Evaluation of 

Electromagnetic

Field Exposures at a

Research Institution’s 

Laboratories and 

Atomic Time Radio 

Stations – Colorado 

Kenneth W. Fent, PhD 

David Conover, PhD 

Health Hazard Evaluation Report 

HETA 2009-0171-3119 

March 2011 

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]. 
CONTENTS
 

REPORT Abbreviations .......................................................................ii
 

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

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

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

Assessment.........................................................................5
 

Results.................................................................................9
 

Discussion .........................................................................18
 

Conclusions.......................................................................20
 

Recommendations.............................................................20
 

References ........................................................................22
 

APPENDIX A Occupational Exposure Limits and Health Effects .............23
 

APPENDIX B E-field Strengths Measured at the Atomic Time Radio 


Stations..............................................................................27
 

APPENDIX C H-field Strengths Measured at the Atomic Time Radio 


Satatons ............................................................................33
 

ACKNOWLEDGMENTS Acknowledgments and Availability of Report .....................37
 

Health Hazard Evaluation Report 2009-0171-3119 Page i
 
 

ABBREVIATIONS
 

~ Approximately 

A/m Amps per meter 

ACGIH® American Conference of Governmental Industrial Hygienists 

B-field Magnetic flux density 

CFR Code of Federal Regulations 

DNR Did not record 

E-field Electric field 

EMF Electromagnetic field 

FCC Federal Communications Commission 

GHz Gigahertz 

GPS Global Positioning System 

HF High frequency (3–30 MHz) 

H-field Magnetic field 

ICNIRP International Commission on Non-Ionizing Radiation Protection 

IEEE Institute of Electrical and Electronics Engineers 

kHz Kilohertz 

kW Kilowatts 

LF Low frequency (30–300 kHz) 

MHz Megahertz 

MPE Maximum permissible exposure 

mT Millitesla 

NA Not applicable 

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 

RF Radio frequency and microwave radiation (30 kHz to 300 GHz) 

RMS Root-mean-square 

STEL Short term exposure limit 

Sub-RF Sub-radio frequency (< 30 kHz) 

TLV® Threshold limit value 

TWA Time-weighted average 

UHF Ultra high frequency (300 MHz to 3 GHz) 

VHF Very high frequency (30–300 MHz) 

V/m Volts per meter 

WEEL Workplace environmental exposure level 

W/m2 Watts per square meter 

Page ii Health Hazard Evaluation Report 2009-0171-3119
 
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 a 

research institution in 

Colorado. Health and 

safety management 

submitted the request 

because of concern 

about possible radio 

frequency and microwave 

radiation (RF) and subRF electromagnetic field 

(EMF) exposures at the 

research institution’s 

laboratories and atomic 

time radio stations. 

What NIOSH Did 

●	 We evaluated the facilities August 31–September 3, 2009. We 

returned to further evaluate the atomic time radio stations 

August 3–5, 2010. 

●	 We measured static magnetic fields at the superconducting 

magnet laboratory and magnetic annealing laboratory. 

●	 We measured RF field strengths at the interoperability 

communications laboratory and atomic time radio stations. 

What NIOSH Found 

●	 Static magnetic flux densities exceeded the occupational 

exposure limit (OEL) for medical device wearers working 

within 3 feet of the superconducting magnet. 

●	 RF electric field strengths exceeded the most conservative 

OELs within 1 foot of the interoperability communications 

laboratory roof-mounted antennas. 

●	 RF electric and magnetic field strengths exceeded the most 

conservative OELs within 30 feet of the 10- and 15-megahertz 

antennas at the atomic time radio stations. 

●	 RF electric and magnetic field strengths exceeded action 


levels at locations along the access road circling the high 


frequency antennas at the atomic time radio stations.
 

●	 RF electric field strengths exceeded action levels within 700 

feet of both helix houses at the atomic time radio stations. 

What Managers Can Do 

●	 Learn more about the potential hazards associated with EMF 

exposure. 

●	 Start a comprehensive EMF safety program. 

What Employees Can Do 

●	 Learn about EMF radiation hazards and the use of warning 

signs and other controls to prevent overexposures to EMF 

radiation. 

●	 Report health and safety concerns to your manager. 

●	 Share ideas on ways to improve the EMF safety program with 

the EMF safety officer. 

Health Hazard Evaluation Report 2009-0171-3119	 Page iii
 
SUMMARY
 

NIOSH evaluated EMF 

exposures at a research 

institution’s laboratories 

and atomic time radio 

stations. We found subRF and RF field strengths 

above action levels and 

OELs. We recommend 

starting a comprehensive 

EMF safety program. 

In June 2009, NIOSH received a health hazard evaluation 

request from a research institution in Colorado. The request 

concerned sub-RF (below 30 kHz) and RF (30 kHz to 300 GHz) 

EMF exposures at the institution’s laboratories and atomic time 

radio stations. The radio stations were located at a remote site 

in Colorado separate from the laboratories. In response to this 

request, we evaluated the facilities on August 31–September 3, 

2009, and August 3–5, 2010. 

During the first evaluation, magnetic flux density (B) fields near or 

above OELs were measured in the magnetic annealing laboratory 

and superconducting magnet laboratory. Electric (E) field strengths 

above OELs were measured at the interoperability communications 

laboratory. Measurements taken at the atomic time radio stations 

demonstrated a potential for overexposure to RF. However, because 

the RF meter we used did not span all broadcasted frequencies and 

potentially perturbed fields, we planned another evaluation of the 

atomic time radio stations using appropriate instrumentation in 

2010. 

During this second evaluation, we measured E and magnetic (H) 

field strengths at the atomic time radio stations. E-field strengths 

exceeded the action levels along the access roads leading to the 

helix houses within 700 feet of the LF north and south antennas. 

E- and H-field strengths exceeded the action levels at locations 

along the access road circling the HF antennas. E- and H-field 

strengths exceeded OELs within 30 feet of the 10- and 15-MHz 

antennas. 

Because EMF field strengths exceeded OELs or action levels in 

some locations at the research institution, we recommended 

implementing a comprehensive EMF safety program. This program 

should be managed by an EMF safety officer. The EMF safety 

officer should maintain an inventory of EMF sources, conduct 

annual EMF safety awareness training, audit the EMF safety 

program annually, and install signage and other controls in areas 

where field strengths are likely to exceed OELs or action levels. 

In addition, a system should exist for employees to report EMF 

exposures incidents and provide feedback to the EMF safety officer. 

Keywords: NAICS 541712 (Research and Development in the 


Physical, Engineering, and Life Sciences), Electromagnetic field, 


EMF, radio frequency, superconducting magnet, radio station, 


antenna
 

Page iv Health Hazard Evaluation Report 2009-0171-3119
 
INTRODUCTION
 

In June 2009 NIOSH received a health hazard evaluation request 

from a research institution in Colorado. The request concerned 

potential EMF exposures at the institution’s laboratories and 

atomic time radio stations. Although the research institution 

had a health and safety office, at the time of the request, it did 

not have a comprehensive EMF safety program. Two evaluations 

were conducted. The purpose of the evaluation on August 

31–September 3, 2009, was to identify the primary sources of 

EMF radiation. The purpose of the evaluation on August 3–5, 

2010, was to more thoroughly assess RF at the atomic time radio 

stations. Four primary EMF sources were identified. These sources 

are described below. All other sources we evaluated (building 

24 antenna laboratory and time domain laboratory) had field 

strengths that were well below applicable OELs, so they are not 

described in this report. 

Magnetic Annealing Laboratory 

A magnetic thermal annealer for 3-inch wafers was contained 

inside a laboratory. The annealing chamber was an enclosed 

stainless steel vacuum chamber plumbed with argon gas. Anneals 

were completed in temperatures ranging from 100°C–600°C. The 

magnet configuration produced a uniform 1 tesla magnetic field 

within the thermal annealer with weaker magnetic fields present 

outside the annealer. 

Superconducting Magnet Laboratory 

A superconducting magnet with a vertical room temperature 

bore was contained inside a laboratory (Figure 1). The maximum 

strength of the static magnetic field in the vertical center of the 

bore was 4.5 tesla. However, the center of the bore was inaccessible 

to employees. One employee worked inside the laboratory during 

our evaluation. 

Health Hazard Evaluation Report 2009-0171-3119 Page 1
 
INTRODUCTION
 

(CONTINUED)
 

Figure 1. Superconducting magnet. 

Interoperability Communications

Laboratory 

This laboratory conducted research on emergency response radio 

communications. VHF (160–170 MHz) and UHF (410–420 MHz) 

signals were transmitted by roof-mounted dipole antennas for 

this research. The VHF and UHF control channels transmitted 

continuously, while VHF and UHF traffic channels transmitted 

after they were automatically assigned to portable radio users. 

Three employees worked at this laboratory during our evaluation. 

Page 2 Health Hazard Evaluation Report 2009-0171-3119
 
INTRODUCTION
 (CONTINUED)
 

Figure 2. Interoperability communications laboratory roof-mounted 

antenna with caution sign located next to the antenna. 

Atomic Time Radio Stations 

The atomic time radio stations were located at a site in Colorado 

separate from the research institution’s laboratories. Five employees 

worked at the radio stations during our evaluation. The LF radio 

station continuously broadcasted time and frequency signals 

at 60 kHz. The LF radio station used two identical antennas—a 

north antenna and a south antenna. Each antenna was a top 

loaded monopole consisting of four 400-foot towers arranged in a 

diamond shape. A system of cables (called a “top hat” by station 

employees) was suspended between the four towers. This top 

hat was electrically isolated from the towers and was electrically 

connected to a downlead suspended from the center of the top 

hat. The combination of the top hat and downlead served as the 

radiating element. The downlead of each antenna was terminated 

at its own helix house under the top hats. Each helix house 

contained a large helical inductor to cancel the capacitance of the 

short antenna and a variometer (variable inductor) to tune the 

antenna system. Each transmitter only had to produce a power of 

about 54 kW for LF to produce its effective radiated power of 70 

kW [National Institute of Standards and Technology 2010a]. 

