Report to the FAA 

on the 

Airliner Cabin Environment

 

Report No. RITE-ACER-CoE-2010-1

National Air Transportation Center of Excellence for

Research in the Intermodal Transport Environment (RITE)

Airliner Cabin Environmental Research (ACER) Program

 prepared by:

Q. Chen, Purdue University

B.W. Jones, Kansas State University

S.M. Loo, Boise State University

W.W. Nazaroff, University of California - Berkeley

R.A. Overfelt, Auburn University

J.D. Spengler, Harvard School of Public Health

C.P. Weisel, University of Medicine and Dentistry of New Jersey

C.J. Weschler, University of Medicine and Dentistry of New Jersey

August 16, 2010
NOTICE

___________

This document is disseminated under the sponsorship

of the U.S. Department of Transportation in the interest

of information exchange. The United States Government

assumes no liability for the contents thereof.

___________

This work was funded by the U.S Federal Aviation Administration 

Office of Aerospace Medicine under 

Cooperative Agreements 04-C-ACE and 07-C-RITE.

___________

This publication is available in full-text from 

the publications Web site of the 

National Air Transportation Center of Excellence for

Research in the Intermodal Transport Environment (RITE) at:

www.acer-coe.org
ii

Table of Contents

1.0 Executive Summary......................................................................................................... 7

1.1 Congressional Mandates and Key Findings ........................................................... 7

1.2 Related Results ....................................................................................................... 9

1.3 Recommendations .................................................................................................. 9

2.0 Introduction ................................................................................................................... 11

2.1 Background .......................................................................................................... 11

2.2 Establishment of the Center.................................................................................. 12

2.3 Organization of this Report .................................................................................. 12

3.0 Ozone in the Passenger Cabin ....................................................................................... 14

3.1 Introduction .......................................................................................................... 14

3.2 Results and Discussion ........................................................................................ 15

3.3 Conclusions .......................................................................................................... 18

3.4 Implications .......................................................................................................... 19

3.5 References ............................................................................................................ 19

4.0 Exposure and Risks of Pesticides on Aircraft ............................................................... 28

4.1 Introduction .......................................................................................................... 28

4.2 Approach .............................................................................................................. 29

4.3 Results and Discussion ........................................................................................ 30

4.4 Conclusions .......................................................................................................... 33

4.5 References ............................................................................................................ 33

5.0 Cabin Pressure .............................................................................................................. 35

5.1 Introduction .......................................................................................................... 35

5.2 Approach............................................................................................................... 38

5.3 Results and Discussion ........................................................................................ 42

5.4 Implications .......................................................................................................... 47

6.0 Incidents - Cabin Air Quality ........................................................................................ 48

6.1 Introduction .......................................................................................................... 48

6.2 Approach............................................................................................................... 49

6.3 Results and Discussion ........................................................................................ 52

6.4 Implications .......................................................................................................... 62

6.5 Approach to On-Board Study .............................................................................. 63

6.6 Progress on On-Board Study ............................................................................... 64

6.7 Air Contaminants Measured in the On-Board Study ........................................... 65

6.8 Implications for the On-Board Study ................................................................... 66

6.9 Portable Sensing System ...................................................................................... 68
iii

7.0 Residue in Filters from Air Quality Incidents ............................................................... 76

7.1 Introduction .......................................................................................................... 76

7.2 Approach .............................................................................................................. 79

7.3 Results and Discussion ........................................................................................ 83

7.4 Conclusions .......................................................................................................... 85

7.5 References ............................................................................................................ 85

8.0 Aircraft Decontamination ............................................................................................. 87

8.1 Introduction .......................................................................................................... 87

8.2 Approach .............................................................................................................. 88

8.3 Results and Discussion ........................................................................................ 93

8.4 Conclusions .......................................................................................................... 96

9.0 Appendices

9.1 Archival Publications of the Center (2005 - 2010) .............................................. 98

9.2 Applicable U.S. Federal Regulations ................................................................. 103

9.2.1 Cabin Ventilation Regulations ............................................................... 103

9.2.3 Ozone Regulations ................................................................................. 105

9.2.3 Cabin Pressure Regulations ................................................................... 107

List of Tables

Table 4.1 Countries Requiring Disinsection of In-Bound Aircraft ......................................... 28

Table 5.1 Characteristics of Participants at Baseline .............................................................. 43

Table 5.2 Number of Notable Desaturations during Cruise According to

Subject Category ..................................................................................................... 43

Table 5.3 Predictors of SaO2 During Flight ........................................................................... 45

Table 6.1 Percentage of Sample Reporting Condition in Past Week by Frequency ............... 54

Table 6.2 Percentage of Flight Attendants Seeking Treatment for Condition in 

Last 12 months ........................................................................................................ 56

Table 6.3 Percentage of Flight Attendants Diagnosed with Particular Medical Conditions 

and the Raw Number Currently Treated for that Condition ................................... 57

Table 6.4 Composite View of Health Conditions Common to Tables 6.1 through 6.3 .......... 61

Table 6.5 List of Analytes Sampled in Cabin Air during On-Board Study ............................ 66

Table 7.1 Typical Bleed Air Temperatures and Pressure (Source: NRC 2002) ..................... 79
iv

List of Figures

Figure 3.1 Real-time ozone data from four consecutive domestic transcontinental U.S. 

segments monitored within a 6-day interval in April, arranged chronologically in 

panels A-D. The direction (EB: eastbound or WB: westbound) is indicated for each 

segment. Panel C represents data from an aircraft equipped with an ozone 

converter; the three other flights were aircraft without converters....................... 22

Figure 3.2 Weighted cumulative distributions of peak 1 h ozone mixing ratios sampled in 

passenger cabins on 68 domestic U.S. flight segments. Data are segregated by the 

presence or absence of an ozone converter. The weighted geometric mean and 

standard deviation, and the lognormal fits using these parameters, are presented for 

each distribution ................................................................................................... 23

Figure 3.3 Ozone levels sampled on eight transoceanic flights. The shaded bars represent peakhour ozone and the diamonds denote cumulative ozone exposure for each flight 

segment ................................................................................................................ 23

Figure 3.4 Section of simulated B-767 located at Technical University of Denmark. Three 

rows, 21 used seats; used carpet, wall sections and HEPA filter;

volume of 28.5 m3................................................................................................ 24

Figure 3.5 Ozone levels with the simulated B-767 when the cabin was empty and when 

16 passengers were present; the ozone generation rate was the same for both 

conditions ............................................................................................................. 24

Figure 3.6 Fraction of ozone remove by the various sinks within the simulated section of the 

Boeing 767............................................................................................................ 25

Figure 3.7 Sum of the organic compounds detected in the cabin air for the four different 

conditions indicated on the X-axis ....................................................................... 25

Figure 3.8 Yield of ozone-derived products at two different air exchange rates – 4.4 and 

8.8 h-1................................................................................................................... 26

Figure 3.9 Assessments of indoor air quality for each of the four conditions (low air exchange, 

low O3; low air exchange, 61 ppb O3; high air exchange, low O3; high air exchange; 

74 ppb O3) after passengers had been on the simulated flight for 3.25 hours. Each 

box represents the interquartile range, and the horizontal line dividing the box is the 

median, whose value appears to the right; all P-values are one-tail ..................... 26

Figure 3.10 Assessments of headache, eye complaints, nasal complaints and perceived skin 

dryness for each of the four conditions................................................................. 27

Figure 4.1 Box and whisker plot of permethrin surface loadings measured in aircraft cabins 

organized by country of destination of the flight ................................................. 31
v

Figure 4.2 Box and whisker plot of permethrin surface loadings measured in aircraft cabins 

organized by location of sample (Insert to right show some individual samples had 

values between 200 and 500 ng/cm2) ................................................................... 32

Figure 5.1 Number of people age 65 and over, by age group, selected years 1900-2006 and 

projected 2010-2050 .............................................................................................38

Figure 5.2 Sample cabin pressures from B737 aircraft ......................................................... 39

Figure 5.3 Data of aircraft altitude during a sample of international flights ......................... 40

Figure 5.4 Association between age and change in SaO2 during flight ................................ 44

Figure 5.5 Frequency of ventricular couplets during flight compared to ground (control)

conditions ............................................................................................................. 46

Figure 5.6 Frequency of ventricular runs [3 or more extra beats] during flight compared to 

ground (control) conditions .................................................................................. 46

Figure 6.1 Flow chart for sample selection and distribution of the survey ........................... 51

Figure 6.2 Summary of the status of the On-Board Study as of May 2010 .......................... 65

Figure 6.3 EMI/EMC approved system ................................................................................ 69

Figure 6.4 Note to crew ......................................................................................................... 70

Figure 6.5 B757 Cabin CO2 Concentration ........................................................................... 71

Figure 6.6 B737 Cabin Pressurization ................................................................................... 72

Figure 6.7 EMB Cabin Temperature ..................................................................................... 73

Figure 6.8 A319 and A320 Cabin Relative Humidity ........................................................... 74

Figure 6.9 B757 Cabin Noise Level ...................................................................................... 75

Figure 7.1 Typical Airliner Bleed Air Supply System (adapted from Hunt et al, 1995) ...... 77

Figure 7.2 Turbofan engine showing bleed air lines and location of pre-cooler ................... 78

Figure 7.3 Hydraulic lines in an aircraft ................................................................................ 78

Figure 7.4 Diagram of aircraft air distribution system .......................................................... 81
vi

Figure 7.5 Recirculation filter installed in aircraft ................................................................ 82

Figure 7.6 Example of filter removed from non-incident aircraft (Note: unusually 

heavily loaded) ..................................................................................................... 83

Figure 7.7 Bleed air simulator and filter exposure facility .................................................... 83

Figure 7.8 Specimen being cut from a recirculation filter ..................................................... 85

Figure 8.1 Field demonstration testing of vaporized hydrogen peroxide decontamination in 

(a) Aeroclave LLC DC9 and (b) B747 at the Civil Aeromedical Institute ......... 89

Figure 8.2 Single-aisle and a twin-aisle aircraft cabins used to computationally 

simulate decontaminant delivery methods ........................................................... 94
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 7

1.0 EXECUTIVE SUMMARY

This report focuses on the results related to specific congressional mandates pertaining to the 

Airliner Cabin Environment Research Program of the National Air Transportation Center of 

Excellence for Research in the Intermodal Transport Environment (RITE). . The report itself is 

intended to be a summary of work related to these mandates and is not intended to be a 

comprehensive report on all of the research conducted by the center since the center’s research 

program extends beyond these initial mandates on the airliner cabin environment. In addition, 

several of the mandates required background research to be conducted before the mandate itself 

could be properly addressed. Not all mandates were fully funded at the time the center was 

created. Some studies are complete, some are still in early phases, and many are still in progress. 

A comprehensive list of publications and presentations for the center may be found in Section 

9.1 of this report. 

The Executive Summary consists of three sections. The first section presents the congressional 

mandates and key findings directly pertaining to these mandates. The second section presents 

related key results. The third section presents recommendations. The focus in these 

recommendations is on potential actions by the FAA. Recommendations are limited to those 

that are clearly based on the results of our research and not just professional opinions of the 

researchers.

1.1 CONGRESIONAL MANDATES AND KEY FINDINGS

MANDATE: Monitor ozone in the cabin on a representative number of flights and aircraft and 

determine compliance with existing Federal Aviation Regulations 

KEY FINDINGS: On 8 of 46 domestic flights without converters, ozone levels exceeded, at 

some point during the flight, the "0.1 parts per million by volume‖ level specified in CFR 

121.578. Ozone levels on one flight exceeded the "0.25 parts per million by volume at any time" 

level specified in CFR 121.578. However, the 0.1 ppm limit applies as a time weighted average 

and only for flight segments exceeding 4 hours. The highest time weighted average over the full 

flight for the 46 domestic flights without converters was within a few percent of the 0.1 ppm 

limit. In addition, the probabilistic flight planning approach specified by the CFR 121.578 only 

requires a statistical confidence of 84% that the limits for ozone levels will not be exceeded. 

Ozone converters reduce ozone levels substantially and there were no instances where the flightaverage limit of 0.1 ppm was exceeded for the 22 flights on aircraft with ozone converters. 

Within the constraints that existed on the number of flights that could be monitored, it is 

concluded that ozone levels in aircraft cabins appear to be consistent with the requirements of 

CFR 121.578.

MANDATE: Collect pesticide exposure data to determine exposures of passengers and crew

KEY FINDINGS: Due to funding limitations, only preliminary research on this topic has been 

completed at this time and the actual exposure of occupants to pesticides has not been quantified. 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 8

A wipe sampling method has been developed and validated for measuring the amount of 

pesticides present on surfaces. Measurements were made on 15 US domestic flights and 46 

international flights with the latter primarily those that go to countries which require pesticide 

treatment or spraying. Little if any measurable pesticide was found on the domestic flights and 

the levels on the international flights were in the tens to hundreds of ng/cm2. 

MANDATE: Analyze and study cabin air pressure and altitude

KEY FINDINGS: General compliance with the 8000 foot cabin altitude limit in 14CFR 25.841 

was found. Human subject studies conducted with a simulated cabin altitude of 7000 feet found 

that a significant portion of the older passengers may be at risk of hypoxia and there was an 

increased risk of arrhythmias in those passengers with cardiac defibrillators.

MANDATE: Identify, analyze, and study incidents of air contamination associated with typical 

flight operations monitored with onboard sensors

KEY FINDINGS: Serious air contamination incidents occur on only a very small fraction of 

flights and are unpredictable, which requires sensors to be deployed on a large number of flights 

if actual incidents are to be monitored. A simple, small portable sampling device was developed 

for this purpose and tested on a small number flights but could not be deployed widely due to 

non-technical reasons. The On-Board project, which is ongoing, has conducted detailed 

measurements on 130 flights. The small portable sensor has been flown on nearly 200 flights. 

These latter measurements have shown general compliance with cabin altitude requirements in 

14CFR 25.841 and the CO2 requirements in CFR 25.831.

MANDATE: Analyze samples of residue from aircraft ventilation ducts and filters after air 

quality incidents to identify the contaminants to which passengers and crew were exposed

KEY FINDINGS: Over 150 filters from non-incident aircraft were analyzed to provide baseline 

information and approximately 25 filters from aircraft with incidents or suspected incidents were 

analyzed. Analysis of filter residue was found to be a useful indicator for identifying 

contaminant sources to guide potential corrective action for problem aircraft but, by itself, was 

not found to be a definitive determination of the nature of a specific air quality incident nor a 

means for quantifying exposures.

MANDATE: Demonstrate decontamination of aircraft by adapting proven technologies such as 

vapor hydrogen peroxide

KEY FINDINGS: Demonstrations were conducted in ground-based DC9 and B747 aircraft. 

Vaporous hydrogen peroxide was effective at deactivating spores at all 28 locations evaluated in 

the DC9 cabin and at approximately 85% of the 28 locations evaluated in the B747 cabin. 

Thermal decontamination systems were able to generate the temperature and humidity levels 

required for efficacious antiviral process throughout the cabins of these aircraft. 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 9

1.2 Related Results

OZONE: Background research was conducted using a B767 cabin mockup designed for air 

quality research. Experiments indicated that more than half of the net ozone removal within the 

cabin was attributable to ozone reactions with passengers and crew. Ozone removal is dominated 

by reactions on surfaces. Ozone reacts rapidly with skin oils present on the exposed skin, hair 

and clothing of the cabin occupants, producing a number of reaction products that become 

airborne. Inhalation of these ozone-derived products may be meaningful for the health of 

passengers and crew members, especially on aircraft with elevated ozone levels. In human 

subject evaluations, occupants judged the air quality worse and reported various symptoms in 

response to exposure to ozone and its oxidation products in the cabin simulations conducted.

The adequacy of the requirements in CFR 25.832 and CFR 121.578 is questionable given that 

they were established about three decades ago and ozone limits for other settings have been or 

are being lowered. 

Measurements on commercial flights found that ozone levels can be moderate to high on 

domestic flights without ozone converters. Elevated ozone levels (up to ~ 0.06 ppm for the peak 

hourly average) were measured on transoceanic flights equipped with converters.

AIR CONTAMINATION: An occupational health survey, completed by over 4000 flight 

attendants from two large US airlines, provides baseline information on flight attendant health 

and demonstrates the feasibility of conducting large-scale epidemiologic studies to assess the 

impact of air contamination. 

DECONTAMINATION: The issues relating to the failure to deactivate biological indicators in 

certain locations in the decontamination demonstrations with vaporous hydrogen peroxide (VHP) 

are engineering issues that can be resolved. 

The effect of VHP on materials is an important limitation that must be considered in any VHPbased decontamination. Laboratory evaluations showed that the mechanical properties of many 

metals, polymers, avionics and textiles, similar to those routinely used in aircraft cabin interiors, 

exhibit minimal to slight degradation after exposure to multiple cycles of vaporized hydrogen 

peroxide. The properties of wool were moderately degraded while leather was severely degraded 

after exposure to multiple cycles of vaporized hydrogen peroxide. Liquid condensed during 

VHP treatments has high concentrations of hydrogen peroxide and can severely degrade acrylics 

(as used in cabin windows) and can cause severe hydrogen embrittlement of high strength steel. 

1.3 Recommendations

Given the elevated ozone found on some aircraft equipped with ozone converters, a periodic

performance check should be required in addition to or as an alternative for the hours-of-service 

standard to ensure effective performance of ozone converters throughout a plane’s service life.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 10

There are no documented safe levels of ozone exposure and limits on ozone exposure are 

compromises between practicality and adverse impacts. As more information about the adverse 

effects of ozone has become available, limits for ozone concentrations in other settings have 

been or are being lowered. Given the evidence of adverse impacts at concentrations below those 

reflected in CFR 25.832 and CFR 121.578, the feasibility of reducing these limits should be 

examined.

Guidance for the medical profession and the elderly flying public as to who should use 

supplemental oxygen or take other measures to mitigate health risks associated with flying in 

commercial aircraft needs to be updated and disseminated.

Guidelines should be developed for the use of filter residue analysis for trouble shooting aircraft 

with recurring air quality problems. In particular, a new recirculation filter should be installed 

on such aircraft so as to minimize the unrelated residue present when it is removed and analyzed 

following an incident or series of incidents.

If whole aircraft disinfection using technologies based upon thermal/humidity sterilization is to 

be employed, then process control regulations or guidelines need to be written that specify the 

temperatures, relative humidity levels, and soak times.

If aircraft decontamination using technology based upon vaporous hydrogen peroxide is to be 

employed, then the process control regulations or guidelines need to be written that specify the 

temperatures, relative humidity levels, vaporized hydrogen peroxide concentration and times 

required to ensure that condensation is prevented within the aircraft.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 11

2.0. INTRODUCTION

2.1 Background

As originally granted in the U.S. Federal Aviation Act of 1958 (Public Law 85-726), regulatory 

authority over the operation of civil aircraft in the United States resides in the Federal Aviation 

Administration (FAA). The Occupational Safety and Health (OSH) Act of 1970 (Public Law 91-

596) was subsequently passed to ensure safe and healthful workplaces across the country and 

federal agencies were allowed the authority to exercise jurisdiction over their own workers. In 

1975, the FAA asserted its jurisdiction over the safety and health of cockpit and cabin crews 

within operating civil aircraft (40 FR 29114, DOT). Since then, the FAA has been authorized to 

also protect the safety and health of passengers (49 USC 40101D and 40 USC 44701A).

The Federal Aviation Regulations (FARs) implement the FAA’s various safety and health 

requirements. Relevant aspects for the design and operation of commercial aircraft are contained 

in "Title 14 - Aeronautics and Space" of the Code of Federal Regulations (14 CFR). Part 25 of 

14 CFR provides the airworthiness standards (i.e., design specifications) for transport category 

airplanes. Part 121 of 14 CFR contains the operating requirements for air carriers and 

commercial operators. Part 125 of 14 CFR covers (i) the certification and operations of aircraft 

having a seating capacity of 20 or more passengers OR a maximum payload capacity of 6000 or 

more pounds and (ii) the rules governing persons on board such aircraft. These regulations 

provide the FAA’s air quality standards with respect to aircraft cabin ventilation and pressure, 

maximum amounts of ozone (O3), carbon monoxide (CO), carbon dioxide (CO2) and other 

harmful or hazardous gases or vapors.

Increasing load factors on airliners and an increasing age of the flying public (with an expected 

decrease of the cardiopulmonary health of older passengers and crew) led to studies by the

National Research Council1,2 and later by the Government Accountability Office.

3

 These studies 

recommended specific research into safety and health issues in airliner cabins. The U.S. 

Congress, in response to these public concerns, appropriated funds in 2004, 2005 and 2006 and 

provided legislative directives to the FAA to perform the needed research in this area. 

Specifically, the U.S. Congress directed the FAA to perform the following research activities 

(Public Law 108–176 (12/03), Section 815):

 conduct surveillance to monitor ozone in the cabin on a representative number of flights 

and aircraft to determine compliance with existing Federal Aviation Regulations for 

ozone;

 collect pesticide exposure data to determine exposures of passengers and crew;

 analyze samples of residue from aircraft ventilation ducts and filters after air quality 

incidents to identify the contaminants to which passengers and crew were exposed;

 analyze and study cabin air pressure and altitude; and

 establish an air quality incident reporting system.

Simultaneously, the U.S. Senate (Senate Report 108-146, page 28, F&E Activity 1) also directed 

the FAA to:
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 12

 identify, analyze, and study incidents of air contamination associated with typical flight 

operations monitored with onboard sensors and 

 demonstrate decontamination of aircraft by adapting proven technologies such as vapor 

hydrogen peroxide. 

2.2 Establishment of the Center

After a nationally competitive process, the Air Transportation Center of Excellence for Airliner 

Cabin Environment Research (ACER) was initiated by the FAA in 2004. In 2007, the charter of 

the Center of Excellence was broadened to include other aspects of intermodal transportation and 

the Center was renamed the National Air Transportation Center of Excellence for Research in the 

Intermodal Transport Environment (RITE). However, the primary research focus of the Center 

continues to be airliner cabin environment research. 

Through the date of this report, the RITE/ACER Center of Excellence consists of seven core 

universities: Auburn University, Boise State University, Harvard University, Kansas State 

University, Purdue University, University of California - Berkeley, and the University of 

Medicine and Dentistry of New Jersey. In addition, a number of large and small organizations 

(companies, research organizations, other state and federal agencies, etc.) serving aerospace 

markets, public health needs and/or associated technology markets are or have been active with 

the RITE/ACER research team. 

Overall, RITE/ACER's mission is to undertake the critical research and technology development 

necessary to (1) inform governmental rulemaking activities and (2) minimize compliance costs to 

the aviation industry. This focus compels RITE/ACER researchers to perform rigorous, 

scientifically valid environmental safety and health research in aircraft cabins and cabin 

simulators to quantitatively assess safety and health risks, and test and develop advanced 

technologies to detect and prevent environmental safety and health incidents within aircraft 

cabins.

2.3 Organization of this Report

This report presents an overview of research results, findings and recommendations as well as 

the current status of the airliner cabin environment research activities being pursued by the 

RITE/ACER team. Since the National Air Transportation Center of Excellence for Research in 

the Intermodal Transport Environment (RITE) was founded initially to address specific concerns 

of the U.S. Congress, this report is structured around the original congressional mandates. 

Section 3 addresses the mandate to monitor ozone in the cabin on a representative number of 

flights and aircraft to determine compliance with existing Federal Aviation Regulations for 

ozone. Section 4 focuses upon the mandate to collect pesticide exposure data to determine 

exposures of passengers and crew. The research activities concerning the mandate to analyze 

and study cabin air pressure and altitude are found in Section 5. Section 6 covers the mandate to 

identify, analyze, and study incidents of air contamination associated with typical flight 

operations monitored with onboard sensors. The related mandates to (i) establish an air quality 

incident reporting system and to (ii) analyze samples of residue from aircraft ventilation ducts 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 13

and filters after air quality incidents to identify the contaminants to which passengers and crew 

were exposed are discussed in Section 7. Section 8 details the research and development 

activities to demonstrate decontamination of aircraft by adapting proven technologies such as 

vaporized hydrogen peroxide. Finally, the Appendices to this report contain both the refereed 

archival publications of the Center relevant to the topics of this report (Section 9.1) as well as the 

relevant federal aviation regulations (Section 9.2).
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 14

3.0 OZONE IN THE PASSENGER CABIN

____________________________________________________________________________________________________________

Congressional Mandate: Monitor ozone in the cabin on a representative number 

of flights and aircraft and determine compliance with existing Federal Aviation 

Regulations

____________________________________________________________________________________________________________

In addition to the above stated Congressional Mandate, the FAA reauthorization bill requires the 

Administrator to carry out the studies and analysis called for in the National Research Council’s 

report ―The Airliner Cabin Environment and Health of Passengers and Crew‖ (National Research 

Council, 2002). In the NRC report, Recommendation 1 called for the FAA to demonstrate the 

adequacy of FARs for cabin air quality. Recommendation 9 called for investigations of how 

ozone concentration in the cabin is affected by various factors (e.g., ambient concentrations, 

reactions with surfaces, the presence and effectiveness of catalytic converters), and the 

relationship between ozone levels and health effects. The research team has attempted to be 

responsive to this broader framing while also addressing the narrower specific charge.

