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NIOSH HEALTH HAZARD EVALUATION REPORT 

HETA #2002-0354-2931 

Horizon Air 

Seattle, Washington 

February 2004 

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally

applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally

applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports

applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports
2 

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health
iii 

PREFACE

The Hazard Evaluation and Technical Assistance Branch (HETAB) of the National Institute for 

Occupational Safety and Health (NIOSH) conducts field investigations of possible health hazards in the 

workplace. These investigations are conducted under the authority of Section 20(a)(6) of the 

Occupational Safety and Health (OSHA) Act of 1970, 29 U.S.C. 669(a)(6) which authorizes the Secretary 

of Health and Human Services, following a written request from any employers or authorized 

representative of employees, to determine whether any substance normally found in the place of 

employment has potentially toxic effects in such concentrations as used or found. 

HETAB also provides, upon request, technical and consultative assistance to federal, state, and local 

agencies; labor; industry; and other groups or individuals to control occupational health hazards and to 

prevent related trauma and disease. Mention of company names or products does not constitute 

endorsement by NIOSH. 

ACKNOWLEDGMENTS AND AVAILABILITY OF REPORT

This report was prepared by Randy L. Tubbs of HETAB, Division of Surveillance, Hazard Evaluations 

and Field Studies (DSHEFS). Field assistance was provided by Chad Dowell, HETAB. Desktop 

publishing was performed by Shawna Watts. Review and preparation for printing were performed by 

Penny Arthur. 

Copies of this report have been sent to employee and management representatives at Horizon Air, the 

Association of Flight Attendants, AFL-CIO, and the Federal Aviation Administration. This report is not 

copyrighted and may be freely reproduced. The report may be viewed and printed from the following 

internet address: www.cdc.gov/niosh/hhe/hhesearch.html. Single copies of this report will be available 

for a period of three years from the date of this report. To expedite your request, include a self-addressed 

mailing label along with your written request to: 

NIOSH Publications Office 

4676 Columbia Parkway 

Cincinnati, Ohio 45226 

800-356-4674 

After this time, copies may be purchased from the National Technical Information Service (NTIS) at 5825 

Port Royal Road, Springfield, Virginia 22161. Information regarding the NTIS stock number may be 

obtained from the NIOSH Publications Office at the Cincinnati address. 

For the purpose of informing affected employees, copies of this report 

shall be posted by the employer in a prominent place accessible to the 

employees for a period of 30 calendar days.
iv

Highlights of the NIOSH Health Hazard Evaluation

Evaluation of Aircraft Cabin Noise at Horizon Air

Flight attendants requested that NIOSH evaluate noise exposures during aircraft operations. The noise 

levels encountered during flight in the Q200, Q400, and CRJ jet were measured in the front, middle, and 

rear sections of the cabin during scheduled flights. Two examples of each type of aircraft were surveyed.

What NIOSH Did

 We measured noise levels in the cabins of 

six aircraft. This was done during take-off, 

landing, and at cruising altitude. 

 We spoke to the flight attendants about their 

noise concerns. 

What NIOSH Found

 The noise levels on individual flights are not 

great enough to increase a flight attendant’s 

or passenger’s risk for hearing loss. 

 If the NVS system is not working on 

turboprop aircraft, there could possibly be 

noise overexposure. 

 The pattern of noise measured in the cabin is 

of a type that can lead to interference in 

communication between employees and 

between employees and the passengers. 

Highlights of Health Hazard Evaluation 

 Aircraft with broken NVS systems should be 

grounded until they are repaired. 

 Horizon Air should apply for approval from

the FAA for flight attendants to wear hearing 

protection devices when the NVS system does 

not operate and the aircraft must be flown. 

 Once approval for hearing protection devices 

is obtained, “musician-type” ear plugs should 

be given to a small group of flight attendants 

to see how they change listening conditions in 

the cabin. 

What the Horizon Air Employees Can Do 

 Flight attendants should report NVS systems 

that do not appear to be working. 

 Flight attendants should volunteer to wear 

specialized hearing protection devices to see if 

they improve listening conditions in the cabin. 

 Crew members should wear hearing protection 

devices whenever they are outside of the 

aircraft on the tarmac. 

What Horizon Air Managers Can Do

What To Do For More Information:

We encourage you to read the full report. If you 

would like a copy, either ask your health and 

safety representative to make you a copy or call 

1-513-841-4252 and ask for 

HETA Report #2002-0354-2931
iv

Health Hazard Evaluation Report 2002-0354-2931 

Horizon Air 

Seattle, Washington 

February 2004 

Randy L. Tubbs 

SUMMARY

A request for a health hazard evaluation (HHE) from flight attendants at Horizon Air in Seattle, 

Washington, was received by the National Institute for Occupational Safety and Health (NIOSH) on 

September 23, 2002. The flight attendants were concerned that their long work shifts may result in 

overexposure to noise from the airplanes to which they were assigned. Particular concern was noted 

about Horizon Air’s fleet of turboprop aircraft when the noise and vibration suppression (NVS) system 

was inoperable. 

