DISCLAIMER: This is a working document provided by the Centers for Disease Control and Prevention (CDC) 

technical support contractor, SC&A, for use in discussions with the National Institute for Occupational Safety and 

Health (NIOSH) and the Advisory Board on Radiation and Worker Health (ABRWH), including its Working Groups or 

Subcommittees. Documents produced by SC&A, such as memorandum, white paper, draft or working documents are 

not final NIOSH or ABRWH products or positions, unless specifically marked as such. This document prepared by 

SC&A represents its preliminary evaluation on technical issues.

NOTICE: This document 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. 

Memorandum

To: Santa Susana Field Laboratory Work Group

From: SC&A, Inc.

Date: June 10, 2019

Subject: Review and Characterization of Boeing Incident Database for SEC-00246

Introduction and background

During the Advisory Board on Radiation Worker Health (Advisory Board) meeting held in 

Redondo Beach, CA, on December 13, 2018, Core Advocacy for Nuclear and Aerospace 

Workers provided thumb drives containing a collection of incident files to the Santa Susana Field 

Laboratory (SSFL) Work Group, the National Institute for Occupational Safety and Health 

(NIOSH), and SC&A. The collection of incident files contained on the thumb drive is titled, 

“BOEING_INCIDENT_FOIA,” and is referred to as “the Boeing incident database” or simply 

“the database” in this memorandum.1 After the Advisory Board meeting, SC&A was tasked with 

reviewing those incident files in the context of Special Exposure Cohort (SEC)-00235 and 

SEC-00246. SC&A’s evaluation of relevant incidents for SEC-00235 is contained in the SC&A 

report, “Review of Remaining Internal Dose Topics Related to the Evaluation of SEC-00235 at 

the Santa Susana Field Laboratory” (SC&A 2019), and is not discussed further here. This 

memorandum represents SC&A’s evaluation of the database in the context of SEC-00246 at 

De Soto (1965–1995). Specifically, the database was evaluated for evidence of potential 

exposure to thorium and/or americium at De Soto. 

1 After the Advisory Board meeting, NIOSH uploaded these incident files to the ABRWH internal server.

Characterization of Boeing incident database

The incident files contained in the database can generally be characterized as two separate types: 

radiological incident reports (784 total) and unusual occurrence reports (486 total). SC&A’s 

sampling of the latter category concluded that these types of records did not refer to events where 

radiological exposure was a possibility. Therefore, SC&A’s review focuses solely on the 

category of radiological incident reports. 

A general characterization of the 784 radiological incident files can be found in Table 1. As seen 

in the table, 95 incident reports contained in the database are related to De Soto during the period 

of interest (~12 percent). The majority of incidents (~79 percent) were not relevant because they 

referred to locations other than De Soto (i.e., SSFL, Canoga, Downey, Vanowen Building, and 

other offsite locations) or to incidents that occurred prior to 1965 and, as such, are covered by 

SEC-00168. The remaining files contained in the database were either repeats of other incident 

 
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Review of Boeing Incident Database, page 2 June 10, 2019

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Privacy Act 5 USC §552a and has been cleared for distribution. 

reports (4.5 percent), were blank incident files indicating that the incident number was not used 

(0.5 percent), or were missing the incident report (4.0 percent). 

Table 1. General characterization of radiological incident documentation in database

Incident report type Total reports (%)

Incidents occurring at De Soto post-1964 95 (12.1%)

Incidents not occurring at De Soto post-1964 334 (42.6%)

Incidents prior to 1965 286 (36.5%)

Repeats of other incident reports 35 (4.5%)

Incident report is missing* 30 (3.8%)

Incident report file not used/blank 4 (0.5%)

Total 784 (100.0%)

* Three of the 30 missing reports related to De Soto during the period of interest. 

Although some of the incident reports were missing, an index of the incident database (Rockwell 

International 1994) contains a list of each incident report number and supplies the date, general 

location, and a shortened sentence describing the incident. Based on this index, SC&A 

determined that 3 of the 30 missing reports related to De Soto during the period of interest. 