3.1 Introduction

Passengers and crew in aircraft cabins may be exposed to elevated ozone that originates naturally 

in the stratosphere. The level of ozone in aircraft cabins depends on ambient concentrations, the 

presence (or absence) of control devices and their effectiveness, the rate of outdoor air supply, 

and the rate of ozone loss through within-cabin transformation processes, such as reactions with 

interior surfaces, including those associated with occupants. Ozone levels outside the aircraft 

vary with season and depend on flight altitude, tropopause height, and on meteorological 

processes that affect vertical mixing between the lower stratosphere and the upper troposphere. 

Exposure to ozone in cabin air has potential health significance for the flight crew and for the 

general flying population, which includes individuals who may be particularly sensitive to 

respiratory health effects, such as asthmatics, infants, and adults with cardiopulmonary 

conditions. Exposure to ground-level ozone and its reaction byproducts are strongly associated 

with adverse respiratory and cardiovascular effects (Levy et al., 2001; Bell et al., 2006; 

Weschler, 2006; Jarrett et al., 2009). Acute effects from short-term exposure range from 

breathing discomfort, respiratory irritation, and headache for healthy adults (Strøm-Tejsen et al., 

2008) to asthma exacerbation and premature mortality for vulnerable populations (Gent et al., 

2003; Bell et al., 2004). Chronic exposure effects may include enhanced oxidative stress (Chen 

et al., 2007), reduced lung function in young adults (Tager et al., 2005), and adult-onset asthma 

in males (McDonnell et al., 1999). Physical activity, as is undertaken by flight attendants, results 

in increased intake. There is no established ―safe‖ level of ozone exposure (Bell et al., 2006).

Real-time measurements made during flights in the 1960s and 1970s revealed that in-cabin 

ozone was commonly above 100 parts per billion by volume (ppb), especially on flight routes 

through high latitudes (Brabets et al., 1967; Bischof, 1973; Nastrom et al., 1980). In 1980, in 

response to these data and to associated health concerns for flight attendants (Reed et al., 1980), 

the Federal Aviation Administration (FAA) established regulations (FAR 25.832 and FAR 

121.578) that are designed to limit levels of ozone in airplane cabins (National Research Council, 

2002). To comply with the regulations, many planes are equipped with ―catalytic converters‖ 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 15

that promote the decomposition of ozone in the ventilation supply air. Alternatively, airlines may 

comply by means of flight-route planning to reduce the probability of encountering elevated 

ozone. Not all planes are equipped with converters, and the probabilistic planning approach 

permits, by design, up to 16% of the flights to encounter elevated ambient ozone concentrations. 

The ozone level in aircraft cabins is neither routinely monitored, nor has it been the subject of 

much additional research since the ozone standards were established. Spengler et al. (2004) 

presented a survey of flight-integrated ozone levels on 106 segments along with 3-h average 

ozone levels measured during the middle of the flight for Pacific segments. The presence or 

absence of an ozone converter was determined by proxy and was not verified. To our knowledge, 

prior to the efforts by ACER/RITE researchers, real-time in-cabin ozone data have been reported 

for just four flights since 1980 (Spicer et al., 2004). To address this data gap, the research team 

made real-time, continuous measurements of ozone levels in the passenger cabins of 76 

commercial flight segments between February 2006 and August 2007. 

When ozone is present in an aircraft cabin, ozone-derived reaction products are also present, both 

in the gas phase and on surfaces. The fact that ozone-initiated chemistry could meaningfully 

increase the level of certain volatile and semivolatile organic compounds in aircraft cabin air was 

first demonstrated in a Boeing-funded study (Wisthaler et al., 2005) conducted in a simulated 

section of a B-767 (3 rows, 21 seats) at the Technical University of Denmark. Given the results 

of this preliminary study, as well as our understanding of ozone chemistry and effects observed 

in various indoor environments, the ACER/RITE research team also undertook studies of the 

reaction of ozone with cabin materials, with a pesticide commonly used to disinsect aircraft, and 

with cabin occupants themselves. 

Results from the various tasks that have constituted the ACER/RITE Ozone Project are 

summarized in the following paragraphs.

3.2 Results and Discussion

Ozone levels. Ozone levels in airplane cabins, and the factors that influence them, were studied 

on northern hemisphere commercial passenger flights on domestic US routes as well as 

transatlantic and transpacific international routes (Bhangar et al., 2008). Real-time data from 76 

flights were collected during 2006 and 2007 with a battery-powered ozone monitor that works on 

the principle of ultraviolet spectrophotometry. Figure 3.1 shows representative ozone 

measurements from four consecutive domestic transcontinental U.S. segments monitored within 

a 6-day interval in April, 2006. Sample average ozone level, peak-hour ozone level, and flightintegrated ozone exposures were highly variable across the 68 domestic flight segments sampled, 

with ranges of <1.5 to 146 ppb for the flight average, 3-275 ppb for the peak hour, and <1.5 to 

488 ppb hour for the flight-integrated exposures, respectively. On planes equipped with ozone 

catalysts (N = 22 flight segments), the mean peak-hour ozone level (4.7 ppb) was about a factor 

of 10 lower than on planes not equipped with catalysts (N = 46 flight segments; 47 ppb). 

Weighted cumulative distributions of peak 1 hour ozone mixing ratios for aircraft with and 

without converters are displayed in Figure 3.2. Peak-hour ozone levels on eight transoceanic 

flight segments, all on planes equipped with ozone catalysts, were in the range <1.5 to 58 ppb 

(Figure 3.3). Seasonal variation on domestic routes without converters is reasonably modeled by 

a sinusoidal curve that predicts peak-hour levels to be approximately 70 ppb higher in February 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 16

and March than in August and September. The temporal trend is broadly consistent with 

expectations, given the seasonal cycle in tropopause height. Episodically elevated (>100 ppb) 

ozone levels on domestic flights were associated with winter-spring storms that are linked to 

enhanced exchange between the lower stratosphere and the upper troposphere.

Ozone reactions with cabin materials. We measured ozone consumption and byproduct 

formation on materials commonly found in aircraft cabins at flight-relevant conditions (Coleman 

et al., 2008). Two series of small-chamber experiments were conducted, with most runs at low 

relative humidity (10%) and high air-exchange rate (20 air changes per hour). New and used 

cabin materials (seat fabric, carpet, and plastic) and laundered and worn clothing fabrics (cotton, 

polyester, and wool) were studied. We measured ozone deposition to many material samples, and 

we measured ozone uptake and primary and secondary emissions of volatile organic compounds 

(VOCs) from a subset of samples. Deposition velocities, reflecting the effective rate of ozone 

uptake on the fabrics, ranged from 0.06 to 0.54 cm s-1. Emissions of VOCs were higher with 

ozone exposure than without ozone in every case. The most commonly detected secondary 

emissions were C1 through C10 saturated aldehydes and also the squalene oxidation products 6-

methyl-5-hepten-2-one and acetone. For the compounds measured, summed VOC emission rates 

in the presence of 55–128 ppb (residual level) ozone ranged from 1.0 to 8.9 millimoles per hour 

per square meter. Total byproduct yield ranged from 0.07 to 0.24 moles of volatile product 

emitted per mole of ozone consumed. Results were used to estimate the relative contribution of 

different materials to ozone deposition and byproduct emissions in a typical aircraft cabin. The 

dominant contributor to both was clothing fabrics, followed by seat fabric. Results indicate that 

ozone reactions with surfaces substantially reduce the ozone concentration in the cabin but also 

generate volatile byproducts of potential concern for the health and comfort of passengers and 

crew.

Ozone reaction with permethrin. Permethrin is commonly used in aircraft cabins for 

disinsection. Theoretical considerations suggest that the reaction of ozone with residual 

permethrin on cabin surfaces could potentially form phosgene. Published evidence on ozone 

levels and permethrin surface concentrations in aircraft cabins indicated that significant 

phosgene formation might occur in this setting. A chemical derivatization technique was 

developed to detect phosgene with a lower limit of detection of 2 ppb. Chamber experiments 

were conducted with permethrin-coated materials (glass, carpet, seat fabric, and plastic) exposed 

to ozone under cabin-relevant conditions: 150 ppb of ozone, 4.5 per hour air exchange rate, <1% 

relative humidity, and 1700 ng/cm2of permethrin (Coleman et al., 2010). Phosgene was not 

detected in these experiments. Reaction of ozone with permethrin appears to be hindered by the 

electron-withdrawing chlorine atoms adjacent to the double bond in permethrin. Experimental 

results indicate that the upper limit on the reaction probability of ozone with surface-bound 

permethrin is low, ~10-7. Extrapolation by means of material-balance modeling indicates that the 

upper limit on the phosgene level in aircraft cabins resulting from this chemistry is ~ 1 μg/m3or 

~ 0.3 ppb. It was thus determined that phosgene formation, if it occurs in aircraft cabins, is not 

likely to exceed relevant, health-based phosgene exposure guidelines.

Ozone removal in a simulated aircraft cabin. As reported in Tamás et al. (2006), a series of 

experiments was conducted at the Technical University of Denmark’s (DTU) simulated aircraft 

cabin facility, a full-scale mock-up of three rows (21 seats) of a Boeing 767 (Figure 3.4). In the 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 17

first set of experiments, ozone concentrations were measured concurrently inside the simulated 

aircraft cabin and in the airstream providing ventilation air to the cabin. Ozone decay rates were 

also measured after cessation of ozone injection into the supply airstream. By systematically 

varying the presence or absence of (a) people, (b) soiled T-shirts, (c) aircraft seats and (d) a used 

HEPA filter, we were able — in the course of 24 experiments — to isolate the contributions of 

these and other factors to the removal of ozone from the cabin air. As is apparent from Figure 

3.5, humans are large sinks for ozone; at the same ozone generation rates, ozone levels were 

much lower when passengers were present than when the cabin was empty. In the case of this 

simulated aircraft, people (including their exposed skin, hair and clothing) were responsible for 

almost 60% of the ozone removal occurring within the cabin and recirculation system; 

respiration can only have been responsible for about 4% of this removal; the aircraft seats 

removed about 25% of the ozone; the loaded HEPA filter, 7%; and the other surfaces, 10% (see 

Figure 3.6). A T-shirt that had been slept in overnight removed roughly 70% as much ozone as a 

person, indicating that skin oils are indeed important in ozone removal within aircraft cabins. 

The presence of the used HEPA filter in the recirculated airstream reduced the perceived air 

quality as judged by human subjects. Over a 5-h period, the overall ozone removal rate by cabin 

surfaces decreased at a rate of about 3% per hour. With people present, the measured ratio of 

ozone’s concentration in the cabin versus that outside the cabin was 0.15–0.21, smaller than 

levels reported in the literature. The results reinforce the conclusion that the optimal way to 

reduce people’s exposure to both ozone and ozone oxidation products is to efficiently remove 

ozone from the air supply system of an aircraft.

Ozone reaction with cabin materials and occupants in a simulated aircraft cabin. In a second 

set of experiments at DTU, we used multiple analytical methods to characterize the gas-phase 

products formed when ozone was added to cabin air during simulated 4-hour flights that were 

conducted in the reconstructed section of a B-767 aircraft containing human occupants 

(Weschler et al., 2007). Two separate groups of 16 females were each exposed to four 

conditions: low air exchange (4.4 air changes per hour) and low (< 2 ppb) ozone; low air 

exchange and elevated (61-64 ppb) ozone; high air exchange (8.8 air changes per hour) and low 

(< 2 ppb) ozone; and high air exchange and elevated (73-77 ppb) ozone. The addition of ozone to 

the cabin air increased the levels of identified byproducts from ~70 to 130 ppb at the lower airexchange rate and from ~30 to 70 ppb at the higher air-exchange rate (Figure 3.7). Most of the 

increase was attributable to acetone, nonanal, decanal, 4-oxopentanal (4-OPA), 6-methyl-5-

hepten-2-one (6-MHO), formic acid, and acetic acid, with 0.25-0.30 moles of quantified volatile 

product generated per mole of ozone consumed. Figure 3.8 shows the yields of the major ozonederived products at both the low and high air exchange rates. Several of these compounds 

reached levels above their reported odor thresholds. A recently published study conducted by 

researchers at NIOSH indicates that in vitro exposure of pulmonary epithelial cells to 4-OPA 

results in expression of various inflammatory markers (Anderson et al., 2010). In our research, 

most of the byproducts of ozone-initiated chemistry were derived from surface reactions with 

occupants and their clothing, consistent with the inference that occupants were responsible for 

the removal of more than 55% of the ozone in the cabin. The observations made in this study 

have implications for better understanding the health hazards of being exposed to ozone and its 

byproducts not only aircraft cabins but also for other indoor settings. Whenever human beings 

and ozone are simultaneously present, one anticipates production of and increased human 

exposure to acetone, nonanal, decanal, 6-MHO, geranyl acetone, and 4-OPA. Being exposed to 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 18

a given level of ozone in a more densely occupied space will tend to pose higher health risks than 

in a less densely occupied space owing to the concomitant exposure to the byproducts of ozoneinitiated reactive chemistry. 

Impact of ozone and ozone oxidation products on occupants’ self-reported symptoms. In a third 

set of experiments conducted in DTU’s reconstructed section of a B-767 aircraft cabin, StrømTejsen et al. (2008) evaluated human subjects’ symptoms related to air quality and comfort 

during simulated 4-h flights identical to those described in the previous paragraph. Twenty-nine 

female subjects, age 19–27 years, were split into two groups. Each group was exposed to four 

conditions: two levels of ozone (less than 2 ppb and 60–80 ppb) were utilized at each of two 

outside air supply rates (4.4 and 8.8 h-1; that is, 2.4 and 4.7 liters of air per second per person). 

The subjects completed questionnaires to provide subjective assessments of air quality and 

symptoms typical of complaints experienced during actual flight. Additionally, the subjects’ 

visual acuity, nasal peak flow and skin dryness were measured. Based on self-recorded responses 

after 3.25 hours in the simulated aircraft cabin, the subjects judged the air quality (Figure 3.9) 

and eleven symptoms to be worse for the elevated ozone condition compared to the low ozone 

condition. Assessments for headache, eye achiness, nasal irritation and skin dryness are shown in 

Figure 3.10. Not shown, but also adversely impacted by ozone/ozone-derived products, are 

assessments for odor, lip dryness, other eye complaints, dizziness, mental tension, and 

claustrophobia. Taken together these results indicate that ozone and products of ozone-initiated 

chemistry are contributing to such complaints, and imply that such complaints are reduced when 

ozone is removed from the ventilation air supplied to an aircraft cabin.

3.3 Conclusions

The research undertaken by ACER/RITE on ozone in aircraft cabins has produced an 

interconnected set of results that significantly advance our understanding about the levels of 

ozone and its reaction byproducts to which passengers and crew are exposed during flight along 

with some important information about the consequences of such exposures. Measurements on 

commercial flights found that ozone levels can be moderate to high on domestic flights without 

ozone converters and moderate on transoceanic flights even though these planes are equipped 

with converters. When ozone is present within the cabin, various oxidation processes occur, 

mainly on surfaces, including those associated with the passengers themselves. Laboratory 

experiments indicate that ozone reacts with numerous cabin materials, yielding carbonyls, 

dicarbonyls, organic acids and other products. Experiments conducted in a reconstructed section 

of a B-767 aircraft cabin identified the same ozone derived byproducts as those measured in the 

laboratory experiments. Strikingly, in these simulated flights, more than half of the net ozone 

removal within the cabin was due to its reactions with passengers and crew. The reaction 

products, a series of carbonyls, dicarbonyls and hydroxycarbonyls, indicate that ozone is reacting 

rapidly with skin lipids on the clothing and other exposed surfaces of the cabin occupants. Selfassessed symptoms during simulated 4-hour flights with and without ozone indicate that ozoneoxidation products, in addition to ozone itself, may contribute to the complaints of mucous 

membrane irritation (e.g., irritated eyes and throat) commonly reported by the flying public. 

Additionally, certain ozone oxidation products (e.g., formaldehyde, acrolein, certain dicarbonyls) 

are known or suspected of adversely affecting human health at elevated levels. Whether repeated 

exposures to the levels that occur on aircraft without ozone converters contribute to long-term 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 19

health effects remains an open question. On a positive note, laboratory studies indicate that if 

phosgene is formed via the reaction of ozone with residuals of permethrin (a commonly applied 

disinsectant), the resulting levels are very likely to be lower than appropriate health-based 

standards.

3.4 Implications

The results derived from the Ozone Project have a number of implications:

• Health and safety evaluations should consider the products of ozone-initiated chemistry in 

addition to ozone itself. Inhalation of certain ozone-derived products may be meaningful for 

passengers and crewmembers, especially on aircraft without ozone destroying catalysts.

• Higher molecular weight products of ozone-initiated reactions with skin oils can accumulate on 

skin and may contribute to psoriasis and dermatitis (Thiele et al., 1997; Podda and Fuchs, 

2004; Wisthaler and Weschler, 2010); however, separate research is needed to investigate this 

subject.

• It would be appropriate for FAA to re-evaluate the FARs for ozone to determine whether they 

are adequately protective of the health of passengers and crew. Concerns arise for the 

following reasons:

- The current FARs do not reflect additional knowledge, accrued since 1980, regarding direct 

adverse health effects of ozone exposure.

- The current FARs do not reflect ozone chemistry and resultant exposures of passengers and 

crew to the byproducts of ozone-intitiated chemistry.

- The flying population may include more individuals who are vulnerable to the adverse 

effects of air pollutant exposure than was the case before 1980.

• Adopting as a standard practice the use of ozone converters on all commercial flights may be 

warranted. This practice appears to be common in northern Europe, based on conversations 

with carriers based in this region.

• A program of random periodic testing of in-service ozone converters could reduce exposures 

that result from degraded or poisoned catalysts.

• Methods to prevent ―poisoning‖ and to extend the useful life of in-service converters is a 

desirable future research goal.

• Studies should be undertaken to investigate the benefits of using filters (e.g., activated carbon) 

to remove ozone and ozone-derived products from recirculating air in aircraft cabins.

3.5 References

Anderson SE, Jackson LG, Franko J, Wells JR, 2010. Evaluation of dicarbonyls generated in a 

simulated indoor air environment using an in vitro exposure system. Toxicological Sciences, 

in press.

Bell ML, McDermott A, Zeger SL, Samet JM, Dominici F, 2004. Ozone and short-term 

mortality in 95 US urban communities, 1987–2000. Journal of the American Medical 

Association 292, 2372–2378.

Bell ML, Peng RD, Dominici F, 2006. The exposure-response curve for ozone and risk of 

mortality and the adequacy of current ozone regulations. Environmental Health Perspectives 

114, 532–536.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 20

Bhangar S, Cowlin SC, Singer BC, Sextro RG, Nazaroff WW, 2008. Ozone levels in passenger 

cabins of commercial aircraft on North American and transoceanic routes. Environmental 

Science & Technology 42, 3938-3943.

Bischof W, 1973. Ozone measurements in jet airliner cabin air. Water Air and Soil Pollution 2, 

3–14.

Brabets RI, Hersh CK, Klein MJ, 1967. Ozone measurement survey in commercial jet aircraft. 

Journal of Aircraft 4, 59–64.

Chen C, Arjomandi M, Balmes J, Tager I, Holland N, 2007. Effects of chronic and acute ozone 

exposure on lipid peroxidation and antioxidant capacity in healthy young adults. 

Environmental Health Perspectives 115, 1732–1737.

Coleman BK, Destaillats H, Hodgson AT, Nazaroff WW, 2008. Ozone consumption and volatile 

byproduct formation from surface reactions with aircraft cabin materials and clothing fabrics. 

Atmospheric Environment 42, 642-654.

Coleman BK, Wells JR, Nazaroff WW, 2010. Investigating ozone-induced decomposition of 

surface-bound permethrin for conditions in aircraft cabins. Indoor Air 20, 61-71.

Gent JF, Triche EW, Holford TR, Belanger K, Bracken MB, Beckett WS, Leaderer BP, 2003. 

Association of low-level ozone and fine particles with respiratory symptoms in children with 

asthma. Journal of the American Medical Association 290, 1859–1867.

Jerrett M, Burnett RT, Pope III CA, Ito K, Thurston G, Krewski D, Shi Y, Calle E, Thun M, 

2009. Long-term ozone exposure and mortality. The New England Journal of Medicine 360, 

1085-1095.

Levy JI, Carrothers TJ, Tuomisto JT, Hammitt JK, Evans JS, 2001. Assessing the public health 

benefits of reduced ozone concentrations. Environmental Health Perspectives 109, 1215–

1226.

McDonnell WF, Abbey DE, Nishino N, Lebowitz MD, 1999. Long-term ambient ozone 

concentration and the incidence of asthma in nonsmoking adults: The Ahsmog study. 

Environmental Research 80, 110–121.

Nastrom GD, Holdeman JD, Perkins PJ, 1980. Measurements of cabin and ambient ozone on 

B747 airplanes. Journal of Aircraft 17, 246–249.

National Research Council (NRC) Committee on air quality in passenger cabins of commercial 

aircraft. The Airliner Cabin Environment and the Health of Passengers and Crew. National 

Academy Press: Washington, DC, 2002.

Podda M, Fuchs J, 2004. [Influence of environmental polluting ozone on the skin]. Der 

Hautarzt: Zeitschrift fur Dermatologie, Venerologie, und verwandte Gebiete 55, 1120-1124.

Reed D, Glaser S, Kaldor J, 1980. Ozone toxicity symptoms among flight attendants. American 

Journal of Industrial Medicine 1, 43–54.

Spengler JD, Ludwig S, Weker RA, 2004. Ozone exposures during trans-continental and transPacific flights. Indoor Air 14, 67–73.

Spicer CW, Murphy MJ, Holdren MW, Myers JD, MacGregor IC, Holloman C, James RR, 

Tucker K, Zaborski R. Relate Air Quality and Other Factors to Comfort and Health 

Symptoms Reported by Passengers and Crew on Commercial Transport Aircraft (Part I). 

ASHRAE Project 1262-TRP. American Society for Heating, Refrigerating, and Air 

Conditioning Engineers: Atlanta, 2004.

Strøm-Tejsen P, Weschler CJ, Wargocki P, Myskow D, Zarzycka J, 2008. The influence of 

ozone on self-evaluation of symptoms in a simulated aircraft cabin. Journal of Exposure 

Science and Environmental Epidemiology 18, 272-281.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 21

Tager IB, Balmes J, Lurmann F, Ngo L, Alcorn S, Kunzli N, 2005. Chronic exposure to ambient 

ozone and lung function in young adults. Epidemiology 16, 751–759.

Tamás G, Weschler CJ, Bako-Biro Z, Wyon DP, Strøm-Tejsen P, 2006. Factors affecting ozone 

removal rates in a simulated aircraft cabin environment. Atmospheric Environment 40, 6122-

6133.

Thiele JJ, Podda M, Packer L, 1997. Tropospheric ozone: an emerging environmental stress to 

skin. Biological Chemistry 378, 1299-1305.

Weschler CJ, 2006. Ozone’s impact on public health: Contributions from indoor exposures to 

ozone and products of ozone-initiated chemistry. Environmental Health Perspectives 114, 

1489–1496.

Weschler CJ, Wisthaler A, Cowlin S, Tamás G, Strøm-Tejsen P, Hodgson AT, Destaillats H, 

Herrington J, Zhang JJ, Nazaroff WW, 2007. Ozone-initiated chemistry in an occupied 

simulated aircraft cabin. Environmental Science & Technology 41, 6177-6184.

Wisthaler A, Tamás G, Wyon DP, Strøm-Tejsen P, Space D, Beauchamp J, Hansel A, Mark TD, 

Weschler CJ, 2005. Products of ozone-initiated chemistry in a simulated aircraft 

environment. Environmental Science & Technology 39, 4823-4832.

Wisthaler A, Weschler CJ, 2010. Reactions of ozone with human skin lipids: Sources of 

carbonyls, dicarbonyls, and hydroxycarbonyls in indoor air. Proceedings of the National 

Academy of Sciences of the United States of America 107, 6568-6575.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 22

Figure 3.1 Real-time ozone data from four consecutive domestic transcontinental U.S. 

segments monitored within a 6-day interval in April, arranged chronologically in 

panels A-D. The direction (EB: eastbound or WB: westbound) is indicated for each 

segment. Panel C represents data from an aircraft equipped with an ozone 

converter; the three other flights were aircraft without converters. 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 23

 

Figure 3.2 Weighted cumulative distributions of peak 1 h ozone mixing ratios sampled in 

passenger cabins on 68 domestic U.S. flight segments. Data are segregated by the 

presence or absence of an ozone converter. The weighted geometric mean and 

standard deviation, and the lognormal fits using these parameters, are presented for 

each distribution.

 

Figure 3.3 Ozone levels sampled on eight transoceanic flights. The shaded bars represent peakhour ozone and the diamonds denote cumulative ozone exposure for each flight 

segment.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 24

Figure 3.4 Section of simulated B-767 located at Technical University of Denmark. Three 

rows, 21 used seats; used carpet, wall sections and HEPA filter; volume of 28.5 m3.

