Health Hazard Evaluation Report 2011-0097-3200 Page 1

Evaluation of Radiofrequency Radiation 

Exposures at an Atomic Time Radio Station

Karl D. Feldmann, MS, CIH

Kenneth W. Fent, PhD, CIH

Report No. 2011-0097-3200

December 2013

U.S. Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
Page 2 Health Hazard Evaluation Report 2011-0097-3200

Contents

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

Abbreviations ..................................... iv

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

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

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

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

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

Appendix A .......................................... 9

Appendix B......................................... 13

References.......................................... 25

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

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

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

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

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

not be related to this Health Hazard Evaluation. Photo by NIOSH.
Health Hazard Evaluation Report 2011-0097-3200 Page i

We evaluated 

radiofrequency exposures 

at an atomic time radio 

station. Electric and 

magnetic field strengths 

exceeded action levels and 

exposure limits in certain 

areas of the antenna 

field, but not inside, just 

outside, or on the roof of 

the radio station building. 

We measured electric and 

magnetic field strengths 

inside the pickup truck 

that tows a mower used 

on the antenna field; 

all were below action 

levels. We recommend 

a comprehensive 

radiofrequency safety 

program.

Highlights of this Evaluation

The Health Hazard Evaluation Program received a request from a federal research institution. 

Health and safety managers submitted the request because of concern about possible 

radiofrequency exposures at the research institution’s atomic time radio station in Hawai’i.

What We Did

● We evaluated radiofrequency electric and magnetic field exposures at the radio station 

in January 2012.

What We Found

● Electric and magnetic field strengths measured on the 

roof, in the office, and in the transmission room of 

the radio station building were below the OELs and 

action levels.

● Electric and magnetic field strengths around the 10- 

and 15-megahertz antennas were below exposure 

limits and action levels inside the pickup truck that 

tows a mower used on the antenna field. 

● Electric and magnetic field strengths exceeded action 

levels near the antennas, an area called the antenna 

field.

● Electric and magnetic field strengths exceeded 

exposure limits near the fences surrounding the 5-, 

10-, and 15-megahertz antennas.

● Magnetic field strengths exceeded exposure limits 

about halfway up the weather station tower.

● Magnetic field strengths near unpowered 10- and 

15-megahertz antennas exceeded exposure limits.

● During activities involving primary or backup antennas 

that were powered off, or when servicing the weather 

station, employees could be overexposed to magnetic 

fields induced from nearby transmitting antennas.

What the Employer Can Do

● Start a comprehensive radiofrequency safety program.

● Install caution signs to identify areas where exposure limits could be exceeded. Tell 

employees not to enter these areas unless the antenna has been turned off or they are inside 

the pickup truck while mowing.

● Reduce power to a primary antenna before working on the standby antenna of the 

same frequency or vice versa.
Page ii Health Hazard Evaluation Report 2011-0097-3200

What the Employer Can Do (continued)

● Reduce power to the 5-megahertz antenna before servicing the weather station. 

● Train employees on the potential hazards associated with radiofrequency exposure.

What the Employee Can Do

● Learn about radiofrequency radiation hazards and the purpose of signs and other 

controls to prevent overexposures to radiofrequency radiation.

● Report health and safety concerns to your manager.

● Share ideas on ways to improve the radiofrequency safety program with the safety officer.
Health Hazard Evaluation Report 2011-0097-3200 Page iii

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Page iv Health Hazard Evaluation Report 2011-0097-3200

Abbreviations

A/m Amps per meter

ACGIH® American Conference of Governmental Industrial Hygienists

CFR Code of Federal Regulations

FCC Federal Communications Commission

GHz Gigahertz

GPS Global positioning system

ICNIRP International Commission on Non-Ionizing Radiation Protection

IEEE Institute of Electrical and Electronics Engineers

kHz Kilohertz

MHz Megahertz

NIOSH National Institute for Occupational Safety and Health

OEL Occupational exposure limit

OSHA Occupational Safety and Health Administration

RF Radiofrequency (30 kHz to 300 GHz)

RMS Root-mean-square

TLV® Threshold limit value

V/m Volts per meter

WEEL Workplace environmental exposure level
Health Hazard Evaluation Report 2011-0097-3200 Page 1

Introduction

The Health Hazard Evaluation Program received a request from a federal research institute. 

The request concerned potential employee exposures to radiofrequency (RF) radiation at the 

institute’s atomic time radio station in Hawai’i. The purpose of the evaluation was to assess 

RF exposures at the radio station from the 2.5-, 5-, 10-, and 15-megahertz (MHz) antennas 

(Figure 1).

Four employees worked 

at the radio station during 

our evaluation. The radio 

station broadcasts time 

announcements, standard 

time intervals, standard 

frequencies, geophysical 

alerts, marine storm 

warnings, and global 

positioning system (GPS) 

status reports. The station 

radiated 5 kilowatts on a 2.5-

MHz antenna array and 10 

kilowatts on 5-, 10-, and 15-

MHz antenna arrays. Each 

frequency was broadcast 

from a separate transmitter. Additionally, a weather station was on top of a 45-foot tower 

[NIST 2012]. Most of the antennas were between the radio station building and the beach. 

For this evaluation we refer to this area as the antenna field.

Methods

We used a factory-calibrated Narda EHP-200 electric and magnetic field analyzer capable of 

measuring RF radiation propagated as electric and magnetic fields at frequencies between 9 

and 30 MHz. The analyzer was connected to an isotropic probe capable of measuring field 

strengths in the X, Y, and Z directions at the same time. Because the human body can alter 

electric and magnetic fields, the probe and analyzer were connected to a laptop computer 

with fiber optic cable to minimize disturbances.

The probe was placed on a fiberglass tripod at groin height (about 3 feet) to collect most 

measurements (Figure 2). We took some additional measurements at head height (about 5.5 

feet) and chest height (about 4 feet) to obtain data for spatial averaging across the human body 

as required by most RF standards. Most of our measurements were collected at groin height 

because we assumed that the groin height measurements would be about the same or higher than 

measurements collected at other heights. The measurements were collected around the 2.5-, 5-, 

Figure 1. Aerial view of the radio station site. NIST Photo. Reprinted 

with permission. 
Page 2 Health Hazard Evaluation Report 2011-0097-3200

10-, and 15-MHz antennas 

as well as areas on the 

inside, outside, and on the 

roof of the radio station 

building.

Field strengths were 

recorded over 30 

seconds and root-meansquare (RMS) values 

calculated. RMS is a 

statistical measure of the 

magnitude of a varying 

quantity. This calculation 

was performed 

automatically by the 

instrument software. 

For the majority of 

our measurements, we 

used 30-second averaging times instead of the 6-minute averaging times specified by most 

standards. In this evaluation a shorter averaging time could be used because the electric and 

magnetic fields at a stationary position were generally constant.

