TM

NIOSH HEALTH HAZARD EVALUATION REPORT 

HETA #2004-0094-2978 

National Park Service 

Hot Springs, Arkansas 

September 2005 

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health
ii

PREFACE

The Hazard Evaluation and Technical Assistance Branch (HETAB) of the National Institute for 

Occupational Safety and Health (NIOSH) conducts field investigations of possible health hazards in the 

workplace. These investigations are conducted under the authority of Section 20(a)(6) of the Occupational 

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

Human Services, following a written request from any employers 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. Mention of company names or products does not constitute 

endorsement by NIOSH. 

ACKNOWLEDGMENTS AND AVAILABILITY OF REPORT

This report was prepared by John Cardarelli II of HETAB, Division of Surveillance, Hazard Evaluations 

and Field Studies (DSHEFS). Field assistance was provided by Amanda Bryson, DSHEFS, and Timothy 

Radtke, Department of the Interior (DOI). Analytical support was provided by Dr. Henry Spitz, HealthRelated Energy Research Branch (HERB), DSHEFS. Mr. James R. Budahn, U.S. Geological Service 

(USGS), conducted the gamma spectrometry analyses, Mr. James D. Cathcart, USGS, conducted the Xray diffraction analyses, and Mr. Robert A. Zielinski, USGS, conducted the scanning electron microscope 

and energy dispersive X-ray analyses. Desktop publishing was performed by Robin Smith and Shawna 

Watts. Editorial assistance was provided by Ellen Galloway. 

Copies of this report have been sent to employee and management representatives at Hot Springs National 

Park and the OSHA Regional Office. This report is not copyrighted and may be freely reproduced. The 

report may be viewed and printed from the following internet address: http://www.cdc.gov/niosh/hhe. 

Single copies of this report will be available for a period of three years from the date of this report. To 

expedite your request, include a self-addressed mailing label along with your written request to: 

NIOSH Publications Office 

4676 Columbia Parkway 

Cincinnati, Ohio 45226 

800-356-4674 

After this time, copies may be purchased from the National Technical Information Service (NTIS) at 5825 

Port Royal Road, Springfield, Virginia 22161. Information regarding the NTIS stock number may be 

obtained from the NIOSH Publications Office at the Cincinnati address. 

For the purpose of informing affected employees, copies of this report 

shall be posted by the employer in a prominent place accessible to the 

employees for a period of 30 calendar days.
iii 

Highlighs of the NIOSH Health Hazard Evaluation

Highlights of the NIOSH Health Hazard Evaluation

Evaluation of Radiation Exposures at Hot Springs National Park

The National Institute for Occupational Safety and Health (NIOSH) received a Health Hazard Evaluation (HHE) 

request from Hot Springs National Park in January 2004 concerning radioactive mineral deposits in piping that were 

was removed from a bath house being renovated. In a site visit, investigators from NIOSH and the Department of 

the Interior (DOI) identified RradiumRadium-226 in the mineral deposits within the piping and provided 

recommendations regarding the safe handling of that material. NIOSH investigators returned to the park to conduct 

radon progeny measurements and collect water samples to evaluate potential exposures to radiation in air and water. 

What NIOSH and DOI Did

 Analyzed the drainage pipe removed from the 

Hale Bathhouse for radiation. 

 Took radiation measurements in several bath 

houses and the Administrative Building in the 

park. 

 Made radiation measurements in the Hale 

Bathhouse and the Administration Building to 

find the ratio between radon and its decay 

products. 

 Collected water samples from the Hale spring 

and the fountain just outside the Administration 

Building for radium and radon. 

 Collected soil and rock samples from the Hale 

Bathhouse basement to check for radioactive 

materials. 

What NIOSH and DOI Found

 High radiation levels were found in some areas 

in the basement of the Hale Bathhouse. 

However, these areas were not routinely 

occupied. 

 Two buildings (Hale Bathhouse and the 

Administration Building) had radon 

concentration levels above the EPA action limit. 

 Park officials had successfully reduced radon 

concentrations below the EPA action limit in 

the Hale Bathhouse basement. 

 The radon equilibrium factors estimated in the 

park buildings were lower than those typically 

found in indoor residential environments. 

 Radium concentration in the water samples 

from the Hale spring and the fountain were 

below the EPA maximum concentration limit. 

 The radon concentration in the water sample 

from the Hale Bathhouse spring (but not the 

public drinking fountain) was above the EPA 

maximum concentration limit. 

What Hot Springs National Park Managers 

Can Do

 Continue to check the radon concentrations in 

park buildings. 

 Complete radon remediation plans for the 

“Tower Room” in the basement of the 

administration building. 

 Start a routine water monitoring program to 

assure that radium and radon levels in publicly 

accessible fountains are below the EPA limits. 

What the Hot Springs National Park 

Employees Can Do 

 Learn more about the health effects associated 

with radon and radium exposures by visiting the 

EPA website www.epa.gov. 

What To Do For More Information:

We encourage you to read the full report. If you 

would like a copy, either ask your health and safety 

representative to make you a copy or call 1- 

513-841-4252 and ask for 

HETA Report #2004-0094-2978
iv 

Health Hazard Evaluation Report 2004-0094-2978 

National Park Service 

Hot Springs, Arkansas 

September 2005

John Cardarelli II, PhD, CHP, CIH, PE 

Timothy Radtke, MSEH, CIH (Dept of the Interior) 

Henry Spitz, PhD 

Amanda Bryson

SUMMARY

The National Institute for Occupational Safety and Health (NIOSH) received a Health Hazard Evaluation 

(HHE) request for technical assistance from the Department of the Interior (DOI) on January 13, 2004. 

The request described concerns about potential exposures to national park employees from naturally 

occurring radioactive mineral deposits in piping removed from renovated bathhouses at Hot Springs 

National Park (HSNP), Hot Springs, Arkansas. 

On January 26, 2004, NIOSH and DOI investigators made on-site radiation measurements and identified 

radium-226 (226Ra) in mineral deposits in water pipes. NIOSH investigators made recommendations 

regarding safe handling of the water pipes and also recommended conducting radon concentration 

measurements throughout HSNP. Gamma-radiation levels measured by NIOSH, the DOI, and the State of 

Arkansas in six bathhouses were low and similar to previously reported values, except for a few localized 

areas in the Hale Bathhouse basement. These areas of higher gamma-radiation were associated with rock 

in the bathhouse foundation which was rich in naturally occurring radioactive material (NORM), 

particularly 226Ra. On July 1, 2004, additional radon-progeny measurements and water samples were 

collected to assess radioactive constituents in the air and spring water. Radon-progeny measurements 

determine the amount of alpha activity in the air that could be inhaled. The alpha activity measurement is 

called a “Working Level” (WL) and determines if a respirator is recommended based on NIOSH criteria. 

These WL measurements are used with radon concentration measurements to calculate the equilibrium 

factor (EF). The EF is an important site-specific parameter because it is used to convert radon 

concentrations (picoCuries [pCi/L]) to WL estimates. The site-specific EF results indicated that the radon 

concentration and WL relationship in HSNP buildings behaved more like thermal spa environments than 

the typical indoor residential environment. 

Following the NIOSH recommendation, indoor radon measurements were made by park officials in every 

HSNP bathhouse and the park’s Administration Building between May 2004 and February 2005. Only the 

Hale Bathhouse and the Administration Building Tower Room had airborne radon concentrations above 

the U.S. Environmental Protection Agency (EPA) recommended remedial action level of 4 pCi/L. The 

Tower Room, not routinely occupied or accessible to building occupants, was posted with a warning sign. 

Water sampling showed that 226Ra concentrations in the Hale spring water were below the proposed EPA 

maximum concentration limit (MCL = 5 pCi/L), but above the proposed EPA MCL (300 pCi/L) for 222Rn 

(the Administration Building public water fountain source did not exceed either proposed limit). 

NIOSH investigators conclude that a potential health hazard exists for some workers at the 

HSNP due to the elevated radon concentrations in the Hale Bathhouse basement and the 

Administration Building Tower Room. Remedial actions and ongoing radiation monitoring 

by HSNP officials have reduced exposure potentials to levels as low as reasonably 

achievable. NIOSH investigators recommend continued routine radon monitoring and starting 

a water monitoring program for radium and radon in public drinking water. 

Keywords: NAICS 712190, Nature Parks and Other Similar Institutions, HSNP, NORM, radiation, 

Radium, radon, working level, equilibrium factor, natural springs, bathhouse 
Table of Contents 

Preface..........................................................................................................................................................ii

Acknowledgments and Availability of Report..........................................................................................ii

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

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

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

Background .................................................................................................................................................1

Hot Springs National Park (HSNP).......................................................................................................1

Creation of Hot Springs..........................................................................................................................2

Discovery of the Radiation Problem..........................................................................................................2

Methods........................................................................................................................................................3

Evaluation Criteria .....................................................................................................................................4

Ionizing Radiation...................................................................................................................................4

Radium.....................................................................................................................................................5

Radon in Air ............................................................................................................................................5

OSHA Interpretation of Radon in the Workplace...........................................................................6

EPA Recommendations and Action Levels for Radon ....................................................................6

Radon in Water.......................................................................................................................................7

Health Effects from Radium and Radon Exposures............................................................................7

Results and Discussion................................................................................................................................8

Historical Radiation Characterization..................................................................................................8

Radiation Measurements........................................................................................................................8

Soil and Rock Samples............................................................................................................................8

Radon Concentrations in Air.................................................................................................................9

Hale Bathhouse Radon Remediation...............................................................................................10

Administration Building Radon Remediation................................................................................10

Working Level (WL) Measurements and Equilibrium Factor (EF) Estimate ............................11

Radium and Radon Concentrations in Water....................................................................................12

Personal Protective Equipment ...........................................................................................................12

Respirator Selection..........................................................................................................................12

Conclusions................................................................................................................................................13

Radiation................................................................................................................................................13

Disposal of Pipe Containing NORM....................................................................................................13
Radon Concentrations in Air...................................................................................................................13

Radium and Radon Concentration in Water .....................................................................................13

Recommendations.....................................................................................................................................13

Radiation................................................................................................................................................13

Disposal of NORM ................................................................................................................................14

Radon Concentrations in Air...............................................................................................................14

Radium and Radon Concentrations in Water....................................................................................14

References..................................................................................................................................................15

Tables .........................................................................................................................................................18

Appendices.................................................................................................................................................23
Health Hazard Evaluation Report No. 2004-0094-2978 Page 1 

INTRODUCTION

The National Institute for Occupational Safety and Health (NIOSH) received a Health Hazard Evaluation 

(HHE) request from the Department of the Interior (DOI) on January 13, 2004. The request concerned 

potential radiation exposures to park employees from radioactive mineral deposits in piping that was 

removed from Hot Springs National Park (HSNP) bathhouses undergoing renovation. Radioactive 

contamination was detected at a salvage yard/landfill that refused to accept the pipes.1

 On January 26, 

2004, a site visit was conducted at HSNP. Investigators from NIOSH and DOI performed radiation 

measurements that identified radium-226, (226Ra) in the mineral deposits within the piping. 