Figure 3.5 Ozone levels with the simulated B-767 when the cabin was empty and when 16 

passengers were present; the ozone generation rate was the same for both 

conditions.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 25

Figure 3.6 Fraction of ozone remove by the various sinks within the simulated section of the 

Boeing 767

0

20

40

60

80

100

120

140

no ozone, 4.4/h

ozone, 4.4/h

no ozone, 8.8/h

ozone, 8.8/h

average level (ppb) .

acids, aldehydes & ketones other

Figure 3.7 Sum of the organic compounds detected in the cabin air for the four different 

conditions indicated on the X-axis.

25%

7%

10%

56%

2%

Seats HEPA Filter

Other Surfaces People

Respiration
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 26

-1.0

-0.5

0.0

0.5

1.0

<2 ppb 61 ppb <2 ppb 74 ppb

2.4 L/s per person 4.7 L/s per person

Indoor Air Quality

Clearly 

acceptable

Clearly 

unacceptable

P<0.001 0.55

0.26

0.50

0.47

0%

5%

10%

15%

20%

25%

30%

4.4/h 8.8/h yield (mole product per mole ozone)

other C=O

acetic acid

formic acid

6-MHO

4-OPA

decanal

nonanal

acetone

Figure 3.8 Yield of ozone-derived products at two different air exchange rates – 4.4 and 8.8 h-1.

Figure 3.9 Assessments of indoor air quality for each of the four conditions (low air exchange, 

low O3; low air exchange, 61 ppb O3; high air exchange, low O3; high air exchange; 

74 ppb O3) after passengers had been on the simulated flight for 3.25 hours. Each box 

represents the interquartile range, and the horizontal line dividing the box is the 

median, whose value appears to the right; all P-values are one-tail.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 27

Figure 3.10 Assessments of headache, eye complaints, nasal complaints and perceived skin 

dryness for each of the four conditions. See Figure 3.9 for further details.

0

20

40

60

80

100

<2 ppb 61 ppb <2 ppb 74 ppb

2.4 L/s per person 4.7 L/s per person

Eyes Aching

Eyes aching

Eyes not

aching

P<0.013 P<0.003 1.8 4.5 1.2

5.3

0

20

40

60

80

100

<2 ppb 61 ppb <2 ppb 74 ppb

2.4 L/s per person 4.7 L/s per person

Headache

Severe 

headache

No headache

P<0.009

13

24

11

20

0

10

20

30

40

50

<2 ppb 61 ppb <2 ppb 74 ppb

2.4 L/s per person 4.7 L/s per person

Nasal Irritation

Overpowering 

irritation

Slight

irritation

Moderate 

irritation

Strong

irritation

Very Strong 

irritation

No

irritation

P<0.043

3.6

4.0

5.2

8.7

0

20

40

60

80

100

<2 ppb 61 ppb <2 ppb 74 ppb

2.4 L/s per person 4.7 L/s per person

Skin Dryness

Skin dry

Skin not dry

P<0.028 P<0.043 31 49

29

53
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 28

4.0 EXPOSURE AND RISKS OF PESTICIDES ON AIRCRAFT

____________________________________________________________________________________________________________

Congressional Mandate: Collect pesticide exposure data to determine exposures 

of passengers and crew 

____________________________________________________________________________________________________________

4.1 Introduction

Disinsection of aircraft, while no longer routinely practiced in the US, is currently mandated by 

twenty five countries all or selected international flights landing in their borders (Table 4.1) to 

prevent inadvertent insects transport on commercial aircraft in order to protect populations and

native animals and plant species. In addition, most countries reserve the right to require 

disinfection when there is a perceived threat of vector borne disease. The application of 

pesticide is done by either by active spraying of the aircraft while passengers are on board or by 

applying a residual level of pesticides onto the surfaces within the cabin and/or the cargo hold. 

Pyrethroids are the currently recommended pesticides to be used on aircraft with the World 

Health Organization recommending four active ingredients resmethrin, bioresmethrin, dphenothrin and permethrin (cis/trans ration 25/75). New Zealand and Australia, two countries 

mandating disinection of aircraft, have published Guidelines for Treatment of Aircraft (New 

Zealand MAF 2007, AQIS 2009), which includes the use of d-phenothrin and permethrin and 

have approved commercially available formulations specific for use on aircraft. The United 

Kingdom recommends using deltamethrin. 

Table 4.1 Countries Requiring Disinsection of In-bound Aircraft

Source: http://ostpxweb.dot.gov/policy/safetyenergyenv/disinsection.htm

Last Updated 4/21/2010

While Passengers on 

Board Residual Treatment Flights from Selected Areas

China Australia Czech Republic

Cuba Barbados France

Grenada Cook Islands Indonesia

India Fiji South Africa

Kiribati Jamaica Switzerland

Madagascar New Zealand United Kingdom

Seychelles Panama

Trinidad & Tobago

Uruguay

Residual application needs to be effective for at least 8 weeks with typical application rates to 

provide surface loading of 0.5 g/m2(50 μg/cm2) on carpets and 0.2 g/m2(20 μg/cm2) on other 

surfaces including seats, trays etc (Rayman 2006, New Zealand MAF 2007, AQIS 2009). The 

application is done using a spray containing 2% of the active insecticide. All surfaces, including 

storage areas, ceilings, walls, curtains, toilets, galleys, flight decks, behind curtains, etc. are to be 

sprayed. Similarly, when cargo compartments are sprayed all surfaces with particular attention 

to sidewall and floor cavities are to be treated. The total amount to be applied is aircraft 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 29

dependent since the surface area varies with aircraft types. These applications are done by 

trained individuals usually while general maintenance is being performed.

Application with passengers aboard is often referred to as Top of Descent disinsection and can 

be combined with a pre-boarding treatment. The pre-boarding treatment is done before 

embarking by treating all surfaces with a pre-flight spray using a 2% permethrin spray no later 

than 1 hour before departure but after catering has been completed while the Top of Descent 

occurs while the passengers are on board immediately prior to commencing the final descent for 

landing with 2% d-phenothrin. An announcement is to be made to the passengers indicating that 

the spraying is being done and they should remain seated. The spraying is performed by trained 

flight crew who spray two cans each while walking down each aisle. The spraying is directed 

towards closed overhead lockers while the crew member walks at a rate of 1 row or step per 

second resulting in a rate of 10gms per 28.3 cubic meters. The application rates have been 

reviewed and approved as safe by the World Health Organization (Rayman, 2006; WHO 1998) 

though others have raised concerns about potential adverse health effects (van Netten 2002, 

Murawski 2005) and recent toxicological studies have identified adverse neurological and 

development effects at low levels of several pyrethroids (Das et al 2008, Breckenridge et al 

2009, DeMicco et al 2010).

Air concentrations of pesticides have been reported during spraying while simulating the Top of 

Descent protocols when the aircraft was on the ground with the air conditioning unit on resulting 

in clearance half lives of 2.7 minutes and average air concentrations of 63  39 g/m3per gram 

of insecticide over a 40 minute sampling duration that included the time of spraying (BergerPrei 2004, 2006). Surface loadings during these experiments were measured on various 

locations and the highest levels were ~0.1 μg/cm2. The only in-flight air concentrations reported 

for commercial flights were in an ASHREA report and two of four domestic flights reported 

detectable levels of permethrin at 1 to 2 ng/m3(Spicer et al 2004).

The studies undertaken within ACER were a review of the literature related to exposure to 

pesticides on commercial aircraft to identify data gaps and design measurement and modeling 

approaches to fill those gaps and assess crew and passenger exposure and potential risk to 

pesticides.

4.2 Approach

To assess the potential pesticide exposure of flight crew and passengers within an the aircraft 

cabin of commercial airlines several steps were undertaken as part of ACER: a review of the 

current state of knowledge of the use of pesticides on-board aircraft; a wipe sampler was 

developed and deployed on in-use commercial aircraft to determine pesticide loading on surfaces 

within the airplane cabin; air concentrations and surface loadings within an aircraft is being 

mathematically modeling during disinsection and measurements to evaluate that model were 

made in the KSU aircraft model; and urinary pesticide metabolite levels are being measured for 

crew members who fly routes into countries requiring disinsection. A risk paradigm is being 

developed to provide the distribution of pesticide exposures and risks associated with 

disinsection for those flying on commercial aircraft.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 30

a) Summary of Current Knowledge

The review of the current information about pesticide application practices was conducted by 

Drs. Randy Maddalena and Thomas McKone of LBNL (Maddalena and McKone 2008). The 

goal of this review was to provide a brief history of pesticide use on aircraft and to identify 

values for key inputs needed to evaluate pesticide exposures. It included a summary of the 

application methods, rates, frequency and the most likely pesticides used. Physiochemical 

properties of pesticides used on aircraft and environmental factors in the aircraft cabin were 

included for use in exposure models. Existing data exposure concentrations in the airliner cabin 

were also summarized.

b) Potential Dermal Exposure

To be able to determine the potential pesticide dermal exposures and provide an estimate of the 

reservoir of pesticide levels in an aircraft that could vaporize, a wipe sampler for the collection 

of pyrethroid pesticides was developed for use on both soft and hard surfaces in an aircraft

(Mohan and Weisel 2010). The wipe sampler uses readily available round 9cm (3 1⁄2 inch) 

diameter cellulose filter paper and a small amount of water as a wetting agent. These materials 

can be taken through security and brought aboard aircraft. The filter paper is placed on the 

surface to be sampled, wet with several drops of the water and the water remaining on the 

surface collected with additional filter paper. This procedure is repeated several times to collect 

the pesticides available on the surface that can be readily transferred to skin or food if on the tray 

table. The filter paper is transported back to the laboratory in a plastic zip-log bag where it is 

stored in a freezer until extracted in hexane facilitated by ultrasonication. The volume of the 

hexane is reduced and the pesticides analyzed by gas chromatography/mass spectrometry. The 

pesticide collection efficiency of the sampler is: 91± 6% from hard surfaces, 40± 4% from the 

seat material and 70± 5% from aircraft carpeting.

c) On-going studies

On-going studies include the collection of urine samples to assess the body burden of flight crew 

on aircraft that are disinsected, mathematic modeling of air concentrations and surface loading of 

pesticides during disinsection and a risk assessment of pesticides for flight attendants and 

passengers.

4.3 Results and Discussion

a) Summary of Current Knowledge

The literature review (Maddalena and McKone 2008) determined that insufficient information is

publicly available from the airlines and other sources for estimating insecticide application rates 

in the U.S. domestic fleet and international fleets or for understanding how frequently equipment 

rotate into domestic routes following insecticide treatment. The World Health Organization 

(WHO) and several countries that require disinsection have recommend several methods for 

treating aircraft with insecticide, though there is evidence that deviations from these guidelines 

may exist. Even so, it still may be possible, based on general information about practices by 

various airlines, where an aircraft has flown, and/or applicator company, that the guidelines may 

be used in combination with how pesticides behave in other indoor environments to provide a 

plausible basis for estimating insecticide loading rates on aircraft, though experimental and 

measurement data are needed to evaluate those estimates. The review also found that while there 

are some measurements of exposure concentrations following simulated aerosol applications, 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 31

measurements within in-use aircraft or during actual applications in domestic and international

aircraft are lacking. No systematic modeling effort of exposure to pesticides within aircraft was 

identified.

b) Potential Dermal Exposure

The wipe sampler was used to measure pesticide loading on various aircraft cabin surfaces from

15 domestic and 46 international flights. The domestic flights were predominantly in the 

southeast during the spring and summer of 2008 when insect infestations are most likely which 

would require disinsection and included samples collected from seat cushions, the front and back 

of tray tables, the wall and other surfaces in the galley and in the lavatory. Permethrin was

detected on only a single domestic flight, near its detection limit of 0.001 ng/cm2and at only one

of the multiple locations sampled from that flight. These results are consistent with disinsection 

not being done on planes that fly only within the US and that no pesticide has been approved for 

use on aircraft within the US by the US EPA.

The samples collected from international flights were selected predominantly, though not 

exclusively, to include those landing in countries that require some form of disinsection or where 

residual treatment is performed. Flights included countries in the Caribbean, South and North 

America, Australia, New Zealand, Asia and Europe from the fall of 2008 to the spring of 2009. 

Pyrethroids were detected on 22 of 46 flights with the mean levels by country given in Figure 

4.1.

 

Figure 4.1 Box and Whisker Plot of Permethrin Surface Loadings Measured in Aircraft 

Cabins Organized by Country of Destination of the Flight.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 32

The highest mean loadings were present in Australia, New Zealand and India which require 

disinsection of aircraft before landing in their country and in Hong Kong, Malaysia and Vietnam, 

countries that have been certified to do residual disinsection. Individual aircraft that landed in 

Germany, South Korea, Thailand and the US had measurable levels, with several samples being 

as in the upper quartile of measured loadings. The flights landing those countries were 

continuation of flights that originated in countries requiring disinsection.

Permethrin was present on all of the surface types sampled and on a deposition sample collected 

by placing a filter in a container on the top of the seat while and after the flight crew were 

conducting top of descent spraying (Figure 4.2).

Figure 4.2 Box and Whisker Plot of Permethrin Surface Loadings Measured in Aircraft Cabins 

Organized by Location of Sample (Bottom figure shows that some individual samples 

had values between 200 and 500 ng/cm2, top figure scale is expanded)

The samples collected during spraying (deposition) confirm that permthrin is one of the 

pesticides being sprayed during the top of descent while passengers were on board the plane. 

The loadings measured were all lower that the application guidelines of residuals on seats of 

20μg/cm2, but pesticides were consistently present on the seats, head rest and arm presenting 

potential dermal exposure and were on both sides of the food tray tables which could result in 

dermal and ingestion exposures. In addition, permethrin and phenothrin were present in extracts 

from approximately 50 of the 100 HEPA filters removed from commercial aircraft, though the 

pesticides could have come spraying around airports rather than the cabin air.

c) On-going studies

We have adapted a CFD model developed by Yan Chen, Purdue University as part of ACER, to 

predict exposure in the air and on passengers and seats within the main cabin of a Boeing 767 

and are evaluating that model with measurements made at the at Kansas State University a 

mockup of the aircraft. We are currently seeking to obtain urine samples from flight attendants 

Location Codes

0 – deposition

Hard Surfaces

1 – galley area

2 – arm rest

3 – tray table

4 – wall

Soft Surfaces

11 – head rest

12 – back of seat

13 – seat

14 – rug
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 33

on aircraft that have been sprayed and those that have not been sprayed, with a focus on 

evaluating differences among biomarker levels in the flight crew due to disinsection.

4.4 Conclusions

The information reported in the literature when ACER was formed is insufficient to determine 

the extent of pesticide exposure to the crew and passengers on commercial airlines. As part of 

the ACER supported research, a method to collect measure loading on in-use commercial flights 

was developed and used to document that little if any pesticides are present in the domestic fleet 

but is consistently present at the tens to hundreds of ng/cm2range in the cabin of aircraft that 

land in countries requiring disinsection, including aircraft that return to the US which can result 

in dermal, and since pesticides are on tray table, ingestion exposure. In addition, inhalation 

exposure to pesticides was documented during top of the descent exposure. The exposure levels 

are currently being measured and risk estimates will be completed within two years.

It is recommended that quantification of the exposure and risk to pesticides in airplanes that land 

in the US and fly to countries requiring or performing disinsection be done since multi-route 

pesticide exposures occurs to flight crew and passengers on those aircraft. While exposures to 

pesticides from foods and residential applications is substantial in the US population 

understanding the additional risk of pesticide exposures to flight attendants, frequent flyers, 

pregnant women and children resulting from encountering pesticide residues in airplanes is 

needed.

4.5 References

Publications from ACER: 

R.L. Maddalena and T.E. McKone ―Pesticide Exposures on Commercial Aircraft: A Literature 

Review and Screening Level Exposure Assessment” Report from the Environmental Energy 

Technologies Division of the Lawrence Berkeley National Laboratory (LBNL-1246E) October 

2008

Mohan, K.R., and Weisel, C.P., 2009. Sampling scheme for pyrethroids on multiple surfaces on 

commercial aircrafts. Journal of Exposure Science and Environmental Epidemiology, 2010 20

(4), 320-325.

Other references:

AQIS (Australian Quarantine and Inspection Service) Schedule of Aircraft Disinsectin 

Procedures, Version 2.0, October 2009.

Berger-Prei E., W. Koch, W. Behnke, S. Gerling, H. Kock, L. Elfein, and K.E. Appel,

In-flight spraying in aircrafts: determination of the exposure scenario. International

Journal of Hygiene and Environmental Health, 2004. 207(5): p. 419-430.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 34

Berger-Prei E., W. Koch, S. Gerling, H. Kock, J. Klasen, G. Hoffmann, and K.E. Appel, 

Aircraft disinsection: Exposure assessment and evaluation of a new pre-embarkation method. 

International Journal of Hygiene and Environmental Health, 2006. 209(1): p. 41- 56.

Breckenridge CB, Holden L, Sturgess N, Weiner M, Sheets L, Sargent D, Soderlund DM, Choi 

JS, Symington S, Clark JM, Burr S, Ray D. Evidence for a separate mechanism of toxicity for 

the Type I and the Type II pyrethroid insecticides. Neurotoxicology. 2009 Suppl 1:S17-

31.

Das PC, Streit TM, Cao Y, Rose RL, Cherrington N, Ross MK, Wallace AD, Hodgson E 

Pyrethroids: cytotoxicity and induction of CYP isoforms in human hepatocytes. Drug Metabol 

Drug Interact. 2008;23(3-4):211-36

DeMicco A, Cooper KR, Richardson JR, White LA. Developmental neurotoxicity of pyrethroid 

insecticides in zebrafish embryos. Toxicol Sci. 2010 113(1):177-186.

Murawski, J., Insecticide use in occupied areas of aircraft, in Air Quality in Airplane

Cabins and Similar Enclosed Spaces. 2005, Springer: Berlin / Heidelberg.

Rayman, R.B., Aircraft Disinsection. Aviation, Space and Environmental Medicine, 2006. 77(7): 

p. 733-736.

Spicer, C.W., M.J. Murphy, M.W. Holdren, J.D. Myers, I.C. MacGregor, C. Holloman, R.R. 

James, K. Tucker, and R. Zaborski, Relate air quality and other factors to comfort and health 

symptoms reported by passengers and crew on commercial transport aircraft (Part I), Battelle 

Science and Technology International. Columbus, OH. 2004, Amercian Society for Heating, 

Refrigerating, and Air Conditioning Engineers: Atlanta, GA.

Van Netten, C., Analysis and implications of aircraft disinsectants. Science of the Total 

Environment, 2002, 293 (1-3): 257-262.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 35

5.0 CABIN PRESSURE

____________________________________________________________________________________________________________

Congressional Mandate: Analyze and study cabin air pressure and altitude 

____________________________________________________________________________________________________________

FAA reauthorization bill requires the Administrator to carry out the studies and analysis called for in 

the National Research Council’s report ―The Airliner Cabin Environment and Health of Passengers 

and Crew1. The report summarized the need for study of the effects of cabin pressure as follows: 

―The partial pressure of oxygen at the currently allowed maximum cabin altitude of 2440m 

(8,000ft) may not be adequate for cabin crew and passengers of varying age and health status, 

such as elderly individuals with cardiopulmonary impairments.‖*

 

5.1 Introduction

In the 50 years from 2000 to 2050, the world population of people age 60 and older will more 

than triple, increasing from 600 million to 2 billion.† Researchers expect the percentage of the 

over-65 population who utilize air travel and the frequency with which they do so will be greater 

than previous over-65 populations because the Boomer generation was the first for which air 

travel was a common part of life including both low-cost business and recreational travel. This 

familiarity with air travel is expected to cause more Boomers to fly more often than previous 

generations.‡

The increase in older passengers means also an increase in unhealthy persons flying. In the U.S. 

11.5% of the population has some type of heart disease, with over 27% of those 65-74 and over 

37% of those 75 or older having some type of heart disease.§ Moreover, the National Heart Lung 

and Blood Institute (NHLBI) estimates that annually 175,000 first heart attacks occur silently, 

without prior symptoms or their recognition.** In several observation studies, cardiac events 

caused 10%-20% of all in-flight incidents ††and accounted for 12 of 15 in-flight deaths on the 

five major US air carriers over a one-year period.‡‡ The issue of cardiac health aboard aircraft 

 

* National Research Council. The Airliner Cabin Environment and the Health of Passengers and Crew. National 

Academy Press, Washington, D.C. 2002.

†

http://www.who.int/en/

‡

http://www.siu.edu/~aviation/facultyhome/hwolfe/NewDelhi.pdf

§ U.S. Centers for Disease Control and Prevention, Summary Health Statistics for U.S. Adults: National Health 

Interview Survey, 2004. Series 10, Number 228. May 2006. 

http://www.cdc.gov/nchs/data/series/sr_10/sr10_228.pdf

** American Heart Association and American Stroke Association. Heart Disease and Stroke Statistics, 2007 Update 

At-A-Glance. http://www.americanheart.org/downloadable/heart/1166712318459HS_StatsInsideText.pdf

†† Possick SE, and Barry M. (2004). Evaluation and management of the cardiovascular patient embarking on air 

travel. Annals of Internal Medicine 141 (2), 148-154.

‡‡ DeJohn C, Veronneau S, Wolbrink A. The evaluation of in-flight medical care aboard selected U.S. air carriers: 

1996 to 1997. Washington, DC: U.S. Department of Transportation, Federal Aviation Administration, Office of 

Aviation Medicine; May 2000. Technical report no. DOT/FAA/AM-0013.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 36

has garnered enough attention to warrant the FAA to mandate the placement of at least 1 

automatic external defibrillator on passenger aircraft.§§

Besides the higher prevalence of cardiac disease in aging Americans, these individuals have 

higher exposures to tobacco smoke from current or past cigarette smoking (either active or 

passive smoking), the number one risk factor for lung disease. The U.S. Surgeon General’s 2004 

report on the health effects of smoking indicates that there is sufficient evidence to infer causal 

relationships between smoking and sub-clinical atherosclerosis, coronary heart disease, stroke, 

abdominal aortic aneurysm and chronic obstructive pulmonary disease morbidity and 

mortality.*** Chronic Obstructive Pulmonary Disease (COPD) affected 11.4 million American 

adults in 2004††† and an additional 12 million demonstrate evidence of impaired lung function, 

indicating a potential under diagnosis of COPD.‡‡‡ Importantly, individuals with either lung or 

heart disease face special challenges in even mildly hypoxic environments such as that aboard 

aircraft.

Even in the absence of overt disease, older passengers may be vulnerable aboard aircraft. 

Medical scientists acknowledge that advanced age is accompanied by a general decline in organ 

function, such as, the function of the heart or lungs.§§§ Although the body generally exhibits 

compensatory mechanisms to maintain equilibrium, response times and performance may be 

compromised under stressful conditions.  For example, vulnerability due to advanced age may 

be particularly true in an aircraft environment pressurized in accordance with research findings 

based on mostly healthy, fit, and younger subjects.

Many industries are studying how to best accommodate the aging population through 

innovations to make their activities both feasible and comfortable given some of the restrictions 

of older age. Boeing, for example, has worked with intergenerational designers to understand 

how to make the cabin design more attuned to the needs of the aging Boomer population and 

some of their changing capacities with respect to diminished vision, hearing, dexterity, 

flexibility, strength, and stamina.†††† 

In addition to the increasing numbers of potentially unhealthy passengers, the consideration of 

possible physiological effects from mild hypoxic environments on pilots and crew is important 

because the public relies on their optimal functioning to protect passenger safety in-flight. The 

 

§§ Federal Register: April 14, 2004. Volume 69, Number 72. 

http://a257.g.akamaitech.net/7/257/2422/14mar20010800/edocket.access.gpo.gov/2004/04-8512.htm

** * U.S. Department of Health and Human Services. The Health Consequences of Smoking. A Report

of the Surgeon General, 2004.

††† National Center for Health Statistics. Raw Data from the National Health Interview Survey, U.S., 2003.

(Analysis by the American Lung Association, Using SPSS and SUDAAN software).

‡‡‡ Mannino DM, Homa DM, Akinbami L, et al. Chronic Obstructive Pulmonary Disease Surveillance - U.S., 1997-

2000. Morbidity and Mortality Weekly Report. Vol. 51 (SS06); 1-16.

§§§ Priebe, H.J. The aged cardiovascular risk patient. British Journal of Anaesthesia. 85 (5):763078. (2000).