An initial site visit was made to Horizon Air in Portland, Oregon on November 12, 2002, to meet with a 

management official and the local flight attendant’s union president to describe the survey. Once 

approval to operate noise measuring equipment aboard aircraft was obtained, a survey of the three types 

of aircraft used by Horizon Air, the Bombardier Q200 and Q400 turboprop and CRJ regional jet, was 

conducted from May 19-22, 2003. Two examples of each aircraft type were chosen by the company, and 

the NIOSH investigator traveled on several scheduled flights to capture noise levels in the front, middle, 

and rear of the passenger cabin. One-third octave band spectra were integrated for 15-second periods and 

stored in the noise analyzer for later analysis. Five minutes of the noise exposures encountered during 

take-off, landing, and at cruising altitude were stored for each aircraft. This measurement protocol 

allowed for the reporting of one-third octave band noise spectra for the various riding locations along with 

overall A-weighted and unweighted noise levels. An estimate of the flight attendants’ noise dose was 

calculated from the spectral measurements collected on each flight. 

Noise measurements showed that the levels encountered on individual flights were not 

enough to increase an employee’s or the public’s risk for hearing loss, and therefore, no 

health hazard was identified. Even when the noise exposures from the multiple flights 

taken by the flight attendants during a day’s schedule were combined, the attendants 

would need to take 12-24 of these flights per day before realizing an increased risk of 

occupational hearing loss. The noise results along with data published by Bombardier do 

show that the NVS system needs to be operating according to specifications to keep the 

noise levels below evaluation criteria. Recommendations about hearing protection and 

the NVS system are offered in this report. 

Keywords: SIC4512 (Air Transportation, Scheduled), flight attendants, noise, spectral levels, noise dose, 

hearing protection devices, HPDs 
Table of Contents 

Preface.........................................................................................................................................................iii

Acknowledgments and Availability of Report.........................................................................................iii

Highlights of Health Hazard Evaluation .................................................................................................iii

Summary.....................................................................................................................................................iv

Introduction.................................................................................................................................................1

Background .................................................................................................................................................1

Methods........................................................................................................................................................2

Evaluation Criteria .....................................................................................................................................2

Results ..........................................................................................................................................................4

Discussion ....................................................................................................................................................5

Conclusions..................................................................................................................................................7

Recommendations.......................................................................................................................................7

References....................................................................................................................................................8
Health Hazard Evaluation Report No. 2002-0354-2931 Page 1 

INTRODUCTION

On September 23, 2002, the National Institute 

for Occupational Safety and Health (NIOSH) 

received a confidential request from flight 

attendants to conduct a health hazard evaluation 

(HHE) at Horizon Air in Seattle, Washington. 

The requestors were concerned about the noise 

exposures encountered by flight attendants in the 

cabin of the aircraft used by the airline. Their 

concern was that flight attendants can work 12-

13 hours per day, which might expose them to 

noise for a sufficient duration to place them at 

risk for occupational hearing loss. However, 

they felt that the noise levels experienced by the 

public were most likely not hazardous because 

of the relatively short time they spend on the 

aircraft. 

A NIOSH investigator visited Horizon Air in 

Portland, Oregon, on November 12, 2002, and 

met with Horizon Air management and the 

president of the Association of Flight 

Attendants, Horizon Council 17 to discuss the 

HHE request and a plan to survey the noise 

encountered by the flight attendants. At this 

meeting, it was decided to measure area noise 

spectra in different locations of the cabin while 

transporting passengers on scheduled flights. 

Only one location in the cabin would be 

measured during a flight to minimize movement 

of the investigator within the cabin while in the 

air. After a delay in receiving approval for the 

NIOSH equipment to be used onboard during 

scheduled flights, the evaluation was conducted 

the week of May 19, 2003. At the end of the last 

day of measurements, a closing conference was 

held with company and union representatives to 

discuss the activities of the survey and show the 

kind of results that would be disseminated in the 

final report. 

BACKGROUND

Horizon Air was founded in Seattle, 

Washington, in 1981. In 1986, the company was 

acquired by Alaska Air Group, Inc., but 

remained independently managed. The general 

office is located in Seattle and its primary 

maintenance base is in Portland, Oregon. It 

currently has about 4000 employees and serves 

more than 40 cities in the Pacific Northwest. 

The fleet consists of 37-seat Bombardier Q200 

and 70-seat Bombardier Q400 turboprop aircraft 

and 70-seat Bombardier CRJ-700 regional jets. 

The Fairchild F-27 turboprop aircraft had been 

phased out of Horizon Air’s fleet at the time of 

the HHE and was not included in any of the 

measurements. The Q200 has two turboprop 

engines with four-blade propellers. The wings 

connect to the top of the fuselage near the 

middle of the cabin. The Q200 has a maximum 

cruise speed of 334 miles per hour (mph). The 

Q400 has two turboprop engines with six-blade 

propellers. The wings connect in a manner 

similar to the Q200 aircraft. The Q400 has a 

maximum cruise speed of 414 mph. The CRJ700 has two turbofan jet engines that connect to 

the fuselage near the rear of the aircraft. The 

regional jets have a maximum cruise speed of 

544 mph. On the Q200, the flight attendant seat 

is next to the main cabin door facing the rear of 

the aircraft. On the Q400, there is the same seat 

forward and also a second jumpseat in the galley 

between the two aft exit doors. On the CRJ-700, 

one flight attendant seat is next to the main cabin 

door behind the cockpit door facing the rear of 

the aircraft. The other flight attendant seat is 

forward facing in the back of the plane next to 

the lavatory. 

Both styles of turboprop aircraft are equipped 

with a noise and vibration suppression (NVS) 

system that reduces the vibrations in the 

fuselage, which stops much of the noise from 

reaching the cabin through an active control 

technology. During flight, microphones 

throughout the cabin transmit noise information 

to a computer. Additional information on 

propeller speed is also fed to the computer. The 

computer continuously analyzes this information 

and sends signals to active tuned vibration 

absorbers mounted on the fuselage frame. The 

absorbers produce vibration that is 180° out of 

phase with the engine vibrations, thus reducing 
Page 2 Health Hazard Evaluation Report No. 2002-0354-2931 

the original vibrations before they are 

transmitted to the passenger cabin. 