Neither the Occupational Safety and Health Administration (OSHA) nor the National 

Institute for Occupational Safety and Health (NIOSH) has occupational exposure limits 

(OELs) for RF electric and magnetic fields. However, OELs for electric and magnetic field 

strengths at the frequencies used at the radio station have been recommended by several 

professional organizations (Appendix A, Tables A1 and A2). According to the radiofrequency 

safety program guidelines established by the Institute of Electrical and Electronics Engineers 

(IEEE), reference levels for uncontrolled or general public exposure should be regarded 

as “action levels” for occupational settings [IEEE 2005a]. These levels are summarized in 

Tables A1 and A2 of Appendix A. In this report, we compared field strength measurements 

to the most conservative OELs and action levels. The most conservative OELs were set by 

the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The most 

conservative action levels were also set by ICNIRP with the exception of electric field 

strengths at 15-MHz, in which case, the American Conference of Governmental Industrial 

Hygienists (ACGIH) action level is most conservative (Appendix A, Table A1).

Because the radio station broadcasted in multiple frequencies, we performed a mixture 

analysis for electric and magnetic field strengths (Appendix B, Tables B13 and B14) as 

described in Annex D.2 of IEEE Standard C95.1-2005 [IEEE 2005b]. Briefly, we obtained 

the ratio of each squared frequency-specific field strength to the square of its frequencyspecific OEL. We then summed the ratios for all frequencies. To comply with OELs, the 

sum of the ratios should not exceed 1 (unity). This formula was also used after spatially 

averaging the field strengths in the locations where we collected head, chest, and groin height 

Figure 2. A Narda RF field analyzer measuring RF electric and magnetic 

fields near the primary 2.5-MHz antenna. Photo by NIOSH. 
Health Hazard Evaluation Report 2011-0097-3200 Page 3

measurements to comply with the mixture analysis and spatial averaging elements of the 

OELs (Appendix B, Tables B13 and B14).

Results and Discussion

The electric and magnetic field strength measurements are provided in Tables B1–B14 

of Appendix B. Because all overexposures were the result of the predominant frequency, 

we present the field strengths for only the predominant frequencies in Tables B1–B12 of 

Appendix B.

Several measurements taken in the antenna field were above OELs or action levels 

(Appendix B, Tables B1–B10). For example, the following measurements exceeded OELs:

● electric and magnetic fields at groin height north of the 15-MHz standby antenna 

(Appendix B, Tables B1 and B2)

● electric and magnetic fields at groin height 30 feet from the 10-MHz antenna 

(Appendix B, Tables B3 and B4).

● magnetic fields at a height of about 16 feet at the weather station tower (Appendix B, 

Tables B9 and B10)

Measurements exceeding action levels included the following:

● electric and magnetic fields at groin height 15 feet from the 5-MHz antenna (Appendix 

B, Tables B5 and B6)

● electric and magnetic fields at groin height at the fence around the 2.5-MHz standby 

antenna (Appendix B, Tables B7 and B8). 

● electric fields at a height of about 16 feet at the weather station tower (Appendix B, 

Tables B9 and B10)

Electric and magnetic field strengths were below the OELs and action levels in the cab of the 

pickup as well as on the roof, in the office, and in the transmission room of the radio station 

building (Appendix B, Tables B1–B4, B9–B12).

Spatial averaging of field strength measurements is required by most RF standards (Appendix 

A). Electric and magnetic fields should be averaged over an area equivalent to the vertical 

cross section of the human body. Electric and magnetic field strengths 30 feet, 130° southeast 

of the primary 15-MHz antenna were among the highest measured. Field strengths were 

collected here for spatially averaged exposure estimations (Tables B13 and B14). Compared 

to the groin height measurements at this location, spatial averaging resulted in a lower 

estimate of exposure for electric fields (Appendix B, Table B13) and a higher estimate of 

exposure for magnetic fields (Appendix B, Table B14).

Our measurements presented in Appendix B suggest that employees could potentially be 

overexposed to electric and magnetic fields while in the antenna field, however employees 

did not typically spend much time in this area. Most of the time, employees worked in 
Page 4 Health Hazard Evaluation Report 2011-0097-3200

the radio station building. By talking with employees, we identified the following routine 

but infrequent activities in the antenna field that could result in electric and magnetic field 

overexposures:

● Cleaning, repairing, and painting antennas

● Maintaining the weather station

● Mowing the antenna field

When employees clean, repair, paint, or perform other work around an antenna, the antenna 

is powered off using lockout/tagout procedures. If the antenna being serviced is a primary 

antenna, the backup is turned on to maintain the transmission for that frequency.

To prepare the primary 10-MHz antenna for these activities, the backup 10-MHz antenna was 

powered on and the primary 10-MHz antenna was powered off. In an attempt to eliminate 

current induced in the primary 10-MHz antenna by the backup, the primary 10-MHz antenna 

was grounded with a grounding strap placed between the antenna and the tuning box. 

To prepare the backup 15-MHz antenna for these activities a grounding strap was placed 

between the backup antenna and the tuning box. The primary 15-MHZ antenna continued to 

broadcast as usual.

We measured electric and magnetic field strengths within a few inches of the powered down 

antennas (Tables 1 and 2). The only electric field measurement location that exceeded an action 

level (but not an OEL) was at the 15-MHz standby antenna nearest the building (Table 1).

Table 1. Electric field measurements* during simulated antenna maintenance, in V/m

Location Measurement

height (feet)

Frequency (MHz)

2.5 5 10 15

At the base of the standby 10-MHz antenna 

(off and grounded at tuning box)

1 6.73 15 16.2 7.47

At the grounding wire for the standby

10-MHz antenna

1 8.54 26.8 22.4 9.78

At the grounded tuning box for the standby 

10-MHz antenna

1 5.38 6.7 11 16.2

At the base of the standby 15-MHz antenna 

nearest beach (off and grounded at the 

transmitter)

1 5.13 16.1 5.55 10.77

Standby 15-MHz antenna nearest building 

(off and grounded at the transmitter)

10 6.71 21.76 13.66 37

ICNIRP OEL (reference levels for occupational exposure) 244 122 61 61

ICNIRP action level (reference levels for general public exposure) 55 40 28 28

V/m = volts per meter

*30-second averaging time unless otherwise noted

Measurements exceeding action levels are underlined.
Health Hazard Evaluation Report 2011-0097-3200 Page 5

Magnetic field strengths exceeded the OELs at the base of the standby 10-MHz antenna and 

about 10 feet high on the standby 15-MHz antenna (Table 2). Note that the 5-MHz magnetic 

field strength was > 90% of the OEL and the 10-MHz magnetic field strength was > 120% 

of the OEL at the base of the standby 10-MHz antenna (Table 2). Even if the primary 10-

MHz antenna was transmitting at 50% power (as a possible control measure), the combined 

magnetic field strengths from the 5- and 10-MHz frequencies could still exceed the OEL

at the base of the standby 10-MHz antenna. Although reducing power to a transmitting 

antenna is a viable control to lessen induced RF fields in an unpowered antenna of the same 

frequency, field strength measurements would be necessary to verify that the power reduction 

level results in combined field strengths below the OEL.

