Noise Exposures and 

Hearing Loss Assessments 

among Animal Shelter 

Workers 

Chandran Achutan, Ph.D.

Health Hazard Evaluation Report

HETA 2007-0068-3042

Louisiana Society for the Prevention of Cruelty to 

Animals

Algiers, Louisiana

May 2007

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

Workplace

Safety and Health

 National Institute for Occupational 

Safety and Health
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].
Health Hazard Evaluation Report 2007-0068-3042 Page 

Repor

Contents

Abbreviations........................................................................ii

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

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

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

Assessment..........................................................................3

Results & Discussion............................................................4

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

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

References...........................................................................8

Contents

Appendix Appendix: Evaluation Criteria ............................................10

Acknowledgment

Acknowledgements and Availability of Report....................13
Page i Health Hazard Evaluation Report 2007-0068-30

AL	 Action Level

CAOHC	 Council for Accreditation in Occupational Hearing Conservation

CFR	 Code of Federal Regulations

dB	 Decibels

dBA	 Decibels, A-weighted scale

HHE	 Health hazard evaluation

HL	 Hearing level

HPD	 Hearing protection device(s)

Hz	 Hertz

kHz	 Kilohertz

LA/SPCA	 Louisiana Society for the Prevention of Cruelty to Animals

MSDS	 Material safety data sheet

NAICS	 North American Industry Classification System

NIHL	 Noise-induced hearing loss

NIOSH	 National Institute for Occupational Safety and Health

OSHA	 Occupational Safety and Health Administration

PEL	 Permissible exposure limit

REL	 Recommended exposure limit

SLM	 Sound level meter

STS	 Standard threshold shift

TWA	 Time-weighted average

Abbreviatio
Health Hazard Evaluation Report 2007-0068-3042 Page 

In December 2006, NIOSH 

investigators received 

a management request 

from the LA/SPCA to 

evaluate noise exposures 

and potential hearing 

loss among workers in 

the kennel area. Between 

December 2006 and 

February 2007, noise 

assessments and hearing 

tests were conducted on 

LA/SPCA employees.

Highlights of 

NIOSH 

Hazard Eval

What NIOSH Did

	We measured personal noise exposures for kennel workers, 

veterinary staff, and client care workers.

	We tested hearing levels of all LA/SPCA employees.

What NIOSH Found

	Noise levels exceeded the NIOSH REL on 16 occasions and 

exceeded the OSHA AL on five occasions.

	Three of 33 employees including two kennel workers, had hearing 

loss.

	Employees were wearing back braces in case they had to lift heavy 

animals.

What LA/SPCA Managers Can Do

	Enroll employees in a hearing loss prevention program.

	Require the use of ear plugs or ear muffs in the kennel area.

	Maintain ear muffs by making sure they are clean and by replacing 

the cushions every 6 months or sooner if necessary.

	Institute a comprehensive lifting program. Do not require 

employees to wear back braces.

	Train employees on the hazards associated with the chemicals they 

use.

What LA/SPCA Employees Can Do

	Wear hearing protectors when working in the kennel area.

	Wear goggles when using SX-64TM to clean kennel cages.

	Always wear gloves (example nitrile) when cleaning dog and cat 

cages, and wash hands after cleaning the cages.
Page iv Health Hazard Evaluation Report 2007-0068-304

On December 1, 2006, NIOSH received a management request for 

an HHE from the LA/SPCA in Algiers, Louisiana. The HHE request 

asked NIOSH to assess the noise levels experienced by workers in the 

kennel area from barking dogs. On December 16–17, 2006, a NIOSH 

investigator measured noise exposure levels for workers in the kennel 

area. NIOSH investigators returned to the facility on February 6–8, 

2007, to conduct hearing tests on all LA/SPCA employees.

