Update 2: A Facebook spokesman said that as a result of the finding, the company evacuated four buildings. Though earlier reports identified the substance as liquid Sarin, the spokesman said it hadn't been identified. Three of the evacuated buildings had been cleared as of 11 am PT (2 pm ET). One more remained to be thoroughly investigated.

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Update: Some more details about the incident have started leaking out. Menlo Park Fire Department officials said a machine at Facebook's mailing facility alerted employees that a package might contain Sarin. No employees were exposed to the substance. Facebook employs machines to scan all of its mail, per NBC.

UPDATE: Menlo Park Fire officials say machine at Facebook's mailing facility alerted employees that a package might contain sarin; the employees themselves were not exposed to the substance. No official word on what the substance actually is: https://t.co/74EAGOfkud — Riya (@loislane28) July 1, 2019

Per Menlo Fire:

- Facebook runs all their mail through a machine that can detect dangerous substances.

- Today, that machine alerted employees that a package might contain sarin; nobody was actually exposed.

- @facebook protocol is to alert the fire dept to remove/test substance — Riya (@loislane28) July 1, 2019

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According to fire officials in Menlo Park, two Facebook employees may have been exposed to Sarin at a company mailing facility, NBC Bay Area reports.

#BREAKING: At least 2 employees may have been possibly exposed to sarin after coming in contact with the chemical at a Facebook mailing facility, Menlo Park fire officials say. https://t.co/fnKE1CC8OW — NBC Bay Area (@nbcbayarea) July 1, 2019

According to the most recent reports, the two employees weren't exhibiting signs of being poisoned. A hazmat crew is on the scene testing materials.

The "material" - the report didn't specify which form the suspicious chemical was in - arrived at the facility in a package. The building, a warehouse reportedly owned by Facebook, has been evacuated, per ABC.