Evaluation of Potential 

Noise Hazards to 

Mechanics and 911 

Dispatchers at a Fire 

Department 

Chandran Achutan, Ph.D 

Chucri A. Kardous, MS, PE 

Health Hazard Evaluation Report 

HETA 2007-0235-3064 

Anchorage Fire Department 

Anchorage, Alaska 

June 2008 

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

Workplace

Safety and Health

 National Institute for Occupational 

Safety and Health 

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/ 
The employer shall post a copy of this report 

for a period of 30 calendar days at or near 

the workplace(s) of affected employees. The 

employer shall take steps to insure that the 

posted determinations are not altered, defaced, 

or covered by other material during such 

period. [37 FR 23640, November 7, 1972, as 

amended at 45 FR 2653, January 14, 1980]. 
Contents
 

RepoRt
 Abbreviations........................................................................ii
 

Highlights.of.the.NIOSH.Health.Hazard.Evaluation............. iii
 

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

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

Assessment..........................................................................1
 

Results.and.Discussion........................................................4
 

Conclusions........................................................................12
 

Recommendations..............................................................13
 

References.........................................................................14
 

Appendix Occupational.Exposure.Limits.and.Health.Effects..............15
 

ACknowledgments Acknowledgements.and.Availability.of.Report....................20
 

Health Hazard Evaluation Report 2007--0235-3064 Page  
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

AbbReviAtions
 

" inch 

AFD Anchorage Fire Department 

AL Action level 

B&K Brüel & Kjær 

CFR Code of Federal Regulations 

dB Decibels 

dBA Decibels, A-weighted scale 

HCP Hearing conservation program 

HHE Health hazard evaluation 

HPD Hearing protection devices 

Hz Hertz 

KEMAR Knowles Electronic Mannequin for Acoustic Research 

kHz Kilohertz 

Leq Equivalent continuous noise level 

Lpeak Peak noise level 

MP3 Moving Picture Experts Group layer 3 

mV Millivolt 

NAICS North American Industry Classification System 

NCB Balanced noise criteria 

NIHL Noise-induced hearing loss 

NIOSH National Institute for Occupational Safety and Health 

OEL Occupational exposure limit 

OSHA Occupational Safety and Health Administration 

PEL Permissible exposure limit 

REL Recommended exposure limit 

SPL Sound pressure level 

TWA Time-weighted average 

V Volt 

Page  Health Hazard Evaluation Report 2007-0235-3064 
HigHligHts of tHe 

niosH HeAltH 

HAzARd evAluAtion 

The National Institute for 

Occupational Safety and 

Health (NIOSH) received a 

management request for 

a health hazard evaluation 

at the Anchorage Fire 

Department (AFD) in 

Anchorage, Alaska. The 

department submitted 

the request because 

its 911 dispatchers 

were concerned 

about feedback noise 

from communication 

headsets, and because 

it wanted to know if its 

mechanics should be in 

a hearing conservation 

program. A NIOSH 

investigator conducted an 

investigation at the AFD 

facilities in May 2007. 

What NIOSH Did 

●	 We monitored mechanics’ noise exposure. 

●	 We measured noise levels in the dispatch area. 

●	 We interviewed 911 dispatchers. 

●	 We looked at worker injury and illness records for trauma 

to the ears. 

●	 We looked at 911 dispatchers’ hearing test results for signs 

of hearing loss. 

●	 We tested 911 dispatchers’ headsets for sound quality and 

response. 

●	 We studied samples of feedback noise heard by 911 

dispatchers.
 

What NIOSH Found 

●	 Mechanics’ exposure to noise was above the NIOSH 

recommended exposure limit.
 

●	 Most of the mechanics’ noise exposures occurred over a 

short time period. 

●	 The potential for harm to 911 dispatchers’ hearing was low 

although the feedback noise was low. 

What AFD Managers Can Do 

●	 Enroll mechanics in a hearing conservation program. 

●	 Train employees on the proper use of radios. 

●	 Consider building a communications center just for the 

911 dispatchers, or modify the existing center to meet 

recommended noise criteria for buildings. 

What AFD Employees Can Do 

●	 Mechanics should wear ear plugs or ear muffs when 

working with loud equipment.
 

●	 911 dispatchers and mechanics should take part in AFD’s 

health and safety committee. 

Health Hazard Evaluation Report 2007--0235-3064	 Page  
summARy
 

AFD mechanics are 

exposed to hazardous 

levels of noise, and 

should be enrolled in a 

hearing conservation 

program. AFD should 

take steps to reduce 

the feedback noise 911 

dispatchers hear through 

their headsets. 

On April 24, 2007, NIOSH received an HHE request from AFD 

management to assess whether the fire department’s mechanics 

should be enrolled in an HCP, and to determine if feedback noise 

(or “squeal”) that the 911 dispatchers heard through their headsets 

was hazardous to their hearing. 

