Health Hazard Evaluation Report 2014-0154-3275 Page 1

Evaluation of a Surgical Staff’s Noise 

Exposures during Total Knee Replacement 

Surgeries

Report No. 2014-0154-3275

March 2017

Kendra R. Broadwater, MPH

Scott E. Brueck MS, CIH

U.S. Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
Page 2 Health Hazard Evaluation Report 2014-0154-3275

Contents

Highlights...............................................i

Abbreviations ..................................... iii

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

Methods ............................................... 1

Results and Discussion........................ 2

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

Recommendations............................. 12

Appendix A ........................................ 14

Appendis B ......................................... 18

References.......................................... 20

Acknowledgements........................... 23

The employer is required to post a copy of this report for 30 days at or near the 

workplace(s) of affected employees. The employer must take steps to ensure 

that the posted report is not altered, defaced, or covered by other material.

The cover photo is a close-up image of sorbent tubes, which are used by the HHE 

Program to measure airborne exposures. This photo is an artistic representation that may 

not be related to this Health Hazard Evaluation. Photo by NIOSH.
Health Hazard Evaluation Report 2014-0154-3275 Page i

We measured surgical staff’s 

noise exposures during total 

knee replacement surgeries. 

One surgeon was overexposed 

to noise on one day. The 

other surgeon and the rest 

of the surgical staff were 

not overexposed to noise. 

We estimated the potential 

range of noise exposures for 

surgeons and found that they 

could be overexposed to noise 

depending on the noise level 

during surgeries, and length 

and number of surgeries. 

We recommended including 

orthopedic surgeons in a hearing 

loss prevention program, using 

quieter surgical tools, and 

providing hearing protection. 

Highlights of this Evaluation

The Health Hazard Evaluation Program received a request from a medical and surgical 

hospital. An employer representative was concerned about the surgical staff’s exposure to 

noise during total knee replacement surgeries. 

What We Did

● We measured surgical staff’s noise exposures in January and July 2015. 

● We observed work practices and spoke informally with employees about their work 

activities and noise. 

● We estimated the surgeons’ potential noise exposures as a function of the number and 

length of surgeries in a work day. 

What We Found

● Noise exposures were highest during surgeries. 

Most of the noise was caused by powered 

surgical tools. 

● One surgeon’s noise exposure was above the 

National Institute for Occupational Safety and 

Health recommended exposure limit on one of 

the days we measured noise. None of the other 

noise exposures were above the limit.

● None of the surgical staffs’ noise exposures 

were above the Occupational Safety and Health 

Administration noise exposure limits.

● We estimated that surgeons’ noise exposures 

could exceed the recommended exposure 

limit, depending on the number and length of 

surgeries and noise levels during surgeries. 

What the Employer Can Do

● Purchase powered surgical tools that generate 

the least amount of noise when replacing or 

buying new surgical tools. 

● Include orthopedic surgeons in a hearing loss prevention program that includes annual 

hearing tests, appropriate hearing protection, training, and noise exposure assessments.

● Offer flat-attenuation ear plugs or noise cancelling earmuffs for surgeons’ use during 

knee replacement surgeries. 
Page ii Health Hazard Evaluation Report 2014-0154-3275

What Employees Can Do

● Wear hearing protection devices during surgery.

● Keep the volume of music in the operating room low to limit background noise levels 

and minimize the potential for speech interference. 
Health Hazard Evaluation Report 2014-0154-3275 Page iii

Abbreviations

ACGIH® American Conference of Governmental Industrial Hygienists

AL Action level

CFR Code of Federal Regulations

dB Decibels

dBA Decibels, A-weighted

Hz Hertz

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

TLV® Threshold limit value

TWA Time-weighted average

WEELTM Workplace environmental exposure level
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Health Hazard Evaluation Report 2014-0154-3275 Page 1

Introduction

The Health Hazard Evaluation Program received a request from employer representatives at 

a hospital. They were concerned about the potential for noise-induced hearing loss (NIHL) 

among operating room employees performing total knee replacement surgeries, also known 

as knee arthroplasty. We visited the hospital in January 2015 and July 2015 to observe 

total knee replacement surgeries, learn more about the equipment and tools used during 

surgeries, and measure noise exposures of surgical staff. A typical surgical team for total knee 

replacement surgeries included a surgical assistant, anesthesiologist, circulating nurse, scrub 

nurse, and surgeon. A surgical fellow may also be present to assist the surgeon. 

Methods

The objectives of this health hazard evaluation were to (1) measure full-shift time-weighted 

average (TWA) personal noise exposures among operating room personnel during total knee 

replacement surgeries and compare exposures to occupational exposure limits (OELs) for 

noise, (2) compute task-based TWA noise exposures during surgeries, (3) compare noise 

exposure measurements taken on the surgeons’ right and left sides, and (4) model surgeons’ 

range of noise exposures using numbers of surgeries, length of surgeries, and noise levels 

during surgeries as variables. 

Personal Noise Monitoring

We measured operating room staff’s full-shift TWA noise exposures using Larson Davis 

SparkTM model 706RC integrating noise dosimeters. The dosimeters integrated noise at a 

50-hertz (Hz) sampling rate and data-logged 1-second averaged noise levels for the duration 

of the measurement period. We measured noise exposure for three job titles: surgeons, 

surgical assistants, and anesthesiologists. We manually tracked the time that surgeons spent 

in surgery versus the time they spent outside surgery. Surgical staff wore dosimeters on 

the waistband of their medical scrubs; we attached the dosimeter microphone in an upright 

position midway between the neck and the end of the shoulder on the outside of the surgical 

gown. We covered the microphone with a windscreen to reduce artifact noise caused by 

accidental bumping or rubbing. Each surgeon wore two dosimeters, with one microphone 

clipped to each shoulder. At the end of the work shift, we downloaded the noise measurement 

data from the dosimeters using the PCB Piezotronics BlazeTM program. 

