In the Eye of the Storm

Tested for code-required wind pressures and the latest impact resistance, highly engineered doors, shutters, and hardware assemblies are turning tornado shelters into aesthetic, functional spaces

In the wake of a series of tornado catastrophes in the past decade, industry associations, code-making bodies, and authorities having jurisdiction have rallied together to provide key guidelines and code requirements for storm shelters in school buildings and critical facilities.

In turn, the building products industry has responded with an assortment of impact-resistant doors, shutters, and hardware to protect occupants from the great dangers posed by winds of up to 250 mph, wind-borne debris, and other dangers created by the awesome and terrifying effects of Mother Nature.

Tornadoes Leaving their Mark

While tornadoes have wreaked havoc on vulnerable cities and towns in the United States for many years, a spate of particularly devastating tornado outbreaks in the past decade have served as a wake-up call to vulnerable tornado-prone areas.

Case in point, a series of 56 confirmed tornadoes drove through the South in the winter of 2007, beginning in Kansas and making its greatest impact on Enterprise, Alabama, where more than $307 million in property damages and significant loss of life occurred.

The single-most deadly tornado to date occurred in Joplin, Missouri, when an EF-5 tornado—the highest category—with more than 200-mph wind speeds killed 162 people, caused close to 1,000 injuries, and damaged or destroyed approximately 8,000 structures, affecting approximately 30 percent of the town of less than 50,000 people.

Then in Moore, Oklahoma, in 2013, 210-mph estimated peak winds took the lives of 24, injured 377, destroyed 1,150 homes, and left $2 billion worth of damage in its wake.

Unlike hurricanes—which are large weather systems that can last up to three weeks and give advance warnings of several days, giving time for residents to evacuate the area—tornadoes are short, intense storms, giving towns little warning of the impending attack. In fact, the National Oceanic and Atmosphere Administration reports that the average tornado warning is just 13 minutes.

“Compared with hurricanes and earthquakes, single tornado events typically affect smaller geographical areas but occur more often and cause more deaths,” explains Ken Kilzer, SE, structural engineer, Olsson Associates, Omaha, Nebraska. According to the National Weather Service, “From 1950 through 2011, tornadoes caused about 5,600 fatalities in the United States, more than hurricanes and earthquakes combined over the same time period.”

In comparison to hurricanes, tornadoes are much smaller, usually no more than a ½ mile wide, lasting from a few minutes up to an hour.

Putting things into perspective, James E. Waller, PE, director of engineering, Remagen Corporation, Monteagle, Tennessee, explains that the wind pressures and forces of a tornado on a structure are approximately four times as great as what engineers design for in coastal areas subject to Category 4 hurricanes, and nearly eight times as great for design of buildings in noncoastal areas.

In addition to the structural damage incurred by extreme winds and flying debris, internal and external pressures induced by the winds can cause damage to buildings as well.

Enter the Building Codes

In order to direct building teams to design and build spaces to protect occupants from tornadoes, the Federal Emergency Management Agency (FEMA) began conducting post-disaster investigations and found that many smaller, interior rooms were surviving, while the rest of structures were destroyed.

“The study of past storms and their affects have allowed engineers, meteorologists, and scientists to determine the wind speeds and debris impact requirements that are appropriate to use for the design of storm shelter structures,” explains Jason Pirtle, PE, M.ASCE, president, Remagen Corporation, Jackson, Tennessee. “Since these load demands are greatly elevated from those used in typical buildings, the development of a Standard to specifically address shelters was needed.”

Emerging from this FEMA research, the agency developed FEMA 320: Taking Shelter from the Storm: Building a Safe Room For Your Home or Small Business, first published in 1998, and FEMA 361: Design and Construction Guidance for Community Safe Rooms, first published in 2000, offering guidance for storm shelter construction. Incidentally, both FEMA P-320 and FEMA P-361compliance are required for building owners seeking construction grants from FEMA.

