by Karen Bishop
This year is shaping up to be a record-breaking one for tornadoes and severe weather. In just the first nine months, nearly 1300 tornadoes swept across the country, according to the National Oceanic Atmospheric Administration’s (NOAA’s) National Weather Service. States like Georgia, Texas, and Missouri have experienced the most severe weather, reporting more than 390 tornadoes since January, while 42 states have experienced at least one.
Even with an alarming number of severe weather incidents, preparedness kept most people safe when disaster struck. Tornado shelters are common throughout the Tornado Alley, the central United States region that is often hit by storms—including portions of Texas, Oklahoma, Kansas, and Nebraska. Since 2009, the International Building Code (IBC) has included standards for these shelters. However, not until the 2015 edition did it require certain buildings in tornado-prone areas to take additional precautionary measures. (Previously, this was mandated by state or local jurisdiction.)
New K–12 facilities with occupant loads of 50 or more, as well as critical emergency operations, are among the structures that are now required to include a storm shelter if they reside in a 402-km/hr (250-mph) wind speed zone per the map in American Society of Civil Engineers (ASCE) 07, Minimum Design Loads for Buildings and Other Structures. There are 22 states where at least a portion of the state is susceptible to these high winds.
Critical emergency operations include public safety facilities like 911 call stations and fire, rescue, ambulance, and police stations. The 2015 IBC mandates these facilities to have a storm shelter built in accordance with International Code Council (ICC) 500-2014, Standard for the Design and Construction of Storm Shelters.
Additionally, storm shelters are required to adhere to other life safety requirements as directed by the IBC and as required in ICC 500. According to Section 601 of ICC 500, nonresidential tornado shelters must be separated from other building areas by fire barriers and horizontal assemblies with a minimum fire-resistance rating of two hours.
Understanding the codes
To offer ultimate safety, tornado-resistant doors must comply with the most stringent life-safety testing standards developed by ICC and National Storm Shelter Association (NSSA). ICC 500 is recognized under IBC as the governing standard for the design, construction, and testing of storm shelters. It includes test requirements simulating a 402 km/hr (250-mph) ground-speed tornado, including the impact force of building materials propelled at 161 km/hr (100 mph).
The tornado guidelines in the United States were established by the Federal Emergency Management Agency (FEMA). FEMA P-361, Safe Rooms for Tornadoes and Hurricanes: Guidance for Community and Residential Safe Rooms, provides guidelines for community storm shelters with an occupant load of 16 or more. FEMA 320, Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business, pertains to residential safe rooms. Community safe rooms must be designed to meet stringent requirements, so it is important to consider both FEMA 361 and ICC 500 when constructing a building in one of the at-risk areas.
Safety starts at the door
Many considerations come into play when designing storm shelters, including door assemblies and windows. For instance, it is important to consider tornado lites for hollow metal tornado door assemblies. These allow natural light to enter the room and add to the door’s overall aesthetics. They also address the liability concerns associated with a lack of visibility when using traditional flush tornado-rated doors.
Without options to provide anything but flush tornado door assemblies in the past, architects and school administrators had their hands tied in providing tornado door assemblies in their shelters. They were forced to forgo desired natural light as well as critical visibility in classrooms. Recent code changes require the aggregate of the building occupancy to be housed by the storm shelter, and may even require space for the community to shelter from storms. Many school shelters have moved from smaller classrooms to large gymnasiums or entire wings of school buildings, which has increased the need for glass lights.
Additionally, tornado door assemblies can be used as shutters to protect windows, allowing daylighting with superior protection when needed.
ICC 500 requires door assemblies be tested and approvals be listed with a third-party, such as Intertek. Additionally, all door assemblies must be labeled as complying with the performance requirements of ICC 500. Door assemblies may only be approved if they pass multiple impacts of a 7-kg (15-lb) 2×4 propelled at 161 km/hr (100 mph) to critical areas of the door assembly. The assembly must also pass multiple pressure loads of at least 302 psf (which exceed the pressures created by a 402-km/hr [250-mph] wind speed). For Americans with Disabilities Act (ADA)-compliant applications, a narrow lite can be used in place of a vision lite. Additionally, the 90-minute fire rating is Intertek-labeled and Steel Door Institute (SDI)-certified. SDI’s testing video is available here.
Beyond the door
Storm shelters have to meet the highest life safety standards to protect the occupants. This means all products must be tornado-rated. However, to provide the correct protection during a severe windstorm event, one must use the locking system designed, tested, and approved with the door assembly. This approved hardware is operationally and aesthetically identical to standard exit and lever devices, but is specifically designed to withstand the wind and impact requirements of ICC500.This means all latches engage when the door is shut and retract simply by rotating the lever or pushing the exit bar, providing superior protection with familiar operation.
The code compliance for storm shelters is not just limited to new construction. In the 2015 International Existing Building Code (IEBC) and the upcoming release of the IBC’s 2018 edition, existing schools within the 402-km/hr (250-mph) wind speed map are mandated to add storm shelters when renovating or creating additions for campus buildings, as well as for new structures.
Karen Bishop has more than 30 years of experience in the door and hardware industry. She oversees code compliance, design, testing, and product certifications for Allegion’s commercial door and frame manufacturers. Bishop is a member of National Storm Shelter Association (NSSA) and Underwriters Laboratories (UL) Fire-testing standards. She can be reached at firstname.lastname@example.org.