On Monday, a routine test at a mail facility for the company tested positive for the substance, prompting the evacuation of four buildings, Federal Bureau of Investigation involvement, and the quarantine of the suspect mailbag.
The item, described as a "large general mail bags" with lots of mail inside, went through one of the Menlo Park facility's mail scanning machines tested positive for sarin, according to Johnston.
No employees were exposed to the toxic chemical, the Menlo Park Fire District told NBC-contrary to earlier reports that two employees may have been jeopardized.
The social media company runs all its mail and packages through a machine that automatically detects risky substances.
There's a report that a test at one of its mailing facilities was positive for the nerve agent sarin.
The false alarm prompted the company to evacuate four nearby buildings on Monday. "As of now, three of the evacuated buildings have been cleared for repopulation", Harrison said.
"This event was contained to the structure of origin and did not present a threat to the broader community", said Menlo Fire Chief Harold Schapelhouman.
The nerve gas is clear, odorless and tasteless but it can product symptoms within seconds.
A spokesperson from Facebook has confirmed to Siliconrepublic.com that at 11am PDT, mail delivered to one of the mailrooms was deemed to be suspicious, though added that the results for tests for potentially unsafe substances came back negative. Mildly exposed people, according to the Centers for Disease Control, usually recover "completely". Exposure to sarin can cause paralysis and death.
Johnston said the Facebook facility tests all incoming packages and initiated standard protocol after a package tested positive for sarin.