Recommendations were provided by NIOSH regarding the safe handling of the material. On July 1, 2004, 

NIOSH investigators returned to HSNP to conduct radon progeny measurements and collect water 

samples to evaluate exposure to radiation and radioactive materials in the air and water. 

BACKGROUND

Hot Springs National Park (HSNP) 

In 1803, HSNP became a U.S. territory as part of the Louisiana Purchase. By 1807, the first permanent 

settlers to reach the Hot Springs area realized the springs' potential as a health resort. In 1832 Hot Springs 

was set aside as a U.S. Government reservation by act of Congress. In its earlier conception, Hot Springs 

could not be considered a national park because the sole purpose of its establishment was as a national 

reservation to alleviate human ills. The waters, believed to possess medicinal value, were available to all 

and their commercial exploitation was prevented.2

 By the 1830s, log cabins and a store had been built to 

accommodate visitors to the springs. In 1877 the U.S. courts formally established government control. 

In 1884 the government enclosed Hot Springs creek in an underground arch for flood and sewage control. 

By 1901 all of the springs had been walled up and covered for protection. Between 1912 and 1922 the 

wooden bathhouses built in the 1880s were replaced by fire-resistant brick and stucco structures (Figure 

1; Superior, Hale, Maurice, Fordyce, Quapaw, Ozark, Buckstaff, and Lamar). A more complete 

chronology of events from 1803 to 1993 is available on the HSNP website.3

Figure 1: Distribution of springs and bathhouses at HSNP. (Source: Epperson and Rhodes, 1990) 

In 1905, a professor from Yale University showed that the hot spring waters contained a measurable level 

of radioactivity, due primarily to the presence of dissolved radon gas, a natural decay product of radium. 

These two elements come from the radioactive decay of uranium and thorium found in the rock through 

which the thermal waters flowed. Both radon and radium were considered historically to have curative 

properties. 
Page 2 Health Hazard Evaluation Report No. 2004-0094-2978 

Following the creation of the National Park Service (NPS) in 1916, the Hot Springs Reservation became 

the 18th national park on March 4, 1921. Its designation as a national park accompanied the final phase of 

remodeling or construction of the current eight bathhouses on Bathhouse Row. However, by the 1960s the 

bathing industry in the park and in the city had declined considerably. The Fordyce Bathhouse was the 

first to close in 1962, followed by the Maurice, the Ozark, and the Hale in the 1970s. Between 1984–

1885, the Quapaw, Superior, and Lamar closed, leaving the Buckstaff as the only bathhouse still 

operating on Bathhouse Row.4

In its current configuration, most of the springs are covered, with their water running through 

underground pipes rather than filtering down over the hillside. The Hot Springs Creek flows through a 

tunnel beneath Central Avenue, and the valley floor has been flattened to make it wider. 

Bathhouse Row and its environs were placed on the National Register of Historic Places on November 

13, 1974. The desire to revitalize Bathhouse Row also led citizens to campaign for adaptive uses of the 

vacant buildings. The most elegant bathhouse, the Fordyce, has been adapted for use as a visitor center 

and museum. Today, nearly all the empty bathhouses are under consideration for adaptive renovation.4 

Creation of Hot Springs 

Thermal springs occur throughout the United States, particularly where there has been recent volcanic 

activity, although they are rare in the central part of the continent. An unusual set of geologic conditions 

has created and maintained the flow of hot waters in central Arkansas. 

Although some believe the hot springs at HSNP originate from waters rising from hot magmas deep in the 

earth, their origin has been determined by USGS geochemists to be the result of rainwater that fell into 

the valley some 4,000 years ago. This rainwater percolated into the earth’s crust about 6,000 to 8,000 feet 

where cracks and fractures then provided a quick route to the surface. This water is heated by the energy 

released from natural radioactive decay of potassium, uranium, and thorium in the earth’s crust as well as 

from heat generated from compression of the planet’s interior by gravity. Carbon-14 dating suggests that 

the spring water is about 4,000 years old. 

The springs emerge in a compact belt along the southwestern slope of Hot Springs Mountain. During the 

past century, excavation and covering of springs have reduced the number of spring openings from 72 to 

fewer than 40. The purpose of this work was to increase and concentrate spring water flow to a central 

reservoir from which the water can be redistributed to individual bathhouses and public drinking 

fountains (Figure 1). While individual springs vary in the amount of water they discharge (some are mere 

seeps), each opening is completely encased in metal and concrete and capped with a gas-tight metal 

hatch.5

 The amount of water discharged by all the hot springs ranges from about 750,000 to 950,000 

gallons per day. USGS studies have shown that the discharge is highest in winter. 

Discovery of the Radiation Problem 

In January 2004, the NPS Midwest Regional Office contacted the DOI concerning the 

bathhouse drainage pipes rejected by a salvage yard/landfill because of radioactive 

contamination. This initiated a series of actions by DOI to assess the potential 

radiological hazards to contractors and NPS employees performing renovation work 

at HSNP, including a technical assistance request to NIOSH to help evaluate the 

potential radiological hazards. 

The pipe (Photo 1) rejected by the landfill was stored in a hazardous waste locker 

in the maintenance area of the park. A NIOSH investigator measured an exposure 

rate near the surface of about 50 micro Roentgens per hour (μR/hr). Although the 

Photo 1: Drainage 

pipe with radioactive 

scale. 
Health Hazard Evaluation Report No. 2004-0094-2978 Page 3 

pipe was wrapped in plastic, the State of Arkansas recommended treating and disposed of it as naturally 

occurring radioactive material (NORM) waste material. 

METHODS

Site visits were conducted by NIOSH investigators in January and July 2004. The purpose of the initial 

evaluation was to positively determine if the radium, radon, and other radionuclides were natural or from 

an external contaminant. Previous DOI measurements at HSNP had identified the following NORM: 

Radium-226 (226Ra), radon-222 (222Rn), and the short-lived radioactive decay products of radon.5

A portable gamma spectrometer (Exploranium GR-135) was used to verify that radiation emitted from the 

piping was NORM. The spectrometer enables the user to locate contamination, estimate dose (measure 

and determine the hazard level), and analyze (identify) nuclides for risk assessment. The spectrometer has 

four detectors (sodium iodide [NaI], Geiger-Müller [GM], neutron, and cadmium-zinc-tellurium [CZT]) 

to measure and analyze multiple radiation fields. The 4.0 cubic inch NaI(Tl) detector is used to detect and 

analyze gamma radiation to identify gamma emitting radionuclides. The GM detector is used to detect the 

presence of gamma radiation while the solid state neutron detector is coupled with a miniature 

photomultiplier tube. The CZT detector’s resolution is approximately twice that of NaI and is used in 

special applications to improve the nuclide identification capability. 

On January 26, 2004, DOI and NIOSH investigators measured 

radiation in the basement of the Hale Bathhouse from which the 

piping was removed (Photo 2). Sampling locations were identified 

using an Exploranium GR-135 (Photo 3) which identified higher 

radiation intensities in the rock and soil. A piece of the rock 

foundation and several basement soil samples were collected and 

sent to a USGS laboratory for mineral analyses by X-ray 

diffraction and gamma spectrometry. Additional gamma-radiation 

measurements were made throughout the basements of the 

remaining seven bathhouses by DOI and State of Arkansas 

investigators. 

During the second site visit in July 2004, 

NIOSH investigators collected water samples 

and measured radon and short-lived radon 

decay products in the basement and on the first 

floor of the Hale Bathhouse. The water 

samples were collected from the spring located 

in the basement of the Hale Bathhouse and 

from the public fountain in front of the HSNP 

Administration Building (Photo 4). These 

samples were sent to a NIOSH contract 

laboratory for analyses of 226Ra and 222Rn 

concentrations. 

Photo 2: Hale Bathhouse. Hot Springs 

National Park, Hot Springs, Arkansas. 

Photo 3: NIOSH investigator 

making radiation measurements 

in the Hale Bathhouse basement. 

This area’s elevated natural 

background radiation level from 

radium-226 was identified via 

gamma spectrometry. 

Photo 4: NIOSH 

investigator collecting 

a water sample from a 

public fountain.
Page 4 Health Hazard Evaluation Report No. 2004-0094-2978 

Measurements of radon progeny concentrations in air were performed using the method described by 

Thomas6

 which involves collecting radon progeny on an air filter and measuring the alpha activity of the 

radon decay products after sampling is ended (Photo 5). The radon 

progeny are RaA: 218Po, RaB: 214Pb, and RaC: 214Bi. The sensitivity of 

the Thomas method is approximately 1 pCi/La

. A 5-minute air sample 

was collected on 37 mm diameter Teflon® (polytetrafluoroethylene) 

filters (0.5 μm pore size). The total alpha disintegrations were 

measured in three successive time intervals and the radon progeny 

concentration was determined in units of Working Level. The activity 

equilibrium between radon and its short-lived progeny in air is 

inversely related to the ventilation of air in the space being measured. 

