This has already been discussed here: <URL url="Changes in Fire Evac Protocols in Michigan]Changes in Fire Evac Protocols in Michigan]
This procedure is increasingly being adopted in schools all across America. I’ve heard that some schools even go so far as to apply full lockdown procedures, which include barricading the doors to the classrooms, as soon as the fire alarm goes off, such that once the need to evacuate the building is confirmed, the people inside the classrooms first have to remove the barricade before being able to get out.