees is our top priority and we will share additional information when it is available.”

Anthony Harrison, Facebook spokesperson

Crews say that there is no threat to the community or public at this time.

Everything in the impacted building continues to be quarantined and crews are working on doing a re-evaluation of the building.