Table 2. Magnetic field measurements* during simulated antenna maintenance, in A/m

Location Measurement

height (feet)

Frequency (MHz)

2.5 5 10 15

At the base of the standby 10-MHz antenna 

(off and grounded at tuning box)

1 0.15 0.31 0.198 0.052

At the grounded tuning box for the standby 

10-MHz antenna

1 0.021 0.025 0.02 0.024

At the base of the standby 15-MHz antenna 

nearest beach (off and grounded at the 

transmitter)

1 0.021 0.06 0.019 0.049

Standby 15-MHz antenna nearest building 

(off and grounded at the transmitter)

10 0.012 0.043 0.03 0.17

ICNIRP OEL (reference levels for occupational exposure) 0.64 0.32 0.16 0.16

ICNIRP action level (reference levels for general public exposure) 0.3 0.15 0.073 0.073

A/m = amps per meter

*30-second averaging time unless otherwise noted

Measurements exceeding occupational exposure limits are bolded.

Measurements exceeding action levels are underlined.

Employees occasionally serviced the weather station near the top of a tower in the antenna 

field. Prior to our evaluation, employees reached the weather station by climbing the tower, 

but currently use a bucket or scissor lift. We measured increasing electric and magnetic field 

exposures with increasing height up the weather station tower (Tables 3 and 4). Electric field 

strengths exceeded action levels at a height of about 8 feet and above (Table 3). Magnetic 

field strengths at the same location exceeded action levels at a height from about 3 to 8 feet 

and exceeded OELs above 16 feet (Table 4).
Page 6 Health Hazard Evaluation Report 2011-0097-3200

Table 3. Electric field measurements* at the weather station tower in V/m (5- and 10-MHz standby 

antennas on)

Location Measurement 

height (feet)

Frequency (MHz)

2.5 5 10 15

Next to the weather station receiving antenna about 3 1.26 11.7 2.49 3.14

1/3 of the way up the weather station antenna about 8 4.6 66 10.2 20

1/2 of the way up the weather station antenna about 16 5.98 75.8 9.2 10.4

ICNIRP OEL (reference levels for occupational exposure) 244 122 61 61

ICNIRP action level (reference levels for general public exposure) 55 40 28 28

*30-second averaging time unless otherwise noted

Measurements exceeding action levels are underlined.

Table 4. Magnetic field measurements* at the weather station tower in A/m (5- and 10-MHz standby 

antennas on)

Location Measurement 

height (feet)

Frequency (MHz)

2.5 5 10 15

Next to the weather station receiving antenna about 3 0.015 0.16 0.019 0.018

1/3 of the way up the weather station antenna about 8 0.025 0.27 0.032 0.024

1/2 of the way up the weather station antenna about 16 0.027 0.35 0.049 0.039

ICNIRP OEL (reference levels for occupational exposure) 0.64 0.32 0.16 0.16

ICNIRP action level (reference levels for general public exposure) 0.3 0.15 0.073 0.073

*30-second averaging time unless otherwise noted

Measurements exceeding occupational exposure limits are bolded.

Measurements exceeding action levels are underlined.

The electric and magnetic fields near the weather station tower and unpowered antennas 

were induced from nearby antennas and suggest that employees could be overexposed 

when working on the weather station or powered down antennas. When employees touch 

the weather station tower or the antennas (called coupling), electric currents induced in 

the structures can pass through their bodies (called induced body current). We did not 

measure induced body current in this evaluation, but these measurements are the best way of 

determining an employee’s RF exposure due to coupling.

According to the employees, mowing accounts for the greatest proportion of time spent 

in the antenna field. Employees mowed the antenna field about twice per year by towing a 

mower behind a pickup truck. Smaller areas not accessible with the pickup truck such as the 

fenced areas surrounding the antennas were mowed with gas powered trimmers and push 

mowers. The antenna was powered off while employees worked in these fenced-in areas. 

When measured outside of the pickup truck (by the window), the electric and magnetic 

field strengths within 30 feet of these antennas exceeded OELs or action levels (Appendix 

B, Tables B1–B4). Our measurements inside the cab of the pickup truck (Tables 5 and 6) 

showed that the cab of the pickup truck reduced electric and magnetic field exposure to the 

occupants even when within 30 feet of a transmitting antenna.
Health Hazard Evaluation Report 2011-0097-3200 Page 7

Table 5. Electric field levels inside the pickup truck within 30 feet of the 10- or 15-MHz antenna 

in V/m

Location Measurement

height

Frequency (MHz)

2.5 5 10 15

Driving around the 10-MHz antennas for 2 minutes Head (window) 0.82 0.58 4.81 0.68

Driving around the 15-MHz antennas for 2 minutes Head (window) 0.56 0.57 0.66 3.8

ICNIRP OEL (reference levels for occupational exposure) 244 122 61 61

ICNIRP action level (reference levels for general public exposure) 55 40 28 28

Table 6. Magnetic field levels inside the pickup truck within 30 feet of the 10- or 15-MHz antenna 

in A/m

Location Measurement

height

Frequency (MHz)

2.5 5 10 15

Driving around the 10-MHz antennas for 

2 minutes

Head (window) 0.01 0.009 0.028 0.008

Driving around the 15-MHz antennas for 

2 minutes

Head (window) 0.009 0.009 0.009 0.031

ICNIRP OEL (reference levels for occupational exposure) 0.64 0.32 0.16 0.16

ICNIRP action level (reference levels for general public exposure) 0.3 0.15 0.073 0.073

Conclusions

Electric and magnetic field strengths measured in the cab of the pickup truck driving near 

transmitting antennas were below the OELs and action levels. Electric and magnetic field 

strengths measured on the roof, in the office, and in the transmission room of the radio station 

building were below the OELs and action levels. Electric field strengths measured near the 

5-, 10-, and 15-MHz antennas exceeded the OELs, but employees spent little time in the 

antenna field. During activities involving primary or backup antennas that were powered off, 

or when servicing the weather station, employees could be overexposed to magnetic fields 

induced from nearby transmitting antennas.

Recommendations

On the basis of our findings, we recommend the actions listed below to create a safer 

workplace. We encourage the research institution 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 the research institution.

1. Develop a comprehensive RF safety program. According to our measurements, the 

radio station meets the criteria of a category three RF safety program, defined as a 

site with the “potential to exceed the exposure limit in accessible areas, if mitigating 

controls are not applied” [IEEE 2005a].
Page 8 Health Hazard Evaluation Report 2011-0097-3200

2. Assign a programmatic RF safety officer to develop and oversee the overall RF safety 

plan for all research sites in this institution [IEEE 2005a]. Assign a deputy RF safety 

officer at this research site.

3. Maintain an inventory of RF sources that have the potential to produce electric and 

magnetic field strengths near or above OELs or action levels. Conduct initial exposure 

monitoring when new sources are introduced and additional exposure monitoring 

when processes are modified.

4. Follow IEEE guidelines for signs (IEEE Standard C95.7-2005, Section 4.3.2.1) in 

areas where action levels may be exceeded and caution signs in areas where OELs 

may be exceeded.

5. Power off the standby 5-MHz antenna when employees maintain the weather station to 

lower their exposures to electric and magnetic fields.

6. Confirm the effectiveness of reducing the power to a transmitting antenna as a 

control measure to reduce induced field strengths when employees are working on a 

nearby powered off antenna by doing field strengths measurements and body-current 

exposure monitoring.

7. Confirm the effectiveness of using a bucket or scissor lift as a control measure to 

reduce induced field strengths when employees service the weather station by doing 

field strength measurements and body-current exposure monitoring.