A NIOSH investigator visited the site to collect full-shift noise 

exposures on the mechanics, to interview the 911 dispatchers about 

their work environment, to measure noise levels in the dispatch 

area, and to review employee records pertinent to noise and 

hearing loss. NIOSH investigators also purchased headsets similar 

in manufacturer and model to those worn by AFD dispatchers 

for laboratory analysis in-house, and tested actual feedback noise 

recordings provided by the AFD. 

Five AFD mechanics provided eight full-shift measures over two 

days. Five measures exceeded the NIOSH REL. One measure 

exceeded the OSHA AL; none exceeded the OSHA PEL. The 

primary source of noise exposure for the mechanics was a 1⁄2" 

impactor gun used to change tires on fire trucks. Of the seventeen 

911 dispatchers who were present at the time of the NIOSH 

evaluation, 15 were interviewed. Nearly all expressed dissatisfaction 

with their work environment. Their main concerns were the 

temperatures in the work area (either too cold or too hot), 

uncomfortable chairs, and the distracting background noise (from 

visitors, alarms, etc.). 

When compared to noise criterion curves, noise levels in 

the dispatch area were higher than recommended for a 

communications center. The headsets were adequate for their 

intended purposes, although the H251N had the best linear 

response between 150 Hz and 2000 Hz and thus provided the 

best sound quality. Analysis of eight feedback noise recordings 

produced average noise levels from 68 to 78 dB; the peak sound 

levels were between 84 and 100 dB. Although average levels were 

below the NIOSH REL, prolonged exposure to peak sound levels 

found in the recordings may result in dispatchers developing 

transient symptoms, such as headache, fatigue, and ringing in the 

ears, that are associated with exposure to high sound levels. 

The high noise levels experienced by AFD mechanics warrant 

enrollment in a hearing conservation program. Also, AFD 

management, with employee input, should increase awareness 

among firefighters and other personnel who use radios of the effect 

Page v Health Hazard Evaluation Report 2007-0235-3064 
summARy (Continued) of feedback noise on the 911 dispatchers. Management should 

consider either building a communications center designed for 

communications work or modifying the existing space. 

Keywords: NAICS 922160 (Fire protection), feedback noise, 911 

dispatchers, mechanics, dosimetry, acoustical mannequin, balanced 

noise curve, room acoustics, communications cente 

Health Hazard Evaluation Report 2007--0235-3064 Page v 
This page intentionally left blank. 
intRoduCtion 

On April 24, 2007, NIOSH received an HHE request from AFD 

management. The request asked NIOSH to help determine if the 

fire department’s mechanics need to be in an HCP, and determine 

if feedback noise (or “squeals”) that dispatchers heard was 

hazardous to their hearing. 

NIOSH investigators purchased four Plantronics® (Santa Cruz, 

California) headsets (H81N, H91N, H131N, and H251N) that were 

similar in manufacturer and model to those worn by the AFD 911 

dispatchers and tested these headsets in the NIOSH Acoustics 

Laboratory in Cincinnati, Ohio. Arrangements were made with the 

AFD to have actual 911 recordings available for analysis. 

From May 7–10, 2007, a NIOSH investigator visited the 

AFD facilities to collect personal dosimetry measurements on 

mechanics and interview the dispatchers in a private setting. The 

NIOSH investigator also reviewed the OSHA Form 300–Log 

of Injuries and Illnesses (“OSHA Logs”), collected area sound 

level measurements, and reviewed audiometric test results for 

dispatchers. 

Assessment
 Detailed information on OELs associated with noise and room 

acoustics, as well as on health effects, is provided in the Appendix. 

Mechanics 

Five AFD mechanics provided eight full-shift measures. The 

employees wore NoiseProTM noise dosimeters from Quest® 

Technologies (Oconomowoc, Wisconsin) while they performed 

their daily activities. The noise dosimeters were attached to the 

wearer’s belt, and a small remote microphone was fastened to the 

wearer’s shirt at a point midway between the ear and the outside 

of the shoulder. A windscreen provided by the manufacturer of 

the dosimeter was placed over the microphone during recordings. 

At the end of the sampling period, the dosimeter was removed 

and paused to stop data collection. The information stored 

in the dosimeters was downloaded to a personal computer for 

interpretation with QuestSuite® Professional II computer software. 

The dosimeters were calibrated before and after the measurement 

periods according to the manufacturer’s instructions. 

