Assessment of Nitrous 

Oxide Exposure in a 

Pediatric Dentistry 

Chandran Achutan, PhD

Marilyn Radke, MD, MPH

Alberto Garcia, MS

Kenneth Mead, PhD, PE

Bradley King, MPH, CIH

Health Hazard Evaluation Report

HETA 2005-0157-3110

Children’s Dentistry at Hamilton Mill

Dacula, Georgia

July 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 2005-0157-3110 Page i

Appendix A

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

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

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

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

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

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

Conclusions.........................................................................6

Recommendations...............................................................6

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

Contents

Acknowledgments and Availability of Report.....................17

Occupational Health Limits and Health Effects .................10

Ventilation Assessment of Dental Clinic ............................15

Acknowledgments

Appendix B
Page ii Health Hazard Evaluation Report 2005-0157-3110

ACGIH® American Conference of Governmental Industrial Hygienists

ACH Air changes per hour

AIA American Institute of Architects

ANSI American National Standards Institute

ASHRAE American Society of Heating, Refrigerating, and Air-Conditioning Engineers

cfm Cubic feet per minute

CFR Code of Federal Regulations

ft3 Cubic feet

GM Geometric mean

HHE Health hazard evaluation

HVAC Heating, ventilating, and air conditioning

Lpm Liters per minute

MDC Minimum detectable concentration

mL/min Milliliters per minute

min Minutes

n Number of samples

NAICS North American Industry Classification System

ND Not detected

NIOSH National Institute for Occupational Safety and Health

N2O Nitrous oxide

OEL Occupational exposure limit

OSHA Occupational Safety and Health Administration

PBZ Personal breathing zone

PEL Permissible exposure limit

ppm Parts per million

REL Recommended exposure limit

STEL Short term exposure limit

TLV® Threshold limit value

TWA Time-weighted average

WEEL Workplace environmental exposure level

Abbreviations
Health Hazard Evaluation Report 2005-0157-3110 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 

Children’s Dentistry at 

Hamilton Mill in Dacula, 

Georgia. Management 

submitted the request 

because employees were 

concerned that nitrous 

oxide (N2O) exposure may 

result in infertility and 

spontaneous abortions.

What NIOSH Did

● We evaluated the dental clinic in March 2005.

● We took short- and long-term air samples for N2O.

● We talked to employees about health concerns due to 

possible N2O exposure.

● We looked at drawings of the building’s ventilation system to 

see if the treatment rooms were getting enough outdoor air.

What NIOSH Found

● Some air samples had N2O concentrations above the NIOSH 

recommended exposure limit.

● Employees reported no health problems.

● The treatment rooms did not get enough outdoor air.

What Managers Can Do

● Improve the clinic’s ventilation system.

● Use and maintain scavenging systems properly to prevent 

overexposures to N2O.

● Check the scavenging system for leaks, particularly after 

an N2O cylinder is changed. Fix any leak points as soon as 

possible.

● Monitor for N2O in the air of the treatment rooms yearly.

● Train employees on proper work practices, controls, and 

hazards associated with N2O exposure.

What Employees Can Do

● Use as little N2O as possible.

● Stay as far as possible from the mouth of a child treated with 

N2O.

● Encourage patients to minimize talking and mouth breathing 

when N2O is used in a procedure.
Page iv Health Hazard Evaluation Report 2005-0157-3110

Summary

NIOSH investigators 

evaluated dentists’ 

and dental assistants’ 

exposure to N2O. We found 

levels of N2O exposure 

above the NIOSH 

recommended exposure 

limit during several 

short-term task-based 

samples and one full-shift 

sample. We recommend 

improvements in the use 

of scavenging units and 

improvements to the 

building ventilation for the 

treatment rooms.

On March 2, 2005, NIOSH received a management request for an 

HHE at Children’s Dentistry at Hamilton Mill in Dacula, Georgia. 

The request was submitted in response to employee concerns 

that continued exposure to N2O may result in infertility and 

spontaneous abortions.

Seventeen task-based and eighteen full-shift PBZ air samples for 

N2O were collected on two dentists and eight dental assistants 

during the survey. One of the full-shift samples, collected on a 

dentist, exceeded the NIOSH REL of 25 ppm as a TWA. Several 

task-based samples also exceeded the NIOSH REL. Additionally, 

two full-shift PBZ samples were collected on receptionists in the 

reception area; neither of these samples contained detectable 

concentrations of N2O. The sampling was done over 2 days using 

passive sampling badges.

NIOSH engineers reviewed drawings of the clinic’s ventilation 

system. The building ventilation system in place during the 

NIOSH evaluation did not supply adequate outdoor air to the 

treatment rooms.

