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Saturday, August 13, 2022

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The flame tower in action.

From Fallout Shelter to Flame Tower

SDSU engineers converted an architectural relic from the Cold War into housing for a tower that can mimic fire's behavior in space.
By Michael Price

“I took one look and realized this would be perfect.”

The Curious Aztec takes you behind the scenes of scientific investigation and discovery taking place at San Diego State University.

What do you do with the 50-year-old ladder hatch from a former nuclear fallout shelter that’s been converted into a physics laboratory? If you are San Diego State University mechanical engineers Subrata Bhattacharjee and Fletcher Miller, you turn it into a flame tower that simulates the effects of microgravity on fire.

Bhattacharjee and Miller are combustion experts who study flames under a variety of conditions. One of their primary areas of research is examining how low- and zero-gravity environments affect the way fire behaves. You see, on earth, fire depends on buoyancy to expel gases away from the flame and suck in new oxygen to feed it. But in space, there’s no up or down, so buoyancy can’t do its thing.

As a result, fire in space burns lower and slower. And that’s important information to have for the engineers who decide which materials are safe and which aren’t for space flight. It’s also important for engineers like Bhattacharjee who are looking to develop a unified theory of fire behavior that can account for buoyancy as a variable.

Several years ago, Bhattacharjee came up with the idea of building a vertical tower in which he could raise or lower a burning piece of fuel. Depending on how fast you raise or lower the flame, you can simulate different buoyancies. But he needed space to build it.

“When I was writing the proposal to build the tower in the summer of 2009, I was wondering, ‘Where will I find a place to build this tower?’” Bhattacharjee said.

Space race

The funding from NASA came through before he could answer that question. Now, there was money to build the tower but nowhere to put it.

“Once we got the funding, Fletcher and I went over many crazy ideas about how to contain the experiment in a sealed chamber while remotely controlling and observing he flame inside,” Bhattacharjee recalled. “Looking for space, I was scouting different labs.”

And then he saw it: a ladder sticking up out of a partially covered hole in the ground in the basement of the Engineering Building, formerly the lab of mechanical engineering associate professor James S. Burns*.

“I took one look and realized this would be perfect,” Bhattacharjee said.

According to Miller, the hatch was once the entryway to the basement when it was converted to a nuclear fallout shelter during the Cold War. According to anthropologist and campus historian Seth Mallios’ SDSU history book “Hail Montezuma!” there were a few other shelters built around campus, shielded from radiation and containing “everything necessary to survive in case of nuclear attack, including food, water, sanitation, and medical supplies.”

Cold War–era rations storage drums.

The shelter in the Engineering basement was no exception.

“Mike Lester, our mechanical engineering technician, cleaned it out, and I remember him bringing up those olive-colored drums of water and rations that the government supplied back in the 1950s,” Miller said. “When I was a kid, my dad worked at the county courthouse and he used to take me into their shelter deep below C Street [in San Diego] and I saw lots of them there, so I was familiar with them.”

Some of these drums still sit on campus in a storage yards.

Tower of power

After these old rations were cleared away, they removed the ladder and the electrical lines running into the hole, leaving a big, square gap in the floor about 3 meters deep.

It was in this hole that Bhattacharjee, Miller, and several engineering students completed construction of the tower in 2010. The structure is 10 meters tall, with its bottom 3 meters sunk into the former hatch. Inside the tower, a cart on a vertical rail can hold a piece of fuel, an igniter and a camera that connects to a laptop. Researchers can ignite the fuel, raise and lower the cart at a controlled speed, and watch from the laptop screen as the fuel burns higher or lower, faster or slower.

Eventually, the engineers plan to make the tower airtight so they can test the effects of flame burning in a vacuum as well. You can read more about the research of Bhattacharjee and Miller in the forthcoming spring 2015 issue of 360: The Magazine of San Diego State University.


* Yes, there’s a flame tower in the former lab of someone whose last name is Burns. These things happen.