8. Provide annual RF safety awareness training. Educate employees on the potential 

hazards associated with RF exposures, the purpose of signage, and other safety 

procedures such as lockout/tagout.

9. Modify the incident reporting system to include possible RF overexposure incidents, 

such as medical device interference, reddening of skin, elevated body temperatures, 

other evidence of burns, and electrical shocks.

10.Audit the RF safety program annually. This audit should include a review of RF 

overexposure incidents and RF monitoring data, and inspection of controls. Review 

feedback and recommendations from employees submitted to the RF safety officer 

and/or deputy.
Health Hazard Evaluation Report 2011-0097-3200 Page 9

Appendix A: Occupational Exposure Limits and 

Health Effects

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

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

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

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

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

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

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

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

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

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

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

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

Most OELs are expressed as a time-weighted average exposure. A time-weighted average 

exposure refers to the average exposure during a normal 8- to 10-hour workday. Some 

chemical substances and physical agents have recommended short term exposure limit or 

ceiling values. Unless otherwise noted, the short term exposure limit is a 15-minute timeweighted average exposure. It should not be exceeded at any time during a workday. The 

ceiling limit should not be exceeded at any time.

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

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

enforceable limits; others are recommendations. 

● The U.S. Department of Labor Occupational Safety and Health Administration 

permissible exposure limits (29 CFR 1910 [general industry]; 29 CFR 1926 

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

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

Act of 1970. 

● NIOSH recommended exposure limits are recommendations based on a critical review 

of the scientific and technical information and the adequacy of methods to identify 

and control the hazard. NIOSH recommended exposure limits are published in the 

NIOSH Pocket Guide to Chemical Hazards [NIOSH 2010]. NIOSH also recommends 

risk management practices (e.g., engineering controls, safe work practices, employee 

education/training, personal protective equipment, and exposure and medical 

monitoring) to minimize the risk of exposure and adverse health effects.

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

values (TLVs), which are recommended by ACGIH, a professional organization, and 

workplace environmental exposure levels (WEELs), which are recommended by the 

American Industrial Hygiene Association, another professional organization. The TLVs 
Page 10 Health Hazard Evaluation Report 2011-0097-3200

and WEELs are developed by committee members of these associations from a review 

of the published, peer-reviewed literature. These OELs are not consensus standards. 

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 

2013]. WEELs have been established for some chemicals “when no other legal or 

authoritative limits exist” [AIHA 2013].

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

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

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

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

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

database, available at http://www.dguv.de/ifa/Gefahrstoffdatenbanken/GESTIS-InternationaleGrenzwerte-für-chemische-Substanzen-limit-values-for-chemical-agents/index-2.jsp, contains 

international limits for more than 1,500 hazardous substances and is updated periodically. 

The Occupational Safety and Health Administration requires an employer to furnish 

employees a place of employment free from recognized hazards that cause or are likely to 

cause death or serious physical harm [Occupational Safety and Health Act of 1970 (Public 

Law 91–596, sec. 5(a)(1))]. This is true in the absence of a specific OEL. It also is important 

to keep in mind that OELs may not reflect current health-based information.

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

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

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

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

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

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

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

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

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

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

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

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

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

existing OELs.

Radiofrequency Health Effects

Electrical currents cause electric and magnetic fields which can be high or low in intensity, 

and continuous or brief in duration. However, once electrical power is turned off, none of 

the fields linger in the environment. Electric fields, such as those present around power lines 

and broadcasting antennas, are strongest at their source. These fields are reduced by walls, 

buildings, and trees. Like electric fields, magnetic fields are strongest close to their source 
Health Hazard Evaluation Report 2011-0097-3200 Page 11

and rapidly decrease with increased distance from the source. Unlike electric fields, magnetic 

fields are not effectively blocked by common materials such as walls or floors of buildings 

[WHO 2010].

Much of what is known about RF biological effects pertains to acute (short-term) exposure; 

relatively little is known about the effects of long-term low-level RF exposure. Human and 

animal studies show that exposure to RF fields above OELs may cause harmful biological 

effects as a result of heating of internal tissues. The extent of heating depends primarily 

on the RF frequency, intensity of the RF field, and duration of exposure. However, some 

researchers have reported that absorption of RF radiation may result in nonthermal effects 

that occur without a measurable increase in tissue temperature, and at RF field strengths 

lower than those that cause thermal effects [NIOSH/OSHA 1979; FCC 1999]. As noted in 

IEEE C95.1-1999, nonthermal mechanisms, such as the electrostimulation of excitable cells 

(nerve stimulation) become important at frequencies between 3 kilohertz (kHz) and 100 kHz. 

Research suggests that fields less than 30 kHz could cause significant biological responses by 

stimulating the nervous or cardiac systems [Bernhardt 1979; Bailey et al. 1997].

Exposure to RF radiation below 0.1 MHz requires special consideration and treatment 

to prevent electrical shock; induction of RF currents in conductive objects may induce 

currents through the body of an individual who contacts them. The amount of current that 

flows through a body depends on how well the individual is electrically grounded and the 

impedance between the source and the individual.

Radiofrequency Occupational Exposure Limits

Most RF exposure levels are intended to protect against acute health effects associated with 

electrostimulation (shocks or pain associated with induced body currents) and tissue and 

whole body heating (RF burns) [IEEE 2005b]. An extensive review of the scientific literature 

on possible health effects from RF exposure was published in 2009 by the International 

Commission on Non-Ionizing Radiation Protection [ICNIRP 2009]. The authors of this 

study reviewed biophysical, cellular, animal, human laboratory, and epidemiologic studies, 

and concluded that there was no evidence of any other health effects related to RF exposure 

[ICNIRP 2009].

The ICNIRP reference levels for time-varying electromagnetic fields (up to 300 Hz) are based 

on short-term, immediate health effects such as stimulation of peripheral nerves and muscles, 

shocks and burns caused by touching conductive objects, and elevated tissue temperatures 

resulting from absorption of energy during exposure to electromagnetic fields [ICNIRP 1998]. 

The IEEE maximum permissible exposures for RF radiation (3 kHz to 300 gigahertz [GHz]) 

are intended to minimize painful electrostimulation in the frequency range of 3 kHz to 5 MHz 

and to protect against adverse heating in the frequency range of 100 kHz to 300 GHz. In the 

transition region of 100 kHz to 5 MHz, the maximum permissible exposures are intended to 

protect against both electrostimulation and thermal effects [IEEE 2005b].
Page 12 Health Hazard Evaluation Report 2011-0097-3200

The Federal Communications Commission (FCC) maximum permissible exposures are 

intended to prevent similar health effects [FCC 1999]. The ACGIH TLVs for RF and 

microwave radiation are based on its thermal effects [ACGIH 2013]. Two areas of the body, 

the eyes and the testes, are known to be particularly vulnerable to heating by RF energy 

because of the relative lack of available blood flow to dissipate the excessive heat load. 

Intense RF exposures to the eyes of animals have been shown to cause cataracts. Intense RF 

exposures to the testes of animals have been shown to cause temporary sterility [FCC 1999].