Health Hazard Evaluation Report 2009-0171-3119 Page 3
 
INTRODUCTION 

(CONTINUED) The HF radio station broadcasted time and frequency information 

including time announcements, standard time intervals, standard 

frequencies, geophysical alerts, marine storm warnings, and GPS 

status reports. The station radiated 10 kW on 5-, 10-, and 15-MHz 

dipole antennas; and 2.5 kW on 2.5- and 20-MHz dipole antennas. 

Each frequency was broadcast from a separate transmitter. 

Each antenna was mounted on a tower approximately one halfwavelength in height. The tallest tower (2.5 MHz) was about 200 

feet in height; the shortest tower (20 MHz) was about 25 feet in 

height [National Institute of Standards and Technology 2010b]. 

Figure 3. HF radio station antennas (background) with RF meter in the 

foreground. 

Page 4 Health Hazard Evaluation Report 2009-0171-3119
 
ASSESSMENT
 

Magnetic Annealer and Superconducting 

Magnet Laboratory 

We used an F.W. Bell® (Milwaukie, Oregon) Model 5170 meter 

with Model STH17-0404 transverse (DC-10 kHz) probe to measure 

RMS B-fields emanating from the annealer and superconducting 

magnet. This meter was calibrated within 1 year of the evaluation. 

Measurements were collected at various heights and distances 

from the annealer and superconducting magnet. The B-fields 

were compared to the following OELs (ceiling limits): ICNIRP 

occupational limits of exposure [ICNIRP 2009], IEEE MPE levels 

for the controlled environment [IEEE 2002], and ACGIH TLVs 

[ACGIH 2010]. Table 1 summarizes the OELs (ceiling limits). 

Appendix A provides a general discussion of OELs and the basis of 

the OELs and action levels referenced in this report. 

Table 1. OELs (ceiling limits) for static B-fields (mT) with the most conservative OELs bolded 

ICNIRP IEEE ACGIH 

Head and 

trunk Limbs Head and torso 

Arms or 

legs 

Whole 

body Limbs Medical device wearers 

2000 8000 353 353 2000 20000 0.50 

Interoperability Communications

Laboratory 

We used a Holaday (ETS-LindgrenTM, Cedar Park, Texas) HI4460 meter and HI-4433-STE isotropic E-field probe (0.5 MHz–5 

GHz) to measure VHF (160–170 MHz) and UHF (410–420 MHz) 

E-fields. The meter and E-field probe were calibrated within 1 

month of the evaluation. The E-field probe measured the field 

strength in each of three axes. The probe performed vector 

addition calculation on the readings from each axis and sent the 

RMS vector magnitude to the meter via a fiber optic cable to 

minimize field perturbation during measurements. Measurements 

were recorded near the roof-mounted antennas, near an employee 

when he was talking and holding transmitting radios, and in the 

offices inside the laboratory. To compare these measurements to 

the OELs with their 6-minute averaging time, the conservative 

assumption was made that employees could be exposed 

continuously for 6 minutes at the sampling locations. The E-field 

strengths were compared to the following OELs: ICNIRP reference 

Health Hazard Evaluation Report 2009-0171-3119 Page 5
 
ASSESSMENT (CONTINUED) levels for occupational exposures [ICNIRP 1998], IEEE MPEs for 

the upper tier (people in controlled environments) [IEEE 2005b], 

ACGIH TLVs [ACGIH 2010], and FCC limits for occupational/ 

controlled exposure [FCC 1999]. In addition, E-field strengths were 

compared to the following action levels as recommended by IEEE 

Standard C95.7-2005 [IEEE 2005a]: ICNIRP reference levels for 

general public exposure [ICNIRP 1998], IEEE action levels (general 

public) [IEEE 2005b], 1/5 the ACGIH TLVs [ACGIH 2010], 

and FCC limits for general population/uncontrolled exposure 

[FCC 1999]. Table 2 summarizes the OELs and action levels for 

E-field strengths at frequencies encountered in the interoperability 

communications laboratory. 

Table 2. OELs and action levels (RMS values averaged over 6 minutes) for VHF and UHF E-field strengths 

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

ICNIRP IEEE ACGIH FCC 

Frequency (MHz) Action Action Action Action OEL OEL OEL OEL level level level level 

VHF 160 –170 61 28 61 28 61 12 61 28
 

UHF 410 – 420 61 28 72* 28* 72* 28* 72* 32*
 

* IEEE, ACGIH, and FCC OELs and action levels for UHF (410 MHz) were converted from power density 

(W/m2) to E-field strengths (V/m) using the following formula: V/m = √(377 × W/m2). 

Atomic Time Radio Stations 

We used a Narda (Hauppauge, New York) EHP-200 E- and H-field 

Analyzer (9 kHz–30 MHz) calibrated within 1 month of the survey 

to measure E- and H-fields at various broadcasted frequencies. The 

analyzer was rented by management at the research institution for 

our use. The isotropic probe connected to a laptop computer (with 

NardaProbe software installed) via fiber optic cable to minimize 

field perturbation during measurements. Field strengths were 

measured on the three separate axes and recorded individually or 

combined as average RMS values over a 30-second sampling period. 

Thirty-second averaging times were used instead of 6-minute 

averaging times (required by most standards). A shorter averaging 

time was used because, according to our direct readings, the E- and 

H-field strengths at a stationary position were generally constant. 

The conservative assumption was made that employees could be 

exposed continuously for 6 minutes at the sampling locations. 

Page 6 Health Hazard Evaluation Report 2009-0171-3119
 
ASSESSMENT (CONTINUED) The probe was positioned on a fiberglass tripod ~2.5 feet above 

the ground for most measurements. Measurements were collected 

around the LF antennas (0.06 MHz) and HF antennas (2.5-, 5-, 10-, 

15-, and 20-MHz) as well as other areas around the radio stations. 

A few measurements were collected at head (~5.5 feet), chest (~4 

feet), and groin height (~2.5 feet) for relatively high E-fields to 

demonstrate variability over the human body and to provide data 

for spatial averaging (required by most standards). The E- and 

H-field strengths were compared to the following OELs: ICNIRP 

reference levels for occupational exposures [ICNIRP 1998], IEEE 

MPEs for the upper tier (people in controlled environments) 

[IEEE 2005b], ACGIH TLVs [ACGIH 2010], and FCC limits for 

occupational/controlled exposure [FCC 1999]. In addition, E- and 

H-field strengths were compared to the following action levels 

as recommended by IEEE Standard C95.7-2005 [IEEE 2005a]: 

ICNIRP reference levels for general public exposure [ICNIRP 

1998], IEEE action levels (general public) [IEEE 2005b], 1/5 the 

ACGIH TLVs [ACGIH 2010], and FCC limits for general public/ 

uncontrolled exposure [FCC 1999]. Table 3 summarizes the 

OELs and action levels for the E-field strengths at the frequencies 

encountered at the radio stations. Table 4 summarizes the OELs 

and action levels for the H-field strengths at the frequencies 

encountered at the radio stations. 

Because the HF radio station broadcasted multiple frequencies, 

mixture analysis was performed for E- and H-field strengths by 

taking the sum of the ratios of the time-averaged squares of the 

measured field strengths to the corresponding squares of the OELs 

as described in Annex D.2 of IEEE Standard C95.1-2005 [IEEE 

2005b]. To comply with OELs, the sum of the ratios should not 

exceed unity. This formula was also used after spatially averaging 

the squares of the E-field strengths (where measured at head, chest, 

and groin height) to strictly comply with both the mixture analysis 

and spatial averaging elements of the OELs. 

Health Hazard Evaluation Report 2009-0171-3119 Page 7
 
ASSESSMENT (CONTINUED) 

Table 3. OELs and action levels (RMS values averaged over 6 minutes) for LF and HF E-field strengths (V/m) 

with the most conservative OELs bolded and action levels underlined 

ICNIRP IEEE ACGIH FCC 

Frequency (MHz) Action Action Action Action OEL OEL OEL OEL level level level level 

LF 0.06 610 87 1842 614 1842 368 NA NA 

HF 2.5 244 55 737 330 737 147 614 330 

HF 5 122 40 368 165 368 74 368 165 

HF 10 61 28 184 82 184 37 184 82 

HF 15 61 28 123 55 123 25 123 55 

HF 20 61 28 92 41 92 18 92 41 

Table 4. OELs and action levels (RMS values averaged over 6 minutes) for LF and HF H-field strengths (A/m) 

with the most conservative OELs bolded and action levels underlined 

ICNIRP IEEE ACGIH FCC 

Frequency (MHz) Action Action Action Action OEL OEL OEL OEL level level level level 

LF 0.06 24.4 5 490* 163* 815 163 NA NA 

HF 2.5 0.64 0.3 6.5 6.5 6.5 1.30 1.63 0.88 

HF 5 0.32 0.15 3.3 3.3 3.3 0.65 0.98 0.44 

HF 10 0.16 0.073 1.6 1.6 1.7 0.33 0.49 0.22 

HF 15 0.16 0.073 1.1 1.1 1.1 0.22 0.33 0.15 

HF 20 0.16 0.073 0.82 0.82 0.8 0.16 0.24 0.11 

*IEEE OEL and action level for 0.06 MHz are for head and torso (OEL and action level for limbs are 900 A/m).
 

