Fire behaves in strange and dangerous ways in space, and understanding it has become a critical concern as humans prepare for long-duration missions, including future journeys to Mars.
In the low-gravity environment of spacecraft and space stations, flames do not act as they do on Earth. Without gravity, hot air does not rise, meaning fire spreads differently and can become far harder to predict and control. This makes even a small onboard fire a potentially deadly threat.
The danger of fire in space has been known since the earliest days of human spaceflight. During preparations for Apollo 1, a tragic fire broke out inside the spacecraft cabin during a ground test in January 1967, killing all three astronauts on board. At the time, the capsule was filled with pure oxygen at low pressure to support breathing, a decision that proved fatal.
“More oxygen means more intense burning,” explained Serge Bourbigot, a researcher at Centrale Lille. He noted that following the Apollo 1 disaster, oxygen levels in crewed spacecraft were reduced to 21 percent, the same concentration found in Earth’s atmosphere.
Even with safer oxygen levels, fire remains uniquely hazardous in space. On Earth, flames stretch upward as heat rises, creating the familiar teardrop shape. In microgravity, however, heat stays in place. If a candle were lit inside a spacecraft, the flame would form a glowing sphere rather than a vertical plume.
“In space, you get a ball of flame,” Bourbigot said. “That ball radiates heat in all directions, allowing the fire to spread outward instead of upward.”
This spherical behaviour changes how heat moves, how materials ignite, and how fires must be extinguished in orbit or during deep-space travel. To better understand these risks, Bourbigot and three fellow scientists have received funding from the European Research Council to study how flames ignite, spread, and can be safely suppressed in space environments.
Their research is expected to play a vital role in designing safer spacecraft, habitats, and fire-prevention systems, essential steps as humanity moves closer to becoming a multi-planet species.