The appropriate level of respiratory protection is determined by the 

WL exposure and is based on the NIOSH Recommended Standard 

for Occupational Exposures to Radon Progeny in Underground 

Mines.7

 Although these bathhouses are not underground mines, the 

radon concentration and radon sources, spring water, and radium 

deposits are similar to those found in underground mines. Therefore 

the NIOSH recommendations for mines are applicable to this 

environment. 

EVALUATION CRITERIA

As a guide to the evaluation of the hazards posed by workplace exposures, NIOSH field staff use 

environmental evaluation criteria to assess a number of chemical and physical agents. For chemical 

agents, the primary sources of environmental evaluation criteria for the workplace are: (1) NIOSH 

Recommended Exposure Limits (RELs),7

 (2) the American Conference of Governmental Industrial 

Hygienists’ (ACGIH®) Threshold Limit Values (TLVs®),8

 and (3) the U.S. Department of Labor, 

Occupational Safety and Health Administration (OSHA) Permissible Exposure Limits (PELs).9

 For 

physical agents such as ionizing radiation, the primary sources of environmental evaluation criteria for the 

workplace are: (1) the National Council on Radiation Protection and Measurements (NCRP) limits of 

exposure to ionizing radiation,10 (2) the International Commission on Radiological Protection (ICRP) 

limits of exposure to ionizing radiation,11 (3) the U.S. Department of Labor, OSHA PELs,9

 (4) the U.S. 

Department of Energy (DOE) standards for external and internal exposure,12 (5) the U.S. Nuclear 

Regulatory Commission (NRC) occupational dose limits,13 (6) the U.S. Environmental Protection Agency 

(EPA) federal radiation protection guidance for occupational exposure,14 (6) the Food and Drug 

Administration (FDA) performance standards for ionizing radiation emitting products,15 (7) the U.S. 

Department of Transportation (DOT) radiation limits for transportation of radioactive materials,16 (8) the 

International Air Transportation Association (IATA) radiation protection and quality assurance 

programs,17 and (9) the International Atomic Energy Agency (IAEA) occupational radiation protection 

safety standards.18 Employers are encouraged to follow the limits most applicable to their specific agency. 

In this work environment the OSHA PELs are the most appropriate criterion. 

Ionizing Radiation 

Natural radiation background exposure varies around the world from less than 0.005 mR/hr to more than 

2.5 mR/hr19, producing an annual dose of about 40 millirem (mrem) to 22,000 mremb

, respectively. The 

greatest dose is due to anomalous, localized deposits of NORM. Variations in the natural radiation 

 

a 1 pCi/L = 37 Becquerel per cubic meters (Bq/m3

)

b A millirem is a unit of measure of ionizing radiation exposure of living tissues that takes into account the differences in biological harm 

(Relative Biological Effectiveness [RBE factor]) caused by different types of ionizing radiation.

Photo 5: Upper left corner shows 

a Pylon® radon monitor. Center 

shows a SKC Airchek HV30 Air 

Sampler and filter cassette, 

which is used to capture radon 

progeny. The filter is removed 

and the alpha disintegrations are 

recorded by a scaler counter.
Health Hazard Evaluation Report No. 2004-0094-2978 Page 5 

background also occur with altitude and living conditions. The average annual background dose in the 

United States has been reported to be about 360 mrem. Radon exposure is responsible for about 55% of 

background dose (about 200 mrem) and is greater where the presence of NORM material (uranium and 

thorium) is elevated. Cosmic radiation produces an annual dose of 27 mrem (8%) and terrestrial radiation 

from NORM in the crust of the earth accounts for 28 mrem (8%). Radiation exposure from internally 

deposited radioactive material, mainly potassium-40, delivers about 39 mrem (11%) to each person. 

Medical and other manmade sources of radiation exposure (including consumer products) account for 

about 63 mrem (18%). Other industrial sources of radiation exposure account for only 3 mrem (0.3%) and 

include the nuclear fuel cycle, fallout, and artificial sources. 

Important forms of ionizing radiation include the alpha and beta particles and gamma rays emitted from 

radioactive materials. These are called ionizing radiation because they can remove (knock) electrons out 

of atoms and molecules, creating electrically charged particles called ions. This ionization process 

transfers energy from the radiation to the irradiated material, and can cause chemical and physical 

changes in human tissue. The various types of ionizing radiation differ widely in their abilities to 

penetrate tissue and deposit energy. Alpha particles travel only a very short distance (less than 1 mm) in 

living tissue and thus cannot penetrate the skin. These particles are present with radon and two of the 

radon decay products. Beta particles are identical to electrons, are thousands of times smaller than alpha 

particles, and can penetrate deeper into tissue. However, they are easily stopped by a thin sheet of metal 

foil. Gamma rays have no mass or electrical charge, and travel much greater distances than either alpha or 

beta particles. This means their energy is deposited over a longer path and is relatively unlikely to damage 

living tissue unless the exposure rate is high.20 It was gamma radiation that was measured from the pipes 

removed from the Hale Bathhouse from naturally enhanced 226Ra (Appendix I). 

Radium 

Radium, formed upon the radioactive decay of uranium and thorium, is a naturally occurring silverywhite radioactive metal that can exist in several forms called isotopes. Two of the main radium isotopes 

found in the environment are 226Ra (uranium decay series; Appendix I) and radium-228 (228Ra, thorium 

decay series). Historically, radium has been used as a radiation source for treating cancer and in 

radiography of metals. It has been combined with other metals as a neutron source for research and 

radiation instrument calibration. Radium was also a component of luminous paints used for watch and 

clock dials, aircraft instrument panels, military instruments, and compasses. The EPA has set a drinking 

water limit of 5 pCi/L for 226Ra and 228Ra (combined). 

Radon in Air 

Radon is a colorless, odorless, tasteless, radioactive gas formed from the radioactive decay of radium in 

the uranium decay chain (Appendix I). Uranium and radium are found around the world in soil, rocks, and 

water at various concentrations. Because radon is a gas, it may escape into the air from the material in 

which it is formed; therefore radon gas is ubiquitous outdoors as well as indoors. High concentrations of 

radon can accumulate in poorly ventilated indoor locations or when a large amount of 226Ra is present. As 

shown in Appendix I, radon decays with a half-life of about 4 days into a series of solid, short-lived 

radioisotopes commonly called radon daughters or progeny. Two progeny, polonium-218 and polonium214, emit alpha particles and are responsible for most of the health effects associated with inhalation of 

radon and its decay products. The following chart shows the concentration limits for radon and radon 

progeny developed by several national and international agencies which are intended to limit the health 

effects from exposure to these radioactive materials. 
Page 6 Health Hazard Evaluation Report No. 2004-0094-2978 

NIOSH Recommended Exposure 

Limits 

1 

0.083 

0.083 

20.8 

16.6 

8.3 

WLM / year (2040 hrs per year) 

WLM (170 hrs) 

WL (average concentration per work shift) 

pCi/L (40% Equilibrium Factor; EF) 

pCi/L (50% EF) 

pCi/L (100% EF) 

100 pCi/L (40 hr work week) 

25 pCi/L (posting requirement for airborne radioactivity) OSHA Permissible Exposure 

Limits (1971 regulation) 

3 pCi/L (40 hr work week for workers less than 18 yrs old) 

NRC Occupational Exposure 30 pCi/L (yearly avg); Derived Air Concentration 

Limits 3 pCi/L (yearly avg for workers less than 18 yrs old); 10% adult 

EPA Recommended Public Limit 4 pCi/L (non-occupational action limit to initiate remediation efforts) 

IAEA Recommended 

Occupational Dose Limits* 

4 

32.4 

WLM 

pCi/L (2000 hrs per year; 40% EF) 

WLM = Working Level Months pCi/L = picoCuries per liter 

* The IAEA recommendations correspond to an annual effective dose of 2 rem (0.02 Sievert, Sv). 

The major route of radon exposure is inhalation. The typical concentration range for radon in ambient air 

is 0.003 to 2.6 pCi/L. A typical level of radon found indoors in homes, schools, or office buildings is 

about 1.5 pCi/L, although much higher concentrations (> 200 pCi/L) have been measured. Persons who 

work with uranium and phosphate fertilizers, persons living near uranium mines and processing facilities, 

and persons handling fossils and other artifacts rich in uranium or radium have a greater chance of being 

exposed to higher levels of uranium, radium, and radon than the general population. 

OSHA Interpretation of Radon in the Workplace 

In December 2002, OSHA provided guidance on its regulations regarding proper interpretation of the 

workplace radon standards (Appendix II).21 The OSHA standard refers to airborne radioactive material 

exposure limits in Table I and Table II of Appendix B to 10 CFR Part 20 that was published by the 

Atomic Energy Commission (AEC) in 1969. Both the AEC and the OSHA limits were for a 40-hour 

exposure in any workweek of 7 consecutive days. In 1996 the OSHA standard was redesignated as 29 

CFR 1910.1096, although no changes were made to the exposure limits. The Nuclear Regulatory 

Commission (NRC) has since changed the format of the tables in Appendix B of 10 CFR Part 20 and 

converted the limits to annual averages, reduced the radon exposure limits, and moved limits for miners 

from the table to the regulatory text. 

Case law supports the interpretation that the original version of a referenced federal regulation is the 

enforceable regulation. Therefore, the 1969 version of Appendix B to 10 CFR Part 20 that was referenced 

in the original OSHA ionizing radiation standard in 1971 is enforceable. The applicable 222Ra exposure 

limit issued by OSHA in 1971 for adult employees is 100 pCi/L averaged over a 40-hour work week. 

However, many requirements of the current NRC regulation provide as much or more protection than the 

OSHA standard for workers exposed to airborne radioactive materials. A series of questions and answers 

regarding radon exposure in the workplace is provided in Appendix II. 