Page 8 Health Hazard Evaluation Report 2009-0171-3119
 
RESULTS
 

Magnetic Annealer Laboratory 

One measurement was collected within 1 inch of the annealing 

chamber. The B-field at this location was 0.4 mT, below the 

ACGIH TLV ceiling limit of 0.5 mT for medical device wearers. 

The B-fields dropped rapidly with increasing distance from the 

annealer. 

Superconducting Magnet Laboratory 

Table 5 summarizes the B-field measurements collected in the 

superconducting magnet laboratory. B-fields exceeding the ACGIH 

TLV ceiling limit for medical device wearers (0.5 mT) are bolded. 

No B-fields exceeded any of the other OELs. A sign warning of 

possible interference with pacemakers was posted on the door of 

the laboratory, and the 0.5 mT field was delineated with tape on 

the floor (~6 feet from the magnet). 

Health Hazard Evaluation Report 2009-0171-3119 Page 9
 
RESULTS (CONTINUED) 

Table 5. Static EMF B-fields measured in the superconducting magnet laboratory with field strengths above the 

ACGIH TLV ceiling limit for medical device wearers bolded 

Height of measurement Distance from B-field Location of measurement (relative to employee magnet (inches) (mT) position) 

Mirror under the magnet Hands (while cleaning mirror) 0 174 

To the right of the magnet Chest (while standing) 1 65 

To the left of the magnet Stomach (while standing) 1 42 

To the right of the magnet Head (while standing) 1 40 

To the right of the magnet Waist (while standing) 1 40 

To the left of the magnet Head (while standing) 1 33 

To the right of the magnet Chest (while standing) 18 9.7 

Optics workstation in front of the magnet Head (while sitting) 24 10 

Optics workstation in front of the magnet Stomach (while standing) 24 6.5 

To the right of the magnet Chest (while standing) 36 1.3 

To the right of the magnet Chest (while standing) 72 0.12 

To the left of the magnet Stomach (while standing) 72 0.080 

To the right of the magnet Chest (while standing) 90 0.080 

Interoperability Communications

Laboratory 

E-field strengths at the VHF and UHF frequencies measured in 

the interoperability communications laboratory and near the roofmounted antennas are summarized in Table 6. E-field strengths 

above the most conservative OELs (61 V/m) are bolded and action 

levels (12 V/m for 160–170 MHz and 28 V/m for 410–420 MHz) 

underlined. We did not measure E-field strengths in the office 

while the traffic channel was transmitting. However, we would not 

expect the traffic channel to add substantially to the field strengths 

in the office because the field strengths in the office were so low. 

During our evaluation, no portable radios were affiliated onto the 

VHF antenna facing the mountains. Thus, only a control channel 

transmitted on this antenna. If a traffic channel also transmitted, 

Page 10 Health Hazard Evaluation Report 2009-0171-3119
 
 

 

RESULTS 

(CONTINUED) then we would expect similar field strengths to those measured 

at the VHF antenna facing the road. On the roof, signs posted 

next to the antennas cautioned people to stay 8 feet away because 

of continuous transmission. Measurements were taken at 7.5 feet 

away from the antennas to ensure safety and compliance with 

applicable standards. E-field strengths at these locations were well 

below OELs and action levels. 

Table 6. VHF and UHF E-field strengths measured in the interoperability communications laboratory with field 

strengths above OELs bolded and action levels underlined 

Height of E-field (V/m) measurement Frequency General area Description (relative to Control (MHz) Control and employee channel traffic channel position) only 

Inside the laboratory 

Inside the laboratory 

Office 

Office 

Stomach 

Stomach 

160 

410 

0 

0 

DNR 

DNR 

Inside the laboratory Holding VHF portable 

adio out to the side 

Hand 160 NA 80 

Inside the laboratory Talking on the VHF 

portable radio (close to 

mouth) 

Mouth 160 NA 134 

Inside the laboratory Talking on the VHF 

portable radio (1 foot from 

mouth) 

Mouth 160 NA 0 

Inside the laboratory Talking on UHF portable 

radio (close to mouth) 

Mouth 160 NA 78 

Inside the laboratory Talking on UHF portable 

radio (close to mouth) 

Forehead 160 NA 22 

On roof facing the road 1 foot from VHF antenna Stomach 160 47 76 

On roof facing the road 4.5 feet from VHF antenna Stomach 160 12 29 

On roof facing the road 7.5 feet from VHF antenna Stomach 160 0 14 

On roof facing the 

mountains 1 foot from VHF antenna Stomach 160 48 NA 

On roof facing the 

mountains 4.5 feet from VHF antenna Stomach 160 5 NA 

On roof facing the 

mountains 7.5 feet from VHF antenna Stomach 160 0 NA 

On roof facing the road 1 foot from UHF antenna Stomach 410 57 101 

On roof facing the road 4.5 feet from UHF antenna Stomach 410 5 36 

On roof facing the road 7.5 feet from UHF antenna Stomach 410 8.3 0 

Health Hazard Evaluation Report 2009-0171-3119 Page 11
 
RESULTS (CONTINUED) Atomic Time Radio Stations 

Figure 4 is a map of the grounds surrounding the atomic time 

radio stations. E- and H-field measurements were collected in 

six distinct areas, which are highlighted by red or blue ovals. All 

measurements at the atomic time radio stations and sampling 

information (including mixture analyses and recorded GPS 

coordinates) are provided in Appendix B for E-fields and Appendix 

C for H-fields. E- and H-field strengths measured in the HF 

building, LF building, and at the main gate were all well below 

action levels. 

The following four tables present E- and H-field strengths 

around the LF and HF antennas that are representative of all 

the measurements collected in these areas. Sample numbers are 

provided to allow readers to cross reference the measurements 

in the body of the report with the measurements in Appendix B 

and C. Table 7 presents the E- and H-field strengths for the RF 

measured near the HF antennas. Field strengths above the most 

conservative OELs are bolded and action levels underlined (Tables 

3 and 4). E- and H-field strengths exceeded the most conservative 

OELs near the 10- and 15-MHz antennas. E- and H-field strengths 

above the most conservative action levels were measured along the 

access road circling the HF antennas. More than one frequency 

contributed > 10% of the OEL to the overall E-field strengths at 

a number of locations. Thus, the sums of ratios (squared field 

strengths/squared OELs or action levels) are provided for each 

sampling location. Ratios above unity represent areas where the 

total field strengths exceeded OELs or action levels. It is important 

to note that the LF E- and H-field strengths measured at the HF 

antennas were insignificant (< 1% of the OEL). 

Tables 8 and 9 present the E- and H-field strengths for the LF 

north and south antennas. No field strengths exceeded the OELs 

for 0.06 MHz (Tables 3 and 4). However, E-field strengths did 

exceed the most conservative action level for 0.06 MHz along the 

access roads leading to the helix houses. It is important to note 

that the HF E- and H-field strengths measured at the LF antennas 

were insignificant (< 1% of the OEL). 

The results presented thus far were collected at groin height. To 

strictly comply with OELs, E- and H-fields should be spatially 

averaged over an area equivalent to the vertical cross section of the 

human body. Table 10 presents spatially averaged E- and H-fields 

Page 12 Health Hazard Evaluation Report 2009-0171-3119
 
RESULTS (CONTINUED)	 measured at locations where field strengths were among the 

highest. According to this table, the highest E-fields were at groin 

height. Although some individual measurements at groin height 

did exceed OELs, the spatial averages were below OELs, and the 

ratios to OELs were below unity for all locations. We found that 

the polarization of the E-fields was predominately along the z-axis 

(vertical direction) near the LF and HF antennas. 

Figure 4. Map of the grounds of the atomic time radio stations with red 


and blue ovals identifying areas where measurements were collected.
 

Health Hazard Evaluation Report 2009-0171-3119	 Page 13
 
 

 

RESULTS 

(CONTINUED) 

Table 7. RF E- and H-field strengths measured at the HF antennas with the field strengths above OELs bolded 

and action levels underlined 

E-field H-field 

Ratio Ratio Sample Freq. Ratio Sample location Ratio to Strength to No. (MHz) Strength to 

(V/m) to action (A/m) action

OELs OELs levels levels 

On access road, near 5-MHz 5 29 0.087

3, 4 0.1 0.9 0.1 0.5 antenna 15 14 0.027 

On access road, 30 feet from 10 13 0.024

120 E, H 3.0 18 2.7 13 south 15-MHz antenna 15 105 0.26 

On access road, 60 feet from 5 15 0.033

121 E, H 1.0 5.8 0.5 2.4 south 15-MHz antenna 15 59 0.11 

On access road, between south 10 19 0.031

7, 8 0.3 1.8 0.2 1.0 15- and 10-MHz antennas 15 28 0.067 

10 80 0.19 In the field, 30 feet from 10-MHz 116 E, H 1.8 8.6 1.4 7.0 antenna 15 15 0.030 

10 54 0.14 On access road, 50 feet from 115 E, H 0.8 3.9 0.8 3.7 10-MHz antenna 15 11 0 

On access road, between north 11, 12 10 22 0.1 0.7 0.055 0.1 0.6 10- and 15-MHz antennas 

On access road, near north 13, 14 10 10 0 0.2 0.028 0 0.2 15-MHz antenna (antenna off) 

On access road, between 15, 16 20 11 0 0.5 0.021 0 0.1 15- and 20-MHz antennas 

On access road, 30 feet from 110 E, H 20 50 0.7 7.6 0.1 0.4 1.7 20-MHz antenna 

On access road, between 19, 20 20 11 0 0.4 0.023 0 0.1 20- and 2.5-MHz antennas 

On access road, near 21, 22 2.5 20 0 0.2 0.035 0 0.1 2.5-MHz antenna 

On access road, near north 23, 24 2.5 9.4 0 0.1 0.015 0 broadband antenna (antenna off) 

