Evaluation of Magnetic 

Field Exposure to Office 

Employees from an 

Electrical Transformer

James Couch, MS, CIH, REHS/RS

Kenneth W. Fent, PhD

Health Hazard Evaluation Report

HETA 2009-0154-3101

Lebanon Correctional Institution

Lebanon, Ohio

January 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 2009-0154-3101 Page i

Appendix A

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

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

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

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

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

Results.................................................................................4

Discussion ...........................................................................7

Conclusions.........................................................................9

Recommendations...............................................................9

References ........................................................................11

Contents

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

Methods.............................................................................13

Occupational Exposure Limits & Health Effects ................14

Acknowledgments

Appendix B
Page ii Health Hazard Evaluation Report 2009-0154-3101

ACGIH® American Conference of Governmental Industrial Hygienists

BEI® Biological exposure index

CFR Code of Federal Regulations

GM Geometric mean

GSD Geometric standard deviation

HCMA Human Capital Management Analyst

HHE Health hazard evaluation

Hz Hertz

IARC International Agency for Research on Cancer

mG milliGauss

NAICS North American Industry Classification System

NIEHS National Institute of Environmental Health Science

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

SD Standard deviation

STEL Short term exposure limit

TLV® Threshold limit value

TWA Time weighted average

WEEL Workplace environmental exposure level

WHO World Health Organization

Abbreviations
Health Hazard Evaluation Report 2009-0154-3101 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 the 

Lebanon Correctional 

Institution in Lebanon, 

Ohio. Management 

made the request due to 

concerns about exposure 

to electromagnetic fields 

after a transformer 

was installed near the 

timekeeping office.

What NIOSH Did

● We evaluated employees’ electromagnetic field exposures in 

June 2009.

● We measured the magnetic fields at and around the 

transformer.

● We measured five employee’s exposure to magnetic fields.

● We measured magnetic fields around electrical devices and 

near electrical lines in the timekeeping office and the front 

lobby.

What NIOSH Found

● We measured a maximum of 100 milliGauss (mG) directly at 

the transformer.

● We measured a maximum of 300 mG near an electric fan in 

the timekeeping office.

● Magnetic field strength dropped quickly when you moved 

away from the transformer.

● All exposure measurements were well below the American 

Conference of Governmental Industrial Hygienists threshold 

limit value of 10,000 mG.

What Managers Can Do

● Encourage employees to learn about magnetic field sources 

and ways to reduce their exposure.

● Design office spaces to maximize the distance between work 

stations and magnetic field sources.

What Employees Can Do

● Learn about magnetic fields and how you can reduce your 

exposure.

● Talk to your supervisor about any work-related health 

concerns you may have.
Page iv Health Hazard Evaluation Report 2009-0154-3101

Summary

NIOSH investigators 

evaluated exposures 

to magnetic fields 

in the timekeeping 

office of a correctional 

institution. All personal 

and area magnetic field 

measurements were well 

below applicable OELs. 

Exposures can be further 

lowered by reducing the 

time spent near magnetic 

field sources and 

increasing the distance 

between these sources 

and employees.

On June 24, 2009, NIOSH investigators conducted an HHE in 

the timekeeping office at the Lebanon Correctional Institution, 

Lebanon, Ohio, in response to a request received from 

management. Management was concerned about magnetic field 

exposures from a transformer installed outside the timekeeping 

office.

Personal magnetic field monitoring was conducted on five 

employees (four in the timekeeping office and one in an office 

across the hall). Area magnetic field measurements were taken at 

an electrical transformer outside the building, along the exterior 

and interior walls of the timekeeping office, near electrical devices 

in the office, and in the front lobby.

The geometric means of personal magnetic field dosimeter 

measurements ranged from 0.47 mG to 3.3 mG. An area 

measurement of 100 mG at the transformer was recorded while 

another area measurement of 300 mG was recorded inside the 

office near a fan. All personal and area measurements were well 

below the ACGIH TLV of 10,000 mG and the ACGIH ceiling 

value of 1,000 mG for individuals with cardiac pacemakers or 

similar medical devices.