Health Hazard Evaluation Report 2007--0235-3064 Page  
Assessment (Continued) The Quest dosimeters collect data for comparison with the three 

different noise criteria used in this evaluation, the OSHA PEL 

and AL and the NIOSH REL. The OSHA guidelines use a 90­

dBA criterion level and a 5-dB exchange rate. The difference 

between the two OSHA criteria is in the threshold level employed, 

a 90 dBA threshold for the PEL and an 80 dBA threshold for the 

AL. The threshold level is the lower limit of noise values included 

in the calculation of the criteria; values less than the threshold 

are ignored by the dosimeter. The NIOSH guidelines differ from 

OSHA in that the criterion level is 85 dBA, and the exchange 

rate is 3 dB. There is no threshold requirement, so the threshold 

level for the dosimeters used in this evaluation was set to OFF. 

This allowed for the integration of all sound levels including those 

below 80 dBA. Table 1 summarizes the dosimeter settings used in 

this evaluation. 

Table 1. Dosimeter settings 

Parameters OSHA AL OSHA PEL NIOSH REL 

Response Slow Slow Slow 

Exchange rate 5 5 3 

Criterion level 90 dBA 90 dBA 85 dBA 

Threshold 80 dBA 90 dBA OFF 

Upper limit 115 dBA 115 dBA 115 dBA 

911 Dispatchers 

Area Noise Measurements 

The spectral area noise measurements were made with a Quest 

Technologies Sound Pro Real-TimeTM Analyzer Model and a 1⁄2"­

diameter random incidence response microphone. 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 dB) from 4 Hz to 21 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 30 seconds and stored in the analyzer for later 

analysis. The analyzer also calculates the overall unweighted value 

as a sound pressure level. 

The area sound levels in the room where the dispatchers worked 

were captured at each workstation. The analyzer was located near 

the position where the employee was seated; the microphone was 

placed where the dispatcher’s ears would be. 

Page  Health Hazard Evaluation Report 2007-0235-3064 
Assessment (Continued) Employee Interviews 

All 911 dispatchers at work on the days of the NIOSH evaluation 

along with the department manager were interviewed privately 

by the NIOSH investigator. Employees were asked about the 

number of years they had worked as dispatchers at AFD and 

in the profession. They were also queried about the physical 

characteristics of their work space (temperature, background noise, 

office ergonomics), whether they had been given a hearing test 

through work or experienced any changes in their hearing ability, 

and any other concerns about health and safety issues at their 

workplace. 

Records Review 

OSHA Logs from 2002–2006 were reviewed for any recordable 

injuries and illnesses related to hearing loss. It should be noted 

that OSHA only started tracking occupational hearing loss in 

2004. Audiograms for 19 dispatchers, including two individuals 

who retired within the past year, were also reviewed for trends in 

hearing decrement. 

Lab Analysis of Headsets 

NIOSH purchased four Plantronics headsets (H81N, H91N, 

H131N, and H251N) and appropriate connectors for testing at the 

NIOSH Acoustics Laboratory. NIOSH was provided with eight 

recordings of feedback noise identified by the AFD dispatchers 

as problematic. The recordings were obtained from AFD servers 

and supplied to NIOSH in MP3 format. A simulated problem 

recording was also obtained from AFD. The recordings were played 

back into an acoustics test fixture, KEMAR, with standard adultsize artificial external ears and 1⁄2" B&K microphones Type 4165 

(Naerum, Denmark). The microphones were powered by a B&K 

2807 power supply, and the output was evaluated with a Stanford 

Research Systems Model SR785 signal analyzer. The microphones 

were calibrated using a B&K 4230 acoustic calibrator that 

produces a 94-dB SPL tone at 1000 Hz. The calibration tone was 

used as a reference signal to evaluate the various sound levels of the 

recordings. The recordings were transferred to a personal computer 

for analysis. The test setup is shown in Photos 1 and 2. 

Health Hazard Evaluation Report 2007--0235-3064 Page  
 

 

 

Assessment
 

(Continued) 

Photo 1. Test setup using KEMAR and SR785 analyzer 

Photo 2. The KEMAR artificial acoustic fixture with B&K 4165 microphones 

The recordings were analyzed using the NIOSH noise 

measurement software that reports average and peak sound levels 

of each recording as well as analyzing the frequency spectrum and 

octave and one-third octave band spectra. In addition to evaluating 

the quality and sound levels produced by the recordings, the overall 

performance of the four headsets was also tested using the sound 

source feature on the SR785 signal analyzer to produce a swept 

sine signal from 100 Hz to 20 KHz with increasing levels of outputs 

from 10 mV to 5 V. 

Results And disCussion 

Mechanics 

Five mechanics provided eight personal noise measures over 

the 2-day evaluation at the maintenance shop. The personal 

noise exposures are shown in Table 2. Five of the eight measures 

exceeded the NIOSH REL of 85 dBA. One measure exceeded the 

OSHA AL of 85 dBA. 

