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ATTACHMENT 4.3-4D 
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Finding 4.3-5: The list of facilities in which thorium-232 was processed, the time periods of 

thorium processing, and the thorium production data shown in the TBD have significant 

gaps. Entire periods of processing and plants in which the work was done have been 

missed. These gaps may affect the feasibility of dose reconstruction for workers during 

certain periods and in certain plants. 

The TBD considers thorium-232 work to have been done mainly in the Pilot Plant and Plant 9. It 

also acknowledges work in Plant 8 and, for a short period, of production in Plant 4. The TBD 

does not mention Plant 6 in connection with thorium production; however, Attachment 4.3-5A 

clearly shows that thorium was processed in Plant 6 at least from 1960 to 1962. 

Table 4.3-1 corresponds to thorium air dust data for Plant 6, as given in Attachment 4.3-5A. 

Furthermore, it is clear that production continued into 1963. The dust survey report from which 

the data in Table 4.3-1 are derived was written in March 1963. Despite the extremely dusty 

conditions in some operations (notably raking cold residue into the furnace at 1,260 Maximum 

Allowable Concentration (MAC)), production was continuing at the time the report was written. 

The report recommended that “this furnace should be shut down immediately after processing 

the thorium now on site.” 

Table 4.3-1: Plant 6 Air Dust Data, 1960 to 1962 

Location Sample 

Year 

Type of 

Sample 

Air 

conc, 

xMAC 

Comments 

Raking excessive cold residue into furnace 1962 BZ 1,260 Recommended for shut down 

July 1, 1963 for clean up 

Unplugging furnace discharge line 1962 BZ 417 

Unplugging furnace discharge line 1961 BZ 4.0 Same location as 1962 

Unplugging furnace discharge line 1960 BZ 4.0 Same location as 1962 

Loading Th metal into 5-gal can from 55-gal 

drums 

1962 BZ 69 

Raking drum residue into Rotex sifter 1962 BZ 27 

Raking drum residue into Rotex sifter 1961 BZ 31 Same location as 1962 

Raking drum residue into Rotex sifter 1960 BZ 33 Same location as 1962 

Changing drum at product canning station 1962 BZ 19 

Changing drum at product canning station 1961 BZ 4.0 Same location as 1962 

Changing drum at product canning station 1960 BZ 4.0 Same location as 1962 

Charging furnace with pieces of metal 1962 BZ 7 

Charging furnace with pieces of metal 1961 BZ 3.0 Same location as 1962 

Charging furnace with pieces of metal 1960 BZ 3.0 Same location as 1962 

Source: Starkey 1963 

Note: 1 MAC = 70 dpm/m3

A Fernald history of thorium residue processing indicates that burning of residues may have 

begun in Plant 6 in late 1959, when a furnace there was modified to burn residues accumulated 

from metal production during 1955 and 1956 in Plant 9 (Attachment 4.3-5B). There were 1500 

drums (or 240,000 pounds) that were sent to the Plant 6 furnace for oxidation (Attachment 4.3-

5C). Hence, there is documentary evidence for thorium residue burning from sometime in 1959 
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until at least July 1963 (see Attachment 4.3-5D). (It is unclear whether thorium operations took 

place in Plant 6 after that date.) A 1954 evaluation of dust levels at various plants involved in 

chemical and metallurgical work with thorium provided recommendations for the steps to be 

taken at Fernald in order to make Plant 6 “suitable for thorium rolling” (Klevin 1954, p. 19). 

Neither Table 5-13 nor Table 5-14 in Vol. 5 of the TBD, which show production data by plant, 

chemical form, and time period, have any thorium production listed for 1960, 1961, 1962, or 

1963. The Site Description (Vol. 2 of the TBD) also does not mention Plant 6 as a thorium 

production location. Finally, one of the main references that NOISH used in compiling the 

thorium production data (Dolan and Hill 1988) also does not list Plant 6 as a production location 

for thorium: 

Thorium was processed at the FMPC throughout much of the thirty-five year 

history of the site. The demand for various thorium materials fluctuated greatly 

and the FMPC developed or modified processes to meet these varying 

requirements. During different periods, thorium was processed through 

Plants 2/3, 4, 8, 9, and the Pilot Plant. [Dolan and Hill 1988, p. 57] 

Thorium tetrafluoride was produced in a “short” campaign in Plant 4, but production data are not 

available: 