Thirteen kennel workers, two veterinary staff, and three client care 

workers provided 22 personal noise dosimetry measures over the 2-

day evaluation. One of the measures collected on a kennel worker was 

invalid because of equipment malfunction. Sixteen of the 21 measures 

exceeded the daily allowable noise dose of 100% as calculated by the 

NIOSH criterion. Five measures also exceeded the OSHA AL. The 

OSHA PEL was not exceeded. Hearing tests were performed on 33 

employees. Three employees showed some degree of hearing loss (> 

25 decibel hearing loss) at one or more test frequencies in one or both 

ears on the NIOSH-administered audiogram. Twenty-one employees 

with normal hearing showed notches (hearing levels worsen over test 

frequencies before improving in the highest frequencies, forming a 

“notch” configuration) in one or both ears between 3000–6000 Hz, 

indicating early signs of hearing loss. 

In addition to noise, the NIOSH investigator observed other hazards. 

Kennel workers without gloves and without proper eye protection 

(safety goggles) were cleaning cages. A constituent of one of the 

disinfectants used to clean the cages is a known eye irritant. In addition, 

kennel workers were required to wear back braces in case there was a 

need to lift heavy animals; NIOSH has determined back braces to be 

ineffective in preventing back injury. 

Recommendations include establishing a hearing loss prevention 

program, wearing HPD when entering the kennel area, and using 

personal protective equipment when cleaning animal cages.

Kennel workers at LA/

SPCA were exposed to 

excessive noise levels. 

Some of the LA/SPCA 

employees have hearing 

loss but it is not possible 

to determine whether 

this is related to noise 

exposures in the kennel. 

To prevent further hearing 

loss, workers should be 

enrolled in a hearing loss 

prevention program, and 

provided with HPD.

Summ

Keywords: NAICS 813312 (Environment, Conservation and Wildlife 

Organizations), noise, dose, hearing loss, dog, notch, audiometric testing, 

back braces 
Health Hazard Evaluation Report 2007-0068-3042 Page 

Introduct

On December 1, 2006, NIOSH received a management request for an 

HHE from LA/SPCA in Algiers, Louisiana. The HHE request asked 

NIOSH to assess employee exposure to noise from barking dogs. On 

December 16–17, 2006, a NIOSH investigator measured noise exposure 

levels for workers in the kennel area. NIOSH investigators returned to 

the facility on February 6–8, 2007, to conduct hearing tests on all LA/

SPCA employees.

Noise Exposures to Domestic Animal 

Handlers

Veterinary hospital workers, animal shelter employees, workers at 

facilities that board animals, and police officers with canine partners 

are potentially exposed to excessive occupational noise levels from 

barking dogs. However, few studies have examined noise exposures 

and the potential for hearing loss among these workers. One study 

measured noise levels as high as 108 dBA in veterinary establishments 

[Senn and Lewin 1975]. Another study in an outdoor animal shelter 

showed noise exposures in excess of the NIOSH REL for occupational 

noise [Achutan 2007]. This evaluation was conducted in the aftermath 

of Hurricane Katrina in St. Bernard Parish, Louisiana, and is not 

representative of typical veterinary staff noise exposure. Three recent 

HHEs on noise exposure and hearing loss assessments of employees at 

animal boarding facilities showed that kennel workers were exposed 

to noise levels up to ten times the NIOSH REL; some of these workers 

either had hearing loss or showed early signs of hearing loss [NIOSH 

2007a,b,c].Two studies examined noise exposures and hearing loss 

among canine police officers [Reid et al. 2004; NIOSH 2006]. Both 

studies found that police officers were exposed to excessive noise from 

canines, and some officers had hearing loss. The design of these studies 

did not enable investigators to determine whether observed hearing loss 

was associated with occupational noise exposures.

Louisiana Society for the Prevention of 

Cruelty to Animals

The LA/SPCA was chartered in 1888 with a mission to eliminate 

animal suffering and educate the public about animal care [LA/SPCA 

2007]. In 2005, after Hurricane Katrina destroyed the LA/SPCA shelter 

on Japonica Street, New Orleans, the animals and the staff temporarily 

evacuated to the Houston SPCA. They subsequently moved to the 

Lamar-Dixon Exposition Center in Gonzales, Louisiana. In October 

2005, LA/SPCA started operating from a former coffee warehouse 

in Algiers, Louisiana. The LA/SPCA expects to move into a new 

permanent facility in Algiers by the spring of 2007. At the time of the 

NIOSH evaluation, there were approximately 150 dogs at the facility. 