In May of 2002, the International Code Council (ICC) and the National Storm Shelter Association (NSSA) initiated a joint project to write a standard for the design and construction of storm shelters. A standard development committee was created, and the first meeting was held in May of 2003. The scope of the standard was established to provide minimum design and construction requirements for storm shelters that provide a safe refuge from storms that produce high winds, such as hurricanes and tornadoes. First published in 2008, ICC 500 became a referenced standard in the 2009 International Building Code (IBC). In the 2009 and 2012 IBC, shelter construction was voluntary, but in cases when a shelter was built, it was regulated by the standard.

As of December of 2014, a revised edition of ICC 500 was published and subsequently referenced in the 2015 IBC, which requires storm shelters in certain Group E educational facilities and critical emergency operation facilities, such as 911 call stations, emergency operation centers, fire, rescue, ambulance, and police stations, in higher wind zones. More specifically, all newly built schools housing 50 or more kindergarten through 12th grade students in 22 U.S. states where wind speeds can potentially approach 250 mph require storm shelters.

In developing ICC 500, the committee “considered the probability of tornadoes of various intensities occurring at various regions by reviewing over 50 years of tornadic history. And, they considered the higher responsibility that schools with an E occupancy have to protect their students during a tornado and that first responders have to serve their communities after a tornado,” explains Benchmark Harris, PE, SE, LEED AP, director of engineering, Huckabee, Fort Worth, Texas.

Simultaneously, Ernst W. Kiesling, PE, Ph.D, executive director, National Storm Shelter Association, Lubbock, Texas, relates that FEMA continues to evaluate post-tornado shelter performance to evaluate standards and steadily upgrade them. “FEMA reports contain recommendations for improving the built environment to provide higher levels of safety,” he says.

Explaining the process in more detail, Kilzer relates that mitigation assessment teams (MAT)—staffed by FEMA professionals, state and local governments, and public and private sector experts in design, construction, and building code development and enforcement—are deployed to study the performance of buildings in the wake of destructive tornados.

“The information the MAT teams accumulate, along with the results of testing performed at universities, such as Texas Tech’s National Wind Institute, provides engineers with real-life lessons and academic data that can be used to improve storm shelter design,” he says. “As more storm shelters are built, more are exposed to tornadic events. And as the post-tornado performance of these shelters is analyzed, more information is available to designers to optimize the performance of the structures.”

Code Compliant

At this point in time, a major aspect of ICC 500 requirements is rigorous testing for the building products and systems going into a certified tornado shelter.

Explaining the background behind these testing requirements, Kiesling, Pirtle, and Waller relate in a Structure magazine article, “NSSA/ICC 500-2014 Storm Shelter Standard—Structural Provisions,” that there hasn’t been enough research to more definitively determine the damage of wind-borne debris missiles, such as wind-driven lumber or roof decking striking shelter surfaces, glazing, and impact-protective systems. “Therefore, to ensure occupant protection, ICC 500 requires laboratory impact testing of the storm shelter structures and all impact-protective systems,” they say.

In order to meet stringent ICC 500 storm shelter requirements, the shelter door assembly must be able to resist a 15-pound, 2-inch by 4-inch board traveling horizontally at 100 mph, which is much higher than Miami-Dade standards for hurricane protection, as tornado winds travel at a higher velocity than hurricane-induced winds.

One mistake that people can unfortunately make is assuming that a standard door with three dead-bolts will withstand a tornado. In reality, a tornado-resistant door typically includes heavy-duty reinforcement plates and is engineered and certified as a complete system, inclusive of all accessory elements. Furthermore, ICC 500 requires that a storm shelter door be able to withstand impact testing in at least three locations—in a central location, within 6 inches of a corner, and within 6 inches of the main latch.

In configuring storm shelters for tornadoes, different failure modes and loadings must be considered based on the assumption that surrounding or host buildings will be completely destroyed, leaving the shelter fully exposed to the wind forces of a storm.