Though information on these three incidents is limited, they are included in the analysis specific 

to De Soto discussed below. 

Figure 1 shows the distribution of De Soto radiological incident reports by year from 1965 to 

1995. The number of radiological incidents at De Soto decreased markedly in the early 1980s, 

which generally corresponds to the decommissioning of Building 1, which housed the majority 

of the De Soto nuclear fuel fabrication operations. The reason for an apparent decrease in 

incident reporting from 1972 to 1975 is not known at this time. 
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Review of Boeing Incident Database, page 3 June 10, 2019

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Privacy Act 5 USC §552a and has been cleared for distribution. 

Figure 1. Number of radiological incident reports for the De Soto Facility by year

SC&A categorized each of the 98 identified incidents at De Soto into six general categories; a 

description of each category follows: 

• Category 1. Uranium Contamination Incident: incident resulted in the detectable release 

of contamination outside of the intended enclosure, such as a glovebox, and represents a 

potential internal exposure source. 

• Category 2. Uranium—No Spread of Contamination: incident involved uranium but did 

not result in any detectable spread of contamination outside of the intended enclosure. 

The most common examples observed were uranium fires contained within a glovebox or 

other sealed location.

• Category 3. Other Identified Contamination Incident: incident involved the spread of 

detectable contamination outside of the intended enclosure, and the primary 

radionuclide(s) were identified in the follow-up investigation. 

• Category 4. Other Incident—No Contamination: incident did not involve an internal 

exposure hazard. Such incidents included radiography (x-ray) overexposures, lost film 

badges, faulty alarms, misplaced sources, general worker complaints, and material 

custody issues.

• Category 5. Other Unidentified Contamination Incident: incidents in which gross beta, 

gamma, and/or alpha contamination was detected; however, the specific radionuclides 

involved were not identified in followup investigations. 

• Category 6. Decladding of Fuel Elements: incident report specifically mentioned the 

decladding of a fuel element at a De Soto facility.
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Table 2 shows the number of incident reports in each of SC&A’s six categories. Also included in 

Table 2 is the frequency in which each incident resulted in internal monitoring2 for the 

individuals involved. As seen in the table, the majority of radiological incident reports were 

associated with uranium events (Categories 1 and 2). Category 3 incidents involved the 

following identified radionuclides: iodine-131, strontium-90, cesium-137, cobalt-60, calcium-45, 

and manganese-54. However, none of the incidents involved americium or thorium. Nearly 

one-third of the incident reports involved events in which there was either no potential for the 

spread of contamination or none was detected in followup surveys (Category 4). These first four 

categories represent 90 percent of the relevant incident documentation for the De Soto 

SEC-00246 period but do not indicate internal exposure potential to americium or thorium that 

would render dose reconstruction infeasible. 

2 In this analysis, internal monitoring includes urinalysis, fecal sampling, or whole body count/lung scan results 

and does not include personal surveys, smears, or nasal swipes.

Table 2. SC&A categorization of De Soto incidents during SEC-00246 period (1965–1995)

SC&A incident 

report category

Number 

of 

reports

Internal 

monitoring 

requested (% 

of report 

category)

No internal 

monitoring 

requested (% 

of report 

category)

Unknown 

(% of 

report 

category)

Internal 

monitoring not 

applicable (% 

of report 

category)

1. Uranium 

Contamination 

Incident 

43 26 (60.5%) 10 (23.3%) 7 (16.3%) 0 (0.0%)

2. Uranium—No 

Spread of 

Contamination

9 2 (22.2%) 3 (33.3%) 2 (22.2%) 2 (22.2%)

3. Other Identified 

Contamination 

Incident

6 2 (33.3%) 3 (50.0%) 1 (16.7%) 0 (0.0%)

4. Other Incident—No 

Contamination 30 0 (0.0%) 0 (0.0%) 0 (0.0%) 30 (100.0%)