All magnetic field exposures measured in this evaluation were well 

below applicable OELs. Magnetic field exposures can be further 

reduced by limiting the amount of time spent working near 

magnetic field sources and by increasing working distance from 

magnetic field sources.

Keywords: NAICS 922140 (Correctional Institutions), 

correctional institution, prison, magnetic fields, executive office
Health Hazard Evaluation Report 2009-0154-3101 Page 1

Introduction

On May 19, 2009, NIOSH received a management request for an 

HHE at the Lebanon Correctional Institution, Lebanon, Ohio. 

The HHE request was submitted because a transformer had 

been installed near the timekeeping office and employees were 

concerned about magnetic field exposures.

On June 24, 2009, NIOSH investigators made a site visit to the 

Lebanon Correctional Institution. We met with management 

and employee representatives and observed work processes/

practices, and workplace conditions. During the opening meeting 

we discussed the nature of the HHE and the types of sampling 

for evaluating magnetic field exposures. Members of the Health 

and Safety Committee for the Lebanon Correctional Institution 

were present during the meeting and provided input into other 

areas of concern within the prison. We measured magnetic 

fields at the transformer, along the exterior and interior walls of 

the timekeeping office, and near electrical equipment used in 

the office such as personal cooling fans, computers, and paper 

shredders. We asked five employees to wear personal monitoring 

devices which measured their magnetic field exposures throughout 

the day. Based upon recommendations from the Health and Safety 

Committee for the Lebanon Correctional Institution we also 

evaluated magnetic field exposures in the front lobby. A closing 

meeting was held on June 24, 2009, with management, the Health 

and Safety Committee, and employee representatives to summarize 

site visit activities and provide preliminary findings. This was 

followed by a letter dated July 7, 2009, that provided a summary of 

our findings and preliminary recommendations.

Workplace Description

The Lebanon Correctional Institution opened in 1960 and 

encompasses 1,900 acres. In 2006, an electrical transformer 

(Areva OA-KNAN 60 Hertz, 12,470 volt, 208Y/120 rated at 416.4 

amps) was installed outside the timekeeping office (Figure 1). A 

replacement transformer was installed in 2008. The electrical lines 

from the transformer enter the building directly underneath the 

timekeeping office.
Page 2 Health Hazard Evaluation Report 2009-0154-3101

Introduction 

(continued)

 The 530 square foot timekeeping office has four employees 

working at individual work stations. Figure 2 illustrates the 

timekeeping office design. The timekeeping office has a copier/

printer, paper shredder, and computer workstations as well as a 

microwave, refrigerator, and personal cooling fans. Employees 

spend most of their time in the office although some tasks require 

them to leave the office for short periods of time.

Figure 1. Transformer located within 7 feet of the exterior wall of the 

timekeeping office. 
Health Hazard Evaluation Report 2009-0154-3101 Page 3

Introduction (continued)

Assessment We monitored magnetic fields from 5 Hz to 2,000 Hz, a frequency 

range that encompasses the electrical power frequency of 60 Hz. 

For this evaluation, magnetic fields were measured in mG. Another 

common unit of measurement is microTesla (1 microTesla equals 

10 mG). The methods used to collect area and personal magnetic 

field measurements are described in Appendix A. Monitored 

employees were asked to complete a log sheet on which they 

recorded any tasks involving trips to the other administrative 

offices or the use of electrical equipment other than typical office 

equipment. Appendix B discusses the OELs and potential health 

effects from magnetic field exposures.