Although the warehouse could accommodate many more animals, the 

shelter limited the number of animals based on the number that could 

be accommodated at the new facility.
Page  Health Hazard Evaluation Report 2007-0068-3042

Introduction (contin

Facility Description

At the time of the NIOSH evaluation, the LA/SPCA was operating out 

of a 45,000-square foot warehouse in Algiers, Louisiana. The middle 

portion of the warehouse housed the majority of the dogs. The dogs 

were housed in cages in the adoption area, the healthy hold area, the 

quarantine area, and the isolation area. Dogs were housed in two types 

of cage configurations. One configuration was a cage with an opaque 

thick plastic panel covering three sides of the cage. The dimension of 

the cage could be modified depending on the size of the dog. The other 

configuration, called a “T” cage, was a 3-foot by 12-foot cage with a 

door in the middle. This door could be raised or lowered to allow the 

animal full access to the cage or partial access, such as when the cage 

was being cleaned. 

The adoption area was open to the public and consisted of dogs 

deemed by the LA/SPCA to be healthy and non-aggressive. A behavior 

evaluator determined whether the animals were safe for adoption. These 

animals were also spayed or neutered. There were 46 regular cages 

arranged in 3 aisles or “runs” and 14 “T” cages arranged perpendicular 

to the regular cages.

The healthy holding, quarantine, and isolation areas were not accessible 

to the public unless accompanied by a staff member. These areas were 

blocked off from the adoption area by stacks of animal cages arranged 

three-deep, and by temporary fences. The healthy holding area housed 

animals brought in by the public or by animal control officers. Animals 

were held for 5–6 days to allow owners to claim their pets. After this 

period, animals were either put up for adoption or euthanized. The 

healthy holding area for dogs had 45 cages arranged in three runs.

The quarantine and isolation areas had 56 “T” cages placed in two runs. 

Dogs in the quarantine area were held on court order for aggression or 

because of owner cruelty. Sick animals at the LA/SPCA were moved 

to the cages in the isolation area, and were tended to by the veterinary 

staff. 

On the south wall of the warehouse were three restrooms and seven 

other rooms. These rooms included a cat/kitten adoption room, a room 

for puppies and rabbits, a break room for staff, dishwashing/laundry/

grooming room, a cat “healthy hold” room, a feral cat room, and a cat 

isolation room. 

On the north wall of the warehouse were large shelves that held 

supplies such as food and litter. Adjacent to the shelves and behind 

some of the “T” cages was a veterinary clinic. The clinic was staffed by 

a veterinarian and three veterinary technicians. In front of the clinic and 

next to the isolation/quarantine cages were three tables placed in an “L” 

formation where the kennel supervisor did paper work. 
Health Hazard Evaluation Report 2007-0068-3042 Page 

Introduction (contin

Assessment

Between the dog adoption cages and the start of the rooms on the south 

wall (close to the warehouse entrance) was a small office where three 

client care workers processed adoptions and received animals brought 

in by the public or by animal control officers. The client care staff also 

brought animals from the adoption area to prospective pet owners. 

Outside the warehouse in the parking lot were two trailers that housed 

the administrative staff, animal control staff, the behavior evaluator, 

and special events coordinators. The latter were the point of contact 

for members of the public wishing to volunteer at the LA/SPCA. Staff 

walked the dogs on a portion of the parking lot.

Kennel Work Activities

The 15 kennel workers reported to work between 6:00 a.m. and 8:30 

a.m., and left work between 3:00 p.m. and 5:30 p.m. Workers got one 

15-minute morning break, and an hour-long lunch break. The main 

kennel work activities were feeding the cats and dogs, cleaning cages, 

and walking the dogs. Workers typically worked in pairs. The two 

workers who came in at 6:00 a.m. started preparing food. The food was 

prepared on a cart in the warehouse and fed to the dogs in stainless steel 

feeding dishes. This took approximately one hour. 