The dosimeters simultaneously collected noise data using three settings to allow comparison 

of noise measurement results with three different noise exposure limits, the Occupational 

Safety and Health Administration (OSHA) permissible exposure limit (PEL), the OSHA 

action level (AL), and the National Institute for Occupational Safety and Health (NIOSH) 

recommended exposure limit (REL). For noise dosimeter measurements, OSHA uses a 

90 decibel, A-weighted (dBA) threshold and a 5-decibel (dB) exchange rate for the PEL 

measurements and an 80 dBA threshold and 5-dB exchange rate for the AL measurements. 

NIOSH uses an 80 dBA threshold and a 3-dB exchange rate for the REL measurements. 

Noise below the threshold level is not integrated by the noise dosimeter for the TWA 
Page 2 Health Hazard Evaluation Report 2014-0154-3275

measurement results. The exchange rate refers to the amount of dB by which the sound level 

may increase if the exposure time is halved, or decrease if exposure time is doubled. NIOSH 

considers noise measured using the 3-dB exchange rate to more accurately relate noise 

exposures to hearing loss risk [NIOSH 1998]. Additional information on noise exposure 

limits and health effects is provided in Appendix A.

Comparing Left and Right Ear Noise Exposures

To compare whether differences occurred between the surgeons’ right and left ear noise 

exposures during surgeries, we took separate personal noise dosimetry measurements on the 

surgeons’ right and left sides. For analysis, we performed two-sided, paired Student’s t-test 

and determined the P value to examine the statistical relationship between the surgeons’ right 

side versus left side noise measurements.

Modeling Surgeon Noise Exposures

We modeled surgeons’ TWA noise exposures on the basis of the following variables: number 

of surgeries, surgical noise level, nonsurgical noise level, surgery duration, and shift length. 

Equation 1 shows how we calculated surgeons’ TWA noise exposures.

Equation 1. Surgeons’ estimated TWA noise exposures

Where:

 W = length of workshift (minutes)

 N = number of surgeries performed

 T = time per surgery (minutes)

 S

avg = measured TWA noise level during surgery (dBA)

avg = measured TWA noise level during nonsurgical periods (dBA)

Results and Discussion

Observations

During the evaluation, each surgical team performed three or four total knee replacements 

on each day of noise monitoring. During one of our days of monitoring, a surgical fellow 

assisted the surgeon. A knee implant vendor representative was also present to help select 

the proper joint replacement components. Surgeries were performed across three operating 

rooms. The rooms were similar in size and design. The operating rooms had vinyl floors and 

drywall ceilings and walls. Surgical procedures required establishing a sterile field around the 

patient to reduce the patient’s risk of acquiring infections. The sterile field included the area 

from the patient’s shoulder to slightly past the patient’s foot and extending about 5 feet on 

either side of the patient. The sterile field was separated from the nonsterile field by plastic 

sheeting at the shoulder of the patient. Personnel movement between the sterile and nonsterile 

 NS
Health Hazard Evaluation Report 2014-0154-3275 Page 3

fields during surgeries was limited to reduce the patient’s risk of infection. On the days we 

monitored, the surgical staff worked 8-hour work shifts. However, surgeons or surgical staff 

reported during informal conversations that they sometimes worked longer shifts.

Surgeon A performed four surgeries on each of 2 days of monitoring. On the first day, he 

performed surgeries on one 58-year-old male and three females (aged 45, 65, and 71 years). 

On the second day, he performed surgery on three males (aged 58, 67, 73 years) and one 

83-year-old female. We monitored surgeon B’s noise exposure for one day. He performed 

surgeries on two males (aged 61 and 65) and one female (aged 74). The surgeons reported 

that noise levels seemed higher during knee replacements on patients with greater bone 

density; younger, male, and larger patients tended to have greater bone density than older, 

female, or smaller patients.

Surgical staff, including the scrub nurse, circulating nurse, surgical assistant, and 

anesthesiologist, prepared the room, equipment, tools, and the patient for surgery. During 

surgeries, the surgeon exposed the knee joint, then removed portions of the tibia and femur 

bones using a surgical saw. The knee was measured for the correct implants, which were then 

fixed to the tibial head and implanted into the femoral head using surgical drills, a hammer, 

and adhesive implant cement. After the implant cement cured, the incision was closed. 

Following surgery, operating room staff disposed of waste, prepared used surgical equipment 

for sterilization, and transported the patient to the recovery room. Between procedures, 

surgeons spoke with patients, typed or dictated post-op notes, prepared for upcoming 

surgeries, and completed other administrative duties. 

The use of pneumatically powered surgical tools (saws and drills) and hammers were the 

primary noise sources in the operating room. Other sources of noise included placing or 

moving surgical equipment and tools on metal surgical trays; noise from vitals sign monitors, 

anesthesia equipment, and lavage equipment; background music; and talking. The surgical 

tool and knee implant vendor representative noted that approximately 6 months before our 

first visit the hospital had begun using a sharper, thinner blade on the surgical saw, which 

reportedly reduced noise during orthopedic surgeries. 

Most surgeries were performed with a surgeon and one surgical assistant on either side 

of the knee undergoing replacement. During two surgeries, an orthopedic surgery fellow 

also worked on the knee. An anesthesiologist worked at the head of the patient, outside the 

sterile field. At the foot of the patient in the sterile field, a scrub nurse provided and collected 

surgical tools and mixed resin for implantation. The circulating nurse recorded surgical 

notes on a computer in the corner of the operating room. Saws and hammers were used 

during every knee replacement. The surgical team used the Stryker® System 6 tool system, 

equipped with a 1.19 millimeter Attune® sawblade. 

