MARYLAND – The 60-square foot exhaust hood in the Bureau of Alcohol, Tobacco, and Firearms Fire Research Laboratory in Beltsville, Md., looms above the test floor, ready to capture smoke and emissions from mass timber compartments the size of shipping containers. One morning in October the hood was in action, sucking up billowing smoke as flames spread through the interior of one compartment while a team of researchers watched the experiment on video monitors.

This test was the third in a series of four experimental burns that researchers from the USDA Forest Service Forest Products Laboratory, Oregon State University, U.S. Environmental Protection Agency and ARUP, an engineering consulting firm, designed to study fire behavior in mass timber structures. The results from their project could inform building codes and fire models for multistory buildings made from wood and add to our understanding of smoke, emissions and char formation.

Mass timber is a category of engineered wood made by bonding smaller pieces of wood together to create durable and versatile structural components. Mass timber can have lower greenhouse gas emissions compared to concrete or steel. Multistory structures like the Ascent building in Milwaukee or Baker’s Place in Madison, Wis., are exciting examples of this emerging building technology. Because mass timber is still a growing industry, fire behavior tests like this project are critical to filling in knowledge gaps and improving building designs. 

At the Alcohol, Tobacco, and Firearms Fire Research Laboratory, the research team designed experiments to see how fire would behave in a building without sprinkler systems, a response from the fire department and other safety checks that exist in real-life scenarios. Testing to failure is important because “if you don’t know the order in which things fail, you don’t know [what] to design for,” said Erica Fischer, a professor at Oregon State University.

Burning full-scale structures in a large fire lab isn’t possible for every study. More frequently, researchers measure emissions, temperature and other data from much smaller samples of material. Next year, this project will continue with smaller-scale testing at the fire lab at the Forest Products Laboratory. The goal is to better understand the strengths and limitations of scaling fire tests, especially in terms of emissions and fire behavior with different materials. “What’s really special about this project is you’ve got all these different fields coming together. Each separate analysis that we’re talking about is then going to be combined into [a bigger picture],” said  Kara Yedinak, a scientist with the USDA Forest Service Northern Research Station.

Another unique aspect of this experiment is the fuel load, or the combustible materials  that’s available to burn. Researchers filled three of the compartments with items that you might find in an overcrowded dorm room – furniture, appliances, household chemicals and stuffed animals. By comparing smoke and emissions from a fully stocked room to one filled with precisely arranged stacks of 2x4s called wood cribs, researchers can get a better idea of what kinds of chemical compounds enter the air when structures burn and any potential public health implications.

The day after test three, Bureau of Alcohol, Tobacco, and Firearms employees set up loud fans to dry the puddles of water left over from extinguishing the flames. A floodlight lit the inside of the burned compartment, now full of char and ash. Team members were preparing a nearby compartment for the fourth and final test. They installed cameras in the walls, to record the early stages of the burn, as well as hundreds of thermocouples, instruments that measure temperature. Meanwhile, Laura Hasburgh, a researcher with the USDA Forest Products Laboratory, and Kara Yedinak drilled through the burned compartment with a tool called a resistance drill to collect data on the remaining thickness of mass timber.

“I’m really looking forward to digging through all the data and seeing the full picture,” said Hasburgh. Once they’re published, results from these tests will add important data to the body of mass timber building design research.