Environmental Engineering Reference
In-Depth Information
in ensuring the accuracy and consistency of in-
spections across a wide range of inspection staff
potentially working within different operational
environments. The nature of the changes being
proposed as ameasured step towards performance-
based inspection is such that effective training and
guidance will be critical to the success of the
proposed method.
A number of mechanisms for providing guid-
ance were investigated as a part of this project.
Brief descriptions of these are listed below:
.
Condition grade descriptions and images
-as
used in the currentmethod of visual inspection for
UK flood defences (Environment Agency, 2007).
These provide a simple method for assessment of
condition but are essentially limited due to their
reliance on a single photograph. Itwas decided that
this approach would be insufficient as the sole
form of guidance for the condition indexing
process.
.
Flowcharts
- provide a highly structured mech-
anismfor assigning condition. The increased struc-
ture and fixed pathways in the flowchart ensure
greater consistency of assessment than a textual
description, which suffers from the ambiguous
nature of natural language. Flowcharts display the
process of condition assessment across all condi-
tion grades within a single chart. This allows the
inspector to understand the differences between
the grades of condition more easily. The produc-
tion of flowcharts is amore complex process than
a text description and must be extensively
trialled to identify any errors and/or omissions.
The rigid structure of the flowchart can also be a
limitation as it will be impossible to include
every possible situation and combination of fac-
tors that may be found on site. Training would
need to emphasize the need to use the flowcharts
as guidancematerial and not as a replacement for
the inspector's knowledge.
.
Checklists
- the use of checklists is a common
approach to visual inspection in many industries.
The USACE Condition Indexing system (McKay
et al. 1999) commonly employs checklists in
the recording of asset condition. This method of
guidance is a good way to ensure consistency of
inspection but can require the assessment and
The confidence assigned to the individual PFs is
used to calculate the minimum and maximum
values for each FI. This produces the range of
potential values for each FI. The larger this range,
the greater the degree of uncertainty associated
with that FI value. The position of the assigned
condition FI within the value range calculated
using the confidence values gives an indication
of the nature of the uncertainty, i.e. whether it is
more likely for the condition to be better or worse
than the condition assigned by the inspector.
Condition index (CI)
The condition index for an asset represents some
indication of its overall condition based on the
assessment of performance features and the cal-
culation of failure mode indices associated with
those performance features.
The calculation of the CI could be achieved by
the same method used to calculate the individual
FIs. Thiswould require a set of contribution values
that represented the relative likelihood of each
failure mode occurring for an asset. The problem
with this approach is that there is no definitive
dataset that could be used for the contributions at
the asset-type level. The potential use of failure
mode contributions needs further research to es-
tablishwhether a set of appropriate values could be
determined that would be useful in terms of visual
inspection of asset performance.
An alternative method of calculating the asset
CI is referred to as the
weakest FI
approach. This
involves theCI being determined as themaximum
value in the set of FIs. If the FIs for an asset with
four failure modes were 2.1, 3.2, 2.2 and 3.7, the
Asset CI is equal to 3.7. The problem with this
approach is that it seems to ignore the FIs other
than the one with the maximum value. However,
it is proposed that in terms of measuring perfor-
mance at the asset level, this is precisely what
should be done.
Guidance and training
Guidance and training are essential to anymethod
of visual inspection. They are the key components
