Tornado season presents a unique worry for residents of the windy South Plains.
The devastation brought by the May 11, 1970 tornado spurred significant innovation in Doppler radar technology, led to the founding of the National Wind Institute at Texas Tech, and ultimately inspired then-University of Chicago Professor Ted Fujita to create the “F-Scale” — a version of which is still used to rate tornado intensity to this day.
Given that the westernmost recorded F5 tornado in U.S. history touched down in Lubbock, some may find it surprising that most buildings constructed since then are not rated to safely withstand winds of similar magnitude.
Marc Levitan, lead research engineer at the National Institute of Standards and Technology’s National Windstorm Impact Reduction Program, said most conventional buildings and structures are not designed for the most powerful tornado-level wind loads because of their rarity.
“We don't design for a category five hurricane in New York, because although it could happen, it's much more rare than the events that we've been designing for,” Levitan said. “We do design for category five in Florida.”
Instead, he said, researchers for the American Society of Civil Engineers designate certain “reliability targets,” like the ones outlined in the latest edition of its authoritative guide on design loads. Known as ASCE 7-22, this iteration of the handbook on design loads includes a chapter on tornado resistance for the very first time.
Tornadic winds include strong updrafts that produce upward pressure on roofs. Levitan, a Texas Tech alumnus who chaired the committee that produced the ASCE guide’s chapter on tornado loads, said tornadoes can also generate pressure differences between the inside and outside of buildings that similarly cause uplifting internal forces.
“So going through all that research, we found that — at least for the more important structures that we build — to meet those criteria, you have to take tornadoes into account,” Levitan said.
Within building codes, structures are sorted into four varying risk categories.
The first category pertains to buildings that present “the least impact to human life,” meaning they remain unoccupied most of the time. The third risk category is reserved for buildings that are frequently inhabited by people like schools while the fourth is assigned to essential facilities like hospitals.
Risk category two, however, is any structure that doesn’t fall into risk categories one, three, or four, Levitan said. Most buildings around town tend to fall into this category, as it pertains to places like retail spaces, homes and apartments.
“For each one of these increasing risk categories, you have a higher level of design that you need to do,” Levitan said. “So, you're designing for a rarer event based on [a structure’s] threat to human life and its importance to the functioning of the community.”
Only buildings that fall under risk categories three and four are required to be designed to resist the tornado loads specified in ASCE 7-22, based on probability of failure requirements in that standard, Levitan said. Lubbock’s current building code calls for some high-risk category buildings to include tornado shelters with limited exceptions, but ASCE’s guidance on reliability requirements is only designed for “the common tornado, not the rare tornado.”
The push to include the new wind-load standard for tornado-resistant design was influenced by a devastating EF5 tornado that struck Joplin, Missouri, in May 2011. The Joplin tornado killed more than 160 people, injured more than 1,150 and damaged over 8,000 buildings in the region.
One of the most vulnerable places anyone can be in the event of a severe windstorm continues to be manufactured homes, which are often called mobile homes. On June 15, an entire mobile home community in Perryton, Texas, was decimated by an EF3 tornado that left three dead and more than 100 injured.
Less than a week later on June 21, another EF3 tornado struck Matador — a town located about 70 miles northeast of Lubbock — and killed four while injuring nine more.
Kishor Mehta, a world-renowned civil engineering professor at Tech and one of the pioneers of the Enhanced Fujita Scale, said that although manufactured home design has improved over the years, they are not bound by building code standards.
“The problem with manufactured homes is that, although the quality of construction is good because they're manufactured inside a factory... [whether] they're tied down to the ground depends on each state and each locality,” Mehta said. “They're not governed by any national standard. They're only governed by the local standard.”
When it comes to adopting International Building Code, Mehta said local authorities have complete control over the process and may make exemptions to certain requirements if they wish. While state-level regulations determine the ability of local jurisdictions to adopt statewide codes, implementation of IBC and International Residential Code standards is noncompulsory.
Many states, including Texas, lack a mandatory statewide building code. Although Texas has adopted the IBC, IRC and International Existing Building Code for residential dwellings, the code does not go into effect by default in unincorporated areas and local authorities must adopt resolutions to compel their implementation.
These jurisdictions are also allowed to amend or modify the code however they see fit. Consequently, many places in Texas have no or very relaxed building codes, and many jurisdictions do not enforce existing building codes.
“The perception is that tornado hazard is random and it's remote,” Mehta said. “And as we are beginning to find out... it is not as random as we think, it’s not as remote as we think. They do occur, and they occur in the middle of the country quite often.”
Still, Mehta said Lubbock residents have no reason to live in fear of tornadoes. Despite tornado outbreaks historically occurring often in regions of northern Texas and south-central Oklahoma, sometimes referred to as “Tornado Alley,” research into the natural phenomenon has found tornado frequency has increased over the years in the eastern part of the country and generally decreased in the central region of the U.S.
Additionally, Mehta said, one’s chances of survival during a tornado are reasonably high if proper precautions are taken and public warnings are observed. The City of Lubbock’s Office of Emergency Management encourages residents to prepare for severe weather by signing up for its emergency notification system and planning out where to take shelter in advance.
But knowing where to seek refuge can be difficult for those who lack continual access to places that aren’t as vulnerable to tornadic threats. Gilbert Quant, Lubbock’s chief building official, said he is not aware of any publicly accessible tornado or storm shelters around town.
“Nothing has changed,” Quant said. “Only those buildings that are prescribed by the IBC are required to have storm shelters, no additional occupancies are required [to have them].”
Lubbock City Council is in the midst of evaluating a newer iteration of IBC standards. Currently, only the 2015 edition of those standards is effective in Lubbock, and Quant said the process of updating Lubbock building codes to the 2021 edition is underway.
First, a committee of professionals called a “working group” reviews the differences between the two sets of standards and recommends amendments to them, if necessary. Once they’re done, the code is presented to the city council for final approval and adoption.
The cycle of considering and adopting new codes occurs every three years, Quant said, and architects are granted a grace period for compliance when changes are made. In 2022, ASCE’s Structural Engineering Institute submitted a proposal to the International Codes Council to adopt ASCE 7-22, along with its innovative chapter on tornado resistance, into the 2024 edition of IBC.
“I think it's a great idea to start building storm shelters in places like schools, 911 emergency centers, and things like that,” Quant said. “Just to keep safety for the citizens in case of an event like that. God forbid it happens.”