Archive for July, 2013

by: Jason A. Sutula

microg flame

I have been extremely fortunate to have had the opportunity to research the physics of fire over widely ranging projects throughout my career. When I get the chance to discuss some of these projects with friends, colleagues, and future engineers, scientists, and investigators, the ones that tend to stand out the most involve my research in the realm of microgravity combustion. Microgravity combustion can be more simply described as how a fire will burn when it is in “Space”. There have been many motivations for this type of research over the years, and many government agencies have provided funding to study combustion in this fashion.

Besides attempting to gain fundamental understanding of the combustion phenomenon, the main motivation to study fire in space is safety. One particular space-related fire safety story that captured my imagination (and was the main motivation for both my Master’s Thesis and Ph.D. Dissertation) is the story of the 1997 fire aboard the Mir space station.

In February of that year, three replacement crew members arrived at the Mir via Soyuz spacecraft to continue joint Russian-American experiments that covered a broad range of scientific inquiry. On arrival, one crew member activated an oxygen generating device designed to boost the concentration of oxygen aboard the station to account for the increased number of people. Immediately after the activation of the device, the holding canister ruptured and began to burn uncontrollably. The fire was described as a “blowtorch-like, white conical flame” that was roughly two feet in length. The crew feared that the fire would impinge on the opposite wall of the Kvant module and threaten a breach and subsequent depressurization of the capsule. Additionally, the fire was situated in a location that cut off the escape route for three of the crew to the Soyuz escape vehicle. In under a minute, the visibility in the space station was reduced to less than a few feet due to the smoke given off by the fire. Some of the crew reported that they could not see their hands in front of their faces. The atmospheric temperature within the space station also began to rise to upward of 100 °F. With breathing becoming difficult, the crew donned compressed air gas masks shortly after the fire began, and attempted to fight the fire and limit its spread. Several foam/water extinguishers were discharged by the crew, but were observed to be ineffective against the flames. Eventually, the fire subsided on its own, most likely from exhausting its fuel supply.

After extinguishment of the fire, the air scrubbing capability of the Mir was put to the test. The crew was able to remove the life saving compressed air gas masks in a few hours, but then had to wear particulate filter masks for several days after the fire incident until the remaining combustion particulates were filtered down to a reasonable exposure level.

This particular fire incident was extremely valuable for pointing out several fire safety concerns with space vehicles, space structures, and manned space exploration. First, in space-based vehicles and structures, there is no easy way to “evacuate” from the vehicle or structure. On earth, if an individual is involved in a structure fire, the easiest method of preserving life and preventing injury is designing the structure with fire notification (a fire alarm system) and an adequate means of escape (such as: an appropriate number of exits from the building, lighted exit signs, posted escape pathways to the nearest exit in hotel rooms, etc.). In the vacuum of space, evacuation to the exterior of the vehicle or structure will be a much more problematic means of fire safety.

Second, extinguishers and extinguishing methods that are used on earth are not as effective in space vehicles and space structures with microgravity conditions. Buoyancy, which drives heat “upward” due to density differences, and the presence of a gravitation field on the surface of the earth are both non-existent when a fire occurs in space. Fire does not burn “up” in these environments. Instead, a fire will follow any local ventilation currents and exist where sufficient oxygen and fuel are available. When extinguishing attempts are made in a microgravity environment, the momentum from the jet of an extinguishing agent (imagine using a kitchen fire extinguisher that is sprayed at a fire) can “push” the flame out of the way. The result may be that the extinguishing agent has completely missed the fire and the fire was able to spread to other mission critical systems.

Third, the inherent flammability of a particular material should be addressed before it is used in a space vehicle or space structure. If the flammability of a material is deemed to be too great, then limiting or not allowing that material on board should decrease the overall risk for a particular space vehicle or space structure. NASA, along with other researchers and groups, has performed work on this very topic to lay the fire safety groundwork for future extraterrestrial missions.

While these three concerns for fire safety in microgravity are a good start, they are certainly not comprehensive for all of the issues surrounding the management of fire in these challenging environments. With amazing and exciting progress being made almost every day by companies such as Scaled Composites, Virgin Galactic, and SpaceX in the fields of commercial space exploration, tourism, and payload delivery, it is only a matter of time before more and more people gain access to and utilize space vehicles and space structures for work and pleasure. Safety and, in particular, fire safety for these individuals must be a top priority.