Evaluation of 

Potential Noise 

Exposures in Hospital 

Operating Rooms 

Lilia Chen, MS, CIH

Scott E. Brueck, MS, CIH

Health Hazard Evaluation Report

HETA 2008-0231-3105

West Virginia University Hospital 

Morgantown, West Virginia

March 2010

Department of Health and Human Services

Centers for Disease Control and Prevention

Workplace

Safety and Health

 National Institute for Occupational 

Safety and Health

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific 

facility evaluated and may not be universally applicable. Any recommendations made are not to be 

considered as final statements of NIOSH policy or of any agency or individual involved. Additional HHE 

reports are available at http://www.cdc.gov/niosh/hhe/
The employer shall post a copy of this report 

for a period of 30 calendar days at or near 

the workplace(s) of affected employees. The 

employer shall take steps to insure that the 

posted determinations are not altered, defaced, 

or covered by other material during such 

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

amended at 45 FR 2653, January 14, 1980].
Health Hazard Evaluation Report 2008-0231-3105 Page i

Appendix A

Report Abbreviations.......................................................................ii

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

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

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

Assessment.........................................................................2

Results and Discussion .......................................................3

Conclusions.........................................................................8

Recommendations...............................................................8

References ..........................................................................9

Contents

Occupational Exposure Limits & Health Effects ................10

Acknowledgments Acknowledgments and Availability of Report.....................13
Page ii Health Hazard Evaluation Report 2008-0231-3105

AL Action level

ANSI American National Standards Institute

ASA Acoustical Society of America

CFR Code of Federal Regulations

dB Decibels

dBA Decibels, A-scale

Hz Hertz

Leq Equivalent continuous noise level

NAICS North American Industry Classification System

NCB Balanced noise criterion

NIHL Noise induced hearing loss

NIOSH National Institute for Occupational Safety and Health

OR Operating room

OSHA Occupational Safety and Health Administration

PEL Permissible exposure limit

REL Recommended exposure limit

SLM Sound level meter

TWA Time-weighted average

Abbreviations
Health Hazard Evaluation Report 2008-0231-3105 Page iii

Highlights of the

NIOSH Health

Hazard Evaluation

The National Institute for 

Occupational Safety and 

Health (NIOSH) received 

a request for a health 

hazard evaluation at 

West Virginia University 

Hospital in Morgantown, 

West Virginia. Hospital 

management was 

concerned with noise 

exposures in operating 

rooms when loud surgical 

instruments were used. 

What NIOSH Did

● We evaluated the operating rooms for noise on April 22–23, 

2009.

● We monitored the surgical staff’s exposure to noise.

● We measured sound levels at different frequencies in several 

operating rooms during surgery.

What NIOSH Found

● The noise levels we measured for employees did not exceed 

occupational exposure limits.

● Sounds over 90 decibels occurred intermittently and for 

short periods of time.

● During a craniotomy, which occurred in an operating room 

with nonsound absorbent walls, ceilings, and floors, noise 

from powered surgical instruments could cause speech 

interference.

What Managers Can Do

● Ensure that currently used instruments are operating as 

quietly as possible. Check them periodically to maintain the 

lowest possible noise level. 

● Research what options are available for surgical instruments 

that are quieter than those currently used.

● Tell instrument manufacturers that noise reduction is an 

important consideration when deciding on a purchase.

● Provide optional hearing protection for employee use.

What Employees Can Do

● Tell management if you notice a change in volume while 

using a surgical instrument. This may indicate that it needs 

servicing.

● Wear hearing protection when high noise activities are 

performed.

● Keep the volume low when music is played during surgeries. 

This will help reduce speech interference.
Page iv Health Hazard Evaluation Report 2008-0231-3105

Summary

Personal noise 

measurements taken 

during surgeries in ORs 

did not exceed the OSHA 

or NIOSH exposure 

limits for noise. Noise 

from powered surgical 

instruments, which occurs 

in rooms with nonsound 

absorbent walls, ceilings, 

and floors, could cause 

speech interference.

Noise exposures should 

be reduced through 

preventive maintenance 

of powered surgical 

instruments. Noise output 

should be considered 

when selecting 

replacement instruments.