The concerned flight attendants reported 

experiencing pain and ringing in their ears by 

the end of their shift. The noise reportedly was 

particularly bad on the smaller Q200 aircraft. 

Often the employees had to work on turboprop 

aircraft with the NVS system out of order which 

made the noise situation worse. The attendants 

reported that the airline did not allow them to 

wear hearing protection devices (HPDs) to 

protect their ears from the noise. 

METHODS

A flight schedule was arranged by Horizon Air 

which allowed the NIOSH investigator to be on 

three consecutive flights of the same aircraft. 

This schedule was repeated for two different 

aircraft from each of the three types flown by the 

company. Thus, the first two days of the survey 

were spent measuring noise levels in two Q200 

and two Q400 airplanes. The regional jet 

measurements were made on the last two days of 

the survey. Because of scheduling changes on 

the second day of regional jet measurements, the 

third leg of the CRJ-700 was made on a different 

aircraft than the first two legs of the itinerary. 

On each aircraft tested, the NIOSH investigator 

was seated in a front, middle, or back location in 

the cabin during an entire leg of the flight 

collecting spectral noise measurements during 

takeoff and landing, and at cruising altitude. 

The spectral noise measurements were made 

with a Larson-Davis Laboratory Model 2800 

Real-Time Analyzer and a Larson-Davis 

Laboratory Model 2559 1⁄2" random incidence 

response microphone. The microphone was 

connected to the analyzer with a 6-ft. cable. The 

analyzer allows for the analysis of noise into its 

spectral components in a real-time mode. The 

1⁄2"-diameter microphone has a frequency 

response range (± 2 decibels [dB]) from 4 Hertz 

(Hz) to 21 kilohertz (kHz) that allows for the 

analysis of sounds in the region of concern. 

One-third octave bands consisting of center 

frequencies from 25 Hz to 20 kHz were 

integrated for 15 seconds and stored in the 

analyzer. The analyzer was set in the auto-store 

mode so that a 15-second sample was 

automatically stored at the end of the period and 

the analyzer reset to instantly begin the next 15-

second sample period. The series of sample 

periods was continued for a total of 5 minutes, 

thus yielding 20 samples for each of the aircraft 

activities. Takeoff sampling was started when 

the aircraft first began to move on the runway 

and ended 5 minutes later. Samples taken at 

cruise altitude were collected once the aircraft 

had leveled off in the sky for a period of 5 

minutes. Finally, landing samples began when 

the pilot lowered the landing gear and continued 

for 5 minutes or, in some cases, until the aircraft 

came to a stop at the gate. 

EVALUATION CRITERIA

As a guide to the evaluation of the hazards posed 

by workplace exposures, NIOSH field staff 

employ environmental evaluation criteria for the 

assessment of a number of chemical and 

physical agents. These criteria are intended to 

suggest levels of exposure to which most 

workers may be exposed up to 10 hours per day, 

40 hours per week for a working lifetime 

without experiencing adverse health effects. It 

is, however, important to note that not all 

workers will be protected from adverse health 

effects even though their exposures are 

maintained below these levels. A small 

percentage may experience adverse health 

effects because of individual susceptibility, a 

pre-existing medical condition, and/or a 

hypersensitivity (allergy). In addition, some 

hazardous substances may act in combination 

with other workplace exposures, the general 

environment, or with medications or personal 

habits of the worker to produce health effects 

even if the occupational exposures are controlled 

at the level set by the criterion. These combined 

effects are often not considered in the evaluation 

criteria. Finally, evaluation criteria may change 

over the years as new information on the toxic 

effects of an agent become available. 

The primary sources of environmental 

evaluation criteria for the workplace are: (1) 

NIOSH Recommended Exposure Limits 
Health Hazard Evaluation Report No. 2002-0354-2931 Page 3

(RELs),1

 (2) the American Conference of 

Governmental Industrial Hygienists’ (ACGIH®) 

Threshold Limit Values (TLVs®),2

 and (3) the 

U.S. Department of Labor, Occupational Safety 

and Health Administration (OSHA) Permissible 

Exposure Limits (PELs).3

 Employers are 

encouraged to follow the OSHA limits, the 

NIOSH RELs, the ACGIH TLVs, or whichever 

are the more protective criteria. 

OSHA requires an employer to furnish 

employees a place of employment that is free 

from recognized hazards that are causing or are 

likely to cause death or serious physical harm 

[Occupational Safety and Health Act of 1970, 

Public Law 91–596, sec. 5(a)(1)]. Thus, 

employers should understand that not all 

hazardous chemicals have specific OSHA 

exposure limits such as PELs and short-term 

exposure limits (STELs). An employer is still 

required by OSHA to protect their employees 

from hazards, even in the absence of a specific 

OSHA PEL. 