EPA Recommendations and Action Levels for Radon 

The recommendations and action levels for indoor radon provided by the EPA are not enforceable for a 

working environment. However, the EPA and the U.S. Surgeon General issued a Health Advisory that 

recommends testing all homes for radon below the third floor and testing schools nationwide for radon. 
Health Hazard Evaluation Report No. 2004-0094-2978 Page 7 

They also recommended abating homes with radon levels that are at or above 4 pCi/L, the EPA National 

Voluntary Action Level. This level represents a radon concentration where the cost of remediation is 

warranted by the risk of health effects. The EPA believes that the indoor radon concentration can be 

lowered to 2 pCi/L fairly simply, and encourages homeowners, home builders, and building code 

organizations to construct radon-resistant homes. Radon testing is encouraged when existing homes are 

sold. The EPA and has published a pamphlet entitled “A Citizen's Guide to Radon: The Guide to 

Protecting Yourself and Your Family from Radon," which is available from the EPA website, 

http://www.epa.gov/iaq/radon/pubs/citguide.html. 

Radon in Water 

The EPA is proposing new public health standards for radon in drinking water. The proposal provides two 

options to states and community water systems for reducing radon health risks in both drinking water and 

indoor air. Information about the proposed rule and information relating to the status of the rule can be 

found at: www.epa.gov/safewater/radon.html. 

The proposed regulation provides that states may adopt Multimedia Mitigation (MMM) programs and the 

Alternative Maximum Contaminant Level (AMCL) in water of 4,000 pCi/L. According to the EPA, the 

AMCL is the most effective approach for radon risk reduction and the one the EPA expects most states to 

adopt. In the absence of this regulatory expectation, small (10,000 or fewer customers) Community Water 

Systems (CWS) are expected to comply with a level of 4,000 pCi/L in drinking water, and develop and 

implement a state-approved local MMM program plan to reduce indoor radon risks from soil and rock 

under homes and buildings. If Arkansas has an approved MMM program plan, the 4,000 pCi/L standard 

for radon in drinking water would be adopted to obtain primacy. Under the proposed requirements, an 

MMM program plan must address four criteria: 

1. Public involvement in development of the MMM program plan 

2. Quantitative goals for existing homes fixed and new homes built radon resistant 

3. Strategies for achieving goals 

4. Plan to track and report results 

The CWS must monitor radon in drinking water22, and report its results to the state. If the radon level is 

below 300 pCi/L, the CWS will need only to continue to meet monitoring requirements and will not be 

covered by the requirements regarding MMM programs.22

Health Effects from Radium and Radon Exposures 

Cancer is the major health effect of concern from exposure to radium, radon, and its short-lived progeny. 

Oral exposure to radium is known to cause lung, bone, brain, and nasal passage tumors in humans. 

Inhalation exposure to radon may cause lung cancer in humans. The EPA has classified radium as a 

Group A, human carcinogen, but it has not classified radon for carcinogenicity. Chronic exposure to 

radon in humans and animals via inhalation has resulted in respiratory effects (chronic lung disease, 

pneumonia, fibrosis of the lung), while animal studies have reported effects on the blood and a decrease 

in body weight. Smokers exposed to radon are at greater risk for lung cancer (approximately 10 to 20 

times) than are nonsmokers similarly exposed. No information is available on the acute (short-term) 

effects of radium or radon in humans.23 
Page 8 Health Hazard Evaluation Report No. 2004-0094-2978 

Photo 6: Radiation measurement in the 

Hale Bathhouse basement. A natural 

spring is on the left behind a wooden 

wall. The radiation intensity exceeded 

2,500 μR/hr at wall contact.

RESULTS AND DISCUSSION

Historical Radiation Characterization 

Studies of the springs at HSNP have found that the radioactivity is due mostly to dissolved radon and 

radon progeny with a small contribution from radium.5

 In 1953, the radon concentration among 25 

springs ranged from 140 to 30,500 pCi/L. In 1990, indoor basement radon concentrations among the eight 

bathhouses ranged from 3.1 to 43.7 pCi/L, with the highest levels in the Hale Bathhouse. Radon 

concentrations in all the remaining bathhouses were below 10 pCi/L. In 1979, the EPA reported radium 

concentration in the waters to be 2.1 ± 0.22 pCi/L. 

Radiation Measurements 

The radiation levels in the six current bathhouses ranged from 5 to 

50 μR/hr and were in general agreement with historical values 

(Table 1). The exceptions were a few localized areas, identified as 

“hot spots,” which had radiation levels above background (greater 

than 100 μR/hr) when measured on contact with the surface (Photo 

6). These stationary “hot spots” are located along the pathway of 

the natural spring water, where NORM (radium) concentrates in 

the rock matrix (see Soil and Rock Samples discussion below). 

The radiation intensity is greatly reduced, however, with 

increasing distance from these stationary locations and present 

little hazard to building occupants because these “hot spots” were 

in non-occupied bathhouse basements. 

Soil and Rock Samples 

The USGS used X-ray diffraction to analyze samples 

taken from the east foundation wall of the Hale 

Bathhouse (Photos 7–8). The non-black rock sample 

was primarily quartz (93.2%) and kaolinite (6.8%). 

The black rock sample consisted of calcite (58.8%), 

quartz (5.6%), romanechite (28.9%), and wurtzite 

(6.7%). Romanechite is a hydrated barium manganese 

oxide and is not a well known mineral. It is the 

primary constituent of psilomelane, which is 

sometimes treated as a mineral, a mixture of 

minerals, or as a rock. However, romanechite is 

being used as the name for specimens previously 

known as psilomelane.24 The floor dust sample 

consists of quartz (91.2%), calcite (5.3%), and albite 

(3.4%). 

Three factors may contribute to the elevated external radiation levels and radon concentrations measured 

in the Hale Bathhouse. First, most of the lower level of the Hale Bathhouse is a full basement with a 

small, unexcavated crawl space. While this configuration is not unique to the Hale Bathhouse, park 

officials believe that a low production, uncaptured geothermal water source may run between the 

overburden and the bedrock, striking the northeast basement wall and under the dirt crawl space. The 

floor is a porous mixture of concrete and natural soil base that permits radon to easily diffuse from the 

soil into the basement. The lack of concrete foundation walls also presents less shielding for radium in the 

Photos 7 and 8: Scanning Electron Microscope 

images from the Hale Bathhouse foundation wall 

(May 2004; USGS). X-ray analyses identified the 

mineral romanechite.
Health Hazard Evaluation Report No. 2004-0094-2978 Page 9 

soil and ground water. Second, a natural spring exists in the accessible basement northeast area that may 

serve as a radon source if the enclosure is opened and the active ventilation system is turned off (Photo 9). 

The third factor is the natural rock wall foundation, which contains deposits rich in NORM material. 

Direct measurements of external radiation were highest near dark-colored foundation material. 

Radioactivity analyses of samples from the basement foundation indicate large amounts of 226Ra and its 

decay products (214Pb, 214Bi, and 210Pb) are in secular equilibrium with 226Ra (Table 2). Secular 

equilibrium conditions exist when the decay products chemically stay with the parent and eventually 

reach the same concentration as the parent. This occurs because 

the decay product half-lives are shorter than their respective 

parent (see Appendix I). 

These three factors suggest that 226Ra concentration has been 

naturally enhanced, most likely due to a geochemical process 

involving the minerals calcite and romanechite identified by 

USGS in the black- colored foundation material. These minerals 

are chemically similar to radium and attract, or scavenge, the 

radium in the water migrating through the rocks and soil, thereby 

enhancing the radium concentration in the mineral. Although 

calcite and romanechite are not naturally radioactive, they can 

become so by this scavenging process. 

Two other observations from the data presented in Table 2 are 

worthy of discussion. First, a portion of the sample of refuse obtained from the black wall may have 

contained basement floor soil. The other basement floor sample was obtained from an area beneath the 

northwest staircase (see Photo 3). According to park officials, the spring water migrates beneath this area 

toward the main drainage conduit in front of the building. This area also had elevated external radiation 

levels with high enough activity to identify 226Ra with the Exploranium GR-135 portable gamma 

spectrometer. This basement soil sample contained calcite (5.3%), which may serve as the chemical 

scavenger for radium from the spring water, thereby accounting for the elevated radium concentration. 

The second observation is the unexpected disparity between the radionuclides of 226Ra and 228Ra, with an 

activity ratio of 226Ra / 228Ra ranging between 1,380 to 2,006 in the black foundation samples; 117 to 120 

in the refuse from the foundation sample, 48 to 53 in the basement soil samples, and 1.8 to 2.5 in the nonblack foundation sample. Actinium-228 (228Ac, half-life of 6.2 hr) is a gamma-emitting decay product in 

the 232Th decay series and is the first progeny of 228Ra (half-life of 6.7 years). Because 228Ac is always in 

equilibrium with 228Ra, it is used to estimate 228Ra concentrations. The apparent difference in the 

concentration of 226Ra (from the uranium decay chain) and 228Ra (from the thorium decay chain) in the 

spring water, rock, and soil is likely due to geological and geochemical factors and the significantly 

greater solubility of uranium that often results in greater amounts of 226Ra relative to 228Ra.25 Additionally, 

there is less information on 228Ra concentrations in groundwater than for 226Ra. However, the data show 

that high concentrations of 226Ra occur more frequently than 228Ra, which may also be due to the higher 

mobility of uranium than thorium or to a local enrichment in the uranium through which the spring water 

migrates.26 In general, the 228Ac results indicate that the thorium decay series only contribute to natural 

background radiation levels in the Hale Bathhouse. 

Radon Concentrations in Air 

Because radium was identified as the radionuclide of concern during the first site visit in January 2004, 

NIOSH and the DOI recommended conducting radon measurements in the Hale Bathhouse and other 

locations throughout the park.27 The park purchased real-time radon monitoring equipment and collected 

hourly radon measurements in several park buildings (Table 3). These data are included in this report 

Photo 9: Natural spring in the basement 

of the Hale Bathhouse. The white pole 

was used to obtain the water samples. 
Page 10 Health Hazard Evaluation Report No. 2004-0094-2978 

because the measurements are relevant to the findings, conclusions, and recommendationsc. The real-time 

hourly indoor radon measurements were conducted at various times and in various locations of every 

bathhouse and the Administration Building between May 2004 and February 2005. Only the Hale 

Bathhouse and the Administration Building exhibited elevated radon concentrations. 