Dog excrement was scraped, scooped, and deposited in a trash can. 

Because there was a shortage of water at the warehouse, the dog cages 

were cleaned by spraying a disinfectant called SX-64TM and wiping the 

floors, cage, and the plastic panels with paper towels. After that, the 

floors were mopped using a mixture of bleach and water. Excess water 

from the floors was removed using a squeegee. The process was similar 

for the “T” cages, except that after the SX-64 is sprayed, the floor of 

the cage was mopped with the water/bleach solution, thus bypassing the 

wipe-down with paper towels. The cages were then lined with absorbent 

pads and a towel, and the drinking dish filled with fresh water. While 

one worker was preparing the cages, the cage occupant was taken for a 

walk by the other worker. The workers usually took turns cleaning the 

cages and walking the dogs. The cleaning of all the cages usually took 

about 5 hours. 

Other activities included washing the feeding and drinking containers, 

laundering soiled cloths, bathing the dogs, cleaning floors of the facility, 

taking out the trash, and disinfecting the soiled scraper, mops, and 

squeegees in a container containing an aqueous bleach solution. In 

addition, the workers who left at 5:30 p.m. ensured that the animals had 

adequate food and water. 

Noise Assessment

On December 16–17, 2006, 18 employees who worked in the kennel 

area (13 kennel workers, two veterinary staff members, and three 

client care workers) contributed 22 full-shift, personal noise measures. 

Quest® Technologies (Oconomowoc, Wisconsin) Model Q-300 Noise 
Page  Health Hazard Evaluation Report 2007-0068-3042

Assessment (continued

Results & Discussi

Dosimeters were worn by the kennel workers 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 dosimeter manufacturer was placed 

over the microphone during recordings. At the end of the workday, 

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 for Windows® computer 

software. The dosimeters were calibrated before and after the 

measurement periods according to the manufacturer’s instructions.

Hearing Loss Assessment

On February 6–8, 2007, hearing tests were performed on 33 LA/SPCA 

employees. All LA/SPCA employees were eligible for the hearing tests. 

Workers reported to a NIOSH mobile test facility prior to starting their 

work shift. Informed consent was obtained from participants before 

they completed a short questionnaire about work history and self 

assessment of their hearing ability. 

A Tremetrics (Eden Prairie, Minnesota) Model AR 901 Hearing Booth 

and OSCAR 7 Electro-Acoustic Ear and Octave Monitor (Eden Prairie, 

Minnesota) provided an appropriate acoustic environment for testing. 

The booth was located inside the mobile test facility. The area was 

controlled for conversations and other extraneous noises during the 

tests. Hearing tests were collected with a Tremetrics Model HT Wizard 

Audiometer that had received a routine calibration check within the past 

year. Hearing tests were conducted by one of the investigators who had 

current certification from CAOHC. The audiometer tested the pure-tone 

frequencies of 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz in the 

computerized mode in each ear, left ear first. 

Test results for each participant were interpreted immediately after 

testing and explained to the participant. In addition, each participant 

was sent a letter summarizing his or her results along with a copy of the 

audiometric test results.

The evaluation criteria for noise and a discussion of the health effects of 

noise are provided in the Appendix.

Noise Assessment

Of the 22 personal noise measures, one collected on a kennel worker 

was invalid because of equipment malfunction. Of the remaining 21 

measures, 16 reached or exceeded the NIOSH REL. Of these, five 

reached or exceeded the OSHA AL. None exceeded the OSHA PEL. 