Fence line east of the 117 E, H 10 3.6 0 0 0.022 0 10-MHz antenna 

Page 14 Health Hazard Evaluation Report 2009-0171-3119
 

0.1 

0.1 
RESULTS (CONTINUED) 

Table 8. E- and H-field strengths measured at the LF north antenna with E-field strengths above the action 

level underlined 

Freq. E-field strength H-field strength Sample No. Sample location (MHz) (V/m) (A/m) 

90 E Concrete slab outside the helix house 0.06 44 2.1 

entrance 

91 E Just inside the entrance of the helix 0.06 12 0.27 

house 

92 E Next to the aluminum gate inside the 

helix house 

0.06 68 2.4 

93 E 70 feet north of the helix house 0.06 444 1.8 

95 E Near anchor for the radio tower north of 0.06 113 0.70 

the helix house 

94 E On access road, 250 feet north of the 

helix house 

0.06 210 0.46 

89 E On access road, 15 feet south of the 

helix house 

0.06 230 1.5 

96 E On access road, 330 feet south of the 

helix house 

0.06 216 1.7 

97 E On access road, 550 feet south of the 

helix house 

0.06 203 DNR 

101 E On access road, 717 feet south of the 

helix house 

0.06 82 DNR 

99 E On access road, 785 feet south of the 

helix house 

0.06 67 DNR 

98 E On access road, 825 feet south of the 

helix house 

0.06 41 DNR 

Health Hazard Evaluation Report 2009-0171-3119 Page 15
 
RESULTS (CONTINUED) 

Table 9. E- and H-field strengths measured at the LF south antenna with E-field strengths above the action 

level underlined 

Freq. E-field strength H-field strength Sample No. Sample location (MHz) (V/m) (A/m) 

61 E, 63 H Just outside the helix house 0.06 255 1.8 

65 E, 64 H Straddling the doorway to the helix 

house 0.06 13 1.0 

67 E, 66 H Just inside the helix house 0.06 91 2.2 

77 E, H Next to aluminum gate in the helix 

house 0.06 58 2.9 

75 E, H Near anchor for radio tower south of 

the helix house 0.06 272 1.3 

74 E On access road, 20 feet north of the 

helix house 0.06 152 DNR 

78 E, H On access road, 35 feet north of the 

helix house 0.06 250 0.88 

80 E On access road, 150 feet north of the 

helix house 0.06 271 DNR 

82 E On access road, 700 feet north of the 

helix house 0.06 91 DNR 

83 E Entrance to access road leading to the 

helix house 0.06 38 DNR 

Page 16 Health Hazard Evaluation Report 2009-0171-3119
 
RESULTS (CONTINUED) 

Table 10. Spatially averaged E- and H-field strengths for three locations with field strengths above OELs bolded and action 

levels underlined 

E-field H-field 

Sample Sample Freq. Ratio Ratio 

Height Spatial Ratio Spatial Ratio location No. (MHz) to Strength to Strength average to average to action (V/m) action (A/m) (V/m) OELs (A/m) OELs levels levels

On access 122 E 20 Head 38 0.077 

road, 30 

feet from 123 E 20 Chest 36 42 NA NA 0.087 0.088 NA NA 

20-MHz 

antenna 124 E 20 Groin 51 0.098 

127 E 10 Head 40.9 0.15 

On access 

road, 50 

feet from 

10-MHz 

antenna 

126 E 

125 E 

127 E 

126 E 

10 

10 

15 

15 

Chest 

Groin 

Head 

Chest 

39 

52 

8.4 

8.1 

44 

10 

0.55 2.7 

0.14 

0.15 

0.017 

0.017 

0.15 

0.018 

0.85 4.1 

125 E 15 Groin 12 0.019 

128 E 10 Head 7.9 0.025 

On access 

road, 50 

feet from 

15-MHz 

antenna 

129 E 

130 E 

128 E 

129 E 

10 

10 

15 

15 

Chest 

Groin 

Head 

Chest 

8.5 

12 

48.6 

54 

10 

59 

0.95 5.6

0.026 

0.022 

0.16 

0.15 

0.024 

0.15 

0.90 4.3 

130 E 15 Groin 71 0.14 

Health Hazard Evaluation Report 2009-0171-3119 Page 17
 
DISCUSSION
 

Static Magnetic Fields 

An important element of an EMF safety program is maintaining 

an inventory of relevant EMF sources. An EMF source should 

be considered relevant if it can produce field strengths (or other 

exposure metrics) near or above OELs or action levels. In this 

evaluation, the four relevant EMF sources we identified included 

(1) the magnetic annealer, (2) the superconducting magnet, (3) 

the interoperability communications radio antennas, and (4) the 

atomic time radio antennas. All these sources produced E-, H-, or 

B-fields that exceeded OELs or action levels except for the magnetic 

annealer. The B-field within 1 inch of the annealer (0.4 mT) was 

just below the ACGIH TLV ceiling limit of 0.5 mT for medical 

device wearers and consequently should be considered a relevant 

EMF source. The other sources we evaluated, (building 24 antenna 

laboratory and time domain laboratory) were low power and did 

not produce field strengths near OELs or action levels. 

A sign warning of possible interference with pacemakers was 

posted on the door of the superconducting magnet laboratory. 

This sign was necessary because B-fields exceeded the ACGIH 

TLV ceiling limit of 0.5 mT inside the laboratory (ranging up to 

174 mT). The 0.5 mT field inside the laboratory was delineated 

with tape on the floor (~6 feet from the magnet). The B-field 

at this location was 0.12 mT, which is < 25% of the ACGIH 

TLV ceiling value for medical device wearers. Thus, if employees 

with pacemakers remain behind the 0.5 mT line, they should 

be protected from EMF interference with the function of their 

pacemakers. 

Radio Frequencies 

To strictly comply with OELs for E- and H-field strengths at RF 

(100 kHz–10 GHz) frequencies, RMS values should be averaged 

over 6 minutes, and spatial averaging should be conducted 

across the vertical cross section of the human body. However, 

we recorded average RMS values for 30 seconds instead of 6 

minutes at the atomic time radio stations because our direct 

readings demonstrated that the field strengths were relatively 

constant. The E-field strengths we measured at the interoperability 

communications laboratory were instantaneous values. Spatial 

averaging was only conducted for relatively high E-fields at the 

atomic time radio stations. To interpret the results we assumed 

that (1) the RF sources are active throughout the day, (2) the 

Page 18 Health Hazard Evaluation Report 2009-0171-3119
 
DISCUSSION (CONTINUED)	 employees could be exposed at the sample location continuously 

for 6 minutes, and (3) the field strengths that were not spatially 

averaged represented conservative estimates of exposure (i.e., do 

not underestimate potential exposures). 

According to our measurements, employees could be exposed to 

E-field strengths exceeding the most conservative OELs at the 

interoperability communications laboratory. The greatest potential 

for exposure would occur if employees worked within 1 foot of the 

roof-mounted antennas while they were transmitting. Signs were 

posted next to these antennas cautioning employees to stay 8 feet 

away because of continuous transmission (control channel). E-field 

strengths at 7.5 feet from the antennas were well below the OELs. 

Thus, if employees remained 8 feet away from the antennas, their 

exposures would be well below OELs. However, for the 160-MHz 

antenna on the roof facing the road, the E-field strength at 7.5 feet 

was just above the action level. 

We measured E-field strengths above OELs when employees 

were operating portable radios inside the interoperability 

communications laboratory. These field strengths were highly 

localized and dropped rapidly with increasing distance from the 

radios. Therefore, spatial averaging across the human body would 

result in lower E-field strengths. Moreover, it is unlikely that 

employees would communicate continuously over the radios for 

6 minutes. Nevertheless, RF exposures to the face are biologically 

relevant because the eyes are vulnerable to the thermal effects of 

RF [FCC 1999]. 

E- and H-field strengths were measured at the atomic time radio 

stations to determine compliance with OELs. In general, E-field 

strengths were greater than H-field strengths (relative to OELs). 

Our measurements at the atomic time radio stations indicate that 

employees could be exposed to E- and H-field strengths above the 

most conservative OELs. The greatest potential for overexposure 

would occur if employees were to work near (within 30 feet) the 

10- or 15-MHz antennas while the antennas were broadcasting. 

However, according to radio station employees, these antennas 

would be deactivated and detuned if they were to be repaired. In 

these situations, E-field strengths from adjacent antennas would 

be the primary sources of exposure. E-field strengths from other 

antennas did contribute to the overall exposures. For example, 

15-MHz E-field strengths above action levels were measured near 

the 10-MHz antenna. However, none of the E-field strengths from 

adjacent antennas were above OELs. 

Health Hazard Evaluation Report 2009-0171-3119	 Page 19
 
DISCUSSION (CONTINUED)	 We know from the spatial averaging measurements that the E-field 

strengths at groin height were greater than those at chest and 

head height. Although OELs require spatial averaging, the most 

conservative approach is to collect measurements at a height where 

the field strengths are the highest. Most of the measurements 

we collected were at groin height. Thus, the majority of our 

measurements are conservative estimates of exposure. Additionally, 

the groin height measurements are biologically relevant because 

all the radio station employees were male, and the testes are 

particularly vulnerable to the thermal effects of radio frequencies 

[FCC 1999]. 

Compliance with OELs and action levels could be determined 

for most sample locations by measuring only the field strengths 

for the predominant frequencies. However, this was not the case 

for sample 121 E (Table 7); on an individual basis, the 5- and 

10-MHz E-field strengths were below OELs, but together the 

E-field strengths exceeded OELs (i.e., ratio to OELs > 1). Thus, 

it was important to consider multiple frequencies in determining 

compliance. 