Hale Bathhouse Radon Remediation 

Prior to remediation, the Hale Bathhouse radon levels ranged between 45 to 90 pCi/L at the natural spring 

near the northeast basement wall, and up to 225 pCi/L in the crawl space (Photo 10). During the second 

site visit, we evaluated the ventilation system in the Hale Bathhouse basement. Two fans (one near the 

northeast corner, the other near the southwest corner) exhausted basement air to the outside, potentially 

creating negative pressure in the basement, which could increase diffusion of radon from the surrounding 

soil into this space. Following a NIOSH recommendation, park officials reversed the airflow in the 

southwest fan to supply outside make-up air to the basement (the northeast fan continued to exhaust air). 

This interim ventilation adjustment eventually reduced the radon concentration in the basement and crawl 

space to 40 pCi/L and 125 pCi/L, respectively. In January 2005, HSNP replaced these fans with four 

higher capacity units balanced so that three fans exhausted air to the 

outside while one supplied outside air to the basement. The exhaust fans 

were installed in the crawl space, near the basement northeast wall, and 

near the northwest staircase. The supply fan was installed in the 

southwest basement area. This more efficient ventilation system reduced 

the basement radon concentrations to below 2 pCi/L. Because the 

general basement area was below the EPA action limit of 4 pCi/L, 

continued monitoring of the crawl space was not warranted. 

Administration Building Radon Remediation 

A 285,000 gallon tank is located below the administration building and 

serves as the main reservoir for the spring water (Figure 1). Radon 

emanating from this tank is the main source for radon in this building. Prior to any remediation efforts, 

the radon concentrations throughout the Administration Building ranged between 40 and 50 pCi/L in the 

basement “Tower Room,” 10 and 12 pCi/L in the general basement area (outside the Tower Room), and 

up to 12 pCi/L on the first and second floors. 

Supply and return air for the building’s ventilation system was located in the basement, an arrangement 

that provided an opportunity for radon-enriched air from the basement Tower Room area to migrate into 

the general basement area and eventually be distributed throughout the building. Park officials recognized 

this problem and installed a plastic sheet barrier (June to August timeframe) in the way door to the Tower 

Room to minimize cross contamination. This effort successfully reduced the radon concentrations in the 

basement to 4 to 5 pCi/L and the first and second floor radon concentrations to less than 2 pCi/L. The 

Tower Room radon concentration was also reduced to 20– 25 pCi/L via a small exhaust fan. Before this 

interim remedial action, park officials stated that the small exhaust fan in the Tower Room was likely 

overwhelmed by the blower fan in the building ventilation system. They have since installed a permanent 

door between the Tower Room and the general basement area that has reduced radon concentrations 

down to 2–4 pCi/L in the general basement area. The Tower Room radon concentrations did not change. 

 

c

 Permission to use these data was obtained through personal communications between the author and a HSNP 

official, 2005. 

Photo 10: Crawl space in the 

Hale Bathhouse 
Health Hazard Evaluation Report No. 2004-0094-2978 Page 11 

Working Level (WL) Measurements and Equilibrium Factor (EF) 

Estimate 

WL measurements of radon progeny were performed in the Hale 

Bathhouse and Administration Buildings (Table 4 and Photo 11). 

The concentration of progeny in equilibrium (EF=100%) with 100 

pCi/L of radon gas in air is defined as 1 WL. The concentration of 

the radon progeny in air is very dependent upon ventilation and 

humidity, so the EF varies accordingly. The EF estimates provide a 

site-specific factor to convert radon concentration measurements 

from pCi/L to WL estimates. WL exposure estimates determine if 

workplaces are compliant with recommended exposure limits and 

also provide guidance on the appropriate level of personal 

protection needed if administrative and engineering controls are 

unable to reduce radon levels to acceptable concentrations. 

Without a site-specific EF estimate, the average residential indoor 

environmental value of 40% is typically used. 28 

Vogiannis et al. reported that EFs in thermal baths range between 5% and 75%.29 The EFs measured in 

the Hale Bathhouse ranged between 5% and 8% and are consistent with Vogiannis et al. This means these 

building environments represent chronic exposure scenarios found in thermal spas (e.g., similar 

temperature and humid conditions). The Hale Bathhouse WL measurements demonstrate the significance 

of ventilation and humidity on the EF. The EF in the basement area near the northeast corner was reduced 

when the building ventilation was activated. The radon concentration and EF were reduced from 91 pCi/L 

to 31.5 pCi/L and 8.16% to 4.98%, respectively, over a period of about 16 hours. More dramatic 

reductions were realized in the Hale basement crawl space measurements, even though the crawl space 

was passively ventilated. Although humidity was not measured, a NIOSH investigator conducted the WL 

measurements in the crawl space and noted that it was substantially hotter and more humid than the 

general basement area. Vogiannis et al. reported that high humidity under chronic conditions reduces the 

EF because of the solubility of radon in water vapor.29 This may explain why the crawl space EF estimate 

was lower than the general basement EF estimate. 

The EF for the Administration Building (9.05%) was greater than all the values for the Hale building. One 

explanation is that the Administration Building, with lower temperatures and relative humidity, is more 

like a residence than a thermal spa. However, the EF was still lower than the 40% typically assumed for 

residential housing. This difference may be explained several factors affecting EF estimates. 

EF Uncertainties 

Several factors could affect the EF estimates including ventilation rates, sampling errors, aerosol profiles, 

sampling times relative to various activities in the building, and meteorological conditions (e.g., humidity 

and atmospheric pressure). The two factors that have a significant impact on the estimates are ventilation 

rates and humidity. Increased ventilation rates tend to decrease the EFs by removing radon progeny from 

the environment. Vogiannis et al. reported that high humidity under chronic conditions lowers EFs, 

probably because of the increased “washout” of aerosols. High humidity may also reduce the detection 

efficiency of the Pylon AB-5 Continuous Passive Radon Detector, thereby resulting in a higher EF than 

true conditions. While it is difficult to say if the “washout” effect offsets the lower radon gas detection 

efficiency, the high humidity (from its climate and internally housed natural springs) is a factor at the 

HSNP. Additionally, NIOSH learned that the filter cassette sampling method may have leaked, resulting 

in some of the sampled air bypassing the filter and lowering the effective sampling rate. NIOSH tested 

some of the unused cassettes in an effort to determine if this air leakage could have significantly reduced 

the estimated EFs. A bypass leak of up to 5% percent was detected in one of the unused cassettes, greater 

Photo 11: Ludlum Model 2000 

scaler counter and Ludlum Model 43-

10 detector used to count alpha 

activity on Teflon filters. The detector 

efficiency was 0.38 cpm / dpm. 
Page 12 Health Hazard Evaluation Report No. 2004-0094-2978 

than the typical 0.2%.30, 31 While the leak test cannot accurately predict mass losses from the filter after 

sampling, it suggests that this problem could be another reason for the low EF estimates. 

Radium and Radon Concentrations in Water 

Water samples collected at the Hale Bathhouse natural spring and publicly 

accessible fountain next to the Administration Building were analyzed for 

226Ra and 222Rn (Table 5). The 226Ra concentrations were below the 

proposed EPA MCL (5 pCi/L) from the Hale spring and Administration 

Building fountain. The 222Rn concentration in water from the Hale spring 

was above the proposed EPA MCL (300 pCi/L), while the water from the 

Administration Building fountain was just below this level. This difference 

may be due to the presence of a 280,000 gallon reservoir tank below the 

Administration Building which is filled by natural springs. The 222Rn offgasses before reaching the fountain so the concentration is further reduced. 

Additional off-gassing occurs at the fountain as storage containers are 

filled by the public. (Photo 12). The park can ensure that radon 

concentration in water consumed from public fountains is below the 

proposed radon EPA MCL by introducing interim storage tanks or taps 

that enhance off-gassing. The variation of 226Ra and 222Rn in water with time and location of publicly 

accessible fountains was not evaluated. 

Personal Protective Equipment 

NIOSH research has determined that a radon progeny exposure limit of 1.0 Working Level Month 

(WLM) per year is technically achievable in mines if effective work practices and engineering controls 

are implemented.7

 Over a 30-year working lifetime, this exposure limit will reduce the risk of lung cancer 

associated with exposure to radon progeny. NIOSH considers respirators to be one of the last options for 

protecting workers, especially for 222Rn. Instead, work practices and engineering controls are more 

effective means for limiting exposures and providing safe environments. Also, respirator use in the HSNP 

may not always be practical for physiological and safety reasons. Therefore, NIOSH recommends using 

administrative and engineering controls where it is technologically reasonable to achieve control of 

occupational exposure to radon progeny. 

The impact of adopting an annual radon progeny exposure limit of 1 WLM implies that the average 

monthly occupational exposure will be 1/12 WL. Assuming an equilibrium factor of 0.40, the average 

radon concentration limit for 2040 hours per year is approximately 21 pCi/L. 

An EF factor of 40% was selected for this purpose because (1) it is consistent with the value used for 

residential indoor environments, (2) it is a conservative assumption based on the estimated EF values in 

the Hale Bathhouse basement and Administration Building (5% to 9% respectively), and (3) it should not 

present an undue burden in keeping potential exposures below the NIOSH recommended exposure limits. 

For average work shift concentrations above 1/12 WL (21 pCi/L; 40% EF), NIOSH investigators 

recommend mandatory respirator use as well as implementation of administrative and engineering 

controls to reduce exposure to radon progeny. Based on recent radon concentration measurements 

conducted throughout the Park (Table 3) after implementation of remedial actions, no areas require this 

level of protection. 

Respirator Selection 

NIOSH investigators make the following recommendations for respirator selection based on the fact that 

radon progeny exists as particles and that workers in HSNP are not exposed to hazardous concentrations 

Photo 12: The general public 

filling containers at the Adm. 