In 1954, Plant 4 was used for a short campaign to produce dry ThF4 from the 

ThO2 dried and calcined in Plant 9 in hydrofluorination Bank 7. The ThF4 was 

returned to Plant 9 and used to produce thorium metal. This was a shortduration process due to mechanical difficulties in Bank 7. Production quantities 

are not available for ThF4 production in Plant 4. [TBD, Vol. 2, p. 24] 

While the TBD does not provide a reference for these statements, it appears that they are based 

on Dolan and Hill (1988, p. 61). However, Dolan and Hill are not as definite that production did 

not occur at other times: 

Production quantities are not available for ThF4 in Plant 4. Because of the 

problems encountered, it is believed that this process was only operated for a 

short period and hence the potential for emissions was very slight. [Dolan and 

Hill 1988, p. 61] [Emphasis added.] 

Since thorium residues, including metal residues, were processed in a furnace in Plant 6 between 

1960 and 1963 (inclusive), the question arises as to where the thorium processing was done to 

produce the metal in this period. Neither the TBD nor Dolan and Hill provide any production 

data for these years. It is plausible that chemical processing of thorium, including production of 

thorium tetrafluoride and reduction of the tetrafluoride to metal, occurred at Fernald during 1960 

to 1963 (possibly only the first half of 1963). It may also have occurred in the late 1950s and in 

other periods. 

Dolan and Hill (1988) concluded that thorium production in the Pilot Plant started in 1964. 

Vol. 2 of the TBD indicates that thorium tetrafluoride was produced in the Pilot Plant and then 
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reduced to metal in the 1969–1971 period. Reduction of ThF4 to metal occurred in Plant 9. 

Dolan and Hill (p. 59) also state that “[t]horium metal was produced in Plant 9 from 1954 

through 1955.” Machining was also done in Plant 9 during this period (p. 59). 

It is possible that these facilities were used in the 1960–1963 period for ThF4 production and 

reduction; however, this needs to be more carefully investigated. In that case, it is also possible 

that Plant 2/3 may have been used to produce the thorium nitrate feedstock that was the starting 

point of the ThF4 production process. 

SC&A has not located any positive documentation that Plant 5, where the UF4 reduction to metal 

was done, was also used for ThF4 reduction. However, a 1954 evaluation (Klevin 1954) of 

thorium health hazards recommends that consideration should be given to the use of the “‘F’ 

machine in charging thorium bombs, since these have proved to be effective in controlling 

airborne contamination and are operationally satisfactory at both MCW and FMPC Plant 5” 

(p. 11). It appears that at least at the time of the evaluation (March 1954), such a machine was 

not available in Plant 9, where the ThF4 reduction was being carried out. Hence, it is possible 

that the charging of the bombs may have been done at Plant 5 for some time until a suitable 

machine was procured for Plant 9. It may also have been used in the later 1960–1963 period. 

SC&A stresses that it is making the above statements about possible work in Plant 4 and Plant 5 

(or additional undocumented work in Plant 9 and/or the Pilot Plant) as pointers for research into 

thorium production history, rather than as conclusions. Thorium data are likely to be one of the 

most critical parts of dose reconstruction for Fernald claimants who worked there from 1954 

onwards. As NIOSH and ORAU acknowledged in the August 18, 2006, conference call, the 

TBD does not reflect a considerable amount of documentation that is available or becoming 

available (see Section 8.1.1). 

The TBD lists Plant 2/3 as a location for thorium processing: 

In 1968, Plant 2/3 was used to process thorium as a thorium production test for a 

short duration. Few details are available regarding this process. Thorium 

nitrate crystals were produced in a denitration pot in Plant 2/3. Interviews with 

long-time employees indicated that this was a short-term operation; probably one 

pot of crystals was produced. Other records discuss the production of thorium 

oxide in Plant 2/3 by a process of denitration, redigestion, and drying. [TBD, 

Vol. 2, p. 20]

No plant-specific data enabling dose reconstruction are provided. Production data shown in 

Table 6 of Dolan and Hill do not contain any data for Plant 2/3 thorium production amounts or 

time periods (Dolan and Hill 1988, p. 20). Since Plant 2/3 was the refinery where uranium ores 

were processed, it may be presumed that thorium ores were also processed there. This has 

considerable significance for worker exposure. The TBD does mention the processing of 

thorium ores at Fernald, but lists them as being processed in the Pilot Plant as part of the thorium 

processing there between 1964 and 1980 (TBD, Vol. 2, p. 11); however, records show that 

thorium production at Fernald went back to 1954. This raises the question whether thorium 

processing took place in Plant 2/3 in connection with early thorium-related processes in Plant 9 
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and Plant 4. The information in Dolan and Hill on thorium was partly based on interviews, but 

NIOSH was unable to provide any interview records to SC&A. 