Page  Health Hazard Evaluation Report 2007-0235-3064 
 

 

 

 

Results And disCussion 

(Continued) 

Table 2. Full-shift personal noise exposures for AFD mechanics 

Sample ID Duration (hh:mm) OSHA AL OSHA PEL NIOSH REL 

Dose TWA Dose TWA Dose TWA 

(%) (dBA) (%) (dBA) (%) (dBA) 

A 10:04 13.5 75.6 8.4 72.1 97.1 84.9
 

B 09:54 3.6 66.1 1.3 58.9 16.9 77.3
 

C 09:58 28.7 81.0 21.8 79.0 263 89.2
 

D 11:03 10.6 73.9 5.0 68.5 59.6 82.8
 

E 10:04 65.8 87.0 55.7 85.8 1351.5 96.3
 

F 10:00 37.2 82.9 31.3 81.6 4631.3 101.7
 

G 10:06 19.5 78.2 10.3 73.6 110.2 85.4
 

H 09:53 22.3 79.2 12.7 75.1 112.7 85.5
 

The various dose percentages are the amounts of noise accumulated during a work day, with 100%
 

representing the maximum allowable daily dose.
 

OSHA AL = 85 dBA; OSHA PEL = 90 dBA; NIOSH REL = 85 dBA
 

The loudest noise exposures occurred when mechanics used a 1⁄2" 

impactor gun to screw or unscrew lugnuts from fire engine tires. 

Spot measurements showed that noise exposures when screwing 

or unscrewing lugnuts could approach or exceed an employee’s 

daily allowable dose in less than one minute. A 48-second exposure 

when unscrewing lugnuts from a tire had an average noise level of 

111 dBA. Average noise levels when screwing lugnuts were 113 dBA 

for a 45-second exposure, and 120 dBA for a 54-second exposure. 

Tires on two trucks were changed during the NIOSH evaluation. 

The mechanics change the tires on the fire trucks at the beginning 

of the summer and winter seasons. In Alaska, the summer season 

is from April to September, and the winter season is from October 

to March. In the late summer season (or the early winter season), 

snow tires are installed on fire trucks, and in the early summer 

season (or late winter season), they are replaced with normal tires. 

At the time of this evaluation (early May) most snow tires on the 

fire trucks had been changed. 

The NIOSH investigator also measured noise levels when 

employees were priming a fire truck. Priming ensures that the 

water lines in the truck are functioning properly. The priming was 

done by switching on a toggle on a side panel of the truck. The 

priming activity observed during this evaluation lasted less than 

one minute. Another source of loud noise was an air vacuum 

pump used to clean up debris (metal shavings, garbage, etc.) after 

a job. The noise spectral data from the 1⁄2" impactor gun, priming, 

and the air vacuum pump are shown in Figure 1. The frequency 

range exceeding 85 dBA associated with the 1⁄2" impactor gun 

Health Hazard Evaluation Report 2007--0235-3064 Page  
 

 

 

 

 

Results And disCussion 

was 500–5000 Hz, the frequency range exceeding 85 dBA for the (Continued) truck priming activity was 315–1600 Hz, and the frequency range 

exceeding 85 dBA was 800–6300 Hz for the vacuum pump. These 

frequencies covered the range associated with NIHL, which usually 

occurs between 2000–6000 Hz. 

Figure 1: Spectral noise data for typical noise exposures 

experienced by AFD mechanics 

110 

1/2" impactor gun 

100 Priming fire truck 

Air vacuum 

90 

80 

70 

60 

50 

40 

One-third Octave Band Center Frequency (Hz) 

911 Dispatchers 

Area Noise Measurements 

Area noise sampling was conducted in the dispatch area during the 

day shift. Noise spectrum data were recorded at each workstation, 

regardless of whether the workstation was occupied by a 911 

dispatcher. Noise levels during the day shift had a median value 

of 60 dB SPL. The third octave band data were combined into 

octave bands to simplify their analysis and to compare the area 

room noise values to the NCB criterion [ANSI 1995]. The octave 

band data for the dispatch area are shown in Figure 2. The NCB55 curve is representative of the room noise at the dispatch center. 

The room noise conditions at this location are characterized as 

light maintenance shops, industrial plant control rooms, office 

and computer equipment rooms (NCB 45–55); shops and garages 

(NCB 50–60); and work spaces where speech or telephone 

Sound Pressure Level (dBA) 

25 50 100 250 500 1000 2500 5000 10000 

Page  Health Hazard Evaluation Report 2007-0235-3064 
 

 

 

 

 

 

Results And disCussion 

communication is not required (NCB 55–70). NCB 45 or less are (Continued) appropriate for an office setting. Therefore, the room acoustics 

in the dispatcher area are not appropriate for a communications 

center. More information on NCB curves is provided in the 

Appendix. 

