Here is a basic louver cut on a standard roof. 

This video is just for people to get better idea of the time it actually takes to make a hole for vertical ventilation.  Notice the sounding technique plus the use of a tool to keep the sawyer aware of how close he is to the edge and working in safe areas without slowing the firefighter down.  This operation is fast and effective.  Ventilation is like any other event on the fireground, assess situation make a decision, complete the task and make sure what you did had the desired effect on the fire.

Safe operations come from being very good at your job, train every day.