Noise-induced loss of hearing is an irreversible, 

sensorineural condition that progresses with 

exposure. Although hearing ability declines with 

age (presbycusis) in all populations, exposure to 

noise produces hearing loss greater than that 

resulting from the natural aging process. This 

noise-induced loss is caused by damage to nerve 

cells of the inner ear (cochlea) and, unlike some 

conductive hearing disorders, cannot be treated 

medically.4

 While loss of hearing may result 

from a single exposure to a very brief impulse 

noise or explosion, such traumatic losses are 

rare. In most cases, noise-induced hearing loss 

is insidious. Typically, it begins to develop at 

4000 or 6000 Hz (the hearing range is 20 Hz to 

20000 Hz) and spreads to lower and higher 

frequencies. Often, material impairment has 

occurred before the condition is clearly 

recognized. Such impairment is usually severe 

enough to permanently affect a person's ability 

to hear and understand speech under everyday 

conditions. Although the primary frequencies of 

human speech range from 200 Hz to 2000 Hz, 

research has shown that the consonant sounds, 

which enable people to distinguish words such 

as "fish" from "fist," have still higher frequency 

components.5

The A-weighted decibel (dBA) is the preferred 

unit for measuring sound levels to assess worker 

noise exposures. The dBA scale is weighted to 

approximate the sensory response of the human 

ear to sound frequencies near the threshold of 

hearing. The decibel unit is dimensionless, and 

represents the logarithmic relationship of the 

measured sound pressure level (SPL) to an 

arbitrary reference sound pressure (20 

micropascals, the normal threshold of human 

hearing at a frequency of 1000 Hz). Decibel 

units are used because of the very large range of 

sound pressure levels which are audible to the 

human ear. Because the dBA scale is 

logarithmic, increases of 3 dBA, 10 dBA, and 20 

dBA represent a doubling, tenfold increase, and 

100-fold increase of sound energy, respectively. 

It should be noted that noise exposures 

expressed in decibels cannot be averaged by 

taking the simple arithmetic mean. 

The OSHA standard for occupational exposure 

to noise (29 CFR 1910.95)6

 specifies a 

maximum PEL of 90 dBA for a duration of 8 

hours per day. The regulation, in calculating the 

PEL, uses a 5 dB time/intensity trading 

relationship, or exchange rate. This means that a 

person may be exposed to noise levels of 95 

dBA for no more than 4 hours, to 100 dBA for 2 

hours, etc. Conversely, up to 16 hours exposure 

to 85 dBA is allowed by this exchange rate. The 

duration and sound level intensities can be 

combined in order to calculate a worker's daily 

noise dose according to the formula: 

Dose = 100 X (C1/T1 + C2/T2 + ... + Cn/Tn ), 

where Cn indicates the total time of exposure at a 

specific noise level and Tn indicates the 

reference duration for that level as given in 

Table G-16a of the OSHA noise regulation. 

During any 24-hour period, a worker is allowed 

up to 100% of his daily noise dose. Doses 

greater than 100% are in excess of the OSHA 

PEL. 

The OSHA regulation has an additional action 

level (AL) of 85 dBA; an employer shall 

administer a continuing, effective hearing 

conservation program when the 8-hour timeweighted average (TWA) value exceeds the AL. 
Page 4 Health Hazard Evaluation Report No. 2002-0354-2931 

The program must include monitoring, 

employee notification, observation, audiometric 

testing, hearing protectors, training, and record 

keeping. All of these requirements are included 

in 29 CFR 1910.95, paragraphs (c) through (o). 

Finally, the OSHA noise standard states that 

when workers are exposed to noise levels in 

excess of the OSHA PEL of 90 dBA, feasible 

engineering or administrative controls shall be 

implemented to reduce the workers' exposure 

levels. 

NIOSH, in its Criteria for a Recommended 

Standard,7

 and the ACGIH,2 propose exposure 

criteria of 85 dBA as a TWA for 8 hours, 5 dB 

less than the OSHA standard. The criteria also 

use a more conservative 3 dB time/intensity 

trading relationship in calculating exposure 

limits. Thus, a worker can be exposed to 85 

dBA for 8 hours, but to no more than 88 dBA 

for 4 hours or 91 dBA for 2 hours. Twelve-hour 

exposures have to be 83 dBA or less according 

to the NIOSH REL.

RESULTS

Fifteen-second, one-third octave band samples 

of the cabin noise were collected for 5 minutes 

each during take-off, landing, and at cruise 

altitude for the Q200, Q400, and CRJ aircraft. 

These noise samples were obtained in three 

different seat locations in each aircraft; the front, 

middle, and rear of the cabin. Each individual 

sample contains the 1/3 octave band sound 

levels from 25 Hz through 20000 Hz along with 

the overall unweighted SPL and the overall dBA 

levels. The overall median SPLs measured for 

the Q200, Q400, and CRJ were 96.6 dB, 93.4 

dB, and 93.3 dB, respectively, for all seat (front, 

middle, and back) and operation (take-off, 

cruise, and landing) conditions. For noise 

measurements made with the A-weighting 

function applied, the three aircraft types had 

median levels of 80.7 dBA, 80.9 dBA, and 80.0 

dBA for the Q200, Q400, and CRJ, respectively, 

across all conditions. For the turboprop aircraft, 

these measurements were obtained with the 

NVS operational. 

To further define the noise measurements, the 

data were analyzed by flight activity and seat 

location for each aircraft type. These data are 

presented in Table 1. There was little difference 

in the A-weighted noise levels at cruise altitude 

between the three aircraft types. The highest 

measured median levels were 83.8 dBA, 83.2 

dBA, and 84.3 dBA for the Q200, Q400, and 

CRJ, respectively. These levels were measured 

in the front of the passenger compartment for the 

two turboprop aircraft and in the rear area of the 

commuter jet. Comparisons between the 

weighted and unweighted noise levels found 

relatively large differences. At cruising altitude, 

the Q200 noise levels were 17.4 dB higher for 

the unweighted measurements, 14.5 dB higher in 

the Q400, and 15.4 dB higher in the CRJ. The 

spectral data from the three aircraft types reveal 

the high levels of low frequency sound as shown 

in Figures 1-3. The low frequency noise 

component is more pronounced in the turboprop 

aircraft. For the Q200, maximum SPL is seen at 

63 and 80 Hz, along with a maximum at the 

harmonic frequencies of 125 and 160 Hz. For 

the Q400, the maximum SPL is at 80 Hz. The 

CRJ does not exhibit such a distinct maximum 

SPL. The highest level was recorded at 100 Hz 

during aircraft operations at cruise altitude. 