During this evaluation, the atomic time radio station transmitted high frequency (2.5–15 

MHz) signals. Tables A1 and A2 present the OELs and action levels for electric and magnetic 

field strengths corresponding to these frequencies.

Table A1. RLs, OELs, and action levels (RMS values averaged over 6 minutes) for electric field 

strengths (V/m) with the most conservative exposure levels bolded and action levels underlined

Frequency 

(MHz)

ICNIRP IEEE ACGIH FCC

RL Action 

level

RL Action 

level

TLV Action 

level

RL Action 

level

2.5 244 55 737 330 737 147 614 330

5 122 40 368 165 368 74 368 165

10 61 28 184 82 184 37 184 82

15 61 28 123 55 123 25 123 55

RL = Reference Level

Table A2. RLs, OELs, and action levels (RMS values averaged over 6 minutes) for magnetic field 

strengths (A/m) with the most conservative exposure levels bolded and action levels underlined

Frequency 

(MHz)

ICNIRP IEEE ACGIH FCC

RL Action 

level

RL Action 

level

TLV Action 

level

RL Action 

level

2.5 0.64 0.3 6.5 6.5 6.5 1.30 1.63 0.88

5 0.32 0.15 3.3 3.3 3.3 0.65 0.98 0.44

10 0.16 0.073 1.6 1.6 1.7 0.33 0.49 0.22

15 0.16 0.073 1.1 1.1 1.1 0.22 0.33 0.15

The OELs include ICNIRP reference levels for occupational exposures [ICNIRP 1998], 

IEEE maximum permissible exposures for people in controlled environments [IEEE 2005b], 

ACGIH TLVs [ACGIH 2013], and FCC limits for occupational/controlled exposure [FCC 

1999]. According to IEEE Standard C95.7, action levels are any of the following criteria: the 

lower tier limits of IEEE Standard C95.1, the general public guidelines of ICNIRP, 1/5 of the 

ACGIH TLVs, and the general public/uncontrolled exposure limits of the FCC [IEEE 2005a].

For this evaluation, the most conservative OELs and action levels were used for making 

decisions regarding the implementation of RF field safety program elements. ICNIRP levels 

are the most conservative for all of the frequencies we evaluated with the exception of 

electric field strength at 15-MHz. In this case, the ACGIH action level is most conservative 

(Appendix A, Table A1).
Health Hazard Evaluation Report 2011-0097-3200 Page 13

Appendix B: Tables

Table B1. 15-MHz outdoor electric field measurements*

Location Measurement 

height

GPS coordinates Results

(V/m)

30 feet, 130° SE of 15-MHz antenna Groin 21 59.429 –

159 45.835

129

30 feet, 130° SE of 15-MHz antenna

(6-minute averaging time) 

Groin 21 59.429 –

159 45.835

93.2

180° S of 15-MHz standby antennas (centerline) Groin 21 59.206 –

159 45.818

92.7

30 feet, 130° SE of 15-MHz antenna Groin 21 59.429 –

159 45.835

92.3

340° N of 15-MHz standby antennas (centerline) Groin 21 59.206 –

159 45.818

89.8

30 feet, 130° SE of 15-MHz antenna Head 21 59.429 –

159 45.835

85

30 feet, 130° SE of 15-MHz antenna Chest 21 59.429 –

159 45.835

84.5

At fence, W/SW of the standby 15-MHz antenna Groin 21 59.208 –

159 45.823

50.9

Standby 15-MHz antenna nearest building

(off and grounded at the transmitter)

10 feet high Not collected 37

At the base of the standby 15-MHz antenna nearest 

beach (off and grounded at the transmitter)

1 foot Not collected 10.8

Driving around the 15-MHz antennas for 2 minutes 

(averaging time)

Head 

(window)

Not collected 3.8

ICNIRP OEL (reference levels for occupational exposure) 61

ICNIRP action level (reference levels for general public exposure) 28†

*30-second averaging time unless otherwise noted

†ACGIH action level = 25 V/m (more conservative than ICNIRP at 15-MHz)

Measurements exceeding occupational exposure limits are bolded.

Measurements exceeding action levels are underlined. 
Page 14 Health Hazard Evaluation Report 2011-0097-3200

Table B2. 15-MHz outdoor magnetic field measurements*

Location Measurement 

height

GPS coordinates Results

(A/m)

340° N of 15-MHz standby antennas (centerline) Groin 21 59.214 –

159 45.818

0.29

180° S of 15-MHz standby antennas (centerline) Groin 21 59.206 –

159 45.818

0.21

Standby 15-MHz antenna nearest building 

(off and grounded at the transmitter)

10 feet Not collected 0.17

At fence, W/SW of the standby 15-MHz antenna Groin 21 59.208 –

159 45.823

0.13

30 feet, 130° SE of 15-MHz antenna Head 21 59.429 –

159 45.835

0.12

30 feet, 130° SE of 15-MHz antenna Chest 21 59.429 –

159 45.835

0.1

30 feet, 130° SE of 15-MHz antenna Groin 21 59.429 –

159 45.835

0.093

30 feet, 130° SE of 15-MHz antenna

(6-minute average) 

Groin 21 59.429 –

159 45.835

0.093

At the base of standby 15-MHz antenna nearest 

beach (off and grounded at the transmitter)

1 foot Not collected 0.049

Driving around the 15-MHz antennas for 2 minutes 

(averaging time)

Head 

(window)

Not collected 0.031

ICNIRP OEL (reference levels for occupational exposure) 0.16

ICNIRP action level (reference levels for general public exposure) 0.073

*30-second averaging time unless otherwise noted

Measurements exceeding occupational exposure limits are bolded.

Measurements exceeding action levels are underlined.
Health Hazard Evaluation Report 2011-0097-3200 Page 15

Table B3. 10-MHz outdoor electric field measurements*

Location Measurement 

height

GPS 

coordinates

Results

(V/m)

At fence, 125° E/SE of standby 10-MHz antenna Groin 21 59.307 –

159 45.804

79.2

30 feet, 200° S/SW of 10-MHz antenna Groin 21 59.297 –

159 45.859

74.4

30 feet from orange fence, 200° S/SE of 

10-MHz antenna

Chest Not Collected 69.2

30 feet, 200° S/SW of 10-MHz antenna Groin 21 59.297 –

159 45.859

67.4

30 feet, 200° S/SW of 10-MHz antenna Chest 21 59.297 –

159 45.859

64.6

30 feet from orange fence, 200° S/SE of 

10-MHz antenna

Groin Not collected 62.9

30 feet, 200° S/SW of 10-MHz antenna

(6-minute averaging time)

Groin 21 59.297 –

159 45.859

62.3

30 feet, 200° S/SW of 10-MHz antenna Head 21 59.297 –

159 45.859

61.7

30 feet from orange fence, 200° S/SE of 

10-MHz antenna

Head Not collected 60.95

15 feet from fence, 125° E/SE of standby 

10-MHz antenna

Groin Not collected 42.1

At the grounding wire for the standby 10-MHz antenna 1 foot Not collected 22.4

At the base of the standby 10-MHz antenna

(off and grounded at tuning box)

1 foot Not collected 16.2

At the grounded tuning box for the standby

10-MHz antenna

1 foot Not collected 11

Driving around the 10-MHz antennas for 2 minutes 

(averaging time)

Head 

(window)

Not collected 4.81

ICNIRP OEL (reference levels for occupational exposure) 61

ICNIRP action level (reference levels for general public exposure) 28

*30-second averaging time unless otherwise noted

Measurements exceeding occupational exposure limits are bolded.

