On Fire

On June 11, 2023, a tanker truck carrying gasoline caught fire on I-95 near Philadelphia. The incident caused the highway’s northbound lanes to collapse and significantly damaged the southbound section. Four years earlier, in Auckland, New Zealand, a fire damaged part of a new convention center under construction but the government was able to salvage many of the steel roofs. 

Insights gained from SAFIR, a computer program that models the behavior of engineering structures subjected to fire, played a crucial role in responses to both events. Co-developed by Thomas Gernay, Johns Hopkins associate professor of civil and systems engineering, SAFIR has been used for everything from postmortem analysis of disasters like the Philadelphia bridge and New Zealand convention center fires to the design of the roof of the Paris 2024 Olympics Aquatic Centre. 

SAFIR—the name is a compression of “safety” and “fire”—is a software program that analyzes structures’ behavior when they are on fire. It allows structural fire engineers to evaluate heat transfer that determines how the structure’s temperature will increase in the case of fire and to study the mechanics at play. 

With more than 300 global users in academia and industry, the product has a devoted following in its niche. SAFIR Day, an online event that Gernay hosts each fall, welcomes about 100 attendees from all over the world who share use cases for the software and learn best practices. 

“As structural engineers, we have the responsibility to design safe and resilient built environments. In doing so, we need to think about extreme events that could destroy these structures, and fire is one of these hazards that we cannot fully control,” says Gernay. A go-to expert for media outlets in the aftermath of devastating fires, such as the one that damaged the Notre Dame Cathedral of Paris in 2019, Gernay says his goal with SAFIR is to help structural engineers design buildings that can withstand fire—or at least not spread it. 

The software relies on the use of finite element analysis, which dices a structure into discrete linked elements and then models the behavior of each in reaction to its environment. Splitting a structure into discrete parts allows for more precision and the study of non-uniform forces as opposed to treating the entirety as a “lumped mass” solution. “If you don’t discretize, the models become very coarse and may not lead to precise solutions,” says Spencer Quiel, associate chair and associate professor of structural engineering at Lehigh University. 

Quiel used SAFIR to analyze the I-95 collapse for the Pennsylvania Department of Transportation (DOT). He zeroed in on evaluating the highway’s girders’ response to the fire, with SAFIR delivering a model that correctly predicted the damage to the north and southbound lanes. The DOT can now use the model to predict the behavior of the state’s other highways under fire stress. 

THE ORIGINS OF SAFIR

Gernay’s passion for structural fire engineering re- search began during his student days at Liège University in Belgium, where he received his doctorate. His advisor, Professor Jean-Marc Franssen, began building SAFIR in the 1990s. 

For his doctoral thesis, Gernay wanted to develop a model to simulate how concrete behaves when it is exposed to fire. Even though concrete doesn’t burn, it loses strength and deforms at elevated temperatures. By the time Gernay completed his PhD in 2012, he had added significantly to SAFIR’s code. SAFIR has gathered momentum since, with both Gernay and Franssen adding to its strengths. Among the newer capabilities: pre- and post-processors that enable users to bypass extensive coding; the addition of interfaces with more types of fire models; and various material models, including timber and novel types of steels. 

Creating a numerical model using SAFIR and validating it through laboratory fire testing enables engineers to ensure that the software accurately represents elevated temperature structural behavior. Once validated, the numerical model can be used to evaluate fire resistance for a specific structure under various conditions. 

This approach has been particularly valuable for the BRE Group, says Octavian Lalu, principal fire engineer at the UK-based structural engineering research facility. The team uses SAFIR to assess the fire resistance of historic buildings and evaluate their compliance with modern building codes. Since in-situ testing is complex and expensive, scenario-based numerical modeling of fire effects with SAFIR provides a practical, cost-effective alter- native. Using SAFIR, the BRE Group has evaluated the safety of several historic landmarks in the UK— including Admiralty Arch, Manchester Town Hall, and the Natural History Museum, among many others—to determine whether existing fire resistance meets regulation or whether remedial solutions (additional protection) may be needed. 

Another advantage of SAFIR is that it facilitates getting buy-in from multiple parties like investors, government officials, and contractors, which is key for industry projects, says Jeremy Chang, technical director at Holmes Aus & NZ, a structural and fire engineering firm headquartered in New Zealand. 

“The greater the number of user-defined variables, the more parameters you have to negotiate and the longer the discussions take,” Chang says. Because SAFIR has key data—like material strength and deformation and more—built-in, those validated parameters need not be reverified, shortening project approval times. Chang turned to SAFIR in the wake of the convention center fire in New Zealand, ultimately finding most of the structure’s remaining steel members were salvageable. 

In addition to using SAFIR for conducting post- mortem analysis after fires, both industry players like Holmes Aus & NZ and academia use the software to provide fire safety recommendations for structures.  For example, engineer Kevin Mueller at global structural engineering firm Thornton Tomasetti used the software to predict the behavior of an airport frontage road in response to a potential tanker truck fuel fire. A service corridor snaked through the lower level of the road, so the project’s goal was to ensure the front-end road structure would survive a fire. 

Such assessments are necessary because “understanding risk is the first step in mitigating it and if we don’t understand risk, we won’t know where to put resources,” Quiel says. 

THE FUTURE WITH SAFIR

Gernay also notes that evolving trends in structure design and materials could introduce unexpected fire risks. The growing popularity of mass timber (in some cases wood is considered a renewable resource) or the use of lithium-ion batteries in data centers, for example, might change the way fire could develop in buildings. New modular constructions have connections that could be weak points for fire. 

Negar Elhami-Khorasani, associate professor in the Department of Civil, Structural and Environmental Engineering at the University at Buffalo, has been researching wildfires, including those that ravaged LA in January 2025. She says SAFIR could be used for the evaluation of urban structures affected by such disasters. The results could inform the design of buildings and structures more resistant to fires. It is an interesting use case for SAFIR because most structural fire modeling assumes the fire originates from within, not outside the structure. 

“As we see [an] evolution in the built environment, we can use SAFIR to design these facilities to make them safe,” Gernay says. 

The key, he adds, is that SAFIR enables performance-based design, which focuses on a building’s performance outcomes rather than simply on construction provisions without attention to system behavior. “Performance-based design is really how structural engineers can bring value and enable innovation to support changes in the built environment,” Gernay says. “SAFIR is a key tool to enable that.”