Preparing for Extreme Weather

What You Need to Know to Design the Safest School Storm Shelters

• By Heather Bender
• February 01, 2021

Across the nation, educational facilities are being designed with not only education in mind – but to ensure students, faculty and staff are protected during extreme weather events. The inclusion of storm shelters, safe rooms and best available refuge areas are steadily increasing, especially due to recent code changes in the heart of the United States. By specifying commercial rolling doors and shutters that meet strict wind load and flying projectile requirements, classroom pods, cafeterias and gymnasiums can maintain a welcoming appeal while able to transform into a safe space within seconds.

While the science is clear behind the lifesaving abilities of these spaces, storm shelters and safe rooms are not common nationwide. This is due to cost and the perceived lack of need in areas outside of “Tornado Alley.” But as the threat of extreme weather continues to grow, including in states that rarely saw tornadoes and extreme weather events in the past, there are more reasons than ever for school districts to create life-saving spaces in schools.

That is why it is increasingly important for facility managers, school administrators and architects to better understand how building for safety — including specific storm shelter and safe room code requirements — can save lives and protect communities.

Understanding Wind Load and Rolling Doors

Aside from the specific code requirements for a safe room, an important place to start for any specifier or decision maker is to learn about the many aspects of designing for wind load. The term “wind load” is used to refer to any pressures or forces that wind exerts on a building or structure. There are three types of wind forces that can be exerted on a building, including uplift , shear and lateral wind load — all common in a tornado, hurricane or strong thunderstorm with straight line winds.

Uplift wind load is an upwards force of wind that affects roof structures or similar horizontal structures in a building, such as canopies or awnings. Shear wind load is a horizontal pressure or force that can cause walls or vertical structural elements to shift or crack, causing a building to tilt. And lateral wind load is another horizontal wind pressure that can make a structure move off its foundations or overturn.

All three of these forces contribute to calculating structural wind loads, but wind shear has a major effect on the performance of rolling doors. Unlike static wind load, shear wind load can change wildly based on weather conditions. Extreme weather, such as hurricanes, tornadoes and thunderstorms with straight line winds, put extreme forces on a building and can lead to doors blowing out due to wild swings in positive and negative pressure.

Even “regular” gusts of wind due to surrounding topography and common weather patterns can affect the performance of a rolling door as well as the building envelope. That’s why rolling door and shutter products are tested for both static and operable wind load. Static wind load specifies the maximum wind load at which a door is able to remain safely in place while closed. Operable wind load speci- fies the maximum wind load at which a particular door is able to safely operate.

Although one can use a simple formula to calculate wind loads from wind speed, it’s not best practice. Architects, designers and engineers should incorporate many additional factors into wind load calculations to ensure structures won't blow over during high winds. This is particularly important in areas of the country where high wind speeds dictate special design considerations.

“It’s vital for specifiers and decision makers to reach out to manufacturers to learn more about wind load requirements, and options for rolling doors and counter shutters,” said Siva Davuluri, vice president, marketing, CornellCookson. “Our architectural specialists and consultants use a Door & Access Systems Manufacturers Association (DASMA) calculator to identify comprehensive wind load needs and create custom closure solutions,” he added. “Plus, they can work with the designer, architect or facility manager to ensure they are making the best decision when it comes to safety.”

How Does This Apply to Schools?

As extreme weather continues to wreak havoc throughout the United States, school districts have a fundamental responsibility to keep occupants safe. This includes installing rolling doors and shutters in safe rooms, storm shelters and areas of best refuge to provide protection against strong winds and flying debris. But this responsibility goes far beyond ethical considerations.

Many school districts are not even aware that the current International Building Code (IBC) requires all educational facilities with more than 50 occupants to provide a safe room to protect students and staff from tornadoes and other extreme weather events in certain areas of the country. This requirement, which first appeared more than a decade ago, applies to any new construction, retrofit addition, or significant improvement projects. The 2015 and 2018 IBC updates include the same requirement, and it is expected to remain in future releases of the IBC.