Personal dosimeters were worn by all four employees in the 

timekeeping office and one employee in an office located across 

the hall from the timekeeping office. Area magnetic field readings 

were taken in the timekeeping office, at the electrical transformer, 

and in surrounding office areas such as the front lobby. Area 

magnetic field measurements were recorded near various electrical 

Figure 2. Scale layout of the timekeeping office showing magnetic field measures along the 

interior wall nearest the transformer. 
Page 4 Health Hazard Evaluation Report 2009-0154-3101

Assessment (continued)

Results

equipment, appliances, and personal fans in the timekeeping 

office. When possible the measurements were taken with the 

electrical equipment turned off and then recorded again when 

the electrical equipment was operating. All area measurements 

were taken as close to the electrical equipment as possible unless 

otherwise noted.

Magnetic Field Personal Measurements 

All personal TWA measurements were well below the ACGIH 

TLV of 10,000 mG (Table 1) [ACGIH 2009]. Geometric mean 

exposures ranged from 0.47 mG to 3.32 mG. The maximum 

measurements ranged from 12.61 mG to 950.40 mG.

Table 1. Magnetic field personal monitoring results

Job Title

Sampling 

Time 

(minutes)

Magnetic Field Levels (mG)

Minimum Maximum Median GM GSD

Account Clerk II 339.5 0.14 40.10 2.06 1.39 2.34

HCMA 1* 373.1 0.14 12.68 3.08 2.26 2.32

HCMA 2 372.3 0.26 12.61 4.21 3.32 1.99

Payroll Assistant 380.8 0.01 950.40 2.82 2.32 3.45

Personnel Director † 376.3 0.01 20.50 0.38 0.47 2.27

* HCMA - Human Capital Management Analyst

† Primary location in office across hallway from the timekeeping office

Magnetic Field Area Measurements 

Measurements were taken at 2 feet intervals approximately 1 foot 

from the transformer and were taken as near to the exterior wall 

of the timekeeping office as possible (Figure 3). Measurements at 

the transformer (located approximately 7 feet from the exterior wall 

of the timekeeping office) ranged from 2 mG to 100 mG due to 

the proximity of the measurement locations to electrical lines and 

the orientation of the transformer. Measurements taken along the 

outside of the exterior wall of the timekeeping office ranged from 

0.8 mG to 15 mG. The maximum level of 15 mG was measured 

near an operating air conditioning wall unit. Figure 3 shows 

the consistent measurements at the wall directly across from the 

transformer and steady decline as the distance increased from the 

transformer. Figure 2 shows the measurements taken at the interior 

wall of the timekeeping office.
Health Hazard Evaluation Report 2009-0154-3101 Page 5

Results (continued)

Table 2 shows the influence on magnetic fields when electrical 

equipment is operating and not operating and with increasing 

distance from a magnetic field source. For example, a level of 

300 mG was measured at a personal fan operating near the 

Payroll Assistant’s desk (0.7 mG when not operating). Additional 

measurements taken at 1 foot (50 mG), 2 feet (9 mG), and 4 feet (1 

mG) from the fan demonstrated the rapid decline in magnetic field 

strength due to increasing distance from the source.

Table 2. Magnetic field area monitoring results in timekeeping office

Equipment Magnetic Field Levels (mG)

Operating Not operating

Microwave 150 2.0

Paper shredder 95 0.7

Personal cooling fan (1) 300 0.7

 1 foot from fan (1) 50 N/A*

 2 feet from fan (1) 9 N/A*

 4 feet from fan (1) 1 N/A*

Personal cooling fan (2) 12 0.7

Personal cooling fan (3) 11 1.0

Electrical power strip 90 N/A*

* Measurements were not taken while not operating

Figure 3. Magnetic field area measurements near transformer and exterior wall of the 

timekeeping office. 
Page 6 Health Hazard Evaluation Report 2009-0154-3101

Results (continued)

Area measurements taken in the front lobby are shown in Figure 

4. The two guards spend most of their time near a metal detector 

used to process visitors. When the metal detector was operating, 

the magnetic field measurements ranged from 8 mG to 15 mG. A 

cabinet x-ray system was also available for use by the security guards 

but was not operational at the time of the site visit. The maximum 

magnetic field level measured near the operating automatic doors 

in the lobby were 4 mG.

