Researchers from FM Global, one of the world’s largest commercial and industrial insurance companies, have been using the Titan supercomputer to model fire spread in mega-warehouses and large distribution centres.
Warehouses are getting larger and larger, posing ever more complex fire protection challenges (123rf / Ken Pylon)
Businesses with large warehouses are at particular risk of fire, because as storage warehouses get bigger, providing adequate protection using traditional ceiling-mounted sprinkler systems is becoming more challenging.
Yi Wang, research scientist with commercial and industrial insurance company FM Global, has been modelling fire spread through research performed on the Titan supercomputer at the Oak Ridge Leadership Computing Facility (OLCF), a US Department of Energy Office of Science User Facility located at Oak Ridge National Laboratory, USA.
To improve understanding of how fires spread and the best methods to suppress them, FM Global built the world’s largest fire technology laboratory at its property loss prevention research campus in West Glocester, Rhode Island, USA. The entire laboratory is 108,000 square feet (10,033 square metres), with a testing area measuring 33,600 square feet (3,121 square metres). These testing rooms have moveable ceilings that can go from 15 to 60 feet (4.5 to 18.2 metres) high, allowing researchers to evaluate fire hazards and test fire suppression techniques at a variety of heights.
FM Global also owns the world’s largest fire calorimeter – a large hood-like device that is hung above a fire to measure its heat release rate, one of the best metrics to gauge fire size and the main driver for determining how many sprinklers should turn on during a fire.
In recent years, FM Global has been considering how it might enhance its fire testing capabilities and gain more insight from each test. Its facility is in high demand –researchers often must reserve the space months in advance. In addition, these tests are expensive, with some experiments costing $100,000 or more.
And despite the company’s football-field-sized fire testing room and calorimeter, FM Global researchers found they might not be able to replicate fires for the world’s newest, largest facilities.
These industrial mega warehouses and distribution centres can exceed 100,000 square feet (9,290 square metres) and rise from 60 to 100 feet (18.2 to 30.48) in height. Many companies choose to use this extra height to store their commodities—in corrugated cardboard boxes— on wooden pallets stacked in tiers, each tier about five feet (1.5 metres) high.
The dangers that fires in warehouses present are well known to the firefighting community (123rf / Duncan Noakes)
As these facilities stack the pallets increasingly higher, they run the risk of helping a fire spread faster. Wang notes that once storage facilities reach a certain height, sprinkler systems may not prevent catastrophic damage as effectively: “Typically, when sprinklers are on the ceiling during a fire, the smoke reaches the ceiling to set off the system,” he says.
“But when warehouses get very tall, the time of the protection system activation can be delayed. In addition, the strong fire plume can prevent the ceiling water spray from penetrating through and reaching the base of the fire in time to achieve effective suppression.”
The high costs of large-scale fire tests, along with the challenges in generalising and extrapolating test results, prompted FM Global research scientists to develop computational models and simulate fires on an internal cluster computer in 2008. Using OpenFOAM, a fluid dynamics code, the team developed FireFOAM, its flagship code for simulating all of the complex physics that occur during an industrial fire.
The researchers made their code open source, available to any researcher studying fires and fire suppression. “Our goal is to develop an efficient computational fluid dynamics (CFD) code for the fire research community, which has all the components to catch all the physics that are important for fire suppression, such as heat transfer, material flammability, water spray, chemical transport, and radiation in larger fires,” Wang notes.
Using supercomputers to simulate industrial fires is more complicated than just virtually igniting a fire and letting it burn. Researchers have to account for the roles of soot formation, oxidation, radiation, and sprinkler spray dynamics, among other processes. In addition to calculating so many different physical processes, researchers also require very fine resolution –small time and spatial scales – to fully capture all of the subtle chemical and physics-related processes occurring during a fire.
Early results for smaller-scale fire simulations using FM Global’s internal cluster were encouraging, the simulations showed very good agreement with physical tests. However, as the team progressed in its fire modelling experience, it realised the need for substantially more computing power than it had internally to model the much larger fires that could occur in clients’ large warehouses accurately. In addition, the team needed access to a very large high-performance computing system to scale FireFOAM up to meet the computational challenge.
While attending a scientific conference on combustion, Wang and the FM Global team met Ramanan Sankaran, a computational research scientist and combustion expert at the OLCF. After discussing their research interests, Sankaran told them about the OLCF’s Industrial Partnerships Programme, which offers researchers in industry the opportunity to access America’s most powerful supercomputer for open research.
FM Global researchers knew that gaining access to a larger supercomputer was necessary to improve their simulations, but it was only part of the challenge—knowing how to make efficient use of a supercomputer with over 299,000 cores was the other part. They successfully scaled FireFOAM from 100 CPUs to thousands of CPUs.
And the team’s relationship with Sankaran continued paying dividends. “We got support from Ramanan early on and identified a bottleneck in the pyrolysis submodel in our code, which deals with solid fuel burning,” Wang’s colleague Ning Ren says. “He worked with us to improve the efficiency of that submodel significantly, and that allowed us to scale our model up so we could simulate sevedn tiers (35 feet; 10.66 metres high) of storage.”
Through those simulations, the team discovered that stacking storage boxes on wooden pallets impedes the horizontal flame spread, substantially reducing the fire hazard in the early stages of fire growth.
As with many large-scale simulations, the team used FireFOAM by dividing its simulations into very fine mesh, with each cell calculating the processes for a very small area and sharing the data with neighbouring grid points. The finer the grid, the more computationally demanding the simulation becomes.
Wang credits his team’s successful simulations to OLCF computing resources. “Without access to leadership computing resources at the OLCF, the team would have no way to study fire spread dynamics in the larger warehouses accurately,” he says. “With Titan, we are doing predictive simulations of seven-tier stacks and gaining important information about the fire hazard that we simply can’t gather through our experimental fire tests.”
After receiving a second award for computing time, the team has been collaborating with OLCF staff to incorporate the Adaptable I/O System (ADIOS) for its FireFOAM code. OLCF staff developed ADIOS to transfer data more efficiently on and off the computer. The team took the improved FireFOAM code and began simulating other commodities stored in warehouses, beginning with simulations for large paper-roll fires in 2015.
Wang sees the collaboration between his group and OLCF staff as a relationship that benefits both parties and society at large. “Our project was the first step, and I think the work we’ve done is very promising,” Wang said. “The collaboration with OLCF adds a lot of value to our research; access to Titan and the experts at the OLCF are enhancing our research capabilities so that we can offer better fire protection solutions for our clients.”
Related Publication: Ren, J. de Vries, K. Meredith, M. Chaos, and Y. Wang, “FireFOAM Modeling of Standard Class 2 Commodity Rack Storage Fires,” published in the Proceedings of Fire and Materials 2015 (February 2–4, 2015): 340.
Source: Newswise / Eric Gedenk