Pressure Relief
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by Andrew H. Dent, PhD

No one is going to claim that air travel during this holiday season is going to be a delight, but there are some innovations that are attempting to make it at least bearable from a health and safety point of view. 

The atmosphere in the cabin of an average jet airliner has been a cause of many gripes about comfort. This is predominantly because of low humidity (approximately 4% in most cabins) and low levels of oxygen, which induces headaches, dizziness and tiredness. Why so low? Cabins need to be pressurized to the equivalent of 8,000 ft above sea level (10. 9 psi) to ensure that the pressure differential between the outside air at 35,000 feet (3.5 psi) and the cabin interior is as low as possible to reduce the load on the aluminum panels and rivets that hold the whole structure together. Indeed the ‘age’ of an aircraft is not measured in years, but rather in number of pressurization and depressurizing cycles as this causes the greatest stress on the frame. Compare the 10.9 psi environment to the 15 psi at sea level that we’re normally accustomed to—not so comfy.

Moving towards aircraft with a polymer composite body such as the Boeing Dreamliner 787 allows a lower cabin pressure to be used; 11.8psi equivalent to 6000 ft above sea level, giving more oxygen. The composite can withstand this greater pressure differential because of its greater overall stiffness and a more monolithic structure with fewer individual parts. In addition, the humidity can be increased from an industry standard arid 4% to a more comfortable 15%. This is the result of inlet valves on the body of the aircraft taking air directly from the atmosphere outside rather that the traditional method of siphoning it through the air intake of the jet engines, which heats and dries the air before it enters the cabin. Increased humidity would also tend to corrode older aluminum planes, leading to reductions in lifetime for the aircraft. Not so for the new composites.

Boeing 787 Dreamliner

What about the bacteria, viruses and other airborne contaminants the air carries? As mentioned, most current planes take air from within the jet turbine, air which needs to be cleaned to remove the jet fuel and oil contaminants and since the 80’s HEPA (high efficiency particulate air) have been used that do this effectively. The HEPA filters also remove the other contaminants that are a result of the 50% recirculating air in the cabin, including bacteria, skin flakes (ew!) dust, VOCs and some larger viruses. Because the filters can only capture sizes of particulates down to about 0.3 microns, some smaller viruses, including the H1N1 swineflu type, are likely to pass through, even though studies show that over 99% of all viruses are captured this way. For those concerned over the remaining fraction of 1 percent, newer facemasks (Filligent) are now coming onto the market that claim to kill 99.9% of viruses in less than a minute, and all within ten. This reduces the kill time compared to most antibacterials which typically take between 10 minutes (Biosafe MC# 6577-01) and 4-24 hours (AgION, a silver based antimicrobial; MC# 6492-01 and Cupron, a copper based version; MC# 5772-01). 

Another major issue with longer flights is of course limited circulation caused by the lack of movement in a confined space. Scares over DVT (deep vein thrombosis) have largely been overblown, but long periods of low blood circulation can still cause discomfort and even pose a real risk for those suffering from certain conditions. Far infrared rays, a type of radiation given off from certain naturally occurring minerals under specific conditions have long been touted by the Japanese as improving circulation and overall ‘wellness’, and are claimed to significantly increase the blood circulation when in close proximity to the skin. The minerals that give off far infrared tend to be a combination of naturally occurring silica (SiO2) and alumina (Al2O3) and can be forced to emit this radiation by heating the ceramic (typically around 300°C; 570°F) which in turn converts the heat energy to electromagnetic radiation at the far-infrared region of the spectrum. Of course to improve circulation in flight, one can’t take a 570°F heater on board, but the recent innovation of far infrared emitter particles that can convert existing ambient light in to the needed far infrared rays has tackled this problem. Holofiber is a small ceramic particulate that is incorporated into nylon yarns for socks or other apparel and is just such as solution. It is a combination of alumina, that band shifts the absorbed light into the infra-red range, silica which shortens the wavelength of the received light and titania that absorbs, scatters and reflects the light. Together in the right formulation the particles emit far-infrared in the presence of ambient light, improving circulation and increasing the amount of oxygen in the blood. Though originally designed for diabetic patients, they are now used by athletes for faster recovery after racing and of course, to improve your experience during that long haul flight to Taiwan.


Dr. Andrew H. Dent, Ph.D. is Vice President, Library & Materials Research for Material ConneXion.  He has contributed to many publications, most recently co-authoring Ultra Materials: How Materials Innovation is Changing the World and writes Material Innovation, a bi-weekly column for BusinessWeek's online Innovation page.



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