CONCLUSIONS
 

The research institution’s laboratories and atomic time radio 

stations contained relevant sources of EMF radiation. Static EMF 

B-fields measured near the superconducting magnet exceeded the 

ACGIH TLV ceiling limit for medical device wearers. RF E-field 

strengths measured near the interoperability communications 

laboratory roof-mounted antennas and HF radio station antennas 

exceeded the most conservative OELs. RF E-field strengths 

measured near the LF radio station antennas exceeded the most 

conservative action levels. On the basis of these results, the 

research institution should implement a comprehensive EMF safety 

program. 

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. 

Page 20	 Health Hazard Evaluation Report 2009-0171-3119
 
RECOMMENDATIONS 

(CONTINUED) 1. Develop a comprehensive EMF safety program. While no 

specific guidelines exist for sub-RF safety programs, IEEE 

Standard C95.7-2005 provides guidelines for developing 

an RF safety program. According to our measurements, the 

interoperability communications laboratory and atomic 

time radio stations meet the criteria of a category 3 RF safety 

program. 

2. Assign an EMF safety officer to implement and oversee the 

EMF safety program at the research institution. A deputy 

EMF safety officer should be assigned to the atomic time 

radio stations. Each EMF safety officer should maintain a 

current copy of the written EMF safety program. 

3. Maintain an inventory of relevant EMF sources that have 

the potential to produce field strengths (or other exposure 

metrics) near or above OELs or action levels. Conduct 

initial exposure monitoring and additional exposure 

monitoring when processes are modified or new sources are 

introduced. 

4. Install informative signs in areas where action levels may 

be exceeded and caution signs in areas where OELs may be 

exceeded. Floor markings can be used on solid surfaces to 

indicate areas where OELs may be exceeded. High voltage 

areas (e.g., LF and HF antennas) can be fenced off to 

prevent inadvertent electrical shocks. 

5. Conduct annual EMF safety awareness training. Employees 

should be educated on the potential hazards associated with 

sub-RF and RF exposures and understand the purpose of 

signage, floor markings, and other safety procedures (e.g., 

lockout/tagout) designed to prevent overexposures to EMF 

or electrical shocks. 

6. Modify the incident reporting system to include possible 

EMF overexposure incidents such as medical device 

interference, reddening of skin, elevated body temperatures, 

other evidence of burns, or electrical shocks. 

7. Audit the EMF safety program annually. This audit should 

include a review of any EMF overexposure incidents and 

EMF monitoring data, inspection of existing controls, and 

a system that allows employees to provide feedback and 

recommendations to the EMF safety officer. 

Health Hazard Evaluation Report 2009-0171-3119 Page 21
 
REFERENCES
 

ACGIH [2010]. Threshold limit values for chemical substances and 

physical agents and biological exposure indices. Cincinnati, OH: 

American Conference of Governmental Industrial Hygienists. 

FCC [1999]. Questions and answers about biological effects 

and potential hazards of radiofrequency electromagnetic fields. 

By Cleveland RF, Ulcek JL. Washington D.C.: 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 NonIonizing Radiation Protection (ICNIRP). 

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

fields. Oberschleissheim, Germany: International Commission on 

Non-Ionizing Radiation Protection (ICNIRP). 

IEEE [2002]. IEEE standard for safety levels with respect to human 

exposure to electromagnetic fields, 0 to 3 kHz. New York: Institute 

of Electrical and Electronics Engineers (IEEE). Standard C95.6­

2002. 

IEEE [2005a]. IEEE recommended practice for radio frequency 

safety programs, 3 kHz to 300 GHz. New York: Institute of 

Electrical and Electronics Engineers (IEEE). Standard C95.7-2005. 

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

human exposure to radio frequency electromagnetic fields, 3 kHz 

to 300 GHz. New York: Institute of Electrical and Electronics 

Engineers (IEEE). Standard C95.1-2005. 

National Institute of Standards and Technology [2010a]. NIST 

Radio Station WWVB. [http://www.nist.gov/pml/div688/grp40/ 

wwvb.cfm]. Date accessed: February 2011. 

National Institute of Standards and Technology [2010b]. Radio 

Station WWV. [http://www.nist.gov/pml/div688/grp40/wwv. 

cfm]. Date accessed: February 2011. 

Page 22 Health Hazard Evaluation Report 2009-0171-3119
 
APPENDIX A: OCCUPATIONAL EXPOSURE LIMITS AND HEALTH EFFECTS 

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

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

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

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

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

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

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

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

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

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

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

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

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

Most OELs are expressed as a TWA exposure. A TWA refers to the average exposure during a normal 8- 

to 10-hour workday. Some chemical substances and physical agents have recommended STEL or ceiling 

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

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

limit is an exposure that should not be exceeded at any time. 

In the United States, OELs have been established by Federal agencies, professional organizations, state 

and local governments, and other entities. Some OELs are legally enforceable limits, while others are 

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

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

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

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

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

Guide to Chemical Hazards [NIOSH 2005]. NIOSH also recommends different types of risk management 

practices (e.g., engineering controls, safe work practices, employee education/training, personal protective 

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

effects from these hazards. Other OELs that are commonly used and cited in the United States include 

the TLVs recommended by ACGIH, a professional organization, and the WEELs recommended by the 

American Industrial Hygiene Association, another professional organization. The TLVs and WEELs are 

developed by committee members of these associations from a review of the published, peer-reviewed 

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

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

hazards” [ACGIH 2010]. WEELs have been established for some chemicals “when no other legal or 

authoritative limits exist” [AIHA 2010]. 

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 

Health Hazard Evaluation Report 2009-0171-3119 Page 23
 
APPENDIX A: OCCUPATIONAL EXPOSURE LIMITS AND HEALTH EFFECTS (CONTINUED) 

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

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

international limits for over 1250 hazardous substances and is updated annually. 

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

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

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

of a specific OSHA PEL. OSHA requires an employer to furnish employees a place of employment free 

from recognized hazards that cause or are likely to cause death or serious physical harm [Occupational 

Safety and Health Act of 1970 (Public Law 91–596, sec. 5(a)(1))]. Thus, NIOSH investigators encourage 

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

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

hierarchy of controls approach to eliminate or minimize identified workplace hazards. This includes, in 

order of preference, the use of: (1) substitution or elimination of the hazardous agent, (2) engineering 

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

(e.g., limiting time of exposure, employee training, work practice changes, medical surveillance), and (4) 

personal protective equipment (e.g., respiratory protection, gloves, eye protection, hearing protection). 

Control banding, a qualitative risk assessment and risk management tool, is a complementary approach 

to protecting employee health that focuses resources on exposure controls by describing how a risk 

needs to be managed. Information on control banding is available at http://www.cdc.gov/niosh/topics/ 

ctrlbanding/. This approach can be applied in situations where OELs have not been established or can be 

used to supplement the OELs, when available. 

Static EMF OELs 

The superconducting magnet and magnetic annealer produced static B-fields. Table 1 (on page 5) presents 

the OELs (ceiling limits) for static B-fields. The OELs we referenced are ICNIRP occupational limits 

of exposure [ICNIRP 2009], IEEE MPEs for the controlled environment [IEEE 2002], and ACGIH 

TLVs [ACGIH 2010]. The most conservative OELs were used for making decisions regarding the 

implementation of EMF safety program elements. 

The ICNIRP occupational limits of exposure for static EMF are intended to prevent vertigo, nausea, 

and other sensations [ICNIRP 2009]. Because these are acute effects, a ceiling limit was specified. The 

IEEE MPEs (0–3 kHz) for the controlled environment are based on avoidance of the following shortterm reactions: aversive or painful stimulation of sensory or motor neurons, muscle excitation that may 

lead to injury while performing potentially hazardous activities, excitation of neurons or direct alteration 

of synaptic activity within the brain, cardiac excitation, and adverse effects associated with induced 

potentials or forces on rapidly moving charges within the body, such as blood flow [IEEE 2002]. For 

frequencies below 0.1 Hz, a maximum averaging time of 10 seconds is considered adequate [IEEE 2002]; 

thus, in practice the IEEE MPE for static EMF may be considered a ceiling limit. The ACGIH TLV 

for static magnetic fields is based primarily on electrical potentials that are magnetically induced in the 

Page 24 Health Hazard Evaluation Report 2009-0171-3119
 
APPENDIX A: OCCUPATIONAL EXPOSURE LIMITS AND HEALTH EFFECTS (CONTINUED) 

major arteries of the central circulatory system. The body extremities contain smaller blood vessels and 

experience smaller induced electrical potentials in strong magnetic fields than do major arteries; hence, 

the higher ceiling limit for the limbs [ACGIH 2001]. 

RF OELs and Action Levels 

The interoperability communications laboratory transmitted VHF (160–170 MHz) and UHF (410–420 

MHz) signals, while the atomic time radio stations transmitted LF (60 kHz) and HF (2.5–20 MHz) signals. 

Table 2 (on page 6) presents the OELs and action levels for VHF and UHF E-field strengths. Tables 3 and 

4 (on page 8) present the OELs and action levels for LF and HF E- and H-field strengths. The OELs we 

referenced are ICNIRP reference levels for occupational exposures [ICNIRP 1998], IEEE MPEs for the 

upper tier (people in controlled environments) [IEEE 2005b], ACGIH TLVs [ACGIH 2010], 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 U.S. 

FCC [IEEE 2005a]. For this evaluation, all were used as action levels. The most conservative OELs 

and action levels were used for making decisions regarding the implementation of EMF safety program 

elements. 