On July 11, 2008, NIOSH received a management request from 

West Virginia University Hospital to assess employee exposures 

to noise in the ORs, especially during procedures where loud 

surgical instruments were used. On April 22–23, 2009, NIOSH 

investigators evaluated employee exposures to noise in the ORs 

during surgeries.

Nine employees (surgical technicians, registered nurses, and a 

surgeon) contributed 12 full-shift noise dosimetry measurements 

over 2 days. None of the measurements exceeded the OSHA or 

NIOSH noise exposure limits. Certain intermittent activities that 

usually lasted less than 30 seconds at a time generated sound 

levels measured at over 90 dBA. Noise-generating activities include 

drilling, surgery preparation, and clean up.

The employer and employees identified surgeries where loud 

instruments were used, and sound level measurements were 

taken during those procedures. Results from the spectral 

analysis indicated that noise levels in the OR were higher than 

levels recommended by ANSI and ASA and may cause speech 

interference for employees.

Reducing noise exposures in an OR can be challenging because 

some sounds are required during surgery (e.g., vital sign monitors, 

alarms, and employee communication) whereas other sounds, 

especially from drilling and sawing instruments, could be reduced. 

Using quieter powered surgical instruments would be the most 

effective way to reduce noise exposures in ORs and to minimize 

speech interference and risk of NIHL.

Keywords: NAICS 622110 (General Medical and Surgical 

Hospitals), intermittent noise, dose, operating rooms, drills, surgery, 

loud music
Health Hazard Evaluation Report 2008-0231-3105 Page 1

Introduction

On July 11, 2008, NIOSH received a management request from 

West Virginia University Hospital to assess employee exposures 

to noise in the ORs, especially during procedures using loud 

surgical instruments. No employees had reported hearing loss 

to management. On April 22–23, 2009, NIOSH investigators 

evaluated employee exposures to noise in several ORs during 

surgeries.

Process Description 

Eighteen ORs are used for a wide variety of surgeries, but 

employers and employees identified higher noise exposures during 

neurosurgeries and orthopedic surgeries. Some examples include 

craniotomies, spine disectomies, hip surgeries, and repairing 

fractured bones. Orthopedic surgeries last 2–4 hours and were 

reported to create more impact noise. Neurosurgeries last from 

4–8 hours and use drilling instruments intermittently for several 

minutes at a time.

Operating rooms include a sterile zone and a nonsterile zone 

during surgical procedures. The sterile zone (work area of highest 

noise exposure) is the area around the surgical patient where sterile 

clothing, sterile instruments, and disinfectants are used to prevent 

the risk of infection by reducing or eliminating the presence of 

bacteria and other microorganisms. It initially is the site where the 

disinfectant is placed on the patient, but extends outward to the 

surgeons and other OR personnel after they put on their sterile 

surgical gowns. The surgeons are assisted by scrub nurses (surgical 

technicians, registered nurses), circulating nurses, anesthesiologists, 

residents, and medical students. Surgeons, scrub nurses, and 

residents are usually located in the sterile zone. The nonsterile 

zone includes the areas of the OR outside of the sterile zone and is 

staffed by the rest of the surgical team. 

The ORs have vinyl floors, drywall walls, observation windows, 

and drywall ceilings. The ceilings include a combination of 

recessed lighting and fluorescent lights covered by plastic panels. 

The ORs are equipped with metal shelves, metal tables, light 

structures, and surgery monitoring equipment. None of the ORs 

contain materials designed specifically to absorb sound or reduce 

reverberation. The loudest instruments used during surgery 

include pneumatic high speed drills used for bone dissection 

and accessing neural structures within the cranial vault, and 
Page 2 Health Hazard Evaluation Report 2008-0231-3105

Introduction 

(continued)

Assessment

powered surgical instruments with sawing, drilling, and cutting 

attachments used in orthopedic surgery. Vital sign monitors and 

other instruments (e.g., electrocautery) can contribute constant 

and intermittent sounds during the surgery. Additionally, during 

surgery preparation and postsurgery clean up, noise is generated by 

metal-to-metal contact between the metal instruments and metal 

trays and tables or when OR staff accidentally drop instruments on 

the floor. Some surgical staff also reported that loud music, ringing 

phones, and beepers contribute to noise exposures in ORs. 

