ASHRAE Journal - April 2010 - 70

Germs, Flying, And the Truth
By Douglas S. Walkinshaw, Ph.D., P .Eng., Fellow ASHRAE significant number of air travelers say they are worried about germs when they travel.1 But because incubation periods between exposure to and contraction of a communicable disease vary up to several days (typically three for influenza and colds), travelers cannot be certain if they contracted the disease on an airplane. However, research and engineering, while still in the initial stages, support this concern. Brundage, et al.,2 found in 1988 that febrile illness rates were 50% higher in sealed-window, air-conditioned barracks than in operable window army barracks. Brundage postulated HVAC system design could play an important role in reducing lost productivity in the U.S. due to respiratory illness, which at that time amounted to billions of dollars annually. More recently, a study found flight attendants and school teachers report a higher prevalence of work-related upper respiratory symptoms, chest illness, and cold or flu than the general working population.3 Other studies indicate, with some caveats, that there has been transmission of smallpox, measles, tuberculosis, SARS (severe acute respiratory syndrome) and seasonal influenza during commercial flights.4–9 Other evidence suggests that transmission of these diseases could have an airborne component that is susceptible to ventilation measures.10,11 Excluding those created as bioweapons, there may still be others.12 Most transportation systems such as subway trains and buses, as well as passenger aircraft, have high occupancy densities (ODs; the number of people per unit volume of conditioned space) compared with buildings. With the exception of cruise ships, the intermixing of persons from different population centers and continents in aircraft is unique. Further, passenger aircraft, with their assigned seating and flights ranging up to
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nearly a day, prolong specific pathogen exposure times over most other venues. A recent study by Wagner, et al.,13 calculated the impact of one H1N1 infectious individual on board a large passenger airliner. It found airborne transmission of this pathogen in the economy section can cause two to five infections during a five-hour flight, five to 10 during an 11-hour flight and seven to 17 during a 17-hour flight. Airborne transmission implicates HVAC systems and crowding, rather than individual responsibility. Naturally, the industry is sensitive to this. One official referred to potentially increased risk of airborne disease transmission on aircraft as “a myth.”14 Others sometimes cite misleading information, e.g., aircraft ventilation systems, as in hospitals, use HEPA (high-efficiency particulate air) filters, and air-change rates are 18 times higher than in buildings. But, consider the facts. The aircraft ventilation system supplies only 15 to 20 cfm/p (7 L/s to 9 L/s) versus some 100 cfm/p (47 L/s) in buildings, even though its air change rate is 20 to 40 times higher. In aircraft, 50% of the ventilation rate per person is outdoor air and 50% is air recirculated through HEPA filters. In offices, 20% of the ventilation rate per person is outdoor air (two to three times that of aircraft) and 80% is recirculated through filters. New office filters (e.g., MERV 13), although some 20% less efficient than HEPA in removing 0.3 micron particles, remove 6.4 times more 0.3 micron particles than aircraft HEPA filters because the flows through them are 10 times higher. Aircraft supply air is directed in a lateral row-wise circular fashion with initial velocities from the slot diffusers typically about 500 to 800 fpm (2.5 m/s to 4 m/s) (based on typical aircraft ventilation slot size and ventilation rates) (versus up to 300 fpm [1.5 m/s] for smaller building diffusers and up to 500 fpm [2.5 m/s] for larger ones).15 Recent research has demonstrated the potential for these flow velocities to produce airborne particle transmission between, as well as within, rows.
ashrae.org	 	 April	 2010