NIOSH physicians invited employees to participate in confidential 

medical interviews. Employee concerns primarily stemmed from 

the potential for N2O to cause infertility, rather than from any 

adverse health effects being experienced when the HHE request 

was made. Factors that affect exposures include work practices, the 

amount of N2O administered to patients, and the effectiveness of 

engineering controls.

Keywords: NAICS 621210 (Offices of Dentists), pediatric dentistry, 

N2O
Health Hazard Evaluation Report 2005-0157-3110 Page 1

Introduction

On March 2, 2005, NIOSH received a management request for an 

HHE at Children’s Dentistry at Hamilton Mill in Dacula, Georgia. 

The request was submitted in response to employee concerns 

that continued exposure to N2O may result in infertility and 

spontaneous abortions.

On March 30–31, 2005, NIOSH representatives visited the 

facility. An opening conference with management, employee, and 

NIOSH representatives was held on March 30, 2005. Following 

the opening conference, NIOSH investigators assessed dental staff 

exposures to N2O and conducted confidential medical interviews.

Workplace Description 

At the time of the NIOSH evaluation, the dental clinic had six 

treatment rooms. Treatment rooms 1, 2, and 3 were in the old 

wing of the clinic, while the new wing (added on to the building 

in 2003) housed treatment rooms 4, 5, and 6. Most surgeries were 

conducted in treatment rooms 1, 2, 4, and 5. Rooms 3 and 6 were 

reserved for complicated surgeries and emergencies. In addition 

to standard dentistry equipment, each treatment room had the 

capability to administer N2O gas piped from tanks in a separate 

room and to exhaust the gas with a scavenging unit dedicated to 

that room. N2O is administered to patients who need to relax 

prior to a dental procedure. Scavenging systems were used while 

patients received N2O. At the time of the NIOSH evaluation, 

two dentists and 10 dental assistants were working at the clinic. 

All employees were women. One dentist was assigned to the old 

wing and another to the new wing. Each dentist moved back and 

forth between patients; dental assistants remained with patients 

throughout their time in the treatment rooms.

Information on the health effects and occupational health limits 

of N2O and the appropriate ventilation criteria are presented in 

Appendix A.
Page 2 Health Hazard Evaluation Report 2005-0157-3110

Task-based and full-shift PBZ air samples for N2O were collected on 

two dentists, eight dental assistants, and two receptionists over 2 

days with passive badges containing activated molecular sieves from 

Assay Technology (Irvine, California). The task-based sampling 

was conducted during short-term tasks in which dentists or dental 

assistants attended to patients to whom N2O was administered. 

The badges used for sampling collected N2O gas via diffusion at 

a rate of 0.75 mL/min. The badges were clipped on the collars 

of the employees’ attire to sample their PBZ air. The badges were 

returned to Assay Technology for analysis by gas chromatography 

with electron capture detection. When feasible, multiple taskbased, short-term samples were collected on employees who were 

also being monitored for full-shift exposures. NIOSH engineers 

reviewed drawings of the clinic’s ventilation system. Employees 

were also invited to participate in confidential medical interviews 

with NIOSH medical officers.

Seventeen task-based and 20 full-shift PBZ air samples were 

collected during the evaluation. The MDC for the samples was 0.3 

ppm, based on a sample collection time of 480 minutes at a rate 

of 0.75 mL/min. One of the full-shift PBZ samples collected on a 

dentist exceeded the NIOSH REL of 25 ppm. Several of the taskbased samples exceeded this limit. Table 1 summarizes the full-shift 

and task-based exposures to employees directly exposed to N2O. 

The table also shows that the average N2O exposures of dentists 

were higher than those of dental assistants. This may be because 

the dentists’ PBZs are closer to the patients’ mouths than the 

dental assistants’ PBZs. Tables 2 and 3 compare task-based, shortterm samples to full-shift samples on the same employee. In most 

instances, the task-based samples registered a higher concentration 

of N2O than full-shift samples because the task-based samples were 

specifically collected during periods when the employees were using 

N2O on patients. The full-shift samples include periods when N2O 

was not used on patients.

Results and Discussion

Assessment
Health Hazard Evaluation Report 2005-0157-3110 Page 3

Results and Discussion (continued)

Table 2. Full-shift and task-based concentrations of N2O for dentists and dental assistants, March 30, 2005

Study Participant Job Title Treatment 

Room Sample Type Sampling Time (min)

Concentration 

(ppm)

Employee 1 Dental assistant 4 Full-shift 431 1.5

Employee 2 Dental assistant 6 Full-shift 424 11

Employee 3 Dental assistant 5 Full-shift

Task-based

422

19

12

69

Employee 4 Dental assistant 1 Full-shift 436 18

Employee 5 Dental assistant 2 Full-shift 418 25

Employee 6 Dentist 1, 2, 3 Full-shift

Task-based

413

7

47

240

Employee 7 Dentist 4, 5, 6 Full-shift

Task-based

404

12

1.7

70

Employee 8 Dental assistant Several Full-shift 312 4.4

Employee 9 Dental assistant 3 Full-shift 300 ND

 

