At what point should the alarm and light indicating low air pressure activate while performing the fanning down procedure?

The fanning down procedure is a process of slowly releasing air from the air system of a commercial vehicle. This is done to prevent the brake system from locking up when the air pressure is too low. The low air pressure warning light and alarm should come on when the air pressure is around 60 PSI. This is the point at which the air pressure is low enough to warrant caution, but still high enough to safely operate the vehicle.