The full-shift TWA values for comparison with the NIOSH REL ranged 

from 82.2 dBA to 91.0 dBA. Table 1 summarizes these results.
Health Hazard Evaluation Report 2007-0068-3042 Page 

Results and Discussion (contin

Table 1

Range of Personal Noise Dosimetry Measures from 18 LA/SPCA Employees in the Kennel Area

Job Title Number of Measures Percent Dose

OSHA AL OSHA PEL NIOSH REL

Kennel Workers 16 17.1–57.9* 4.4–37.3 52.5–398.4**

Veterinary Technicians 2 10.9–27.1 4.7–12.5 49.8–100.7***

Client Care Workers 3 6.3–15.4 1.4–6.7 23.6–60.3

* OSHA AL reached or exceeded 5 times

** NIOSH REL reached or exceeded 15 times

*** NIOSH REL reached once

Personal noise levels exceeding the NIOSH REL were not surprising 

because (1) the barking of 150 dogs in a metal warehouse will result in 

noise reverberation, and (2) the shortage of water to the facility meant 

employees spent long hours cleaning the cages, thus increasing their 

duration of exposure. However, the personal noise levels at LA/SPCA 

were significantly lower (unpaired t-test, p<0.05) when compared to 

those at the SPCA in Cincinnati, Ohio [NIOSH 2007c]. The two facilities 

were comparable with respect to kennel work activities but differed 

in facility design. Most of the dog cages at LA/SPCA were arranged 

so that dogs did not see each other, resulting in less barking. This was 

accomplished by hanging a thick plastic panel on three of four sides of 

the cage. In addition, unused cages, pallets, and other items were stacked 

in such a way as to restrict public access to certain areas. The panels and 

the stacked items absorbed or redirected sound from the dogs.

Hearing Loss Assessment

Hearing tests were given to 33 LA/SPCA employees. These included 

nine kennel workers, four client care workers, four veterinary staff, six 

animal control officers, one behavior evaluator, three special events 

coordinators, and six administrative employees. The mean age of the 33 

employees was 35 years (range = 19–59). The mean age of the kennel 

workers was 25 years (range = 19–42). The median hearing levels and 

interquartile ranges for these employees are shown in Figure 1. The data 

showed considerable variability among individuals (as measured by the 

interquartile range). Three of the 33 workers showed hearing levels at 

one or more frequencies that exceeded 25 dB HL, indicating hearing 

loss. Two of the four were kennel workers. One employee had moderate 

to profound hearing loss in the right ear, and was advised to consult a 

physician. Twenty-one workers with normal hearing showed notches 

(hearing levels worsen over test frequencies before improving in the 

highest frequencies, forming a “notch” configuration) in one or both 

ears between 3000 and 6000 Hz indicating early signs of hearing loss. 

There were 46 notches in one or both ears of the 33 employees. 
Page  Health Hazard Evaluation Report 2007-0068-3042

Results and Discussion (contin

Noise control strategies in dog kennels are complicated. Soundabsorbing materials such as spray-on foam and fibrous mineral wool, 

which are usually used in industry and other indoor settings to reduce 

noise exposures, are not appropriate in kennels because they are 

difficult to clean while maintaining dryness in order to avoid mold 

and mildew. One approach may be to use sound-absorbing material 

on surfaces that do not need to be cleaned routinely, such as ceilings. 

Acoustical ceiling tiles that are waterproof and washable can be 

installed to reduce noise [Carter 2007]. In addition, floors can be 

covered with rubber mats to absorb sound from the barking dogs and to 

reduce noise from feeding and drinking dishes hitting on hard (concrete 

and tile) surfaces. These approaches may offer some reduction in 

noise levels, but do not eliminate the direct noise path from the dog 

to the worker. The new LA/SPCA facility will have sound-absorbing 

baffles installed in the ceilings. A noise survey should be conducted 

after controls are in place to determine if personal noise exposures to 

workers are reduced. 

Frequency (kHz) Left Ear Right Ear

25th percentile 75th percentile 25th percentile 75th percentile

0.5 10 20 5 15

1 0 10 0 5

2 0 10 0 10

3 5 10 0 10

4 5 15 0 15

6 5 20 5 20

8 0 15 0 15

Figure 1: Median Hearing Levels and Interquartile Ranges for 33 LA/SPCA Employees

0

5

10

15

20

0 1 2 3 4 5 6 7 8

Frequency (kHz)

Median Hearing Level (dB)

Left Ear Right Ear
Health Hazard Evaluation Report 2007-0068-3042 Page 

Results and Discussion (contin

Other Observations

We observed kennel workers wearing back braces to protect their backs 

from injury in case they had to lift a heavy dog. Research has shown 

that back braces do not prevent back injury; a comprehensive program 

for lifting, including informing employees on the correct way to lift 

heavy objects would be more beneficial [NIOSH 1994]. 