Employees did not wear hearing protection devices. One employee inserted pieces of paper 

that had been rolled into balls into the ear canals as protection against noise exposure. The 

employee reported doing this for every orthopedic surgery. The hospital did not provide 

hearing protection devices in the surgical staff locker room, the employee break room, the 

surgical suite hand wash area, or the operating rooms. 
Page 4 Health Hazard Evaluation Report 2014-0154-3275

Personal Noise Exposure Measurements

A summary of TWA personal noise exposure measurements is provided in Table 1. Detailed 

exposure results are in Appendix B, Table B1. Surgeons and surgical fellows used the 

surgical tools and were closest to noise sources during surgeries, and had the highest noise 

exposures. In contrast, the anesthesiologists were further from noise sources and had the 

lowest noise exposures. Surgical assistants’ and the anesthesiologists’ full-shift TWA noise 

exposures were below NIOSH and OSHA 8-hour TWA noise exposure limits. NIOSH 

reported similar results for surgical staff (registered nurses and surgical technicians) during 

orthopedic surgeries in a previous evaluation [NIOSH 2010a]. 

Table 1. Summary of surgical staff full-shift TWA noise exposure measurements

Job title Number

of 

measurements

NIOSH REL 

criterion 

(dBA)

OSHA AL 

criterion 

(dBA)

OSHA PEL 

criterion 

(dBA)

Surgeon 

(right shoulder measurement)

3 81.4–86.8 76.5–83.5 68.1–78.2

Surgeon 

(left shoulder measurement)

3 77.9–83.2 71.3–77.9 62.3–73.0

Surgical fellow 

(right shoulder measurement)

1 81.5 74.3 70.4

Surgical fellow 

(left shoulder measurement)

1 83.0 75.6 72.5

Surgical assistant 3 76.0–78.7 64.2–70.8 58.2–65.4

Anesthesiologist 2 67.8–71.8 58.2–75.8 38.4–46.1

Noise exposure limits (8-hour work shift) 85 85 90

On one of the days we monitored noise, one of the surgeons was exposed to a TWA noise 

level that was above the NIOSH REL, but below the OSHA AL and PEL on his right 

side measurement. All the other TWA noise measurements on surgeons were below noise 

exposure limits. 

Using the NIOSH REL noise measurement criterion, both surgeons’ TWA noise measurement 

results taken on their right side were significantly higher than those taken on their left side. 

The noise measurement results for surgeon A were 1.4–5.0 dBA higher on the right side 

than the left side, with a mean difference of 3.0 dBA. For surgeon B the noise measurement 

results were 0.2–1.6 dBA higher on the right side than the left side, with a mean difference 

of 0.9 dBA. Using a two-sided, paired Student’s t-test for statistical analysis, we found that 

results of noise exposure measurements taken on the surgeon’s right side using NIOSH REL 

noise measurement criterion were significantly higher than exposures measured on the left 

side (P = 0.04). 

Surgeons’ right side noise measurements were most likely higher because both surgeons 

were right handed and held the powered surgical tools and hammers on their right sides. As 
Health Hazard Evaluation Report 2014-0154-3275 Page 5

a result, their right ears were closer to the noise sources. In contrast, the surgical fellow had 

higher noise measurements on the left side for the first two surgeries, ranging 2.2–2.9 dBA 

higher on the left side versus the right side. We noted that sometimes the fellow stood on the 

surgeon’s right side during surgeries; therefore, the left ear was closer to the surgical tools 

used by the surgeon. In contrast, the fellow’s right side measurement during the third surgery 

was 2.3 dBA higher than the left side measurement. 

Figure 1 shows the time history profile for surgeon A on the first day of noise monitoring. The 

surgeon completed four surgeries during the work shift. Noise levels were above 85 dBA, the 

NIOSH REL, for a greater proportion of time during the surgeries than during the time outside 

surgeries. Additionally, noise exposures were sometimes 90–100 dBA during surgeries, and 

fluctuated substantially because of intermittent surgical tool use. During knee replacements, 

surgeons used reciprocating saws, drills, and hammers multiple times for periods generally 

ranging from 1–30 seconds. We measured sound levels approximately 6 feet from the surgeon; 

those levels ranged from 80–93 dBA when the surgeon or surgical assistant was using saws 

and hammers. Because sound decreases with distance according to the inverse square law, the 

sound levels at the surgeon’s ear during tool use are likely to be several decibels higher than we 

measured. Researchers have previously measured noise levels ranging from 90–110 dBA near 

surgeons during use of reciprocating saws [Dodenhoff 1995; Fritsch et al. 2010; Kamal 1982; 

Mullett et al. 1999; Nott and West 2003; Willett 1991].

Figure 1. Time history profile showing surgeon A’s noise exposure (outlined in boxes in figure) during 

four knee replacements on January 13, 2015, using NIOSH noise measurement criterion.
Page 6 Health Hazard Evaluation Report 2014-0154-3275

Figure 2 provides a histogram showing the surgeons’ percent time exposed to various sound levels 

during surgeries. Most of the time the surgeons’ and surgical fellow’s noise exposures were below 

80 dBA during surgeries. During the two work shifts we monitored, surgeon A’s noise exposure 

was above 85 dBA for 18% of the time on the first day of monitoring and 15% of the time on 

the second day of monitoring. The surgical fellow and surgeon B spent about 10%–12% of their 

time during surgeries exposed to sound levels above 85 dBA. Both surgeons and the surgical 

fellow spent a comparable percent of time (5%–7%) during surgery exposed to noise levels 

above 90 dBA; this noise was primarily from surgical tools. Similarly, Willett [1991] found that 

powered instrument use accounted for 4% of the time of an operation. Although powered surgical 

instrument use comprised only a small proportion of time, it contributed significantly to total noise 

exposures according to our noise exposure measurements. Overall, the TWA noise measurements 

for surgeons during surgeries were slightly greater than those reported by Love [2003] in a study 

of surgeons’ noise exposures during total knee and total hip replacements. In that study, noise 

exposures during total knee replacements were 79.7 and 82.1 dBA.

