When rescue teams are diving under ice-covered ponds or rivers, or when Navy SEALs perform dives in Arctic waters, the experience can be very painful at best, not to mention the extremely limited survival time even in the best wetsuits which is as little as tens of minutes.
Finding means to prolong that survival time without obstructing mobility has been an important aspect for the U.S. research and Navy divers, as two MIT engineering professors learned during a new program that took them to various naval facilities.
According to the researchers, that visit resulted in a two-year association that has currently produced a significant result - that is, an easy treatment that can enhance the survival time for a traditional wetsuit by a factor of three.
The latest findings, which can possibly be applied immediately, have been published in the journal RSC Advances, in a paper by Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering; Jacopo Buongiorno, the TEPCO Professor and associate head of the Department of Nuclear Science and Engineering; and five others at George Mason University and MIT.
The team discovered a process, in which the standard neoprene wetsuit is placed within a pressure tank autoclave that is the size of a beer keg and filled with a heavy inert gas, for approximately one entire day. Buongiorno, who is a keen wetsuit user himself, explained that the treatment lasts for roughly 20 hours, which is much longer than anyone would spend on a dive. Buongiorno participated in a triathlon only last week. The process can also be performed beforehand, by simply placing the wetsuit in a closed bag which can then be opened just before use, says he.
While Strano and Buongiorno are both on the MIT faculty, they had never met one another until they were part of the Defense Science Study Group for the Department of Defense. “We got to visit a lot of bases, and met with all kinds of military people up to four-star generals,” states Buongiorno, whose area of expertise in nuclear engineering has to do with heat transfer, particularly via water.
Both Buongiorno and Strano learned about the specific requirements of military and were asked to create a technological project to deal with one of those requirements. Following their meet with a team of Navy SEALs, which included the elite special-operations diving corps, they decided the requirement for longer-lasting protection in frigid waters was something that they could handle.
Both Strano and Buongiorno looked at the various strategies used by different animals to survive in these icy waters, and they eventually came across three types: internally produced heat, as with certain animals and fish (including great white sharks, which, remarkably, are warm-blooded); air pockets trapped in feathers or fur, as with penguins and otters; or a layer of insulating material that considerably slows the body’s heat loss, as with whales’ and seals’ blubber.
Then following lab tests and simulations, they finally ended up with a combination of two of these types - a blubber-like insulating material that also uses trapped pockets of gas, albeit in this case, the gas is a heavy inert gas, specifically krypton or xenon, and not air.
Neoprene has become the standard material for wetsuits. This material is cheap and is a combination of synthetic rubber materials which are processed into a kind of foam, yielding a closed-cell structure that resembles styrofoam. Pockets of air are trapped inside that structure, taking up over two-thirds of the volume and accounting for 50% of the heat that is transferred through it
Buongiorno and Strano observed that when the trapped air is substituted with krypton or xenon, the insulating properties of the material increase significantly. According to them, this results in a material that has the lowest heat transfer of any wetsuit ever developed. “We set a world record for the world’s lowest thermal conductivity garment,” Strano says — conductivity nearly as low as air itself. “It’s like wearing a coat of air.”
They both observed that this could enhance survivability in water which is colder than 10 °C, increasing it from just less than an hour to two or three hours.
This latest finding could prove useful to those working in the most adverse environments as well as to those who use wetsuits in cold waters, such as surfers, swimmers, athletes, and all kinds of professional divers.
“As part of this project, I interviewed dozens of wetsuit users, including a professional underwater photographer, divers working at the New England Aquarium, a Navy SEAL friend of mine, and random surfers I approached on a San Diego beach,” says Jeffrey Moran PhD ’17, co-author and former MIT postdoc and now an assistant professor at George Mason University. “The feedback was essentially unanimous — there is an urgent need for warmer wetsuits, both in and out of the Arctic. People's eyes lit up when I told them about our results.”
At present, dry suits are the only feasible cold-water alternatives to wetsuits because they have a layer of air between the skin and the suit that have to be preserved either with a pump and a hose, or a warm-water suit, which likewise needs a pump and hose connection. In both cases, a tear or cut in the suit, or a failure of the pump can lead to a sudden loss of insulation that can prove life-threatening within a matter of minutes.
However, the krypton- or xenon-infused neoprene does not need any such support system and also does not lose its insulating properties quickly, which means it does not carry the associated risk. “We can take anyone’s neoprene wetsuit and pressurize it with xenon or krypton for high-performance operations,” says Strano. Anton Cottrill, a co-author of the paper and MIT graduate student, adds, “The gas actually infuses more quickly during treatment than it discharges during its use in an aquatic environment.”
According to them, another possibility is to develop a wetsuit that has the same insulating properties as the current ones, but with a small fraction of the thickness so that it allows more freedom of movement and comfort that may appeal to athletes. “Almost everyone I interviewed also said they wanted a wetsuit that was easier to move around in and to put on and take off,” says Moran. “The results of this project suggest that we could make wetsuits that provide the same thermal insulation as traditional ones, but are about half as thick.”
The researchers said that their next step would be to explore ways on how to develop a stable and long-term model of a xenon-infused neoprene, and added that they could this by attaching a protective layer over it. Meanwhile, the researchers are also looking for ways to treat the neoprene garments of interested users so that performance data can be collected.
Their approach to the problem is a remarkable feat of materials science and also very clever engineering. They’ve managed to achieve something close to an ideal air-like thermal barrier, and they’ve accomplished this using materials that are more compatible with end-uses like scuba diving than previous concepts. The overall performance characteristics could be a game-changer for a variety of applications.
John Dabiri, a professor of civil and environmental engineering and of mechanical engineering at Stanford University, but was not part of the study
Charles Amsler, a professor of biology at the University of Alabama at Birmingham, who has made nearly 950 research dives in Antartica but was not involved in this work, says, “It could be very beneficial in cases where flexibility, lack of bulkiness, swimming speed, or reduced drag with diver propulsion vehicles are at a premium, or where environmental hazards make the chance of dive suit puncture high. Normally, diver thermal protection in very cold water is by use of dry suits rather than wetsuits. But wetsuits typically allow much more diver flexibility.”
Amsler further added that “One concern with drysuits is that … should the suit be badly punctured, a diver loses much or all of that insulation. … In a deep or long duration dive where staged decompression would be required to prevent decompression illness (“the bends”), wearing one of these thermally enhanced wetsuits would significantly reduce the chance that a diver with a punctured suit would have to make the choice between potentially fatal hypothermia and potentially debilitating or fatal decompression illness.”
The research group also included former MIT postdoc Jeffrey Moran PhD ’17, currently at George Mason University; MIT graduate students Zhe Yuan and Anton Cottrill; former postdoc Jesse Benck; and postdoc Pingwei Liu.
The U.S. Office of Naval Research, the U.S Department of Energy, and King Abdullah University of Science and Technology supported the study.