The SX-64 chemical used to clean the dog cages contained quarternary 

ammonium compounds that are an eye irritant, per the chemical’s 

MSDS. Therefore, employees should wear goggles when working 

with this chemical. An MSDS for every chemical used at the facility 

was filed in an area easily accessible to the kennel workers. However, 

employees were not trained in how to use the information in the 

MSDSs. 

Some employees were observed not wearing gloves when cleaning dog 

cages. This can cause the spread of diseases when combined with poor 

personal hygiene. 

This evaluation showed that kennel workers and some veterinary staff 

with the LA/SPCA were exposed to hazardous noise levels. In addition, 

three employees who participated in this evaluation showed hearing 

loss. However, because of the small sample size, inability to control 

for other sources of noise, and the relative youth of the workers with 

respect to time needed to develop hearing loss, it was not possible 

to determine whether the observed hearing loss was related to noise 

exposure at the kennel.

Based on the observations and findings of this evaluation, the following 

recommendations are offered to better protect the hearing of workers at 

the LA/SPCA.

1. Establish a hearing loss prevention program for the kennel 

workers and veterinary staff. The basic elements of the 

program should, at a minimum, meet the requirements for a 

hearing conservation program as outlined in the OSHA hearing 

conservation amendment [29 CFR 1910.95]. Other sources 

for defining effective hearing conservation programs are also 

available [Suter 2002; NIOSH 1996; Royster JD and Royster 

LH 1990]. 

2. Wear hearing protection devices (ear muffs or ear plugs) when 

working in the kennel areas. Train employees on the proper fit, 

selection, and maintenance of hearing protectors. For example, 

ear plugs should be deeply inserted into ear canals, and 

cushions on ear muffs should not be cracked or creased, and the 

head bands not sprung.

Conclusion

Recommendatio
Page  Health Hazard Evaluation Report 2007-0068-3042

Recommendatio

(continued) 3. Develop a comprehensive lifting program for employees

instead of the requirement that employees wear back braces.

4. Provide goggles to employees who are working with chemicals 

that cause eye irritation such as SX-64. 

5. Train employees on how to use the information in the MSDSs 

as required by the OSHA Hazard Communication Standard [29 

CFR 1910.1200].

6. Always wear gloves (for example nitrile or other suitable 

material based on the chemicals used) when cleaning animal 

cages and wash hands thoroughly after cleaning the cages.

Achutan C [2007]. Occupational noise levels during emergency relief 

operations in the aftermath of Hurricane Katrina. J Occup Environ Hyg 

4(4):D33-D35.

Carter T [2007]. Ask the builder: acoustical ceiling tiles — sound 

properties. [http://www.askthebuilder.com/B148_Acoustical_Ceiling_

Tiles_Sound_Properties.shtml]. Date accessed: May 4, 2007.

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

Printing Office, Office of the Federal Register.

Louisiana Society for the Prevention of Cruelty to Animals [2007]. 

[www.la-spca.org]. Date accessed: May 4, 2007.

NIOSH [1994]. Back belts: do they prevent injury? 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. 94-127. 

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

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. 96-110.

NIOSH [2006]. Health hazard evaluation report: Cincinnati Police 

Canine Unit, Cincinnati, OH. 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 Report No. 2006-0223-3029.

NIOSH [2007a]. Health hazard evaluation report: Liberty Veterinary 

Hospital, Liberty Township, OH. 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 Report No. 2006-0196-3036.

Referenc
Health Hazard Evaluation Report 2007-0068-3042 Page 

Rferences (continu

NIOSH [2007b]. Health hazard evaluation report: Kenton County 

Animal Shelter, Covington, KY. 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 Report No. 2006-0212-3035.

