Validity of the Use of Generic Failure Frequencies in a QRA

Abstract

In QRA calculations the frequency of an accident scenario is assessed by a generic failure frequency approach, defined in the Dutch Purple Book. In this paper we will examine the origin of certain failure frequencies in the Purple Book. The credibility and validity of the failure frequencies are reviewed here by means of a literature search. A study to revise and update these failure frequencies has been initiated.

History of Dutch process equipment failure frequencies and the Purple Book

“…The various, later publications by Uijt de Haag et al (2001) and Beerens et al (2003) and Beerens et al (2006) focused on failure of pressure vessels because these data are very determining overall risk, and this paper will do the same. The data on the vessels selected for the COVO study by Cremer & Warner originated from survey reports of the UK Atomic Energy Authority by Phillips and Warwick (1969) and by Smith and Warwick (1974), and from a publication by Bush (1975).…”

“…In the more recent Bevi regulation, the Decree on External Safety of Establishments (Besluit externe veiligheid inrichtingen) from 2004, relevant for licensing and spatial planning, the sphere of application with respect to installations covered, widened extensively compared to the BRZO. Two, more recent papers by the same Dutch authors (Beerens, Uijt de Haag, Post, & Ale, 2003;Beerens, Post, & Uijt de Haag, 2006) treated more explicitly the history of the data. In summary and using their scheme as shown in Fig.…”

“…In Fig. 2, borrowed from Beerens et al (2003) and Beerens et al (2006), the assumed pressure storage vessel data are shown at the top line (pressure reactor vessels are an order of magnitude worse). In Table 9.1 'Base failure rate data' of Appendix IX of COVO catastrophic failure of pressure vessel was quoted as 10 À6 /yr with a range of 6.3•10 À7 e4.6•10 À5 /yr and for serious leakage 10 À5 and range of 6 Â 10 À6 e2.6 Â 10 À3 /yr.…”

“…Failure data on chlorine equipment originated from AKZO, a company which had considerable experience with that chemical. However the data on catastrophic failure of chlorine pressure vessels have been calculated by means of fault tree analysis because of lack of historical data, while only leakage failures could be based on observations (Beerens et al, 2003;Beerens et al, 2006). Appendix IX of the COVO study: 'Failure rate data' (In Fig.…”

“…1. Flow scheme of information on process equipment failure frequency data in use in the Netherlands for QRA as given by Beerens et al (2003) and Beerens et al (2006) of RIVM.…”