There are plenty of good storm shelters out there, but I don't know of any with thicker steel than 3/8". This one is double the gauge of many certified shelters, and again, the shape puts the strength off the charts. Concrete is great for shelters, but not space-efficient because the walls need to be several inches thick to do the job. For strength AND space-efficiency, thick steel is the answer.
The domed cylindrical shape of the New Day shelter really makes it tough! Like a commercial aircraft, this form causes the metal structure to be as strong as physically possible. Also like a plane, this shelter is slick in super-high winds. We don't think much about stationary objects needing to be aerodynamic, but certainly a safe room should be when it is in winds approaching Mach 0.4! (Its drag coefficient is just 0.63 producing near-zero lift!)
New Day Tornado Shelters
Nominal Specifications
Shelter Overall Height, 80" (6' 8")
Shelter Footprint, 42" (3' 6")
Shelter Weight, 1,100#
Shelter Drag Coefficient, 0.63
Wall Material, SA-455 Carbon Steel
Wall Thickness, 3/8"
Wall-to-Dome Connection, Submerged Arc Weld
Dome Arc Radius, 21"
Dome Material, SA-455 Carbon Steel
Dome Thickness, 1/4"
Door Opening, 24"W x 46"H
Door Material, A-36 Cold-Rolled Steel
Door Thickness, 3/8"
Door Weight, 148#
Door points of attachment, 6
Door Threshold, 12"
Door Connection, Metal Inert Gas Weld
Lock Bolts, 3/4" Cold-Rolled Bar Stock
Anchor Brand, Hilti
Anchor Type, HUS Removable
Anchor Dimensions, 1/2" x 6"
Anchor Ideal Quan per Hilti, 7-9
New Day Anchor Quantity, 9
Minimum Ventilation per Standard, 6 Sq In
New Day Ventilation Area, 24 Sq In
New Day Max Vent Gap, Aprox, 1/4"
Interior Padding, .45" Closed-Cell Polyolefin, Blue
Flooring, 1/2" Anti-Fatigue Mat, Gray
Lighting, (2) LED Switch Lamps, with batteries
Earmuffs, up to (4), -17db Rated
Seating, 7-gallon "bucket seat"
There are advantages to each. In this case, the outward-swinging door is designed larger than the door opening so that gross impacts from outside cannot possibly force the door in toward the occupants.
Actually, the Federal Emergency Management Agency doesn't certify storm shelters. The New Day shelters are known by third-party evaluation to be in compliance with the guidelines of FEMA, publication 320 and publication 361.