NIOSH [2007c]. Health hazard evaluation report: Society for the 

Prevention of Cruelty to Animals, Cincinnati, OH. 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 Report No. 2006-0222-3037.

Reid A, Dick F, Semple S [2004]. Dog noise as a risk factor for hearing 

loss among police dog handlers. Occup Med (London) 54(8):535–539.

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

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

Senn CL, Lewin JD [1975]. Barking dogs as an environmental problem. 

J Am Vet Med Assoc 66 (11):1065–1068.

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

Council for Accreditation in Occupational Hearing Conservation.
Page 10 Health Hazard Evaluation Report 2007-0068-304

The primary sources of evaluation criteria for noise in the workplace are: (1) the NIOSH REL [NIOSH 1992], and 

(2) 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.

Noise-induced hearing loss 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 decibel 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% 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, HPDs, 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 exposure criteria of 85 dBA as a TWA for 8 hours, 

5 dB less than the OSHA standard [NIOSH 1998]. 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 

Appendix: Evaluation Cr
Health Hazard Evaluation Report 2007-0068-3042 Page 

Appendix: Evaluation Criteria (con

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.

Audiometric evaluations of workers are conducted in quiet locations, preferably in a sound-attenuating chamber, 

by presenting pure tones of varying frequencies at threshold levels (i.e., the level of a sound that the person can 

just barely hear). Audiograms are displayed and stored as tables or charts of the HL at specified test frequencies 

[ANSI 1996]. Zero dB HL represents the hearing level of an average, young, normal-hearing individual. In 

OSHA-mandated hearing conservation programs, thresholds must be measured for pure-tone signals at the test 

frequencies of 500, 1000, 2000, 3000, 4000, and 6000 Hz. Each employee’s annual audiogram is compared to his 

or her own baseline audiogram to determine the amount of STS that occurred between the two tests. Specifically, 

OSHA states that an STS has occurred if the average threshold values at 2000, 3000, and 4000 Hz have increased 

by 10 dB or more in either ear when comparing the annual audiogram to the baseline audiogram [29 CFR 

1910.95]. The NIOSH recommended threshold shift criterion is a 15-dB shift at any frequency in either ear from 

500–6000 Hz measured twice in succession [NIOSH 1998]. Practically, the criterion is met by immediately 

retesting an employee who exhibits a 15-dB shift from baseline on an annual test. If the 15-dB shift persists on 

the second test, a confirmatory follow-up test should be given within 30 days of the initial annual examination. 

Both of these threshold shift criteria require at least two audiometric tests. In cases where only one audiogram 

is available, a criterion has been proposed for single-frequency impairment determinations [Eagles et al. 1968]. 

It employs a lower fence (the amount of hearing loss necessary before a hearing handicap is said to exist) of 25 

dB HL. With this criterion, any person who has a hearing level of 26 dB HL or greater at any single frequency 

is classified as having some degree of hearing loss. The degree of loss can range from mild (26–40 dB HL) to 

profound (>90 dB HL). 

The audiogram profile is a plot of the hearing test frequencies (x-axis) versus the hearing threshold levels (y-axis). 

Hearing threshold levels are plotted in reverse (the highest hearing level up to 0 or -10 dB). For many workers, the 

audiogram profile tends to slope downward toward the high frequencies with an improvement at the audiogram’s 

highest frequencies, forming a “notch” [Suter 2002]. A notch in an individual with normal hearing may indicate 

the early onset of hearing loss. Although there is no universal criterion to define what constitutes a “notch,” 

several mathematical models that attempt to identify notches are presented in the scientific literature [Dobie and 

Rabinowitz 2002; Niskar et al. 2001; Cooper and Owen 1976]. The relative strength and weaknesses of these 

models have also been reviewed [Rabinowitz and Dobie 2003]. For this evaluation, a notch is defined as the 

frequency where the hearing level is preceded by an improvement of at least 10 dB at the previous test frequency 

and followed by an improvement of at least 5 dB at the next. The notch from occupational noise exposures can 

occur between 3000 and 6000 Hz, depending on the frequency spectrum of the noise, and the anatomy of the 

individual’s ear [ACOM 1989; Osguthorpe and Klein 2001]. It is generally accepted that a notch at 4000 Hz is 

indicative of occupational hearing loss [Prince et al. 1997]. Some researchers have argued that the notch at 6000 

Hz may not be a good marker for occupational hearing loss because it is widely seen in young adults and others 

with little documented occupational noise exposure [McBride and Williams 2001]. An individual may have 

notches at different frequencies in one or both ears [Suter 2002]. 

