Fires aboard ISS can pose significant hazards to crew and equipment. Extinguishing techniques used on Earth are inadequate in Space due to differences in the physical properties of flames in Space.
NASA’s FLEX – Flame Extinguishing Experiment – aims to address these challenges. “We hope to gain a better knowledge of droplet burning, improved spacecraft fire safety and ideas for more efficient utilization of liquid fuels on earth,” Principal Investigator Forman Williams, University of California, San Diego, said according to NASA. “The experiments will be used to verify numerical models that calculate droplet burning under different conditions.”
In Space there are no convective forces which cause hot gases to rise on Earth, meaning flame behaviour in Space is driven by molecular diffusion. Flames in Space burn with a lower temperature, at a lower rate, and with less oxygen than in normal gravity according to NASA. This means that materials used to extinguish the fire must be present in higher concentrations.
“Thus far the most surprising thing we’ve observed is continued apparent burning of heptane droplets after flame extinction under certain conditions; currently, this is entirely unexplained,” said Williams according to NASA.
The FLEX program, which began in 2009, studies these behaviours by igniting fuel droplets inside a combustion chamber and recording the progression of the burn from ignition through extinction.
The video below shows the progression of a heptane droplet burn in the FLEX apparatus.