Building fountain. 
Health Hazard Evaluation Report No. 2004-0094-2978 Page 13 

of non-particulate contaminants. If protection against non-particulate contaminants is required, different 

types of respirators must be selected. 

1. A respirator is not required for exposure to average work shift concentrations less than or equal to 

1/12 WL (21 pCi/L radon; 40% EF). 

2. For exposure to average work shift concentrations greater than 1/12 WL (120 pCi/L radon; 40% 

EF), NIOSH recommends those respirators listed in Table 6.

CONCLUSIONS

Radiation 

Radiation measured throughout the park was due to NORM, predominantly from 226Ra. The highest 

exposure rate (2,500 μR/hr) was found in the Hale Bathhouse basement on contact with a localized area 

of contamination on the east foundation wall. While this is substantially higher than the background rate 

of 5 to 10 μR/hr, this location poses no immediate danger to building occupants as the area is not 

routinely accessed by workers or the public. Furthermore, the radiation levels decrease to background 

about 10 feet from the localized spot with the highest exposure rate. 

Disposal of Pipe Containing NORM 

The HSNP hired a contractor to handle and dispose of NORM-contaminated pipe removed from the Hale 

Bathhouse. 

Radon Concentrations in Air 

Radon concentrations above the EPA action limit of 4 pCi/L were measured by HSNP in only two 

buildings, the Hale Bathhouse and the Administration building. The park has implemented successful 

remediation techniques to reduce radon concentrations below the EPA action limit in most locations. The 

one exception is the Tower Room, located in the basement of the Administration Building. Although the 

radon concentrations in this room were only reduced to about 20 pCi/L, it is not routinely occupied by 

park officials and the park has posted a sign on the door warning of the elevated radon exposure potential. 

Radium and Radon Concentration in Water

Radium concentrations in the water samples collected from the Hale spring and the fountain just outside 

the Administration Building were below the EPA MCL of 5 pCi/L. Radon concentration in the Hale 

spring was above the EPA MCL of 300 pCi/L but the foundation water sample was below this limit. 

RECOMMENDATIONS

Radiation 

Identify and limit access to areas within the HSNP where the elevated external radiation exceeds 5100 

μR/hr. The most cost effective and efficient method to reduce unnecessary external radiation exposures is 

to avoid occupying these areas or maintain sufficient distance between the radiation source and the 

individual. The value of 50 μR/hr was chosen because it can result in an occupational dose of 100 mrem 

during a work year, which is the recommended dose limit for the general population (2,000 hours per 

work year times 50 μR per hour = 100,000 μR or 100 mR per work year; 100 mR is considered equal to 

100 mrem for the purpose of this report). 
Page 14 Health Hazard Evaluation Report No. 2004-0094-2978 

Disposal of NORM 

Consult with the Arkansas Department of Health (24-hour telephone: 501-661-2136) to develop 

appropriate disposal procedures for any NORM materials uncovered during renovation projects. 

Radon Concentrations in Air 

Continue the routine radon measurement program to check indoor radon concentration in each of the 

bathhouses and the Administrative Building office spaces. Depending on results of the monitoring, 

mitigation may include sealing foundation cracks, sealing exposed dirt in crawl spaces, and increasing or 

installing ventilation. Other remediation actions to reduce radon levels are available in an IAEA 

document entitled “Radiation Protection Against Radon in Workplaces Other than Mines.” This 

document is free online at http://www-pub.iaea.org/MTCD/publications/PDF/Pub1168_web.pdf.

Radium and Radon Concentrations in Water 

Start a routine water monitoring program to measure radium and radon concentrations in the drinking 

water available to the general public. Although water samples from the Administration Building fountain 

were below the proposed EPA MCLs (5 pCi/L for 226Ra and 300 piC/L for 222Rn ), the radon 

concentration in the Hale spring water exceeded the proposed EPA MCL. The EPA provides guidance to 

States and community water systems (CWSs) regarding implementation of “The Radionuclides Rule” 

published in the Federal Register on December 7, 2000 (65 FR 76708). A guidance document is available 

online at http://www.epa.gov/safewater/rads/final_rads_implementation_guidance.pdf.
Health Hazard Evaluation Report No. 2004-0094-2978 Page 15 

REFERENCES 

1. Radtke T [2004]. Memorandum of January 29, 2004, from T. Radtke, Office of Managing Risk and 

Public Safety, Department of the Interior to Superintendent, Hot Springs National Park. 

2. NPS [2000]. Glimpses of our National Parks (On-line Book). 

[http://www.cr.nps.gov/history/online_books/glimpses1/glimpses19.htm]. Date accessed: June 16, 2004. 

3. NPS [2002a]. The Hot Springs of Arkansas through the years: A chronology of Hot Springs Events. 

[http://www.nps.gov/hosp/expanded/text/history/chronology/chronology2.htm]. Date accessed: June 16, 

2004. 

4. NPS [2002b]. The Hot Springs of Arkansas through the years: A chronology of Hot Springs Events. 

Brief Summary of Park History. 

[http://www.nps.gov/hosp/expanded/text/history/chronology/chronology1.htm]. Date accessed: June 16, 

2004. 

5. Epperson CE, Rhodes NR [1990]. Characterization of Radioactivity in Hot Springs National Park, 

Arkansas. Proceedings Arkansas Academy of Science 44:125-127. 

6. Thomas J [1972]. Measurement of Radon Daughters in Air. Health Physics 23:783-789. 

7. NIOSH [1992]. Recommendations for occupational safety and health: compendium of policy 

documents and statements. Cincinnati, OH: U.S. Department of Health and Human Services, Public 

Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety 

and Health, DHHS (NIOSH) Publication No. 92-100. [http://www.cdc.gov/niosh/88-101.html] 

8. ACGIH [2005]. 2005 TLVs® and BEIs®: threshold limit values for chemical substances and physical 

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

9. CFR [1997]. 29 CFR 1910.1000. Code of Federal Regulations. Washington, DC: U.S. Government 

Printing Office, Office of the Federal Register. 

10.NCRP [1993]. National Council on Radiation Protection and Measurements. Report No. 116. 

Limitation of Exposure to Ionizing Radiation. Bethesda, MD. 

11. ICRP [1997]. International Commission on Radiological Protection. General Principles for the 

Radiation Protection of Workers, Publication No. 75, Pergamon Press, Oxford and New York (1997). 

12. CFR [2003]. 10 CFR 835.202. Code of Federal Regulations. Washington, DC: U.S. Government 

Printing Office, Office of the Federal Register. 

13. CFR [1991]. 10 CFR 20.1201. Code of Federal Regulations. Washington, DC: U.S. Government 

Printing Office, Office of the Federal Register. 

14. 52 Fed. Reg. 2822 [1987]. Radiation Protection Guidance to Federal Agencies for Occupational 

Exposure. January 27, 1987. 
Page 16 Health Hazard Evaluation Report No. 2004-0094-2978 

 

15. CFR [2003]. 21 CFR 1020.40. Code of Federal Regulations. Washington, DC: U.S. Government 

Printing Office, Office of the Federal Register. 

16. CFR [2003]. 49 CFR 173.441. Code of Federal Regulations. Washington, DC: U.S. Government 

Printing Office, Office of the Federal Register. 

17. IATA [2003]. 10.11 Radiation Protection and Quality Assurance. International Air Transport 

Association. Dangerous Good Regulation. 44th Edition. Montreal, Quebec, Canada. 

18. IAEA [1999]. International Atomic Energy Agency. Safety Standards Series: Occupational Radiation 

Protection. Safety Guide No. RS-G-1.1. Vienna. 

19. UNSCEAR [2000]. United Nations Scientific Committee on the Effects of Atomic Radiation: Sources 

and Effects of Ionizing Radiation.United Nations, New York. 

[http://www.unscear.org/reports/2000_1.html] Date accessed: April 4, 2005. 

20. Department of Energy. Science, Society and America’s Nuclear Waste: Ionizing Radiation Unit 2; 

First Edition. DOE/RW-0362 SR. 

21. OSHA [2002]. 12/23/2002 – Occupational exposure limits, access restrictions, and posting 

requirements for airborne radioactive materials. 

[http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=2449

6]. Date accessed: June 15, 2004. 

22. 64 Fed. Reg. 211 [1999]. Environmental Protection Agency: National Primary Drinking Water 

Regulations; Radon-222; Proposed Rule. (To be codified at 40 CFR Parts 141 and 142). 

23. CFR [2005]. U.S. Environmental Protection Agency: Radiation information, World Wide Website, 

March 28, 2005. http://www.epa.gov/radiation/radionuclides/radon.htm

24. Mineralogical Society of America [2005]. Romanechite Mineral Data. Website: 

http://webmineral.com/data/Romanechite.shtml 

25. Eisenbud, M [1987]. Environmental radioactivity from natural, industrial, and military sources. 3rd 

ed. New York: Academic Press, pp. 133-134. 

26. IAEA [1990]. International Atomic Energy Agency Technical Reports Series No. 310: The 

Environmental Behavior of Radium, Volume 1. Vienna. 

27. Radtke T [2004]. Memorandum of January 29, 2004, from Industrial Hygienist, Office of Managing 

Risk and Public Safety, Department of the Interior to Superintendent, Hot Springs National Park. 

28. IAEA [2003]. International Atomic Energy Agency Safety Reports Series No. 33: Radiation 

Protection against Radon in Workplaces other than Mines. Vienna. Available for free at [http://wwwpub.iaea.org/MTCD/publications/PDF/Pub1168_web.pdf]. 

29. Vogiannis E, Niaounakis M, Halvadakis CP. [2003]. Contribution of 222Rn-bearing water to the 

occupational exposure in thermal baths. Environmental International 30:621-629. 
Health Hazard Evaluation Report No. 2004-0094-2978 Page 17 

 

30. Baron P. [2002]. Using a Filter Bypass Leakage Test for Aerosol Sampling Cassettes. Applied 

Occupational and Environmental Hygiene. 17(9):593-597. 

