Why flames in microgravity transform into dangerous, floating spheres
On Earth, gravity pulls warm air upward, creating the familiar teardrop shape of a candle. In the weightless environment of a spacecraft, this convection vanishes. The result is a spherical flame that behaves unpredictably, making fire suppression in the confines of a space station a unique and terrifying challenge.
In the absence of gravity, the fundamental mechanism of combustion changes. On Earth, less dense warm air rises and is replaced by cooler ambient air from below, a process known as convection. In microgravity, this circulation effect does not occur. Instead, flames take on a spherical shape. This lack of natural air movement makes fire in space much more dangerous, particularly within the enclosed environments of a spacecraft where astronauts cannot simply exit the building to find safety.
To study these risks, NASA’s Biological and Physical Sciences Division has sponsored decades of controlled experiments. Researchers use facilities like the Combustion Integrated Rack (CIR) on the International Space Station to study ignition and the flammability of materials. One notable series, the Saffire experiments, conducted larger-scale studies on the Northrop Grumman Cygnus spacecraft. The final mission, Saffire-VI, concluded in January 2024. This specific iteration was unique because it simulated crewed spacecraft conditions by using higher oxygen concentrations and lower pressure during 19 different experiment runs.
The implications of this research extend to our future in the solar system. As the Artemis program prepares to return humans to the Moon, scientists are investigating how partial gravity affects fire. The FM2 study will be the first to test flammability on the lunar surface, evaluating how flame size, intensity, and spread differ from Earth. By understanding how materials like cotton, Nomex, or plexiglass burn in these environments, engineers can design safer habitats and more efficient, less polluting vehicles for deep space exploration.
Source: Why Fires In Space Are So Dangerous