Figure 2. Histogram of the surgeons’ and surgical fellow’s noise exposures during surgeries.
Health Hazard Evaluation Report 2014-0154-3275 Page 7

We computed the surgeons’ task-based TWA noise exposures during surgeries and during the 

time outside surgeries, on the basis of the time they spent in each task. The duration of each 

surgery ranged from 49–113 minutes and varied with the complexity of each surgery and 

surgeons’ individual techniques. The total time in surgery accounted for 49%–53% of each 

surgeon or the surgical fellow’s 8-hour work shift. Reducing the total time in surgery during a 

shift of fixed length would reduce TWA noise exposures.

Table 2 shows the task-based range of TWA noise exposure levels during surgeries and 

during the time outside surgeries. As expected, noise exposures were higher during surgeries 

than during the time between surgeries. Surgeons have very little exposure to high noise 

levels outside of surgeries. Surgeon A’s noise exposure during surgeries on the first day of 

monitoring was higher than his exposures on the second day of monitoring, and higher than 

surgeon B’s noise exposures. These differences in noise exposures are most likely related 

to differences in complexity of the surgeries, tool use, bone densities of patients, length of 

surgeries, and surgeons’ techniques. 

Table 2. Surgeons’ TWA noise exposures during surgical and nonsurgical periods

Task

duration

(minutes)

NIOSH REL 

criterion 

(dBA)

OSHA AL 

criterion 

(dBA)

OSHA PEL 

criterion 

(dBA)

Surgeon A

January 13, 2015

Surgery (n = 4) 50–69 86.2–89.2 83.6–86.4 76.8–82.8

Not in surgery 199 81.6 78.0 66.2

TWA noise exposure 432 86.8 83.5 78.2

Surgeon A

January 20, 2015

Surgery (n = 4) 49–74 81.9–84.0 76.6–80.7 70.6–72.9

Not in surgery 190 76.2 70.5 48.3

TWA noise exposure 444 81.4 76.5 68.1

Surgeon B

July 22, 2015

Surgery (n = 3) 64–113 84.0–85.3 78.6–79.9 74.9–76.7

Not in surgery 100 77.5 72.4 53.1

TWA noise exposure 357 83.8 78.0 74.0

Surgical fellow

July 22, 2015

Surgery (n = 3) 64–113 81.3–86.1 74.4–79.0 71.2–77.6

Not in surgery 140 75.1 68.5 47.1

TWA noise exposure 397 83.0 75.6 72.5
Page 8 Health Hazard Evaluation Report 2014-0154-3275

Noise Exposure Estimates Based on Number of Surgeries

We used the noise exposure data that we collected during our three site visits to model an 

expected range of surgeons’ full-shift TWA noise exposures by shift length, number of 

surgeries, surgery duration, and noise exposure levels during and outside of surgeries. Figures 

3 through 8 show the estimated TWA noise exposure ranges for 8-, 10-, and 12-hour shifts 

using the shortest and the longest surgery durations we documented and the range of noise 

exposures we measured during surgeries (on the basis of NIOSH measurement criterion). 

NIOSH adjusts the REL for longer works shifts. The REL is 84.0 dBA for 10-hour work 

shifts and 83.2 dBA for 12-hour work shifts. Surgeons’ noise exposure levels could exceed 

the REL, depending on the number, duration, and noise exposure levels during surgeries. 

Figure 3. Range of surgeons’ estimated noise exposures for an 8-hour work shift on the basis of the 

range of noise levels during surgeries and number of surgeries with a 49-minute duration.
Health Hazard Evaluation Report 2014-0154-3275 Page 9

Figure 4. Range of surgeons’ estimated noise exposures for an 8-hour work shift on the basis of the 

range of noise levels during surgeries and number of surgeries with a 113-minute duration.

Figure 5. Range of surgeons’ estimated noise exposures for a 10-hour work shift on the basis of the 

range of noise levels during surgeries and number of surgeries with a 49-minute duration.
Page 10 Health Hazard Evaluation Report 2014-0154-3275

Figure 6. Range of surgeons’ estimated noise exposures for a 10-hour work shift on the basis of the 

range of noise levels during surgeries and number of surgeries with a 113-minute duration.

Figure 7. Range of surgeons’ estimated noise exposures for a 12-hour work shift on the basis of the 

range of noise levels during surgeries and number of surgeries with a 49-minute duration.
Health Hazard Evaluation Report 2014-0154-3275 Page 11

Figure 8. Range of surgeons’ estimated noise exposures for a 12-hour work shift on the basis of the 

range of noise levels during surgeries and number of surgeries with a 113-minute duration.

Noise Exposure and Hearing Loss in Surgeons

With the exception of one TWA full-shift noise measurement, surgeons’ noise exposures were 

below OELs. However, exposures are variable, and our estimate of potential noise exposures 

show that, at times, noise exposures could exceed the NIOSH REL. NIOSH research has 

shown that workers exposed to average daily noise levels of 80–85 dBA have a 1%–8% 

risk of material hearing impairment over a 40-year working lifetime, demonstrating that 

noise exposure should be limited as possible, even to levels below the REL [NIOSH 1998]. 

Furthermore, previous studies have shown that up to 50% of orthopedic operating room 

personnel exposed to noise from powered instruments experienced low-level NIHL, and that 

the severity correlates with duration of employment [Kamal 1982; Willett 1991]. 

Because powered surgical tools generate the highest noise levels in the operating room, noise 

reduction efforts should focus on using surgical instruments that generate the least amount 

of noise. Research has shown that the saw blade design for reciprocating surgical saws 

can affect noise levels [Sydney et al. 2007]. A “Buy Quiet” strategy should be used when 

purchasing or replacing surgical tools or tool components. Specifically, the amount of noise 

generated by the new equipment should be considered as part of the purchasing decision. 

