Authorities have confirmed that a suspicious package discovered Monday at a Facebook mailing facility in Menlo Park, California, has tested negative for "any potentially dangerous substance," a Facebook spokesperson said Tuesday.

Emergency hazmat crews spent several hours at the mailing facility after a machine that can detect dangerous substances alerted employees Monday morning that a package might contain the chemical nerve agent sarin, the Menlo Park Fire District said.

No employees were ever exposed to the substance in question, according to the fire district. Four buildings in the area were evacuated, but the evacuation orders have since been lifted, according to a Facebook spokesperson.

After multiple agencies crafted a course of action, a hazmat team around 6 p.m. Monday entered the building where the package was, cleared all of the rooms and eventually tested the package, the fire district said. The team exited at about 6:45 p.m. and was decontaminated.

Later Monday night, during a second sweep of the building utilizing "more sophisticated detection equipment," the hazmat team recovered the package, put it in a mobile containment device and removed it from the building, according to the fire district. Test results for any dangerous substances later came back negative.

The Centers for Disease Control and Prevention defines sarin as a "human-made chemical warfare agent classified as a nerve agent." Sarin was originally developed in 1938 in Germany as a pesticide. It is a "clear, colorless, and tasteless liquid that has no odor in its pure form" and even a small drop on the skin can cause sweating and muscle twiching. Mildly exposed people usually recover completely, the CDC said.

Fire officials initially reported that at least two people may have been possibly exposed to sarin.