Measurements exceeding action levels are underlined.
Page 16 Health Hazard Evaluation Report 2011-0097-3200

Table B4. 10-MHz outdoor magnetic field measurements*

Location Measurement 

height

GPS 

coordinates

Results

(A/m)

At the base of the standby 10-MHz antenna

(off and grounded at tuning box)

1 foot Not collected 0.198

30 feet, 200° S/SW of 10-MHz antenna Groin 21 59.297 –

159 45.859

0.19

30 feet from orange fence, 200° S/SE of 

10-MHz antenna

Groin Not collected 0.16

30 feet from orange fence, 200° S/SE of 

10-MHz antenna

Chest Not collected 0.16

30 feet from orange fence, 200° S/SE of 

10-MHz antenna

Head Not collected 0.16

30 feet, 200° S/SW of 10-MHz antenna Chest 21 59.297 –

159 45.859

0.118

30 feet, 200° S/SW of 10-MHz antenna Head 21 59.297 –

159 45.859

0.118

At fence, 125° E/SE of standby 10-MHz antenna Groin 21 59.307 –

159 45.804

0.054

On roof corner, near pole, 120° E/SE of standby 

10-MHz antenna (on)

Groin 21 59.279 –

159 45.787

0.05

Driving around the 10-MHz antennas for 2 minutes 

(averaging time)

Head (window) Not collected 0.0275

At the grounded tuning box for the standby 

10-MHz antenna

1 foot Not collected 0.02

ICNIRP OEL (reference levels for occupational exposure) 0.16

ICNIRP action level (reference levels for general public exposure) 0.073

*30-second averaging time unless otherwise noted

Measurements exceeding occupational exposure limits are bolded.

Measurements exceeding action levels are underlined.
Health Hazard Evaluation Report 2011-0097-3200 Page 17

Table B5. 5-MHz outdoor electric field measurements*

Location Measurement 

height

GPS 

coordinates

Results

(V/m)

Directly in the middle of the 5-MHz antennas Groin Not collected 143

3 feet from fence surrounding 5-MHz antenna Groin Not collected 134

Next to fence facing the building surrounding the 

standby 5-MHz antenna

Groin Not collected 84.3

Near guide wire between 5-MHz antenna (on block) Groin Not collected 70.2

15 feet from the 5-MHz antenna Groin Not collected 67.7

25 feet, S of fence surrounding 5-MHz antenna 

(between guide wires)

Groin 21 59.182 –

159 45.756

57.9

5-MHz antenna western guide wire Groin Not collected 30.9

Next to the building across from the standby 

5-MHz antenna

Groin Not collected 5.01

ICNIRP OEL (reference levels for occupational exposure) 122

ICNIRP action level (reference levels for general public exposure) 40

*30-second averaging time unless otherwise noted

Measurements exceeding occupational exposure limits are bolded.

Measurements exceeding action levels are underlined.

Table B6. 5-MHz outdoor magnetic field measurements*

Location Measurement 

height

GPS 

coordinates

Results

(A/m)

Next to fence facing the building surrounding the 

standby 5-MHz antenna

Groin Not collected 0.389

15 feet from the 5-MHz antenna Groin Not collected 0.245

Near guide wire between 5-MHz antenna (on block) Groin Not collected 0.13

25 feet, S of fence surrounding 5-MHz antenna 

(between guide wires)

Groin 21 59.182 –

159 45.756

0.0887

5-MHz antenna western guide wire Groin Not collected 0.0874

3 feet from fence surrounding 5-MHz antenna Groin Not collected 0.0794

Directly in the middle of the 5-MHz antennas Groin Not collected 0.055

Corner of PV array nearest 5-MHz standby antenna about 14 feet 21 59.254 –

159 45.769

0.0394

Next to the building across from the standby 

5-MHz antenna

Groin Not collected 0.036

ICNIRP OEL (reference levels for occupational exposure) 0.32

ICNIRP action level (reference levels for general public exposure) 0.15

*30-second averaging time unless otherwise noted

Measurements exceeding occupational exposure limits are bolded.

Measurements exceeding action levels are underlined.
Page 18 Health Hazard Evaluation Report 2011-0097-3200

Table B7. 2.5-MHz outdoor electric field measurements*

Location Measurement 

height

GPS 

coordinates

Results

(V/m)

At fence, 220° W/SW of 2.5-MHz standby antenna Groin 21 59.317 –

159 45.774

130

10 feet from the fence surrounding the 

2.5-MHz antenna

Groin Not collected 58.4

25 feet, 175° S of fence surrounding the 

2.5-MHz antenna near conduit

Groin 21 59.343 –

159 45.874

46.4

6 feet from sand line surrounding the 

2.5-MHz antenna

Groin Not collected 42.1

15 feet, 232° W/SW of the 2.5-MHz antenna Groin 21 59.349 –

15 45.880

34.6

ICNIRP OEL (reference levels for occupational exposure) 244

ICNIRP action level (reference levels for general public exposure) 55

*30-second averaging time unless otherwise noted

Measurements exceeding action levels are underlined.

Table B8. 2.5-MHz outdoor magnetic field measurements*

Location Measurement 

height

GPS 

coordinates

Results

(A/m)

At fence, 220° W/SW of 2.5-MHz standby antenna Groin 21 59.317 –

159 45.774

0.61

10 feet from the fence surrounding the 

2.5-MHz antenna

Groin Not collected 0.338

6 feet from sand line surrounding the 

2.5-MHz antenna

Groin Not collected 0.33

25 feet, 175° S of fence surrounding the 

2.5-MHz antenna near conduit

Groin 21 59.343 –

159 45.874

0.29

15 feet, 232° W/SW of the 

2.5-MHz antenna

Groin 21 59.349 –

15 45.880

0.221

ICNIRP OEL (reference levels for occupational exposure) 0.64

ICNIRP action level (reference levels for general public exposure) 0.3

*30-second averaging time unless otherwise noted

Measurements exceeding action levels are underlined.
Health Hazard Evaluation Report 2011-0097-3200 Page 19

Table B9. Miscellaneous outdoor electric field measurements (V/m)*

Location Measurement 

height

GPS 

coordinates

Frequency (MHz)

2.5 5 10 15

Next to the weather station 

receiving antenna (5- and 

10-MHz standby antennas on)

Groin 21 59.263 –

159 45.774

1.26 11.7 2.49 3.14

1/3 of the way up the weather 

station antenna

about 8 feet 21 59.263 –

159 45.774

4.6 66 10.2 20

1/2 of the way up the weather 

station antenna

about 16 feet 21 59.263 –

159 45.774

5.98 75.8 9.2 10.4

Corner of PV array nearest 

5-MHz standby antenna

about 14 feet 21 59.254 –

159 45.769

4.3 20.1 3.8 2.7

On roof, 350° N/NW (nearest) of 

the weather station antenna 

(with standby 5- and 10-MHz 

antennas on)