According to the TBD, much of the thorium data was destroyed in the 1970s: 

Much of the thorium production data has been lost, and the plant and bioassay 

monitoring data recovered to date has been sparse. A comprehensive effort to 

reconstruct the effluent of uranium and thorium from the Fernald plants in 1988 

discovered that a large number of records and files were destroyed in the early 

1970s during declassification efforts (Dolan and Hill 1988). Reviews of AEC 

records in Oak Ridge and Atlanta failed to uncover additional details. [TBD, 

Vol. 5, p. 18] 

There are other problems with the production data as well. For instance, Vol. 2 of the TBD 

states that thoria gel production for 1964 and 1965 was estimated based on a linear extrapolation 

of the quantity produced in 1966 through 1970: 

Production records also indicate that 492 metric tons of thorium as thoria gel 

were produced from 1966 to 1970. Production for 1964 and 1965 was estimated 

based on a linear extrapolation of the quantity produced in 1966 through 1970. 

The estimated total production from this process is 686 metric tons assuming 

linear production from 1964 to 1970. (TBD Vol. 2, p. 11). 

No justification for this assumption is provided in the TBD. Furthermore, the data shown in 

Table 5-13 of the TBD (Vol. 5, p. 20) show that NIOSH assumed that only thoria gel was 

produced in 1964 and 1965, even though there was other processing and at least one other 

chemical form (thorium oxalate) produced in the Pilot Plant in the 1966 to 1970 period. If the 

average of the total production in the Pilot Plant were extrapolated backwards, the estimated 

production of thorium in the Pilot Plant in 1964 and 1965 would be 238 metric tons in each year, 

or about 2.4 times the amount estimated by NIOSH (98 metric tons in each year). No 

explanation is provided for the more limited extrapolation. 

Furthermore, if thoria gel was produced in 1964 and 1965, one would expect purified thorium

nitrate solution also to have been produced. However, the text only discusses production from 

1966 onward. Was there any such production in 1964 and 1965? In fact, though Table 5-14 

shows that thorium nitrate was produced in the Pilot Plant, it is not explicitly mentioned in 

Table 5-13 where production estimates are provided. In this same context, it is confusing that 

some items of production have quantitative estimates (but without references) in Volume 2 of the 

TBD, but there is no counterpart tabulation in Volume 5 on internal dose reconstruction. For 

instance, thorium nitrate production is not shown in Table 5-13 of Volume 5; however, 

Volume 2 gives a rather precise value of 790.4 metric tons for the 1966–1973 period for the Pilot 

Plant (p. 11). 

Finally, a 1988 thorium records search document (Bonfer 1988) also indicates that the TBD 

compilation of production at Fernald is incomplete. The starting date for thorium production of 

1954 appears to be correct according to Bonfer 1988, which provides a date of January 26, 1954, 
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with metal production operations starting on February 15, 1954—all in Plant 9. Bonfer 1988 

also mentions “extraction studies” being started in the laboratory in April 1954. These studies 

continued well into 1955. Furthermore, while Tables 5-13 and 5-14 show Plant 9 production 

only in 1954 and 1955, there is clear evidence that Plant 9 production covered a longer time 

span. For instance, Bonfer states the following: 

The final Plant 9 process of manufacturing massive thorium metal continues into 

1956. [Bonfer 1988, p. 2] 

Similarly, while Tables 5-13 and 5-14 show Pilot Plant production only beginning in 1964, 

Bonfer 1988 states the following: 

A project was initiated during July 1956 in the Pilot Plant to demonstrate the 

sylvania reduction process for calcium reduction of thorium oxide to thorium 

metal powder. [Bonfer 1988, p. 2] 

Attachment III in Bonfer 1988 is a catalog of orders for a variety of forms of thorium. It 

includes orders that were filled in 1957, 1958, and 1959—years that are not discussed for 

thorium production in the TBD. In this context, it is noteworthy that while the TBD does not 

mention thorium metal production in Plant 9 in 1956, the history of residue recovery does. The 

quantity of production must have been significant, because the residues from 1955 and 1956 

amounted to 80 tons (Mead 1972, p. 86). Finally, Attachment II in Bonfer (1988) also shows 

three orders in 1985, but it is not clear whether these orders were filled with material that had 

already been produced prior to that time or whether there was post-1979 production at Fernald. 