**** Priebe, H.J. The aged cardiovascular risk patient. British Journal of Anaesthesia. 85 (5):763078. (2000).

†††† Ehrenman G. (March 2005). Mechanical Engineering Design. 

http://www.memagazine.org/supparch/desmar05/grayskies/grayskies.html)

15 Aerospace Medical Association.. Cabin Cruising Altitudesfor Regular Transport Aircraft. Aviation, Space, and Environmental 

Medicine, Volume 79, Number 4, April , 2008 , pp. 433-439(7).
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 37

Aerospace Medical Association, Aviation Safety Committee, released a position paper 15

recommending further research about the effects of mild hypoxia for passengers and for these 

worker groups in particular. A number of research studies have shown performance decrements 

between 5,000 and 10,000 feet, notably at altitudes below the current requirement for 

supplemental oxygen. In addition, the aging workforce of crew and pilots may be vulnerable 

because of the reduced oxygen capacity related to aging and because of the increased metabolic 

demands for oxygen in crew as they push utility carts down the aisles of jumbo planes at 34,000 

feet.

In sum, the current FAA regulations for limiting cabin pressures to 8,000 ft. equivalent altitudes 

allow for mildly hypoxic conditions. Theses environments are expected to have little effect on 

healthy passengers, pilots or crew, however, older individuals and persons with compromised 

cardiopulmonary status may be at risk. More than thirty years has passed since the thresholds for 

pressure were set. In the meantime, new composite materials in the fuselage that withstand 

greater pressure differential between the cabin and outside air provide a potential for reducing 

the maximum cabin altitude to less than 8000ft. Newer aircraft are able to fly higher and for 

longer periods, extending the exposure to hypoxia. Also, new portable devices that concentrate 

and deliver personal oxygen have been approved for medical conditions and for in-flight use. Yet 

experts argue that current guidelines that determine medical fitness for flying or need for inflight oxygen lack sufficient scientific evidence for health protection15. The need for closing 

these gaps in information has never been more important given the rise in older and health 

compromised passengers (see Figure 5.1). The COE pressure studies attempted to answer this 

need by establishing the health effects of current cabin pressures in susceptible passengers.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 38

Figure 5.1 Number of people age 65 and over, by age group, selected years 1900-2006 and 

projected 2010-2050 

Following the NRC recommendations, ACER/RITE researchers collected data about cabin 

pressures and examined pressure-related health effects. A number of complimentary studies were 

conducted to understand the relationship between cabin pressures and altitude and the health 

effects in susceptible passengers. Three projects aimed to collect the following information: 1) 

measurement of typical pressures and altitudes aboard commercial flights 2) measurement of the 

physiological responses in older passengers and susceptible passengers (passengers with chronic 

disease) in a monitored simulated flight [hypobaric chamber] and 3) measurement of 

physiological responses in passengers aboard actual commercial flights.

5.2 Approach

5.2.1 The design and deployment of miniaturized sensors to read pressure and altitude

To understand the effects of pressure on human health and comfort, it is necessary to know the 

range of cabin pressures that passengers typically experience aboard commercial flights. This 

information about pressure levels can be linked to personal monitoring of human responses in 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 39

flight. To this end, Boise State and Kansas State investigators designed a portable sensor to 

capture cabin pressures. Pressure has been recorded on over 200 flights in the cabin throughout 

ascent, cruise and descent. These devices supported also a succession of health studies with 

passengers wearing personal monitors recording cardiac and respiratory function. 

Data from these sensors explored the relationship between aircraft altitudes and cabin pressures. 

Scientists were able to chart usual pressures as seen in Figures 5.2 and 5.3. In total, minimum 

cabin pressure has been recorded on over 300 flights and no significant excursions above 8000ft 

cabin altitude (less than 75 kPa cabin pressure) have been found. 

Figure 5.2 Sample cabin pressures from B737 aircraft
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 40

Figure 5.3 Data of aircraft altitude during a sample of international flights

5.2.2. The study of physiological responses of older passengers and susceptible 

passengers (passengers with chronic disease) in the course of simulated flight

and actual commercial flight.

Study Design

To understand the effects of mild hypoxia in older healthy and compromised passengers, we 

monitored individuals before, during, and after, a 5-hour flight in a hypobaric chamber with 

pressurization equivalent to a commercial flight at 7,000 feet altitude (While commercial 

airplanes usually fly at altitudes around 34,000 feet, pressurization of the cabin results in a 

pressure equivalent to less than 8,000 feet.) In addition, we monitored these individuals for the 

same period of time on another day, including the time in the chamber, however, pressures were 

near sea level altitudes while individuals were in the chamber. Subjects were assigned to one of 

seven weeks to complete both chamber days (control day and exposure day) with 5 to 6 

participants in each trial. Each group was blinded to the exposure condition (decreased pressure) 

and, the order of the exposure day varied among the groups.

For a subset of the participants (N=6), we repeated the physiological measurements over 3 days 

during 3 commercial flights between Oklahoma City and Baltimore, Baltimore and Las Vegas, 

and Las Vegas and Oklahoma City.

Study Sample

Participants in the study had a prior history of air travel and no contraindications for flying. In 

addition, participants were over 50 years of age, either male or female, and met criteria for one of 

three subgroups of particular study interest: ―healthy‖ non-smokers, ―healthy‖ smokers (i.e. 

smokers without diagnosed cardiac or respiratory disease), and stable cardiac patients without 

restricted activities of daily living. These subgroups were chosen to represent a ―typical‖ older 

passenger, albeit, in the upper range of healthy for seniors. We targeted older passengers because 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 41

few studies addressed the health consequences of mildly hypoxic aircraft environments for older 

passengers specifically, despite the known association between age and oxygen saturation in the 

blood. We included high functioning cardiac patients given the prevalence of the disease and the 

known risks for hypoxia with cardiovascular impairment. Finally, we selected smokers because 

of the potential for oxygen deprivation in the presence of carbon monoxide or mild respiratory 

disease secondary to smoking.

In the Fall of 2007, subjects were recruited via medical clinics, newspapers, senior centers and 

fitness centers in the greater Oklahoma City area because of access to the hypobaric chamber at 

the Federal Aviation Administration (FAA) Civil Aerospace Medical Institute (CAMI) in 

Oklahoma City. Volunteers were screened by a nurse practitioner on the telephone and scheduled 

for a physical exam if they met inclusion criteria. The clinical evaluation further excluded 

individuals with serious health conditions and documented the baseline health status for qualified 

individuals.

Selected subjects participated in 2 days of monitoring in a hypobaric chamber and one follow up 

day, in a given week during the period December 2007 through June 2008. Six of these subjects 

participated also in 3 commercial flights in the next calendar year. For the chamber experiment, 

researchers provided meals and paid participants three hundred dollars. For the commercial 

flight, participants received monies for meals, airline tickets and travel-related expenses. All 

study participants were consented in accordance with the protocols approved by the Human 

Subjects Committees at Harvard School of Public Health, CAMI, and the Oklahoma University 

Medical Center. 

The final sample for the chamber study consisted of 14 healthy seniors, 13 cardiac patients (12 of 

the cardiac patients had a diagnosis of mild to moderate heart failure), and 14 smokers. All 

subjects completed both days of the chamber experiment except for one cardiac patient who did 

not return for the second day because of a work conflict. For the commercial flight, 4 of the 

cardiac subjects and 2 of the healthy non-smoking subjects were included. 

Instrumentation -measures

The CAMI hypobaric chamber contained 12 commercial airline seats arranged in 4 rows with 3 

seats across. Participants were seated one on the aisle and one against the window, and the 

middle seat empty, in rows 2 through 4. Chamber gauges recorded humidity, temperature, noise, 

pressure, carbon dioxide, and pressure. A medical monitor and a research assistant were present 

in the chamber with the participants during the experiments.

Each participant wore a LifeShirtTM (Vivometrics, Inc. Ventura, CA, USA) to monitor cardiac 

and respiratory parameters. The LifeShirt is a fitted vest made of light weight lycra material and 

embedded with non-invasive sensors; a single-axis electrocardiograph and two respiratory 

sensors at the level of the rib cage and abdomen. The respiratory sensors are used for inductive 

plethsmography to derive respiratory measures such as minute ventilation (a proxy for oxygen 

consumption and directly related to metabolic activity) tidal volume, respiratory rate, fractional 

inspiratory ratio and peak inspiratory flow. The cardiopulmonary measures were recorded with 

an attached data logger that also recorded ambulatory blood pressure and pulse oximetry from 

peripheral devices. The recorder transmitted physiological waveforms to computers displays 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 42

outside the chamber for monitoring of participants in real time throughout the experiment. 

Vivometrics software is used to process and analyze these data according to time, waveform or 

derived variables.

Subjects completed cognitive performance tests (ANAM test battery) on laptops while in the 

chamber. These tests included measures of reaction time, memory, and higher order mental 

processing. The tests were administered every two hours. In addition, subjects competed a 

series of surveys every hour to account for symptoms of altitude sickness (e.g. Acute Mountain 

Syndrome).

While in the hypobaric chamber, participants were encouraged to conduct themselves as they 

would aboard a commercial flight. They could eat, sleep, rest, read, watch movies, move about 

or talk freely. Meals and snacked were served by the research assistant. The back of the chamber 

also contained a bathroom.

When participants were exposed to hypoxia, research phlebotomists collected blood specimens at 

the height of maximal exposure after entering and leaving the chamber through an outside 

pressure-locked room.

In the morning of the experimental day, and in the morning of the following day, the researchers 

collected urine and blood samples, including overnight urine samples from the night before and 

the night after the hypoxic exposure. Each day of the protocol, researchers collected data about 

cognition, performance, health status, sleep quality, and fatigue. 

5.3 Results and Discussion

Participants across the subgroups of ―healthy‖, ―cardiac‖, and ―smokers‖, had similar sea level 

oxygen saturation and weight, however, the ―healthy‖ group was slightly older on average and 

the ―cardiac‖ group had decreased lung function as noted by the forced expiratory volume at one 

minute (FEV1) and forced vital capacity (FVC) (see Table 5.1). 

Despite good oxygen saturation at sea-level in all of the participants, half in each group markedly 

desaturated for the majority of the simulated flight. Marked desaturation (Table 5.2) was noted as 

peripheral oxygen saturation less than 90% (SpO2<90), the level at which patients typically 

receive oxygen in the emergency room.

Of note, age was associated with greater declines in oxygen, although this effect was diminished 

after 67 years of age (see Figure 5.4).
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 43

Table 5.1 Characteristics of Participants at Baseline

* FEV1 and FVC are based on percent of predicted capacity based on age, gender and ethnicity

 Table 5.2 Number of Notable Desaturations during Cruise 

According to Subject Category
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 44

Figure 5.4. Association between age and change in SaO2 during flight.

In addition to age, other factors that were associated with declines in oxygen saturation at 

altitude ~ 7,000 feet were: female gender, smoking history, history of hypertension, being 

overweight or obese, decreased lung function, lower oxygen saturation at sea level, and sitting in 

window seat compared to an aisle seat. Each of these factors contributed to the level of 

desaturation in flight (See Table 5.3). Interestingly, only impaired lung function, such as chronic 

and severe asthma, emphysema, pulmonary fibrosis or chronic obstructive lung disease, typically 

triggers consideration of the need for in-flight oxygen by patients and medical providers. Yet, 

based on our results, other factors need to be considered also to more accurately predict of inflight desaturation. Most importantly most medical guidelines suggest that a sea-level oxygen 

reading of less than 95% is an appropriate predictor of in-flight desaturation. Our results suggest 

this guideline would grossly understimate the number of passengers likely to desaturate given 

that half of our participants destaurated and most of them were clearly above that cut off for 

recommending in-flight oxygen.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 45

Table 5.3: Predictors of SaO2 During Flight

We also looked at other effects of flight conditions on physiological outcomes. Specifically, 

because oxygen desaturation causes compensatory reactions, such as increased heart rate, we 

looked at the risk of arrhythmias during flight. We found an increased rate of lower chamber 

beats (ventricular couplets and runs) (see Figures 5.5 and 5.6) during flight in passengers with 

susceptibility to arrhythmia (diagnosed heart disease with implanted cardiac defibrillators). In 

patients with implantable cardioverter-defibrillators, premature ventricular beats are the most 

common instigator of monomorphic ventricular tachycardia16. In addition, the presence of any 

prematureventricular beat in healthy men is associated with an increased risk of sudden cardiac 

death17, suggesting that increased VE may put subjects at risk for malignant arrhythmia.

 

16 Saeed M, Link MS, Mahapatra S, Mouded M, Tzeng D, Jung V, Contreras R, SwygmanC, Homoud M, 

Estes NA 3rd, Wang PJ. Analysis of intracardiac electrograms showing monomorphic ventricular 

tachycardia in patients with implantable cardioverter-defibrillators. Am J Cardiol. 2000 Mar 1;85(5):580-

7. PubMed PMID:

11078271.

17 Abdalla IS, Prineas RJ, Neaton JD, Jacobs DR Jr, Crow RS. Relation between

ventricular premature complexes and sudden cardiac death in apparently healthy

men. Am J Cardiol. 1987 Nov 1;60(13):1036-42. PubMed PMID: 3673904.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 46 0 1 2 3 4

0 - 1 2 - 4 5 - 8 9 - 16 17 - 32 33 - 64 65 - 128

Simulated flight

Ventricular couplets per hour

0 1 2 3 4

0 - 1 2 - 4 5 - 8 9 - 16 17 - 32 33 - 64 65 - 128

Control period Frequency

Figure 5.5 Frequency of ventricular couplets during flight compared to ground (control) 

conditions.

0 2 4 6 8

0 - 1 2 - 4 5 - 8 9 - 16 17 - 32 33 - 64

Simulated flight

Ventricular runs per hour

0 2 4 6 8

0 - 1 2 - 4 5 - 8 9 - 16 17 - 32 33 - 64

Control period Frequency

Figure 5.6 Frequency of ventricular runs [3 or more extra beats] during flight compared to 

ground (control) conditions.

The findings discussed above apply to the simulated flight (chamber study). The in-flight study, 

aboard commercial planes is still in progress, although temporarily halted because of heightened 

on-board security this past summer. With just six passengers completing actual flight, the results 

show no significant differences between the simulated flights and the actual flights in terms of 

altitudes and cabin pressures, suggesting that the in-flight studies will add valuable information 

about the flight experience and health effects. 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 47

5.4 Implications

These studies are the first single-blinded investigations of the physiological effects of pressure in 

susceptible passengers we know of. These studies suggest that a significant portion of older 

passengers may be at risk of hypoxia at 7,000 feet equivalent cabin pressures. Further, there was 

an increased risk of arrhythmias in passengers with implanted cardiac defibrillators. 

None of the passengers in the study had received a recommendation from their doctors to use 

supplemental oxygen in flight and they never considered inquiring about it. Further, according to 

current medical guidelines, oxygen would not be suggested for these individuals. This research 

brings into question the protections against significant desaturation at 7,000 feet equivalent 

pressures for susceptible individuals. Also, the risk of cardiac arrhythmias in flight demands 

more study to evaluate the safety of current cabin pressures in susceptible passengers, 

considering that our study evaluated only 7,000 feet equivalent altitudes when the FARs allow 

up to 8,000 feet. Additionally, this study raises other questions about the possible prolonged 

effects of cabin pressures in susceptible passengers in the context of ultra-long flights (the 

current study included 3.5-4.5 hour flights only) or when these passengers fly to high altitude 

destinations. 

Still to be considered in terms of the health effects of pressure are pilots and crew. Crew may be 

at greater risk of desaturation because of increased activity that consumes more oxygen in the 

first place. Therefore, future studies should target these groups in particular.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 48

6.0 Incidents - Cabin Air Quality

____________________________________________________________________________________________________________

Congressional Mandate: Identify, analyze, and study incidents of air contamination 

associated with typical flight operations monitored with onboard sensors

____________________________________________________________________________________________________________

FAA reauthorization bill requires the Administrator to carry out studies of cabin air quality events 

including a series of studies to assess the feasibility of collecting in-flight exposure data and the 

possible relationship to health symptoms in cabin crew. 

6.1 Introduction

In this study, we sought to advance information about specific cabin environmental contaminants 

that may affect the health and performance of flight attendants. We planned and tested a process 

for gathering the relevant data including the development and deployment of portable air 

monitoring devices. Another outcome of the project was the systematic collection of data about 

prevalent health conditions in this highly mobile workforce that had not been fully characterized. 

The study, ― Cabin Air Quality Incidents Project‖, was funded by the FAA to research the 

incidence and prevalence of health effects in flight crew due to exposure to bleed air 

contaminated with pyrolyzed engine oil or hydraulic fluid. ―Bleed air‖ refers to outside air that is 

compressed in the aircraft engines or auxiliary power unit (APU), conditioned and cooled in the 

aircraft environmental control systems, mixed with about 50% recirculated air (typically, only 

applies to the cabin), and then routed to the cabin and flight deck. The design, operation, and 

maintenance of the bleed air system could lead to pyrolyzed engine oil or hydraulic fluid leaks 

into the cabin and flight deck air supply. Some causes of contamination include worn oil seals 

that would otherwise separate the dry and wet sides of the engine/APU compressors, overfilling 

the engine oil reservoir, burst hydraulic fluid lines, and positioning the APU inlet at the six 

o’clock position in the aircraft tail. No systematic fleet-wide or industry-wide audits have been 

conducted to document the incidence of bleed air events.

There are two other research components conducted in response to this Congressional Mandate 

relates to assessing the air contaminants associated with ―typical‖ operations. ACER 

investigators joined with Battelle Memorial Laboratories to assess passenger and crew responses 

to multiple flight parameters including air quality. This joint effort funded by ASHRAE and 

FAA is still ongoing with over 100 flight segments completed and 24 currently being monitored. 

In this research component, the instruments are fitted into ―suitcases‖ that can be carried on 

board. In the second research component, a highly portable sensing system is used. Sections 6.2 

through 6.4 relate to the feasibility of conducting an evaluation of incidents of bleed air 

contamination with the primary focus on evaluation of the baseline health status of flight 

attendants. Section 6.5 thought 6.8 pertain to the research and preliminary findings of the joint 

ACER/Battelle ASHRAE study of on-board conditions. Section 6.9 shows the approach and 

findings of the portable sensing system. 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 49

To address concerns expressed in the Congressional Mandate and provide the basis for the 

eventual creation of appropriate standards, ASHRAE developed the RP-1262 program to relate 

air quality and other factors to the comfort and health of airline passengers and crew. Battelle 

conducted Part 1 of the RP-1262 program and the Battelle-ACER project team was awarded a 

contract to conduct Part 2. The project team has been working in close collaboration with other 

partners in the Federal Aviation Administration (FAA)-sponsored Center of Excellence (CoE) on 

Airliner Cabin Environment Research (ACER) and now Research in the Intermodal Transport 

Environment (RITE) to address complimentary project

6.2 Approach

The Study of Possible Health Effects in Cabin Crew Related to Incident Events. 

Study Design

We obtained baseline health information in a sample of flight attendants via a health survey. The 

information could be used as a baseline for future comparisons with repeated administration, 

including after a fume event. Although the contemporaneous collection of exposure information 

with updated health surveys was not possible in this pilot study, we gathered important data 

about prevalent health conditions in a flight attendant workforce. This survey was the largest 

random sample of flight attendant health we know, and establishes benchmarks for health 

promotion activities and occupational health and safety prevention programs, including further 

investigations into the work-relatedness of health symptoms and workplace interventions to 

mitigate them. 

Instrumentation - Measures

The flight attendant health survey fulfilled three main purposes: (1) to collect a baseline 

description about the health of the flight attendant population; (2) to collect health information 

that could be used for later comparisons in the event of particular exposures; and (3) to test the 

feasibility of recruiting flight attendants to participate in further monitoring and evaluation, 

including the possibility of on-board air sampling of fume events.

The survey questions were developed after we conducted several focus groups with flight 

attendants to discuss their work and their health. We recruited volunteers through union 

websites, posters displayed in crew rooms, and flyers distributed by the Association of Flight 

Attendants-CWA, AFL-CIO (AFA) labor union. We held a total of six focus groups in Chicago 

and Los Angeles in the fall of 2005. The focus group participants helped us to define specific 

content to be included in the survey. With the benefit of the focus group member insights, we 

identified specific subject matter for the survey, using standardized survey questions whenever 

possible or developing new questions tailored to the work of flight attendants. 

Study Sample

To insure that our findings were not biased and represented the larger workforce, we 

administered the survey in two ways (see Figure 6.1). The first method was a mailed survey 

based on a subset of addresses selected by randomization from a union list that included two 

airlines, referred to as Airline A and Airline B. We selected from only those addresses 
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 50

connected to five airport hubs (the largest hubs for each airline). We randomly chose 50% of the 

flight attendant addresses from those hubs to receive a survey in the mail 

(n =5398)‡‡‡‡. 

The randomized pick of addresses was important to insure that all flight attendants had an equal 

chance of receiving a survey. With randomization, we were likely to have the same distribution 

of flight attendant characteristics in our sample, such as age and gender, as in the overall 

population. In addition, if we selected participants in a random way, the respondents would be 

less likely to reflect only flight attendants with health interests (because they were very healthy 

or very unhealthy) if a fair number of the invited participants responded. The response rate from 

the mailed survey was close to half of those we invited (48%) and exceeded our expectations. 

We had been forewarned by union representatives, focus group participants and airline 

management to expect a participation rate between 3 and 10 percent. We considered this 

response sufficient to guard against significant reporting bias (such that non-participants were

remarkably different than participants). 

We mailed a survey packet to every address selected from the master list of flight attendants in 

target hubs. The survey packet contained a nine-page double-sided questionnaire with a cover 

sheet explaining the study and a postage-paid return envelope. All flight attendants targeted 

through the mail received two copies of the survey packet over a several week period. The 

specific protocol included the mailing of a survey packet, a reminder postcard, and a second 

survey packet in the 6th or 7th week. The AFA union publicized the study through print materials 

such as newsletters, faxes and posters, in addition to messages on their website. Participation was 

encouraged by the chance to win lottery prizes with the return of a completed survey. The 

Human Subjects Committees at Harvard School of Public Health and the University of Oregon 

approved all protocols. 

 

‡‡‡‡ Importantly, there were some differences in procedures between the two airlines. Airline A had the opportunity 

to complete an online survey, but this mechanism was chosen least by flight attendants. Another difference was that 

we oversampled Airline A to capture more full-time workers that were less prevalent in this population (selecting 

70% of the hub population for the mailed survey versus 50% at Airline B). 

The second method of survey administration involved on-site distribution of the survey at the five target hubs. 

Generally this was done in public spaces close to the flight attendant crew rooms (i.e. where the flight attendant 

would go at the airport to prepare/check-in for their flights or check-out after flight). We spent approximately 250 

hours on location distributing surveys along with a postage paid envelope for return mail if the flight attendant 

preferred to complete it at a later time. Otherwise, we collected the surveys in the airport. At the same time, as a 

visible draw for the survey campaign, we displayed gifts that would later be raffled among survey participants. 

Airline B also had an incentive donation of $1 to their union relief fund for every survey returned.
__________ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) ___________

_________________________________________________________________________________________________________________________________________________________ 51

Figure 6.1 Flow chart for sample selection and distribution of the survey

Step 3: Survey distribution on-site at five target hubs

Airline A

Convenience

Sample 

Airline B

Convenience

Sample 

from 

target 

hubs

from 

other 

hubs

from

target 

hubs

from 

other 

hubs

Step 2: Mailed Survey 

To a subset of the FA hub 

population

(n=5398)

Airline B

Random Sample

Airline A

Random Sample

On-line 

option

Step 1: Identification of all employees at five target hubs between 2 airlines

Airline A

 all employees in target hubs

Airline B

all employees in target hubs

Random Survey Returns

(random FA selection 

from target hubs)

n=2,613

Convenience Survey 

Returns

(new FAs recruited on-site)

n=1086 from target hubs

n=302 from other hubs

Final Sample n=10 hub missing

n=4011

Study

Publicity

Study

Publicity
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 52

We handed out the survey in person to supplement our mailed sample because we 

expected very low participation in this highly mobile workforce (we projected at 3-10% 

returns rate based on feedback from our focus groups and reports from the union and 

statements from the airlines). In addition, because we were unable to obtain airline 

management support to distribute and collect the survey on the job despite nearly two 

years of effort, we were concerned about how management’s objections would affect 

employee participation. 

The on-site campaign targeted flight attendants not selected by the random pick for the 

mailed survey. We also accepted surveys from flight attendants chosen at random to 

receive a survey by mail. Numerous flight attendants mentioned that they had received 

the survey in the mail but that it was easier for them to complete and return one to us onsite. All surveys were tracked with numerical codes and only one survey per flight 

attendant counted. All survey names selected by the random draw for the mailing were 

classified as such, even when the survey was collected on-site. For all takers of the onsite survey, our physical presence was intended as a convenience and as an invitation for 

participation. In addition, by being on-site, we attracted participation from 605 flight 

attendants from outside the target hubs who happened to be passing through the hubs 

while we were on the premises. 

The final tally of surveys collected by mail or by our researchers stationed at the hubs 

was 4011. The flight attendants in this sample included: 1) flight attendants randomly 

selected for the mailed survey (n =2615), 2) flight attendants not randomly chosen for the 

mailed survey, but nonetheless employees from that hub that we reached while on the 

premises (n = 1086), and 3) flight attendants, not part of the target hub populations yet 

employees from other domiciles of the same airlines, ―on-route or passing though‖ while 

we were on location. Flight attendants from domiciles outside the target hubs comprised 

605 of the 1086 surveys collected on site. Not considering this last group of participants, 

we successfully recruited 37% of the entire population in the target hubs. The large 

majority of the surveys (almost two-thirds) were chosen at random, the preferred 

participation to avoid a self-selected non-representative participant sample. 

