Risk screening

The SF program is an approach that encourages pollution prevention in new chemical development through the transfer of OPPT s chemical risk screening methodologies. 

Risk screening (Section 4.3) Information used in consequence modeling I Generic frequency data on events of concern from similar plants I Risk tolerance criteria or methodologies ... 

For screening purposes, however, the analysis has shown that a building of low blast resistance and high episodic occupancy, and that is potentially impacted by three different process units may present an undue aggregate risk and should be evaluated further. In retrospect, this conclusion should have been obvious without the need to resort to the risk-screening analysis. 

Because few generic frequency data were available on VCEs in similar facilities, a risk screening per Chapter 4 of this book was not performed. Instead, as a next step, the decision was made to perform a qualitative risk assessment. 

Buildings 2 and 3 require further evaluation after the consequence screening is completed. Risk screening can be performed first by calculating the maximum individual risk and then by determining the aggregate risk for occupants of the buildings. 

Occupant vulnerabilities are one of the key factors in determining the levels of both individual and aggregate risks for building occupants. Occupant vulnerabilities are used in risk screening as discussed in Chapter 4 and are used in detailed risk assessments. 

Development of Generic Frequency Data to improve Risk-Screening Tools... 

Risk screening relies upon generic frequency data to provide conservative approximations of individual and aggregate risks. Table 4.9 offers an example of generic frequencies for major explosions for certain types of refinery process units. A methodology is also offered to predict expected event frequencies where generic data are not available. 

Additional generic frequency data for other industrial segments would help improve risk screening. Specifically, improved data for Table 4.9, as... 

The initial, consequence, or risk screening results indicated that the building was designed or sited such that it was not a concern relative to explosion or fire events. As a result, the building was screened out as not needing further consideration. 

The initial, consequence, or risk-screening results did not clearly determine that the building was a major concern, nor could the building be removed from further evaluation on the basis of any of the screens. 

The initial, consequence, or risk-screening results indicated that the building design or siting presented significant concern. 

From the calculated building damage versus response relationship and the empirical probability of serious injury or fatality versus damage relationship discussed above, the relationship between explosion overpressure (or other effects) and probability of serious injury or fatality may be constructed in a manner that accounts for the detailed structural characteristics of plant buildings. The steps involved are similar to risk screening (Chapter 4), with the addition of detailed quantitative structural evaluation of plant buildings and detailed quantitative frequency assessment as described in the next section. 

Internal company risk tolerance criteria had been established prior to performing the risk screening. When Figures 6.3 and 6.4 were compared to these internal criteria, it was concluded that Building 3 did not present sufficient risk to occupants to be of concern, while additional evaluation was required for Building 2. 

Development of generic frequency data to improve risk-screening tools... 

For companies to make risk-based decisions from risk screening or quantitative risk assessments, company-specific risk tolerance criteria or methodologies should be developed for both individual risk and aggregate risk. Chapter 4 provides a discussion of risk criteria and methodologies, and offers guidance for companies to consider in developing their own approaches to risk tolerability. 

The methodologies offered in this book allow some degree of building evaluation without the development of explicit risk tolerance criteria. However, additional guidance in the development and selection of risk tolerance criteria will benefit those companies that wish to fully utilize risk screening and quantitative risk assessment as evaluation tools. 

Hertwich EG, Mateles SF, Pease WS, McKone TE (2001) Human toxicity potentials for life cycle assessment and toxics release inventory risk screening. Environ Toxicol Chem 20 928-939... 

A. D. Little, Inc., ADL FIRST Facility Risk Screening Tool. AD. Little, Cambridge, MA, 1992. 

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