Video of a so-called Transportation Security Administration “freeze drill” has been posted online, showing a TSA officer instructing passengers to remain in place at Phoenix’s Sky Harbor International Airport before permitting them to leave.

The TSA told the New York Times in 2011 that the drills are a training tool for officers to practice quickly shutting down a security checkpoint in the event of a security breach. TSA spokeswoman Kristina Lee said the agency has “wide-ranging legal authority to carry out security-related responsibilities.”