Groin 21 59.270 –

159 45.779

5.17 13.6 10.69 3.98

On roof corner, near pole, 120° E/

SE of standby 10-MHz antenna 

(on)

Groin 21 59.279 –

159 45.787

13.58 18.8 16.7 6.62

1/2 way between 2.5- and 

10-MHz antennas, 330° from the 

10-MHz

Groin 21 59.329 –

159 45.865

14 3.38 15.45 2.12

Between the 10- and 15-MHz 

antennas, 106 feet (345° N/NE) 

from the 15-MHz antenna

Chest 21 59.274 – 

159 45.884

6.23 4.38 15.03 17.89

Between the 10- and 15-MHz 

antennas, 106 feet (345° N/NE) 

from the 15-MHz antenna

Head 21 59.274 –

159 45.884

5.86 4.5 15.3 18.55

Between the 10- and 15-MHz 

antennas, 106 feet (345° N/NE) 

from the 15-MHz antenna

Groin 21 59.274 –

159 45.884

6.21 4.2 16.88 17.85

Between the 5- and 15-MHz 

antennas, 265 feet (140° SE) from 

the 15-MHz antenna

Groin 21 59.225 –

159 45.804

4.09 19.87 1.45 3.4

80 inches from the NE corner of 

building outside secretary’s office

Head Not collected 12.1 2.01 0.97 1.07

ICNIRP OEL (reference levels for occupational exposure) 244 122 61 61

ICNIRP action level (reference levels for general public exposure) 55 40 28 28†

*30-second averaging time unless otherwise noted

†ACGIH action level = 25 V/m (more conservative than ICNIRP at 15-MHz)

Measurements exceeding action levels are underlined. 
Page 20 Health Hazard Evaluation Report 2011-0097-3200

Table B10. Miscellaneous outdoor magnetic field measurements (A/m)*

Location Measurement 

height

GPS 

coordinates

Frequency (MHz)

2.5 5 10 15

On roof, 350° N/NW (nearest) of 

the weather station antenna 

(with standby 5- and 10-MHz 

antennas on)

Groin 21 59.270 –

159 45.779

0.011 0.032 0.016 0.017

On roof corner, near pole, 

120° E/SE of standby 

10-MHz antenna (on)

Groin 21 59.279 –

159 45.787

0.016 0.037 0.050 0.021

Next to the weather station 

receiving antenna (5- and 10-MHz 

standby antennas on)

Groin 21 59.263 –

159 45.774

0.015 0.164 0.019 0.018

1/3 of the way up the weather 

station antenna

about 8 feet 21 59.263 –

159 45.774

0.025 0.274 0.032 0.024

1/2 of the way up the weather 

station antenna

about 16 feet 21 59.263 –

159 45.774

0.027 0.349 0.049 0.039

1/2 way between 2.5- and 

10-MHz antennas, 330° from the 

10-MHz

Groin 21 59.329 –

159 45.865

0.032 0.01 0.043 0.009

Between the 10- and 15-MHz 

antennas, 106 feet (345° N/NE) 

from the 15-MHz antenna

Chest 21 59.274 –

159 45.884

0.014 0.013 0.027 0.038

Between the 10- and 15-MHz 

antennas, 106 feet (345° N/NE) 

from the 15-MHz antenna

Head 21 59.274 –

159 45.884

0.014 0.012 0.027 0.04

Between the 10- and 15-MHz 

antennas, 106 feet (345° N/NE) 

from the 15-MHz antenna

Groin 21 59.274 –

159 45.884

0.014 0.013 0.026 0.035

Between the 5- and 15-MHz 

antennas, 265 feet (140° SE) from 

the 15-MHz antenna

Groin Not collected 0.011 0.03 0.009 0.01

80 inches from the NE corner of 

building outside secretary’s office

Head Not collected 0.032 0.015 0.014 0.008

ICNIRP OEL (reference levels for occupational exposure) 0.64 0.32 0.16 0.16

ICNIRP action level (reference levels for general public exposure) 0.3 0.15 0.073 0.073

*30-second averaging time unless otherwise noted

Measurements exceeding occupational exposure limits are bolded.

Measurements exceeding action levels are underlined.
Health Hazard Evaluation Report 2011-0097-3200 Page 21

Table B11. Indoor electric field measurements (V/m)*

Location Frequency (MHz)

2.5 5 10 15

Inside transmitter room by primary 2.5-MHz transmitter 0.330 0.420 0.460 0.182

Inside transmitter room by primary 5-MHz transmitter 0.299 0.510 0.190 0.210

Inside transmitter room by primary 10-MHz transmitter 0.230 0.257 0.288 0.297

At dean’s desk, by window 0.620 3.900 0.830 0.357

Inside transmitter room backside of primary 10-MHz cabinet 

(power off to simulate maintenance)

0.290 0.190 0.540 0.390

Inside transmitter room backside of primary

10-MHz transmitter

0.270 0.170 0.266 0.423

Inside transmitter room by primary 15-MHz transmitter 0.260 0.172 0.187 0.622

Middle of secretary’s workstation 14.1 1.21 1.49 0.792

Inside transmitter room between primary 10-MHz and 

2.5-MHz transmitters

0.829 1.290 2.190 0.885

Inside transmitter room by standby 5-MHz transmitter (not on) 0.490 0.280 0.185 1.870

Inside transmitter room by standby 15-MHz transmitter 

(not on)

0.430 0.280 0.150 1.890

Inside cabinet 0.345 0.760 4.310 3.090

At desk near window 0.929 5.044 0.529 Not 

Collected

ICNIRP OEL (reference levels for occupational exposure) 244 122 61 61

ICNIRP action level (reference levels for general public 

exposure)

55 40 28 28†

*30-second averaging time unless otherwise noted

†ACGIH action level = 25 V/m (more conservative than ICNIRP at 15-MHz)
Page 22 Health Hazard Evaluation Report 2011-0097-3200

Table B12. Indoor magnetic field measurements (A/m)*

Location Frequency (MHz)

2.5 5 10 15

Inside transmitter room backside of primary 10-MHz 

cabinet (power off to simulate maintenance)

0.01 0.003 0.009 0.003

Inside transmitter room backside of primary 

10-MHz transmitter

0.012 0.003 0.004 0.003

Inside transmitter room by primary 

15-MHz transmitter

0.003 0.003 0.0023 0.006

Middle of secretary’s workstation 0.052 0.015 0.01 0.008

Inside transmitter room by standby 

15-MHz transmitter (not on)

0.003 0.003 0.002 0.008

Inside transmitter room by standby 5-MHz transmitter 

(not on)

0.003 0.003 0.002 0.009

Inside cabinet Not 

collected

Not 

collected

0.013 0.0121

At dean’s desk, by window 0.0042 0.014 0.004 0.002

At desk near window 0.0070 0.011 0.005 0.002

ICNIRP OEL (reference levels for 

occupational exposure)

0.64 0.32 0.16 0.16

ICNIRP action level (reference levels for 

general public exposure)

0.3 0.15 0.073 0.073

*30-second averaging time unless otherwise noted
Health Hazard Evaluation Report 2011-0097-3200 Page 23

Table B13. Spatial average and mixture analysis. Electric field strengths 30 feet, 130° SE of the 

