Trial application of the worker safety assessment methodology Page: 2 of 4
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WSAM has been developed to enable its
implementation within the Process Safety Management (PSM)
framework being considered by DOE for all worker hazards.
Process Hazards Analysis (PrHA) forms an important element
of PSM as well as of WSAM. PrHA involves systematic
procedures to identify the processes at a facility, select an
assessment technique, and perform a systematic hazards
analysis. PrHA is utilized in WSAM as a first step to provide
semi-quantitative estimates of risks. In many cases, the semi-
quantitative estimates are adequate to demonstrate that the
risks are below proposed goals. In some cases, the risks
estimated with PrHA may be sufficiently close to the threshold
risk level to require more refined estimation involving
quantitative analysis. Quantitative Risk Analysis (QRA) is
performed by using standard techniques such as fault tree
analysis for frequency quantification, and applying an accident
analysis approach for consequence evaluation.
One of the recommendations resulting from the
development of the Worker Safety Assessment Methodology
was that trial applications of the method should be performed
in order to: (1) determine the feasibility of performing the
assessment, (2) assess the expected resources needed for the
assessment, and (3) evaluate whether the expected benefits
from the assessment can be realized. Preliminary results from
the first of the recommended trial applications are presented
The facility investigated utilizes a number of processes
including plutonium metal production and fabrication,
radioisotope heat source development, fabrication of uranium
and plutonium based ceramic fuel, and recovery of plutonium
and tritium. It incorporates a large number of glove boxes to
carry out these processes while providing containment of
airborne contaminants. Airborne contaminants are also
contained within a four-zone ventilation system that maintains
progressively lower pressures from uncontaminated areas to
those with the potential for contamination, ensuring air flow
from areas of lower contamination to those with higher
contamination. The intake and exhaust of the ventilation
system are provided with High Efficiency Particulate Air
(HEPA) Filters to reduce release of particulate radioactivity to
the environment. The facility is housed in a reinforced
concrete building designed to withstand a 0.38g seismic event.
The PrHA team had identified and recorded 1435
scenarios having potential consequences to workers, the
public and the environment. Each of these scenarios was
reviewed as part of this study to determine if the risk is due to
a radiological hazard, and if the risk recipient is a worker. Of
the total number of scenarios, 533 were identified as posing
radiological risks to workers. The PrHA had assigned
frequency ranges and consequence categories A (loss of life),
B (dose greater than maximum permissible body burden
uptake), C (dose causing temporary work restriction), and D
(dose causing minor or no injury) to each of the scenarios.
The consequences categories in the PrHA represent effects
differing by orders of magnitude as can be seen when
expressed in dose ranges as illustrated in the table below.
Table 1 Relationship Between PrHA Consequence
Categories, Maximum Possible Consequence, and
Corresponding Dose Ranges
Consequence Maximum Possible Maximum Individual
Category (PrHA) Consequence (PrHA) Dose Range (CEDE)
A Lossof ure >25Orem
B Dose> MPBB Uptake 250 rem> Dose> 25 rem
C Dose Causing 25 rem>Dosc>2.5 rem
D MinororNoInjury <2.5 rem
Given the likelihood and consequence categories, a
risk matrix can be defined, and each scenario can be assigned
to an element of the risk matrix. The risk matrix is labeled in
terms ofthe frequencies of the events (per year) and maximum
individual doses (CEDE rem). The proposed goals, which are
defined in terms of the same units, can now be overlaid on the
risk matrix to allow a direct comparison of the scenario risks
with the proposed goals. This is illustrated in Figure 1, which
shows the structure of the risk matrix with the proposed goals
overlaid. The function of the proposed goals is to demarcate
the risk matrix into regions of higher risk and dose (above the
10' fatality per year risk threshold and 250 rem dose cap),
medium risk and dose (below the 101 per year risk threshold
and 250 rem dose cap, but above the 10-5 fatality per year risk
goal), and lower risk (below the 10' fatality per year risk
goal). Frequency Category I (operating events) and Category
V (events with frequency < 10' per year), although outside
the scope of the present study, have been included in the risk
matrix because the PrHA included these frequency ranges.
To compare the in-facility worker risks to the
proposed goals, the accident frequencies and doses to the
maximally exposed worker for each of the 533 scenarios were
binned on the risk matrix (Figure 2). Of these, 171 scenarios
were found to exceed either a fatality risk of 10' per year, or
the 250 rem dose cap. There are two accident scenarios, both
belonging to risk category BU and representing releases from
glove boxes, that exceed a risk level of 10 fatality per year.
There are 24 accident scenarios, belonging to risk category
AIV and representing 21 criticality events, 2 releases from
glove boxes, and 1 high intensity seismic event, which exceed
the 250 rem dose cap, and some of which may exceed a risk
level of 10'5 fatality per year. There are 20 accident scenarios
in risk category BiIM and 125 scenarios in risk category CII,
most (if not all ) of which exceed a risk level of 10' fatality
per year, and a few of which may exceed a risk level of 101
fatality per year. Finally, there are 62 accident scenarios in
risk category CIII some of which may exceed the risk level of
10'5 fatality per year. A similar process applied to the risks
posed to the ex-facility workers shows that there are 3
scenarios in risk category CII that exceed the risk level of 10'
fatality per year, and some of which may exceed the risk level
of 101 fatality per year as well. There is I accident scenario
in risk category AIV for which the 250 rem dose cap is
exceeded; and there are 4 accident scenarios in risk category
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Marchese, A.R. & Neogy, P. Trial application of the worker safety assessment methodology, article, December 31, 1995; Upton, New York. (digital.library.unt.edu/ark:/67531/metadc667119/m1/2/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.