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Tornado-resistant safe rooms are crucial in the United States where an average of 1253 tornadoes occur annually, producing wind speeds up to 200 mph or more. Safe rooms in schools are especially important because our children count on us to protect them. In 2013, the need for safe rooms in schools became tragically apparent. A tornado with winds of 210 mph hit and destroyed two elementary schools in Moore, Oklahoma - killing seven children. Structural deficiencies in the schools were blamed for the buildings collapsing. Tornado-proof safe rooms in the schools could have prevented this loss of life.
Since 2015, the International Building Code (IBC) and the International Existing Building Code (IEBC) have required storm shelters (safe rooms) in K-12 school buildings (Educational Group E). These specifications apply to schools with at least 50 occupants and located in areas with shelter design wind speeds of 250 mph, as specified by the International Code Council (ICC) ICC-500, Figure 304.2(1). The ICC-500 is the ICC/NSSA standard for the design and construction of storm shelters. Its purpose is to protect the occupants in buildings from dangerous winds and flying debris caused by hurricanes and tornados. The IBC along with the International Residential Code (IRC), site the ICC-500 as the governing standard for the design and construction of storm shelters. There are several specific features of a safe room required by the ICC-500.
Besides a solid outer structure, the design of a safe room must include several other features.
The Federal Emergency Management Association guidelines (FEMA P-320 and FEMA 361), which also use ICC-500 as a referenced standard, also specify requirements for a safe room. The FEMA guidelines, however, are considered slightly more conservative than the IBC and IRC requirements.
A school safe room must be designed and built in compliance with the standards mandated by the IBC, IEBC, and FEMA. Safe rooms must maintain their integrity during the high wind forces of a tornado or hurricane. Also, the materials used for the entire envelope of the safe room must combat structural damage by windborne debris. Finally, the safe room(s) must be large enough to hold everyone in the school and be located either within the school or no more than 1000 feet from at least one of the school's exterior doors. A safe room can be an assigned single use space or a multiple use space like a gymnasium, cafeteria, or other large community space. Safe rooms built to codes and standards will provide students, teachers, and others the best protection during a dangerous tornado or hurricane event.
A school save room designed with a strong continuous load path should maintain its structural integrity during a severe wind event. A continuous load path ensures that the connections between the roof, walls, and foundation will have the strength to resist the vertical and lateral loads during severe weather. The components of a safe room must also resist the impact of wind-borne debris, flood loads, and buoyancy forces.
The Walls of A School Safe Room
The walls are the main component of the safe room that resists the lateral-loads (horizontal wind forces). They also are bearing/shear walls. The wind forces on the roof, transfer to the walls. The walls then transfer these forces to the foundation, and ultimately to the ground. The walls must also have the strength to support the roof. An ideal product for safe room construction is the Bautex™ Block Wall Assembly. The Bautex Blocks have the continuous load path needed to resist the strongest winds. Bautex Blocks meet the Federal Emergency Management Agency FEMA 320 and FEMA 361 guidelines in storm zones with wind speeds up to 250 mph.
Foundation and Anchoring Criteria for Safe Rooms
The foundation of a safe room receives the loads from of the walls and directs the forces into the ground. The design and anchoring of the foundation must follow the criteria in FEMA P-361, as specified by the ICC-500. The ICC-500 (Section 308.1.1.2) mandates that the design of slab-on-grade foundations be in accordance with ICC-500. During extreme wind events, the foundation of a safe room must resist uplift, overturning, and sliding forces. Slabs must have a minimum thickness of 3.5-inches with a minimum of 6-inch X 6-inch, W 1.4-inch X W 1.4-inch welded wire reinforcement. Or the slabs can have number four bars spaced at a maximum of 18-inches on center in two perpendicular directions.
The Roof and Doors of a Safe Room
A safe room roof must be securely and sufficiently connected to the walls so as to withstand the wind forces of a tornado. Roofs of a safe room must be built to resist the impact of a 15-pound 2-inch X 4-inch shot at 67 mph. The roofs must also be impermeable to water. Reinforced concrete roofs, like concrete walls, can withstand the wind forces, attacks by debris caused by a tornado, and when properly installed are waterproof.
The doors of a safe room must withstand wind forces and flying debris. Doors used in safe rooms should have documented proof that they are compliant with the most current version of FEMA P-361 and FEMA P-320 or the ICC 500 for tornado wind speed of 250 mph.
The entire envelope of school safe room must protect the room’s occupants from flying debris during tornadoes and hurricanes. A study by Texas Tech University compared the effect of wind-generated debris against walls constructed of plywood, metal combinations, finished concrete masonry unit (CMU), reinforced concrete, and others. The study proved that concrete walls for a safe room are the best choice for protecting occupants from flying debris. Bautex Block Wall Assembly’s insulated concrete block has the strength and mass to combat the impact to wind driven debris at speeds greater than 100 mph. The Bautex Blocks meets or exceeds the following ICC-500 FEMA standards for debris impact.
A safe room is crucial for the protection of those that work and study in a school, particularly in tornado-prone regions like Tornado Alley. After the announcement of a tornado warning, occupants of a school have on average 13 minutes to seek shelter from the up to 250 mph winds and the large flying debris caused by a tornado. A school safe room constructed with Bautex Blocks will protect children and teachers in a school by withstanding the winds and dangerous debris of the strongest tornado.