"Construction is solid steel plate[, and ]units can be concrete filled for improved radiation shielding, sound reduction or temperature insulating capacity...[The doors] withstand forces up to 1000 PSI or even higher...The units are fabricated per procedures outlined in the American Welding Society AWS Structural Welding Code for Steel and designs comply with AISC specifications and Dept. of the Army Technical Manual TM5-1300 "Structures to Resist the Effects of Accidental Explosions". Refer to the page on our web-site Establishing Blast Criteria for design assistance...."
http://www.protectivedoor.com/missile-tornado-resistant.php
http://www.protectivedoor.com/missile-tornado-resistant.php