Not unlike a spacecraft tearing through the atmosphere, NASA’s hope is that its material will be able to weather a wildfire’s blazing heat—saving lives in the process—unlike any emergency shelter before.
In the summer of 2013, 19 firefighters died fighting a wildfire in Yarnell Hill, Arizona, their emergency fire protection shelters unable to withstand the extreme 2,000℉ heat. In the aftermath of the tragedy, two NASA employees wondered if their work on advanced thermal materials could have helped.
This January, NASA reached an agreement with the US Department of Agriculture's Forest Service to test prototype fire shelters made from the space agency's next-generation thermal protection systems (TPM) materials—intended, initially, to protect future spacecraft upon re-entry (in fact, a first generation of the material has already been tested on the agency's third Inflatable Reentry Vehicle Experiment vehicle, IRVE-3).
Not unlike a spacecraft tearing through the atmosphere, NASA's hope is that its material will be able to weather a wildfire's blazing heat—saving lives in the process—unlike any emergency shelter before.
These prototype shelters were tested for the first time in late June, when NASA's Langley Research Center, University of Alberta adjunct professor :Mark Ackerman, and the US Department of Agriculture's Forest Service travelled to Fort Providence in Canada's Northwest territories to conduct series of controlled outdoor burns.
Though the results thus far are preliminary, "it does appear that there is a potential solution here that would improve the fire protection of these shelters for the next generation," said Anthony Calomino, NASA lead on flexible TPS development.
The US Forest Service already has a portable fire shelter system that works quite well in certain circumstances, Calomino said in an interview, but there are still areas that can be improved—namely scenarios such as the one in which the Yarnell Hill firefighters were killed. While the aluminium coating used in the Forest Service's current design is effective at resisting radiant heat, for example, convective heat poses more of a challenge.
"The heat really comes in two forms when you're trapped in a fire," Calomino explained. "There's one that's radiant heat. Just being exposed to the flames, and the radiation from those flames is one aspect. The other one is convective which is just hot gasses coming over the top. So you're not looking at the temperature of the flames so much as the temperature of the gasses coming over you, and that's the part that we call convective."
"If it's in a fire that has a lot of hot gas or is burning material near the tent, the convective resistance of these tents is one area that could be improved, and that's the area that's NASA is focusing on," Calomino said.
Mark Ackerman, an adjunct professor at the University of Alberta, has been conducting forest fire research in the Northwest Territories since 1997. He said the US Forest Service started its fire shelter redevelopment program around 2000, and has been working with the University of Alberta to test potential designs since. The university has a plot of land about 2,000 acres in size on which controlled burns are held, and where there are often heightened wind and temperature conditions that can't easily be replicated in the lab.
"We've got a very narrow window to operate up there because typically the fire season up there starts about middle of June to end of June," Ackerman explained. "The optics are bad if, say, a community is threatened and we're out there starting more forest fires. So what happens is, we go up there, they offer us up some crews, and we run a series of experiments."
With assistance from Ackerman, NASA had initially planned to test 12 tents over the course of three burns, starting June 22, with configurations ranging from light to medium and heavy. Unfortunately, weather conditions were only good enough to have the shelters out for a single burn on June 25—after which a real forest fire nearby required fire crews to be diverted. But the results were, nonetheless, encouraging.
"All three types performed very well," Calomino said. "We had cameras on the inside of all the tents and we've gone through all of the video imaging that we've done there, and the inside of the tents all look like they handled the fire very well. It was a pretty intense fire that they were exposed to. The outside temperatures on the tents got up to about 1,800℉"— nearly 1,000℃.
Unlike a spacecraft's heat shield, the goal isn't to design a shelter that can withstand many minutes of sustained, intense heat. In fact, a high intensity ground fire, according to Ackerman, may only last just two minutes at most. Rather, the goal is to keep the temperature of the interior walls of the shelter low enough that a firefighter trapped inside will still have access to breathable air, until the fire passes and the occupant can emerge.
Already, Calomino says they've seen results indicating internal temperatures of about 600℉, or 150℃. That might still sound high, but it's within acceptable range.
Still, there is more optimization ahead to get the tents down to the weight and size requirements that match current designs, and Calomino cautioned that deployment time isn't a focus of their team at this stage. Mary Beth Wusk, another NASA research who is working with Calomino, said in a NASA blog post that current shelters are "about the same size and weight as a half-gallon of milk—about 4.3 pounds (1.95 kilograms)," and that the new shelter has to weigh about the same, and be about the same size.
"The challenge [is], it's always a tradeoff," said Ackerman. "We can certainly build a fire shelter that will withstand pretty much any sort of fire you want to throw at it. But the trouble is you've got to change your tactics and you've got to somehow decide how you're going to deploy this thing. Because if it gets too heavy, individual firefighters can't carry it."
Calomino likens it to designing a building to withstand an earthquake with such a magnitude that it may only happen every 500 years—it's possible, but at enormous cost and complexity.
NASA has more tests planned for September, and anticipates having a functional shelter ready to deliver to the USDA Forest Service by 2018.