The TBD does not discuss these orders or cite Bonfer (1988). 

In conclusion, it is very likely that production estimates in the TBD are significant 

underestimates. It is clear that Tables 5-13 and 5-14 (TBD, Vol. 5, p. 20) do not capture a large 

amount of the processing that was done, even from readily available documentation. The 

locations and time periods of processing are also significantly incomplete. A thorough revision 

of the TBD is necessary to establish when the workers were at risk of exposure due to 

production, and in which plants they were at risk. 
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ATTACHMENT 4.3-5A 
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ATTACHMENT 4.3-5B 
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ATTACHMENT 4.3-5C 
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ATTACHMENT 4.3-5D 
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Finding 4.3-6: NIOSH Lacks the Necessary Data for Defining Thorium Exposure During 

Post-Production Periods

Table 5-13 of the FMPC TBD identifies discrete years during which thorium was processed at 

the Pilot Plant, Plant 8, and Plant 9. Because much of the thorium production data has been 

lost/destroyed, these dates, as well as locations can neither be assumed accurate nor complete, as 

discussed separately under Finding 4.3-5 above. 

However, independent of these uncertainties, thorium exposures at any process facility must be 

assumed to have continued well after thorium processing ceased due to residual contamination 

that may have co-mingled with newly-created uranium contamination. 

In this context, it is important to note that even 1 MAC exposure to thorium for certain organs 

yields a committed dose much higher than exposure to uranium, the main material processed and 

produced at Fernald for certain organs. (At the time, 1 MAC for thorium and uranium was 

defined as being the same number—70 dpm/m3

 until 1970 and 100 dpm/m3 thereafter.) SC&A 

has pointed out the critical importance of this fact for dose reconstruction in other reports (see 

SC&A 2006, for instance). For convenience, we have reproduced Table 4.3-2 from SC&A 2006 

herein. 

Table 4.3-2: 50-Year Organ Dose Conversion Factors for U-234 and Th-232 – Inhalation 

(in sieverts per becquerel and ratios) 

Organ U-234 Type 

M, Sv/Bq 

U-234 Type 

S, Sv/Bq 

Th-232 Type 

S, Sv/Bq 

Ratio Th S/U 

M 

Ratio Th S/ U 

S 

Bone Surface 3.90E-06 5.03E-07 2.86E-04 7.33E+01 5.69E+02 

Breast 1.37E-07 1.63E-08 8.29E-07 6.05E+00 5.09E+01 

Liver 5.34E-07 6.93E-08 5.05E-06 9.46E+00 7.29E+01 

Red Marrow 4.03E-07 5.21E-08 1.00E-05 2.48E+01 1.92E+02 

Testes 1.37E-07 1.63E-08 2.62E-06 1.91E+01 1.61E+02 

Source: Federal Guidance Report 13, U.S. EPA, published on CD in 2002. 

Reproduction of Table 4 from SC&A 2006. 

Note: DCFs are based on AMAD = 1 μm

These data show that a 1-MAC level of air contamination with Type S thorium-232 is equivalent 

to 569 MAC of Type S uranium-234 for bone surface dose. Thus even ~0.1% Th-232 dust in the 

air (in terms of dpm/m3

) mixed in with uranium can make a significant contribution to bone 

surface dose. The dose conversion factors (DCFs) show that a few tenths of 1% can make a 

significant contribution of dose of the testes and red bone marrow. When assessed against these 

facts, the TBD/ER are particularly deficient in regard to residual thorium air concentration 

during times when personnel were monitored for uranium (via urinalysis) and/or by air sampling 

that blindly assessed for alpha activity. 
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Finding 4.3-7: The Guidance in the TBD Regarding Exposures from Redrumming 

Thorium is not Well Founded and is Not Claimant Favorable. 