6.3 Results and Discussion

Flight Attendant Sample - Personal and Job Characteristics

In the series of graphs and figures that follow, we show the personal and job 

characteristics of the survey respondents. 

Gender

Overall, the sample was predominately female (80 %). Airline A had a slightly higher 

ratio of male to female flight attendants
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 53

Age

The mean age was 47 years with forty flight attendants between 64 to 76 years. Fiftyeight percent of the flight attendants were 45 years of age or older and the average age of 

the participants in Airline B was slightly higher. Overall, the average age of the 

respondents matched the mean age for the entire crew population in the target hubs 

(including non-participants) at Airline A and Airline B, 45 and 47 years respectively.

Education

The number of respondents in the sample with a 4-year college degree or higher level of 

education was 45 %. Relative to Airline A, Airline B had slightly more years of 

education. 

Smoking

We asked about current and past smoking. The majority of respondents did not smoke.

Job Characteristics

We asked specific questions about the job such as length of service, average hours 

worked in the previous three days, past month or last year. Two-thirds of respondents 

worked as a flight attendant for their current employer for more than 10 years and 36% 

worked for the same employer 20 or more years. Forty-one percent had 20 more years of 

experience as a flight attendant counting previous employers (not shown below). Once 

again, the sample characteristics mirrored the experience profile of the entire crew 

workforce in the target airline hubs; for Airline A, the average tenure was13 years, and 

for Airline B, the average tenure was 18 years.

Flight Attendant Health - Prevalence of Conditions

Self-Reported Health

In the survey, we asked the flight attendants about their health in several ways to 

understand the most prevalent health conditions. We queried the participants about 

symptoms, diagnoses, care seeking, treatment and work-related injuries to chart the most 

common conditions in the workforce.

We attempted to characterize health conditions according to descriptions of temporality, 

frequency and severity. For example, we sorted conditions that were active by asking 

whether the flight attendant had experienced these conditions in the last week or in the 

last 12 months, or whether they had been diagnosed ever with a condition. For the most 

recent problems, we asked the flight attendant to delineate how often the problem 

occurred over the last several days. We assumed that more frequent problems were 

suggestive of greater severity (i.e. problems that the flight attendant experienced almost 

everyday in the past week). Further, we assumed that more severe problems would lead 

to seeking care (i.e. the flight attendant saw a health care provider), although we asked 

about care seeking over the last year to account for intermittent or chronic conditions. 

Also, as an alternative proxy for severity, we asked about all conditions that drew a 

medical diagnosis by a health care provider (e.g. ―Did a health care provider ever tell you 

that you had...‖).
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 54

The information about health is presented in a series of tables below that correspond also 

to four main questions in the survey; questions about health experience in the past week, 

questions about health experience in the past 12 months, questions about health 

experience defined by particular diagnoses, questions about work-related injury or illness.

Health Experienced over the Past Week

We asked the flight attendants about specific health symptoms over the previous week to 

index active or current problems. We gauged the severity of these problems by eliciting 

information about frequency or duration. For example, for any condition in the survey, 

the flight attendant could respond according to the number of days that he/she 

experienced the condition in the last week, such as ―Never; 0 days‖, ―Rarely; 1-2 days‖, 

―Sometimes; 3-4 days‖, ―Often; 5-6 days‖ and ―Everyday; 7days‖. 

We categorized the problems according to the most prevalent conditions. In the table 

below (Table 6.1), we note the most frequent problems (i.e. ―Often‖ or ―Everyday‖] in 

red. These conditions were cited by at least 20% of the flight attendants. The symptoms 

highlighted in blue designate slightly less common conditions in comparison reported by 

at least 10% of flight attendants. In all, these symptoms profile the current health 

experience of the flight attendants in the past week. 

The more notable conditions in order of most prevalent among flight attendants include: 

sleep problems (35%), all types of musculoskeletal pain (between 23-28%), sinus 

congestion (28%), fatigue (26%), anxiety/stress (20%) and bloating (20%). 

Considering all frequent conditions together, the most prevalent conditions fall into 

several main categories according to body system affected (listed in no particular order): 

1) respiratory (sinus, ear, cough) 2) neurological/psychological (dizziness, loss of 

coordination/balance, muscle weakness, fatigue, irritability, anxiety, depression) 3) 

musculoskeletal (general aches and back/shoulder/elbow/wrist/hand/feet pain) 4) eye 

problems 5) other general problems (bloating).

 Table 6.1 Percentage of Sample Reporting Condition in Past Week by 

Frequency

CONDITION

In the past week, how many days did you experience the symptom?

Never

(0 days)

Rarely 

(1-2 

days)

Sometimes 

(3-4days)

Often

(5-6 

days)

Everyday

(7days)

Number of

Flight 

Attendants

Eye irritation, pain 43.3% 27% 18.8% 7.3% 3.5% 3,707

Blurred /altered vision 57.2% 21.6% 13.7% 5.1% 2.4% 3,623

Sinus congestion 26.5% 20.5% 24% 18.1% 10.9% 3,789

Ear pain/blockage 46.3% 25.6% 18% 7.5% 2.4% 3,705

Nosebleeds/irritation 72% 15.7% 7.3% 3.7% 1.3% 3,666

Sore throat/irritated/burn 55.2% 24.1% 13.7% 5% 2% 3,696

Cough 48% 25% 16.2% 6.2% 4.6% 3,743

Hoarseness/loss voice 66.2% 18.6% 10.1% 3.5% 1.6% 3,704
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 55

(Table 6.1 continued)

CONDITION

In the past week, how many days did you experience the symptom?

Never

(0 days)

Rarely 

(1-2 

days)

Sometimes 

(3-4days)

Often

(5-6 

days)

Everyday

(7days)

Number of

Flight 

Attendants

Shortness of breath 66.3% 19.0% 9.8% 3.5% 1.5% 3,721

Chest tightness 76.2% 14.2% 7.1% 1.8% .6% 3,694

Chest pain 84.7% 10.4% 3.8% ,8% .2% 3,671

Heart racing/pounding 67.7% 19.8% 9% 2.7% .7% 3,706

Stomach pain 62.1% 21.5% 11.7% 3.4% 1.4% 3,715

Nausea 67.2% 21.7% 8.2% 2.3% .5% 3,703

Vomiting 91.3% 7.2% 1.3% .1% .08% 3,684

Diarrhea 64.7% 21.7% 9.8% 3.0% .8% 3,703

Bloating 30.4% 21.0% 23.4% 17.2% 8% 3,750

Fainting 95.5% 3.1% 1.1% .3% .05% 3,670

Dizziness 62.4% 25.3% 8.5% 3.1% .7% 3,708

Coordination/balance loss 66.0% 22.6% 8.2% 2.5% .8% 3,702

Shaking/tremors 87.9% 7.8% 2.8% .8% .6% 3,650

Numbness/tingling-

 face,extremities 68.8% 16.5% 8.2% 3.5% 3%

3,714

Severe headache 57.9% 23.9% 11.6% 5.5% 1% 3,729

Confusion, difficulty 

 Thinking/finding words 56.3% 22.5% 13.2% 5.4% 2.5% 3,737

Difficulty concentrating 45.3% 30.5% 15% 6.8% 2.5% 3,746

Fatigue/unusual tiredness 20.4% 27.3% 25% 17.5% 9.9% 3,817

Anxiety or stress 30.4% 29% 20.7% 13% 7% 3,778

Depressed mood 46.2% 27.2% 15.1% 7.8% 3.8% 3,751

Apathy 58.4% 21.8% 12.1% 5.2% 2.5% 3,662

Irritability 31.0% 36.1% 20% 9% 3.8% 3,696

Sleep disturbances

 Inability to stay awake or

 Go to sleep

16.9% 23.1% 25% 20% 15% 3,827

Alterations in taste/smell 81% 11.2% 5% 1.8% 1.1% 3,706

Chemical sensitivity 77.8% 10.4% 6.0% 3% 2.7% 3,684

Calf pain 64.2% 17% 11% 4.6% 3.1% 3,687

Back pain 26.4% 23.2% 22.7% 15.6% 12.1% 3,787

Foot pain 28.4% 22.5% 20.6% 15.2% 13.3% 3,775

Shoulder/elbow/

 wrist/hand pain 31% 19.7% 19.8% 15.3% 14.1% 3,792

Generalized muscle aches 30.1% 24.9% 21.7% 12.3% 11% 3,775

Muscle weakness 54.7% 20.8% 12% 6.3% 6% 3,721

Health Experienced over the Last Year 

In order to capture health problems that may be chronic or disabling, we asked the flight 

attendant about several health conditions that resulted in seeking care or treatment in the 

past twelve months. Table 6.2 summarizes these problems. The conditions highlighted in 

red were reported most frequently. Notably, health conditions experienced in the past 

year are not always the same as the health conditions experienced in the past week (see 

Table 6.1). In other words, problems in the past week or in the past year were not asked 

in the same way.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 56

Table 6.2 Percentage of Flight Attendants Seeking Treatment for Condition 

in Last 12 months

CONDITION # Respondents

SOUGHT TREATMENT 

(as percentage of respondents)

Body System Symptom NO YES

Respiratory

System

Reactive airways, 

sinusitis,allergies

3,850 45.3% 54.7% 

Shortness of 

breath/ 

reduced lung 

capacity

3,787 84.5% 15.5% 

Other respiratory 

symptoms

3,436 85.4% 14.6%

Neurological

System

Severe headache 3,804 76.6% 23.4%

Coodination/

Balance loss 3,795 90.9% 9.1%

Tremors/shaking 3,785 96.3% 3.7%

Seizures/ Loss of

consciousness 3,782 99% 1%

Memory 

loss/Lack of 

concentration

3,783 85.3% 14.2%

Altered vision 

(unrelated to 

glassess/contacts)

3,776 88.9% 11.1%

Numbness/

tingling

Face/extremities

3,801 83% 17%

Dizziness/

lightheaded

3,796 80.6% 19.4%

Fatigues/ unusual 

tiredness 3,809 63.2% 36.8%

Muscle weakness 3,778 83.75 16.3%

Other Joint pain/aches 3,813 66.7% 33.3%

Nausea 3,778 88.8% 11.2%

Rashes/hives 3,805 84.5% 15.5%

By far the most common conditions associated with care seeking in the past year include 

reactive airways, sinusitis or allergies (55%). Given that 39% of the flight attendants 

reported a diagnosis of allergies (see Table 6.3), this diagnosis probably contributed 

substantially to this category. 

The next most significant conditions requiring treatment were fatigue (37%) followed by 

diffuse joint aches and pains (33%). These problems were ranked high also in the report 

of health conditions experienced in the last week mentioned previously. 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 57

Taken altogether, the report of symptoms in the past year shows that most medical 

attention is sought for problems of the respiratory system, the neurological system, and 

the musculoskeletal system.

Medical Conditions Diagnosed and Currently Treated

We elicited further information about chronic conditions by asking the flight attendant 

whether a health care provider had ever diagnosed them with particular conditions. 

Specifically, we asked the flight attendant, ―Did a health care provider ever tell you that 

you had any of the following conditions...‖, (see the Flight Attendant Health Survey in 

the Appendix, Question #15, pages 6-8)

We asked also about conditions that were currently receiving treatment. These conditions 

are worth noting separately because they denote more severe conditions. To elicit the 

status of treatment, the respondent answered, ―yes‖ for current treatment next to the 

diagnosis. We noticed however, that some respondents checked ―yes‖ for treatment even 

without checking ―yes‖ for the diagnosis. (For example, the number of individuals 

responding about treatment in the far right column was sometimes larger than the number 

of respondents who said ―yes‖ they had the condition— e.g., Parkinson’s disease.) We 

believe these rare inconsistencies do not detract from the overall picture of flight 

attendant health because each results in an undercount of diagnoses rather than an 

overcount. Further, the raw numbers of flight attendants receiving treatment for certain 

conditions underscores the relative scope of the problem. 

Importantly, this accounting of medical diagnoses will likely miss the most serious and 

debilitating illnesses because flight attendants with these problems would be unable to 

perform their work and would likely leave the job. This censoring of disease prevalence 

in a working population, commonly referred to as ―the healthy worker effect‖, will 

usually underestimate the full burden of illness in the population.

 Table 6.3 Percentage of Flight Attendants Diagnosed with Particular 

Medical Conditions and the Raw Number Currently Treated 

for that Condition

CONDITION

Diagnosed by 

Health Care Provider

Currently receiving treatment 

for this condition

Overweight/Obesity 12.2% (n= 3,877) (n=121)

High blood pressure 16.7% (n = 3,882) (n =402)

Heart disease 2.5% (n = 3,858) (n= 64)

Heart attack .5% (n = 3,859) (n=12)

Stroke .5% (n = 3,864) (n=8)

Aneurysm .3% (n= 3,864) (n=4)

Chronic Obstructive Pulmonary 

Disease (COPD) .9% (n= 3,933) (n=18)

Lung fibrosis .2% (n= 3,927) (n= 6)
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 58

(Table 6.3 -Continued)

CONDITION

Diagnosed by 

Health Care Provider

Currently receiving treatment 

for this condition

Pulmonary embolism, 

 blood clots , Deep Vein 

 Thrombosis (DVT)

 2.2% (n= 3,897)

 

(n=29)

Pneumonia 16.2% (n = 3,860) (n=57)

Chronic bronchitis 15.6% (n= 3,910) (n=125)

Asthma 13.2% (n= 3,918) (n=258)

Cancer Skin

 Bone

 Blood

 Lung

 Brain

 Reproductive

 

 GI

 Kidney

 Liver

 6.9% (n = 3,918) (n=104)

 .05% (n=3900) (n=1)

 .3% (n=3,905) (n=7)

 .1% (n= 3,902) (n=0)

 .05% (n= 3,872) (n=1)

 4.1% (n=3,911) (n=64)

 1.69% (n=3,897) (n=36)

 .4% (n= 3,904) (n=5)

 .1% (n= 3,900) (n=2)

Kidney disease 1.2% (n= 3,925) (n=22)

Liver disease 1.1% (n=3,925) (n=16)

Parkinson’s disease 0% (n=3,925) (n=1)

Multiple sclerosis .6% (n=3,918) (n=14)

Epilepsy/Seizure disorder .5% (n=3,920) (n=11)

Migraine headache 19.4% (n= 3,934) (n=371)

Infertility 8.7% (n= 3,849) (n= 61)

Dysmennorhea 4.5% (n= 3,828) (n=34)

Adverse pregnancy outcomes 7.6% (n=3,809) (n=38)

Hormonal irregularities 20.2% (n=3,831) (n=367)

Hearing loss 17% (n= 3,853) (n=78)

Vertigo 12% (n=3,845) (n=72)

Meniere’s syndrome 1.3% (n=3,830) (n=20)

Low back pain 52.6% (n= 3,861) (n=748)

Rheumatoid Arthritis 4.7% (n= 3,839) (n=70)

Osteoarthritis 8.7% (n=3,839) (n=154)

Fibromyalgia 3.9% (n= 3,832) (n=68)

Chronic Fatigue syndrome 6% (n=3,837) (n=71)

Thyroid disorders 11.7% (n=3,846) (n=333)

Sleep disturbances 33.7% (n=3,852) (n=606)

Depression/Anxiety 36.3% (n=3,851) (n=687)

Multiple chemical 

sensitivity disorder

 2.2% (n= 3,832) (n=25)

Immune Disorders (i.e. 

HIV, Lupus, etc)

 4.3% (n=3,850) (n=117)

Eczema 10.8% (n= 3,845) (n=174)

Psoriasis 4.6% (n=3,832) (n=98)
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 59

(Table 6.3 -Continued)

CONDITION

Diagnosed by 

Health Care Provider

Currently receiving treatment 

for this condition

Allergies 39% (n=3,831) (n=696)

Chronic intestinal disease 7% (n=3,825) (n=156)

Other illness 15.8% (n=3,348) (n=310)

Once again, not all conditions in Table 6.3 overlap with the conditions reviewed in the 

previous tables (i.e., Table 6.1 and Table 6.2 that reflected problems in the last week or 

last year). As before, the most prevalent conditions are noted in red. This perspective 

does not take into account, however, the expected rates of the condition in the general 

population considering other risk factors such as age, gender, and smoking. For example, 

the prevalence of hearing loss in this sample of flight attendants may be considered high 

in comparison to a sample of workers who are not flight attendants but of similar age, 

gender and smoking status, although this was not part of this analysis. 

The most prevalent conditions in Table 6.3 include low back pain (52.6% with close to 

one in five flight attendants currently receiving treatment), allergies (39% of flight 

attendants with approximately 1 in 5 attendants currently receiving treatment) 

depression/anxiety (36% with close to 1 in 5 flight attendants currently receiving 

treatment), and sleep disturbances (34% with approximately 1 in 6 flight attendants 

currently receiving treatment for sleep problems).

Other notable conditions are hormonal irregularities (20%), migraine headaches (19%), 

high blood pressure (17%), pneumonia (16%), chronic bronchitis (16%), asthma (13%), 

hearing loss (17%) and vertigo (12%). 

Work Related Injuries and Illnesses in the Past Year

We asked the flight attendants about the number of work-related injuries or illnesses (e.g. 

0, 1, 2, 3, 4 or more) they experienced over the past year. Close to half of flight 

attendants (47%) told us they experienced one or more work-related injuries/illnesses in 

the past year and 29% said they had more than one injury in the last year. (n = 3,667) 

Of the 47% of flight attendants who experienced one or more injuries, we asked them to 

describe their injuries. If the flight attendant had more than one injury, he/she could 

choose a description for up to the first 3 injuries. In addition, more than one description 

could be selected if the injury/illness involved multiple health effects. The choices for the 

description of the injury included the following:

 Musculoskeletal: strain or sprain, joint aches and pains or fracture, contusion, 

laceration

 Respiratory: trouble breathing, infection

 Neurological: dizziness, headaches, numbness and tingling, fatigue

 Psychological: anxiety, stress, depression

 Cardiac: chest pain or tightness, high blood pressure, clots

 Other
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 60

We found that the large majority of problems were musculoskeletal in nature (35%) 

followed by respiratory (21%), neurological problems (17%) and psychological problems 

(14%).

Integrated View of Health Conditions in the Flight Attendant Respondents

Table 6.4 reflects a composite profile of the prevalence of certain health conditions that 

are common to all previous queries about health in the past week, in the past year, or ever

(as diagnosed by a health care provider), although different questions may reference the 

similar conditions in unique ways. For example, some health conditions are referenced by 

subjective symptoms while other health conditions are referenced by a medical diagnosis 

(usually involving one or more symptoms). Information about acute conditions comes 

from Table 6.1. Information about chronic conditions comes from Table 6.2 under the 

column heading ―sought treatment in the last year‖ and comes from Table 6.3 under the 

column ―told by a provider that FA has the condition‖. ―NA‖ or ―not applicable‖ in the 

chart below denotes that information about a condition was asked about in this way. Also, 

we note that some conditions are not exactly the same but have some overlapping 

characteristics. In this case, we added notation about how the condition was interpreted in 

the corresponding box.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 61

 Table 6.4 Composite View of Health Conditions Common to Tables 6.1 

through 6.3

Health condition Acute

(often or everyday)

Chronic

 

sought 

treatment

in last year

Told by provider

FA has condition

Fatigue 27% (n =3817) 37% (n=3,809) NA

Sleep 35% (n=3827) NA 34% (n=3852)

Low back pain 28% (n =3787) NA 53% (n=3861)

Headaches-severe 6.5% (n=3729) 23% (n=3804) 19.4% (n=3,934)

migraine

Rash or hives NA 15% (n=3804) 10.8% (n=3,845)

 eczema

4.6% (n=3,832)

 psoriasis

Shortness of breath 5% (n=3721) 15.5% (n=3787) 13.2 (n=3,918)

 asthma

Dizziness 4% (n =3708) 19.4% (n=3796) 12% (n=3,845)

 vertigo

1.3% (n=3,830)

 Meniere’s

Loss of memory/ 

concentration

9% (n=3746)

difficulty concentrating

15% (n=3783) NA

Nausea 3% (n=3703) 11.2% (n=3778) 7% (n=3,825)

Chronic intestinal/

Stomach disease

Depression 12% (n=3751) NA 36% 

Anxiety/stress 20%(n =3778) NA anxiety/depression

Numbness/tingling 6% (n=3714) 17% (n=3801) NA

Muscle weakness 12.4% (n=3721) 16.3% (n=3778) NA

Altered vision 7.5% (n=3623) 11% (n=3776) NA

Coordination/balance 

loss

3% (n=3,702) 9.1% (n=3,795) NA

General/diffuse 

muscle aches

12.3% (n=3,721) 33.3%(n=3,813) NA

Tremors/shaking 1.4% (n=3,714) 3.7% (n=3,785) NA
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 62

6.4 Implications

We know relatively little about the health consequences of flight attendant work 

compared to other occupations, even pilots. A comprehensive review of the literature 

revealed only a handful of studies (n=21) (Nagda and Koontz, 2003). In addition, prior 

studies had one or more of the following problems; small sample size, selection bias, low 

participation, no objective measures, or narrowly defined health outcomes. To our 

knowledge, this current study represents the largest systematic survey of general health in 

a flight attendant population and a significant opportunity to advance the understanding 

of health and wellbeing in these employees.

Increasing the understanding of flight attendant health is important because the context of 

the job has changed dramatically over the last several decades. Today’s senior flight 

attendants are the first group to be exposed to this type of work for an extended period of 

time, such as throughout most of their adult working lives. Before the civil rights 

movement, the flight attendant’s average tenure was only about two years because of 

rules against getting married or age limits (Lessor, 1984). The turnover rate before 1970 

was 30%, compared to today in which the majority of flight attendants work for the same 

employer well past 10 years. For example, in our study sample, 36% worked with their 

current employer for more than 20 years.

Given this long-term employment relationship, the health and safety of the flight 

attendant would seem a smart investment for prevention efforts on the part of the 

employer. Yet, some of the problems we learned about from the survey, such as 

musculoskeletal and respiratory problems, frequently plagued a significant portion of the 

workforce. Other problems that were commonly known for years, such as sleeping 

problems, are still prevalent today. Further, reports of frequent work related injury, 

anxiety and depression, are associated with lost productivity and disability, and 

consequently, substantial costs. Finally, particular conditions raise concern for the safe 

performance of the job, such as impaired memory, concentration and balance, and 

hearing loss, dizziness, and fatigue. 

Without the ability to measure cabin exposures in conjunction with measures of flight 

attendant health we are limited in drawing conclusions about the work-relatedness of the 

health conditions. In addition, the health problems were self-reported only and cannot be 

further substantiated. Yet, the broad description of health in this population offers a 

window into prevalent health conditions. In order to fully characterize any excess burden 

of disease in this population, and lacking a comparative group of ―non-exposed‖ workers 

in terms of the cabin environment (control group), further study is needed to sort out the 

relationship between the reported health conditions and the working environment or 

sources of exposure in the cabin. Important areas to investigate in terms of their impact of 

the health and productivity of the workforce would include: 1) fatigue 2) noise 3) 

musculoskeletal disorders 4) respiratory conditions and 5) neurological conditions. Some 

of these conditions have already been flagged as priorities in the recent FAA 

Reauthorization Bill (2010), namely, fatigue and noise. Now that FAA is establishing a 

more prominent role in occupational health and safety, these data and research tools can 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 63

be useful in measuring the effectiveness of prevention programs and the need for future 

rule-making.

6.5 Approach to On-Board Study

The principal aim of this research project is to relate perceptions of discomfort or healthrelated symptoms of flight attendants, flight deck crew, and passengers aboard 

commercial transport aircraft to possible causal factors, including cabin and bleed air 

quality and other factors such as reduced air pressure, jet lag, inactivity, humidity, flight 

attendant duty schedule and fatigue, circadian rhythm, stress, and noise. In particular, the 

following specific objectives are to be addressed in this project: 

 Measure and characterize contaminants in cabin air in a variety of aircraft types.

 . Assess ventilation rates

 Investigate the relationship of the measured cabin air contaminants, ventilation 

rates, and other factors with reported discomfort and health-related symptoms 

among passengers and flight crew. 

Data are being collected on a sample of flights recording cabin air quality and other 

parameters. In parallel, perceptions of cabin and flight deck crew, and passengers are 

being recorded using questionnaires. The design of the study considers a variety of 

objective parameters such as aircraft type, air quality, cabin altitude, passenger load, 

length of flight, and thermal environment. The subjective parameters to be considered 

include passenger and crew comfort during flight, health status at the beginning and 

during flights, and indicators of susceptibility. The following specific parameters are 

being investigated:

 Aircraft type

 Cabin altitude

 Passenger load

 Length of flight

 Chemical and physical cabin conditions

 Ground air supply

 Ventilation

 Ozone scrubber in operation

 Passenger and crew comfort and health surveys during flight

 Indicators of susceptibility

 Additions effects (if possible)

o Source of ground air supply

o Cleaning and cleaning materials

o Fueling and service equipment

o Age of aircraft

o Age of service equipment
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 64

The greatest impact to the community of air travelers and airline professionals is in 

having the data from the project available to participating airlines and eventually to 

aircraft manufacturers through ASHRAE and national and international rulemaking and 

advisory organizations (e.g., International Air Transport Association, International Civil 

Aviation Organization, Air Transport Association, FAA, etc.). The Battelle project team, 

including Harvard University, seeks participation in the ASHRAE project from additional 

airlines to complete the study design.