Table 1. Summary data on employee exposure to N2O during dental procedures

Job Title Full-shift samples

 n GM Range (ppm)

Task-based samples

 n GM Range (ppm)

Dentists

Dental assistants

Receptionists

4

14

2

5.96

1.68

—

1.7 – 47 

ND – 25

ND

7

10

0

72.5

21.1

—

ND – 460

ND – 200

—
Page 4 Health Hazard Evaluation Report 2005-0157-3110

Results and Discussion (continued)

Because of the limited exposure data collected on the dentists, 

we were not able to discern any meaningful exposure differences 

between the two dentists. However, we noticed that the dentists 

had different work practices that may affect their individual 

exposure to N2O: (1) one dentist set the flow of N2O to 30%, 

while the other started at 20% and increased it as needed; (2) one 

dentist performed dental procedures with the door open for better 

ventilation and closed the door if a patient became agitated, while 

Table 3. Full-shift and task-based concentrations of N2O on dentists, dental assistants and receptionists, 

March 31, 2005

Study Participant Job Title Treatment 

Room Sample Type Sampling Time (min)

Concentration 

(ppm)

Employee 2 Dental assistant 4 Full-shift

Task-based

Task-based

545

31

28

ND

ND

61

Employee 3 Dental assistant 5 Full-shift

Task-based

Task-based

Task-based

484

29

16

106

ND

ND

65

14

Employee 4

Employee 5

Dental assistant

Dental assistant

1

2

Full-shift

Task-based

Full-shift

Task-based

Task-based

Task-based

361

27

422

47

45

19

4.9

110

ND

2.8

200

ND

Employee 6 Dentist 1, 2, 3 Full-shift

Task-based

Task-based

401

19

30

2.6

ND

220

Employee 7

Employee 8

Employee 9

Employee 10

Employee 11

Employee 12

Dentist

Dental assistant

Dental assistant

Dental assistant

Receptionist

Receptionist

4, 5, 6

Several

5

1, 2, 3

—

—

Full-shift

Task-based

Task-based

Task-based

Full-shift

Full-shift

Full-shift

Full-shift

Full-shift

474

8

54

110

414

451

240

478

337

6.0

ND

460

76

ND

ND

6.5

ND

ND
Health Hazard Evaluation Report 2005-0157-3110 Page 5

Results and Discussion (continued) the other almost always closed the door; and (3) one dentist used 

a magnifying eyepiece to maintain a distance from the patients’ 

mouths, while the other did not.

Review of Ventilation Diagrams 

A complete set of “as-built” drawings, supporting documentation, 

and sequence of operations for the design and operation of 

the HVAC system were requested to support the design review. 

We received only a partial set of drawings (dated November 26, 

2001); these drawings contained no supporting documentation 

or sequence of operations. Because of the limited information 

available, ventilation calculations were performed for two 

treatment rooms on the older wing of the clinic to provide basic 

estimates and to determine whether the treatment rooms had 

adequate ventilation and adequate supply of outdoor air. Based on 

the drawing notes, the design intent was to mechanically supply 20 

cfm of outdoor air per person. Ideally, this design intent should be 

evaluated with information on the occupancy level for each room 

in the facility; however, in this case, occupancy information was 

not available and had to be assumed for the review. If we assume 

maximum design occupancy of three persons (patient, dentist, 

assistant), each room would require a minimum of 60 cfm of 

outdoor air to meet the 20 cfm of outdoor air per person design 

intent stated on page M-1 of the drawings. The actual design fails 

to meet this requirement as the 12.4 cfm of outdoor air delivered 

to each room is less than that required for even one person 

(Appendix B).

For each room, the calculated ACHs were 0.8 ACH of outdoor air 

and 6.7 ACH of total ventilation. These ACH rates failed to meet 

either AIA or ASHRAE requirements for operating rooms, and 

they failed to meet ASHRAE’s 2 ACH outdoor air requirements 

for treatment rooms (Appendix B) [AIA 2006; ASHRAE 2007].

NIOSH [1994] recommends using scavenging and/or local 

exhaust equipment and a negative pressure air balance (i.e., more 

air is exhausted from the room than is supplied to the room) 

within rooms where N2O is used. Because no documentation was 

provided on the scavenging or auxiliary exhaust systems used at this 

facility, we are unable to comment on their selection or operation. 