Until noise levels from surgical equipment are reduced, offering and encouraging the use of 

hearing protection can help protect surgeons from long-term risk of hearing loss. However, 

hearing protection must be chosen carefully, because hearing protectors that excessively 

attenuate noise may substantially interfere with vital surgical staff communication or the 

ability to hear patient monitoring equipment. On the basis of the surgeons’ noise exposures 

and their need for communication, hearing protection that attenuates noise evenly across all 
Page 12 Health Hazard Evaluation Report 2014-0154-3275

frequencies (i.e., flat attenuation earplugs) and has a low noise reduction rating would be an 

appropriate option. Noise cancellation earmuffs provide another option for hearing protection 

[Fritch et al. 2010].

Conclusions

Powered surgical tools were the primary sources of noise in the orthopedic operating room 

and noise levels were highest during surgical procedures. One of the surgeon’s personal 

noise exposure exceeded the NIOSH REL on one of the days we did noise monitoring, but 

the other personal noise exposure measurements for surgeons and other surgical staff were 

below all OELs. On the basis of our noise measurements and our estimates of potential noise 

exposures, surgeons’ noise exposures may exceed the NIOSH REL, depending on surgery 

length, shift length, and number of surgeries in a shift. Surgeons can reduce their risk of 

hearing loss by using flat attenuation ear plugs or noise cancellation earmuffs. 

Recommendations

On the basis of our findings, we recommend the actions listed below. We encourage the hospital 

to use a labor-management health and safety committee or working group to discuss our 

recommendations and develop an action plan. Those involved in the work can best set priorities 

and assess the feasibility of our recommendations for the specific situation at the hospital. 

Our recommendations are based on an approach known as the hierarchy of controls. This 

approach groups actions by their likely effectiveness in reducing or removing hazards. In 

most cases, the preferred approach is to eliminate hazardous materials or processes and 

install engineering controls to reduce exposure or shield employees. Until such controls 

are in place, or if they are not effective or feasible, administrative measures and personal 

protective equipment may be needed. 

Engineering Controls

Engineering controls reduce employees’ exposures by removing the hazard from the process or by 

placing a barrier between the hazard and the employee. Engineering controls protect employees 

effectively without placing primary responsibility of implementation on the employee. 

1. Replace the current blades in the reciprocating surgical saws with blades designed to 

generate less noise, if available. 

Administrative Controls

The term administrative controls refers to employer-dictated work practices and policies 

to reduce or prevent hazardous exposures. Their effectiveness depends on employer 

commitment and employee acceptance. Regular monitoring and reinforcement are necessary 

to ensure that policies and procedures are followed consistently.

1. Ensure that powered surgical tools are operating as quietly as possible and are 

maintained regularly. A change in volume of an instrument may indicate that the 
Health Hazard Evaluation Report 2014-0154-3275 Page 13

instrument needs service or replacement.

2. Use a “Buy Quiet” strategy to identify and purchase surgical tools and equipment that 

generate the least amount of noise. Investigate whether newer models of powered 

surgical tools or blades, or equipment from other manufacturers produces less noise. 

Information about Buy Quiet programs can be found at 

https://www.cdc.gov/niosh/topics/buyquiet/.

3. Reduce the likelihood of surgeons’ noise exposures exceeding the NIOSH REL by 

taking into account the number of surgeries, duration of surgeries, and length of shift 

when preparing each surgeon’s daily surgical schedule. 

4. Establish a hearing loss prevention program for orthopedic surgeons. The program 

should include annual audiometric exams, provide hearing protection, provide training 

on hearing loss and use of hearing protection, and include periodic noise exposure 

assessments. For additional information on noise and guidance on developing a 

hearing loss prevention program, refer to the NIOSH document, Occupational Noise 

Exposure, at https://www.cdc.gov/niosh/docs/98-126/default.html. 

5. Keep the volume of music played in the operating room low to limit background noise 

and minimize the potential for speech interference. 

Personal Protective Equipment

Personal protective equipment is the least effective means for controlling hazardous 

exposures. Proper use of personal protective equipment requires a comprehensive program 

and a high level of employee involvement and commitment. The right personal protective 

equipment must be chosen for each hazard. Supporting programs such as training, changeout schedules, and medical assessment may be needed. Personal protective equipment should 

not be the sole method for controlling hazardous exposures. Rather, personal protective 

equipment should be used until effective engineering and administrative controls are in place.

1. Offer and encourage surgeons to use flat attenuation ear plugs or noise cancelling 

earmuffs during knee replacement surgeries. These types of hearing protectors 

attenuate noise, but have less effect on speech comprehension. 
Page 14 Health Hazard Evaluation Report 2014-0154-3275

Appendix A: Occupational Exposure Limits and 

Health Effects of Noise

NIOSH investigators refer to mandatory (legally enforceable) and recommended OELs for 

chemical, physical, and biological agents when evaluating workplace hazards. OELs have 

been developed by federal agencies and safety and health organizations to prevent adverse 

health effects from workplace exposures. Generally, OELs suggest levels of exposure that 

most employees may be exposed to for up to 10 hours per day, 40 hours per week, for a 

working lifetime, without experiencing adverse health effects. However, not all employees 

will be protected if their exposures are maintained below these levels. Some may have 

adverse health effects because of individual susceptibility, a pre-existing medical condition, 

or a hypersensitivity (allergy). In addition, some hazardous substances act in combination 

with other exposures, with the general environment, or with medications or personal habits of 

the employee to produce adverse health effects. Most OELs address airborne exposures, but 

some substances can be absorbed directly through the skin and mucous membranes.

Most OELs are expressed as a TWA exposure. A TWA refers to the average exposure during 

a normal 8- to 10-hour workday. Some chemical substances and physical agents have 

recommended short-term exposure limits or ceiling values. Unless otherwise noted, the shortterm exposure limit is a 15-minute TWA exposure. It should not be exceeded at any time 

during a workday. The ceiling limit should not be exceeded at any time.

In the United States, OELs have been established by federal agencies, professional 

organizations, state and local governments, and other entities. Some OELs are legally 

enforceable limits; others are recommendations. 

● The U.S. Department of Labor OSHA PELs (29 CFR 1910 [general industry]; 29 CFR 

1926 [construction industry]; and 29 CFR 1917 [maritime industry]) are legal limits. 