Figure 2: Spectral data from communications center 

and comparison with NCB curves. 100 

Octave Band Center Frequency (Hz) 

Employee Interviews 

Of the seventeen 911 dispatchers present during the NIOSH site 

visit, 15 were interviewed. Of the 15, five were men and 10 were 

women. Their ages ranged from 26–56 years (mean age was 42 

years). Fourteen 911 dispatchers (93%) said the temperature in the 

dispatch area was either too hot or too cold. Most 911 dispatchers 

said that their chairs were uncomfortable, and because they may 

spend approximately 10 hours sitting down, chair comfort was of 

great concern. They suggested that management survey their needs, 

and ensure that enough chairs suitable for the 911 dispatchers be 

made available during each shift. 

Many of the 911 dispatchers said that they were distracted during 

their annual hearing tests, done in a mobile test facility, because 

of the noisy ambient environment. For example, employees 

mentioned that they could hear airplanes when taking the 

audiometric test. They also said that annual audiometric testing 

Sound Level (dB SPL) 

31.5 63 125 250 500 1000 2000 4000 8000 

0 

20 

40 

60 

80 

45 dB balanced noise criterion curves 

55 dB balanced noise criterion curves 

Communication center levels 

NCB-10 

NCB-20 

NCB-30 

NCB-40 

NCB-50 

NCB-60 

Health Hazard Evaluation Report 2007--0235-3064 Page  
Results And disCussion 

was done at the end of the work day, and questioned whether, after (Continued) a full shift of noise exposures, the annual tests would accurately 

reflect their hearing ability. 

Records Review 

The OSHA Logs showed no hearing loss or ear injuries. Three 

of the nineteen audiograms only had baseline data; of the 16 

audiograms with multiple tests, none indicated that the employees’ 

hearing levels decreased because of their employment with AFD. 

Two employees showed moderate hearing loss in their baseline 

audiograms. The baseline audiograms for all employees were 

administered shortly after they were hired. 

Lab Analysis of Headsets 

The average and peak sound levels from the test signal and each of 

the feedback noise recordings are shown in Table 3. The average 

length of each squeal was 500–700 milliseconds. 

Table 3. Average and peak sound pressure levels 

Event Leq (dB) Lpeak (dB) Comment 

Test Signal 67–68 84–85 Peak at 1.4 kHz 

Squeal 1 69–71 85–87 Peak at 2.6 kHz 

Squeal 2 74–77 97–99 Peak at 2.4 kHz 

Squeal 3 68–69 84–85 Peak at 2.7 kHz 

Squeal 4 72–75 93–95 Peak at 2.4 kHz 

Squeal 5 74–76 94–97 Peak at 2.3 kHz 

Squeal 6a 69–70 87–90 Peak at 1.4 kHz 

Squeal 6b 69–72 90–91 Peak at 2.6 kHz 

Squeal 7 77–78 97–100 Peak at 1.7 kHz 

The results show that while the average noise levels from the 

recorded radio squeals and the test signals were below the 

NIOSH REL, peak sound levels reached as high as 100 dB on the 

medium volume setting. These spikes in sound levels appeared 

at frequencies ranging from 1.4 kHz to 2.7 kHz, which have been 

shown to cause more damage to hearing than low frequency sound 

levels [NIOSH 1996]. The NIOSH REL provides that exposure at 

the 100 dB levels not exceed 15 minutes during an 8-hour work 

shift. Dispatchers would have to be exposed to a high number of 

these spikes in their working day before they reach their maximum 

allowable limit. However, repeated and prolonged exposures at the 

peak levels found in this evaluation can result in symptoms such as 

headache, fatigue, or ringing in the ears. 

Page  Health Hazard Evaluation Report 2007-0235-3064 
 

 

Results And disCussion 

Previous studies on telephone and call center operators found (Continued) that the risk of hearing damage is minimal [Alexander et al. 1979; 

Patel and Broughton 2002]. In the call center study, the noise 

exposures of 150 operators from 15 call centers across a wide range 

of industry sectors were evaluated [Patel and Broughton 2002]. The 

study found that while exposure to high-level noise was possible, 

the daily personal noise exposure level was unlikely to exceed 85 

dBA. 

Performance of Headsets 

The four Plantronics headsets were tested for linearity, quality of 

sound, and frequency response. Figures 3–6 show that all four 

headsets were capable of producing output levels in excess of 110 

dB SPL. The y-axis shows the sound level in dB SPL and the x-axis 

shows the frequency in Hz. A swept-sinusoidal signal was applied to 

each headset at 10 mV, 100 mV, 1 V, and 5 V. The corresponding 

output response is plotted in each figure. All four headsets cut off 

sound signals above 4 kHz, thus limiting harmful high frequency 

signals from reaching the ear. The H251N headset showed lower 

output as the input exceeded the 1V signal level. This indicates 

the presence of a noise-limiting circuit in the headset itself. The 

presence of the noise limiting circuitry in the headset makes the 

H251N superior for protection against spurious noise signals. 