We were provided no information regarding the exhaust volumes 

from each room, so we cannot assess room pressurization from the 

ventilation drawings. Clearly, however, air from these rooms was 

recirculated to other areas of the building, potentially exposing 

others (patients, staff, and children) to anesthetic gas.
Page 6 Health Hazard Evaluation Report 2005-0157-3110

Results and Discussion (continued) Employee Interviews 

While all staff members were offered an interview with the NIOSH 

medical officer to discuss health concerns related to potential 

N2O exposures, a limited number accepted. No fertility or other 

diagnosed medical problems were reported. Three employees 

reported symptoms. One had an occasional episode of temporary 

paresthesia in the hands that resolved. Two others reported an 

occasional headache, but did not know if the headaches were 

caused by N2O or the routine work stress of dealing with pediatric 

patients. None of the three sought medical evaluation.

Based on sampling conducted, N2O exposures exceeded the 

NIOSH REL of 25 ppm, particularly during short-term sampling. 

Factors that affect exposures include work practices, use of 

engineering controls, and the amount of N2O administered 

to patients. The ventilation systems in place at the time of the 

evaluation were inadequate in supplying outdoor air to the 

treatment rooms. Employee concerns primarily stemmed from the 

potential for N2O to cause infertility, and not from any adverse 

health effects employees experienced.

Based on our findings, we recommend the actions listed below 

to create a more healthful workplace. We encourage Children’s 

Dentistry at Hamilton Mill to use a labor-management health and 

safety committee or working group to discuss the recommendations 

in this report 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 Children’s 

Dentistry at Hamilton Mill. Our recommendations are based on 

the hierarchy of controls approach (Appendix A: Occupational 

Exposure Limits and Health Effects). 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/or 

personal protective equipment may be needed.

Recommendations

Conclusions
Health Hazard Evaluation Report 2005-0157-3110 Page 7

Recommendations

(continued) Elimination and Substitution 

Elimination or substitution of a toxic/hazardous process 

or material is a highly effective means for reducing hazards. 

Incorporating this strategy into the design or development phase 

of a project, commonly referred to as “prevention through design,” 

is most effective because it reduces the need for additional controls 

in the future. Eliminating N2O use is not feasible as a control 

method because of its requirement as an anesthetic gas, so the use 

of engineering controls as discussed below is the preferred primary 

recommendation for controlling such exposures.

Engineering Controls

Engineering controls reduce exposures to employees by removing 

the hazard from the process or placing a barrier between the 

hazard and the employee. Engineering controls are effective at 

protecting employees without placing primary responsibility of 

implementation on the employee.

1. Use and maintain the N2O scavenging units as 

recommended by NIOSH. In the 1994 hazard alert 

“Controlling Exposures to Nitrous Oxide During Anesthetic 

Administration” [NIOSH 1994 a] and 1994 technical report 

“Control of Nitrous Oxide in Dental Operatories” [NIOSH 

1994 b], NIOSH recommends a variety of specific actions to 

be implemented in conjunction with the use of scavenging 

units to control exposures to N2O, including the following:

a. Conduct a comprehensive leak check of the N2O 

delivery system and repair all leak points. Implement a 

preventive maintenance program that includes reviewing 

the N2O delivery system and conducting periodic leak 

checks. Every time a cylinder is changed, the connections 

should be checked for leaks. Visually inspect all N2O 

equipment for worn parts, cracks, holes, or tears. 

Following visual inspection, leak test the equipment and 

connections. This is best performed with an infrared 

spectrophotometer, but can also be accomplished by 

applying a soap solution to the fittings and observing for 

bubbles, which indicate the presence of a leak.

b. Monitor ambient N2O levels annually. Monitoring data 

should also be obtained whenever the N2O delivery 

system is modified to ensure exposures are maintained 

below the NIOSH REL.
Page 8 Health Hazard Evaluation Report 2005-0157-3110

Recommendations

(continued) c. Ensure the scavenging system exhaust rates are 

approximately 45 Lpm. A flow meter connected to the 

scavenging system vacuum line and visible to dental 

personnel would allow them to monitor the flow rate.

d. Ensure the scavenging system is always on when N2O is 

used. All exhaust air from the scavenging units should be 

vented directly outside.

2. Hire a ventilation engineer familiar with healthcare facilities 

to configure the HVAC system so that the treatment rooms 

have adequate ventilation and that potentially contaminated 

air from the treatment rooms is not recirculated to 

other portions of the facility. Specific ventilation 

recommendations include:

a. Use supply register louvers in the ceilings that are 

designed so that outdoor supply air is directed toward 

the dental chair. This will maximize the ability to provide 

mixing and dilution of the air in the operatory. Exhaust 

air vents ideally should be at or near the floor.

b. Increase room airflow if the concentration of N2O is 

above 25 ppm for dental personnel for further mixing 

and dilution of the room air.

c. Exhaust contaminated air directly outdoors away 

from windows, doors, and HVAC air intakes. The 

recirculation of operatory air is not recommended.

d. Maintain a negative pressure differential between the 

operatory room and surrounding areas. In such a 

situation, more air is exhausted than supplied in the 

operatory rooms, prohibiting the flow of N2O-containing 

air from circulating into surrounding rooms.