5. Other Unidentified 

Contamination 

Incident

8 1 (12.5%) 3 (37.5%) 4 (50.0%) 0 (0.0%)

6. Decladding of Fuel 

Elements 2 1 (50.0%) 1 (50.0%) 0 (0.0%) 0 (0.0%)

Category 5 incidents represent contamination events in which the primary contaminant is not 

identified in the available documentation; therefore, it is not clear if the incident could have 

involved americium or thorium. These eight incidents are summarized in Table 3. Without 

further information pertaining to these incidents, it is not possible to know the specific source of 

exposure. As noted in Tables 2 and 3, followup internal monitoring is often not discussed as part 

of the incident. 

 
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Table 3. De Soto incident reports describing unidentified contamination (Category 5)

Incident 

report 

identifier* 

Year of 

incident Brief description of incident

a-0163 1986 The incident occurred in room 411-64 of building 4 at De Soto when lowlevel radioactive contamination, mixed with mercury, leaked onto the 

floor during a cutting operation of a drain line. A radiation survey of the 

area found fixed contamination below the drain line but no loose 

contamination. The tools used in the cutting operation were 

decontaminated and cleaned. A checklist associated with the incident 

response indicated bioassay was not required.

a-0419 1966 The full incident report for this event is currently missing. However, the 

Energy Technology Engineering Center Master Index (Rockwell 

International 1994) indicates an employee had a lodged in 

their hand while working in a in building . As the full incident 

report is currently not available, there is no other information pertaining 

to the material that was being handled nor any indication of followup 

internal monitoring.

a-0611 1967 A fire occurred while cutting into a for in 

building . The original workers, as well as the 

 workers involved in the fire suppression, were contaminated 

on their . All energy employees (EEs) involved were 

scheduled to submit bioassay results. The results of the bioassay 

sampling is not provided in the incident report.

a-0614 1967 While exiting building , an EE noticed “a of ” that had 

been left under a at . Health Physics smeared the area 

and determined that the material and the area under the were 

contaminated. No other information pertaining to the levels or type of 

contamination is provided, nor is any followup internal monitoring 

indicated. The immediate area was covered with plastic until the 

contaminated material could be disposed of and the replaced. 

The incident report concludes by asking if the employees of 

 are fully instructed in handling radioactive materials. 

a-0623 1967 Maintenance workers were removing vacuum exhaust lines in 

room 111-10 of building 1 when sparks were observed. Approximately 

4.5 quarts of black powder were scraped from the ductwork exhaust 

lines and placed in a criticality safe configuration before being sent to the 

vault for further analysis. This incident is summarized in a periodic health 

physics report rather than an individual report specific to the incident. 

The summary does not contain any further information about the nature 

of the material or followup internal monitoring. It is possible that the 

black powder in question was uranium dioxide rather than thorium oxide, 

which is generally lighter in color.
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Privacy Act 5 USC §552a and has been cleared for distribution. 

Incident 

report 

identifier* 

Year of 

incident Brief description of incident

a-0626 1967 Elevated air-sampling results were identified in the Powder Room of 

building 1 at De Soto (5×10-9 μCi/cc); followup high-volume air samples 

showed airborne contamination levels of 5×10-11 μCi/cc. The document 

states that the contamination was found throughout the room, but the 

type of radioactivity is not specifically identified. Personnel were 

evacuated until decontamination was effected. This incident is 

summarized in a periodic health physics report rather than an individual 

report specific to the incident. The summary does not contain any further 

information about the nature of the material or followup internal 

monitoring.

a-0628 1967 A fire occurred during the modification of radioactive ductwork above the 

furnace room (room 119-33A in building 1). Subsequent smears of the 

area found contamination below the duct; however, nasal smears of the 

workers involved were negative. There was no indication of followup 

internal monitoring in the incident report.

a-0646 1980 While maintenance was being performed on a set of fume hoods, a 

worker became contaminated when they into a 

. The worker was decontaminated without any 

indication of followup internal monitoring. The incident report did not 

specify the type of contamination.