The ICNIRP reference levels for time-varying EMF (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 

conducting objects, and elevated tissue temperatures resulting from absorption of energy during exposure 

to EMF [ICNIRP 1998]. The IEEE MPEs for RF radiation (3 kHz to 300 GHz) are intended to minimize 

aversive or 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 MPEs are intended to protect against both electrostimulation and thermal effects [IEEE 

2005b]. The FCC MPEs are intended to prevent similar health effects [FCC 1999]. The ACGIH TLVs for 

RF and microwave radiation are based upon the belief that the primary adverse physiological effects of 

electromagnetic energy in this wavelength and frequency region are thermal [ACGIH 2006]. 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]. 

References 

ACGIH [2001]. Static magnetic fields. In: Documentation of the threshold limit values and biological 

exposure indices. Cincinnati, OH: American Conference of Governmental Industrial Hygienists 

(ACGIH). 

Health Hazard Evaluation Report 2009-0171-3119 Page 25
 
APPENDIX A: OCCUPATIONAL EXPOSURE LIMITS AND HEALTH EFFECTS (CONTINUED) 

ACGIH [2006]. Radiofrequency and microwave radiation In: Documentation of the threshold limit values 

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

Hygienists (ACGIH). 

ACGIH [2010]. Threshold limit values for chemical substances and physical agents and biological exposure 

indices. Cincinnati, OH: American Conference of Governmental Industrial Hygienists. 

AIHA [2010]. AIHA 2010 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. 

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

electromagnetic fields. By Cleveland RF, Ulcek JL. Washington D.C.: 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). 

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

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

IEEE [2002]. IEEE standard for safety levels with respect to human exposure to electromagnetic fields, 0 to 

3 kHz. New York: Institute of Electrical and Electronics Engineers (IEEE). Standard C95.6-2002. 

IEEE [2005a]. IEEE recommended practice for radio frequency safety programs, 3 kHz to 300 GHz. New 

York: Institute of Electrical and Electronics Engineers (IEEE). Standard C95.7-2005. 

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

electromagnetic fields, 3 kHz to 300 GHz. New York: Institute of Electrical and Electronics Engineers 

(IEEE). Standard C95.1-2005. 

NIOSH [2005]. NIOSH pocket guide to chemical hazards. Cincinnati, OH: U.S. Department of Health 

and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational 

Safety and Health, DHHS (NIOSH) Publication No. 2005-149. [http://www.cdc.gov/niosh/npg/]. Date 

accessed: February 2011. 

Page 26 Health Hazard Evaluation Report 2009-0171-3119
 
APPENDIX B: E-FIELD STRENGTHS MEASURED AT THE ATOMIC TIME 

RADIO STATIONS 

Health Hazard Evaluation Report 2009-0171-3119 Page 27 H-field
 Sample
 No.
 4
 6
 8
 10
 12
 14
 16
 18
 20
 22
 24
 GPS Coordinates 40 40.708 - 105 02.432 40 40.748 - 105 02.430 40 40.769 - 105 02.434 40 40.797 - 105 02.439 40 40.825 - 105 02.456 40 40.845 - 105 02.469 40 40.867 - 105 02.489 40 40.887 - 105 02.504 40 40.905 - 105 02.526 40 40.921 - 105 02.554 40 40.858 - 105 02.576 Sample
 No.
 3
 5
 7
 9
 11
 13
 15
 17
 19
 21
 23
 Date 8/3/2010 8/3/2010 8/3/2010 8/3/2010 8/3/2010 8/3/2010 8/3/2010 8/3/2010 8/3/2010 8/3/2010 8/3/2010 Location On access road, near 5-MHz antenna On access road, near 15-MHz antenna On access road, between 15- and 10-MHz towers On access road, near 10-MHz tower On access road, between 10- and 15-MHz towers On access road, near 15-MHz tower (antenna off) On access road, between 15- and 20-MHz towers On access road, near the 20-MHz tower On access road, between 20- and 2.5-MHz towers On access road,
 near 2.5 MHz
 tower
 On access
 road, near north
 broadband tower
 (antenna off)
 Area HF antennas HF antennas HF antennas HF antennas HF antennas HF antennas HF antennas HF antennas HF antennas HF antennas HF antennas Conservative OEL Conservative action level Results RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL 61087 24455 12240 6128 6125 6118 60 kHz 2.5 MHz 5 MHz 10 MHz 15 MHz 20 MHz Sum total 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.6 0.00 0.00 2.6 0.00 0.00 2.3 0.00 0.00 2.8 0.00 0.00 3.8 0.00 0.00 4.9 0.00 0.01 10.4 0.00 0.04 8.2 0.00 0.02 12.3 0.00 0.05 19.5 0.01 0.13 9.4 0.00 0.03 290.06 0.53 8.7 0.01 0.05 9.1 0.01 0.05

70.000.035.40.000.022.60.000.002.60.000.002.40.00

0.002.40.000.000.770.000.002.10.000.00 

3.50.000.02

12

0.040.18

19

0.100.46

46 

0.572.70

22

0.130.62

10.4

0.030.146.50.010.055.10.01

0.032.70.000.012.20.000.013.20.000.01 

14

0.050.31

66

1.176.97

28

0.211.258.70.020.124.20.000.034.10.000.032.60.000.011.90.00

0.011.50.000.001.40.000.001.70.000.00 

0.000.000.890.000.000.970.000.001.20.000.002.10.000.0140.000.05

10.9

0.030.37

58

0.90

10.38

11 

0.030.343.970.000.0530.000.03 

0.10.91.27.20.31.80.62.90.10.70.00.20.00.50.9

10.4

0.00.40.00.20.00.1 
 

Sample


No.


29
35
37
39
42


61 E
62 E
65 E
67 E
68 E
69 E


70 E
 

H-field

Sample

No.

63 H64 H66 H 

Date

8/3/20108/3/20108/3/20108/3/20108/3/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/2010

8/4/2010 

Location

In front of the

10-MHz control

panel

Left edge of

5-MHz control

panel

Right edge of

5-MHz control

panel

Left edge of

second 5-MHz

control panel

Right edge of

second 5-MHz

control panel

Outside helix

house south

(door opened)

Outside helix

house south

(door closed)

Straddling the

doorway to helix

house south

Inside helix

house south

Inside helix

house south

(head height)

Inside helix

house south

(above aluminum

fence)

Access road

under the main 

Area

HF

building

HF

building

HF

building

HF

building

HF

building

LF southLF southLF southLF southLF south

LF southLF south 

GPS

Coordinates

40 40.553 -

105 02.555 

Conservative OEL

Conservative

action level

Results

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m) 

610

87 

244

55 

122

40 

6128 

6125 

6118 

60 kHz 2.5 MHz 5 MHz 10 MHz 15 MHz 20 MHz Sum total 

0.000.000.000.000.000.000.000.000.000.00

255

0.17

8.59

243

0.167.80

13.3

0.000.02

90.5

0.021.08

54.6

0.010.39

94.5

0.021.18

67.6

0.010.60 

0.000.000.000.000.000.000.000.000.000.000.00

0.000.000.000.000.000.000.000.000.00

0.000.000.000.00 

0.000.000.000.000.940.000.001.20.000.000.830.000.000.00

0.000.000.000.000.000.000.000.000.00

0.000.000.000.00 

0.720.000.000.640.000.000.000.000.770.000.001.70.000.000.00

0.000.000.000.000.000.000.000.000.00

0.000.000.000.00 

0.000.000.000.000.660.000.000.000.000.000.000.00

0.000.000.000.000.000.000.000.000.00

0.000.000.000.00 

0.000.000.000.000.000.000.000.000.000.000.00

0.000.000.000.000.000.000.000.000.00

0.000.000.000.00 

0.00.00.00.00.00.00.00.00.00.00.2

8.60.27.80.00.00.01.10.00.4

0.01.20.00.6 

APPENDIX B: E-FIELD STRENGHTS MEASURED AT THE ATOMIC TIME 

RADIO STATIONS (CONTINUED) 

Page 28 Health Hazard Evaluation Report 2009-0171-3119
 71 H 40 40.470 - 105 02.690 
APPENDIX B: E-FIELD STRENGHTS MEASURED AT THE ATOMIC TIME 

RADIO STATIONS (CONTINUED) 

Health Hazard Evaluation Report 2009-0171-3119 Page 29 H-field
 Sample
 No.
 75 H
 76 H
 77 H
 GPS
 Coordinates
 40 40.545 -
 105 02.761
 Sample
 No.
 74 E
 75 E
 76 E
 77 E
 78 E
 79 E
 80 E
 81 E
 82 E
 83 E
 84 E
 Date 8/4/2010 8/4/2010 8/4/2010 8/4/2010 8/4/2010 8/4/2010 8/4/2010 8/4/2010 8/4/2010 8/4/2010 8/4/2010 Location 20 feet in front of the helix house south Downlead location closest to the ground Straddling the doorway to helix house south (check 65 E) Next to aluminum gate in helix house south On access road 35 feet from helix house south (about middle) On access road 35 feet from helix house south (about middle) On access road 150 feet from helix house south On access road, 742 feet from helix house south On access road, 700 feet from helix house south Entrance to access road leading to helix house south Just outside the door of building 5701 Area LF south LF south LF south LF south LF south LF south LF south LF south LF south LF south LF building Conservative OEL Conservative action level Results Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level 61087 24455 12240 6128 6125 6118 60 kHz 2.5 MHz 5 MHz 10 MHz 15 MHz 20 MHz Sum total 1520.06 3.05 2720.20 9.77 130.00 0.02 580.01 0.44 2500.17 8.26 2370.15 7.42 2710.20 9.70 61.4 0.01 0.50 90.8 0.02 1.09 37.5 0.00 0.19 3.8 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.1 3.1 0.2 9.8 0.0 0.0 0.0 0.4 0.2 8.3 0.2 7.4 0.2 9.7 0.0 0.5 0.0 1.1 0.0 0.2 0.0 0.0 
 

Sample

No.