For example, wind pressures for storm shelters are calculated using the American Society of Engineers ASCE 7-10: Minimum Design Loads for Buildings and Other Structures. When analysis for wind pressure is not practical, ICC 500 provides requirements and procedures for laboratory pressure testing walls and roof assemblies. Impact-protective systems, including doors, are always required to be subjected to physical testing to ensure their performance. Architects and structural engineers should also be aware that there cannot be any breach in the building envelope. This includes all the transitions between the doors and windows to the wall.

With regards to vetting storm shelters, ICC 500 requires peer reviews or independent third-party evaluations for community shelters with 50 or more occupants, daycare shelters with 16 or more occupants, school shelters, and shelters in Risk Category IV, as defined by the IBC, such as police stations, fire stations, and emergency operations facilities.

As Corey Schultz, AIA, LEED BD+C, vice president, Schultz Squared Architects, Wichita, Kansas, explains in his company blog, “Storm Shelters – Peer Reviews,” many designers erroneously believe that shelters are nothing more than adding some more rebar in the walls, putting those shutter “thingies” over the windows, installing vault doors, and putting concrete or dirt on the roof.

“Unfortunately, it is well beyond those issues, well beyond. Because of these reasons, ICC 500 and FEMA P-361 call for peer reviews as a shelter/safe room requirement, for both architectural and structural, for any shelter that protects more than 50 occupants. It is a second set of eyes to help assure that the end users of that shelter are safe in a tornadic event,” he writes.

Architects must also submit a quality assurance plan in the design drawings and specifications, and the contractor must submit a written statement of quality control responsibility to the authority having jurisdiction, the design professional, and the owner before commencing construction.

Then, during construction, a number of special inspections are required. For example, with community shelters, structural observations must be performed by a registered design professional during significant phases of construction.

Locating the Shelter

Offering some perspective on the evolution of storm shelter standards, Jim Bell, CSI, CDT, windstorm coordinator, ASSA ABLOY, Smithville, Tennessee, explains, “In the past, you just went out and bought a $7 sign and hung it up somewhere, declaring that it was a shelter. Then we went to the idea that if you’re going to put a sign on something and direct a large number of people to a space with the implicit direction that you will be safer if you go there, then you have to actually provide a level of safety to them. And from that, we’ve evolved to: You shall provide safety to the occupants in the K–12 environment.”

When designing storm shelters for tornado protection in K–12 schools and other buildings, design teams must first determine where the shelter will be located within the floorplate.

“Architects should look to interior areas of buildings to design reinforced six-sided enclosures to resist the highest winds from tornadoes or straight line gusts,” explains George M. Blackburn III, M.Arch., AIA, BCxA, Carrollton, Texas. However, “the area within the building should be selected with a consideration for the possibility of rising water.”

If a large space like a gymnasium or auditorium is selected, the structure must be reinforced to withstand a tornado. Advantages of this location include housing a large number of people and an absence of exterior windows, in some cases. Furthermore, these spaces lend themselves to hardening with concrete walls and roof structures and highly engineered doors.

On the other hand, drawbacks include the fact that these areas may be located far from classrooms—even a different floor—and being that tornadoes can appear with little to no warning, there may not be sufficient time to transport students to the shelter.

When the shelter is located underground, Patrick Glenn, AIA, REFP, LEED AP, partner, managing principal, Glenn Partners, Dallas, points out that these spaces must meet additional siting criteria and flood design requirements. Aboveground and integrated storm shelter design—as opposed to separate, isolated, and underground cellars—are becoming more the norm as more manufacturers, material vendors, and construction teams gain experience in this particular field, he says.

One area that is not recommended for shelter spaces are corridors that often have openings that continue through to the outside at either end, thereby creating a wind tunnel effect. “The speed of this air can actually increase and move faster that the air on the exterior of the building,” explains Shauna Schultz, AIA, CDT, in a Schultz Squared Architects blog on tornado shelters. “Most tornados carry debris with the wind, and that debris can find itself moving very swiftly through the corridor where the inhabitants are taking shelter.”

Another problem, says Shauna Schultz, is isolating a shelter to a corridor running through the middle of a non-shelter building, as the design needs to separate the structure so that the non-shelter can “blow away” without damaging the structural integrity of the shelter.