Nine employees (four surgical technicians, four registered nurses, 

and one surgeon) contributed 12 full-shift personal noise measures 

over 2 days. Spark® 706RC noise dosimeters (Larson Davis, Provo, 

Utah) were worn by the employees 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 

scrubs 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 measurements to reduce 

or eliminate artifact noise, which can occur if objects bump 

against an unprotected microphone. The dosimeters averaged 

noise levels every second. At the end of the sampling period, the 

dosimeter was removed and paused to stop data collection. The 

noise measurement information stored in the dosimeters was 

downloaded to a personal computer for interpretation with Larson 

Davis Blaze® computer software. The dosimeters were calibrated 

before and after the measurement periods according to the 

manufacturer’s instructions.

The dosimeters collect data by using different settings so that one 

can directly compare the noise measurement results with the three 

different noise exposure limits referenced in this survey, including 

the OSHA PEL, the OSHA AL, and the NIOSH REL. OSHA 

uses a 90-dBA criterion and a 5-dB exchange rate. The difference 

between the OSHA PEL and AL is the threshold level used for 

each. The PEL has a 90 dBA threshold, and the AL has an 80 dBA 

threshold. During noise dosimetry measurements, noise levels 

below the threshold level are not integrated by the dosimeter for 

accumulation of dose and calculation of TWA noise level. The 

NIOSH REL for noise differs from the OSHA PEL in that the 

NIOSH criterion level is 85 dBA, the NIOSH threshold level is 80 

dBA, and NIOSH uses a 3-dB exchange rate. These dosimeters also 
Health Hazard Evaluation Report 2008-0231-3105 Page 3

Assessment (continued)

Area noise levels and octave band frequency spectrum analysis 

(measurement of noise in different frequencies) were measured 

with System 824 SLM and real-time frequency analyzers (Larson 

Davis, Provo, Utah). The SLMs were equipped with 0.5-inch 

random incidence Type 1 electret microphones, and the 

instruments measured noise levels between 16 and 157 dBA. The 

SLMs were calibrated before and after the measurement periods 

according to the manufacturer’s instructions. SLMs were mounted 

on a tripod at a height of approximately 5 feet. Because of space 

limitations and the desire to keep the SLM outside the sterile zone, 

the instruments were located approximately 3 meters from the OR 

table. 

More information on occupational exposure limits and health 

effects for noise can be found in the Appendix.

Table 2 shows the personal noise dosimetry results. None of the 

employees’ TWA results exceeded the OSHA or NIOSH exposure 

limits for noise during our visit. Two registered nurses and one 

surgical technician had TWA noise exposures at or above 80 dBA, 

based on NIOSH noise measurement settings. Time-weighted 

average noise exposures of surgeons during total knee replacement 

and total hip replacement surgeries have been previously reported 

to range from 74.8–82.1 dBA [Love 2003]. Although the noise 

exposures we measured were below occupational exposure 

limits, noise exposures could be higher depending on the type 

allow a user-defined fourth setting. For this evaluation the fourth 

setting, designed to be a true Leq, was identical to the NIOSH 

setting with the exception that the threshold level was set to OFF. 

This allowed for the integration of all sound levels, including those 

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

this evaluation. 

Table 1. Dosimeter settings

Parameters OSHA 

AL

OSHA 

PEL

NIOSH

 REL

Leq

Response Slow Slow Slow Slow

Exchange rate 5 5 3 3

Criterion level 90 90 85 85

Threshold 80 90 80 off

Upper limit 115 115 115 115

Results and Discussion
Page 4 Health Hazard Evaluation Report 2008-0231-3105

Results and Discussion (continued)

Employees working outside the sterile zone, further from noise 

generating surgical instruments, had lower noise exposures. When 

employees entered the sterile zone, an additional sterile gown was 

placed over their scrubs and removed when they left the zone. At 

times, this gown covered the dosimeter microphone and could 

have slightly reduced the sound levels recorded by the dosimeter. 