Figure 3: Frequency response of the H81N headset 

Peak Sound Pressure

Level (dB)
 

140 

120 

100 

80 

60 

40 

20 

0 

10 mV 100 mV 1000 mV 5000 mV 

10 100 1000 10000 100000 

Frequency 

Health Hazard Evaluation Report 2007--0235-3064 Page  
 

 

 

Results And disCussion 

(Continued) 

Figure 4: Frequency response of the H91N headset 

140 

Peak Sound Pressure

Level (dB) 

120 

100 

80 

60 

40 

20 

0 

10 mV 100 mV 1000 mV 5000 mV 

10 100 1000 10000 100000 

Frequency 

Figure 5: Frequency response of the H131N headset 

0 

20 

40 

60 

80 

100 

120 

Peak Sound Pressure

Level (dB) 

10 100 1000 10000 100000 

Frequency 

10 mV 100 mV 1000 mV 5000 mV 

Page 0 Health Hazard Evaluation Report 2007-0235-3064 
 

 

Results And disCussion 

(Continued) 

Figure 6: Frequency response of the H251N headset 

Peak Sound Pressure

Level (dB)
 

120 

100 

80 

60 

40 

20 

0 

10 100 1000 10000 100000 

Frequency 

10 mV 100 mV 1000 mV 5000 mV 

A comparison of the responses of the four headsets to the same 

signal in Figure 7 shows that the H251N headset exhibited the 

best linear response of the four headsets over a frequency range of 

150 Hz to 2000 Hz; thus this headset was capable of providing the 

best sound quality. Because most of the radio “squeals” happened 

between 1.4 and 2.7 kHz, the H131N frequency response exhibited 

the worst performance in comparison to the other headsets in 

limiting high level transmission at these frequencies. The results 

are also comparable to previous studies that have shown insert-type 

headsets provide 7–9 dB of increased sound output relative to overthe-ear headsets [Fligor and Cox 2004]. 

Health Hazard Evaluation Report 2007--0235-3064 Page  
 

 

Results And disCussion 

(Continued) 

Figure 7: Comparison of Plantronics headsets at 100 mV 

120 

100 

80 

60 

40 

20 

0 

H81N H91N H131N H251N 

Peak Sound Pressure

Level (dB)
 

10 100 1000 10000 100000 

Frequency 

ConClusions 

This evaluation found high noise exposures among mechanics. 

Of the full-shift personal noise measures, 63% exceeded the 

NIOSH REL despite the short exposure durations. Most of the 911 

dispatchers expressed dissatisfaction with their work environment, 

stating that their work space was either too cold or too hot, their 

chairs were uncomfortable, and that there was distraction from 

visitors and loud alarms. Based on the sound levels measured in 

the dispatch area, the room acoustics are not considered optimal 

for a communications center. The high background noise caused 

the dispatchers to increase the headset volume level to overcome 

the masking provided by the noisy environment. If the background 

noise is reduced (for example through administrative measures 

such as limiting visitors to the dispatch area) then 911 dispatchers 

should be able to reduce the headset volumes, thereby reducing 

the potential for high level squeals. Based on the review of the 

audiograms there was no evidence of NIHL among the 911 

dispatchers. 

The recordings produced peak sound levels up to 100 dB. 

However, average levels that provide a better representation of 

Page  Health Hazard Evaluation Report 2007-0235-3064 
ConClusions 

(Continued) daily exposure were not considered hazardous, because they did 

not exceed the NIOSH REL. Repeated and prolonged exposure to 

peak sound levels found in the recordings can result in dispatchers 

developing symptoms, such as headache, fatigue, or ringing in the 

ears, that are associated with exposure to high sound levels. 

ReCommendAtions
 The following recommendations are provided to reduce hazards 

to the hearing of mechanics and dispatchers at AFD that are 

associated with exposure to high noise levels. 

1.	 Establish an HCP for AFD mechanics. The basic 

elements of the program should, at a minimum, meet 

the requirements of the OSHA hearing conservation 

amendment [29 CFR 1910.95]. Other sources for defining 

effective hearing conservation programs are also available 

[Royster and Royster 1990; NIOSH 1996; Suter 2002]. 

2.	 Mechanics should be required to wear HPDs while 

maintaining fire trucks.
 

3.	 Most of the dispatchers’ headsets are adequate for their 

intended use. However, the quality of the sound production 

and the overall performance of the H251N headset were 

superior to the other headsets. The dispatchers should 

consider quality when selecting their headset. 

4.	 AFD should train firefighters and others who use the radio 

equipment on proper use of these radios and the effect 

of feedback signals that can be transmitted into the 911 

dispatchers’ headsets. 

