After a white powder material was discovered in an envelope, Apple Park was partially evacuated.

According to NBC Bay Area, a portion of the Apple Park campus in Cupertino was evacuated after first responders discovered an envelope containing a white powder substance. According to the incident report from the Santa Clara County Fire Department, a fire alarm and hazmat response were activated at Apple’s headquarters shortly after noon local time.

According to the publication, emergency personnel has since concluded that the situation is under control, and staff has been allowed to return inside. What the substance could have been being unknown.

According to an email acquired later in the day by The Verge, Apple assured the staff at Apple Park that “authorities concluded that there was no presence of hazardous items.” According to the email, campus operations are back to normal, and “all sections are open.”

Apple did not respond to a request for comment on the situation right away. Apple will begin a “phased approach” to its hybrid work program in April, after deferring return-to-office plans for its staff numerous times.