This highlights the fact that there is a need to distinguish
between what is meant by a barrier and the influence management
has on its effective operation. For instance, in some
approaches ‘training’ is considered a barrier, whereas in the
current conception ‘training’ (i.e. competence) is something
that is provided by management to ensure correct functioning
of some barriers. Similar reasoning applies to the other
‘behavioural’ delivery systems – e.g. ‘procedures’, ‘commitment’,
‘availability’ – these all being behavioural elements of
barriers that should be provided and maintained by management.
Hence, these systems do not appear as separate barriers
in the bow tie but rather are defined as the means management
has to influence their effectiveness. Evidently, the approach
elaborated here somewhat deviates from other developments
of fault and event trees where such barriers commonly are
defined. Moreover, the idea of ‘barriers for barriers’ (see
Schupp et al. [11]) also will not be applied here. Rather the
aim is to link management quality to barrier effectiveness in
a practical and comprehensible way.
Because several scenarios are considered in the ARAMIS
audit and, therefore, many barriers are involved, a classifi-
cation system has been developed to reduce the amount of
barriers to a limited number of categories that supposedly
have common management influences for all members of
one category but different across categories. This classifi-
cation system is based on three barrier characteristics: the
main barrier tasks – detect, diagnose and act – the cognitive
effort to carry out these tasks – skill (s), rule (r) or
knowledge (k) based – and whether the barrier has a control
(positioned in fault tree or left-hand side of bow tie)
or safety function (positioned in both fault and event trees).
This would actually result in 3 × 3 × 2 = 18 types, but the distinction
between some types is so small that their categories
have been merged. The 11 resulting types are provided in
Table 1.
Table 1 shows how different combinations (first column)
result in different types of barrier, which require different
types of management. For passive hardware the emphasis is
on design and installation. For active hardware the involvement
of workers becomes important in the functioning of
barriers and aspects like inspection and maintenance, competence
(at either skill, rule or knowledge based level) and
commitment are highly relevant.