85 E86 E

87 E,

88 E89 E90 E91 E92 E

93 E,

131 E

94 E95 E96 E97 E 

H-field

Sample

No.

87 H,

88 H89 H90 H91 H92 H93 H94 H95 H96 H 

Date

8/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/2010 

Location

Parking lot on

blacktop near

building 5701

Front desk inside

building 5701

Security gate

next to call box

15 feet from front

door of helix

house north

Concrete slab

outside door to

helix house north

Inside front door

to helix house

north

Next to

aluminum gate

inside helix

house north

70 feet behind

the helix house

north

250 feet north of

helix house north

Near anchor for

radio tower

Access road to

helix house north

(330 feet from door)

Access road to

helix house north

(550 feet from door) 

Area

LF

building

LF

building

Main

gate

LF northLF northLF northLF northLF northLF northLF northLF northLF north 

GPS

Coordinates

40 40.840 -

105 03.024

40 40.876 -

105 03.069

40 40.868 -

105 03.048

40 40.802 -

105 02.972 

Conservative OEL

Conservative

action level

Results

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL 

610

87 

244

55 

122

40 

6128 

6125 

6118 

60 kHz 2.5 MHz 5 MHz 10 MHz 15 MHz 20 MHz Sum total 

10.4

0.000.0100.000.00

28.8

0.000.11 

229.6

0.146.96

43.5

0.010.25

11.5 

0.000.02

68

0.010.61

444

0.53

26.05

210

0.125.83

113 

0.031.69

216

0.136.16

203

0.11 5.44 

0.000.000.000.000.720.000.000.000.000.000.000.000.000.000.000.870.000.000.000.000.000.000.000.000.000.00 

0.000.000.000.0030.000.010.000.000.000.000.000.000.000.000.280.000.00

0.000.000.000.000.000.000.000.00 

0.000.000.000.001.10.000.000.000.000.000.000.000.000.000.000.380.000.00

0.000.000.000.000.000.000.000.00 

0.000.000.000.000.880.000.000.000.000.000.000.000.000.000.000.290.000.000.000.000.000.000.000.000.000.00 

0.000.000.000.0000.000.000.000.000.000.000.000.000.000.000.220.000.00

0.000.000.000.000.000.000.000.00 

0.00.00.00.00.00.10.17.00.00.30.00.00.00.60.5

26.0

0.15.80.01.70.16.20.15.4 

APPENDIX B: E-FIELD STRENGHTS MEASURED AT THE ATOMIC TIME 

RADIO STATIONS (CONTINUED) 

Page 30 Health Hazard Evaluation Report 2009-0171-3119
 
APPENDIX B: E-FIELD STRENGHTS MEASURED AT THE ATOMIC TIME 

RADIO STATIONS (CONTINUED) 

Health Hazard Evaluation Report 2009-0171-3119 Page 31 Sample
 No.
 98 E
 99 E
 101 E
 104 E
 105 E
 110 E
 111 E
 112 E
 114 E
 115 E
 116 E
 117 E
 H-field Sample No. 110 H 111 H 112 H 114 H 115 H 116 H 117 H Date 8/4/2010 8/4/2010 8/4/2010 8/4/2010 8/4/2010 8/5/2010 8/5/2010 8/5/2010 8/5/2010 8/5/2010 8/5/2010 8/5/2010 Location
 Access road to
 helix house north
 (825 feet from
 door)
 Access road to
 helix house north
 (785 feet from
 door)
 Access road to
 helix house north
 (717 feet from
 door)
 Outside the
 entrance to the
 WWV building
 Inside the
 entrance to the
 WWV building
 Access road
 near 20-MHz
 tower (30 feet
 from tower)
 Access road
 near 20-MHz
 tower (40 feet
 from tower)
 Fenceline
 directly below
 20-MHz tower
 near jet ski club
 Access road in front of 15-MHz tower (tower off) Access road in front of 10-MHz tower (50 feet from tower) 30 feet from 10­ MHz tower Fenceline below the 10-MHz tower GPS Coordinates 40 40.741 - 105 02.892 40 40.756 - 105 02.911 Conservative OEL Conservative action level Results Ratio to action level RMS E-field (V/m) RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) RMS E-field (V/m) Ratio to OEL Ratio to action level RMS E-field (V/m) Ratio to OEL Ratio to action level 61087 24455 12240 6128 6125 6118 60 kHz 2.5 MHz 5 MHz 10 MHz 15 MHz 20 MHz Sum total 410.00 0.22 670.01 0.59 82.4 0.02 0.90 1.9 0.00 0.00 0.07 0.00 0.00 3.2 0.00 0.00 3.5 0.00 0.00 0.65 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

90.000.0380.000.021.20.000.0050.000.012.90.000.0030.000.000.910.000.00 

0.000.000.000.000.000.000.000.000.00

0.002.40.000.002.10.000.000.830.000.002.10.000.008.30.000.048.50.000.050.980.000.00 

0.000.000.000.000.000.000.000.000.00

0.005.80.010.045.90.010.041.30.000.00

11.2 

0.030.16

53.7

0.773.68

80

1.728.163.60.000.02 

0.000.000.000.000.000.000.000.000.00

0.0020.000.0120.000.010.780.000.0040.000.03

11.1 

0.030.20

15

0.060.362.20.000.01 

0.000.000.000.000.000.000.000.000.00

0.00

50 

0.667.56

44 

0.515.846.20.010.123.90.000.0520.000.0110.000.000.000.00 

0.00.20.00.60.00.90.00.00.00.00.77.60.55.90.00.10.00.20.83.91.88.60.00.0 

Area

LF northLF northLF north

HF

building

HF

building

HF

antennas

HF

antennas

HF

antennas

HF

antennas

HF

antennas

HF

antennas

HF

antennas 

40 40.838 -

105 02.400 
 

Sample


No.


118 E
 119 E
 

120 E
121 E


135 E,


136 E


137 E,


138 E
 

H-field

Sample

No.

118 H 119 H 

120 H121 H 

Date

8/5/20108/5/20108/5/20108/5/20108/5/20108/5/2010 

Location

10 feet from the

fenceline below

the 10-MHz

tower

Access road in

front of 15-MHz

tower (50 feet

from tower)

Access road in

front of 15-MHz

tower (30 feet

from tower)

Access road in

front of 15-MHz

tower (60 feet

from tower)

Main road

entrance to

facility

Main road to

facility just past

the gate 

Area

HF

antennas

HF

antennas

HF

antennas

HF

antennas

Main

gate

Main

gate 

GPS

Coordinates

40 40.588 -

105 02.655 

Conservative OEL

Conservative

action level

Results

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level

RMS E-field (V/m)

Ratio to OEL

Ratio to action level 

610

87 

244

55 

122

40 

6128 

6125 

6118 

60 kHz 2.5 MHz 5 MHz 10 MHz 15 MHz 20 MHz Sum total 

0.000.000.000.000.000.000.000.00

81

0.020.87

78

0.020.80 

30.000.002.80.000.003.10.000.002.50.000.001.70.000.001.40.000.00 

30.00

0.01

10

0.010.069.30.010.05

15.3

0.020.152.10.000.003.40.000.01 

7.20.010.07

13.4

0.050.23

13.4

0.050.238.20.020.091.20.000.000.960.000.00 

3.20.00

0.02

77

1.599.49

105

2.96

17.6459

0.945.570.990.000.0010.000.00 

20

0.11 1.2310.000.0010.000.0010.000.000.210.000.000.220.000.00 

0.1

1.31.69.83.0

17.9

1.05.80.00.90.00.8 

APPENDIX B: E-FIELD STRENGHTS MEASURED AT THE ATOMIC TIME 

RADIO STATIONS (CONTINUED) 

Page 32 Health Hazard Evaluation Report 2009-0171-3119
 
APPENDIX C: H-FIELD STRENGTHS MEASURED AT THE ATOMIC TIME 

RADIO SATATONS 

Health Hazard Evaluation Report 2009-0171-3119 Page 33 GPS
 Coordinates
 40 40.708 - 105
 02.432 40 40.748 - 105 02.430 40 40.769 - 105 02.434 40 40.797 - 105 02.439 40 40.825 - 105 02.456 40 40.845 - 105 02.469 40 40.867 - 105 02.489 40 40.887 - 105 02.504 40 40.905 - 105 02.526 40 40.921 - 105 02.554 40 40.858 - 105 02.576 Sample
 No.
 

468

101214161820

2224 

Date

8/3/20108/3/20108/3/20108/3/20108/3/20108/3/20108/3/20108/3/20108/3/2010

8/3/20108/3/2010 

Location

On access road,

near 5-MHz

antenna

On access road,

near 15-MHz

antenna

On access road,

between 15- and

10-MHz towers

On access road,

near 10-MHz

tower

On access road,

between 10- and

15-MHz towers

On access road,

near 15-MHz

tower (antenna

off) 

On access road,

between 15- and

20-MHz towers

On access road,

near the 20-MHz

tower

On access road,

between 20- and

2.5-MHz towers

On access road,


near 2.5-MHz


tower


On access


road, near north


broadband tower


(antenna off)
 

Area

HF

antennas

HF

antennas

HF

antennas

HF

antennas

HF

antennas

HF

antennas

HF

antennas

HF

antennas

HF

antennas

HF

antennas

HF

antennas 

Conservative OEL

Conservative

Action level

Results

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level 

24.4

5 

0.640.3 

0.320.15 

0.160.073 

0.160.073 

0.160.073 

60 kHz 2.5 MHz 5 MHz 10 MHz 15 MHz 20 MHz Sum total 

0.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.00

0.000.000.000.000.000.00 

0.000.000.000.000.000.000.000.000.000.000.000.000.0160.000.000.0180.000.00

0.026

0.000.010.0350.000.010.0150.000.00 

0.0870.070.340.0310.010.040.020.000.020.0160.000.010.0140.000.010.011 0.000.010.000.000.000.00

0.000.000.000.000.000.00 

0.0130.010.030.0230.020.100.0310.040.180.161.004.800.0550.120.570.0280.030.150.0150.010.040.0130.010.03

0.014

0.010.040.0140.010.040.0120.010.03 

0.0270.030.140.150.884.220.0670.180.840.0190.010.070.0150.010.040.0120.010.030.000.000.000.00

0.000.000.000.000.000.00 

0.000.000.000.000.000.000.000.000.000.000.000.000.0210.020.080.120.562.70

0.023

0.020.100.0150.010.040.011 0.000.02 

0.10.50.94.40.21.01.04.90.10.60.00.20.00.10.62.7

0.00.10.00.10.00.1 
 

Sample

No.