6.6 Progress on On-Board Study

Although substantial progress has been made in collecting data for the target parameters 

(i.e., flight duration, load factor, aircraft type), the dataset is incomplete, particularly with 

respect to the number of aircraft sampled and their ventilation rates. Our ability to 

complete the project matrix has depended on the flight options available to us with the 

cooperating airlines. Sampling on aircraft across the range of specified ventilation rates 

is a critical design component of the study. The aircraft sampled to date sufficiently 

represent aircraft with relatively high ventilation rates, but low ventilation aircraft, such 

as the Boeing 757 (B757) and Airbus 310 (A310), have not been sampled. The two 

airlines who have voluntarily participated in the study did not have these aircraft in their 

fleet. Thus, participation with at least one additional airline will be required to sample 

flights on 6 aircraft types, including at least one aircraft on the low end of the ventilation 

rate. (Actual approximate ventilation rates have not yet been calculated for flights 

sampled to date.) In addition, more robust data sets with respect to other parameters, 

such as use of ozone scrubbers, long duration flights, flights crossing more than 5 time 

zones, and summertime flights. As such, we aim to distribute surveys and conduct 

measurements on additional airlines to complete the parameter matrix in a way that 

provides sufficient data to meet the project goals. 

In June 2010 a research teaming agreement was signed between Harvard, Battelle and a 

third airlines. A series of domestic and international flights were started in early July and 

were completed in mid-August. These additional 24 flight segments, while not fully 

optimizing our initial design do provide additional model types and routes. Laboratory 

and analytical work will be preformed in the fall of 2010. 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 65

Figure 6.2 Summary of the Status of the On-Board Study as of May 2010

The participation of the 3rd airlines will yield a total of 130 flight segments, 6 aircraft 

models and over 6000 surveys from passengers and crew.

6.7 Air Contaminants Measured in the On-Board Study

The On-Board Study will provide a comprehensive set of measurements of cabin air 

environmental conditions. Monitored continuously during cruise were air temperature, 

humidity, noise, pressure, CO, CO2, Ozone, and ultra fine particles. In addition, 

integrated air samples were collected for the analysis of set of carbonyls, volatile organic 

and semi-volatile organic compounds. Table 6.5 provides a listing of the analyst tested 

for in the cabin air.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 66

Table 6.5 List of Analytes Sampled in Cabin Air during On-Board Study

The preliminary findings have confirmed the occasional presence of elevated ozone in 

cabin air. However, the OnBoard Study is providing new insight about the formation of 

reaction products and ultrafine particles. No incident of bleed air contamination was 

evident during the monitoring on the first 2 airlines. The TCP (Tricresylphosphate) 

compounds were detected on a few flights at very low levels near the analytical limit of 

detection. A few flights did have distinctly higher levels of a set of VOCs indicative of 

fuel combustion compounds. These few occurrences are being evaluated further to 

determine if passengers or crew perceived the cabin air quality different on these flights 

from others with more ―typical‖ pattern of VOCs. 

6.8 Implications for the On-Board Study

The need for advances in air cabin comfort and well-being is more important than ever. 

Despite the economic crisis, air travel remains a large and growing industry. ―Frequent 

flyers‖ now form a substantial proportion of the travelling public and the volume of air 

traffic has risen steeply in recent years. The forecasted growth in the number of 

passengers over the next 10 years is expected to rise 4.1%, according to Airbus and 

Boeing.

The goal of comfortable flight is challenged by the increasing time passengers may spend 

in the cabin. With modern long-range aircraft, the need for ―stop-overs‖ has been reduced 

leading to an increase in the duration of flights. The passenger capacity of these long-
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 67

distance aircraft is also increased leading to larger numbers of people travelling aboard a 

single aircraft over long distances. 

The goal of providing comfort in the air is challenged also by the reality that an 

increasing percentage of the flying public will be older and sicker. The number of 

individuals over the age of 60 is expected to triple in the next decades and many will 

need special accommodations because of disabilities or disease. For example, at least 

70% of those passengers over sixty will likely have some form of cardiovascular disease 

and passengers with more severe conditions may experience moderate hypoxia in an 

already mildly hypoxic cabin environment. In these instances, the pursuit of comfort may 

begin with an individual oxygen concentrator, for example, to avoid risk and medical 

diversions. 

To meet the challenge of comfortable and healthy air travel in the 21st century, a 

strategic plan is needed. In order to achieve the ―right‖ conditions for cabin health and 

comfort, the following objectives are proposed:

1. A comprehensive understanding of the current range of environmental conditions 

inside the aircraft.

2. A comprehensive understanding of the range of human responses during flight. 

This understanding must necessarily include an appreciation of the overall 

characteristics of passengers as well as the need-based characteristics that relate to 

disability and the expected class of service. 

3. An analysis of the relationship between cabin environment and passenger and 

crew comfort, health and well-being. 

4. Recommendations for changes in the cabin environment, as well as passenger 

services offerings.

As analysis of the On-Board Study data continues, we will address the following issues.

 Environmental Factors (i.e. temperature, pressure, humidity and ventilation) that 

impact on passenger comfort, along with recommendations for possible 

interventions that could improve passenger comfort and enhance the in-flight 

passenger experience

 The relationship between passenger health symptoms and their physiological 

response to the flight environment as determined by their experience of comfort 

and level of satisfaction.

 Analysis of factors that might be used to identify passengers with particular 

vulnerabilities making them more susceptible to symptoms and discomfort, along 

with recommended interventions (e.g. extra services for aged passengers, 

passengers with pre-existing conditions such as heart disease, diabetes)

 Characterization of the flight attendant experience and their physiological 

response to the flight environment, along with factors that impact on these issues.

Data will be collected and presented in such a way as to potentially serve as a 

baseline indication for a larger, follow-up study on flight attendant fatigue
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 68

6.9 Portable Sensing System

Developing a clear picture of the range of conditions in aircraft cabins and how various 

factors affect those conditions within commercial aircraft across the full range of flights 

conducted is a daunting task. The variety of aircraft used is large. When all of the 

makes, models and various derivatives (737-200, 737-300, 737-400, etc) are considered, 

over 30 different types of aircraft are used on regularly scheduled medium to long 

distance flights by US carriers alone. This variety does not include the multiple engine 

options and cabin layouts that are used with many of these aircraft. There is not an 

accurate accounting of all of the possible combinations in use, but certainly it is 

significantly larger than the 30 base aircraft models. However, the variety of aircraft in 

use is small compared to the variety of other factors. There are literally thousands of 

different flights every day from departure points and destinations ranging from the 

tropics, to deserts, to the arctic. Even for any given departure point and destination, the 

route, altitude, duration, turbulence, etc. can vary from flight to flight depending on the 

weather, traffic, aircraft being flown, etc. All of these factors can potentially affect the 

conditions in the aircraft cabin and the total possible number of combinations is nearly 

infinite. There is no such thing as a typical aircraft, typical flight, or typical operating 

conditions. Conducting environmental measurements on a few dozen flights, or even a 

few hundred flights, is not likely to capture the full range of possibilities. While these 

numbers of measurements should be able to address important, specific questions 

adequately, they are not likely to give a complete picture of the variety of conditions 

encountered. This may lead to questions about the generality of the results for relatively 

small data sets.

In order to get a complete picture, one has to think in terms of measurements on 

thousands of flights, not hundreds. Deploying a complete set of high grade 

instrumentation on this many flights is not feasible from an economic perspective and, 

even if it were economically feasible, it would not be practical from a disruption 

perspective. The airlines, understandably, are not likely to accommodate an intrusive 

presence on thousands of flights. Consequently, a small instrument package that can 

collect useful environmental data and be readily carried on most any aircraft and flight is 

needed. The purpose of this task is to develop and test such an instrument package and to 

establish the feasibility of implementing a program to deploy the packages and establish a 

database from the collected data for use by RITE/ACER members.

Figure 6.3 shows a system that was approved for aircraft cabin operation in 2007. This 

system contains CO2, pressure, humidity, temperature, and sound level sensors. It is 

powered using four AA batteries. This system is also designed to incorporate wireless 

capability, which may not be necessary for the proposed task and may be eliminated 

(pluggable module) due to its impact on EMI certification. This integrated sensor 

package has secure digital flash memory (SD flash memory, similar to those in cameras 

and digital music players) for long-term storage. This system meets all the desired design 

goals, with the exception of operating time. Testing shows that this unit has ~10 hours of 

operating time. This has been further extended by implementing a low-power mode using 

a subset of sensors. When the battery has been drained extensively, the system will shut 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 69

down the relatively power hungry CO2 sensor and continue to operate for several more 

hours. 

 

Figure 6.3 EMI/EMC approved system

In order to keep costs for this task minimal, flights of convenience16 were used. A simple 

measurement protocol (see Figure 6.4) was established such that most any educated 

individual can deploy the device in an aircraft and extract the data. Other than putting the 

device in place and turning it on (and off), the only information the operator will need to 

provide is the airline, flight number, departure and arrival airports, and date. With this 

information, the public flight track information can be used to determine the flight path 

and altitude, which through the time and date stamp can be directly combined temporally 

with the recorded date. Aircraft identification is also available from this source. 

In addition to the note as shown in Figure 6.4, a whitepaper has been prepared to instruct 

individual operators what to do and what not to do. For example, if the flight crew 

objects to using the system, the researcher must politely refrain from using it. The 

system operator or carrier is instructed to place the system on the tray or hang the system 

on the seat pocket. It is advised that the unit be placed outside of any breathing zone, 

such that higher than normal cabin CO2 is not being recorded. 

 

16 Whenever RITE/ACER researcher has business trip.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 70

Figure 6.4 Note to crew. 

For the duration of this project, we collected data on the following aircraft models: A319, 

A320, B737, B757, B767, CRJ, EMB, DC9, MD80, MD88, and MD90. The specific 

aircraft derivative (e.g. 737-200, 737-300, or 737-400) was not recorded. Data from 

nearly 200 individual flights have been recorded and a sample of these data is here.

The system is normally turned on near 10,000 ft (aircraft altitude) while ascending (when 

permission was given for electronic devices) and turned off on descent around 10,000 ft 

as required during landing. In some cases, the system was operating from gate to gate as 

the system without wireless communications meets EMI requirements for all phases of 

flight. 

Cabin CO2

Figure 6.5 show a sample recorded carbon dioxide concentrations. The concentrations of 

carbon dioxide for these flights typically fell between 900 and 1700 ppm, with only 

occasional measurements registering higher values. For these higher concentration 

readings, it is suspected that the CO2 sensor was being breathed upon. Ignoring these 

higher values, the carbon dioxide concentrations never rose to the FAA regulation limit 

of 5000 ppm. The occasional spike to zero in the data is an anomaly of the CO2 sensor 

and does not reflect actual CO2 concentrations in the cabin.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 71

Figure 6.5 B757 Cabin CO2 Concentration

Cabin Pressure

A sample of the cabin pressure data measured can be seen in Figure 6.6. None of the 

recorded flights had pressure readings below 74 kPa, which corresponds to 8000 ft cabin 

altitude as specified in CFR 25.841. Generally speaking, the cabin pressure drops on 

take-off, reaches a steady level at cruise altitude, then rises again as the aircraft descends 

for a landing.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 72

Figure 6.6 B737 Cabin Pressurization

Cabin Temperature

On most of the flights, the cabin temperature ranged from 22C to 29C (or 71.6F to 

84.2F), see Figure 6.7 for sample data. Data would be needed from more flights to 

establish any correlations between temperature and other factors. There are occasional 

―blips‖ in some of the data. It is believed that these blips are an anomaly in the 

instrumentation and not actual temperature spikes.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 73

Figure 6.7 EMB Cabin Temperature

Cabin Humidity

For the most part, the humidity data (see Figure 6.8 for sample data) demonstrate a trend 

of starting at around 35-50% relative humidity at the beginning of the flight and dropping 

to around 10-25% as the flight progresses. 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 74

Figure 6.8 A319 and A320 Cabin Relative Humidity

Cabin Noise Level

A sample of cabin noise level is showed in Figure 6.9. The measured sound level of the 

cabin was typically around 86 dBA (± 2 dBA). This is above the level at which 

permanent hearing damage can occur (80 dBA and above) over long periods of time. 

However, this is below OSHA’s limit of 90 dBA for an 8-hour duration. As the data 

show, newer generations of aircraft, are better at controlling noise in the cabin especially 

compared to the older MD-80 series. However, this difference may also be attributed to 

the difference between wing mounted and fuselage mounted engines. The row location 

for the data collection was not recorded. We may attempt to include this information in 

future work as the front of the aircraft is generally quieter than the rear. It should also be 

noted that we have not independently verified the accuracy of the sound level 

measurements.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 75

Figure 6.9 B757 Cabin Noise Level
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 76

7.0 RESIDUE IN FILTERS FROM AIR QUALITY INCIDENTS

____________________________________________________________________________________________________________

Congressional Mandate: Analyze samples of residue from aircraft ventilation ducts and 

filters after air quality incidents to identify the contaminants to which passengers and 

crew were exposed.

____________________________________________________________________________________________________________

7.1 Introduction

Essentially all modern airliners in the fleet today use compressor bleed air for cabin 

pressurization and ventilation when in flight. Figure 7.1 shows a schematic of a typical 

bleed air system. Figure 7.2 is a photo of a typical high-bypass turbofan aircraft engine 

with the cowling removed to expose the bleed air ducts. Typically, there are highpressure and low-pressure bleed air ports to allow the source pressure to be matched to 

systems needs with different engine and compressor speeds. The bleed air is heated by 

the compression processes and leaves the engine at high temperature and pressure. Table 

7.1 outlines representative temperatures and pressures for different phases of flights.

When bleed air supplied to the cabin has been sampled under normal operating 

conditions, no evidence of contamination from engine sources is found (Nagda 2001). 

However, under certain circumstances, the compressor seals can leak lubricating oil into 

the compressor and, ultimately, into the bleed air stream. In addition, modern aircraft 

contain a myriad of hydraulic control lines (Figure 7.3) including controls in and around 

the engines. Under certain conditions, leakage from hydraulic lines can be ingested by 

the engine compressor and ultimately end up in the bleed air. Both engine lubricating oil 

and hydraulic fluid are serious contaminants in the cabin supply air and are inconsistent 

with 14 CFR 25.831 which states, in part ―....the ventilation system must be designed to 

provide a sufficient amount of uncontaminated air......‖

Shortly after the bleed air is extracted from the engine, it passes through the pre-cooler. 

Thus, it only stays at high temperature for a very short time. Figure 7.2 shows the 

location of the pre-cooler. Although bleed air is cooled quickly, the temperatures and 

residence times are sufficiently high and long to create the potential for pyrolysis of 

contaminants in the bleed air adding further concern about the seriousness of the 

contamination in the air supplied to the cabin. 

While incidents of bleed air contamination occur on a very small percentage of flights, 

given the number of aircraft flying, they still occur with some regularity with varying 

degrees of severity. They may be of relatively short duration and sporadic in nature, 

making it very difficult to analyze actual incidents as they occur. Unless large numbers 

of sampling devices are deployed on aircraft or large numbers of aircraft are equipped 

with sophisticated onboard instrumentation, the odds of having good measurements of the 

air during actual incidents are small. Once an aircraft lands after a contamination event, 

there may be little information available about the nature of the contamination that 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 77

occurred and all systems may be functioning normally. However, it is important to know 

the nature of the exposure to which crew members and passengers were subjected and it 

is important to know the nature of the actual contaminants so the appropriate 

maintenance and other corrective actions can be performed to prevent future incidents in 

the aircraft.

If the contamination levels are high enough, one would expect residue to remain on 

various surfaces. Theoretically, an analysis of this residue could provide information 

about the nature of the contaminant and answer questions as to whether or not it came 

from engine lubricating oil, for example. Such information then could provide valuable 

guidance for follow up actions; hence, the motivation for the Congressional directive.

Figure 7.1 Typical Airliner Bleed Air Supply System (adapted from Hunt et al, 1995)
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 78

 

Figure 7.2 Turbofan engine showing bleed air lines and location of pre-cooler.

 

Figure 7.3. Hydraulic lines in an aircraft.

Bleed Air 

Lines

Connection to 

Pre-cooler
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 79

Table 7.1 Typical Bleed Air Temperatures and Pressure (Source: NRC 2002)

Mode of Operation Temperature

oC (o

F)

Absolute Pressure

kPa (psi)

Extraction Stage

Top of climb 310 (590) 690 (100) Low pressure

Cruise 250 (490) 340 (50) Low pressure

Initial descent from 

cruise

185 (365) 200 (29) High pressure

End of descent 

(ground level)

230 (445) 460 (67) High pressure

High pressure to low 

pressure switch-over

280 (535) 480 (70) High pressure

Ground operations 170 (340)

 -

APU

7.2 Approach

In light of the Congressional mandate and the underlying challenge, a three-part 

experimental plan to address the challenge was developed. Attention was focused on the 

aircraft recirculation filters. The vast majority of the US airliners use recirculation filters 

for the cabin air. Figure 7.4 shows how they are incorporated into the system and Figure 

7.5 shows an actual recirculation filter in an aircraft. In a typical aircraft, approximately 

50% of the air exiting the cabin passes through these filters. Additionally, most aircraft 

use HEPA-grade recirculation filters which make them effective at trapping even the 

smallest aerosolized droplets and particles (e.g. smoke). Given the large amount of cabin 

air that passes through the recirculation filters and their effectiveness in trapping air 

contaminants, they provided a far more promising opportunity for gathering and 

examining contamination residue than other surfaces in the aircraft, air ducts in 

particular. 

Attempting to examine residue from an air contamination incident from any surface poses 

a major challenge. Those surfaces may have been exposed to air for thousands of hours 

and the contamination incident may have been relatively short in duration. Residue that 

has accumulated for thousands of hours is present along with the residue from the 

relatively short incident. The filters are very effective at concentrating and collecting the 

air contaminants that are present during an incident but these contaminants are mixed in 

with other matter the filters may have been collecting for up to several thousand hours 

(Figure 7.6). Attempting to differentiate what came from the incident with what came 

from a host of other possible sources is a daunting task. It would be very easy to 

misinterpret the results of the analyses.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 80

A three part experimental program was developed to address the challenges associated 

with collecting, measuring, and interpreting contaminants collected on recirculation 

filters:

 Part 1 developed a baseline database of contaminants found on aircraft 

recirculation air filters on non-incident aircraft.

 Part 2 Conducted laboratory measurements with controlled contamination of 

simulated bleed air. 

 Part 3 evaluated filters removed from incident aircraft.

In Part 1, filters were collected from a cross-section of the aircraft fleet to establish a 

baseline database. Filters from aircraft known to have had or suspected of having a 

contamination incident were excluded from this database. The residue on these filters in 

the database was characterized using gas chromatograph-mass spectrometry (GC-MS) 

and instrument neutron activation analysis (INAA) methods. The intent was to be able to 

establish the characteristics of non-incident residue as a basis of comparison for incident 

residue. It also was used to develop and refine analysis procedures and techniques 

appropriate to this application.

In Part 2, oil and hydraulic fluid contamination events were simulated in the laboratory. 

A bleed air simulator and filter exposure facility was developed (Figure 7.7) to provide 

controlled exposure with controlled bleed air conditions. This part of the work 

established the detection limits of the analysis methods and the ability to identify known 

bleed air contaminants on filters.

In Part 3, filters were removed from incident aircraft and analyzed using the methods 

developed in Parts 1 and 2 to help identify possible causes of air contamination in aircraft 

with known or suspected air quality incidents.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 81

Figure 7.4 Diagram of aircraft air distribution system

Galley Lavatory

Mix Manifold

Cold Air from

Pack 1

Cold Air from

Pack 2

Trim 

Air

Ground

Supply

Connector

Exhaust Fan

Recirculation

Filter and Fan

Zone 1 Zone 2

Outflow

Valve
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 82

Figure 7.5 Recirculation filter installed in aircraft.

Recirc Filter
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 83

Figure 7.6 Example of filter removed from non-incident aircraft (Note: unusually 

heavily loaded).

Figure 7.7 Bleed air simulator and filter exposure facility.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 84

7.3 Results and Discussion

In total, nearly 200 recirculation filters were obtained from a variety of sources. One or 

more specimens were cut from each of these filters (Figure 7.8). Most of the filters were 

removed during routine servicing and were from aircraft that were not known to have had 

significant air contamination incidents. However, we were able to obtain approximately 

25 from incident or suspected incident aircraft. In addition, a number of filter specimens 

from controlled simulated incidents in the laboratory were analyzed. Data analysis and 

additional laboratory experiments are ongoing but preliminary results can be 

summarized.

By analyzing samples of oil, we were able to identify a set of compounds that can serve 

as a fingerprint of oil contamination. For any one compound, there are multiple sources 

that could explain its presence in the cabin and on the recirculation filters. However, the 

simultaneous presence of all of the markers is a good indication that the source is indeed 

the lubricating oil. Ultimately, we used the simultaneous presence of tricresyl phosphate 

(TCP), and its isomers in the correct ratios plus the presence of synthetic hydrocarbons as 

an indicator of engine lubricating oil contamination. The synthetic hydrocarbon is a 

major component of engine oil and, thus, would be expected to be present in abundance 

during a lubricating oil incident. Its absence is a fairly definitive indication there has not 

recently been major lubricating oil contamination. However, there are other possible 

sources so its presence is not a definitive indicator of engine oil contamination. While 

less common, TCP does have other sources as well. However, by looking at the isomers

and their ratios, a strong link to engine lubricating oil is established. The combined 

presence of the TCP with isomers in the correct ratio plus the synthetic hydrocarbon is a 

pretty clear indicator that there has been engine oil contamination in the cabin air. 

Of the filters sampled, those from the main database, which excluded aircraft without 

known or suspected air contamination events, had a much lower frequency of indicated 

engine oil contamination using the above criteria than for those filters from the known or 

suspected incident aircraft. Thus, there is good reason to believe measurements and 

criteria are valid and can be used as useful evidence that there has or has not been a 

serious engine oil contamination event. 

It should be made clear that it is only evidence and cannot be used as single definitive 

means to determine the presence or absence of engine oil contamination. Also, a 

positive indication does not tell when the contamination occurred and does not 

differentiate a low-level long-term problem from a short-duration but intense event. For 

aircraft with repeating problems, it is advised that the filters be replaced after initial 

indications of problems. The presence of the markers on a nearly new filter is a more 

definitive indication of the source and also narrows the potential time period for the 

detected contamination, providing a more useful assessment.

The filters specimens exposed in the laboratory covered a wide range of contamination 

levels ranging from 100 nanograms to 100 micrograms of oil on a specimen in 

increments of a factor of 10. Specimens from unused filters were also included. These 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 85

specimens were analyzed blindly in the laboratory and the detection limit is between 0.1 

and 1.0 micrograms. This level of detection has not yet been related back to the 

magnitude of oil contamination or exposure to cabin occupants due to the non-specificity 

of the time of exposure as explained above.

Figure 7.8 Specimen being cut from a recirculation filter

7.4 Conclusions

The methodologies developed can be applied to aircraft with a known or suspected air 

contamination incident to help identify the source of the contamination. While not 100% 

definitive, they can provide valid evidence of the presence or absence of substantial 

amounts of engine lubricating oil contamination. They are now being applied, to a 

limited extent, to aircraft with a history of air quality problems to help identify the source 

of the problems and guide appropriate actions to remedy the problems.

While these methods provide a means of after-the-fact assessment, they do not provide 

warnings of incipient contamination events nor do they provide information to the 

cockpit crew during an event to aid in quickly determining the correct response and 

minimizing the exposure of crew members and passengers. The next R&D step, which 

has been initiated, is to develop real time sensing systems to provide this information.

7.5 References

Hunt, E.H., D.H. Reid, D.R. Space, and F.E. Tilton, 2005, ―Commercial Airliner

Environmental Control System, Engineering Aspects of Cabin Air Quality,‖ Aerospace 

Medical Association Annual Meeting, Anaheim, CA, USA.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 86

NRC (National Research Council); 2002, The Airliner Cabin Environment and the Health 

of Passengers and Crew, Washington, DC, National Academy Press.