5.	 Administer audiometric tests at the beginning of the shift 

to prevent bias from any temporary threshold shift that may 

have occurred during the day. Also, hearing tests should be 

conducted in a quiet environment such as an audiologist’s 

office. 

6.	 Consider, in consultation with a room acoustics engineer, 

building a dedicated communications center for the 

dispatchers or modifying the existing area to meet NCB 

criteria. 

7.	 Implement specific administrative control measures such 

as providing a wider selection of noise limiting headsets, 

providing chairs that are ergonomically suitable, and 

Health Hazard Evaluation Report 2007--0235-3064	 Page  
ReCommendAtions 

(Continued) ensuring a quiet working environment, to minimize health 

and comfort concerns among 911 dispatchers. 

8. Encourage 911 dispatchers and mechanics to actively 

participate in AFD’s health and safety committee. 

RefeRenCes
 

Alexander RW, Koenig AH, Cohen HS, Lebo CP [1979]. The 

effects of noise on telephone operators. Occup Med 21(1):21–25. 

ANSI [1995]. American national standard: criteria for evaluating 

room noise. New York, NY: Acoustical Society of America, 

American National Standards Institute, ANSI S12.2-1995. 

CFR. Code of Federal Regulations. Washington, DC: U.S. 

Government Printing Office, Office of the Federal Register. 

Fligor BJ, Cox C [2004]. Output levels of commercially available 

portable compact disc players and the potential risk to hearing. Ear 

and Hearing 25(6):513–527. 

NIOSH [1996]. Preventing occupational hearing loss–a practical 

guide. 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. 96-110. 

Patel JA, Broughton K [2002]. Assessment of the noise exposure of 

call centre operators. Ann Occup Hyg 46(8):653–661. 

Royster JD, Royster LH [1990]. Hearing conservation programs: 

practical guidelines for success. Chelsea, MI: Lewis Publishers. 

Suter AH [2002]. Hearing conservation manual. 4th ed. Milwaukee, 

WI: Council for Accreditation in Occupational Hearing 

Conservation. 

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Appendix: oCCupAtionAl exposuRe limits And HeAltH effeCts 

In evaluating the hazards posed by workplace exposures, NIOSH investigators use both mandatory (legally 

enforceable) and recommended OELs for chemical, physical, and biological agents as a guide for making 

recommendations. OELs have been developed by Federal agencies and safety and health organizations 

to prevent the occurrence of adverse health effects from workplace exposures. Generally, OELs 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. However, not all workers will be protected 

from adverse health effects even if their exposures are maintained below these levels. A small percentage 

may experience adverse health effects because of factors such as individual susceptibility, or pre-existing 

medical condition. 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 exposure limit. 

The primary sources of evaluation criteria for noise in the workplace are the NIOSH REL [NIOSH 1992], 

and the U.S. Department of Labor, OSHA PEL [29 CFR 1910.95]. Employers are encouraged to follow 

the more protective NIOSH REL, although they are required to adhere to the OSHA PEL for compliance 

purposes. 

NIHL 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 

[Ward et al. 2000]. 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, NIHL 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 [Suter 1978]. 

The 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 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 hundred-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 specifies a maximum PEL of 90 dBA for of 

8 hours per day [29 CFR 1910.95]. The regulation, in calculating the PEL, uses a 5-dB time/intensity 

Health Hazard Evaluation Report 2007--0235-3064 Page  
Appendix : oCCupAtionAl exposuRe limits And HeAltH effeCts 

(Continued) 

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 (C /T + C /T + ... + C /T ) 1 1 2 2 n n

where C n 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% exceed the OSHA PEL. 

The OSHA regulation has an additional AL of 85 dBA; an employer shall administer a continuing, 

effective hearing conservation program when the 8-hour TWA value exceeds the AL. The program must 

include monitoring, employee notification, observation, audiometric testing, HPD, 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, proposes an exposure criterion of 85 dBA as a 

TWA for 8 hours, 5 dB less than the OSHA standard [NIOSH 1998]. The criterion also uses a more 

conservative 3-dB exchange rate 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. The NIOSH REL for a 12­

hour exposure is 83 dBA or less. 

Because of the different 8-hour criteria and exchange rates, the dose equations used to calculate the 

equivalent TWA values are different for the NIOSH and OSHA criteria. 

The OSHA dose equation is 

TWA = 16.61 x log10 [Dose/100] + 90, 

and the NIOSH equation is 

TWA = 10.00 x log10 [Dose/100] + 85. 

The occupational noise regulation promulgated by OSHA and the NIOSH criterion are designed to 

prevent hearing losses from exposures to intense noise levels. However, noise of intensities lower than that 

which may cause a loss of hearing can be disruptive in the workplace. 

