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Subparameter B was previously called “operating density”, because it con-
siders the possibility of a train entering an occupied track. For hot box de-
tection and in particular for derailments, this aspect is not crucial. Thus, the
original meaning of the quantitative parameter B was used in this case, which
is the “confrontation probability of disadvantageous circumstances”, defined
by [7]. This confrontation probability implies a situation in which at least
one counter measure exists that can prevent the impending loss. Here, this
probability is considered as how likely a hot box leads to a derailment. The
experts judgment of every fifth to tenth hot box leading to a derailment is
interpreted as a rarely. Thus, for parameter B, value 2 is chosen (refer to
Table 1.). Note, that we assumed, that a hot box already exists. Thus the
mitigation factor of not having a hot box, when the hot box detection fails
is not considered here and has to be included in a following causal analysis.
Tabl e 1 . Probability of confrontation (Parameter B)
B
probability of confrontation
explanation
1
low
hardly ever does the hazard lead
to an accident
2
regular
rarely does the hazard lead to an
accident
3
high
frequently does the hazard lead
to an accident
Subparameter M assesses if human mitigation is possible. Thus, it assesses
a situation where the hazard already exists and where only human interven-
tion can prevent an accident. For hot box detection this could be the train
driver or an on-site staff member (e.g. a station inspector). The train driver
has no possibility to detect a hot box by himself - sometimes he doesn't even
recognize a derailment when only one wheel derails and the air pipe is still
working well. Therefore the only potential intervention can be carried out by
an on-site staff member who could observe a hot box and then prevent the
train form driving on (e.g. by immediate stopping of the train in terms of
interlocking system). We assume that this can be considered as a rule-based
action, because it is not daily routine, but still possible. Hence, the M value
is determined to be 3 for the on-site staff member and 5 for the train driver,
if you refer to Table 2. Therefore we can take 4 the value for parameter M.
Accordingly, parameter G has the following value: G = B + M = 2 + 4
=6
To assess the potential damage S, three sub parameters are used: param-
eter T, V and A.
Subparameter T considers the mass of the trains, because parameter S
takes the kinetic energy into account. As Table 3. illustrated, the more mass
the trains have, the higher is the T-value and thus the higher will be the
