Paper Info
Title
A conservative bound for the probability of failure of a 1-out-of-2 protection system with one hardware-only and one software-based protection train.
Abstract
Redundancy and diversity have long been used as means to obtain high reliability in critical systems. While it is easy to show that, say, a 1-out-of-2 diverse system will be more reliable than each of its two individual “trains”, assessing the actual reliability of such systems can be difficult because the trains cannot be assumed to fail independently. If we cannot claim independence of train failures, the computation of system reliability is difficult, because we would need to know the probability of failure on demand (pfd) for every possible demand. These are unlikely to be known in the case of software. Claims for software often concern its marginal pfd, i.e. average across all possible demands. In this paper we consider the case of a 1-out-of-2 safety protection system in which one train contains software (and hardware), and the other train contains only hardware equipment. We show that a useful upper (i.e. conservative) bound can be obtained for the system pfd using only the unconditional pfd for software together with information about the variation of hardware failure probability across demands, which is likely to be known or estimatable. The worst-case result is obtained by “allocating” software failure probability among demand “classes” so as to maximize system pfd.
Year
DOI
Venue
2014
10.1016/j.ress.2014.04.002
Reliability Engineering & System Safety
Keywords
DocType
Volume
Software reliability,Redundancy and diversity,Probability of failure on demand,1-out-of-2 system,Protection system
Journal
130
ISSN
Citations 
PageRank 
0951-8320
1
0.38
References 
Authors
5
6
Name
Order
Citations
PageRank
Peter G. Bishop110.38
Robin E. Bloomfield222744.91
Bev Littlewood3741105.77
Peter T. Popov418118.14
Andrey Povyakalo5577.53
Lorenzo Strigini675768.26