31. Baron PA, Khanina A, Martinez AB, Grinshpun SA. [2002]. Investigation of Filter Bypass Leakage 

and a Test for Aerosol Sampling Cassettes. Aerosol Science and Technology. 36: 857-865. 
TABLES

Table 1 

Radiation Measurements* 

HETA 2004-0094-2978: Hot Springs National Park 

January 26 and 27, 2004 

Bathhouse Location μR/hr** 

Lamar 1st floor and basement 

Near boilers 

5–10 

10 

Ozark 1st floor and basement 

North side stairwell at floor level 

5–12 

40–42 

Quapaw 1st floor and basement 

In display spring and above mineral deposits 

In spring drain 

Jack-hammered open dirt 

5–10 

20–30 

500 

220 

Maurice 1st floor and basement 5–10 

Maurice Spring In the spring opening 50 

Hale 1st floor contractor office desk 

Above basement hotspot: 

Basement hotspot 

5–10 

25

2,500

Superior 1st floor in tubs 

Throughout 1st floor and basement 

On floor near open drain in basement 

On dirt pile in NE corner of basement 

15 

5–10 

30–35 

50 

Ral Spring On ground in depression 1,100 

* Radiation measurement obtained by DOI and State of Arkansas Radiation Officer using the 

NIOSH radiation instrument Inovision 451P ionization chamber. 

**μR/hr = microRoentgen per hour. An exposure rate to external radiation equal to 1,000 

μR/hr is approximately equal to a dose rate of 1 mrem / hr. Natural background radiation rates 

in this area range between 5 to 10 μR/hr. 
Table 2 

Gamma Spectrometry Results From Soil and Rock Samples 

Hale Bathhouse Basement Foundation and Floor 

Analyses by U.S. Geological Service, Denver Federal Center 

HETA 2004-0094-2978: Hot Springs National Park 

Activity in disintegrations per minute per gram of material 

Decay products in the 238U series (Appendix I) Decay product, 

232Th series 

Location 

234Th 226Ra# 214Pb 214Bi 210Pb 228Ac 

East Foundation Wall (Photo 6) 

Non-black rock sample 

 GE-A@ 

 GE-1 

ND@ 

0.5 

2.3 

2.6 

2.2 

2.1 

2.1 

2.1 

ND 

2.1 

0.9 

1.4 

East Foundation Wall 

Black rock sample 

 GE-A 

 GE-1 

ND 

<7 

3,010 

2,760 

2,735 

2,760 

2,630 

2,750 

ND 

2,565 

1.5 

2.0 

Refuse from black wall sample* 

 GE-A 

 GE-1 

ND 

0.8 

144 

129 

149 

143 

141 

133 

ND 

137 

1.2 

1.1 

Basement floor soil sample 

 GE-A 

 GE-1 

ND 

2.7 

70 

72 

67 

69 

75 

68 

ND 

75 

1.3 

1.5 

* Refuse from the black wall sample also contains portions of the basement floor materials. 

#

 For comparison, most natural soils and rocks contain approximately 0.5–5 pCi/g (1.1–11.1 

dpm/g) of total radium.‡ A nominal background value of 1.4 pCi/g (3.1 dpm/g) has been 

used for various clean-up efforts. 

@ The designation of ND indicates "not determined." The gamma-ray energies of detector GE1 is more sensitive than detector GE-A for measuring 234Th (63.3, 92.4, 92.8 keV) and 210Pb 

(46.5 keV) are too low to be adequately detected. 

‡ USGS [1999]. Naturally Occurring Radioactive Materials (NORM) in Produced Water and Oil-Field 

equipment - An Issue for the Energy Industry. [http://pubs.usgs.gov/fs/fs-0142-99/fs-0142-99.pdf] 

Date accessed: March 30, 2005. 
Table 3 

Radon Concentration in Air* 

Collected by Hot Springs National Park Officials 

HETA 2004-0094-2978: Hot Springs National Park 

May 2004 to February 2005 

Location Radon Concentration (pCi/L) 

Hale Bathhouse Basement 

Prior to remediation 

Basement area behind the natural spring near the east wall 

Crawl space (1/3 basement ) 

Modified existing ventilation (Push/Pull) July 1, 2005 

Basement area behind the natural spring near the east wall 

Crawl space (1/3 basement) 

Final remediation (Push/Pull) January, 2005 

Basement area behind the natural spring near the east wall 

Crawl space (1/3 basement) 

 45–90 

 up to 225 

 leveled off to about 40 

 leveled off to about 125 

 less than 2 

 not measured 

Administration Building (285,000 gallon tank) 

Prior to remediation (open doorway) 

Basement (Tower Room) 

General basement area (outside Tower Room) 

First and Second Floors 

Installed plastic sheets 

Tower Room (exhaust fan in pump room operational) 

General basement area (outside Tower Room) 

First and Second Floors 

Installed permanent door 

Tower Room (exhaust fan in pump room and signage) 

General basement area (outside Tower Room) 

First and second floors 

 40–50 

 10–12 

 up to 12 

 20–25 

 4–5 

 less than 2 

 20–25 

 2–4 

 less than 2 

Superior Bathhouse 

Maurice Bathhouse 

Fordyce Bathhouse 

Quapaw Bathhouse 

Ozark Bathhouse 

Buckstaff Bathhouse 

Lamar Bathhouse

All real-time radon measurements 

taken on all floors at various times 

between May, 2004 and February, 

2005 were below 4 pCi/L. If the 

basement concentration was below 

4 pCi/L then the remaining upper 

floors were not measured. 

* Cardarelli J [2005]. Telephone conversation on March 29, 2005, between J. Cardarelli, NIOSH and 

S. Rudd, Hot Springs National Park, Chief Park Ranger. 
Table 4 

Working Level (WL) and Equilibrium Factor (EF) Estimates 

HETA 2004-0094-2978: Hot Springs National Park 

June 30 – July 1, 2004

Location Gross Alpha Counts 

per time interval@ 

post sample 

(time) = (cts) 

Radon 

Progeny Conc. 

(pCi/L) 

Measured 

222Rn 

Conc.$

(pCi/L) 

WL# EF

(%) 

Hale basement near northeast 

corner (ventilation off) 

June 30 2:40 pm 

(2 to 5) = 3,083 

(6 to 20) = 8,190 

(21 to 30) = 4,532

218Po = 18.6 

214Pb = 4.5 

214Bi = 1.7 

91 0.074 8.16 

Hale basement near northeast 

corner (ventilation on) 

July 1 7:36 am 

(2 to 5) = 720 

(6 to 20) = 1,637 

(21 to 30) = 886

218Po = 6.7 

214Pb = 1.3 

214Bi = 0.6 

31.5 0.016 4.98 

Hale basement crawl space & 

(ventilation off; very humid) 

June 30 3:23 pm 

(2 to 5) = 6,362 

(6 to 20) = 14,093 

(21 to 30) = 7,436

218Po = 59.2 

214Pb = 9.8 

214Bi = 5.3 

224 0.132§ 5.90 

Hale basement crawl space & 

(ventilation on; very humid) 

July 1 – early morning 

(2 to 5) = 944 

(6 to 20) = 2,178 

(21 to 30) = 1,192

218Po = 8.7 

214Pb = 1.7 

214Bi = 0.7 

38.6 0.021 5.33 

Hale basement crawl space & 

(ventilation on; very humid) 

July 1 – late morning 

(2 to 5) = 736 

(6 to 20) = 1,809 

(21 to 30) = 1,002

218Po = 6.4 

214Pb = 1.5 

214Bi = 0.7 

33.1 0.017 5.05 

Administration Building 

basement Tower Room 

(ventilation on), July 1, morning 

(2 to 5) = 1,060 

(6 to 20) = 1,755 

(21 to 30) = 877

218Po = 12.3 

214Pb = 0.9 

214Bi = 0.1 

20* 0.018 9.05 

@ Five-minute air samples were collected on 37 mm Teflon (Polytetrafluoroethylene) filters (0.5 μm pore size) 

with a flow rate of 22 liters per minute. The background count rate was 3.28 counts per minute with a detector 

efficiency of 0.38 counts per minute/disintegrations per minute. 

$

 Radon concentrations were measured with a Pylon AB-5 monitor with a continuous passive radon detector. 

Each result is the average concentration measured during the sampling period. 

#

 One Working Level corresponds to radon progeny concentration in equilibrium with 100 pCi/L radon. 

 & Ventilation in the crawl space was only passively affected by the building ventilation system. 

The radon concentration was estimated based on previous measurements in this location. 

Table 5 

Radium-226 and Radon-222 Concentration in Spring Water 

HETA 2004-0094-2978: Hot Springs National Park 

July 1, 2004 

Laboratory Analyses Hale Spring Water 

pCi/L 

Fountain Water 

pCi/L 

Radium-226 # General Engineering Laboratory 3.14 ± 0.47 2.03 ± 0.13 

Radon-222 369 ± 74 203 ± 69 

#

 Radium-226 results are below the EPA limit for drinking water (5 pCi/L). 
Table 6 

Respirator Recommendations for Radon Progeny 

HETA 2004-0094-2978: Hot Springs National Park 

July 1, 2004 

Average work shift concentration 

of radon progeny (WL) or radon 

concentration 

(pCi/L at 40% EF) 

Respirator recommendations 

0 to .083 (1/12) WL or 

0 to 20.8 pCi/L 

No respirator required 

> 0.083 to ≤ 0.42 WL or 

> 20.8 to ≤ 105 pCi/L 

Any disposable respirator equipped with a HEPA$ filter 

Any air-purifying half-mask respirator equipped with a HEPA 

filter 

> 0.42 to ≤ 0.83 WL or 

> 105 to ≤ 208 pCi/L 

Any SAR# equipped with a half-mask and operated in a 

demand (negative-pressure) mode 

Any powered PAPR* equipped with a hood or helmet and a 

HEPA filter 

> 0.82 to ≤ 2.08 WL or 

> 208 to ≤ 520 pCi/L 

Any supplied-air respirator with a hood or helmet and 

operated in a continuous flow mode 

Any air-purifying, full facepiece respirator equipped with a 

HEPA filter 

Any PAPR equipped with a tight fitting facepiece and a 

HEPA filter 

Any SAR equipped with a full facepiece and operated in a 

demand (negative-pressure) mode 

Any SAR equipped with a tight-fitting facepiece and operated 

in a continuous-flow mode 

> 2.08 to ≤ 4.15 WL or 

> 520 to ≤ 1,038 pCi/L 

Any self-contained breathing apparatus (SCBA) equipped 

with a full facepiece and operated in a demand (negativepressure) mode 

pCi/L = picoCuries per liter 

WL = working level 

#

 SAR = supplied-air respirator 

* PAPR = powered air-purifying respirator 

$

 HEPA = high-efficiency particulate air 

NOTE: This table was adopted and edited for Hot Springs National Park applications from Table I-1 of NIOSH 

