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Tornado Survival Could Improve with Better Building Codes

Home construction standards and techniques designed to withstand hurricanes along the Gulf Coast could enhance tornado protection inland, too
tornado damage


Mississippi National Guard members respond in Tupelo after several tornadoes struck the area on April 28, 2014.
Credit: Mississippi National Guard via Flickr

In late April 2011, a tornado touched down near Tuscaloosa, Ala., and tore its way east toward Birmingham, leaving a gash of wrecked homes and buildings more than a mile wide. Sixty-two tornadoes hit Alabama that day, April 27, leaving 250 people dead and 23,000 homes damaged or destroyed.

In the ensuing days, Butch Grimes was on the ground doing damage assessment. The task was something Grimes, an architect with three decades of experience in the public and private sector, was used to. But as he examined the wreckage after this storm a half-mile from his office in Tuscaloosa, something stood out.

"The damage we had on the edges [of the tornado] could have been avoided with simple construction techniques," Grimes said in an interview.

Last Sunday and Monday night, more tornadoes struck in Arkansas and Oklahoma, killing at least 35 people and leaving the little town of Vilonia, Ark., looking as if a giant maul had battered its homes. The severe weather continued yesterday and left residents of "tornado alley" in the southern and central United States to debate how they might have been better prepared.

The answer might be found just a few miles farther south, where communities on the Gulf and Atlantic coastlines have been adapting to hurricanes—intensified by climate change—for several years (ClimateWire, Feb. 4).

'Fairly modest changes' can make a difference
The strongest hurricane winds on the coast can reach 180 mph. Hurricane Katrina topped out at 125 mph. The strongest hurricane ever recorded—Allen in 1980—reached wind speeds of 190 mph, according to the National Hurricane Center. The strongest tornadoes, category EF-5, have wind speeds of 200 to 250 mph.

Tornadoes that strong are rare, but even lower-category EF-2 or EF-3 tornadoes have wind speeds in the 100- to 150-mph range. It's these lower wind speeds, around hurricane strength, that are most common—even on the edges of stronger storms—according to Grimes.

"It's probably not practical to design for EF-5 damage," he said. Weaker storms, however, can and should be designed for, he added. Coastal areas have been doing so for years.

Steve Cauffman, head of disaster resilience at the National Institute of Standards and Technology and author of a recent report on the devastating 2011 tornado in Joplin, Mo., said coastal states are "probably somewhat ahead of the rest of the country" in terms of thinking about resilience.

Marc Levitan, a co-author of the Joplin report and head of research and development in the NIST National Windstorm Impact Reduction Program, said that although coastal hurricanes and inland tornadoes can't be prepared for in the exact same way, there are some areas where using resilience measures against both disasters could overlap.

"Fairly modest changes in building design and construction, and code changes and practices, can lead to dramatic improvements in wind hazard resistance of structures," Levitan said.

The tornado that hit Joplin in May 2011 killed 161 people. The NIST report found that structural collapses in Joplin began with failure of the roof system, causing walls to collapse. "Available design information showed that the roof connections of these buildings were adequate for code-level design wind pressures," the report said, referring to wind speeds under 115 to 120 mph.

Codes get weaker farther inland
There may be some room for structural survival here. Only one chink in a building's armor can be the difference between destruction and surviving a storm unscathed, Grimes explained. And that one crack could be prevented with some simple resilience measures that have been tried and tested in coastal areas.

Hurricane clips are one potential quick fix, said Grimes, also a disaster assistance coordinator for the American Institute of Architects. In Alabama, the clips are required for buildings built within 5 miles of the Gulf of Mexico but remain optional farther inland. The clips help hold a roof in place by transferring load pressure on the roof through the walls to the building's foundations.

Reinforced windows can also provide invaluable protection during hurricanes and tornadoes, even when battered by 200-mph winds. One of the ironies of these stops is that the biggest threat to a home may not be the tornado itself but the buildings upwind where owners have not built in resiliency.

Debris from shattered homes can be the most devastating aspect of a storm, sending a cloud of shrapnel-like pieces of scrap metal and wood flying at hundreds of miles an hour into house after house.

You could have the best wind protection on the market, Grimes added, but if your neighbor's refrigerator smashes through your wall, it would all be undone. He's seen pine needles that have moved so fast they've stuck like arrows into wood and metal walls instead of crumpling.

"It's a domino effect," he said. "If one person does the best they can to make their building structurally sound and safe, [it doesn't matter] if a neighbor upwind does a bad job."

Buildings have several options to protect against flying debris, including roll-down hurricane shutters and 3/8-inch-thick hurricane glass. Special windows are often the best option, because tornadoes can strike so quickly that homeowners may not have time to even roll down shutters in time.

Some municipalities—which determine local building codes, often based on state and international guidelines -- have recently moved to require some of these defenses. Southern Alabama adopted a more stringent code in 2012 that placed a heavier emphasis on wind and water protection, the Mobile Press-Register reported.

Miami-Dade County, Fla., requires protection on every opening in a building. The doors and shutters of new homes in Florida now also have to pass a "missile test" in which an air cannon fires wood debris at the door or shutter at 34 mph. The door, window or wall assembly has to withstand two or three volleys in order to pass.

Resiliency begins with awareness
Such retrofits can become expensive, but they do provide a range of options. A refit with hurricane glass can cost $13,000, for example, but hurricane clips can be bought for less than a dollar each. Installing them, though, can get pricey.

Russell Davis, executive vice president of the Home Builders Association of Alabama, said measures like hurricane clips would be costly and of little help against the strongest tornadoes.

"We're not anti-hurricane clips," he said, "but at the same time, you've got to develop a system that's affordable to the home-buying public."

Alabama updated its statewide code in 2011 but doesn't require hurricane-resistant techniques in northern areas.

Updating such codes can be a tedious and grueling process, especially given how varied codes can get across jurisdictions. Following Hurricane Katrina, coastal Baldwin County, Ala., adopted new codes that required four different levels of wind durability based on proximity to the coast, the Associated Press reported. The statewide code is more relaxed than all four Baldwin County variations.

After hurricanes like Andrew and Katrina devastated southern Alabama a decade ago, the region responded. Now northern Alabama is seeing a reason why it might have to build in a response.

While similar responses could be applied farther inland against wind hazards, people like Levitan at NIST cautioned against simply copying hurricane techniques. Hurricanes attack with more straight-line winds compared with a tornado's spiral. They are also easier to prepare for, providing days of advanced warning.

The national average tornado warning time is 14 minutes, according to the NIST Joplin report.

"You can't just say this particular provision worked for hurricanes, so we can copy and paste it over and get the same result," Levitan said.

But he's also noticing an increased interest in improved resilience in inland areas, particularly since the devastating 2011 tornado season that included the Alabama and Joplin tornadoes.

"At least anecdotally, there does seem to be a significant change in interest," he said. "Hopefully, we can use some lessons learned from the hurricane community."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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