Offering a good rule of thumb for locating storm shelters in an International Masonry Institute continuing education unit titled “Tornado & High Wind Sheltering,” Tom Elliott, CSI International, lists the following as good shelter solutions: multipurpose spaces, classrooms, music rooms, media center, gym/cafeteria, locker rooms, and wrestling rooms. He classifies not-so-good shelter solutions as corridors, storage rooms, science labs, restrooms, stair enclosures, basements, mechanical/ electrical equipment rooms, and separate buildings.

Shelter Design

In terms of taking a more aesthetic, architectural approach to the design, Schultz Squared Architects views storm shelter design as designing educational spaces that are serving as shelters, not shelters that are serving as educational spaces. “We want people to walk into a classroom and say, ‘This doesn’t look like a shelter to me,’” states Corey Schultz. Bell agrees, saying, “We want it to look like a classroom, not a bank vault.”

One way to accomplish this is to have a classroom serve as the hardened shelter space. “The key to this approach is to install specialized doors, or shutters, which normally stand open against the wall next to a window but can quickly be swung 180 degrees to cover the window and protect the classroom in the event of a tornado,” says Corey Schultz. “The face of the shutter can hold a whiteboard or displays of artwork so the teacher doesn’t lose wall space. When they need it, it’s there, but day in and day out, they don’t need it.”

Storm shutters are a great product, says Harris, as they allow conventional windows to be used in the shelter, matching the host building.

“Storm shelters should not look like World War II bomb shelters, but rather architecturally pleasing structures or spaces with attractive entrances, good lighting, interior finishes, and furnishings,” adds Waller. “A storm shelter can, and in many cases, should have dual uses, such as breakrooms, restrooms, conference rooms, and the like.”

Along these lines, Joe Jamgochian, AIA, CPHC, LEED AP BD+C, architect, Perkins+Will, Atlanta, suggests that the biggest factor is incorporating some transparency into the design. “This can be achieved by either incorporating storefront glazing systems tested to the ICC-500/FEMA P-361 requirements or by arranging the storm shelter doors so they can be held open during normal occupancy,” he explains. “Another way architects can prevent the underground cellar aesthetic is to utilize high ceilings, bright interior finishes, and quality lighting.”

Pirtle—who also serves as NSSA’s president—agrees, suggesting that the specification of certain finishes and structural components will enable the shelter space to look, feel, and function just like any other space in a facility.

“For example, architects can couple ICC-compliant shelter wall components that replace interior steel studs without increasing the wall thickness with ICC-compliant ceiling panels to form an interior space that offers the occupants protection near or in their classrooms or workspaces,” he adds. “Wall and ceiling finishes can be attached just as they are to a steel stud framed room, forming a shelter space while not disrupting the floor plan.”

As a word of caution, Harris advises minimizing hanging objects as sudden changes in interior wind pressures from exposure to a tornado can shift hanging items and dislodge them, making them potentially lethal flying objects.

Glenn also notes that modern construction techniques, such as precast envelopes and insulated concrete form structural systems, can potentially enable higher-quality architectural design. That said, the shelter location may ultimately determine how creative the design can be. For example, athletic locker room spaces, which contain the plumbing fixtures required by code, are often selected. However, these areas are traditionally not considered “high-design” areas and are more known for functionality, high durability, and low maintenance.

Specifying Doors and Shutters

In tandem with the trend of storm shelters evolving from dark, underground cellars into daylit, aesthetic spaces, ICC 500-compliant doors tested for pressure and impact resistance can be made to look and operate like standard passage doors, enabling architects to further the aesthetic appeal of a shelter. “No architect likes a door which looks like a security door or vault door,” says Waller.

Window shutters are also a great way to bring natural light into the shelter space. Tested and labeled shutters are operated from the inside and are available with self-latching features. For regular latching, Glenn recommends placing operational instructions within 60 inches of the floor.

Designers can also select ICC 500-compliant hardware that permits unlatching the door with a single motion, helping to make the door ADA accessible. In addition, ICC 500-listed doors with a labeled fire rating are available.