The underground electrical lines from the transformer entered the 

building directly below the timekeeping office. Magnetic field levels 

measured at the floor surface near the employee desk for HCMA 2 

ranged from 5 mG to 7 mG. These magnetic field levels declined 

to 2 mG to 3 mG when measured 3 feet above the floor (Table 3).

Table 3. Magnetic field area monitoring results above electrical lines in timekeeping office

Distance from exterior wall 

nearest the transformer

Magnetic Field Levels (mG)

Floor level 3 feet above floor

2 feet 7 2

4 feet 7 3

6 feet 6 3

8 feet 5 3

Figure 4. Magnetic field measurements in front lobby of the Lebanon Correctional Institution. 
Health Hazard Evaluation Report 2009-0154-3101 Page 7

Electric and Magnetic Fields

The term radiation is commonly used to refer to ionizing radiation, 

which is energy that is able to ionize atoms or molecules of the 

substance in which the energy is absorbed. This causes chemical 

changes that damage tissues and structural materials in the body. 

Nonionizing radiation refers to the lower energy forms of the 

magnetic field spectrum such as radio waves, microwaves, infrared, 

and visible light, and does not carry enough energy to ionize atoms 

or molecules.

Magnetic field radiation is composed of both electric fields and 

magnetic fields. Electric fields are produced by voltage and increase 

in strength as the voltage increases. Magnetic fields result from the 

flow of current through wires or electrical devices and increase in 

strength as the current increases. Electric fields were not monitored 

during this survey because they are shielded or weakened by 

materials that conduct electricity, even materials that conduct 

poorly, including building materials and human skin [NIEHS 

2002]. In contrast, magnetic fields are not easily shielded and can 

pass through the human body, where they could potentially affect 

biological systems.

Personal exposures measured in this survey were well below the 

ACGIH TLV of 10,000 mG [ACGIH 2009]. This and other 

recommended OELs for magnetic field exposures are based on 

acute effects, such as induced currents in cells or nerve stimulation, 

which are known to occur at high exposures—more than 1,000 

times higher than magnetic field levels typically found in 

occupational settings [NIEHS 2002]. More information on OELs 

and health effects related to magnetic field exposures is provided in 

Appendix B.

Extremely low frequency magnetic fields are ubiquitous because 

they are present wherever there is electricity. However, the amount 

of extremely low frequency magnetic fields in the environment has 

increased due to electricity demand, advancing technology, and 

changes in work practices [WHO 2002]. Extremely low frequency 

magnetic fields are in the range of 3 Hz to 3000 Hz with most 

exposure coming from the power-line frequency of 50 Hz to 60 

Hz. Exposure to magnetic fields in homes is relatively consistent 

throughout the world, with GMs between 0.55 mG and 1.1 mG 

[WHO 2007]. Occupational exposures can be much higher, with 

exposures up to 100 mG near electrical conductors. Magnetic field 

exposures average 4 mG to 6 mG for electricians and electrical 

Discussion
Page 8 Health Hazard Evaluation Report 2009-0154-3101

Discussion (continued) engineers, 10 mG for power-line employees and greater than 

30 mG for welders, railway engine drivers, and sewing machine 

operators [WHO 2007].

Magnetic field levels decrease with increasing distance from the 

source. Although 300 mG was measured at a personal fan during 

operation, 1.0 mG was measured at the desk just 4 feet away. 

Magnetic field levels were 7 mG when measured at the floor 

surface directly above the electrical lines entering the building but 

decreased to 2 mG when measured 3 feet above the floor.

