Monday, November 12, 2012
Dr. Walkinshaw is an internationally recognized expert in Indoor Air Quality.
Wednesday, April 7, 2010
Dr. D.S. Walkinshaw
Tuesday, December 8, 2009
The research has not been done.
The spokespersons then cite misleading information, such as aircraft ventilation is great because it recirculates air through HEPA (high-efficiency particulate air) filters like those used in hospitals. They say air-change rates are 18 times higher than in buildings, and air does not circulate between rows.
Relevant facts give a different view.
Regarding ventilation rates, in spite of the HEPA filters, ventilation engineering equations indicate that airborne-pathogen concentrations will be at least four times higher than in typical office environments even though their air changes are higher. This is because aircraft cabin ventilation and recirculation rates per person are lower than in buildings, and buildings use recirculation filters that, while not as efficient as HEPAs, remove more particles because the flows through them are 10 times higher.
On top of this, and because their occupancy density (the numbers of persons per unit volume of space) is 40 times higher than in an office building, aircraft-cabin pathogen concentrations reach their peak equilibrium values sooner, with the result that time-weighted exposure ratios are about five times higher than in offices for the same source strength. As another comparison, passenger-aircraft cabin occupancy densities are over three times higher than those of classrooms.
Regarding air movement between cabin occupants, the aircraft-cabin ventilation system not only moves air in a circular fashion side-to-side, which is bad enough as this movement can pass some of the air exhaled by one person in a row past others in the same row. It can also pass a portion of each person’s exhaled air six or more rows forward and the same number backwards (if there are that many rows available) due to the turbulence induced at the boundaries of the air supply and the fundamental instability of most indoor air flows, including those in aircraft cabins.
Sneezing and occupant movement can also create air movement fore and aft.
To add to this, research published in 2007 indicates that low humidity air such as occurs in aircraft cabins, particularly on long flights, increases the potential for influenza infections when a source is present.
In September of this year, the U.S. Transportation Research Board combined with the National Academy of Sciences to hold a symposium of key infectious-disease professionals on the subject. Researchers presented findings on the movement of particles and infections between rows fore and aft of the source, demonstrating that there are no systems or measures in place to prevent the spread of infectious disease over several rows.
Several researchers observed that window seats were less prone to disease transfer than aisle seats. One study found influenza virus in the exhaled normal breath of some infected persons, indicating that coughing is not the only potential source of infectious aerosols.
In conclusion, it would be helpful for everyone if spokespersons were to honestly say that while the risk of getting a respiratory infection from either hand-to-face contact or airborne movement versus other environments is not yet known, and while it may be safer onboard aircraft than in other crowded public transportation environments (that research has not been done yet either), there are some simple-to-implement safety measures recommended for us all.
Pre-flight, these are: immunization shots; rest; and the purchase of disinfectant wipes, hand sanitizers and face breathing masks.
In flight, these are: if you are ill, wear a mask to protect others (airlines might even offer these to coughers); cough into your sleeve; don’t touch your face with your hands (wearing a mask helps here also); periodically disinfect/sanitize your hands and your surroundings (hard surfaces such as the tray table, arm rests and magazines); don’t face your neighbor when talking; use an open cup of water to raise the humidity in your breathing zone; and point your overhead air vent (if there is one) between you and a neighbor (do not point it at your face) to help prevent any exchange of airborne pathogens and to draw any towards the floor returns where they can be exhausted or filtered out.
These measures can be simply and easily described by flight attendants as part of the safety instructions given at the beginning of the flight.
This article previous appeared as a Guest Commentary on NapleNews.com
Saturday, November 7, 2009
I was surprised to learn how many persons involved in infectious diseases and the aircraft industry attendees at the National Academy of Sciences/Transportation Research Board Symposium Washington, DC, Sep 18-19, 2009: Research on the Transmission of Disease in Airports and Aircraft, believed that because air change rate is high in aircraft (some 18 times that in buildings), ventilation is not a problem and in fact is better than in office buildings or classrooms when it comes to dealing with pathogen air pollutants.
Air quality measurements and ventilation theory both refute this! The problem with this belief is that air change rate is high in aircraft, not because ventilation rate per person is high which is what governs bioeffluent exposure both in theory and in measurements, but because occupancy density (the number of people per unit volume of space) is high.
The fact that human bioeffluent concentrations vary as ventilation rate per person, rather than air change rate, is not just theory. Measurements of bioeffluent VOC concentrations in aircraft are more than double those in office buildings where the fresh air ventilation rate per person is more than double that of airplanes (see Table 1 below). This higher VOC concentration in aircraft occurs in spite of the fact that the fresh air change rate in offices is some 18 times lower than in passenger aircraft.