In researching products, Corey Schultz cautions architects to be wary of labels like “storm resistant,” “meets the ICC 500,” and “FEMA approved.” Firstly, there are many types of storms, and not all products have been tested and certified for tornado applications. Secondly, ICC 500 has significantly different requirements for tornadoes and hurricanes, and thirdly, FEMA does not “approve” products. When selecting doors, shutters, and hardware, architects should verify that the products have been tested for wind pressures and impact from wind driven debris.

“For a door, it should be tested as a unit, including a specific door type, door size, frame type, frame attachment, and specified hardware,” explains Pirtle. “Similar to a UL wall or ceiling assembly, this door unit must be constructed, as tested, in the field to ensure proper performance under the wind loading and debris impacts that it will experience during a tornado.”

In addition, architects should ensure that testing requirements and procedures were performed on the largest and smallest doors, double and single doors, and in the direction of the door swing as they will be installed. Furthermore, Glenn instructs, “Proper architectural and structural coordination is essential in ensuring correct installation, operation, and long-term maintenance for the building and the building owner.”

Offering a list of best practices for architects and contractors, Glenn also advises:

• Reaching out to the door manufacturer for anchoring details
• Verifying the rough opening requirements and tolerances
• Regarding the flooring condition, the bottom strike needs to be mounted with anchoring directly to the concrete
• Never substituting tornado storm doors
• Holding a preconstruction meeting prior to storm shelter door installation
• Ensuring that the opening is square and plumb
• Following the manufacturer’s installation details and anchor requirements
• Creating a punch list checklist

Harris also points out that impact-protective devices are only permitted where the rated pressure is greater than the wind pressure that will occur at the location where they are used. Therefore, architects should consult with their structural engineer for a determination of the wind pressure that could occur at each location of an impact-protective device.

Offering some valuable lessons-learned information, Schultz relates an unfortunate tragedy involving the failure of a supposed tornado-resistant door when an EF 4 tornado ripped through the towns of Vilonia and Mayflower, Arkansas, in the spring of 2014. Sadly, a door in a homemade, aboveground masonry shelter blew open, killing the wife and seriously injuring the husband.

In the aftermath, Corey Schultz says that the door and frame were analyzed at Texas Tech University Wind Science Lab to determine why the door failed. Firstly, the researchers found that the door and frame were light-duty hollow metal with three residential-grade dead bolts and three standard-duty hinges.

Secondly, as Corey Schultz explains in his blog, “Tornado Shelters – Arkansas Tornado Shelter Door Failure,” there was no anchorage securing the frame to the masonry walls, the cavity of the frame was filled with mortar, and the adhesion between the mortar and the masonry was the only thing holding the door in the opening.

In conclusion, “the door, frame, and hardware were not designed or constructed to withstand tornadic wind forces. The door was apparently struck by a piece of OSB or plywood in the center of the door, bending it, and destroying the center dead bolt and the lock set. Further, the top dead bolt failed, and the door hinges and hinge screws were also damaged.”

ICC 500 vs. FEMA P-361

Underscoring the importance of only specifying and installing fully tested door assemblies, designers should request documentation from manufacturers proving that their products are listed to the ICC 500 requirements for tornadoes. That said, it should be noted that some proprietary systems legitimately list FEMA P-361 as the reference to which their products were tested.

To better understand the difference between the two documents, FEMA P-361 is a best practices guideline, whereas ICC 500 is an enforceable standard that uses language such as “required” and “shall” as opposed to “recommended” and “should.”

Whereas FEMA P-361 safe rooms are intended to provide “near-absolute protection” to occupants, ICC 500 storm shelters provide “life safety,” explains Kilzer. Furthermore, FEMA P-361 has more stringent siting requirements when building in flood-prone areas. “The scope of FEMA P-361 includes not only the criteria from ICC 500 but also emergency management considerations and risk assessment commentary that are beyond the scope of ICC 500,” he adds.

