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This working document was prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final 

NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents 

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redact any information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Basis for a Bounding Estimate of Radon 

Exposure at Allied Chemical and Dye

National Institute for Occupational Safety and Health

Division of Compensation Analysis and Support

February 10, 2017

James W. Neton

Dave Allen
Page 2 of 5 

This working document was prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final 

NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents 

preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and 

redact any information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Basis for a Bounding Estimate of Radon Exposure at Allied Chemical and Dye

February 10, 2017 

James W. Neton

Dave Allen

Introduction 

As part of the 17th set of dose reconstruction reviews, the Advisory Board tasked Sanford Cohen 

and Associates (SC&A) with performing a blind review of a case with employment at the Allied 

Chemical and Dye Corporation. In their December 2014 report, SC&A raised a question 

regarding the internal exposures that NIOSH used in the dose reconstruction for this case. In 

particular, SC&A believed that the radon exposure estimate assigned for this case was not 

necessarily bounded by the data that was used by NIOSH. The radon levels uses for this dose 

reconstruction were based on 10% of the 95 percentile values contained in ORAU-OTIB-0043. 

This white paper evaluates the potential for radon exposure at Allied Chemical and Dye, given 

what is known about the nature of the radium source-term and the laboratory experiments that 

were performed there. In that light, the suitability of using the existing phosphate plant data in 

ORAU-OTIB-0043 to bound exposure to radon with sufficient accuracy is evaluated. 

Background on Allied Chemical and Dye 

According to a 1977 DOE letter, Allied Chemical and Dye Corporation’s plant in Claymont 

Delaware was involved in research and development and small pilot scale operations in the 

recovery of uranium. This work, which was conducted in the early 1950s, took place under two 

Atomic Energy Commission (AEC) contracts.1 DOE interviews with former workers indicated 

that the Claymont work focused on filtration development and that, less than 2 to 10 pounds of 

uranium were produced (SRDB 16503). The research under these contracts established the basis 

for the designation of Allied Chemical and Dye as a covered Atomics Weapons Employer 

facility under EEOICPA. Because the contracts could not be located, and the phosphoric acid 

plant was in existence until early 1970, the covered period on the DOE website is listed as the 

“early 1950s – late 1960s.” For purposes of dose reconstruction, NIOSH has interpreted this to 

be January 1, 1950 through December 31, 1969. There is also a residual contamination period at 

Allied Chemical that covers 1970 through 1977. 

 

1 The AEC contract numbers were: AT (49-1)-610 and AT (49-6)-913.
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This working document was prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final 

NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents 

preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and 

redact any information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

At the time of the dose reconstruction, the information above was all that was available on the 

nature of the AEC activities at Allied Chemical and Dye. Recently, however, NIOSH has 

discovered an Allied Chemical and Dye progress report to the AEC Raw Materials Division (the 

sponsor of Allied’s research) that sheds some light on type of research performed at Allied 

Chemical and the magnitude of that activity (SRDB 159354). The report, which is a summary of 

work accomplished through March of 1954 under AEC contract AT (49-6)-913, discusses 

progress in two areas: leach zone filtration studies and uranium extraction from phosphoric acid. 

Because the radium source term had been removed from the phosphoric acid, the leach zone 

filtration studies is the only work that could generate a radon exposure potential. 

Evaluation of Radon Exposure Potential using Source-Term Information

The leach zone ore studies involved laboratory-scale research into the optimum conditions under 

which gypsum could be precipitated and quantitatively filtered. To accomplish this, a typical 

batch was reported to use 150 grams of leach zone ore2. Although the number of batch runs that 

were made are not reported in the study, the effect of 11 different factors or variables were 

reported to have been evaluated. Under future work, the report states that Allied Chemical and 

Dye intended to verify the reported results in 45 additional batch runs. 

There are several possible approaches that can be used to estimate or bound the magnitude of the 

radon exposure associated with the amount of material used in the experiments described above. 

First, a simple source term model can be used to produce an estimate of the magnitude of the 

potential exposures. 

Assuming that each experiment used 150 grams of leach zone ore containing 0.014% natural 

uranium by weight3, it is possible to estimate the amount of radon that would be in a laboratory 

room at equilibrium. The only parameters required to place an upper bound of the estimate are 

the air ventilation rate and the size of the room. If we use an air turnover rate of 1 exchange per 

hour and a small room of dimensions 10 foot length and width and a ceiling height of 8 feet, the 

equilibrium concentration of radon in the room would be 0.002 pCi/L or 9.3E-06 WL, assuming 

40% progeny equilibrium in indoor air. If we assume that all 45 batch runs are processed at the 

same time in the same room, the concentration would be 0.105 pCi/L or 0.00042 WL if there is 