There were extensive thorium redrumming, packaging, and shipping operations in the 1980–

1986 period. Such operations were also carried out during the period of thorium processing. For 

instance, a 1965 “Request for Engineering Services” began as follows (see Attachment 4.3-7): 

The thorium residue drums are disintegrating. [Name] started redrumming these 

residues but was stopped by the IH&R Department due to high dust levels of 

contamination arising from dust generated by the redrumming operation. Prior 

to the IH&R shutdown of the redrumming operation, the sump cake had been 

redrummed in 900 drums and 100 drums of floor sweepings had been redrummed.

...About 30% of the drums are so corroded that they cannot be lifted off their 

pallets without falling apart. This is the fourth time this material has been 

redrummed. There are approximately 2000 drums of this material. [DeFazio 

1965, emphasis added] 

The inference from the engineering request for ventilation system design is that the prior 

redrumming operations were carried out at least three times without such ventilation and that half 

the job in question (redrumming of 1,000 out of 2,000 drums) was also similarly carried out 

without ventilation. SC&A has not found BZ air dust data corresponding to the discrete 

redrumming operations. 

SC&A concludes that air concentrations during periodic redrumming efforts were high as 

implied in a 1968 memorandum, which stated: 

As you well know, most of our air dust at FMPC over the years have resulted 

from drumming and dumping dry materials. Any time that we can eliminate 

either of these operations our air dust problems become greatly reduced. 

[Starkey 1968] 

However, needed data for assessing intakes to workers engaged in redrumming efforts are 

lacking at two levels: (1) it is unlikely that the identity of the workers engaged in redrumming 

can be obtained, and (2) it is equally unlikely that BZ air sampling data for redrumming efforts 

exist. 
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Finding 4.3-8: Thorium intakes due to fugitive emissions and resuspension in nonproduction areas may have been significant in some locations and during some periods. 

The TBD does not address the issue of fugitive emissions from production areas into nonproduction areas. Furthermore, the TBD does not provide a method to estimate 

exposure/intakes for those workers without lapel air sampling.

If NIOSH intends to estimate thorium exposure/intakes based on BZ air sampling data for 

thorium processing locations and time periods, exposures from fugitive releases will not be 

included. There is clear evidence of significant problems with fugitive emissions of thorium 

from production areas. These problems were not confined to early production. A 1970 

memorandum on “Thorium Metal Production Housekeeping” is worth quoting at length in this 

regard (see Attachment 4.3-8): 

1. Probably the worst housekeeping problem in the facility is the Ball Mill. 

This equipment leaks excessively at practically every joint. All horizontal 

surfaces have a thick covering of dust. In operation, this dust becomes 

airborne and adds to the dust coming from the leaks. Since the ventilation 

is inadequate and there is no proper enclosure, a bucket was placed under 

the largest leak to help contain the spilled dust. This is not adequate. It is 

recommended that Engineering Division be requested to inspect the Ball 

Mill and associated equipment and recommend methods of improving both 

the dust problem and the housekeeping problem. 

2. During the operation of removing the calcined ThF4 and CaF2 from the 

retorts, the stack of trays is left standing on a skid near the south annex 

door. The door is left open to aid in cooling the trays. The wind coming 

through the door blows the loose powder from the trays and spreads it 

generously through the annex. Removing the trays from the support 

requires heavy effort and this dislodges more powder to be spread by the 

wind. It is recommended that this stack of trays be put inside the 

enclosure used for grinding, weighing, and blending their contents.

[Ross 1970] 

Quantitative data for the problem of high fugitive dust over time does not exist, but the document 

indicates that the levels of thorium dust were high both indoors and outdoors, and that industrial 

hygiene measures were poor. Moreover, the same memorandum makes it clear that significant 

residual contamination from the poorly controlled processes was present in many locations. 

They included the following: 

...the drying oven area, the bottom of the blending enclosure, the saws and the 

saw area, the entrance to the furnace room when used to remove dezinced derbies 

from their holders, the top deck of the furnace room, the ThF4 enclosure and the 

area surrounding it, and others. [Ross 1970] 

These circumstances indicate that both thorium production workers as well as those who did not 

directly work with thorium may have experienced significant thorium intakes due to faulty 
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equipment, lack of adequate ventilation, and poor location of the equipment. Maintenance 

workers who repaired the equipment may also have had large exposures due to resuspension of 

dust from the heavily contaminated surfaces. In view of the high DCFs of thorium relative to 

uranium for several organs, it is essential that dose reconstruction must account for all worker 

exposures to thorium. 
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ATTACHMENT 4.3-8 
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Attachment 4.3-8 (Continued) 
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Finding 4.3-9: The Inability to Assess Internal Exposures from the Ingestion of Thorium

When estimates of internal exposure to thorium are restricted to air sampling, there is no 

accountability of internal exposure that resulted from the ingestion of thorium. 

