Microgravity Fire Hazard Series – The Strange Behavior of Fire in the Final Frontier

Posted: June 8, 2015 in Fire Protection, Fire Science, Microgravity Research
Tags: , , , , , , ,

by: Jason A. Sutula

In a previous post on the topic of fire in space, I discussed the 1997 fire incident aboard the Mir Space Station. The case study still resonates today and provides valuable lessons for both NASA and the private commercial space companies on what fire hazards can be expected and need to be defended against in both manned and unmanned spacecraft missions. The single most important lesson that the Mir incident taught us is that the process of a fire burning in space is not intuitive.

Gravity, the driving force for natural fluid flow on the earth, cannot exert its influence on people, objects, and even fire when they are in a spacecraft circling the globe. In free fall around the plant earth, hot gases do not rise, and cold gases do not fall. The effects of buoyancy as seen in earth-bound fires are removed, which results in drastic differences in the appearance and structure of flames.

Fortunately, research in these areas has continued over the past few decades. Several on-going research studies are currently being conducted independently as well as in conjunction with NASA and the International Space Station in efforts to more fundamentally understand the fire hazards in microgravity environments.

One study by McGrattan, Kashiwagi, Baum, and Olson (McGrattan et al., 1996) demonstrated some strange fire behavior in microgravity conditions. For the study, a thin cellulosic fuel was suspended in a combustion test rig designed for a 2.2 second drop tower. The 2.2 second drop tower provided of a short amount of simulated microgravity conditions while the fire was burning. Ignition occurred in the middle of the sample and the flame was allowed to spread both vertically “upward” and “downward” at the same time. As a further variable, the researchers forced an air flow across the fuel sample at various speeds. The results were very surprising. The researchers initially expected the flame to propagate more rapidly in the downstream direction of the flow of air (think of how a camp fire will flare up when you blow on the coals). Instead, the fire burned more readily in the upstream or “opposed” direction of the flow, and the downstream flame died out quickly.

McGrattan et al. formulated a two-dimensional, time-dependent combustion model using computational fluid dynamics to better understand the phenomenon. Their computational study demonstrated that the flame moving in the opposite direction to the flow created an “oxygen shadow” in relation to the flame moving in the same direction as the air flow. This resulted in the downstream flame extinguishing since the flame moving toward the flow had already consumed all of the available oxygen!

In the embedded YouTube video above, Dr. Sandra Olson of the NASA Glenn Research Center, presents actual footage of the flame front burning as it is dropped in the 2.2 second drop tower. The full video is geared toward a younger, more kid friendly audience, so if you want to skip ahead, the microgravity combustion video and discussion begins at 0:51.

More research and computational studies will need to be conducted by NASA and commercial space ventures to better understand all of the fire hazard risks associated with microgravity environments. Fortunately, there are pioneers in this field laying the groundwork for fire safety in the final frontier.

McGrattan, K.B., Kashiwagi, T., Baum. H.R., and Olson, S.L., “Effects of Ignition and Wind on the Transition to Flame Spread in a Microgravity Environment,” Combustion and Flame, 106: pp 377-391, 1996.

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Comments
  1. lola gayle says:

    Thought you might be interested in this. WIll be posting to Crush later today or tomorrow. But thought you might like to get a first look. http://www.eurekalert.org/pub_releases/2015-06/du-tso060215.php

    Like

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