40% equilibrium between the radon gas and its progeny. We consider these calculated values to 

be upper estimates because:

• It is assumed that the amount of radon emanating from the leach zone ore is 100%; 

 

2 Leach zone ore is from the upper layer of a phosphate ore deposit that is not used in the production of phosphoric 

acid. It is normally scraped off the surface and placed in piles at the mine site. The uranium content of leach zone 

ore is not considerably different from the phosphate ore that is mined. 3 For this analysis uranium and radium are considered to be in secular equilibrium.
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This working document was prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final 

NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents 

preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and 

redact any information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

• It is likely that the laboratory room was larger than the dimensions used; and 

• The filtration experiments were likely to have been done in a laboratory hood, given that 

the experimental protocol called for digestion of the sample in 140 to 208° Fahrenheit 

nitric acid. 

 

As part of their review of the Allied Chemical dose reconstruction, SC&A prepared a source 

term calculation dated June 30, 2015. Their source-term analysis was significantly more refined 

that the simple, bounding analysis discussed above. It considered a number of additional 

parameters, including the possible production of ten pounds of uranium material per year, 

variation in room ventilation rates, and the emanation fraction of radon from dry phosphate ore, 

from wet phosphate ore and from sulfuric acid. The results of their analysis was a lower

estimated radon concentration of 0.0042 pCi/L or 0.000017 WL assuming 40% equilibrium 

between radon gas and its progeny. 

Radon levels in Phosphate Plants 

As previously stated. NIOSH used the radon data in ORAUT-OTIB-0043 to bound exposures at 

Allied Chemical. ORAU-OTIB-0043 relied on the radon data that were contained in a Florida 

Institute of Phosphate Research (FIPR) report, which were collected a number of phosphate 

plants in Florida. The 130 applicable radon values in the report were found to fit a lognormal 

distribution with a geometric mean of 0.75 pCi/L and a geometric standard deviation of 1.99. 

The 95th percentile of the distribution is 2.33 pCi/L or 0.0093 WL if a 40% equilibrium factor is 

applied4. To account for the difference in scale between a phosphate production facility and the 

levels of radium that were present at Allied Chemical, the dose reconstruction used a value of 

10% of this, or 0.00093 WL. 

In 1983, ten radon measurements were taken at various locations at the Blockson Chemical plant 

in Joliet, Illinois, while the plant was still in operational mode. The highest value, which was 

taken at the Sodium Tri Polyphosphate (STPP) area, was reported to be 0.0042 WL (SRDB 

30623). Although the Blockson plant and the Florida-based facilities that were included in the 

OTIB-043 analysis were different, with the Florida plants likely to have been more ventilated, 

the upper values are only about a factor of 2 apart (0.0042 vs 0.0093 WL). In fact, it of interest 

to note that the value measured at Blockson is approximately one-half of the 95th percentile value 

in the FIPR report. Reducing the measured levels at Blockson Chemical by a factor of 10, as 

was done for the FIPR data, results in a value of 0.00042 WL. 

 

4 The use of 40% equilibrium is consistent with literature values cited for indoor air.
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This working document was prepared by NIOSH’s Division of Compensation Analysis and Support (DCAS) or its contractor for use in 

discussions with the ABRWH or its Working Groups or Subcommittees. Draft, preliminary, interim, and White Paper documents are not final 

NIOSH or ABRWH (or their technical support and review contractors) positions unless specifically marked as such. This document represents 

preliminary positions taken on technical issues prepared by NIOSH or its contractor. NOTICE: This report has been reviewed to identify and 

redact any information that is protected by the Privacy Act 5 USC §552a and has been cleared for distribution.

Comparison and Conclusion 

Table 1 provides a comparison of the estimated exposure radon exposure at Allied Chemical that 

were calculated above.

Basis of Estimate Value (WL) Comment

NIOSH Source-term 

(1 sample processed at a time)

9.3E-06 Upper bound using 150 gram 

samples and small room

NIOSH Source-term

(45 samples processed at a time)

0.00042 Upper bound using 150 gram 

samples and small room

SC&A Source-term 0.000017 Allows for the annual 

production of 10 pounds of 

uranium

OTIB-043 adjusted by a factor of 10 0.00093 95th percentile of measured 

data

Blockson Chemical adjusted by a 

factor of 10

0.00042 Largest value measured

It can be seen in the comparison that a value of 10% of the FIPR production facility 

measurements provides a bounding estimate when compared to both the NIOSH and SC&A 

source term calculations. Given the levels of uncertainty in the above estimates, NIOSH believes 

that it is claimant favorable to continue the use of the adjusted OTIB-043 value in assessing 

radon exposures at Allied Chemical. While the difference between the source-term estimates 

and the measured plant data is on the level of an order of magnitude, this is not unreasonable 

given the low levels of exposure predicted by both.