At FMPC, substantial internal exposure resulting from the ingestion of both soluble and 

insoluble thorium compounds must be assumed for the following reasons (also see 

Attachments 4.3-9A through 4.3-9C): 

(1) Large source terms of thorium compounds existed that were readily introduced into air 

and ubiquitously dispersed throughout the workplace. 

(2) In combination, the absence of worker training, poor housekeeping, and poor work 

practices allowed workers to come into close contact with materials and contamination in 

the workplace. 

(3) These problems were compounded by the failure to employ adequate engineering 

controls in the workplace (e.g., ventilation systems, automation of manual processes, etc.) 

and the failure to supply and/or enforce the use of anti-Cs, respirators, and other measures 

that would mitigate internal exposure. 

(4) Workers were not monitored for skin and clothing contamination. 

(5) Even for the post-1968 period when a limited number of workers were assessed by in 

vivo measurements/lung counting (i.e., MIVRML), these data are of limited value for 

quantifying the ingestion of thorium compounds – in particular, insoluble thorium 

compounds, which would have transiently exposed only epithelial cells of the 

gastrointestinal tract. 

SC&A concludes that ingestion of thorium compounds at FMPC was inevitable; and ingestion 

may have contributed to significant internal exposures that were not monitored and are, 

therefore, unaccountable. 
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applicability within the requirements of 42 CFR 82. 

ATTACHMENT 4.3-9A 
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Attachment 4.3-9A (Continued) 
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ATTACHMENT 4.3-9B 
Effective Date: 

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ATTACHMENT 4.3-9C 
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applicability within the requirements of 42 CFR 82. 

Finding 4.3-10: The Unanswered Question of Data Integrity for Air Monitoring

Concerns about the integrity of air sampling data for FMPC must be raised due to sworn 

statements made in 1993 in the form of an affidavit (see Attachment 4.3-10). 

The affidavit in Attachment 4.3-10 is that of a former FMPC employee who served as an 

industrial hygienist during a period covering the 1950s–1970s. Among the most relevant 

statements in the affidavit are statements #4, #5, #7, and #13, which are partially reproduced 

below: 

 Statement #4 (Excerpts): 

I did air dust surveys in all the plants at Fernald. I used a homemade sampler

which consisted of a small vacuum with a Whatman filter where air was drawn....

[Emphasis added.] 

 Statement #5: 

When I did air dust surveys, I could get a higher reading if I stood in the direction 

that the dust was blowing from the employee that I was sampling. Conversely, I 

would get a lower reading if I stood in the opposite direction from the way that 

the dust was blowing. Where I stood could make 100% difference in the results 

that I recorded depending on how dirty the operation was. For example, if I 

stood on one side, the reading might be zero while on the other side, the reading 

might be 50 times Maximum Allowable Concentration (“MAC”). [Emphasis 

added.] 

 Statement #7 (Excerpts): 

On several occasions during the term of my employment, when I got air dust 

survey results that were above the MAC. I was told by my supervisors that the 

results were in error and I was told to go back and resample. . . I think that my 

results were correct the first time that I sampled because they were similar to the 

results that I had obtained before the modifications and the modifications were 

not effective. . . I was sent back by my supervisors five or six times. Finally, I 

stood in the opposite direction from the employee from the way that the dust was 

blowing and I obtained a result that was below the MAC. When I returned the 

result that was below the MAC to the Health & Safety Division it was an 

acceptable result. 

 Statement #13: 

In the 1950s no industrial hygienists worked on the second shift, third shift or 

on weekends. It is my understanding that many operations that would not be 

condoned by the Health & Safety Division would be done on the second shift, 
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third shift and on weekends when no industrial hygienists were present. 

[Emphasis added.] 

SC&A concludes that (1) the use of a “homemade” air sampling device, (2) air sampling that 

was limited to the first shift on Mondays through Fridays, and (3) management pressure to select 

favorable air sampling data raise justifiable concerns about the credibility of air monitoring data 

that NIOSH considers key to the reconstruction of thorium exposure/intakes. 
Effective Date: 

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applicability within the requirements of 42 CFR 82. 

ATTACHMENT 4.3-10