What about ventilation?
In designing a safe room, it is important that the ventilation openings are narrow so as not to allow significant debris to enter. The metered gap around the door is about ten feet in circumference to get all the cross-sectional area needed to exceed the requirements of the ICC/NSSA Standard for per-occupant ventilation. The battery-powered fan on the door draws in and circulates air, and even the sound of it is said to be a plus during severe weather.