In states or localities that have adopted IBC 2015 or newer and are in an area that has an increased risk of tornadoes (identified as the 250-mph wind zone), educational facilities are also subject to ICC-500 standards. This international code provides the minimum requirements to safeguard public health, safety, and general welfare relative to the design, construction, and installation of storm shelters constructed for protection from high winds associated with tornadoes and hurricanes.

At a base level, a safe room in these facilities must protect against high winds and flying objects. How high and how much of an impact depends on if the safe room is designed to withstand a tornado or a hurricane. Tornadoes involve short, violent wind bursts, pressures, and impacts. Hurricanes typically come on slower, last longer, and can deliver sustained wind and flooding. So top hurricane design wind speeds are 235 mph, while top tornado design wind speeds are 250 mph.

Impact speeds are similarly different — more intense for tornadoes, and less so for hurricanes. As such, hurricane shelters have impact test criteria of being able to withstand a 110 mph impact with a 9 lb. 2x4 projectile. Tornado shelters must be able to withstand a 100 mph impact with a 15 lb. 2x4 projectile.

It’s difficult to picture the difference between impact ratings, because different tests use different projectile weights, speeds, etc. Doors on normal Florida buildings would have to withstand (with a less than 3 inch permanent dent) a 16 lb bowling ball dropping from a two-story building. A door that is rated for a tornado safe room needs to be able to withstand that same 16 lb. bowling ball dropping from a 32-story building.

But there are additional considerations to make when it comes to specifying rolling doors in areas prone to extreme weather. This includes states that fall within the Federal Emergency Management Agency (FEMA) 250-mph wind speed zone for tornadoes, areas of Florida that are covered by Miami-Dade wind load requirements, and other regional codes and requirements areas.

“We introduced an entirely new product a few years ago to combat natural disasters,” Davuluri said. “This advanced rolling steel door is designed specifically for safe room protection against life-threatening tornadoes and hurricanes and is one of few rolling door products tested and certified to meet ICC- 500 and FEMA P-361 standards.”

Davuluri went on to explain that a single maximum protection rolling door can be used to cover multiple openings, or even banks of windows to maximize natural light — because of this, typical safe room spaces such as cafeterias, classroom pods and gymnasiums can be open and airy instead of dark and claustrophobic — helping designers create positive, learning-focused spaces that can also transform into safe rooms when needed.

When a storm is nearing and the tornado siren goes off, the rolling door can automatically deploy, turning an open space into an ICC-500/FEMA P-361 rated safe room to protect occupants from harsh winds and deadly projectiles. After the storm, the door coils back into the structure until it is needed again.

“Rolling doors like these are best used in spaces with multiple points of ingress and egress because they provide maximum protection at all openings,” Davuluri said. “They also have added psychological benefits, by covering windows and eliminating the chance that students can see a tornado barrel down on a school–something that tornado rated glass doesn’t do.”

These same products can be used for a best available refuge area. This refers to an area in an existing building that has been deemed by a registered design professional as likely to protect building occupants during an extreme wind event better than other areas in the building when a safe room is not available.

In addition to maximum protection rolling doors for best available refuge areas, manufacturers sell operational wind load doors as well as several other rolling door options. These allow specifiers to protect building occupants and contents in the event of extreme weather. However, it should be noted that they do not meet FEMA-361 and ICC-500 standards.

“New operable wind-rated products are designed with special wind locks which allow the door to seamlessly glide through the guides when exposed to a wind load of 20 psf (referred to as “operable wind-load rating”) – which equates to roughly 88 miles per hour,” Davuluri said. “These doors are designed for facilities that must be accessed regardless of weather, including fire stations, hospitals, military facilities and airports, but are also helpful when installed in best available refuge areas in schools.”

Wind load doors aren’t the only products that can help protect occupants. Companies manufacture a variety of other rolling doors and counter shutters that address static and operable wind load requirements. These include rolling service doors, insulated doors, fire doors, insulated fire doors and counter doors.

This article originally appeared in the January February 2021 issue of Campus Security Today.