* Identifiers are associated with incident report numbers in the Boeing incident database. 

Based on the information provided for the Category 5 incidents described in Table 3, SC&A did 

not identify evidence that the incidents with unknown contamination were likely to involve 

americium or thorium.

The final incident category (Category 6) is the most important because it relates to SEC-00246, 

as the decladding of fuel elements (if irradiated) could represent a feasible source of internal 

exposure potential to transuranic material such as americium. Two incidents were identified 

among the 98 relevant De Soto incident reports that indicated possible decladding activities. 

These two incidents are described as follows:

• Report Identifier a-0492 (Atomics International 1965): 

– Incident occurred in 1965 at location . 

– From Rockwell International 1994, p. 19: “Employee was cutting and grinding on 

irradiated component in clean lab.” The location is given as “ .” 

– From Atomics International 1965, p. 1:“Unknown quantities of grindings from 

irradiated element were generated by [name redacted], Dept. , allegedly 

without [EE’s] knowledge of the potential spread of contamination.” 

– EE immediately submitted a bioassay sample (type is unspecified), with results 

listed as no detectable activity.

• Report Identifier a-0654 (Rockwell International 1975):

– Incident occurred in November 1975 in Building 1 at De Soto. 
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– From Rockwell International 1975, p. 1: “an EBR-II fuel element with xenon tag 

gas was inadvertently included in a batch of elements for destructive inspection 

and was stripped of its cladding at about 11:00 a.m. This released the tag gas to 

the working atmosphere.”

– Exposure was estimated to the release of krypton-85, which was comingled with 

the nonradioactive xenon gas. It is not clear if the fuel element that underwent 

decladding had been irradiated.

Conclusion

SC&A’s review of the Boeing incident database did not find any direct references to internal 

exposure from americium or thorium among the 98 documented radiological events at De Soto 

starting in 1965. Not surprisingly, most of the incidents involved uranium operations, which was 

the primary fuel fabrication mission occurring during the SEC-00246 period. However, SC&A 

did identify two incidents that describe the decladding of fuel elements occurring at De Soto. 

An incident occurring in 1975 involved the decladding of an Experimental Breeder Reactor-II 

(EBR-II) fuel element. However, it is not clear from the documentation whether the element had 

been irradiated. Therefore, it is not clear whether an internal exposure potential to transuranic 

material could have existed. It is possible that the site was performing destructive testing on 

unirradiated elements prior to acceptance of the fabricated fuel by the customer (in this specific 

case, Argonne National Laboratory-West).

However, the decladding incident described in January of 1965 specifically describes “cutting 

and grinding on irradiated component in clean lab” (Rockwell International 1994, p. 19). SC&A 

recognizes that this incident occurred in the first month of the SEC-00246 period and that the 

incident database did not identify any similar events at later times. However, it is also a realistic 

possibility that this incident may only have been reported because it took place in a clean 

laboratory in building 5 (generally considered a nonradiological area). Other such operations 

may have gone undocumented in the hot laboratory or other areas of De Soto if they were 

considered routine by the health and safety staff.

References

Atomics International. (1965, February 11). Incident report [Incident file no. a-0492].

Rockwell International. (December 12, 1975). Decladding of gas-tagged EBR-II fuel element

[Incident file no. A0654]. Retrieved from SRDB Ref. ID 19690

Rockwell International. (May 9, 1994). Master Incident File (MIF) status [Internal letter]. 

Retrieved from SRDB Ref. ID 166143

SC&A, Inc. (2019). Review of remaining internal dose topics related to the evaluation of 

SEC-00235 at the Santa Susana Field Laboratory (SCA-TR-2019-SEC002, rev. 0). Arlington, 

VA: SC&A, Inc. Retrieved from SRDB Ref. ID175490