A dosimeter worn by the surgeon malfunctioned and took 

measurements for about an hour instead of the surgeon’s full shift. 

Over that hour, the instrument measured the OSHA PEL TWA 

at 56 dBA, the OSHA AL TWA at 65 dBA, and the NIOSH REL 

TWA at 74 dBA. Because the surgeon was working in the sterile 

zone, and the entire duration of the surgery was not measured, the 

actual noise exposure may have been higher. However, the surgeon 

was also wearing a loose-fitting hood that may have acted as a noise 

barrier. 

of surgeries performed and surgical instruments used. For daily 

noise exposures of 80 dBA to 85 dBA, NIOSH considers the risk 

of material hearing impairment to be 1% to 8% over a 40-year 

working lifetime. NIOSH defines material hearing impairment 

as an average hearing threshold level that exceeds 25 dB at 1000, 

2000, 3000, and 4000 Hz [NIOSH 1998]. Observations of noise 

induced hearing loss were reported in 11 of 22 OR personnel 

studied [Willet 1991]. Personnel with hearing loss had 22 years of 

exposure, on average. However, hearing loss observed in the Willet 

study did not meet the NIOSH definition for hearing impairment.

Table 2. Full shift personal noise exposure levels measured on April 22 and 23, 2009

Job Title Sterile Duration OSHA PEL OSHA AL NIOSH REL

Zone (h:mm) TWA Dose* TWA Dose* TWA Dose*

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

Registered nurse Yes 8:43 72 7.7 76 15 83 60

Registered nurse Yes 8:17 68 4.6 72 8.5 81 44

Registered nurse No 7:05 43 0.1 63 2.2 71 4.4

Registered nurse No 7:50 46 0.2 60 1.6 70 3.4

Surgical technician Yes 7:35 64 2.8 74 11 80 29

Surgical technician Yes 7:44 55 0.8 70 6.3 77 16

Surgical technician Yes 6:56 48 0.3 65 3.0 73 6.2

Surgical technician Yes 7:49 38 0.1 58 1.1 68 2.2

Surgical technician Yes 9:07 Dosimeter Malfunction - Microphone Fault

Circulating nurse Yes 7:54 55 0.8 69 5.1 76 11

Surgeon Yes 1:02 Dosimeter Malfunction - Logged data only 1 hour

Exposure Limits 90 100 85 100 85 100

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

representing the maximum allowable daily dose. 
Health Hazard Evaluation Report 2008-0231-3105 Page 5

Results and Discussion (continued) NIOSH investigators observed and recorded times when noiseproducing activities (drill use, music use, and during postsurgery 

clean up) were performed in several of the ORs. After correlating 

the observation times with the results from the employees’ 

dosimeters, the sound level ranges for specific activities were found 

to range from 76–95 dBA during drill use, 67–94 dBA during 

playing of music, and 69–90 dBA during postsurgery clean-up 

activities. For all activities observed, sound levels over 90 dBA 

were observed for 1 to 20 seconds and occurred intermittently. 

Intermittent and short duration exposure of surgical staff to higher 

noise levels generated by surgical instruments may be less damaging 

to hearing than constant or long duration exposures [Ullah et al. 

2004]. 

A separate study found noise levels similar to ours during use of 

drills for orthopedic surgeries, ranging from 71–95 dBA across 

10 different surgeries [Nott and West 2003]. These researchers 

also noted that noise levels during set up of surgical instruments 

ranged from 94–104 dBA as instruments were placed in surgical 

trays. Several other noise researchers have found noise levels during 

use of surgical instruments (drills and saws) exceeding 90 dBA 

[Dodenhoff 1995; Mullett et al. 1999; Siverdeen et al. 2008].

