Current safety regulations ensure that only low-flammable materials are brought into space. Fires in locations like the International Space Station (ISS), however, are still possible.
Short circuits happen, for example. Cosmic rays may cause structural damage to materials, altering their flammability.
At present, the ISS has a CO2 gas extinguisher, combined with a water mist, to dilute the local oxygen concentration and remove heat.
The method, however, leaves harmful fumes in the enclosed space. Crewmembers who put out the fires must put on oxygen masks due to the risk of the high concentration of CO2 in the cabin.
Researchers from the Toyohashi University of Technology in Japan have developed a new type of fire extinguisher that is optimized for space-use and does not require the use of any oxygen masks.
The Vacuum Extinguish Method (VEM), a concept demonstrated in the academic journal Fire Technology, is a bit like the hoover in your living room, says lead researcher Dr. Yuji Nakamura.
“Think of it as simply sucking the flame like a vacuum cleaner to ‘clean up’ your firing zone,” Dr. Nakamura told Tech Briefs. “Then, the flame, as well as any other harmful products, is sucked in.”
The extinguishing system has two boxes. Once the first vacuum box is filled, a valve opens, sending the collected gas to the second container; the first box, meanwhile, continues its vacuuming.
The pressure difference between the suction container and the cabin allows the VEM system to draw in the toxic gases – smoke, fumes, and particulates, for example – and the fire source. Then, extinguishing treatments, like the spraying of chemical agents, are conducted within the box.
To test the effectiveness of VEM, researchers successfully demonstrated the technology on a small-scale electric wire with a polymer sheath.
In a Q&A below, Dr. Nakamura tells Tech Briefs about the initial VEM design – and what will need to happen before we truly see fire-vacuums up in space.
Tech Briefs: How is the Vacuum Extinguish Method (VEM) different from conventional methods of putting out fires?
Dr. Yuji Nakamura: VEM is a fire extinguishing method based on a vacuuming operation.
The existing fire-extinguishing method sprays the extinguisher agent — inert gas, water, chemical powder — toward the firing zone to put out the fire.
VEM sucks the firing material as well as combustion products, just like a vacuum cleaner, and collects them into a vacuum box. During the vacuuming operation, the fire may go out. If not, we can operate any fire-extinguishing procedure within the box, totally isolated from the living space.
This is the most featuring point of VEM; namely, we can isolate the firing source and harmful product from the living space in a quick manner assisted by vacuum operation.
Tech Briefs: What happens in the box, once the fire elements are sucked in? You mention “we can operate any fire-extinguishing procedure in the box.” What does that mean exactly, especially using the example of your small-scale test wire?
Dr. Nakamura: In the small-scale test, the flame is quenched during the suction operation so that no additional extinguishing procedure is necessary.
Suppose the burning material is sucked in the box and continuously burns. We can spray extinguisher agents — like chemical powder to quench the reaction — to extinguish the fire. During this operation, the suction pipe continuously draws in the fire. Therefore, it should be more precise to say that the suction and extinguished operation are done simultaneously in the box.
At this moment, however, we do not have such a box. The above scenario is only my concern when it is really ready for use. We have proposed the concept, and we’ve verified its feasibility in the academic journal (see: Fire Technology). Suitable design must be followed in the future. Any design can be made based on the request, because the final form is not fixed yet.
Tech Briefs: What inspired the “reverse” idea — to vacuum the fire?
Dr. Nakamura: We wanted an optimized fire extinguisher in space. Conventionally, a CO2-gas extinguisher is often used. Once it is sprayed, harmful combustion products, as well as extinguisher agents, spread throughout the cabin.
Because the ambient gas must be controlled very well to maintain a healthy condition, clean-up, or flushing, of the air is mandatory. Such a post-process takes time to complete and delays space mission, which is the main task for astronauts.
Furthermore, wearing an oxygen mask is necessary before the spraying operation, because O2 concentration is temporarily reduced in order to put out the fire. Of course, quick action to fight the fire is essential, so wearing an oxygen mask is not always realistic.
Such issues do not need to be considered if VEM is introduced. VEM does not change O2 concentration, so the masks are not necessary.
VEM can collect the harmful gas at the isolated space from the cabin, so that the post-process cleaning of the air may only take a short amount of time.
Moreover, we have a “rich” vacuum environment in space so that no external hardware or extra work is necessary to generate the vacuum condition. In this regard, we believe that VEM is optimized as a fire-extinguishing method for space use.
Tech Briefs: What is the level of pressure created by VEM? Is it possible for the VEM pressure to be strong enough to damage space-station components?
Dr. Nakamura: Vacuum level can be managed at any level. Strong suction flow (created by the largest pressure difference) could induce the immediate quench.
You are right, though: if it is too strong, it might affect some components. However, we just need the product to suck in the flame. Thus, it should not be very strong.
Tech Briefs: Why would agencies like NASA be hesitant to use this technology? Is it because a vacuum could damage components?
Dr. Nakamura: I doubt most agencies are hesitating because of this reason. Rather, they are simply sensitive to introduce a new concept because they would like to exclude potential unexpected problems. Thus, most of technologies used in space are not new. The technologies are rather classical, which is dependable.
Tech Briefs: What are the shortcomings for how fires are currently addressed in space?
Dr. Nakamura: Currently, cleaning the air and removing CO2 is achieved by a disposal filter. Suppose that the conventional CO2-gas extinguisher is used. Much more time is needed to remove all of the carbon dioxide and other combustion products. Additionally, a number of filters must remove all CO2.
Therefore, on a longer-term space mission, we must carry a number of filters, which occupy space and carry weight. By introducing VEM, we do not need to worry about such a thing. With even shorter- or longer-missions, we have exactly the same set of fire-extinguish methods.
Tech Briefs: What has the reaction been from space professionals to VEM?
Dr. Nakamura: Unfortunately, any space agencies like NASA, ESA, and JAXA prefer to introduce established and mature technologies in space use. They are all concerned that new technology may result in unexpected dangers facing astronauts, which must be prevented.
In this regard, their current concern is to reduce the chance of fire inherently (by classifying the precise flammability of the materials in space). Consequently, their reaction seems negative for this new technology, but they do show interest and curiosity.
As a professional researcher on this field, our main task is to introduce a new concept, which might be (or might not be) used in the future.
Tech Briefs: Where else can this be used?
Dr. Nakamura: The VEM concept can be applied any place. It is not limited to the kind of fire. A preferable environment for VEM is in a highly-enclosed space, even a submarine cabin or aircraft.
What do you think of VEM's chances to "clean up" space fires? Share your questions and comments below.