Page 130 - 360.revista de Alta Velocidad - Nº 5

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

acceptable with adequate control. Therefore, events that are “Incredible”, that is, extremely
unlikely or that it can be assumed that the threat will not occur, are exempted from further
verification regardless of their consequences. Events that are “improbable,” that is, unlikely
but possible or that the threat can be assumed to occur exceptionally, are tolerable under
control even if they have very serious consequences.
This highlights the danger of using not only vague and inaccurate, that is, unquantified or
grossly quantified frequencies, but also imprecise boundaries between events requiring a safety
analysis and those free of it. In other words, it is clear that this methodology, despite of being
a recommendation of the European authorities, is not only the most appropriate but should be
corrected as soon as possible.
Fortunately, there are recommendations that already correct these defects, such as, for
example, the important work of (Beales, 2002). Given that these recommendations imply a
major change of the initial content of the rules, in fact they indirectly recognize their serious
deficiencies. Thus, an urgent change of the current code is needed.
For the sake of illustration, Table 4 is the table for risk assessment recommended in the document
published by the RSSB (Railway Safety Standards Board), which leads to safety analysis of many
events not included in Table 3.
Table 4 Table for risk assessment recommended in the document published by the RSSB (Railway Safety Standards
Board).
Consequence
2 3 4 5

Fatalities/event
1 fatality in
Frequency 1 fatality in every 1 fatality in 1 fatality in 5 fatalities in
125 events every 25 every 5 events every event every event
events
No/year 0.008 0.04 0.2 1 5
0.25 1.25 6.25 31.25 156.25
7 31.25
8 9 10 11 12
0.05 0.25 1.35 6.25 31.25
6 6.25
7 8 9 10 11
0.01 0.05 0.25 1.35 6.25
5 1.25
6 7 8 9 10
0.002 0.01 0.05 0.25 1.35
4 0.25
5 6 7 8 9
0.0004 0.002 0.01 0.05 0.25
3 0.05
4 5 6 7 8
0.00008 0.0004 0.002 0.01 0.05
2 0.01
3 4 5 6 7
0.000016 0.00008 0.0004 0.002 0.01
1 0.002
2 3 4 5 6

Units are fatalities per year

128 360.revista de alta velocidad