Administrative Controls 

Administrative controls are management-dictated work practices 

and policies to reduce or prevent exposures to workplace hazards. 

The effectiveness of administrative changes in work practices 

for controlling workplace hazards is dependent on management 

commitment and employee acceptance. Regular monitoring and 

reinforcement are necessary to ensure that control policies and 

procedures are not circumvented in the name of convenience or 

production.

1. Encourage dentists to adopt work practices that lower their 

exposure to N2O. These practices include limiting the use 
Health Hazard Evaluation Report 2005-0157-3110 Page 9

Recommendations

(continued) of N2

O as much as possible, using the lowest level of N2O 

possible, and maintaining the furthest distance possible 

from the patient’s mouth. The magnifying eyepiece used 

by one of the dentists in this evaluation may be a means 

to achieve this. Encouraging patients to minimize talking 

and mouth-breathing during dental surgery also helps to 

minimize potential exposures.

2. Management should ensure that all staff members who 

administer N2O are trained on potential hazards. Such 

training includes recognizing the health effects associated 

with exposures to N2O and training on proper work 

practices and use of engineering controls to reduce N2O 

concentrations.

AIA Academy of Architecture for Health, Facility Guidelines 

Institute, and United States Department of Health and Human 

Services [2006]. Guidelines for design and construction of health 

care facilities. 2006 ed. Washington, DC: American Institute of 

Architects Press.

ASHRAE [2007]. Health care facilities. In: 2007 ASHRAE 

handbook: heating, ventilating, and air-conditioning applications. 

Atlanta, GA: American Society of Heating, Refrigerating and AirConditioning Engineers.

NIOSH [1994 a]. NIOSH alert: Controlling exposures to nitrous 

oxide during anesthetic administration. 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. 1994–100.

NIOSH [1994 b]. NIOSH Technical report: control of nitrous 

oxide in dental operatories. 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. 1994–129.

References
Page 10 Health Hazard Evaluation Report 2005-0157-3110

Appendix A: Occupational Health Limits and Health Effects

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

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

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

prevent the occurrence of adverse health effects from workplace exposures. Generally, OELs suggest levels 

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

lifetime without experiencing adverse health effects. However, not all employees will be protected from 

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

experience adverse health effects because of individual susceptibility, a preexisting medical condition, and/

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

workplace exposures, the general environment, or with medications or personal habits of the employee 

to produce health effects even if the occupational exposures are controlled at the level set by the exposure 

limit. Also, some substances can be absorbed by direct contact with the skin and mucous membranes in 

addition to being inhaled, which contributes to the individual’s overall exposure.

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 STEL or ceiling 

values where health effects are caused by exposures over a short period. Unless otherwise noted, the STEL 

is a 15-minute TWA exposure that should not be exceeded at any time during a workday, and the ceiling 

limit is an exposure that 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, while 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 enforceable in 

workplaces covered under the Occupational Safety and Health Act. NIOSH RELs are recommendations 

based on a critical review of the scientific and technical information available on a given hazard and the 

adequacy of methods to identify and control the hazard. NIOSH RELs can be found in the NIOSH Pocket 

Guide to Chemical Hazards [NIOSH 2005]. NIOSH also recommends different types of 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 from these hazards. Other OELs that are commonly used and cited in the United States include 

the TLVs recommended by ACGIH, a professional organization, and the WEELs 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, peer-reviewed 

literature. They are not consensus standards. ACGIH TLVs are considered voluntary exposure guidelines 

for use by industrial hygienists and others trained in this discipline “to assist in the control of health 

hazards” [ACGIH 2009]. WEELs have been established for some chemicals “when no other legal or 

authoritative limits exist” [AIHA 2009].

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

both legal and recommended limits. Since 2006, the Berufsgenossenschaftliches Institut für Arbeitsschutz 

(German Institute for Occupational Safety and Health) has maintained a database of international 

OELs from European Union member states, Canada (Québec), Japan, Switzerland, and the United 

States available at http://www.dguv.de/bgia/en/gestis/limit_values/index.jsp. The database contains 

international limits for over 1250 hazardous substances and is updated annually.
Health Hazard Evaluation Report 2005-0157-3110 Page 11

Appendix A: Occupational Health Limits and Health Effects (continued)

Employers should understand that not all hazardous chemicals have specific OSHA PELs, and for some 

agents the legally enforceable and recommended limits may not reflect current health-based information. 