During take-off, the highest median noise levels 

for the five-minute measurement period were 

81.7 dBA, 83.7 dBA, and 83.1 dBA for the 

Q200, Q400, and CRJ, respectively (Table 1). 

The seat location where these measurements 

were captured was in the front for the Q200 and 

in the rear of the passenger compartment for the 

Q400 and CRJ. During landing, the highest 

median noise levels for the three aircraft were 

found to be less intense. Levels of 79.9 dBA, 

79.6 dBA, and 78.9 dBA were measured in the 

same seat locations as for take-off in the Q200, 

Q400, and CRJ, respectively. The above noise 

levels are median values over the entire fiveminute measurement periods which do not take 

into account the individual variations in noise 

emissions during take-off and landing 

operations. Inspection of each 15-second 

measurement revealed similar patterns in the 

three aircraft surveyed. The highest levels for 

the Q200 were 87.0 dBA and 88.2 dBA for takeoff (middle seat) and landing (front seat) during 
Health Hazard Evaluation Report No. 2002-0354-2931 Page 5

a 15-second measurement. These maximum 

levels consistently occurred during the first 30 

seconds of take-off and during the 45 seconds 

following touchdown on the runway. For the 

Q400, the highest take-off measurement was 

91.8 dBA in a middle seat and 88.4 dBA in a 

back seat. The same pattern of occurrence 

during take-off and landing operations was seen 

in the Q400 as was observed in the Q200. The 

maximum levels measured during take-off and 

landing occurred later in the operation for the 

CRJ. The highest measurements were 90.0 dBA 

during take-off and 90.3 dBA during landing, 

both in a middle seat. These maximum levels 

generally happened 2-3 minutes after the aircraft 

initiated movement on the runway during takeoff and about 1 minute after touchdown. 

To compare the flight attendants noise exposures 

to the NIOSH evaluation criteria, dose 

calculations for each of the five-minute 

measurement periods were made according to 

the NIOSH REL formula. The allowable time 

(T) at the measured dBA level (L) was 

determined according to the following formula.7

 480 

T(min) = 

 2 (L-85) / 3

The accumulated dose for each flight leg was 

calculated by adding the dose at take-off with 

the dose measured during landing along with the 

noise dose accumulated during the time at 

cruising altitude. For the calculations, it was 

assumed that the 5 minutes measured at cruising 

altitude would be representative of the complete 

time the aircraft was in the air. Therefore, the 

landing and take-off times were subtracted from 

the total flight time. The remaining time was 

used to prorate the dose that would accumulate 

during the total cruising altitude period. For 

example, for a 60-minute flight, the take-off 

time (5 minutes) and landing time (5 minutes) 

are subtracted from the total flight time leaving 

50 minutes of cruising altitude time. The 

accumulated dose for the measured five-minute 

period is multiplied by 10 (10, five-minute 

periods in the remaining 50 minutes of cruising 

altitude) giving the dose for cruising. The 

cruising dose is added to the landing dose and 

the take-off dose, yielding the total dose for that 

particular flight. These values for the three 

riding positions in each of the six aircraft 

evaluated during the survey are shown in Table 

2. Flight times ranged from 15 minutes to 98 

minutes. The shortest measured flights of 15 

minutes yielded an accumulated dose of less 

than 1%. The maximum dose calculated for the 

flights was 11.44% for an approximate one-hour 

flight in the back of a Q400. If this dose was the 

only noise to which an individual was exposed 

on that day, this would equate to an 8-hour 

TWA of 75.6 dBA. 

DISCUSSION

The highest median noise levels for all three 

types of aircraft measured at cruising altitude 

were 83-84 dBA over the five-minute 

measurement period. Noise levels were 

measured between 87 and 92 dBA during takeoff and landing operations. While some of these 

noise levels exceed the NIOSH and OSHA 

recommendations and regulations,1,6 it should be 

noted that these reported values are for very 

short time frames, 15 seconds or 5 minutes. To 

compare these measured noise levels to the 

criteria, the person would have to be constantly 

exposed to the noise for 8 hours to produce a 

TWA. However, both flight attendants and 

airline customers are not constantly exposed to 

these noise levels. The data in Table 2 show the 

longest flight taken during this survey was 98 

minutes which accounted for 6.0% – 6.5% of a 

daily noise dose which is allowed to reach 100% 

and still be within the REL. For the airline 

customer, these individual flight exposures 

represent very little risk for hearing loss. The 

highest measured dose was 11.4% for a onehour flight in the rear of the Q400. The flight 

crew on this same flight was also on the other 

two legs of the Q400 for that day and they 

would have accrued a total of 24.1% of their 

daily noise dose during this schedule. Using this 

group of flights as an example, a crew could fly 

these three legs up to four times in a day and still 

not exceed the NIOSH REL. For the flight 

attendants on the Q200, the three legs yielded 

accumulated noise doses of 8.9% and 12.5% for 

flight times of 99 and 107 minutes, respectively. 
Page 6 Health Hazard Evaluation Report No. 2002-0354-2931 

A crew would be able to fly this triad flight 

schedule eight times in a day and be equal to the 

NIOSH REL. On the longer CRJ flights, the 

attendants accrued a total of 19.0% and 17.4% 

daily noise doses for the three flight legs 

equaling 213 and 211 minutes, respectively. 

