Screaming "fire" in a crowded spacecraft may still create a panic just as it would here on Earth, but putting out the flames isn't as easy as grabbing the nearest fire extinguisher.
Fire behaves very differently in zero or low-gravity. Here on Earth, hot air rises, pulling combustible material way from the flame and drawing oxygen toward it. That's why candle flames look like a teardrop.
In space, the flame burns in all directions like a blob, according to Daniel Dietrich, an aerospace engineer at NASA's Glenn Research Center in Cleveland, Ohio. He said it's also tough for astronauts to find the source of the fire.
"If you take a smoke detector here on Earth, it's usually near the ceiling," Dietrich said. "When there's a fire, smoke will move up. You don't have that case in zero-g."
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Dietrich and Forman Williams, professor of engineering at the University of California San Diego, are running the Flame Extinguishment Experiment 2 (FLEX2) this month aboard the International Space Station to figure out better how stuff burns in outer space and to make space travel safer.
"You want to know better the basic information to have a better idea to put out a fire on a Mars trip," Williams said. "These experiments are in Earth orbit, but it is developing fundamental knowledge to design for a space travel."
If astronauts are going to ever leave the friendly confines of Earth orbit, they'll have to figure out how to put out fires by themselves. That happened back in 1997, when a four-foot flame erupted from an oxygen tank aboard the Russian Mir spacecraft, forcing a near-evacuation. The fire burned for 14 minutes before petering out. Astronauts currently aboard the ISS routinely do fire drills, including one last month.
Flames in space burn at a lower temperature, slower and with less oxygen than in normal gravity. This means that materials used to extinguish fire must be present in higher concentrations. The ISS uses C02 extinguishers.
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The first FLEX experiments ran from 2009 until last year.
During FLEX 2, Dietrich and Williams operate the experiment by remote control inside the Destiny science module, a unit that contains racks of science projects. They light small droplets of flame and watch how they burn in different concentrations of ambient gases. (Watch the video here. )
NASA's Dietrich said they've figured out that flames burning methanol and heptanes -- two common fuels onboard -- will burn as long as there is at least 12 to 13 percent oxygen levels in the spacecraft. Humans need around 14 to 15 percent oxygen minimum to survive.
Knowing the exact point at which the flame goes out will help engineers build better firefighting gear, and astronauts make better decisions should another disaster occur.
That might include changing the mix of gases inside the module to kill the fire. The two researchers plan on presenting their findings at a combustion meeting this summer in Poland.