ASHRAE Journal - April 2010

Table of Contents for the Digital Edition of ASHRAE Journal - April 2010

ASHRAE Journal - April 2010
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
The Science of Evaporation is Key to Defense in Murder Trial
Selecting DOAS Equipment with Reserve Capacity
Technology Award Case Studies: Greening Hospitals
Technology Award Case Studies: Sustainable Remedy for Hospital
Building Sciences
Emerging Technologies
Technical Topics: Selecting Efficient Fans
Technical Topics: Dual-Capacity Heat Pumps
IAQ Applications
International Column
Classified Advertising
Advertisers Index
ASHRAE Journal - April 2010 - Intro
ASHRAE Journal - April 2010 - ASHRAE Journal - April 2010
ASHRAE Journal - April 2010 - Cover2
ASHRAE Journal - April 2010 - 1
ASHRAE Journal - April 2010 - 2
ASHRAE Journal - April 2010 - Contents
ASHRAE Journal - April 2010 - Commentary
ASHRAE Journal - April 2010 - 5
ASHRAE Journal - April 2010 - Industry News
ASHRAE Journal - April 2010 - 7
ASHRAE Journal - April 2010 - 8
ASHRAE Journal - April 2010 - 9
ASHRAE Journal - April 2010 - 10
ASHRAE Journal - April 2010 - 11
ASHRAE Journal - April 2010 - 12
ASHRAE Journal - April 2010 - 13
ASHRAE Journal - April 2010 - 14
ASHRAE Journal - April 2010 - 15
ASHRAE Journal - April 2010 - 16
ASHRAE Journal - April 2010 - 17
ASHRAE Journal - April 2010 - Letters
ASHRAE Journal - April 2010 - 19
ASHRAE Journal - April 2010 - Meetings and Shows
ASHRAE Journal - April 2010 - 21
ASHRAE Journal - April 2010 - The Science of Evaporation is Key to Defense in Murder Trial
ASHRAE Journal - April 2010 - 23
ASHRAE Journal - April 2010 - 24
ASHRAE Journal - April 2010 - 25
ASHRAE Journal - April 2010 - 26
ASHRAE Journal - April 2010 - 27
ASHRAE Journal - April 2010 - 28
ASHRAE Journal - April 2010 - 29
ASHRAE Journal - April 2010 - Selecting DOAS Equipment with Reserve Capacity
ASHRAE Journal - April 2010 - 31
ASHRAE Journal - April 2010 - 32
ASHRAE Journal - April 2010 - BRC1
ASHRAE Journal - April 2010 - BRC2
ASHRAE Journal - April 2010 - 33
ASHRAE Journal - April 2010 - 34
ASHRAE Journal - April 2010 - 35
ASHRAE Journal - April 2010 - 36
ASHRAE Journal - April 2010 - 37
ASHRAE Journal - April 2010 - 38
ASHRAE Journal - April 2010 - 39
ASHRAE Journal - April 2010 - 40
ASHRAE Journal - April 2010 - 41
ASHRAE Journal - April 2010 - Technology Award Case Studies: Greening Hospitals
ASHRAE Journal - April 2010 - 43
ASHRAE Journal - April 2010 - 44
ASHRAE Journal - April 2010 - 45
ASHRAE Journal - April 2010 - 46
ASHRAE Journal - April 2010 - 47
ASHRAE Journal - April 2010 - 48
ASHRAE Journal - April 2010 - 49
ASHRAE Journal - April 2010 - Technology Award Case Studies: Sustainable Remedy for Hospital
ASHRAE Journal - April 2010 - 51
ASHRAE Journal - April 2010 - 52
ASHRAE Journal - April 2010 - 53
ASHRAE Journal - April 2010 - Building Sciences
ASHRAE Journal - April 2010 - 55
ASHRAE Journal - April 2010 - 56
ASHRAE Journal - April 2010 - AP1
ASHRAE Journal - April 2010 - AP2
ASHRAE Journal - April 2010 - AP3
ASHRAE Journal - April 2010 - AP4
ASHRAE Journal - April 2010 - 57
ASHRAE Journal - April 2010 - 58
ASHRAE Journal - April 2010 - 59
ASHRAE Journal - April 2010 - Emerging Technologies
ASHRAE Journal - April 2010 - 61
ASHRAE Journal - April 2010 - 62
ASHRAE Journal - April 2010 - 63
ASHRAE Journal - April 2010 - Technical Topics: Selecting Efficient Fans
ASHRAE Journal - April 2010 - 65
ASHRAE Journal - April 2010 - Technical Topics: Dual-Capacity Heat Pumps
ASHRAE Journal - April 2010 - 67
ASHRAE Journal - April 2010 - 68
ASHRAE Journal - April 2010 - 69
ASHRAE Journal - April 2010 - IAQ Applications
ASHRAE Journal - April 2010 - 71
ASHRAE Journal - April 2010 - 72
ASHRAE Journal - April 2010 - 73
ASHRAE Journal - April 2010 - International Column
ASHRAE Journal - April 2010 - 75
ASHRAE Journal - April 2010 - 76
ASHRAE Journal - April 2010 - 77
ASHRAE Journal - April 2010 - 78
ASHRAE Journal - April 2010 - 79
ASHRAE Journal - April 2010 - 80
ASHRAE Journal - April 2010 - 81
ASHRAE Journal - April 2010 - 82
ASHRAE Journal - April 2010 - 83
ASHRAE Journal - April 2010 - 84
ASHRAE Journal - April 2010 - 85
ASHRAE Journal - April 2010 - Classified Advertising
ASHRAE Journal - April 2010 - 87
ASHRAE Journal - April 2010 - Advertisers Index
ASHRAE Journal - April 2010 - Cover3
ASHRAE Journal - April 2010 - Cover4
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