Sound level and octave band frequency spectrum measurements 

were collected every second during two craniotomies. Spectral 

measurements during pneumatic drilling (loudest activity) were 

graphed to illustrate octave band noise levels (Figure 1). Octave 

band measurements provide information about the frequency 

distribution of noise. Because the energy from noise is usually 

widely distributed over many frequencies, the frequency range is 

broken into a smaller range of frequencies (called bandwidths), 

the most common being the octave band (defined as a frequency 

band where the upper band frequency is twice the lower bandedge frequency). Octave band analysis allows for determination 

of the dominant noise frequencies in a work area and can be 

useful for identifying potential engineering controls. For example, 

if low frequency noise is dominant (i.e., the highest octave-band 

sound levels occur in frequencies of 500 Hz or less), noise is likely 

generated by vibration, and noise controls that reduce or isolate 

the vibration from tools or equipment might decrease noise levels. 

If high frequency noise is dominant (i.e., the highest octaveband sound levels occur in frequencies of 2000 Hz or greater), 

installation of noise enclosures, barriers, or sound absorption 

systems is typically the most effective approach for noise reduction 
Page 6 Health Hazard Evaluation Report 2008-0231-3105

Results and Discussion (continued) [Driscoll and Royster 2003]. The highest sound pressure levels 

occurred primarily in the lower frequencies (less than 1000 Hz) at 

31.5 Hz, 500 Hz, and 630 Hz. Because the SLMs were placed about 

3 meters from the operating table, measurements underestimate 

sound levels closer to the source.

Figure 1. Spectral data in operating rooms during pneumatic drill use. 

0

10

20

30

40

50

60

70

80

12.5

162025

31.5

40506380

100125160200250315400500

630800

1000125016002000250031504000500063008000

10000125001600020000

Sound Pressure Level [dB]

One-third Octave Band Center Frequency [Hz]

OR 23

OR 25

The third octave band data were combined into octave bands 

to simplify their analysis and to compare the room noise values 

to the NCB criterion [ANSI/ASA 1995]. NCBs are used to 

specify acceptable noise levels in occupied areas. The room noise 

conditions at this location are characterized as hospital and clinicsoperating rooms and are recommended not to exceed NCB 25–30 

[ANSI/ASA 1995]. The octave band data for the OR during a 

craniotomy in the morning and afternoon are shown in Figure 

2. The NCB 63 curve was representative of the room noise in 

the afternoon, and room noise exceeded the NCB 65 curve in 

the morning. The NCB 65 curve represents acoustical noise 

criteria limits necessary for occupied indoor work spaces where 

communication and speech are not required [ANSI/ASA 1995]. 

During the craniotomy, noise generated by surgical instruments in 

a room with nonsound-absorbent walls, ceilings, or floors resulted 

in room noise conditions in which communication between 

surgical staff may be adversely affected. More information on NCB 

curves is provided in the Appendix. 
Health Hazard Evaluation Report 2008-0231-3105 Page 7

Results and Discussion (continued)

Because pneumatic surgical instruments generated the highest 

noise levels in the OR, noise reduction efforts should focus on 

using surgical instruments that generate less noise. In a comparison 

of two different types of saw blades for knee arthroplasty, 

researchers found that a modified saw blade produced significantly 

less noise than a standard design [Sydney et al. 2007]. The 

modified saw blade used an oscillating tip that allowed the shaft of 

the blade to remain stationary, whereas the design of the standard 

blade required the entire blade to oscillate. Noise levels in the OR 

could also be reduced by playing radios at a lower volume. As a 

general rule, surgical staff should be able to speak to each other 

without needing to raise their voices when the radio is in use. 

Surgical personnel could also wear hearing protection to reduce 

their noise exposure. However, hearing protection should be 

chosen carefully, because hearing protectors that excessively 

attenuate noise may substantially interfere with communication or 

the ability of surgical staff to hear patient monitoring equipment. 

Flat response hearing protectors that have a low noise reduction 

rating and attenuate noise evenly across all frequencies might be an 

appropriate type of insert-type hearing protector for the OR staff. 

Figure 2. Spectral data from operating room and comparison with NCB curves.