According to the job exposure matrix for power-line frequency 

magnetic fields [Bowman et al. 2008], GM exposures are 1.7 mG 

for computer operators and 1.0 mG for programmers. Exposures 

to the Account Clerk II (GM = 1.4) and Personnel Director (GM 

= 0.47) who perform similar, but not identical jobs, are consistent 

with the GMs reported by Bowman et al. The magnetic field 

exposure to the Payroll Assistant (GM = 2.32 mG) was slightly 

higher. While the exposures we measured are only slightly higher 

than those reported in the literature, the jobs are not identical and 

are within the range of exposures that would normally be expected 

in an office environment.

The HCMA 2 had a GM of 3.32 mG which was higher than 

the GM of 1.7 mG reported by Bowman et al. for a similar 

occupational group. The higher HCMA 2 GM maybe due to the 

position of the employee’s desk above the electrical lines entering 

the building directly beneath the floor under the desk. Other 

measurements around the desk were not higher than what would 

normally be expected from standard office equipment. A geometric 

SD of 1.99 mG and a maximum measurement of 12.61 mG suggest 

that magnetic field exposures were consistent throughout the shift.

The HCMA 1 had a GM of 2.26 mG which is higher than the 

GM of 1.7 mG reported by Bowman et al. Although this employee 

was located on the same side of the timekeeping office that 

the electrical lines entered the building these lines did not run 

underneath the employee’s desk. Area measurements did not 

indicate that magnetic field strength from the lines was higher than 

background at the floor level near the employee’s desk. A power 

strip outlet was measured at 90 mG and was located near the 

employee’s feet underneath the desk. The power strip appeared to 

be an older model and area measurements taken at the power strip 

were appreciably higher than any other power strip located in the 

timekeeping office.
Health Hazard Evaluation Report 2009-0154-3101 Page 9

All magnetic field exposures were well below the ACGIH TLV 

of 10,000 mG [ACGIH 2009]. Two job titles (Account Clerk II 

and Personnel Director) had GM exposures lower than similar 

job categories reported in the scientific literature [Bowman et al. 

2008]. Three job titles (HCMA 1, HCMA 2, and Payroll Assistant) 

had GM exposures greater than similar job titles reported in the 

scientific literature [Bowman et al. 2008]. However, the job titles 

are not identical to the ones reported by Bowman et al. and overall 

are well within the range of exposures consistent with typical office 

workers.

These findings show that the magnetic field exposure levels are 

related to movement patterns and the length of time spent near 

magnetic field sources and for that reason are likely to vary from 

day to day. Because measurements were taken during a span of 

about 8 hours on one day, the annual range of typical exposures 

over time could not be determined.

The magnetic field exposures measured in this survey did not 

exceed the ACGIH TLV of 10,000 mG [ACGIH 2009]. The 10,000 

mG TLV is based on potential acute health effects. No OELs 

are based on the potential health effects from chronic magnetic 

field exposures; however, exposures should be reduced whenever 

possible. Based on our findings, we recommend the actions listed 

below to create a more healthful workplace. We encourage the 

Lebanon Correctional Institution to use these recommendations 

to develop an action plan based, if possible, on the hierarchy of 

controls approach (refer to Appendix B: 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.

Elimination and Substitution

Elimination or substitution of a toxic/hazardous process material 

is a highly effective means for reducing hazards. Incorporating 

this strategy into the design or development phase of a project, 

Conclusions

Recommendations
Page 10 Health Hazard Evaluation Report 2009-0154-3101

Recommendations

(continued) commonly referred to as “prevention through design,” is most 

effective because it reduces the need for additional controls in the 

future.

1. Remove unnecessary magnetic field sources (personal fans) 

from the office.

2. Replace certain electrical devices with ones are rated to 

produce lower magnetic field emissions (i.e., the power strip 

outlet that measured 90 mG was much higher than other 

power strips in the office).

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 very effective 

at protecting employees without placing primary responsibility of 

implementation on the employee.

1. Increase distance between magnetic field sources and 

employees. For example, potential magnetic field sources 

in the timekeeping office (microwave, paper shredder, 

refrigerator, photocopier, etc.) could be relocated to the area 

of the office where the electrical lines enter the building. 