Similarly, the recirculation rate per person in offices is 8 times that in passenger aircraft. With office HVAC systems using MERV 13 filters removing some 80% of 0.3 micron and larger particles, pathogen concentrations where source strengths are similar when measured will be some 4 times higher in aircraft (20 CFM/p free of 0.3 micron particles and larger in aircraft air supplies versus 84 CFM/p free of these particles in office air supplies). Further, the high occupancy density in aircraft versus buildings and classrooms makes VOC and pathogen exposure dose (area under the concentration vs time curve) for the same source strength even higher (see Figure 1 below).
The above measurements and calculations do not include the proximity impact on transmission rate. This factor will increase exposure the closer the seating.
Thus the risk of in flight infectious disease transmission between aircraft passengers and crew [e.g. incidences of febrile illness(colds, flu..), TB...], ) is estimated to be at least five times higher than in offices. This is especially noteworthy during current concerns about an influenza-type pandemic (i.e. H1N1).
Douglas S. Walkinshaw, Ph.D., P.Eng.
ASHRAE Fellow and Member of the ISIAQ Academy of Fellows.
Indoor Air Technologies Inc.
ECHO Air, Inc.
VEFT Aerospace Technology Inc..
Friday, October 10, 2008
Stuffy air in aircraft passenger cabins is a common problem but its impacts on passenger and crew health, where coincidentally the lower cabin air pressure contributes to decreased blood oxygen content while flying versus normal on-the-ground levels, are not known.
Why is stuffy air common in passenger cabins? It is due to the crowding of many people in a small space, and the low air circulation rates being provided (circulation rates are one-sixth those in offices, for example). While turning on overhead gaspers or personal air outlets will improve the air circulation and help eliminate stuffiness, the high velocity gasper air stream will coincidently entrain air-borne germs emanating from nearby persons and bring them to the breathing zone. Furthering disease spread opportunities while flying is obviously not a good idea! It is particularly worrisome when you realize that your neighbours on the plane could be from another city or even another country and could well be expiring germs to which you and your children have not developed an immunity.
This gasper air stream pathogen-entrainment concern will be remedied by a new device soon to be available. With it, turning on your overhead gasper will be a way for improving the quality of the air surrounding you and eliminating ‘stuffy’ air. Known as the Personal Environment Airflow Controller or PEACE, this device will modify gasper air flows so as to filter and supply the air currently being entrained unfiltered by your gasper. With the PEACE device add-on, a gasper outlet will become your personal on-board air cleaner and air circulation device to turn on, regulate and direct. If you want to know more about the PEACE technology, please fill out the VEFT Aerospace Inquiry Form.
Saturday, October 4, 2008
Apparently, it is not the recirculation of air that causes the spread of disease in aircraft. Rather it is more likely the direct transmission of disease between persons even up to several rows apart, either through air transmission or mutual contacts. Why could this transmission be by the air route and why is it so noticeable after flying? There are several reasons:
- The diversity of sources and lack of immunity to the various pathogen exposures encountered in aircraft with the intermixing of persons from different population centers and continents is uniquely high for air travel in comparison with other venues such as theaters or classrooms where the occupants come from one geographic region.
- The filtered air supply rate to aircraft passengers is low (e.g.1/6th that provided to office workers).
- The volume of air surrounding passengers for buffering contaminant spread is relatively low (e.g. 1/30th that of the buffering zone for office workers and 1/10th that available in classrooms).
- The relative humidity on flights is lower than in most other environments (e.g. it is less than 20% on overseas flights versus 30-40% in buildings in winter and 50-60% in summer), and lower humidity has been shown to favor the airborne transmission of certain pathogens including influenza A virus.
I would be interested in your thoughts on the above so feel free to leave a comment. If you are interested in trying the PEACE device let me know by filling out the VEFT Aerospace Inquiry Form so that you can be informed when it is available.
Tuesday, September 30, 2008
For the past 20 years I have owned and operated a consulting and technology development firm, Indoor Air Technologies, specializing in indoor environment problem solving in buildings and aircraft. This firm has problem solving ventilation technologies licensed in the building and aircraft fields. One of these, the ECHO System (a basement radon gas and water entry prevention and mold exposure and odor mitigation system), was installed in 1992 in the Prince Edward Island energy conservation demonstration house.
I have conducted over 400 indoor air quality investigations in all sorts of indoor environments. In the course of this work, I have developed protocols for investigating systemic sources of a number of indoor air contaminants and for measuring ventilation and sorption parameters. I'll provide more information concerning my findings in future articles.
With the Indoor Air Technologies blog I intend to address indoor air quality (IAQ) problems and solutions in buildings and aircraft. I'll also be discussing our ECHO Air, VEFT, PEACE and ECHO Systems technologies. I invite you to drop by on a regular basis.
Dr. Douglas Walkinshaw