Nagda, N.L., H.E. Rector, Z. Li, and E.H. Hunt, 2001. ―Determine Aircraft Supply Air 

Contaminants in Engine Bleed Air Supply System on Commercial Aircraft,‖ ENERGEN 

Report AS20151, Prepared for the American Society of Heating, Refrigerating and Airconditioning Engineers, ENERGEN Consulting Engineers, Germantown, MD.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 87

8.0 AIRCRAFT DECONTAMINATION

____________________________________________________________________________________________________________

Congressional Mandate: Demonstrate aircraft decontamination by proven technologies 

such as vapor hydrogen peroxide

____________________________________________________________________________________________________________

8.1 Introduction

Field evaluations were conducted of (i) a stand-alone thermal decontamination system 

and (ii) the usage of the stand-alone technology as a means of delivery of vaporized 

hydrogen peroxide (VHP®) in full-size aircraft. AeroClaveLLC’s thermal 

decontamination system and STERIS Corporation’s VHP® were used in the field 

evaluation studies discussed here. Among all the large-scale disinfection and/or 

decontamination technologies available, vaporized hydrogen peroxide (VHP®) is of 

particular interest due to rapid sterilization, easy usage, intrinsic environmental 

friendliness (i.e., simple by-products composed of only water and oxygen) and 

compatibility with many materials and systems. VHP®has been used for years in 

decontamination studies, but prior attempts to apply VHP®to aircraft, i.e., C–141 

demonstration, were not compatible with airline operations. In those previous attempts, 

bulk vaporizers were required to be mounted within the cabin. The studies reported here 

used vaporized hydrogen peroxide concentrations in the range of 150 - 600 ppm and 

cycle times of 80 - 120 min.1,2 Maximum concentrations of hydrogen peroxide vapor 

were carefully controlled to avoid condensation in cool locations within the aircraft 

cabins. 

A typical VHP®process cycle consists of an initial dehumidification step, then a 

conditioning phase followed by the actual sanitization/decontamination process. Finally 

an aeration phase is employed to remove any remaining residual hydrogen peroxide 

vapor. During the dehumidification phase, warm, dry air flows into the enclosure to 

lower the relative humidity to less than 10% which allows a higher concentration of 

hydrogen peroxide vapor to be injected into the enclosure while avoiding condensation. 

Hydrogen peroxide liquid concentrate (35% liquid H2O2 with a pH ~ 3) is then flash 

vaporized and injected into the enclosure during the initial conditioning phase as well as 

during the sanitization/decontamination phase. The purpose of the conditioning phase is 

to rapidly increase the hydrogen peroxide concentration to minimize overall cycle time. 

During the sanitization/decontamination phase, a steady concentration of hydrogen 

peroxide vapor (typically approximately 100- 450 ppm) is maintained to give the desired 

sanitization/decontamination cycle as often measured by the 6-log kill (i.e., 106

reduction) of a commercial biological indicator (BI) spore population of Geobacillus 

stearothermophilus. Once the sanitization/decontamination phase is completed, the 

 

 VHP is a trademark of STERIS Corporation, Mentor, OH.

 AeroClave LLC is based in Orlando, FL.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 88

enclosure is then aerated with fresh air while any residual hydrogen peroxide vapor 

breaks down into environmentally benign water and oxygen.

Many polymeric and textile materials are known to be susceptible to absorption of 

moisture. The small water molecules can diffuse into the matrix and force apart the 

macromolecules causing swelling. Increases in the distance between polymer chains 

reduce the strength of the secondary intermolecular bonds and increase the softness and 

ductility of the polymer. However, highly cross-linked epoxies used in aerospace-grade 

fiber composites as well as aviation avionics minimize moisture absorption and these 

materials exhibit good resistance to degradation in wet environments. While molecules 

of H2O2 vapor should be even less absorbed by epoxies than the smaller H2O molecules, 

the intermolecular cross-links might be degraded by oxidation from the hydrogen 

peroxide. The extensive usage of polymers in aerospace structures and avionics dictates 

that the compatibility of these materials with hydrogen peroxide vapor be examined.3-5

In addition, a preliminary examination of the compatibility of common metal alloys 

used in airframes (2024 and 7075 aluminum alloys) and galleys and lavatories (304 

austenitic stainless steel) has also been conducted.6,7 The extensive presence of hydrogen 

atoms also mandates that any potential for hydrogen embrittlement of high strength steels 

be carefully evaluated.

8.2 Approach

8.2.1 Field Demonstrations

The two full size aircraft used in the field demonstrations were a DC9 owned by 

Aeroclave LLC in Orlando, FL and a B747 at the Civil Aeromedical Institute (CAMI) in 

Oklahoma City, OK. It is important to note that the engines and auxiliary power units 

had been removed from both aircraft used in the evaluation; without these it was not 

possible to operate the aircraft’s environmental control system and supplementary fans 

had to be used to distribute the decontamination chemicals. Furthermore, no effort was

made to decontaminate the cargo bay of either aircraft.

The thermal decontamination system, as a stand-alone technology, was deployed in its 

standard configuration. The thermal decontamination system was designed to deliver 

heated or cooled air under feed-back control from a self contained unit housed in an 

adjacent semi-trailer. See Figure 8.1. The thermal decontamination system in its original 

configuration did not include a humidification capability. Thus Aeroclave LLC opted to

add a steam-based humidification system to obtain the desired temperature and humidity 

conditions. The unit was connected to the cabin via flexible air delivery and return hoses. 

Custom aircraft door plugs connected to the inlet and outlet hoses were employed. In this 

configuration, the air inlets were at the emergency exit doors above the wing and the air 

outlets at the front and rear cabin doors. Air was also blown into the preconditioned air

inlet with the intent of decontaminating the ductwork. In the stand-alone configuration, 

the thermal decontamination system is intended to deliver hot air of controlled humidity 

to achieve viral decontamination and then cool the aircraft back to a desired temperature 

and relative humidity so that people may re-enter the cabin.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 89

(a) 

(b) 

Figure 8.1 Field demonstration testing of vaporized hydrogen peroxide decontamination in 

(a) Aeroclave LLC DC9 and (b) B747 at the Civil Aeromedical Institute.

The cabins of the DC–9 and the 747 were instrumented with 2 relative humidity 

sensors (one in the front and one in the rear of the cabin) and 36 thermocouples. All data 

were logged continuously. 

In the case of the VHP®add-in, VHP® was injected into the air delivery system from 

an external bank of four hydrogen peroxide vaporizers located in a second trailer adjacent 

to the thermal decontamination system. The thermal decontamination system, when 

used in conjunction with the VHP®add-in, produces environmental preconditioning, 

prior to the injection of VHP®. This involves reducing the RH to below 40%, ideally 30% 

or lower, delivery of vapor to the cabin, and aeration to extract hydrogen peroxide vapor

from the cabin. The cabin was instrumented with the same instrumentation (2 relative 

humidity sensors, one in the front and one in the rear, and 36 thermocouples) as for the 

stand-alone thermal decontamination system. In addition, six hydrogen peroxide vapor 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 90

sensors for the working concentration of the VHP® were included in both the DC9 as 

well as the 747 aircraft. 

Twenty-eight Apex 6 log G. Stearothermophilus biological indicators (BIs) were 

placed throughout the DC9 cabin for the formal evaluation; thirty BIs were used in the 

747 evaluation. Some were located in partially occluded locations, to the extent 

reasonably practicable. 

Peripheral sensors were placed around the aircraft, including near the outlet used to 

flush the VHP®, to demonstrate compliance with OSHA exposure limits. Handheld 

sensor(s) with manual data recording were used in lieu of suitably calibrated automated 

sensors that were not available on-site.

Multiple runs were performed with both aircraft, including one formal evaluation run

on each aircraft. Runs were performed under the following conditions. The VHP®

concentration was maintained at 150 ppm or higher at all locations sampled for at least 

two hours and was not allowed to exceed 500 ppm at any location to minimize the risk of 

condensation. VHP®concentrations were monitored on entering the cabin after each run 

using suitable hand held instrumentation. This did not exceed the 1 ppm personal 

exposure limit for those runs in which aeration was allowed to run to completion.

8.2.2 Materials Compatibility

All sample exposures to vaporized hydrogen peroxide were performed with a 1000ED 

Bio-decontamination Unit (STERIS Corporation, Mentor OH, USA) using VAPROX®as 

the sterilant in an enclosed chamber for 1, 10, or 25 VHP cycles. The exposure chamber 

was dehumidified to 10% relative humidity prior to VAPROX®injection to minimize any 

chance of unintended condensation of the hydrogen peroxide vapor. The chamber 

concentration was maintained at 450ppm H2O2 for 4.8 hours. Hydrogen peroxide 

concentrations were monitored with ATI Sensors (ATI Inc., Collegeville, PA, USA). 

These sensors are reported by the manufacturer as having an accuracy of +5% at 

concentrations above ~50ppm. 

In order to investigate possible effects of hydrogen peroxide spillage or accidental 

condensation during a decontamination cycle, dip exposures of samples to 35% liquid 

phase hydrogen peroxide was carried out in opaque PVC bottles (Fisher Scientific, Fair 

Lawn NJ, USA) for 24 hours and 168 hours. After dip exposure, all dip specimens were 

rinsed in DI-water and then air-dried in an electrostatic film drying cabinet (Delta 1, 

CPM, Inc. Dallas TX) for 1 day. 

Thin commercial-grade sheet samples of 2024-T351 aluminum (1.27 mm thick), 7075-

T6 aluminum (1.22mm thick) and annealed 304 stainless steel (1.22 mm thick) were 

acquired from McMaster Carr Corporation (Atlanta, GA, USA). Thin sheets were chosen 

to maximize the surface area-to-volume ratio of the materials and enhance the potential 

measurable effects on the mechanical properties of the materials. A few samples of 2024 

were solution heat treated and aged to the T6 condition.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 91

Commercial-grade sheet samples of Hexcel Corporation epoxy impregnated carbon 

fiber fabric composites (6 fabric layers, 3.2 mm thick overall) were acquired from 

McMaster Carr Corporation (Atlanta, GA, USA). The carbon fibers in the fabric were 

oriented along the length direction as well as the transverse direction (i.e., 0/90 

orientations) and exhibited a total fiber volume of 55% of the overall sheet volume. 

Additional samples of woven carbon/glass fiber fabrics impregnated with epoxy resin (2 

fabric layers, 1.6 thick overall) from Acculam Corporation were acquired from McMaster 

Carr Corporation (Atlanta, GA, USA). These laminates were then sectioned into 75 X 

12.5 mm test coupons for hydrogen peroxide exposure and mechanical testing.

Epoxy-impregnated glass fiber fabric composites known as FR4 laminate for printed 

circuit board manufacture (3 layer lamination, uncoated: 5.0 mm thick and coated 5.15 

mm thick) were acquired from Park Electrochemical Corp. (Fullerton, CA). Some 

samples of the FR4 laminate were conformal coated with a 0.075 mm thick 1B31 

protective acrylic coating at Humiseal Protective Coatings (Woodside, NY) before being 

sectioned into 152 X 12.7 mm test samples for 3 point bending mechanical tests. 

Tension testing and flexural testing of the metals and epoxy-based composite samples 

was performed according to ASTM Standards E8M-00b and D790-0 (6) in an 

environmentally conditioned laboratory (21 ± 1 oC, 65 ± 2 % relative humidity) using a 

screw driven Instron 4400R (Instron Inc., Canton MA, USA) universal materials testing 

machine. Hydrogen embrittlement testing was conducted per ASTM Standard F519-06. 

A minimum of 5 samples were tested for each condition. Samples were taken from the 

sheets in either the longitudinal or transverse orientation. 

Sample weights were measured by an accuSeriesaccu-124 balance (Fisher Scientific, 

Arvada CO, USA) before and after hydrogen peroxide exposures. The reported accuracy 

of this device is +100 g. Samples of the composites were dried in a vacuum dessicator 

for 48 hrs and then a standard calcium sulfate filled dessicator for 48 hours prior to 

measuring the initial weights. The same sample drying procedures were followed after 

hydrogen peroxide exposures and prior to post-exposure weight measurements. Weight 

changes of the FR4 samples were measured immediately before and after the VHP®

processes. Dipped FR4 specimens were air dried for at least 1 day prior to weight change 

measurement.

Detailed examination of metallographic samples (before and after exposure) was 

performed with an Olympus PME3 inverted metallurgical microscope. Keller’s reagent 

(2.5mL HNO3, 1.5mL HCl, 1 mL HF and 95 mL H2O) was used to etch the aluminum 

samples while an acidic mixture (2.5 mL HF, 10 mL HNO3, 10 mL HCl and 27.5 mL 

H2O) was used to etch the stainless steel samples. Electron microsopy was performed 

using a JEOL JSM 7000F field emission scanning electron microscope operating at 20kV 

with energy disdersive X-ray spectroscopy (EDS) employing an ultrathin window 

detector and Princeton Gamma-Tech analyzer.

 



accuSeries is a registered trademark of Fisher Scientific, Fair Lawn, NJ, USA.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 92

Chemical analyses of the composite samples were performed using Fourier Transform 

Infrared Spectroscopy (FTIR) using an IR Prestige – 21 (Shimadzu Scientific 

Instruments, Columbia, MD, USA) spectrometer over a scan range from 400 cm-1to 

4000 cm-1. Raman spectroscopy was employed to complement the infrared spectroscopy. 

Raman spectra were acquired using an Invia Confocal Raman Microscope (Renishaw, 

Wotton-under-Edge, Gloucestershire, UK) using a 514.5 nm wavelength and 1 mW laser 

excitation source. Spectra were recorded using a 50X objective lens which generated a 

1μm laser spot.

Analysis of variance of the test results was performed using the SAS statistical analysis 

software package (SAS Institute Inc., Cary, NC, USA) to evaluate the statistical 

significance of the observed changes due to hydrogen peroxide exposure.

8.2.3 Avionics Compatibility

In order to study different avionics compatibility characteristics, tests were performed 

on several different dummy circuit board layouts, as well as an active circuit board and 

also aviation wire. The three dummy board layouts were (i) wire, (ii) interdigitated and 

(iii) pad. An HP4263B inductance, capacitance, and resistance (LCR) meter was used to 

measure the impedance of the traces on each board. For the wire boards, the impedances 

of all 16 traces were measured at 100mV, 1kHz. For the interdigitated boards, the 

impedances were measured at 100mV (1kHz and 10kHz). For the pad boards, the 

impedances were measured at 100mV (1kHz). The resistance of the wires was measured 

and subtracted from the trace measurements to obtain the impedance of the traces 

themselves. Since conformal coatings are normally applied to avionics circuit boards, 

some of the samples were coated with 1B31 acrylic coating (HumiSeal Protective 

Coatings; Woodside, NY.) Multiple tests were performed for each board layout 

(uncoated, uncoated-VHP®exposed, conformal coated, and conformal coated-VHP®

exposed).

To test the active boards, sine and square waves were generated by the active boards to 

verify the signal output capabilities. As the active circuit was digital in nature, the square 

wave output could be directly generated. The sine wave signal was generated through 

pulse-width-modulation and a filter circuit. The signals for the unexposed boards and the 

VHP®exposed boards were recorded and compared by using an oscilloscope. For input 

acquisition tests on the active boards, a function generator was configured to output a 

sine wave or square wave, which would be captured with the analog-to-digital converter 

present in the active circuit board.

To test for any potential degradation of the aviation wire insulation (MIL227597/34-

20), a high-voltage power supply and current measuring electronics were set up to apply 

high-voltage stress to the insulation. This was done in to determine the effect of VHP®

exposure on the time-to-breakdown of the wire insulation. In these tests, ~18.5 KV RMS 

and ~10 KV RMS at 60 Hz was applied to ~1 ft sections of aviation wire. One terminal 

was connected to one end of the wire with the insulation intact. The other terminal was 

connected to the wire's conductor. The high-voltage power supply system kept a record 

of when the insulation breakdown occurred (VHP®-exposed wires versus non-VHP®
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 93

exposed wires). Twenty samples were tested for both exposed and non-exposed wires. 

Breakdown was detected by the current spike associated with the resulting short circuit.

Chemical analyses on the printed circuit boards and aviation wire insulation were 

performed by Raman spectroscopy. This process used an Invia Confocal Raman 

Microscope with a 514.5 nm wavelength and 1 mW laser excitation source. The spectra 

were recorded using a 50x objective lens which generated a 1 μm laser spot. Additional 

examination of the surface composition of copper layer on the test boards was 

accomplished using X-ray photoelectron spectroscopy (XPS) and Auger electron 

spectroscopy. The glass transition temperature of the wire insulation layer was measured 

by differential scanning calorimetry (DSC).

8.3 Results and Discussion

8.3.1 Field Demonstrations

As long as the DC9’s cargo bay temperature was excluded from the stand-alone 

thermal/humidity decontamination evaluations, it was possible to achieve stable cabin 

surface temperatures in excess of 60 oC at all 28 locations, with the surface temperature 

adjacent to the air inlet remaining significantly below 70 oC. The addition of a 

humidifier enabled a RH of around 50 % to be maintained, which is important as an 

elevated RH is needed to achieve antiviral efficacy. Some thermal oscillation was seen 

in the measured surface temperatures inside the DC9 aircraft temperatures. These were 

considered to be due to the thermal decontamination unit’s heating system being

oversized and not properly ―matched‖ for the volume of the DC-9. 

It proved possible to heat the majority of the 747 cabin to approximately 60oC and hold 

near to this temperature for an extended period with the use of two thermal 

decontamination units. Although the two thermal decontamination units appeared to be 

well matched to the thermal mass of the 747, in some cases it was not possible to hold at 

60 oC for 2 hours, as stipulated in the test protocol. Surface temperatures in other 

locations (e.g. adjacent to the inlet) were found to exceed 65 oC, with a maximum 

temperature of 71 oC being observed where the incoming air stream impinged on the 

cabin. In addition, it was not possible to bring the cabin RH above 20%, using the 100 

kW steam generator.

The combined system (thermal+humidity+VHP) appeared to be capable of controlling 

the VHP concentration in both the DC9 and the 747 cabins, based on the output from the 

six hydrogen peroxide sensors. It was possible to maintain an average cabin hydrogen 

peroxide concentration of around 175 ppm under non-condensing conditions, which 

should be sufficient to produce a sporicidal action (concentrations above ~ 80 ppm are 

usually considered sporicidal). The hydrogen peroxide concentration measured adjacent 

to the inlet did not exceed 275 ppm, and hence there does not appear to be a risk of 

macroscopic condensation of the peroxide (localized condensation would require pockets 

of high humidity). However, some condensed peroxide was apparent in the return air 

cabinet of the thermal decontamination system air handler and at weather-induced 

breaches to the temporary wooden door plugs. 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 94

Front Door Back Door

 First class Economy class

Twenty-eight biological indicators (BIs) were placed throughout the DC9 cabin, and 

all of these were deactivated, except in the case of experimental runs for which there 

were known control issues. At both the 48-hour interim evaluation and 7-day final 

evaluation, all exposed biological indicators were negative for growth, and all positive 

controls showed normal growth.

The BIs placed throughout the 747 cabin did not achieve complete kill in a few cases 

(~15%). These BIs were placed in locations where peroxide access proved difficult to 

achieve. The only cases of extensive kill failures in large portions of the cabin were due 

to weather-generated equipment failures that caused condensation of the peroxide. In 

both the DC-9 as well as the 747 aircraft, some additional issues were encountered with

residual release of hydrogen peroxide that had been trapped in seat fabrics, cushions, etc. 

Optimization of the aeration cycle seemed to help significantly in addressing this 

problem, although this still remains an issue. 

Computational simulations of the decontamination of a narrow-body aircraft as 

well as a wide-body aircraft were performed using Fluent. Schematics of the aircraft 

cabins investigated are shown in Figure 8.2. The single-aisle cabin had three rows of 

seats in first class and 25 rows of economy class. The twin-aisle airliner cabin had three

rows of seats in first class in front and 30 rows of economy class. The self-enclosed 

spaces, i.e., closets, galleys and lavatories, were not modeled in the calculations. The 

overarching results of the simulations showed that predicted uniformities of vaporized 

hydrogen peroxide decontaminants were generally better (1) in the narrow-body and (2) 

with the aircraft environmental control system fans stopped. These computational 

predictions are consistent with the experimental findings.

Figure 8.2 Single-aisle and a twin-aisle aircraft cabins used to computationally simulate

decontaminant delivery methods. Red squares indicate mixing fans and 

arrows indicate airflow directions. 

 First class

Front door

L

L

L

L

Back door

G

C G

A

G

G

G

Economy class
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 95

8.3.2 Materials Compatibility

Extensive materials compatibility evaluations of the effects of hydrogen peroxide 

exposure on the physical and mechanical properties of aerospace grade textiles, 

composites, metals, and avionics have been conducted. 

The tensile strength and the elongation to failure of Nomex® were unchanged by 

exposure to 450 ppm vaporized hydrogen peroxide. The tensile strength of (i) nylon was 

minimally degraded (<10% loss), (ii) polyester were slightly degraded (~10% loss), and 

(iii) wool was moderately degraded (~20-30% loss) by exposure to 450 ppm vaporized 

hydrogen peroxide. The tensile strength and the elongation to failure of leather were 

severely degraded (~50% loss) by exposure to 450 ppm vaporized hydrogen peroxide. 

Minimum changes were seen in the tensile properties of the following metals by 

exposures to either 450 ppm vapor phase or 35% liquid phase hydrogen peroxide: 2024-

T351, 2024-T6 and 7075-T6 aluminum, and 304 stainless steel. However, although 

exposure of 4340 high strength steel to vaporized hydrogen peroxide levels as high as 

1000 ppm did not cause hydrogen embrittlement, process conditions that led to 

condensation of the vapor on the 4340 high strength steel DID cause embrittlement. 

Work continues in this area.

Finally, carbon fiber/epoxy, glass fiber/carbon fiber epoxy and FR4 printed circuit 

board materials exhibited no significant changes in flexural strength or strain at peak load 

after 10 exposures to 450 ppm VHP®. However, some mechanical degradation in the 

composite samples was observed after 168 hour exposure to 35% liquid hydrogen 

peroxide. Delamination of the 1B31 acrylic confocal coating was observed on FR4 

printed circuit board materials when exposed to liquid hydrogen peroxide. Finally,

crazing of acrylics were also detected when the vapor process conditions enable 

condensation to form on the acrylic material.

8.3.3 Avionics Compatibility

The average resistance of the long, medium, and short length traces was about 11, 8, 

and 7 mOhms, respectively. The longer traces had slightly more resistance than the 

shorter ones, but there was only about a 1 mOhm difference between the non-exposed 

versus exposed boards. This difference is so small that it would not affect the DC 

characteristics of the traces. The impedance between the traces was also measured on the 

interdigitated board samples. No significant difference was found due to vaporized 

hydrogen peroxide exposures. 

The pad board resistance had a maximum difference of approximately 2 mOhms 

between the uncoated and uncoated-exposed boards. Since the standard deviation was 

about 1 mOhm, this change was also insignificant. These tests were carried out on 

boards without solder mask. Solder mask (as is found on a typical PCB) would have 

provided another layer of protection against corrosion. A very thin layer of copper 

oxidation was detected on the tested boards. However, some oxidation due to air 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 96

exposure would have occurred on these unprotected boards even without the presence of 

VHP®.

From all the sine and square waveforms test, the pre-and post-generated/measured 

waveforms were found to match with only minor deviations that may be attributed to 

expected noise. The input and output signals of unexposed boards and VHP®exposed 

boards were compared. No statistical difference was found, and the ability of the active 

boards to output or acquire signals was not found to be diminished in any way by the 

exposure to VHP®. However, some oxidation was visible on unprotected tin contacts.

In first set of high voltage wire test, ~18.5 KVRMS was used. Wires not exposed to 

VHP®failed within 16 minutes on average. The wires that were exposed to VHP®failed 

on average within only 4 minutes, potentially indicating that VHP®decreased the 

dielectric strength of the wire insulation at this test voltage. However, in the interest of 

increasing the speed at which the breakdown would occur, the voltage stress applied was 

outside the operational voltages experienced by aviation wire. The stress voltage was 

~18,500 VRMS for these tests, whereas the normal aircraft operating voltage is only 28 

Volts at 400 Hz. In a second set of high voltage wire tests, ~10,000 VRMS was used. In 

this second test, the average (17 samples) fail time was 2 hours, 31 minutes and 36 

seconds for the unexposed wires while the VHP®-exposed wires exhibited an average (17 

samples) fail time of 3 hours, 36 minutes and 26 seconds. The VHP®-exposed wire 

samples thus lasted longer than the non-exposed wires. Thus the effects of VHP®

exposure on wire insulation appear to be insignificant.

No statistical differences in chemical compositions or weight change were found 

among the circuit boards and aviation wires due to exposure to VHP®. XPS results on 

the circuit board copper layer revealed small surface changes due to oxidation on the 

sample exposed to 25 VHP®cycles. 

8.4 Conclusions

8.4.1 Field Demonstrations

The thermal decontamination system appears to be capable of reproducing in full size 

aircraft the temperatures/humidities needed for an efficacious antiviral process. Further 

work is needed to improve the temperature control to eliminate overheating of some 

cabin surfaces. Reaching a relative humidity > 20 % was found to be a problem in the 

larger volume 747 cabin, but this appears to be addressable with the additional steam 

generation capacity. 