Employee desks could then be arranged to provide the most 

distance between their workstations and the magnetic field 

sources.

Administrative Controls

Because magnetic fields cannot be easily shielded, administrative 

controls are the most feasible option to reduce employees’ 

exposures. 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 depends 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. The following administrative controls 
Health Hazard Evaluation Report 2009-0154-3101 Page 11

Recommendations

(continued) are recommended to reduce the employees’ personal exposures to 

the magnetic fields.

1. Encourage employees to arrange their workstations so 

that magnetic field sources are located away from where 

they spend most of their time (normally their chair at the 

computer) but at a distance that is feasible for everyday 

usage.

Management and employees may want to learn more about 

magnetic fields and other forms of magnetic field radiation. The 

following websites provide more information on occupational and 

environmental exposures, scientific research, and health concerns 

related to magnetic field radiation:

● NIOSH: www.cdc.gov/niosh/topics/emagnetic field/

● OSHA: www.osha.gov/SLTC/elfradiation/index.html

● NIEHS: www.niehs.nih.gov/health/topics/agents/emagnetic 

field/

● WHO: www.who.int/peh-emagnetic field/en/

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.

Bowman J, Touchstone J, Yost M [2008]. Job exposure matrix 

for power-frequency magnetic fields. Cincinnati, OH: National 

Institute for Occupational Safety and Health [www.cdc.gov/niosh/

topics/emagnetic field/jem-powerfreq/jempowerfreq.html]. Date 

accessed: December 2009.

NIEHS [2002]. Electric and magnetic fields associated with the 

use of electric power. [www.niehs.nih.gov/health/topics/agents/

emagnetic field/]. Date accessed: December 2009.

WHO [2002]. Establishing a dialog on risks from electromagnetic 

fields. Geneva, Switzerland: Radiation and Environmental Health, 

Department of Protection of the Human Environment, World 

Health Organization.

References
Page 12 Health Hazard Evaluation Report 2009-0154-3101

References (continued) WHO [2007]. Extremely low frequency fields. Environmental 

health criteria 238 Geneva: World Health Organization. [www.

who.int/peh-emagnetic field/publications/elf_ehc/en/index.html]. 

Date accessed: December 2009.
Health Hazard Evaluation Report 2009-0154-3101 Page 13

Magnetic field measurements were collected using instruments that were calibrated within 1 month of 

the evaluation. Area measurements were collected using the HI-3627 ELF-Magnetic Field Meter (Holaday 

Industries Inc., Eden Prairie, Minnesota). This meter is designed to measure the flux density of magnetic 

fields in the frequency range of 5 Hz to 2000 Hz. It computes the root mean square value of the 3-axis 

magnetic flux density and directly displays it on an analog meter. It is capable of measuring magnetic field 

strength from 0.2 mG to 20,000 mG, independently of the 3-axis probe orientation. Measurements were 

taken at a variety of locations throughout the workplace at a height of 48 inches to characterize levels near 

the torso of an employee.

Personal magnetic field measurements were collected using the EMDEX II (Enertech Consultants, 

Campbell, California). This instrument is a programmable data-acquisition meter that measures the 

orthogonal-vector components of the magnetic field through its internal sensors in the frequency range of 

40 Hz to 800 Hz. The instrument was set to record measurements every 1.5 seconds. Five employees wore 

the meters on their waists for 3 or more hours during the morning.

Appendix A: Methods
Page 14 Health Hazard Evaluation Report 2009-0154-3101

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 

Appendix B: Occupational Exposure Limits & Health Effects
Health Hazard Evaluation Report 2009-0154-3101 Page 15

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

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

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

limits for over 1250 hazardous substances and is updated annually.

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 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.