[1987]. An EF factor of 40% was selected for this purpose because (1) it is consistent with the value used for 

residential indoor environment, (2) it is a conservative assumption based on the estimated EF values in the Hale 

Bathhouse basement and Administration Building (5% to 9% respectively), and (3) should not present an undue 

burden in keeping potential exposures below the NIOSH recommended exposure limits. 
APPENDICES

Appendix I 

Uranium-238 Decay Series (4n + 2)a 

Major Radiation Energies (MeV) and Intensitiesb

Nuclide Half-life α β γ

MeV % MeV % MeV % 

U238

92 y 9 4.468 ×10 4.15 22.9 

4.20 76.8 0.496 0.07 

↓ 

Th 234

90 24 .1 d

0.076 2.7 

0.095 6.2 

0.096 18.6 

0.1886 72.5 

0.0633 3.8 

0.0924 2.7 

0.0928 2.7 

0.1128 0.24 

↓ 

Pa 234

91 1.17 m 2.28 98.6 0.766 0.207 

1.001 0.59 

↓ 

Pa 234

91 6.7 h

22 ßs

E Avg = 0.224 

Emax = 1.26 

0.132 19.7 

0.570 10.7 

0.883 11.8 

0.926 10.9 

0.946 12 

0.053 0.12 

0.121 0.04 

↓ 

U234

92 244,500 y

4.72 27.4 

4.77 72.3 

↓ 

Th 230

90 y

4 7.7 ×10 4.621 23.4 

4.688 76.2 

0.0677 0.37 

0.142 0.07 

0.144 0.045 

↓ 

Ra 226

88 1600 ± 7 y

4.60 5.55 

4.78 94.4 0.186 3.28 

↓ 

Rn 222

86 3.823 d 5.49 99.9 0.510 0.078 

↓ 

Po 218

84 3.05 m 6.00 -100 0.33 0.02 0.837 0.0011 

↓ 
Appendix I Continued 

Major Radiation Energies (MeV) and Intensitiesb

Nuclide Half-life α β γ 

MeV % MeV % MeV % 

Pb 214

82 26.8 m

0.67 48 

0.73 42.5 

1.03 6.3 

0.2419 7.5 

0.295 19.2 

0.352 37.1 

0.786 1.1 

↓ 

Bi 214

83 19.9 m

5.45 0.012 

5.51 0.008 

1.42 8.3 

1.505 17.6 

1.54 17.9 

3.27 17.7 

0.609 46.1 

1.12 15.0 

1.765 15.9 

2.204 5.0 

↓ 

Po 214

84 164 μs 7.687 100 0.7997 0.010 

↓ 

Pb 210

82 22.3 y 3.72 0.000002 0.016 80 

0.063 20 0.0465 4 

↓ 

Bi 210

83 5.01 d

4.65 0.00007 

4.69 0.00005 

4.65 0.00007 

4.69 0.00005 

↓ 

Po 210

84 138.378 d 5.305 100 5.305 100 0.802 0.0011 

↓ 

Pb 206

82 stable 

a

 This expression describes the mass number of any member in this series, where n is an integer. For 

example: Pb 206

82 (4n + 2)...(4 x 51) + 2 = 206 

b

 Intensities refer to percentage of disintegrations of the nuclide itself, not to original parent of series. 

Gamma %s: in terms of observable emissions, not transitions. 
Appendix II 

OSHA Interpretation of Radon Exposures in the Workplace 

The following are excerpts from a recent interpretation of the OSHA regulations provided to 

the U.S. Army Corps of Engineers (USACE) concerning occupational exposure limits to 

radon gas. These questions and answers may also apply to the HSNP radon situation.d

Question 1: Although the USACE does not use or transport radon, is the presence of radon in 

structures considered "possession," making 29 CFR 1910.1096 applicable to USACE 

structures? 

Reply: Yes. If the presence of radon in a structure controlled by the employer exposes 

employees to hazardous concentrations of airborne radiation as set forth in the standard, 29 

CFR 1910.1096 would apply. 

Question 2: If workers are only required to enter an area occasionally during a calendar 

quarter, can their exposures be averaged over the calendar quarter instead of one week to 

determine whether they should be allowed to enter the area? 

Reply: No, not for airborne radioactive materials. Neither the OSHA nor the NRC ionizing 

radiation standard allows airborne radon concentrations to be averaged over a calendar 

quarter. The OSHA radon exposure limit is an average concentration for 40 hours in any 

workweek of 7 consecutive days. The still applicable 1971 radon-222 exposure limit for 

adult employees is 1 x 10-7 microcuries per milliliter (μCi/ml) [100 picoCuries/liter 

(pCi/L)] averaged over a 40-hour workweek. However, OSHA would consider it a de 

minimis violation if an employer complied with the current NRC radon-222 (with daughters 

present) exposure limit for adult employees of 3x10-8 μCi/ml [30 pCi/L] averaged over a 

year (DAC-derived air concentrations). 

Question 3: Does the provision at 1910.1096(c)(2), dealing with exposure to airborne 

radioactive materials by employees under the age of 18, apply to USACE structures? 

Reply: Yes. According to paragraph 1910.1096(c)(2), the radon-222 exposure limit for 

employees under the age of 18 is 3x10-9 μCi/ml [3pCi/L] averaged over a 40-hour 

workweek as it was in 1971. However, OSHA would consider it a de minimis violation if 

an employer complied with the current NRC radon-222 exposure limit for employees under 

the age of 18 of 3x10-9 μCi/ml [3pCi/L] averaged over a year (i.e., 10% of the adult limit). 

Question 4: Are we required to monitor and track workplaces where radon concentrations are 

below 4 pCi/L? 

Reply: No. You must make surveys in order to comply with the provisions in 1910.1096. 

In addition, you must supply appropriate personnel monitoring equipment to adult 

employees who enter a restricted area and receive, or are likely to receive, a dose in any 

calendar quarter in excess of 25% of the applicable value in 1910.1096(b)(1). Likewise, 

personnel monitoring equipment must be supplied to employees under the age of 18 who 

 

d

 OSHA [2002]. 12/23/2002 – Occupational exposure limits, access restrictions, and posting 

requirements for airborne radioactive materials. 

[http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=2

4496]. Date accessed: June 15, 2004. 
enter a restricted area and are exposed to 5% of the applicable value in 1910.1096(b)(1). 

The OSHA dose limit for whole body radiation is 1.25 rem per calendar quarter. 

It should be noted that the Environmental Protection Agency (EPA) and other public health 

officials publish radon guidelines, but these guidelines are not occupational safety and 

health standards and do not carry the weight of law. EPA recommends remediation when 

the radon level is 4 pCi/L or higher. However, radon levels less than 4 pCi/L pose a risk 

and in many cases may be reduced. 

Question 5: Must we restrict individuals under the age of 18 from entering areas where the 

radon concentration is greater than 3.0 pCi/L? Note: USACE feels this would place an undue 

burden on organizations that either employ persons under the age of 18 or that allow members 

of the public under the age of 18 to enter their facility. 

Reply: Yes. You must provide access control to areas where your employees may be 

exposed over the applicable limits. This may be accomplished by restricting the employees' 

exposure time. OSHA does not regulate the general public. 

Question 6: 29 CFR 1910.1096(e)(4)(i)(b) defines an "airborne radioactivity area" as "Any 

room, enclosure or operating area in which airborne radioactive materials exist in 

concentrations which, averaged over the number of hours in any week during which 

individuals are in the area, exceed 25 percent of the amounts specified in column 1 of Table 1 

of appendix B to 10 CFR part 20." Are we required to post areas that exceed 4 pCi/L if they 

are occupied for more than 75 hours a week? Are we required to post continuously occupied 

areas that exceed 1.8 pCi/L? Is there a lower concentration where posting is no longer 

required? 

Reply: You are required to post airborne radioactive areas. The 1971 version of Appendix 

B to 10 CFR Part 20 lists the adult limit for radon-222 in column 1 of Table 1 as 1 x 10-7

microcuries per milliliter (μCi/ml) [100 pCi/L]. Thus, you must post a sign in accordance 

with 29 CFR 1910.1096(e)(4)(ii) when the weekly average exceeds 25% of these levels. 

The NRC uses similar language to define "airborne radioactive area," except that the 

regulation at 10 CFR 20.1003 refers to the derived air concentrations (DAC) in Appendix B 

§§ 20.1001-20.2401 or the average weekly intake by an individual of 0.6 percent of the 

annual limit. Using the NRC's definition of an airborne radioactive area, posting is required 

in areas where the weekly average radon exposure limit is 0.18 pCi/L (30 pCi/L x 0.006 = 

0.18 pCi/L). OSHA does not enforce this posting limit. 
DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health 

4676 Columbia Parkway 

Cincinnati, OH 45226-1998 

OFFICIAL BUSINESS 

Penalty for private use $300 

Delivering on the Nation's promise: 

Safety and Health at work for all people 

through research and prevention

To receive NIOSH documents or information 

about occupational Safety and Health topics 

contact NIOSH at: 

1-800-35-NIOSH (356-4674) 

Fax: 1-513-533-8573 

E-mail: pubstaft@cdc.gov

or visit the NIOSH web site at: 

www.cdc.gov/niosh/homepage.html

S A F E R • H E A L T H I E R • P E O P L ETM