0

10

20

30

40

50

60

70

80

90

100

16 31.5 63 125 250 500 1000 2000 4000 8000

Sound level [dB]

Octave band center frequency [Hz]

NCB 60

NCB 50

NCB 40

NCB 30

NCB 20

NCB 10

Operating room levels AM

Operating room levels PM

NCB 65
Page 8 Health Hazard Evaluation Report 2008-0231-3105

Inherent challenges exist in reducing noise exposures in OR 

settings because some sounds are required during surgery (e.g., 

vital sign monitors, alarms, and employee communication), 

whereas other sounds could be reduced (e.g., drilling, sawing, 

radio volume). Personal noise measurements taken during our 

visit did not exceed the OSHA or NIOSH exposure limits for 

noise. Because of loud surgical instrument use and room design 

conditions, noise levels measured during some surgeries were at 

levels that may interfere with communication between surgical 

personnel. 

On the basis of our findings, we recommend the actions listed 

below to create a more healthful workplace. 

1. Ensure that existing instruments are operating as quietly as 

possible, and check them periodically to maintain the lowest 

possible noise level. A change in volume of an instrument 

may indicate that the instrument needs servicing or 

replacement.

2. Contact instrument manufacturers and inquire about 

surgical instruments that may be quieter than models 

currently used. Indicate that noise reduction is an important 

consideration for purchase. Try several different models to 

see if some are quieter.

3. Although noise levels were below noise exposure limits, 

hearing protection could be worn when loud activities are 

being performed. If worn, hearing protection should have 

a flat frequency response to reduce the effect on speech 

communication. 

4. Keep the volume low when music is played during surgeries. 

This can also help reduce speech interference for employees.

Conclusions

Recommendations
Health Hazard Evaluation Report 2008-0231-3105 Page 9

References

ANSI/ASA [1995]. American national standard: criteria for 

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

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

1995.

Dodenhoff RM [1995]. Noise in the orthopaedic operating theatre. 

Ann R Coll Surg Eng (Suppl) 77:8–9.

Driscoll DP, Royster LH [2003]. Noise control engineering. In: 

Berger EH, Royster LH, Royster JD, Driscoll DP, Layne M. eds, 

The noise manual, 5th ed. Akron, OH: American Industrial 

Hygiene Association, pp. 279–378; [Reference: Table 9.5, pp. 

298–300].

Love H [2003]. Noise exposure in the orthopaedic operating 

theatre: a significant health hazard. ANZ J Surg 73:836–838.

Mullett H, Synnott K, Quinlan W [1999]. Occupational noise 

levels in orthopaedic surgery. Ir J Med Sci 168(2):106.

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.

Nott MR, West PDB [2003]. Orthopaedic theatre noise: a potential 

hazard to patients. Anaesthesia 58(8):784–787.

Siverdeen Z, Ali A, Lakdawala A, McKay C [2008]. Exposure to 

noise in orthopaedic theatres – do we need protection? Int J Clin 

Prac 62(11):1720–1722.

Sydney SE, Lepp AJ, Whitehouse SL, Crawford RW [2007]. 

Noise exposure due to orthopedic saws in simulated total knee 

arthroplasty surgery. J Arthroplasty 22(8):1193–1197.

Ullah R, Bailie N, Crowther S, Cullen J [2004]. Noise exposure 

in orthopaedic practice: potential health risk. J Laryngol Otol 

118(6):413–416.

Willett KM [1991]. Noise-induced hearing loss in orthopaedic staff. 

J Bone Joint Surg [Br] 73B(1):113–115.
Page 10 Health Hazard Evaluation Report 2008-0231-3105

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. 

NIHL is an irreversible, sensorineural condition that progresses with exposure. Although hearing ability 

declines with age (presbycusis) in all populations, exposure to noise produces hearing loss greater than 

that resulting from the natural aging process. This noise-induced loss is caused by damage to nerve cells 

of the inner ear (cochlea) and, unlike some conductive hearing disorders, cannot be treated medically 

[Ward et al. 2000]. While loss of hearing may result from a single exposure to a very brief impulse noise or 

explosion, such traumatic losses are rare. In most cases, NIHL is insidious. Typically, it begins to develop 

at 4000 or 6000 Hz (the hearing range is 20 Hz to 20000 Hz) and spreads to lower and higher frequencies. 

Often, material impairment has occurred before the condition is clearly recognized. Such impairment 

is usually severe enough to permanently affect a person’s ability to hear and understand speech under 

everyday conditions. Although the primary frequencies of human speech range from 200 Hz to 2000 Hz, 

research has shown that the consonant sounds, which enable people to distinguish words such as “fish” 

from “fist,” have still higher frequency components [Suter 1978]. 

