3.3. Quantification
The ARAMIS audit is part of a chain of methods that
together arrive at an estimation of the possible impact a particular installation, plant or site will have on its surroundings
if one of the major hazard scenarios were to transpire, given
its current barrier solutions, its current safety management
and various other local conditions.
Although the quantification of the audit results has not
been a main concern in the development of the audit, it is
an objective of the ARAMIS project to have a numerical
indication of the quality of management of barriers, the so
called M-index. For rather pragmatic reasons, it had been
decided that this should be only one number, with which any
given barrier would be judged.
Within the chemical industry it has become common practice
to assign a so-called SIL-value, which stands for safety
integrity level and which is part of the international IEC
61508 standard. It is an expression of a barrier’s assumed
reliability on a three-point scale. The number actually reflects
the exponent x in the formula 10−x rounded-off to the lowest
integer. So a SIL-value of 3 corresponds to a probability
of failure on demand between 10−4 and 10−3. The
M-index resulting from the ARAMIS audit can be used to
modify the SIL-values of any barrier in any scenario under
investigation.
The procedure for calculating the M-index is still rather
experimental, in that it is not based on empirical evidence
on management influences or experience. First of all, a decision
has been made that the delivery systems ‘risk analysis
and barrier selection’ and ‘learning and change management’
should be excluded from the quantification phase (see above).
The remaining seven delivery systems however do contribute
to current barrier effectiveness.
These delivery systems first had to be brought back to one
single number, instead of a separate rating per step. Therefore,
several persons with a certain degree of expertise (some
members from the ARAMIS consortium and 13 delegates
from a master’s course in safety) judged all steps within
these delivery systems for their influence on barrier effectiveness.
This resulted in a split between delivery systems
having equally weighted steps and systems having unequally
weighted steps. For the equally weighted delivery systems,
a geometrical mean is calculated to arrive at their overall
numerical rating (please note that all steps have been rated
on a five-point scale). For the unequally weighted ones, however,
a different reasoning applies. An average is first taken,
but when steps within a particular delivery system are judged
more important than others, the final mean rating of such a
system cannot be higher than the lowest scoring important
step. Or put in other words, the quality of less important
steps cannot compensate for the lesser quality of important
steps.
Hence, for one group of delivery systems all steps are
assumed to contribute equally to the quality of the delivery
system:
a. manpower planning;
b. communication;
c. purchase/install hardware.
240 F. Guldenmund et al. / Journal of Hazardous Materials 130 (2006) 234–241
Whereas for another group of delivery systems a few steps
are assumed to contribute more dominantly to the quality of
the delivery system:
3.3. QuantificationThe ARAMIS audit is part of a chain of methods thattogether arrive at an estimation of the possible impact a particular installation, plant or site will have on its surroundingsif one of the major hazard scenarios were to transpire, givenits current barrier solutions, its current safety managementand various other local conditions.Although the quantification of the audit results has notbeen a main concern in the development of the audit, it isan objective of the ARAMIS project to have a numericalindication of the quality of management of barriers, the socalled M-index. For rather pragmatic reasons, it had beendecided that this should be only one number, with which anygiven barrier would be judged.Within the chemical industry it has become common practiceto assign a so-called SIL-value, which stands for safetyintegrity level and which is part of the international IEC61508 standard. It is an expression of a barrier’s assumedreliability on a three-point scale. The number actually reflectsthe exponent x in the formula 10−x rounded-off to the lowestinteger. So a SIL-value of 3 corresponds to a probabilityof failure on demand between 10−4 and 10−3. TheM-index resulting from the ARAMIS audit can be used tomodify the SIL-values of any barrier in any scenario underinvestigation.The procedure for calculating the M-index is still ratherexperimental, in that it is not based on empirical evidenceon management influences or experience. First of all, a decisionhas been made that the delivery systems ‘risk analysisand barrier selection’ and ‘learning and change management’should be excluded from the quantification phase (see above).The remaining seven delivery systems however do contributeto current barrier effectiveness.These delivery systems first had to be brought back to onesingle number, instead of a separate rating per step. Therefore,several persons with a certain degree of expertise (somemembers from the ARAMIS consortium and 13 delegatesfrom a master’s course in safety) judged all steps withinthese delivery systems for their influence on barrier effectiveness.This resulted in a split between delivery systemshaving equally weighted steps and systems having unequallyweighted steps. For the equally weighted delivery systems,a geometrical mean is calculated to arrive at their overallnumerical rating (please note that all steps have been ratedon a five-point scale). For the unequally weighted ones, however,a different reasoning applies. An average is first taken,but when steps within a particular delivery system are judgedmore important than others, the final mean rating of such asystem cannot be higher than the lowest scoring importantstep. Or put in other words, the quality of less importantsteps cannot compensate for the lesser quality of importantsteps.Hence, for one group of delivery systems all steps areassumed to contribute equally to the quality of the deliverysystem:a. manpower planning;b. communication;c. purchase/install hardware.240 F. Guldenmund et al. / Journal of Hazardous Materials 130 (2006) 234–241Whereas for another group of delivery systems a few stepsare assumed to contribute more dominantly to the quality ofthe delivery system:
การแปล กรุณารอสักครู่..