These limits are enforceable in workplaces covered under the Occupational Safety and 

Health Act of 1970. 

● NIOSH RELs are recommendations based on a critical review of the scientific and 

technical information and the adequacy of methods to identify and control the hazard. 

NIOSH RELs are published in the NIOSH Pocket Guide to Chemical Hazards [NIOSH 

2010b]. NIOSH also recommends risk management practices (e.g., engineering 

controls, safe work practices, employee education/training, personal protective 

equipment, and exposure and medical monitoring) to minimize the risk of exposure and 

adverse health effects.

● Other OELs commonly used and cited in the United States include the threshold limit 

values (TLVs), which are recommended by the American Conference of Governmental 

Industrial Hygienists, a professional organization, and the workplace environmental 

exposure levels (WEELs), which are recommended by the American Industrial Hygiene 

Association, another professional organization. The TLVs and WEELs are developed 

by committee members of these associations from a review of the published, peerreviewed literature. These OELs are not consensus standards. TLVs are considered 
Health Hazard Evaluation Report 2014-0154-3275 Page 15

voluntary exposure guidelines for use by industrial hygienists and others trained in 

this discipline “to assist in the control of health hazards” [ACGIH 2016]. WEELs have 

been established for some chemicals “when no other legal or authoritative limits exist” 

[AIHA 2016].

Outside the United States, OELs have been established by various agencies and organizations 

and include legal and recommended limits. The Institut für Arbeitsschutz der Deutschen 

Gesetzlichen Unfallversicherung (Institute for Occupational Safety and Health of the German 

Social Accident Insurance) maintains a database of international OELs from European Union 

member states, Canada (Québec), Japan, Switzerland, and the United States. The database, 

available at http://www.dguv.de/ifa/GESTIS/GESTIS-Internationale-Grenzwerte-fürchemische-Substanzen-limit-values-for-chemical-agents/index-2.jsp, contains international 

limits for more than 2,000 hazardous substances and is updated periodically. 

OSHA requires an employer to furnish employees a place of employment free from 

recognized hazards that cause 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))]. This is 

true in the absence of a specific OEL. It also is important to keep in mind that OELs may not 

reflect current health-based information.

When multiple OELs exist for a substance or agent, NIOSH investigators generally 

encourage employers to use the lowest OEL when making risk assessment and risk 

management decisions. NIOSH investigators also encourage use of the hierarchy of controls 

approach to eliminate or minimize workplace hazards. This includes, in order of preference, 

the use of (1) substitution or elimination of the hazardous agent, (2) engineering controls 

(e.g., local exhaust ventilation, process enclosure, dilution ventilation), (3) administrative 

controls (e.g., limiting time of exposure, employee training, work practice changes, medical 

surveillance), and (4) personal protective equipment (e.g., respiratory protection, gloves, 

eye protection, hearing protection). Control banding, a qualitative risk assessment and risk 

management tool, is a complementary approach to protecting employee health. Control 

banding focuses on how broad categories of risk should be managed. Information on control 

banding is available at http://www.cdc.gov/niosh/topics/ctrlbanding/. This approach can be 

applied in situations where OELs have not been established or can be used to supplement 

existing OELs.

Noise

NIHL is an irreversible condition that progresses with noise exposure. It is caused by damage 

to the nerve cells of the inner ear and, unlike some other types of hearing disorders, cannot 

be treated medically [Berger et al. 2003]. More than 22 million U.S. workers are estimated to 

be exposed to workplace noise levels above 85 dBA [Tak et al. 2009]. NIOSH estimates that 

workers exposed to an average daily noise level of 85 dBA over a 40-year working lifetime 

have an 8% excess risk of material hearing impairment. This excess risk increases to 25% for 

an average daily noise exposure of 90 dBA [NIOSH 1998]. NIOSH defines material hearing 

impairment as an average of the hearing threshold levels for both ears that exceeds 25 dB at 

frequencies of 1,000 Hz, 2000 Hz, 3000 Hz, and 4000 Hz. 
Page 16 Health Hazard Evaluation Report 2014-0154-3275

Although hearing ability commonly declines with age, exposure to excessive noise can increase 

the rate of hearing loss. In most cases, NIHL develops slowly from repeated exposure to noise 

over time, but the progression of hearing loss is typically the greatest during the first several 

years of noise exposure. NIHL can also result from short duration exposures to high noise 

levels or even from a single exposure to an impulse noise or a continuous noise, depending 

on the intensity of the noise and the individual’s susceptibility to NIHL [Berger et al. 2003]. 

Noise exposed workers can develop substantial NIHL before it is clearly recognized. Even mild 

hearing losses can impair one’s ability to understand speech and hear many important sounds. 

In addition, some people with NIHL also develop “tinnitus.” Tinnitus is a condition in which 

a person perceives hearing sound in one or both ears, but no external sound is present. Persons 

with tinnitus often describe hearing ringing, hissing, buzzing, whistling, clicking, or chirping 

like crickets. Tinnitus can be intermittent or continuous and the perceived volume can range 

from soft to loud. Currently, no cure for tinnitus exists.

The preferred unit for reporting of noise measurements is the decibel, A-weighted. 

A-weighting is used because it approximates the “equal loudness perception characteristics 

of human hearing for pure tones relative to a reference of 40 dB at a frequency of 1,000 Hz” 

and is considered to provide a better estimation of hearing loss risk than using unweighted 

or other weighting measurements [Earshen 2003]. The dB unit is dimensionless, and it 

represents the logarithmic ratio of the measured sound pressure level to an arbitrary reference 

sound pressure (20 micropascals, which is defined as the threshold of normal human hearing 

at a frequency of 1,000 Hz). Decibels are used because of the very large range of sound 

pressure levels audible to the human ear. Because the dB is logarithmic, an increase of 3 dB 

is a doubling of the sound energy, an increase of 10 dB is a 10-fold increase, and an increase 

of 20 dB is a 100-fold increase in sound energy. Noise exposures expressed in decibels 

cannot be averaged by taking the arithmetic mean.