However, an employer is still required by OSHA to protect its employees from hazards even in the absence 

of a specific OSHA PEL. 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))]. Thus, NIOSH investigators encourage 

employers to make use of other OELs when making risk assessment and risk management decisions to 

best protect the health of their employees. NIOSH investigators also encourage the use of the traditional 

hierarchy of controls approach to eliminate or minimize identified 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 that focuses resources on exposure controls by describing how a risk needs 

to 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 the OELs, when available.

Nitrous Oxide

N2O has been used as an anesthetic agent since 1844 and is often used in conjunction with other 

anesthetic gases [ACGIH 2009]. However, with the development of more effective local anesthetics, N2O 

is now used primarily to relieve anxiety in patients [Frost 1985]. For many years, the only adverse health 

effects associated with exposure to N2O have been those of asphyxiation when N2O physically displaces 

oxygen, creating an oxygen insufficiency [Hathaway and Proctor 2004; ACGIH 2009]. However, some 

laboratory studies have also shown adverse reproductive effects (smaller litter, increased incidence of 

fetal resorption and skeletal anomalies) among rats exposed to high (e.g., 1000 ppm or greater) N2O 

concentrations during the early stages of pregnancy [Viera et al. 1980]. Human studies have reported 

a higher than expected incidence of spontaneous abortions among female workers directly exposed to 

N2O and other anesthetic gases [Cohen et al. 1975]. Other studies suggest the incidence of congenital 

abnormalities and spontaneous abortion is slightly higher in the offspring of wives of exposed dentists, as 

well as reduced fertility in women occupationally exposed [Cohen et al. 1980; Rowland et al. 1992]. It has 

also been suggested that mood factors (sleepiness, mental tiredness, etc.) may increase following exposures 

to as low as 50 ppm [Venables et al. 1983]. In many of these human studies, exposure concentrations are 

poorly defined and dose-response relationships are difficult to identify.

OSHA has not established a PEL for N2O. The NIOSH REL is 25 ppm averaged over the duration of 

anesthetic administration. The NIOSH REL is based on a report of decrements in audiovisual tasks 

following exposure at 50 ppm and is intended to prevent decreases in mental performance, audiovisual 

ability, and manual dexterity during exposures to N2O [NIOSH 1977; NIOSH 1994]. Additionally, 

concern for reproductive effects such as reduced fertility; spontaneous abortion; and neurological, renal, 

and liver disease has led NIOSH to recommend minimizing worker exposures [NIOSH 1994]. ACGIH 

has recommended an 8-hour TLV-TWA of 50 ppm [ACGIH 2009]. The ACGIH TLV-TWA is based on 

prevention of embryo-fetal toxicity (spontaneous abortion) in humans and significant decrements in 

human cognitive functions.
Page 12 Health Hazard Evaluation Report 2005-0157-3110

Appendix A: Occupational Health Limits and Health Effects (continued)

Measures for controlling exposures to N2O in dental operatories include effective scavenging devices, 

proper equipment, maintenance and routine leak checks of the N2

O delivery system, and good work 

practices on the part of the dentist and assistants. Scavenging systems to control N2

O at the point of use is 

the preferred method. A common scavenging system design is the “mask within a mask” unit, with tubes 

supplying oxygen and N2

O to the inside of the interior mask, and two tubes ventilating the space between 

the two masks (where the patient exhales). The recommended flow rate for this type of system, shown in 

figure A1, is 45 Lpm [NIOSH 1977].

These types of scavenging systems, while shown effective in reducing anesthetic gas exposure, do not 

consistently reduce N2

O to concentrations below the NIOSH REL of 25 ppm [NIOSH 1990]. Additional 

auxiliary ventilation has shown mixed results [Micklesen 1993]. Once ventilated, the collected anesthetic 

gas must be properly vented to a point away from personnel. Nonrecirculating air-conditioning systems, 

the central office suction system, and a separate duct system have successfully been used to accomplish this 

[NIOSH 1977]. Complete descriptions of scavenging systems, proper maintenance protocols, and work 

practices are detailed in the NIOSH Criteria Document on Waste Anesthetic Gases [NIOSH 1977].