15-MHz antenna*

Measurement 

height

Results (V/m) Frequency (MHz)

2.5 5 10 15 Total 

Ratio

Head RMS electric field 4.3 6.1 5.9 85 —

Weighted ratio of OEL 0 0 0.01 1.94 2

Weighted ratio of action level 0.01 0.02 0.04 11.56 11.6

Chest RMS electric field 4.5 6.99 5.7 84.5 —

Weighted ratio of OEL 0 0 0.01 1.92 1.9

Weighted ratio of action level 0.01 0.03 0.04 11.42 11.5

Groin RMS electric field 4.6 6.4 6.2 92.3 —

Weighted ratio of OEL 0 0 0.01 2.29 2.3

Weighted ratio of action level 0.01 0.03 0.05 13.63 13.7

Spatial 

Average

RMS electric field 4.5 6.5 5.9 87.3 —

Weighted ratio of OEL 0 0 0.01 2.1 2.1

Weighted ratio of action level 0.01 0.03 0.04 12.2 12.3

ICNIRP OEL (reference levels for occupational exposure) 244 122 61 61 —

ICNIRP action level (reference levels for general public 

exposure)

55 40 28 28† —

*30-second averaging time unless otherwise noted

†ACGIH action level = 25 V/m (more conservative than ICNIRP at 15-MHz)

Measurements exceeding occupational exposure limits are bolded. 
Page 24 Health Hazard Evaluation Report 2011-0097-3200

Table B14. Spatial average and mixture analysis. Magnetic field strengths 30 feet, 130° SE of the 

15-MHz antenna*

Measurement 

height

Results (A/m) Frequency (MHz)

2.5 5 10 15 Total 

Ratio

Head RMS electric field 0.01 0.02 0.02 0.12 —

Weighted ratio of OEL 0 0 0.02 0.56 0.6

Weighted ratio of action level 0 0.02 0.08 2.7 2.8

Chest RMS electric field 0.013 0.02 0.019 0.1 —

Weighted ratio of OEL 0 0 0.01 0.39 0.4

Weighted ratio of action level 0 0.02 0.07 1.88 2

Groin RMS electric field 0.013 0.018 0.013 0.093 —

Weighted ratio of OEL 0 0 0.01 0.34 0.3

Weighted ratio of action level 0 0.01 0.03 1.62 1.7

Spatial 

Average

RMS electric field 0.012 0.019 0.017 0.10 —

Weighted ratio of OEL 0 0 0.013 0.43 0.44

Weighted ratio of action level 0 0.017 0.06 2.07 2.14

ICNIRP OEL (reference levels for occupational exposure) 0.64 0.32 0.16 0.16 —

ICNIRP action level (reference levels for general public 

exposure)

0.3 0.15 0.073 0.073 —

*30-second averaging time unless otherwise noted

Measurements exceeding action levels are underlined.
Health Hazard Evaluation Report 2011-0097-3200 Page 25

References

ACGIH [2013]. 2013 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 [2013]. AIHA 2013 Emergency response planning guidelines (ERPG) and workplace 

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

Hygiene Association.

Bailey WH, Su SE, Bracken TD, Kavet R [1997]. Summary and evaluation of guidelines 

for occupational exposure to power frequency electric and magnetic fields. Health Physics 

73(3):433–445.

Bernhardt J [1979]. [Biological effects of electromagnetic fields (author's transl)]. Zeitschrift 

fur Naturforschung. Section C: Biosciences, 34(7-8):616–627.

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

of the Federal Register.

FCC [1999]. Questions and answers about biological effects and potential hazards of 

radiofrequency electromagnetic fields. By Cleveland RF, Ulcek JL. Washington DC: U.S. 

Federal Communications Commission (FCC), OET Bulletin 56, 4th edition.

ICNIRP [1998]. Guidelines for limiting exposure to time-varying electric, magnetic, 

and electromagnetic fields (up to 300 GHz). Oberschleissheim, Germany: International 

Commission on Non-Ionizing Radiation Protection.

ICNIRP [2009]. Guidelines on limits of exposure to static magnetic fields. Oberschleissheim, 

Germany: International Commission on Non-Ionizing Radiation Protection.

IEEE [2005a]. IEEE recommended practice for radiofrequency safety programs, 3 kHz to 300 

GHz. New York: Institute of Electrical and Electronics Engineers. Standard C95.7-2005.

IEEE [2005b]. IEEE standard for safety levels with respect to human exposure to 

radiofrequency electromagnetic fields, 3 kHz to 300 GHz. New York: Institute of Electrical 

and Electronics Engineers. Standard C95.1-2005.

NIOSH [2010]. 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. 2010-168c. [http://

www.cdc.gov/niosh/npg/]. Date accessed: December 2013.
Page 26 Health Hazard Evaluation Report 2011-0097-3200

NIOSH/OSHA [1979]. Joint NIOSH/OSHA current intelligence bulletin 33--radiofrequency 

(RF) sealers and heaters: potential health hazards and their prevention. U.S. Department of 

Health, Education, and Welfare, Center for Disease Control, NIOSH. U.S. Department of 

Labor, Occupational Safety and Health Administration. Cincinnati, OH: DHEW (NIOSH) 

Publication No 80-107.

NIST [2012]. National Institute of Standards and Technology Radio Station WWVH. [http://

tf.nist.gov/stations/wwvh.htm]. Date accessed: December 2013.

WHO [2010]. The international EMF project. Geneva, Switzerland: World Health Organization 

[http://www.who.int/peh-emf/about/WhatisEMF/en/]. Date accessed: December 2013.
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Keywords: North American Industry Classification System 541712 (Research and Development in the Physical, Engineering, and Life Sciences [except Biotechnology]), radiofrequency, RF, radio station, non-ionizing radiation, electric field, magnetic field
Health Hazard Evaluation Report 2011-0097-3200 Page 29

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

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

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

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

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

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

Disclaimer

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

evaluated and may not be applicable to other workplaces.

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

National Institute for Occupational Safety and Health (NIOSH).

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

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

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

of the publication date.

Acknowledgments 

Desktop Publishers: Mary Winfree

Editor: Ellen Galloway

Health Communicator: Stefanie Brown

Industrial Hygiene Field Assistance: Michael K. Blumer, NIST

Logistics: Donnie Booher

Availability of Report

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

and local health department and the Occupational Safety and Health Administration 

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

reproduced. 

This report is available at http://www.cdc.gov/niosh/hhe/reports/pdfs/2011-0097-3200.pdf.

Recommended citation for this report:

NIOSH [2013]. Health hazard evaluation report: evaluation of radiofrequency radiation 

exposures at an atomic time radio station. By Feldmann K, Fent K. Cincinnati, OH: U.S. 

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

National Institute for Occupational Safety and Health, NIOSH Report No. 2011-0097-3200.
Delivering on the Nation’s promise:

Safety and health at work for all people through research and prevention

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occupational safety and health topics, please contact NIOSH:

Telephone: 1–800–CDC–INFO (1–800–232–4636)

TTY: 1–888–232–6348

CDC INFO: www.cdc.gov/info

or visit the NIOSH Web site at www.cdc.gov/niosh

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