Page 128 - 360.revista de Alta Velocidad - Nº 5

Grande, Zacarías. Blanco López, Marta. García Tamames, Alberto. Castillo, Enrique.

1. Introduction and motivation

Probabilistic safety analyses are mandatory and used regularly in the safety assessment of
nuclear power plants because of the serious implications of nuclear accidents. However, this
type of analysis is not mandatory in the case of railway lines. In this paper the convenience
of performing probabilistic safety assessments of railway lines is analyzed and seriously
recommended following the trend of introducing new computational methods in Railway lines
initiated by (Amit & Goldfarb, 1971) (Assad, 1980), (Burdett & Kozan, 2010) (Cacchiani & Toth,
2012), (Caprara, et al., 2002) (Carey, 1994) (Carey & Crawford, 2007) (Carey & Lockwood,
1995), (Castillo, et al., 2015) (Castillo, et al., 2011) (Castillo, et al., 2009) (Castillo, et al.,
2016) (Cordeau, et al., 1998) (D’Ariano & Pranzo, 2004) (D’Ariano, et al., 2007) (Haghani, 1987)
(Haghani, 1987) (Lin & Ku, 2013) (Ouyang, et al., 2009) (Pachl, 2014) (Petersen, et al., 1986)
(Sahin, 1999) (Yang & Hayashi, 2002), etc.

The actual protocols to evaluate risk in railway lines start with an evaluation of each possible
hazardous event to decide whether or not the associated combination of frequency of occurrence
and consequences is important enough to deserve a detailed analysis of such event and decide
the required actions if needed. In this context, Table 1 of Risk Assessment, which is taken from
the European Standard 50126 and the Spanish UNE-EN-50126, is used.

Table 1 Risk levels considered in the European safety analysis of railway lines

Frequency of occurren-
ce of hazardous event Risk level

Frequent Undesirable Intolerable Intolerable Intolerable
Probable Tolerable Undesirable Intolerable I ntolerable
Occasional Tolerable Undesirable Undesirable Intolerable
Remote Insignificant Tolerable Undesirable Undesirable
Improbable Insignificant Insignificant Tolerable Tolerable
Incredible Insignificant Insignificant Insignificant Insignificant

Insignificant Minimum Critical Cathastrophic

Severity levels of hazard consequences

Table 1 shows the different risk levels considered in the European and Spanish standards. Though
the word risk is normally associated with the probability of occurrence of an event, here the
concept of risk is actually the expected damage (product of the probability of occurrence of
the event by the damage produced). Since both the frequencies and the severity levels are
given by a rather imprecise terminology, in Table 2 the frequency levels according to the ADIF
methodology are explained. Although each frequency is defined in two different ways, it is still
very imprecise and can lead to different interpretations by different experts, which means
that two different experts may assign a different level of frequency and risk level to the same
undesirable event. As we shall see, this is rather serious because of its negative consequences
on safety.

126 360.revista de alta velocidad