 Figure A1. Scavenging system mask airflow

Design and Operational Criteria of the Ventilation System 

Proper ventilation of dental operatory rooms is important because of the types of surgical procedures 

performed and the anesthetic gases used in them. Therefore, appropriate ventilation design criteria should 

be considered. These criteria include the Guidelines for Design and Construction of Health Care Facilities

published by the AIA and the Health Care Facilities chapter of the ASHRAE Handbook: HVAC Applications

[AIA 2006; ASHRAE 2007]. When anesthetic gases are used and surgical procedures occur, the most 
Health Hazard Evaluation Report 2005-0157-3110 Page 13

Appendix A: Occupational Health Limits and Health Effects (continued)

appropriate ventilation criteria in these guidelines are those identified for “operating rooms.” For less 

invasive procedures performed without anesthetic gases, the criteria identified for “treatment rooms” 

are most appropriate. In the AIA Guidelines, Table 2.1-2 shows a minimum ventilation requirement 

of 6 ACH of total ventilation (outdoor air plus recirculated air) for treatment rooms and a minimum 

ventilation requirement of 15 ACH for “operating/surgical cystoscopic rooms” with a minimum of 3 

ACH of outdoor air [AIA 2006]. (2001 AIA guidelines published at the time of the development of the 

ventilation system drawings included identical requirements.) ASHRAE’s HVAC Applications Handbook

includes a similar table (Table 3) of ventilation requirements. The ASHRAE recommendation in this table 

for treatment rooms is also 6 ACH of total ventilation. However, ASHRAE also stipulates a minimum of 

2 air changes of outdoor air per hour. The ASHRAE recommendations for operating rooms (recirculating 

HVAC design) are a minimum of 20 ACH of total ventilation with a minimum of 4 ACH of outdoor air 

[ASHRAE 2007]. Both the AIA and ASHRAE design criteria state that a separate air exhaust system or a 

scavenging system is required when anesthetic gases are used [AIA 2006; ASHRAE 2007].

ANSI/ASHRAE also publishes Standard 62: Ventilation for Acceptable Indoor Air Quality, which provides 

guidelines on suitable outdoor air requirements for ventilation rates in healthcare facilities. Current 

and past versions of this standard indicate requirements of 15 cfm of outdoor air per person for medical 

procedure rooms of healthcare facilities and 30 cfm of outdoor air per person for operating rooms 

[ASHRAE 1999; ANSI/ASHRAE 2007].

References

ACGIH [2009]. 2009 TLVs® and BEIs®: threshold limit values for chemical substances and physical 

agents and biological exposure indices. Cincinnati, OH: American Conference of Governmental 

Industrial Hygienists.

AIHA [2009]. AIHA 2009 Emergency response planning guidelines (ERPG) & workplace environmental 

exposure levels (WEEL) handbook. Fairfax, VA: American Industrial Hygiene Association.

AIA Academy of Architecture for Health, Facility Guidelines Institute, and United States Department of 

Health and Human Services [2006]. Guidelines for design and construction of health care facilities. 2006 

ed. Washington, DC: American Institute of Architects Press.

ASHRAE [1999]. Ventilation for acceptable indoor air quality. American Society of Heating, Refrigerating 

and Air-Conditioning Engineers standard 62–1999. Atlanta, GA: American Society of Heating, 

Refrigerating, and Air-Conditioning Engineers, Inc.

ASHRAE [2007]. Health care facilities. In: 2007 ASHRAE handbook : heating, ventilating, and airconditioning applications. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning 

Engineers.

ANSI/ASHRAE [2007]. Ventilation for acceptable indoor air quality. American National Standards 

Institute/American Society of Heating, Refrigerating and Air-Conditioning Engineers standard 62.1–2007. 

Atlanta, GA: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.
Page 14 Health Hazard Evaluation Report 2005-0157-3110

Appendix A: Occupational Health Limits and Health Effects (continued)

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

Federal Register.

Cohen E, Brown B, Bruce D, Cascorbi H, Corbett T, Jones T, Whitcher C [1975]. A survey of anesthetic 

health hazards among dentists. J Am Dent Assoc 90(6):1291–1296.

Cohen E, Brown B, Wu J, Whitcher C, Brodsky J, Gift H, Greenfield W, Jones T, Driscoll E [1980]. 

Occupational disease in dentistry and chronic exposure to trace anesthetic gases. J Am Dent Assoc 

101(1):21–31.

Frost A [1985]. A history of nitrous oxide. In: Eger E II, ed. Nitrous oxide. New York: Elsevier, pp. 1–22.

Hathaway GJ, Proctor NH [2004]. Chemical hazards of the workplace, 5th ed. Hoboken, NJ: John Wiley 

& Sons, Inc.

Micklesen R, Jacobs D, Jensen P, Middendorf P, O’Brien D, Fischbach T, Beasley A [1993]. Auxiliary 

ventilation for the control of nitrous oxide in a dental clinic. Appl Occup Environ Hyg 8(6):564–570.

NIOSH [1977]. Criteria for a recommended standard: occupational exposure to waste anesthetic gases and 

vapors. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers 

for Disease Control, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication 

No. 77–140.

NIOSH [1990]. In-depth survey report: control of anesthetic gases in dental operators at University of 

California at San Francisco, Oral Surgical Dental Clinic. U.S. Department of Health and Human Services, 

Centers for Disease Control, National Institute for Occupational Safety and Health, Division of Physical 

Science and Engineering, Engineering Control Technology Branch. NIOSH Report ECTB 166–12b.

