Hurricane resistance ratings are expressed in pounds-per-square-foot (PSF) values, and unlike fire ratings, there are no standard increments. In addition to the PSF values, they are either listed with or without “missile” impact ratings. In this instance, a missile refers to a 2 x 4 piece of lumber weighing 9 lbs. that is fired at the door at 35 miles-per-hour. A door assembly must withstand 3 impacts in order to have a missile impact listing. A typical door listing would be expressed as;
Design Pressure Rating +75/-65 PSF Large Missile Impact - Yes
This listing indicates that the door assembly is rated for 75 PSF when loaded against the stops of the frame, and 65 PSF when loaded away from the stops of the frame