Astronauts To Fight Fire With Fog During Space Shuttle Flight
"The fire-fighting industry is in search of a new tool that doesn't use dangerous chemicals or douse fires with huge quantities of water that cause extensive property damage," said Mark Nall, director of the Space Product Development Program at NASA's Marshall Space Flight Center in Huntsville, AL. "By flying this commercial experiment on the STS-107 Columbia mission, NASA is helping industry design a cost-effective, environmentally friendly system for putting out fires."
Until recently, halons, bromine-based compounds, were used to attack fires chemically -- especially in places like computer rooms, aircraft, and document storage rooms where water sprinklers were inappropriate. In 1998, the production of these chemicals was banned worldwide because they damage Earth's protective ozone layer. This part of the atmosphere shields us from the Sun's harmful ultraviolet radiation.
We are working to find an acceptable replacement for halons, and water mist appears to be the best choice," said Dr. Thomas McKinnon, lead scientist for the research at The Center for Commercial Applications of Combustion in Space (CCACS) at the Colorado School of Mines in Golden. This NASA Commercial Space Center specializes in helping industry conduct combustion research in space through NASA's Space Product Development Program at the Marshall Center.
"The shuttle tests use a humidifier-like device to produce water drops about 20 microns in size," said Dr. Angel Abbud-Madrid, the project scientist at the NASA Commercial Space Center. "That's about one-tenth the diameter of a human hair, as opposed to drops produced by conventional sprinklers that are about one millimeter, or 50 times the size of our droplets."
The water mist research team is working with MicroCool Inc., a division of Nortec Industries Inc., in Palm Springs, CA, and Fogco Systems Inc. in Gilbert, AZ. These companies manufacture water mist systems for putting out fires and for other purposes, such as outdoor cooling and industrial humidification.
"Firefighters in Denver and at the Arvada Fire Training and Research Center have tested our ultra-fine mist nozzles," said Mike Lemche, general manager of MicroCool. "The cooling effect of this mist removes one of the key components of fire – heat."
Gary Wintering, president of Fogco, said his company will use information from the STS-107 experiment to fine-tune their designs of fire-fighting systems. Water mist systems create a fog instead of sending out blasts of water. Since the fog removes heat and replaces oxygen as the water evaporates, it prevents the fire from expanding and starting new fires.
This is particularly important when fire starts in a closed compartment on a ship, aircraft, or even on the Space Shuttle. The U.S. Navy is already working with the airline industry and The Center for Commercial Applications of Combustion in Space on water mists studies.
"With halon replacements expected to be an important part of the billion-dollars-a-year fire suppression industry, it is easy to understand why companies are flying this experiment," said Dr. Frank Schowengerdt, director of The Center for Commercial Applications of Combustion in Space. "These companies are testing the system in space because it's easier to observe the interaction between a flame and water when Earth's gravity does not cause air currents around the flame and does not cause water droplets to settle."
Prior combustion experiments have shown that space is the ideal place to study the physics of fire. On Earth, gravity causes lighter, hotter air to rise -- creating air currents that make it difficult to study combustion processes. In microgravity -- the low-gravity inside the shuttle orbiting Earth – air currents are reduced or eliminated, making it easier for scientists to observe exactly how water interacts with a flame to put it out.
"The Shuttle experiment will help us determine the optimum water concentration and water droplet size needed to suppress fires," said Abbud-Madrid. "We have learned from short tests on NASA's KC-135 reduced-gravity aircraft and inside drop towers that water mists take one-tenth the water of traditional sprinklers to extinguish a flame."
More extensive measurements in periods of microgravity longer than a few minutes will be possible during the Space Shuttle Columbia's16-day mission. A mixture of propane and air will ignite inside a clear tube to produce a thin flame -- known as a laminar flame. On the opposite end of the tube, a water mist will be released. Digital images will record how different size water droplets and water concentrations affect the flame.
The experiment will take place inside the safety of the Combustion Module -- a NASA facility flown on a previous Shuttle flight. It was developed by NASA's Glenn Research Center in Cleveland, and is the forerunner of a similar facility under development for the International Space Station. Future water mist investigations on the Space Station will be larger and longer, enabling companies to test different water injection systems, droplet sizes, and fire scenarios.