Workers exposed to noise should have baseline and yearly hearing tests to evaluate their 

hearing thresholds and determine whether their hearing has changed over time. Hearing 

testing should be done in a quiet location, such as an audiometric test booth where 

background noise does not interfere with accurate measurement of hearing thresholds. In 

workplace hearing conservation programs, hearing thresholds must be measured at 500 Hz, 

1,000 Hz, 2,000 Hz, 3,000 Hz, 4,000 Hz, and 6,000 Hz. Additionally, NIOSH recommends 

that 8000 Hz should also be tested [NIOSH 1998]. The OSHA hearing conservation standard 

requires analysis of changes from baseline hearing thresholds to determine if the changes 

are substantial enough to meet OSHA criteria for a standard threshold shift. OSHA defines a 

standard threshold shift as a change in hearing threshold relative to the baseline hearing test 

of an average of 10 dB or more at 2,000 Hz, 3,000 Hz, and 4,000 Hz in either ear [29 CFR 

1910.95]. If a standard threshold shift occurs, the company must determine if the hearing loss 

also meets the requirements to be recorded on the OSHA Form 300 Log of Work-Related 

Injuries and Illnesses [29 CFR 1904.1]. In contrast to OSHA, NIOSH defines a significant 

threshold shift as an increase in the hearing threshold level of 15 dB or more, relative to the 

baseline audiogram, at any test frequency in either ear measured twice in succession [NIOSH 1998]. 

Hearing test results are often presented in an audiogram, which is a plot of an individual’s 

hearing thresholds (y-axis) at each test frequency (x-axis). Hearing threshold levels are 
Health Hazard Evaluation Report 2014-0154-3275 Page 17

plotted such that fainter sounds are shown at the top of the y-axis, and more intense sounds 

are plotted below. Typical audiograms show hearing threshold levels from −10 or 0 dB to 

about 100 dB. Lower frequencies are plotted on the left side of the audiogram, and higher 

frequencies are plotted on the right. NIHL often manifests itself as a “notch” at 3,000 Hz, 

4,000 Hz, or 6000 Hz, depending on the frequency spectrum of the workplace noise and the 

anatomy of the individual’s ear [ACOM 1989; Osguthorpe and Klein 2001; Schlaucha and 

Carneya 2011; Suter 2002]. A notch in an individual with normal hearing may indicate early 

onset of NIHL. For health hazard evaluations, a notch is defined as the frequency where the 

hearing threshold 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 test frequency.

NIOSH has an REL for noise of 85 dBA, as an 8-hour TWA. For calculating exposure limits, 

NIOSH uses a 3-dB time/intensity trading relationship, or exchange rate. Using this criterion, 

an employee can be exposed to 88 dBA for no more than 4 hours, 91 dBA for 2 hours, 

94 dBA for 1 hour, 97 dBA for 0.5 hours, etc. Exposure to impulsive noise should never 

exceed 140 dBA. For extended work shifts NIOSH adjusts the REL to 84.5 dBA for a 9-hour 

shift, 84.0 dBA for a 10-hour shift, 83.6 dBA for an 11-hour shift, and 83.2 dBA for a 

12-hour work shift. When noise exposures exceed the REL, NIOSH recommends the use of 

hearing protection and implementation of a hearing loss prevention program [NIOSH 1998]. 

The OSHA noise standard specifies a PEL of 90 dBA and an AL of 85 dBA, both as 8-hour 

TWAs. OSHA uses a less conservative 5-dB exchange rate for calculating the PEL and AL. 

Using the OSHA criterion, an employee may be exposed to noise levels of 95 dBA for no 

more than 4 hours, 100 dBA for 2 hours, 105 dBA for 1 hour, 110 dBA for 0.5 hours, etc. 

Exposure to impulsive or impact noise must not exceed 140 dB peak noise level. OSHA does 

not adjust the PEL for extended work shifts. However, the AL is adjusted to 84.1 dBA for a 

9-hour shift, 83.4 dBA for a 10-hour shift, 82.7 dBA for an 11-hour shift, and 82.1 dBA for a 

12-hour work shift. OSHA requires implementation of a hearing conservation program when 

noise exposures exceed the AL [29 CFR 1910.95].

An employee’s daily noise dose, based on the duration and intensity of noise exposure, can 

be calculated 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 

exposure duration for which noise at that level becomes hazardous. A noise dose greater than 

100% exceeds the noise exposure limit. 

To calculate the noise dose using NIOSH criteria, the reference duration (Tn) for each time 

period must be calculated using the following formula: T (minutes) = 480/2(L−85)/3, 

where L = the measured noise exposure level for each time period. To calculate noise dose 

using OSHA criteria, the reference duration (Tn) for each time period must be calculated 

using a slightly different formula: T (minutes) = 480/2(L−90)/5, where L = the measured 

noise exposure level for each time period.
Page 18 Health Hazard Evaluation Report 2014-0154-3275

Appendix B: Individual Exposure Results

Table B1. Surgical staff time-weighted average personal noise exposure measurement results

Job title Date Duration 

(minutes)

NIOSH REL 

criterion 

(dBA)

OSHA AL 

criterion 

(dBA)

OSHA PEL 

criterion 

(dBA)

Anesthesiologist A 1/13/2015 355 71.8 62.8 46.1

Anesthesiologist B 1/20/2015 476 68.7 58.2 38.4

Surgeon A 

(right shoulder measurement)

1/13/2015 297* 86.8 83.5 78.2

Surgeon A 

(left shoulder measurement)

1/13/2015 432 83.2 77.9 71.8

Surgeon A 

(right shoulder measurement)

1/20/2015 444 81.4 76.5 68.1

Surgeon A 

(left shoulder measurement)

1/20/2015 444 77.8 71.2 62.6

Surgeon B 

(right shoulder measurement)

7/22/2016 357 83.8 78.0 74.0

Surgeon B 

(left shoulder measurement)

7/22/2016 357 82.9 75.9 73.0

Surgical fellow 

(right shoulder measurement)

7/22/2016 397 81.5 74.3 70.4

Surgical fellow 

(left shoulder measurement)

7/22/2016 397 83.0 75.6 72.5

Surgical assistant A 1/13/2015 459 78.7 70.8 65.4

Surgical assistant B 1/13/2015 49† 75.3 68.1 52.8

Surgical assistant C 1/20/2015 386 76.0 67.8 58.2

Surgical assistant C 

(right shoulder measurement)

7/22/2016 465 78.2 64.2 65.4

Surgical assistant C 

(left shoulder measurement)

7/22/2016 465 71.9 61.3 51.4

*Surgeon did not wear dosimeter on right side until after the first surgery had been completed.

