Review of the Prince William Sound, Alaska, Risk Assessment Study (1998) / Chapter Skim
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3 Data Collection and Use
3 Data Collection and Use
Pages 19-30
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From page 19... ...
, and operational performance. Data on traffic patterns were used to develop the traffic simulation model, but in spite of diligent efforts, the environmental data were not as complete as the PWS Study team desired.
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From page 20... ...
The data were not in a common format, were not all high quality, and were often incomplete, and they did not cover weather at the two most critical sites in the PWS, the Narrows and He Hinchinbrook Entrance. The PWS Study notes that '`the measured weather data poorly represents site-specific conditions being used to make closure conditions .
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From page 21... ...
The PWS Study developed an apparently large database on PWS traffic but had difficulty f~nding operational performance data. Eventually, using confidential information from the shim pers, the PWS Study team compiled a set of 50 databases, which were supplied to the committee in a letter dated February IS, 1977.
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From page 22... ...
In other technical operations, such as nuclear reactors, near-m~sses are caned precursors, and collecting data on precursors is important to identifying the potential causes of accidents, which can then be addressed.3 MANAGEMENT AUD1IS The PWS Study team used recognized procedures for its company audits, ship visits, and survey questionnaires. DNV performed the management audits at the headquarters of eight shippers, followed by visits to one or two ships of each company to "verify the The blank survey forms are included in ID 2.3 and 2.4.
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From page 23... ...
The method was based on the unsupported assumption that the scores of the management audits and the failure data were inversely proportional. HUMAN ERROR Based on substantial work on the contributing role of human factors in accidents in other fields, such as aviation safety and nuclear reactor safety, the committee has some serious concerns about how human factors were treated in the PWS Study.
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From page 24... ...
Expert judgments have long been used to assess relative probabilities in studies of risk, but the usefulness of expert judgments depends on the experts' ability to make judgments and the analysts' ability to aggregate these opinions properly. In the PWS Study, experts were expected to make judgments about the likelihood that failures would occur In specific situations.
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From page 25... ...
. QUESTIONNAIRES Because of the lack of essential objective data, the PWS Study team found it necessary to elicit and analyze expert judgments to complete their models.
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From page 26... ...
Respondents were asked to abbess 160 compansons. Expert Survey m: Assessing the Likelihood of an Accident Caused by a Mechanical Reliability Incident on a TAPS Tanker Respondents were told that one of three types of reliability failures had occurred: propulsion, steenng, or all critical operating systems.
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From page 27... ...
These questions were used to develop relative probabilities for vessel reliability failures and relative probabilities for human error (PWS Study 4.341. Expert Surrey V: Assessing the Likelihood of a Mechanical Reliability Incident or Vessel Operational Incident on TAPS Tankers in PWS Two vessels were described in terms of 11 characteristics (e.g., flag, management, vessel size)
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From page 28... ...
No actual responses were provided. The PWS Study team informed the NRC committee that these questions were used to check for anything missing from the list of risk reduction measures developed by the study team in conjunction with the PWS steering committee (personal communication from J
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From page 29... ...
Using expert judgments involves comparing pairs that are statistically treated to yield a ranking structure. Using the value scheme of the questionnamres, We PWS Study team developed a weighted ranking structure (relative values of frequencies of incidents and accidents under different conditions)
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From page 30... ...
Expert judgments were also used to fiD gaps and augment weather data. Although attempts were made to minimize errors from expert judgments, they are inherently subject to distortion and bias.
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