Interference with speech is a possible result of unwanted noise. The noise can interfere with the efficiency 

and productivity of the staff and can be detrimental to the occupants’ comfort, health, and sense of well 

being. One set of noise criteria for occupied interior spaces, the NCB curves, has been devised to limit 

Page  Health Hazard Evaluation Report 2007-0235-3064 
 

 

 

 

Appendix: oCCupAtionAl exposuRe limits And HeAltH effeCts 

(Continued) 

noise to levels where satisfactory speech intelligibility is achieved [Beranek 1988, 1989; ANSI 1995]. The 

noise criteria were devised through the use of extensive interviews with personnel in offices, factories, and 

public places along with simultaneously measured octave band sound levels. The interviews consistently 

showed that people rate noise as troublesome when its speech interference level is high enough to make 

communications difficult. The recommended space classifications and suggested noise criteria range for 

steady background noise heard in various indoor occupied activity areas are shown in Table A-1. 

*Table A-1. Suggested NCB range for various occupied indoor areas 

Type of space and acoustical requirements NCB curve 

Concert halls, opera houses, and recital halls 10–15 

Large auditoriums, large drama theatres, and large churches Not to exceed 20 

Small auditoriums, small theaters, small churches, music rehearsal rooms, large Not to exceed 30 

meeting and conference rooms, and executive offices 

Bedrooms, hospitals, residences, apartments, hotels 25–40 

Private or semi-private offices, small conference rooms, classrooms, libraries 30–40 

Large offices, reception areas, retail shops and stores, cafeterias, restaurants 35–45 

Lobbies, lab work spaces, drafting and engineering rooms, general secretarial areas 40–50 

Light maintenance shops, industrial plant control rooms, office and computer equipment 45–55 

rooms, kitchens, and laundries 

Shops, garages 50–60 

Work spaces where speech or telephone communication not required 55–70 

* ANSI S12.2-1995 Criteria for Evaluating Room Noise 

References 

ANSI [1995]. American national standard: criteria for evaluating room noise. New York, NY: Acoustical 

Society of America, American National Standards Institute, ANSI S12.2-1995. 

Beranek LL [1988]. Criteria for noise and vibration in communities, buildings, and vehicles. In: Beranek 

LL, ed. Noise and vibration control. Rev. ed. Cambridge, Massachusetts: Institute of Noise Control 

Engineering, pp. 554–623. 

Beranek LL [1989]. Balanced noise criterion (NCB) curves. J Acoust Soc Am 86(2):650–664. 

CFR. Code of Federal Regulations. Washington, DC: U.S. Government Printing Office, Office of the 

Federal Register. 

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Appendix : oCCupAtionAl exposuRe limits And HeAltH effeCts 

(Continued) 

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. 

NIOSH [1998]. Criteria for a recommended standard: occupational noise exposure (revised criteria 1998). 

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. 98-126. 

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. 

Ward WD, Royster LH, Royster JD [2000]. Anatomy & physiology of the ear: normal and damaged 

hearing. 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. 

Page  Health Hazard Evaluation Report 2007-0235-3064 
ACknowledgements And 

AvAilAbility of RepoRt 

The Hazard Evaluations 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. 

This report was prepared by Chandran Achutan of HETAB, 

Division of Surveillance, Hazard Evaluations and Field Studies 

and Chucri A. Kardous of the Division of Applied Research and 

Technology (DART). Employee audiograms were reviewed by Dr. 

Thais Morata of DART. Desktop publishing was performed by 

Robin Smith. Editorial assistance was provided by Ellen Galloway. 

Health Communication assistance was provided by Stefanie Evans. 

Copies of this report have been sent to employee and management 

representatives at the Anchorage Fire Department and the OSHA 

Regional Office. This report is not copyrighted and may be freely 

reproduced. The report may be viewed and printed from the 

following internet address: http://www.cdc.gov/niosh/hhe. Copies 

may be purchased from the National Technical Information Service 

at 5825 Port Royal Road, Springfield, Virginia 22161. 

Health Hazard Evaluation Report 2007--0235-3064 Page  
Below is a recommended citation for this report: 

NIOSH [2008]. Health Hazard Evaluation Report: Evaluation of potential noise 

hazards to mechanics and 911 dispatchers at a fire department, Anchorage, 

Alaska. 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, NIOSH HETA No. 2007-0235-3064. 

To receive NIOSH documents or information about 

occupational safety and health topics, contact NIOSH at: 

1-800-CDC-INFO (1-800-232-4636) 

TTY: 1-888-232-6348 

E-mail: cdcinfo@cdc.gov 

or visit the NIOSH web site at: www.cdc.gov/niosh. 

For a monthly update on news at NIOSH, subscribe to 

NIOSH eNews by visiting www.cdc.gov/niosh/eNews. 

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Safety and health at work for all people 

through research and prevention.

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Safety and Health