Magnetic Fields 

Although OSHA and NIOSH have not established OELs for magnetic fields in the extremely low 

frequency range (3 to 3000 Hz), several organizations have, including the American National Standards 

Institute, the Institute of Electrical and Electronics Engineers, and the ACGIH. Among these 

organizations, the ACGIH has published frequency-dependent TLVs. Because the magnetic fields at 

the Information Services Department come primarily from 60 Hz power lines, the whole-body TLV of 

10,000 mG applies. The health and safety basis for this TLV is that magnetic fields greater than this level 

can induce currents in the body and cause magnetophosphenes in the visual system [ACGIH 2006]. The 

ACGIH also recommends a power frequency ceiling value of 1,000 mG for employees wearing cardiac 

pacemakers or similar medical electronic devices to protect against the interference with the function of 

these devices [ACGIH 2009]. Neither the TLV, nor any of the other OELs, address potential health effects 

from chronic magnetic field exposures.

Much research has been conducted during the past decade to determine if slightly elevated magnetic field 

exposures (greater than 2 mG) pose a health threat. The NIEHS evaluated many of these studies and, in 

1999, concluded that “... the probability that magnetic field exposure is truly a health hazard is currently 

small. The weak epidemiological associations provide only marginal, scientific support that exposure to 
Page 16 Health Hazard Evaluation Report 2009-0154-3101

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

this agent is causing any degree of harm.” However, the report also states that magnetic field exposures 

“cannot be recognized as entirely safe” and that efforts should continue to reduce exposures [NIEHS 

1999]. More recently, in 2002, the IARC classified extremely low frequency magnetic fields as possibly 

carcinogenic to humans based on epidemiology studies of childhood leukemia. This classification is 

used to denote an agent that has limited evidence of carcinogenicity in humans and less than sufficient 

evidence for carcinogenicity in experimental animals. Evidence for all other cancers in children and adults 

was inadequate to classify due to insufficient or inconsistent scientific information [IARC 2002]. A 2007 

update of this evaluation did not change the classification based upon more recent studies [WHO 2007].

References

ACGIH [2006]. Sub-radiofrequency (30 KHz and below) magnetic fields. In: Documentation of the 

threshold limit values and biological exposure indices. Cincinnati, OH: American Conference of 

Governmental Industrial Hygienists.

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.

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

Federal Register.

IARC [2002]. Monographs on the evaluation of the carcinogenic risks to humans: non-ionizing radiation, 

part 1: static and extremely low frequency electric and magnetic fields. Vol. 80. Lyon, France: World 

Health Organization, International Agency for Research on Cancer.

NIEHS [1999]. NIEHS report on health effects from exposure to power-line frequency electric and 

magnetic fields. By Boorman G, Bernheim N, Galvin M, Newton S, Parham F, Portier C, Wolfe M. 

Research Triangle Park, NC: U.S. Department of Health and Human Services, National Institutes of 

Health, National Institute for Environmental Health Sciences (NIEHS) Publication No. 99-4493.

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. [www.cdc.gov/niosh/npg/]. Date accessed: 

November 2009.

WHO [2007]. Extremely low frequency fields. Environmental health criteria 238 Geneva: World Health 

Organization [www.who.int/peh-emagnetic field/publications/elf_ehc/en/index.html]. Date accessed: 

December 2009.
Health Hazard Evaluation Report 2009-0154-3101 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 (OSHA) Act of 1970, 29 U.S.C. 669(a)(6) which 

authorizes the Secretary of Health and Human Services, following 

a written request from any 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 not 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 James Couch and Kenneth W. Fent of 

HETAB, Division of Surveillance, Hazard Evaluations and Field 

Studies. Health communication assistance was provided by Stefanie 

Evans. Desktop publishing was performed by Robin Smith.

Copies of this report have been sent to employee and management 

representatives at Lebanon Correctional Institution, the state 

health department, and the OSHA Regional Office. This report 

is not copyrighted and may be freely reproduced. The report may 

be viewed and printed at 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: evaluation of magnetic field 

exposure to office employees from an electrical transformer, Lebanon, OH. 

By Couch J, Fent KW. 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. 2009-0154-3101.

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