63 H64 H66 H71 H75 H76 H77 H78 H

87 H,

88 H89 H

90 h

91 H 

Date

8/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/20108/4/2010 

GPS


Coordinates


40 40.470 - 105


02.690

40 40.840 - 105

03.024 

Location

Just outside helix

house south

(door closed)

Straddling the

doorway to helix

house south

Inside helix

house south

Access road

under main

Downlead near

the ground

Straddling the doorway to helix house south

(check of 64 H)

Next to the

aluminum gate in the helix house

south

35 feet from

the helix house

(middle of the

access road)

Security gate

next to the call

box

Helix house north

(15 feet from the

front door)

Helix house north

(concrete slab

outside door)

Inside the door of

the helix house

north 

Area


LF south
LF south
LF south
LF south
LF south
LF south
LF south
LF south


Main gate


LF north
LF north
LF north
 

Conservative OEL

Conservative

Action level

Results

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level 

24.4

5 

0.640.3 

0.320.15 

0.160.073 

0.160.073 

0.160.073 

60 kHz 2.5 MHz 5 MHz 10 MHz 15 MHz 20 MHz Sum total 

1.80.010.131.030.000.042.20.010.191.260.000.061.340.000.071.260.000.062.850.010.320.880.000.030.040.000.001.50.000.092.10.010.180.270.000.00 

0.000.000.000.000.000.000.000.000.000.000.000.000.00

0.000.000.000.000.000.000.000.000.000.000.00 

0.000.000.000.000.000.000.000.000.000.000.000.000.00

0.000.000.000.00490.000.000.000.000.000.000.000.00 

0.000.000.000.000.000.000.000.000.000.000.000.000.00

0.000.000.000.000.000.000.000.000.000.000.00 

0.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.00 

0.000.000.000.000.000.000.000.000.000.000.000.000.00

0.000.000.000.000.000.000.000.000.000.000.00 

0.00.10.00.00.00.20.00.10.00.10.00.10.00.30.00.00.00.00.00.10.00.20.00.0 

APPENDIX C: H-FIELD STRENGHTS MEASURED AT THE ATOMIC TIME 

RADIO SATATONS (CONTINUED) 

Page 34 Health Hazard Evaluation Report 2009-0171-3119
 
APPENDIX C: H-FIELD STRENGHTS MEASURED ATTHE ATOMIC TIME 

RADIO SATATONS (CONTINUED) 

Conservative OEL

Conservative

Action level

Results

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level

RMS H-field (A/m)

Ratio to OEL

Ratio to action level 

24.4

5

60 kHz

2.40.010.231.80.010.130.460.000.010.70.000.02

0.170.000.000.000.000.000.000.000.000.000.000.000.000.000.000.000.00 

0.640.3

2.5 MHz

0.000.000.000.000.000.000.000.00

0.000.000.000.000.0220.000.010.000.000.000.000.000.000.000.000.000.00 

0.320.15

5 MHz

0.000.000.000.000.000.000.000.00

0.000.000.000.000.000.000.000.000.000.000.000.000.0170.000.010.000.00 

0.160.073

10 MHz

0.000.000.000.000.000.000.000.00

0.00 

0.160.073

15 MHz

0.000.000.000.000.000.000.000.00

0.00 

0.160.073 

Sample

No. Date Location Area GPS Coordinates

40 40.876 - 105

03.069

40 40.868 - 105

03.048

40 40.802 - 105

02.972

40 40.838 - 105

02.400 

20 MHz

0.000.000.000.000.000.000.000.000.000.000.100.351.690.080.221.060.020.020.100.000.000.000.000.000.000.000.00 

Sum total

0.00.20.00.10.00.00.00.00.00.00.41.70.21.10.00.10.00.10.83.71.47.00.00.1 

92 H 8/4/2010 

Next to the metal

gate inside helix

house north 

LF north 

93 H 8/4/2010 70 feet behind helix house north LF north 

94 H 8/4/2010 

Access road, 250

feet from helix

house north 

LF north 

95 H 8/4/2010 Anchor for tower LF north 

96 H 8/4/2010 

Access road to

helix house north

(330 feet from door) LF north 0.00

0.000.000.0160.010.050.000.000.0220.020.090.140.773.680.191.416.770.0220.020.09 

0.000.000.000.000.000.000.000.000.000.000.000.030.040.170.0140.010.04 

110 H 8/5/2010 

Access road near

20-MHz tower

(30 feet from tower) 

HF

antennas 

111 H 8/5/2010 

Access road near

20-MHz tower

(40 feet from tower) 

HF

antennas 

112 H 8/5/2010 

Fenceline directly below 20-MHz

tower near jet ski club 

HF

antennas 

114 H 8/5/2010 

Access road in

front of 15-MHz

tower (tower off) 

HF

antennas 

115 H 8/5/2010 

Access road in

front of 10-MHz

tower (50 feet

from tower) 

HF

antennas 

116 H 8/5/2010 30 feet from 10­ MHz tower HF antennas 

117 H 8/5/2010 Fenceline below the 10-MHz tower HF antennas 

Health Hazard Evaluation Report 2009-0171-3119 Page 35
 
APPENDIX C: H-FIELD STRENGHTS MEASURED ATTHE ATOMIC TIME 

RADIO SATATONS (CONTINUED) 

Page 36 Health Hazard Evaluation Report 2009-0171-3119
 GPS Coordinates Sample
 No.
 118 H 119 H 120 H 121 H Date 8/5/2010 8/5/2010 8/5/2010 8/5/2010 Location 10 feet from the fenceline below the 10-MHz tower Access road in front of 15-MHz tower (50 feet from tower) Access road in front of 15-MHz tower (30 feet from tower) Access road in front of 15-MHz tower (60 feet from tower) Area HF antennas HF antennas HF antennas HF antennas Conservative OEL Conservative Action level Results RMS H-field (A/m) Ratio to OEL Ratio to action level RMS H-field (A/m) Ratio to OEL Ratio to action level RMS H-field (A/m) Ratio to OEL Ratio to action level RMS H-field (A/m) Ratio to OEL Ratio to action level 24.4 5 0.64 0.3 0.32 0.15 0.16 0.073 0.16 0.073 0.16 0.073 60 kHz 2.5 MHz 5 MHz 10 MHz 15 MHz 20 MHz Sum total 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.029 0.01 0.04 0.033 0.01 0.05 0.033 0.01 0.05 0.033 0.04 0.20 0.023 0.02 0.10 0.024 0.02 0.11 0.017 0.01 0.05 0.00 0.00 0.17 1.13 5.42 0.26 2.64 12.69 0.11 0.47 2.27 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.0 0.2 1.2 5.6 2.7 12.8 0.5 2.4 
ACKNOWLEDGMENTS AND AVAILABILITY OF REPORT 

The Hazard Evaluations and Technical Assistance Branch 

(HETAB) of the National Institute for Occupational Safety and 

Health (NIOSH) conducts field investigations of possible health 

hazards in the workplace. These investigations are conducted 

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

and Health Act of 1970, 29 U.S.C. 669(a)(6) which authorizes 

the Secretary of Health and Human Services, following a written 

request from any employer or authorized representative of 

employees, to determine whether any substance normally found 

in the place of employment has potentially toxic effects in such 

concentrations as used or found. HETAB also provides, upon 

request, technical and consultative assistance to federal, state, and 

local agencies; labor; industry; and other groups or individuals to 

control occupational health hazards and to prevent related trauma 

and disease. 

The findings and conclusions in this report are those of the 

authors and do not necessarily represent the views of NIOSH. 

Mention of any company or product does not constitute 

endorsement by NIOSH. In addition, citations to websites 

external to NIOSH do 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 Kenneth W. Fent of HETAB, Division 

of Surveillance, Hazard Evaluations and Field Studies and David 

Conover, an independent contractor. Industrial hygiene field 

assistance was provided by James Couch of HETAB. Expertise 

and field assistance in measuring magnetic fields was provided 

by Joseph Bowman of the Division of Applied Research and 

Technology. Health communication assistance was provided 

by Stefanie Evans of HETAB. Editorial assistance was provided 

by Ellen Galloway of the Education and Information Division. 

Desktop publishing was performed by Robin Smith of HETAB. 

Copies of this report have been sent to employee and management 

representatives at the research institution, the Colorado 

Department of Public Health and Environment, and the 

Occupational Safety and Health Administration Region 8 Office. 

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

report may be viewed and printed at http://www.cdc.gov/niosh/ 

hhe/. Copies may be purchased from the National Technical 

Information Service at 5825 Port Royal Road, Springfield, Virginia 

22161. 

Health Hazard Evaluation Report 2009-0171-3119 Page 37
 
Below is a recommended citation for this report: 

NIOSH [2011]. Health hazard evaluation report: evaluation of electromagnetic field 

exposures at a research institution’s laboratories and atomic time radio stations 

– Colorado. By Fent KW and Conover D. 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. 2009-0171-3119. 

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