Another noted difference is required wind-speed design. While ICC 500 requirements can vary from 130 mph to 250 mph depending on the project’s location, FEMA P-361 requires a 250-mph wind speed to be used in all areas, according to Pirtle.

Harris points out that building teams pursuing FEMA P-361, as compared to the requirements of ICC 500, will need to coordinate more with the local emergency planning committee, and the shelter will often incur additional costs.

“It should be noted that if a safe room is being constructed with FEMA grant funds, adherence to all of the FEMA Recommended Criteria is required,” adds Kilzer.

Case Studies

At Ewalt Elementary School in Wichita, Kansas, this was actually the case, with partial funding from FEMA’s Hazard Mitigation Grant Program supporting a classroom shelter space for 600 occupants. Meeting FEMA P-361 requirements, the shelter was part of a four-classroom addition to a Pre-K–5 school built in the mid-90s.

“One of the goals for this addition was to match the existing building facade and to make the classrooms not appear to be storm shelter space,” explains Corey Schultz, architect of record on the project.

However, matching the 8-foot by 8-foot classroom windows in the existing building was a little tricky. “In terms of a tornado shelter, these window openings were quite large, making this project somewhat unique. The school district also wanted the windows in the shelter classrooms to have operable vents, allowing teachers to open them for fresh air,” he adds.

By specifying a tornado-tested shutter assembly—consisting of a pair of reinforced hollow metal shutter panels in a four-sided hollow metal frame, which did not require an intermediate vertical mullion—the architects were able to deliver the desired aesthetic.

“The window shutters and frames are painted to match the wall color, and the teachers are allowed to use them in the normal position as magnetic bulletin boards so they do not loose wall space within the classroom,” explains Corey Schultz. “For purposes of sheltering, the shutters are deployed—i.e., closed and locked—providing protection for these large openings.”

“Tornado-tested access doors were also designed at each end of the corridors leading to the classroom and held in the open position under normal use,” he adds. “This minimizes daily wear and tear on the door hardware, which is extremely important, as these types of door systems must be in working order at the exact time the shelter occupants need the shelter.”

For another recent project at Auburn High School in Auburn, Alabama, Perkins+Will specified 23 tornado-resistant doors for the school’s gymnasium to make it a code-compliant tornado shelter space. Because the doors also had to support emergency egress, a variety of tornado-tested, ADA-accessible, panic-exit hardware was included in the design.

“While the doors are a steel, tornado-resistant design with heavier construction, they appear like normal doors with no exposed rivets or steel bands,” says Jamgochian.

Moving Forward

In the grand scheme of things, Kilzer observes that over the past few code cycles, tornado shelter design has evolved from recommended to required in certain occupancies and wind zones. “I anticipate this trend to continue as more engineers and architects get familiar with shelter design,” he says.

Similarly, Jamgochian predicts, “as more shelters are constructed and it becomes apparent that they are feasible to build even on projects with tight budgets, I think you will see more states and local municipalities requiring storm shelters.”

Currently, the interpretation of the ICC 500 storm shelter design requirements varies considerably from city to city. However, Thomas Campbell P.E., LEED AP, associate, senior project manager, Parkhill Smith & Cooper, Frisco, Texas, anticipates that the code will evolve to more clearly define items such as occupancy requirements, the minimum scope that triggers the need for adding a storm shelter when renovations/additions to existing schools occur, and travel distance to storm shelters.

Eventually resulting from research being conducted on the behavior of tornadoes and their effects on buildings and other structures, experts anticipate future refinements in the design of shelters and how they are sited within a facility.

In fact, NSSA’s Design Practices Committee, which Harris chairs, is currently writing guidelines for owners, design professionals, building officials, and contractors on how to apply ICC 500-2014 to tornado shelters for schools and first-response centers where required by the IBC. Furthermore, the group is proposing some changes to the next cycle of development for the next edition of ICC 500.

Reiterating Pirtle’s comment on the eventual effects of current research, Kiesling states, “With design experience comes innovation and upgrading in design practice which will eventually be reflected in standards upgrades. Performance assessments will continue to be made, and recommendations growing out of the assessments will impact standards.”

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