NIOSH [1994]. NIOSH Alert: Controlling exposures to nitrous oxide during anesthetic administration. 

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. 

1994–100.

NIOSH [2005]. NIOSH pocket guide to chemical hazards. 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. 2005–149. [http://www.cdc.gov/niosh/npg/]. Date 

accessed: December 2009.

Rowland A, Baird D, Weinberg C, Shore D, Shy C, Wilcox A [1992]. Reduced fertility among women 

employed as dental assistants exposed to high levels of nitrous oxide. New Engl J Med 327(14):993–997.

Venables H, Cherry N, Waldron H, Buck L, Edling C, Wilson H [1983]. Effects of trace levels of nitrous 

oxide on psychomotor performance. Scand J Work Environ Health 9(5):391–396.

Vieira E, Cleaton-Jones P, Austin J, Moyes D, Shaw R [1980]. Effects of low concentrations of nitrous 

oxide on rat fetuses. Anesth Anal 59(3):175–177.
Health Hazard Evaluation Report 2005-0157-3110 Page 15

Appendix B: Ventilation Assessment of Dental Clinic

On page M-1 of the drawings dated November 26, 2001, two 4-ton rooftop units are identified to supply 

conditioned air for 14 rooms plus ancillary areas (hallways, closets, entryways). The two rooftop units 

are labeled rooftop unit A (RTU-A) and rooftop unit B (RTU-B). The total ventilation capacity and the 

percentage of outdoor air for each unit are summarized below.

RTU-A:

● Total cfm provided from the unit = 1610 cfm

● From bullet # 2 under Mechanical Equipment description: “Existing rooftop units (RTU-A) shall 

have coils cleaned and new filters provided before and after construction. Set outside air to 200 

cfm.” 

● Total outdoor air for unit A expressed in percentage:

% Outdoor Air = 200 cfm / 1610 cfm = 0.1242 or 12.42%

RTU-B:

● Total cfm provided from the unit = 1600 cfm

● From bullet # 2 under Mechanical Equipment description: “Existing rooftop units (RTU-A) shall 

have coils cleaned and new filters provided before and after construction. Set outside air to 200 

cfm.” 

● Total outdoor air for unit B expressed in percentage:

% Outdoor Air = 200 cfm / 1600 cfm = 0.125 or 12.5%

For summary discussion purposes, a more detailed analysis is provided below for rooms identified as 

Treatment Room 3 and Treatment Room 4 (Analysis B-1). Ventilation is supplied to these rooms by 

RTU-A.
Page 16 Health Hazard Evaluation Report 2005-0157-3110

Appendix B: Ventilation Assessment of Dental Clinic (continued)

Analysis B-1: Analysis of Air Changes per Hour in Treatment 

Rooms 3 and 4
Health Hazard Evaluation Report 2005-0157-3110 Page 17

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 

and Health 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 employer 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.

The findings and conclusions in this report are those of the 

authors and do not necessarily represent the views of NIOSH. 

Mention of any company or product does not constitute 

endorsement by NIOSH. In addition, citations to websites 

external to NIOSH do no constitute NIOSH endorsement of 

the sponsoring organizations or their programs or products. 

Furthermore, NIOSH is not responsible for the content of these 

websites. All Web addresses referenced in this document were 

accessible as of the publication date.

This report was prepared by Chandran Achutan, Marilyn Radke, 

and Bradley King of HETAB, Division of Surveillance, Hazard 

Evaluations and Field Studies and Alberto Garcia and Kenneth 

Mead of the Engineering and Physical Hazards Branch, Division 

of Applied Research and Technology. Medical field assistance was 

provided by Elizabeth Safran. Analytical support was provided 

by Assay Technology Laboratories (Irvine, California). Health 

communication assistance was provided by Stefanie Evans. 

Editorial assistance was provided by Ellen Galloway. Desktop 

publishing was performed by Robin Smith.

Copies of this report have been sent to employee and management 

representatives at Children’s Dentistry at Hamilton Mill, the 

state health department, and the Occupational Safety and Health 

Administration Regional Office. This report is not copyrighted and 

may be freely reproduced. The report may be viewed and printed at 

http://www.cdc.gov/niosh/hhe/. Copies may be purchased from the 

National Technical Information Service at 5825 Port Royal Road, 

Springfield, Virginia 22161.
Below is a recommended citation for this report:

NIOSH [2010]. Health hazard evaluation report: assessment of nitrous oxide 

exposures in a pediatric dentistry, Dacula, GA. By Achutan C, Radke M, Garcia A, 

Mead K, King B. 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. 2005-0157-3110.

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