References

ACOM [1989]. Occupational noise-induced hearing loss. ACOM Noise and Hearing Conservation Committee. J 

Occup Med 31:996.

ANSI [1996]. American national standard specification for audiometers. Melville, NY: Acoustical Society of 

America, American National Standards Institute, ANSI S3.6-1996.

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

Register.
Page 2 Health Hazard Evaluation Report 2007-0068-30

Appendix: Evaluation Criteria (con

Cooper JC, Owen JH [1976]. Audiologic profile of noise-induced hearing loss. Arch Otolaryngol 102:148–150.

Dobie RA, Rabinowitz PM [2002]. Change in audiometric configuration helps to determine whether a standard 

threshold shift is work-related. Spectrum 19(Suppl 1):17.

Eagles EL, Hardy WG, Catlin FI [1968]. Human Communication: The public health aspects of hearing, 

language, and speech disorders (NINDB monograph #7). Washington, D.C. Government Printing Office, USPHS 

Publication 1745.

McBride DI, Williams S [2001]. Audiometric notch as a sign of noise induced hearing loss. Occup Environ Med 

58:46–51.

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, Centers for Disease Control and Prevention, 

National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 98-126.

Niskar AS, Kieszak SM, Holmes AE, Esteban E, Rubin C, Brody DJ [2001]. Estimated prevalence of noiseinduced hearing threshold shifts among children 6 to 19 years of age: The Third National Health and Nutrition 

Examination Survey, 1988-1994, United States. Pediatrics 108(1):40–43.

Osguthorpe JD, Klein AJ [2001]. Occupational hearing conservation. Clin Audiol 24(2):403–414.

Prince M, Stayner L, Smith R, Gilbert S [1997]. A re-examination of risk estimates from the NIOSH occupational 

noise and hearing survey (ONHS). J Acous Soc Am 101:950–963.

Rabinowitz PM, Dobie RA [2003]. Use of the audiometric configuration to determine whether hearing loss is 

noise-induced: can “notch criteria” help? NHCA Spectrum 20(1):8–11.

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.

Suter AH [2002]. Hearing conservation manual. 4th ed. Milwaukee, WI: Council for Accreditation in Occupational 

Hearing Conservation.

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.
Health Hazard Evaluation Report 2007-0068-3042 Page 

Acknowledgement

and Availability

Repor

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.

This report was prepared by Chandran Achutan of HETAB, Division 

of Surveillance, Hazard Evaluations and Field Studies (DSHEFS). 

Field assistance was provided by Donnie Booher, Judith Eisenberg, 

and Kevin L. Dunn of DSHEFS. Desktop publishing was performed by 

Robin Smith and Donna Pfirman. Editorial assistance was provided by 

Ellen Galloway.

Copies of this report have been sent to employee and management 

representatives at the Louisiana Society for the Prevention of Cruelty to 

Animals; 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.
NIOSH [2007]. Health Hazard Evaluation Report: Noise Exposures and Hearing 

Loss Assessments among Animal Shelter Workers, Louisiana Society for the 

Prevention of Cruelty to Animals, Algiers, Louisiana: 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. 2007-0068-3042.

To receive NIOSH documents or information about 

occupational safety and health topics contact NIOSH at:

1-800-35-NIOSH (1-800-356-4674)

Fax: 1-513-533-8573

E-mail: pubstaft@cdc.gov

or visit the NIOSH web site at:

http://www.cdc.gov/niosh

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through research and prevention.

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Safety and Health