†Dosimeter only operated for 31 minutes at beginning of work shift and 18 minutes at the end of 

the work shift.
Health Hazard Evaluation Report 2014-0154-3275 Page 19 Table B2. Full shift and task-based time-weighted average personal noise exposure measurement results for surgeons Surgery time Duration (min) Right ear measurement NIOSH REL criterion (dBA) Left ear measurement NIOSH REL criterion (dBA) Right ear measurement OSHA AL criterion (dBA) Left ear measurement OSHA AL criterion (dBA) Right ear measurement OSHA PEL criterion (dBA) Left ear measurement OSHA PEL criterion (dBA) Surgeon A January 13, 2015 Surgery 1 8:25–9:18 56 NA 80.7 NA 76.7 NA 64.6 Surgery 2 10:23–11:32 69 88.9 86.7 86.1 82.7 82.2 78.9 Surgery 3 12:50–13:48 58 89.2 87.8 86.4 84.2 82.8 79.9 Surgery 4 14:14–15:04 50 86.2 81.9 83.6 77.3 76.8 69.4 No surgery — 199 81.6 75.7 78.0 69.8 66.2 48.8 TWA 432 86.8 83.2 83.5 77.9 78.2 71.8 Surgeon A January 20, 2015 Surgery 1 7:56–9:10 74 81.9 80.0 76.6 74.0 70.6 67.5 Surgery 2 10:17–11:17 60 83.6 81.0 79.9 76.4 71.9 67.0 Surgery 3 11:50–12:39 49 84.0 78.9 80.7 73.6 72.9 62.5 Surgery 4 13:27–14:38 71 83.2 79.6 78.8 73.5 72.1 65.4 No surgery — 190 76.2 68.7 70.5 59.4 48.3 18.7 TWA 444 81.4 77.9 76.5 71.3 68.1 62.3 Surgeon B July 22, 2015 Surgery 1 9:07–10:27 80 84.9 83.4 79.2 76.5 76.2 74.4 Surgery 2 11:16–13:09 113 85.3 85.1 79.9 78.9 76.7 76.4 Surgery 3 13:41–14:45 64 84.0 83.0 78.6 76.3 74.9 73.7 No surgery — 100 77.5 73.3 72.4 66.2 53.1 37.7 TWA 357 83.8 82.9 78.0 75.9 74.0 73.0 Surgical fellow July 22, 2015 Surgery 1 9:07–10:27 80 83.8 86.1 76.5 79.0 77.6 77.6 Surgery 2 11:16–13:09 113 81.7 84.6 75.0 78.2 75.7 75.7 Surgery 3 13:41–14:45 64 83.6 81.3 76.9 74.4 71.2 71.2 No surgery — 140 75.8 75.1 69.0 68.5 47.1 47.1 TWA 397 81.5 83.0 74.2 75.6 70.4 72.5
Page 20 Health Hazard Evaluation Report 2014-0154-3275

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Page 22 Health Hazard Evaluation Report 2014-0154-3275

Keywords: North American Industry Classification System 622110 (General Medical and 

Surgical Hospitals), Ohio, Noise, Surgery, Orthopedic, Knee Surgery, Arthroplasty, Hospital, 

Hearing Loss
Health Hazard Evaluation Report 2014-0154-3275 Page 23

The Health Hazard Evaluation Program investigates possible health hazards in the workplace 

under the authority of the Occupational Safety and Health Act of 1970 (29 U.S.C. § 669(a)

(6)). The Health Hazard Evaluation Program also provides, upon request, technical assistance 

to federal, state, and local agencies to investigate occupational health hazards and to prevent 

occupational disease or injury. Regulations guiding the Program can be found in Title 42, Code 

of Federal Regulations, Part 85; Requests for Health Hazard Evaluations (42 CFR Part 85).

Disclaimer

The recommendations in this report are made on the basis of the findings at the workplace 

evaluated and may not be applicable to other workplaces.

Mention of any company or product in this report does not constitute endorsement by NIOSH.

Citations to Web sites external to NIOSH do not constitute NIOSH endorsement of the 

sponsoring organizations or their programs or products. NIOSH is not responsible for the 

content of these Web sites. All Web addresses referenced in this document were accessible as of 

the publication date.

Acknowledgments

Desktop Publisher: Shawna Watts 

Editor: Ellen Galloway 

Logistics: Donnie Booher, Kevin Moore

Availability of Report

Copies of this report have been sent to the employer and employees at the facility. The state and 

local health department and the Occupational Safety and Health Administration Regional Office 

have also received a copy. This report is not copyrighted and may be freely reproduced. 

Recommended citation for this report:

NIOSH [2017]. Evaluation of a surgical staff’s noise exposures during total knee 

replacement surgeries. By Broadwater KR, Brueck SE. Cincinnati, OH: U.S. 

Department of Health and Human Services, Centers for Disease Control and 

Prevention, National Institute for Occupational Safety and Health, NIOSH Health 

Hazard Evaluation Report 2014-0154-3275, 

http://www.cdc.gov/niosh/hhe/reports/pdfs/2014-0154-3275.
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