What happens when fire ignites in space?

When fire breaks out in the low-gravity, high-stakes conditions inside spacecraft or space stations, it behaves very differently than back here on Earth.

So, as humans aim to set foot on Mars in the coming decades, researchers are seeking to learn how flames spark and spread in space -- and how best to stamp them out.

The deadly threat fire poses in space goes all the way back to the first mission of NASA's Apollo programme, which would go on to put the first humans on the Moon.

Just days before the Apollo 1 mission was scheduled to launch in January 1967, its three crew members were killed by a fire that broke out in the spacecraft's cabin during a training exercise on the ground.

"At that time, the capsules were filled with 100 percent pure oxygen at low pressure, instead of atmospheric pressure, so the astronauts could breathe," explained Serge Bourbigot, a researcher at France's Centrale Lille institute.

"However the more oxygen you have, the more it burns," he told AFP.

Since the Apollo 1 disaster, the oxygen levels in spacecraft carrying astronauts have been set to 21 percent — the same amount as here on Earth.

But fire still acts differently in these cramped conditions hurtling through the vastness of space.

A spherical flame

When you light a candle on Earth, the heat rises because hot air is less dense than cold air.

However if you lit that candle inside a spacecraft or a station orbiting our planet, the heat would stay put because of the lack of gravity.

So instead of seeing a feather-shaped plume rise from the candle's wick, "you get a ball of flame," Bourbigot said.

"This ball will create and radiate heat, sending heat into the local environment — the fire will spread that way," expanding in every direction, he added.

To find out more, Bourbigot and three other scientists have been awarded a grant from the European Research Council.