Facebook Inc evacuated four buildings after a packet with possible Sarin — a potentially deadly nerve agent — was detected in the social networking giant’s Silicon Valley mailing facility on Monday.

Meanwhile, two people, who are suspected of being exposed to the nerve agent, are being examined.

According to a report in Reuters, the people who came in contact with the suspicious package did not show any symptoms of exposure to sarin, said Jon Johnson, fire marshall for the city of Menlo Park.

“The (Facebook) facility tests all of the packages that come in and they had a positive test, so they just initiated their standard protocol. Now we’re just waiting to verify whether that’s true or not,” he said.

Facebook spokesman Anthony Harrison said the company evacuated four buildings following the positive test and was cooperating with police in the investigation.

“Authorities have not yet identified the substance found. As of now, three of the evacuated buildings have been cleared for repopulation,” Harrison said.

Exposure is lethal even at very low concentrations, where death can occur within one to 10 minutes after direct inhalation of a lethal dose, owing to suffocation from lung muscle paralysis, unless antidotes are quickly administered.

Sarin is generally considered a weapon of mass destruction. Production and stockpiling of Sarin was outlawed as of April 1997 by the Chemical Weapons Convention of 1993, and it is classified as a Schedule 1 substance.

(With agency inputs)