This kind of schedule could be repeated five 

times in a day and result in noise levels below 

the REL. 

A major complaint reported in the HHE request 

by the flight attendants was flying the turboprop 

aircraft when the NVS system was not 

operating. This condition did not occur during 

the NIOSH evaluation. However, it is possible to 

reasonably predict what the noise levels would 

be if the system was not operational. The maker 

of the Q200 and Q400 has information on their 

website about the noise suppression capabilities 

of the NVS system.8

 They supply a figure on 

the harmonic components of the aircraft cabin 

noise both with and without the NVS activated. 

At 80 Hz, one of the predominant frequencies 

measured in the Q200 and Q400 in this survey 

(Figure 1 and 2), they report a noise reduction of 

11.3 dB afforded by the suppression system. At 

160 Hz, the reduction is reported at 17.0 dB. 

This noise suppression system is necessary to 

keep the cabin noise below the OSHA and 

NIOSH noise criteria. A 10-15 dBA increase in 

cabin noise would change the levels measured at 

cruising altitude in this survey to 93-98 dBA, 

which would increase the risk of potential 

hearing damage to employees if the exposures 

were allowed to continue for long periods. At 

98 dBA, the NIOSH REL allows a daily 

exposure for 23 minutes and 49 seconds, a time 

period well within the flight attendants’ routine 

flight schedules. 

The Federal Aviation Administration (FAA), 

U.S. Department of Transportation, published a 

Federal Register notice in 1975 asserting its 

complete and exclusive responsibility for the 

regulation of occupational safety and health 

standards of employees engaged in civil aircraft 

operations.9

 Because OSHA has statutory 

authority governing the occupational safety and 

health of most employees, the FAA and OSHA 

entered into a Memorandum of Understanding in 

August 2000 to establish a procedure for 

coordinating and supporting enforcement of the 

Occupational Safety and Health Act with respect 

to the working conditions of employees on 

aircraft in operation (other than flight deck crew) 

and for resolving jurisdictional questions. An 

FAA / OSHA Aviation Safety and Health Team 

was formed and a report was issued in 

December 2000. Included in this report was a 

section on occupational exposure to noise where 

the team looked at the application of OSHA’s 

general industry standards on occupational noise 

to employees on aircraft in operation. Although 

the team reports that they have no data as to the 

levels of noise encountered by employees during 

operation, they felt that many of the OSHA 

provisions, such as training and testing, could be 

applied without any effect on aviation safety. 

However, the team felt that engineering and 

administrative controls and the use of HPDs 

would impact aviation safety and would 

therefore require FAA approval. On June 18, 

2002, the Aviation Safety and Health Team 

released an Action Plan proposing an Aviation 

Safety and Health Partnership Program which 

would expand the FAA’s role in worker safety 

and health issues. OSHA’s role in this program 

would be advisory only. On May 15, 2003, the 

FAA issued a Departmental Order (1110.134) 

describing a voluntary Aviation Safety and 

Health Partnership Program (ASHPP) with a 

rulemaking committee consisting of members 

from the FAA, air carriers, and air carrier 

employee unions. 

While it appears that the use of HPDs during 

airborne operations by flight attendants requires 

FAA approval, the noise levels measured in this 

HHE survey show that they may not be 

necessary to protect the hearing of the 

employees under normal operating 

circumstances. The noise intensities and the 

flight durations do not exceed the NIOSH REL 

for occupational noise. However, the use of 

specialized HPDs by flight attendants may help 

improve communication conditions between 

attendants and between the attendants and the 

passengers. The spectral noise data show three 

or four third-octave bands that are greater than 

the rest of the bands, particularly for the 

turboprop aircraft (Figures 1-2). These 

predominant bands are low frequency sounds, 
Health Hazard Evaluation Report No. 2002-0354-2931 Page 7

between the 63 and 250 Hz center frequencies. 

They will mask the speech levels contained 

within these bands as well as mask higher 

frequency speech signals due to an upward 

spread of masking.10 The NIOSH spectral data 

are confirmed by the data reported by the 

manufacturer.8

 There are HPDs on the market 

that are characterized as flat spectrum, moderate 

attenuation devices, sometimes referred to as 

“musician earplugs”.11 They offer levels of 

attenuation from 9 – 25 dB and tend to lower 

sound equally over the entire spectrum. Thus, 

they do not have the characteristic shape of 

increasingly higher attenuation of sound in the 

high frequencies. For the turboprop aircraft, this 

type of HPD would reduce the low frequency 

sound that tends to mask speech while not 

adversely lowering the higher frequencies that 

contain consonant sound information. 

CONCLUSIONS

The results of this survey show that the flight 

attendants who work on the Q200 and Q400 

turboprop aircraft and the CRJ regional jet 

should not be exposed to enough hazardous 

noise in the passenger cabin during normal flight 

operations (including a fully functional NVS 

system) to adversely affect their hearing. The 

noise doses calculated from the data demonstrate 

that flight attendants could fly 12 to 24 legs per 

day, five days a week, of the type surveyed by 

NIOSH in this evaluation. It must be noted that 

measurements were not made for other 

situations where flight attendants may receive 

additional noise exposures, such as when aircraft 

are parked on the tarmac waiting for customers 

to board and disembark the aircraft. These noise 

doses would be added to the values calculated 

for the cabin during flight operations to calculate 

the daily noise burden. For the general public 

who fly only 1-3 legs in a day, there is no risk 

for hearing loss solely from the exposures that 

they would encounter in the aircraft surveyed. 