The dBA is the preferred unit for measuring sound levels to assess employee noise exposures. The dBA 

scale is weighted to approximate the sensory response of the human ear to sound frequencies near the 

threshold of hearing. The decibel unit is dimensionless, and represents the logarithmic relationship of 

the measured sound pressure level to an arbitrary reference sound pressure (20 micropascals, the normal 

threshold of human hearing at a frequency of 1000 Hz). Decibel units are used because of the very large 

range of sound pressure levels which are audible to the human ear. Because the dBA scale is logarithmic, 

increases of 3 dBA, 10 dBA, and 20 dBA represent a doubling, tenfold increase, and hundred-fold increase 

of sound energy, respectively. It should be noted that noise exposures expressed in decibels cannot be 

averaged by taking the simple arithmetic mean. 

The OSHA standard for occupational exposure to noise specifies a maximum PEL of 90 dBA for of 8 

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

employee’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, 

an employee is allowed up to 100% of his daily noise dose. Doses greater than 100% exceed the OSHA 

PEL. 

Appendix A: Occupational Exposure Limits & Health Effects
Health Hazard Evaluation Report 2008-0231-3105 Page 11

Appendix A: Occupational Exposure Limits & Health Effects (continued)

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, hearing protection devices, 

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 employees 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 employees’ exposure levels. NIOSH, in its Criteria for a Recommended Standard, proposes 

an exposure criterion of 85 dBA as a TWA for 8 hours, 5 dB less than the OSHA standard [NIOSH 1998]. 

The criterion also uses a more conservative 3-dB exchange rate in calculating exposure limits. Thus, an 

employee can be exposed to 85 dBA for 8 hours, but to no more than 88 dBA for 4 hours or 91 dBA for 2 

hours. The NIOSH REL for a 12 hour exposure is 83 dBA or less. 

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

equivalent TWA values are different for the NIOSH and OSHA criteria. The OSHA dose equation is

TWA = 16.61 x log

10 

[Dose/100] + 90, 

and the NIOSH equation is

TWA = 10.00 x log

10 

[Dose/100] + 85. 

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

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

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

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

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

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

limit noise to levels where satisfactory speech intelligibility is achieved [Beranek 1988, 1989; ANSI/ASA 

1995]. The noise criteria were devised through the use of extensive interviews with personnel in offices, 

factories, and public places along with simultaneously measured octave band sound levels. The interviews 

consistently showed that people rate noise as troublesome when its speech interference level is high 

enough to make communications difficult. The recommended space classifications and suggested noise 

criteria range for steady background noise heard in various indoor hospital occupied activity areas are 

shown in Table A1.
Page 12 Health Hazard Evaluation Report 2008-0231-3105

Appendix A: Occupational Exposure Limits & Health Effects (continued)

References

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

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

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

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

Engineering, pp. 554–623. 

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

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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.

Table A1. Example NCB specifications for occupied activity areas in hospitals and clinics*

Areas NCB Curve

Private rooms 25–30

Wards 30–35

Operating rooms 25–30

Laboratories 33–43

Corridors 33–43

Public areas 38–43

*ANSI S12.2-1995 Criteria for Evaluating Room Noise
Health Hazard Evaluation Report 2008-0231-3105 Page 13

Acknowledgments and

Availability of Report

The Hazard Evaluations and Technical Assistance Branch 

(HETAB) of the National Institute for Occupational Safety and 

Health (NIOSH) conducts field investigations of possible health 

hazards in the workplace. These investigations are conducted 

under the authority of Section 20(a)(6) of the Occupational Safety 

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the Secretary of Health and Human Services, following a written 

request from any employer or authorized representative of 

employees, to determine whether any substance normally found 

in the place of employment has potentially toxic effects in such 

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NIOSH [2010]. Health hazard evaluation report: evaluation of potential noise 

exposures in hospital operating rooms, Morgantown, WV. By Chen L, 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 HETA No. 2008-0231-3105.

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