The thermal decontamination + VHP add-in combination was found to be sporicidal at 

all locations within the narrow body DC9 and at most locations within the wide-body 747 

cabin. The impact of issues relating to the failure to deactivate biological indicators in 

certain locations with limited peroxide penetration is an engineering issue that must be 

addressed. Issues related to the presence of residual peroxide in the cabin after aeration 

also must be corrected. Finally, additional engineering development is needed to prevent 

condensation of peroxide within the cabin of aircraft. 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 97

8.4.2 Materials Compatibility

Vaporized hydrogen peroxide conditions that lead to condensation can cause 

hydrogen embrittlement of high strength steel. Condensation must be avoided to prevent 

this very serious degradation of high strength steel. The tensile properties (0.2% offset 

yield strength, ultimate tensile strength and % elongation to failure) of samples of 2024-

T351, 2024-T6, 7075-T6 and 304 stainless steel were unaffected by the various exposures 

to both vapor phase and 35% liquid phase hydrogen peroxide.

The carbon fiber/epoxy, the glass fiber/carbon fiber epoxy and the FR4 printed 

circuit board materials exhibited no significant changes in flexural strength after 10 VHP 

exposures.

Exposures of textile samples (wool, nylon, polyester and Nomex®to vaporized or 

liquid phase hydrogen peroxide caused increases in weight presumably due to absorption 

of water vapor from the treatment as well as decomposition of H2O2 to oxygen and water 

vapor. Exposure to 10 cycles of vaporized hydrogen peroxide caused the following 

changes in the textile materials: 

 The tensile strength of wool was moderately degraded (~20-30% loss). 

 The tensile strength of polyester was slightly degraded (~10% loss). 

 The tensile strength of nylon was minimally degraded (<10% loss). 

 The tensile strength of Nomex® were unchanged.

 The tensile strength of leather were severely degraded (~50% loss).



All preliminary flammability results for Nomex®- both as-received as well as after 

all exposures to hydrogen peroxide - were within the limits of FAR 25.853 for both 

vertical and horizontal flammability testing. The preliminary flammability testing of 

wool, nylon and polyester indicated complex effects on flame/burn times, burn lengths 

and horizontal burn rates presumably due to the presence of absorbed water vapor from 

the hydrogen peroxide exposures as well as the pre-test conditioning treatments. 

Additional research into these effects is necessary to fully understand and rigorously 

characterize this important behavior. 

8.4.3 Avionics Compatibility

VHP®exposure had no significant effect on the electrical performance of the circuit 

boards or the electrical wire insulation materials. The discoloration of the copper boards 

would have occurred even in ambient environmental conditions. 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 98

9.0 Appendices

9.1 Archival Publications

9.1.1 2010 Publications

Coleman BK, Wells JR, Nazaroff WW, 2010. Investigating ozone-induced 

decomposition of surface-bound permethrin for conditions in aircraft cabins. Indoor Air 

20, 61-71.

―Improvements on FFD modeling by using different numerical schemes,‖ Zuo, W., Hu, 

J., and Chen, Q., Accepted by Numerical Heat Transfer.

―Flow and contaminant transport in an airliner cabin induced by a moving body: Scale 

model experiments and CFD predictions,‖ Poussou, S., Mazumdar, S., Plesniak, M.W., 

and Sojka, P. and Chen, Q., Accepted by Atmospheric Environment.

―On a hybrid RANS/LES approach for indoor airflow modeling,‖ Wang, M. and Chen, 

Q., Accepted by HVAC&R Research.

―Comparison of different decontaminant delivery methods for sterilizing unoccupied 

commercial airliner cabins,‖ Chen, X. and Chen, Q., Building and Environment, 45(9), 

2010 2027-2034.

―Characterizing exhaled airflow from breathing and talking,‖ Gupta, J.K., Lin, C.-H., 

and Chen, Q., Indoor Air, 20 (2010) 31-39.

―Fast and informative flow simulations in a building by using fast fluid dynamics model 

on graphics processing unit,‖ Zuo, W. and Chen, Q., Building and Environment, 45(3),

2010, 747-757.

―Ventilation performance prediction for buildings: Model assessment,‖ Chen, Q., Lee, 

K., Mazumdar, K., Poussou, S., Wang, L, Wang, M., and Zhang, Z., Building and 

Environment, 45(2), 2010, 295-303.

9.1.2 2009 Publications

"Sampling Scheme for Pyrethroids on Multiple Surfaces on Commercial Aircrafts" K. 

Mohan, and C.P. Weisel, Journal of Exposure Science and Environmental Epidemiology, 

in press 2009.

"Copper nanoparticles and carbon nanotubes-based electrochemical sensing System for 

fast identification of tricresyl-phosphate in aqueous samples and air," Valber A. Pedrosa, 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 99

Rigved Epur, Jessica Benton, Ruel A. Overfelt, Aleksandr L. Simonian, accepted for 

publication in Sens. Actuators B: Chem. Vol. 140, n 1 (2009) pp. 92-97.

"Effect of vapour phase hydrogen peroxide, as a decontaminant for civil aviation 

applications, on microstructure, tensile properties and corrosion resistance of 2024 and 

7075 age hardenable aluminium alloys and 304 austenitic stainless steel," Gale, W.F.; 

Sofyan, N.I.; Gale, H.S.; Sk, M.H.; Chou, S.-F.; Fergus, J.W.; Shannon, C.G., Materials 

Science and Technology, v 25, n 1, p 76-84, January 2009

"Inactivating Influenza Viruses on Surfaces Using Hydrogen Peroxide or Triethylene 

Glycol at Low Vapor Concentrations," Rudnick SN, McDevitt JJ, First MW, Spengler 

JD, DOT/FAA/AM-09/7, April 2009.

"Experimental and numerical investigation of airflow and contaminant transport in an 

airliner cabin mockup," Zhang, Zhao; Chen, Xi; Mazumdar, Sagnik; Zhang, Tengfei; 

Chen, Qingyan, Building and Environment, Vol 44, No 1 (2009) pp 85-94.

"Prediction of particle deposition onto indoor surfaces by CFD with a modified 

Lagrangian method," Zhang, Z.; Chen, Q., Atmospheric Environment, Vol. 43, No. 2 

(2009) pp 319-328.

―Assessment of various turbulence models for transitional flows in enclosed 

environment,‖ Wang, M. and Chen, Q. HVAC&R Research, 15(6), 2009, 1099-1119.

―Flow dynamics and characterization of a cough,‖ Gupta, J.K., Lin, C.-H., and Chen, Q., 

Indoor Air, 19, 2009, 517-525.

"A simplified approach to describe complex diffusers in displacement ventilation for 

CFD simulations," Zhang, T., Lee, K.S., and Chen, Q., Indoor Air, 19(3), 2009, 255-267.

"Ventilation performance prediction for buildings: A method overview and recent 

applications," Chen, Q., Building and Environment, 44(4), 2009, 848-858.

"Real time or faster-than-real-time simulation of airflow in buildings," Zuo, W. and 

Chen, Q., Indoor Air, 19(1), 2009, 33-44.

"A one-dimensional analytical model for airborne contaminant transport in airliner 

cabins," Mazumdar, S. and Chen, Q. 2009, Indoor Air, 19(1). 3-13.

"Effects of Hydrogen Peroxide on Common Aviation Textiles," Chou SF, Overfelt RA, 

Gale WF, Gale HS, Shannon CG, Buschle-Diller G, Watson J, DOT/FAA/AM-09/16, 

August 2009.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 100

9.1.3 2008 Publications

"Ozone consumption and volatile byproduct formation from surface reactions with 

aircraft cabin materials and clothing fabrics," Beverly Coleman, Hugo Destaillats, Alfred 

Hodgson, William Nazaroff, Atmospheric Environment, Vol. 42 (4), February 2008, pp. 

642-654.

"Ozone levels in passenger cabins of commercial aircraft on North American and 

transoceanic routes," Seema Bhangarm Shannon Cowlin, Brett Singer, Richard Sextro, 

William Nazaroff, Environmental Science and Technology, Vol. 42, No. 11, June 2008, 

pp 3938-3943.

"The influence of ozone on passenger symptoms in a simulated aircraft cabin," Peter 

StrØm-Tejsen, Charles J Weschler, Pawel Wargocki, Danuta MyskÓw, Julita Zarzycka, 

Journal Exposure Science & Environ. Epidemiology, Vol. 18, 2008, p. 272.

"Effect of chelating agents on the preferred orientation of ZnO films by sol-gel process" 

Yoon, Sang Hoon; Liu, Dan; Shen, Dongna; Park, Minseo; Kim, Dong-Joo; Journal of 

Materials Science, Vol 43, n 18 (2008) pp 6177-6181.

"Effect of vapour phase hydrogen peroxide, as a decontaminant for civil aviation 

applications, on microstructure, tensile properties and corrosion resistance of 2024 and 

7075 age hardenable aluminium alloys and 304 austenitic stainless steel," Gale, W.F.; 

Sofyan, N.I.; Gale, H.S.; Sk, M.H.; Chou, S.-F.; Fergus, J.W.; Shannon, C.G., Materials 

Science and Technology, v 25, n 1, p 76-84, January 2009

"Field Evaluation of Whole Airliner Decontamination Technologies Wide-Body Aircraft 

With Dual-Use Application for Railcars," Gale WF, Gale HS, Watson J, DOT/FAA/AM08/2, Febuary 2008.

"Field Evaluation of Whole Airliner Decontamination Technologies for Narrow-Body 

Aircraft," Gale WF, Gale HS, Watson J, DOT/FAA/AM-08/4, January 2008.

"Modular, Portable, Reconfigurable, and Wireless Sensing System for the Aircraft 

Cabin," S. M. Loo, Michael Owen, Josh Kiepert, Arlen Planting, Journal of ASTM 

International, Vol. 4, No. 4, 9 pages, April 2008.

"Influence of cabin conditions on placement and response of contaminant detection 

sensors in a commercial aircraft," Mazumdar, S. and Chen, Q., Journal of Environmental 

Monitoring, 10, 2008, pp. 71-81.

9.1.4 2007 Publications

"Ozone-initiated chemistry in an occupied simulated aircraft cabin," Charles J. Weschler, 

Armin Wisthaler, Shannon Cowlin, Gyöngyi Tamás, Peter Strøm-Tejsen, Alfred 

Hodgson, Hugo Destaillats, Jason Herrington, Junfeng Zhang, William Nazaroff, 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 101

Environmental Science and Technology, Vol. 41, No. 17, September 2007, pp. 6177-

6184.

"The Influence of Ozone on Self-Evaluation of Symptoms in a Simulated Aircraft Cabin" 

Peter Strøm-Tejsen, Charles J Weschler, Pawel Wargocki, Danuta MySkÓw, Julita 

Zarzycka, Journal of Exposure Science and Environmental Epidemiology, Vol. 18 (2008) 

pp 272-281.

"Novel air distribution systems for commercial aircraft cabins," Zhang, Tengfei; Chen, 

Qingyan (Yan), Building and Environment, Vol 42, No 4 (2007) pp 1675-1684.

"Optimal sensor placement for airborne contaminant detection in an aircraft cabin," 

Zhang, Tengfei; Chen, Qingyan; Lin, Chao-Hsin, HVAC & R Research, Vol 13, No 5 

(2007) pp. 683-696.

"Evaluation of various turbulence models in predicting airflow and turbulence in 

enclosed environments by CFD: Part 1 - Summary of prevalent turbulence models," Zhai, 

Zhiqiang; Zhang, Zhao; Zhang, Wei; Chen, Qingyan, HVAC and R Research, Vol 13, No 

6 (2007) pp 853-870.

"Comparison of the Eulerian and Lagrangian methods for predicting particle transport in 

enclosed spaces," Zhang, Z.; Chen, Q., Atmospheric Environment, Vol 41, No 25 (2007) 

pp 5236-5248.

"Computer modeling of multiscale fluid flow and heat and mass transfer in engineered 

spaces," Chen, Qingyan, Zhai, Zhiqiang; Wang, Liangzhu, Chemical Engineering 

Science, Vol 62, No 13 (2007) pp 3580-3588.

"Ozone-initiated chemistry in an occupied simulated aircraft cabin," Charles J. Weschler, 

Armin Wisthaler, Shannon Cowlin, Gyöngyi Tamás, Peter Strøm-Tejsen, Alfred 

Hodgson, Hugo Destaillats, Jason Herrington, Junfeng Zhang, William Nazaroff, 

Environmental Science and Technology, Vol. 41, No. 17, September 2007, pp. 6177-

6184.

"Magnetostrictive Microcantilever as an Advanced Transducer for Biosensors" Liling Fu, 

Suiqiong Li, Kewei Zhang, I-Hsuan Chen, Valery A. Petrenko and Zhongyang Cheng, 

Sensors, 7, 2929 – 2941, 2007

"Identification of contaminant sources in enclosed spaces by a single sensor," Zhang, T. 

and Chen, Q., Indoor Air, 17(6), 2007, 439-449.

"Evaluation of various turbulence models in predicting airflow and turbulence in 

enclosed environments by CFD: part-2: comparison with experimental data from 

literature," Zhang, Z., Zhang, W., Zhai, Z., and Chen, Q., HVAC & R Research, 13(6), 

2007, 871-886.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 102

"Identification of contaminant sources in enclosed environments by inverse CFD 

modeling," Zhang, T. and Chen, Q., Indoor Air, 17(3), 2007, 167-177.

9.1.5 2006 Publications

"Factors affecting ozone removal rates in a simulated aircraft cabin environment," 

Gyöngyi Tamás, Charles J. Werschler, Zsolt Bakó-Biró, David P. Wyon, Peter StrømTejsen, Atmospheric Environment , Vol. 40, No. 32., 2006, p. 6122.

"A fluorescence-based biosensor for the detection of organophosphate pesticides and 

chemical warfare agents," Viveros, L.; Paliwal, S.; McCrae, D.; Wild, J.; Simonian, A.; 

Sensors and Actuators, B: Chemical, Vol 115, n 1 (2006) pp 150-157.

"TCP electrochemical detection," Vertelov, G.K.; Gale, W.F.; Simonian, A.L.; ECS 

Transactions, Vol. 3, n 10, (2006) pp 21-34,

"Experimental measurements and numerical simulations of particle transport and 

distribution in ventilated rooms," Zhang, Z.; Chen, Q., Atmospheric Environment, Vol 40, 

No 18 (2006) pp 3396-3408.

"Comparison of Large Eddy Simulation Predictions with Particle Image Velocimetry 

Data for the Airflow in a Generic Cabin Model" C.H. Lin, T.T. Wu, R.H. Horstman, P.A. 

Lebbin, M.H. Hosni, B.W. Jones, B.T. Beck, HVAC & R Research, Vol 12, No 3 (2006) 

pp. 935 – 951

9.1.7 2005 Publications

"Nanoparticle-based optical biosensors for the direct detection of organophosphate 

chemical warfare agents and pesticides," Simonian, A.L.; Good, T.A.; Wang, S.-S.; Wild, 

J.R.; Analytica Chimica Acta, Vol 534, n 1 (2005) pp 69-77.

"Prediction of Particle Transport in Enclosed Environment" Q. Chen and Z. Zhang, 

China Particuology, Vol 3, No 6 (2005) pp 364 – 372.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 103

9.2 Applicable U.S. Federal Regulations

The federal aviation regulations applicable to the design and operation of commercial 

aircraft are contained in "Title 14 - Aeronautics and Space" of the Code of Federal 

Regulations (14 CFR). Part 25 of 14 CFR provides the airworthiness standards for 

transport category airplanes. Part 121 of 14 CFR contains the operating requirements for 

air carriers and commercial operators. Part 125 of 14 CFR covers (i) the certification and 

operations of aircraft having a seating capacity of 20 or more passengers OR a maximum 

payload capacity of 6000 or more pounds and (ii) the rules governing persons on board 

such aircraft. The current and full text of 14 CFR can be found on the U.S. Government 

Printing Office website.

9.2.1 Ventilation Regulations

14 CFR § 25.831 Ventilation.

(a) Under normal operating conditions and in the event of any probable failure conditions 

of any system which would adversely affect the ventilating air, the ventilation system 

must be designed to provide a sufficient amount of uncontaminated air to enable the 

crewmembers to perform their duties without undue discomfort or fatigue and to provide 

reasonable passenger comfort. For normal operating conditions, the ventilation system 

must be designed to provide each occupant with an airflow containing at least 0.55 

pounds of fresh air per minute.

(b) Crew and passenger compartment air must be free from harmful or hazardous 

concentrations of gases or vapors. In meeting this requirement, the following apply:

(1) Carbon monoxide concentrations in excess of 1 part in 20,000 parts of air are 

considered hazardous. For test purposes, any acceptable carbon monoxide detection 

method may be used.

(2) Carbon dioxide concentration during flight must be shown not to exceed 0.5 percent 

by volume (sea level equivalent) in compartments normally occupied by passengers or 

crewmembers.

(c) There must be provisions made to ensure that the conditions prescribed in paragraph 

(b) of this section are met after reasonably probable failures or malfunctioning of the 

ventilating, heating, pressurization, or other systems and equipment.

(d) If accumulation of hazardous quantities of smoke in the cockpit area is reasonably 

probable, smoke evacuation must be readily accomplished, starting with full 

pressurization and without depressurizing beyond safe limits.

(e) Except as provided in paragraph (f) of this section, means must be provided to enable 

the occupants of the following compartments and areas to control the temperature and 
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 104

quantity of ventilating air supplied to their compartment or area independently of the 

temperature and quantity of air supplied to other compartments and areas:

(1) The flight crew compartment.

(2) Crewmember compartments and areas other than the flight crew compartment unless 

the crewmember compartment or area is ventilated by air interchange with other 

compartments or areas under all operating conditions.

(f) Means to enable the flight crew to control the temperature and quantity of ventilating 

air supplied to the flight crew compartment independently of the temperature and 

quantity of ventilating air supplied to other compartments are not required if all of the 

following conditions are met:

(1) The total volume of the flight crew and passenger compartments is 800 cubic feet or 

less.

(2) The air inlets and passages for air to flow between flight crew and passenger 

compartments are arranged to provide compartment temperatures within 5 degrees F. of 

each other and adequate ventilation to occupants in both compartments.

(3) The temperature and ventilation controls are accessible to the flight crew.

(g) The exposure time at any given temperature must not exceed the values shown in the 

following graph after any improbable failure condition.

[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25–41, 42 FR 36970, 

July 18, 1977; Amdt. 25–87, 61 FR 28695, June 5, 1996; Amdt. 25–89, 61 FR 63956, 

Dec. 2, 1996]
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 105

14 CFR § 121.219 Ventilation.

Each passenger or crew compartment must be suitably ventilated. Carbon monoxide 

concentration may not be more than one part in 20,000 parts of air, and fuel fumes may 

not be present. In any case where partitions between compartments have louvres or other 

means allowing air to flow between compartments, there must be a means convenient to 

the crew for closing the flow of air through the partitions, when necessary.

14 CFR § 125.117 Ventilation.

Each passenger or crew compartment must be suitably ventilated. Carbon monoxide 

concentration may not be more than one part in 20,000 parts of air, and fuel fumes may 

not be present. In any case where partitions between compartments have louvres or other 

means allowing air to flow between compartments, there must be a means convenient to 

the crew for closing the flow of air through the partitions when necessary.

9.2.2 Ozone Regulations

14 CFR § 25.832 Cabin ozone concentration.

(a) The airplane cabin ozone concentration during flight must be shown not to exceed—

(1) 0.25 parts per million by volume, sea level equivalent, at any time above flight level 

320; and

(2) 0.1 parts per million by volume, sea level equivalent, time-weighted average during 

any 3-hour interval above flight level 270.

(b) For the purpose of this section, "sea level equivalent" refers to conditions of 25 °C 

and 760 millimeters of mercury pressure.

(c) Compliance with this section must be shown by analysis or tests based on airplane 

operational procedures and performance limitations, that demonstrate that either—

(1) The airplane cannot be operated at an altitude which would result in cabin ozone

concentrations exceeding the limits prescribed by paragraph (a) of this section; or

(2) The airplane ventilation system, including any ozone control equipment, will maintain 

cabin ozone concentrations at or below the limits prescribed by paragraph (a) of this 

section.

14 CFR § 121.578 Cabin ozone concentration.

(a) For the purpose of this section, the following definitions apply:
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 106

(1) Flight segment means scheduled nonstop flight time between two airports.

(2) Sea level equivalent refers to conditions of 25° C and 760 millimeters of mercury 

pressure.

(b) Except as provided in paragraphs (d) and (e) of this section, no certificate holder may 

operate an airplane above the following flight levels unless it is successfully 

demonstrated to the Administrator that the concentration of ozone inside the cabin will 

not exceed—

(1) For flight above flight level 320, 0.25 parts per million by volume, sea level 

equivalent, at any time above that flight level; and

(2) For flight above flight level 270, 0.1 parts per million by volume, sea level equivalent, 

time-weighted average for each flight segment that exceeds 4 hours and includes flight 

above that flight level. (For this purpose, the amount of ozone below flight level 180 is 

considered to be zero.)

(c) Compliance with this section must be shown by analysis or tests, based on either 

airplane operational procedures and performance limitations or the certificate holder's 

operations. The analysis or tests must show either of the following:

(1) Atmospheric ozone statistics indicate, with a statistical confidence of at least 84%, 

that at the altitudes and locations at which the airplane will be operated cabin ozone 

concentrations will not exceed the limits prescribed by paragraph (b) of this section.

(2) The airplane ventilation system including any ozone control equipment, will maintain 

cabin ozone concentrations at or below the limits prescribed by paragraph (b) of this 

section.

(d) A certificate holder may obtain an authorization to deviate from the requirements of 

paragraph (b) of this section, by an amendment to its operations specifications, if—

(1) It shows that due to circumstances beyond its control or to unreasonable economic 

burden it cannot comply for a specified period of time; and

(2) It has submitted a plan acceptable to the Administrator to effect compliance to the 

extent possible.

(e) A certificate holder need not comply with the requirements of paragraph (b) of this 

section for an aircraft—

(1) When the only persons carried are flight crewmembers and persons listed in 

§121.583;

(2) If the aircraft is scheduled for retirement before January 1, 1985; or
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 107

(3) If the aircraft is scheduled for re-engining under the provisions of subpart E of part 

91, until it is re-engined.

9.2.3 Cabin Pressure Regulations

14 CFR § 25.841 Pressurized cabins.

(a) Pressurized cabins and compartments to be occupied must be equipped to provide a 

cabin pressure altitude of not more than 8,000 feet at the maximum operating altitude of 

the airplane under normal operating conditions.

(1) If certification for operation above 25,000 feet is requested, the airplane must be 

designed so that occupants will not be exposed to cabin pressure altitudes in excess of 

15,000 feet after any probable failure condition in the pressurization system.

(2) The airplane must be designed so that occupants will not be exposed to a cabin 

pressure altitude that exceeds the following after decompression from any failure 

condition not shown to be extremely improbable:

(i) Twenty-five thousand (25,000) feet for more than 2 minutes; or

(ii) Forty thousand (40,000) feet for any duration.

(3) Fuselage structure, engine and system failures are to be considered in evaluating the 

cabin decompression.

(b) Pressurized cabins must have at least the following valves, controls, and indicators for 

controlling cabin pressure:

(1) Two pressure relief valves to automatically limit the positive pressure differential to a 

predetermined value at the maximum rate of flow delivered by the pressure source. The 

combined capacity of the relief valves must be large enough so that the failure of any one 

valve would not cause an appreciable rise in the pressure differential. The pressure 

differential is positive when the internal pressure is greater than the external.

(2) Two reverse pressure differential relief valves (or their equivalents) to automatically 

prevent a negative pressure differential that would damage the structure. One valve is 

enough, however, if it is of a design that reasonably precludes its malfunctioning.

(3) A means by which the pressure differential can be rapidly equalized.

(4) An automatic or manual regulator for controlling the intake or exhaust airflow, or 

both, for maintaining the required internal pressures and airflow rates.
____ National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) _____

____________________________________________________________________________________________________________________________________________ 108

(5) Instruments at the pilot or flight engineer station to show the pressure differential, the 

cabin pressure altitude, and the rate of change of the cabin pressure altitude.

(6) Warning indication at the pilot or flight engineer station to indicate when the safe or 

preset pressure differential and cabin pressure altitude limits are exceeded. Appropriate 

warning markings on the cabin pressure differential indicator meet the warning 

requirement for pressure differential limits and an aural or visual signal (in addition to 

cabin altitude indicating means) meets the warning requirement for cabin pressure 

altitude limits if it warns the flight crew when the cabin pressure altitude exceeds 10,000 

feet.

(7) A warning placard at the pilot or flight engineer station if the structure is not designed 

for pressure differentials up to the maximum relief valve setting in combination with 

landing loads.

(8) The pressure sensors necessary to meet the requirements of paragraphs (b)(5) and 

(b)(6) of this section and §25.1447(c), must be located and the sensing system designed 

so that, in the event of loss of cabin pressure in any passenger or crew compartment 

(including upper and lower lobe galleys), the warning and automatic presentation 

devices, required by those provisions, will be actuated without any delay that would

significantly increase the hazards resulting from decompression.