The use of HPDs by the flight attendants is not 

necessary to protect them from noise 

experienced in the cabin under normal operating 

conditions. However, when the NVS system is 

not operating on the Q200 or Q400, the noise 

levels could be intense enough to warrant their 

use. Also, the noise levels around the aircraft 

while they are parked on the tarmac are loud 

enough to necessitate the use of HPDs by crew 

members who must walk around the aircraft.12

The flight attendants may also want to try some 

of the moderate attenuation, flat spectrum 

devices available on the market to help improve 

communications during flight operations. 

However, FAA approval appears necessary for 

HPD use by the flight attendants. 

RECOMMENDATIONS

Based on the findings and observations of this 

evaluation and on other research published on 

airline noise exposures, the following 

recommendations are offered to Horizon Air to 

improve the work environment of their flight 

attendants. 

1. The NVS system on the turboprop 

aircraft is necessary to keep cabin noise levels 

below workplace regulations and guidelines. 

The flight crew needs to report system 

malfunctions to maintenance immediately when 

they feel the system is not working. Horizon Air 

should take these aircraft out of service until 

repairs are made because the increased noise 

levels will exceed workplace regulations within 

the time period that these aircraft normally fly 

between scheduled destinations. If they must be 

flown, HPDs should be available to the crew and 

the passengers to reduce exposures until the 

NVS system is operational. If FAA approval is 

necessary for HPD usage, then the company 

should begin to seek approval as soon as is 

possible to prevent noise overexposures during 

equipment malfunction. 

2. If FAA approval of hearing protection is 

obtained for the flight attendants, a small 

program should be initiated to evaluate the flight 

attendants perceptions of changes in 

communications between attendants and pilots, 

attendants and passengers, and between 

themselves when the musician-type ear plugs are 

worn during all or part of the flight. 
Page 8 Health Hazard Evaluation Report No. 2002-0354-2931 

3. Hearing protection should be available 

to all flight crew members for use whenever 

personnel are required to leave the aircraft and 

move about the tarmac. Several of the airports 

surveyed by NIOSH had commuter aircraft park 

on the tarmac in close proximity to each other. 

Even if the aircraft to which a crew member is 

assigned has turned off its engines, adjacent 

aircraft may still be producing high levels of 

noise. Additional noise can come from ground 

equipment used during operations, such as 

ground power units (GPUs) and air-conditioning 

carts. 

REFERENCES

 1. NIOSH [1992]. Recommendations for 

occupational safety and health: compendium of 

policy documents and statements. Cincinnati, 

OH: U.S. Department of Health and Human 

Services, Public Health Service, Centers for 

Disease Control and Prevention, National 

Institute for Occupational Safety and Health, 

DHHS (NIOSH) Publication No. 92-100. 

 2. ACGIH [2003]. 2003 TLVs® and BEIs®: 

threshold limit values for chemical substances 

and physical agents and biological exposure 

indices. Cincinnati, OH: American Conference 

of Governmental Industrial Hygienists. 

 3. CFR [1997]. 29 CFR 1910.1000. Code of 

Federal Regulations. Washington, DC: U.S. 

Government Printing Office, Office of the 

Federal Register. 

 4. Ward WD, Royster LH, Royster JD [2000]. 

Anatomy & physiology of the ear: normal and 

damaged hearing. Chapter 4. In: Berger EH, 

Royster LH, Royster JD, Driscoll DP, & Layne 

M, eds. The noise manual. 5th ed. Fairfax, 

VA: American Industrial Hygiene Association, 

pp 101–122. 

 5. Suter AH [1978]. The ability of mildly 

hearing–impaired individuals to discriminate 

speech in noise. Washington, DC: U.S. 

Environmental Protection Agency, Joint 

EPA/USAF study, EPA 550/9–78–100, 

AMRL –TR–78–4. 

 6. CFR [1997]. 29 CFR 1910.95. Code of 

Federal Regulations. Washington, DC: U.S. 

Government Printing Office, Office of the 

Federal Register. 

 7. NIOSH [1998]. Criteria for a 

recommended standard: occupational noise 

exposure (revised criteria 1998). Cincinnati, 

OH: U.S. Department of Health and Human 

Services, Centers for Disease Control and 

Prevention, National Institute for Occupational 

Safety and Health, DHHS (NIOSH) Publication 

No. 98-126. 

 8. Bombardier Aerospace [2003]. Regional 

Aircraft / Q Series / Noise and Vibration 

Suppression System. World Wide Web 

[URL=http://www.bombardier.com/en/3_0/3_1/

3_1_2_1_2.html], December. 

 9. 40 Fed. Reg. 29114 [1975]. Federal 

Aviation Administration: Occupational Safety 

or Health Standards for Aircraft Crewmembers. 

Washington, DC: U.S. Government Printing 

Office, Office of the Federal Register. 

 11. Egan JP, Hake HW [1950]. On the 

masking pattern of a simple auditory stimulus. 

Journal of the Acoustical Society of America. 

Vol. 22(5):622-630. 

 11. Hager LD [2003]. Hearing conservation - 

Encouraging compliance. Advance for 

Audiologists, Merion Publications, Inc.: King 

of Prussia, PA, November/December, 32-34. 

 12. Tubbs RL [2000]. Noise exposure to 

airline ramp employees. In Tharr, D.G., Ed. 

Case Studies: Applied Occupational and 

Environmental Hygiene. Vol. 15(9):657-663.
Health Hazard Evaluation Report No. 2002-0354-2931 Page 9

Table 1 

Median Noise Levels for Seat Location and Operation in Each Aircraft Type 

Horizon Air 

Seattle, WA 

HETA 2002-0354 

 May 19-22, 2003 

Flight 

Operation 

Seat 

Location 

Q200 Q400 CRJ 

 dB SPL dBA dB SPL dBA dB SPL dBA 

Take-off 

 Front 97.9 81.7 92.1 78.9 83.8 75.8 

 Middle 95.8 79.8 95.0 81.9 92.5 79.9 

 Back 100.5 80.4 97.7 83.7 97.8 83.1 

 

Cruise 

 Front 101.2 83.8 90.9 83.2 84.0 80.1 

 Middle 92.9 78.7 93.8 82.7 95.9 80.5 

 Back 99.2 81.2 97.0 82.5 95.5 84.3 

 

Landing 

 Front 90.5 79.9 87.7 77.3 89.7 74.6 

 Middle 88.3 75.8 89.7 75.3 94.5 77.6 

 Back 93.4 78.2 93.5 79.6 92.6 78.9 

The median overall noise levels, both unweighted (dB SPL) and weighted (dBA), from the real-time 

analyzer are shown for the three riding positions during each of the three flight operations. The Q200 and 

Q400 are turboprop aircraft and the CRJ is a regional jet aircraft. 
Page 10 Health Hazard Evaluation Report No. 2002-0354-2931 

Table 2 

Accumulated Noise Doses for Seat Location in Each Aircraft 

Horizon Air 

Seattle, WA 

HETA 2002-0354 

 May 19-22, 2003 

Aircraft Seat Origin Destination Flight Time 

[min] Dose 8-hr TWA[dBA] 

Q200 - #360 

 

 1B Portland Pendleton 41 4.83% 71.8 

 4D Pendleton Pasco 15 0.70% 63.5 

 8E Pasco Portland 43 3.39% 70.3 

Q200 - #354 

 

 1B Portland Pendleton 42 7.47% 73.7 

 5E Pendleton Pasco 15 0.97% 64.8 

 8E Pasco Portland 50 4.09% 71.1 

Q400 - #407 

 

 1B Portland Redding 63 6.70% 73.3 

 8A Redding Eureka/Arcata 27 2.32% 68.6 

 18E Eureka/Arcata Portland 61 5.50% 72.4 

Q400 - #413 

 

 1B Portland Redding 61 9.15% 74.6 

 8D Redding Eureka/Arcata 24 3.54% 70.5 

 17E Eureka/Arcata Portland 63 11.44% 75.6 

CRJ - #604 

 

 1B Seattle/Tacoma Fresno 98 6.03% 72.8 

 9A Fresno Portland 85 6.71% 73.3 

 15D Portland Seattle/Tacoma 30 6.28% 73.0 

CRJ - #605 

 

 1B Seattle/Tacoma Fresno 98 6.54% 73.2 

 9A Fresno Portland 89 6.86% 73.4 

 #614 15D Portland Seattle/Tacoma 32 3.96% 71.0 

The calculated dose percentages were obtained from the spectral data collected on the aircraft and are 

shown for each flight taken by the NIOSH investigator. The dose from the five minute take-off period 

plus the dose from the five minute landing period were added to the dose calculated for the cruising 

altitude value over the remaining flight time period. The 8-hr TWA is calculated from the dose 

percentage according to the NIOSH formulation. 
Health Hazard Evaluation Report No. 2002-0354-2931 Page 11

31.5

6

3

12

5

2

5

0

5

0

0

10

0

0

2

0

0

0

4

0

0

0

8

0

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16

0

0

0

1/3 Octave Band Center Frequency [Hz]

40

50

60

70

80

90

100

110

S

oun

d

Pre

s

sure

L

e

v

el [d

B]

Figure 1

One-Third Octave Band Spectra

Q 200 - Cruise Altitude, Front of Cabin

Horizon Airlines

Seattle, WA

May 19-22, 2003

31.5

6

3

12

5

2

5

0

5

0

0

10

0

0

2

0

0

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4

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8

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16

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1/3 Octave Band Center Frequency [Hz]

40

50

60

70

80

90

100

110

S

o

u

n

d

Pre

s

s

ure

L

e

v

el [d

B]

Figure 2

One-Third Octave Band Spectra

Q 400 - Cruise Altitude, Front of Cabin

Horizon Airlines

Seattle, WA

May 19-22, 2003
Page 12 Health Hazard Evaluation Report No. 2002-0354-2931 

31.5

6

3

12

5

2

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5

0

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0

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1/3 Octave Band Center Frequency

40

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100

110

S

o

u

n

d

Pre

s

s

ure

L

e

v

el d[ B]

Figure 3

One-Third Octave Band Spectra

CRJ - Cruise Altitude, Rear of Cabin

Horizon Airlines

Seattle, WA

May 19-22, 2003

Each of the three figures shows the riding position on each aircraft that yielded the maximum noise 

spectrum. 
DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention National Institute for Occupational Safety and Health 4676 Columbia Parkway Cincinnati, OH 45226-1998 OFFICIAL BUSINESS Penalty for private use $300 

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contact NIOSH at: 

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